Categories
Blood-Brain Barrier Neurosciences Uncategorized

[Sciences/BBB] T Lymphocytes and Cytotoxic Astrocyte Blebs Correlate across Autism Brains (DiStasio et al., Ann Neurol 2019)

I  have been recently approached on social media to discuss about the recent study published by Anderson and colleagues in Annals of Neurology (https://onlinelibrary.wiley.com/doi/abs/10.1002/ana.25610), in which the authors reported the presence of residing CD8 cytotoxic T-cells in the perivascular space of brain samples from ASD patients. I wrote about it, and gave my first impressions about reading the study. After such discussion, I realized that I have an interesting review that worth being shared here on my blog.
Here is the summary of my review of this paper as I wrote it on social media. I made some corrections (mostly spelling and grammar), as well as some changes in the writing style (I wrote these comments on the spur of the moment, as I went through the paper). Also due to copyrights, I will not show any figures and tables from the study.

About the authors: The first author is Dr. Marcello DiStasio (MD/PhD) and the senior author is Dr. Matthew P. Anderson, MD/PhD. He is a clinical faculty of Harvard Medical School and member of the Department of Neurology and Pathology a Beth Israel Deaconess Medical Center, with an affiliation with Boston Children’s Hospital Intellectual and Developmental Disabilities Research Center.  So we have some high profile and experts in neurodevelopment disabilities.

About the journal: The journal is published under Wiley, and is the official journal of the American Neurological Association and the Child Neurological Society. It has an impact factor of 9.49 and is in the top quartiles of neurology and neurosciences journal. Therefore, we have a study published in a very good journal that is relevant to the topic.

About the study design: The study is mostly observational and relies mostly on histological methods (tissue sections followed by staining using chemical dyes and/or antibodies targeting specific proteins). Tissue samples are freshly isolated from postmortem patients (which is a big plus compared to formalin-fixed samples, and opens up the ability to perform protein and RNA analysis if the samples are immediately treated for extraction). The sample size is pretty decent (N=25-30) with a large age spectrum and various types of ASD represented. First interesting to note, 50% of the ASD brain (N=25, not bad) have a history of seizures. Less than 30% of control brains (N=30) have history of seizures. Important thing to consider as a comorbidities and evenutally as a cofounding factor.

About the results: This is my summary of the different figures. By copyright concerns I am not showing the actual figures, but you can overlap my comments to the figures as I have separated them into sections.
Figure 1: Me being cranky, I wanted to see control brain pictures, but not avail. Also with immuno pictures, you have to be super-precautious because there is a high risk of cherry-picking a brain slice, and claim it is representative of all brain. Nevertheless lets discuss it here. On the left panel, we have an H&E staining. Pretty much a vanilla staining. Now, if you want to show a certain protein, you can do it with the right antibody and staining (DAB/peroxidase stain). It appears as the dark brown color. We can see a strong GFAP staining around the vasculature (hollow structure). Astrocytes usually line up blood vessels by forming end-feet process. S100B and ALDH1L1 are pretty standard proteins for astrocytes. However seeing GFAP expression in human astrocytes means these cells are stressed out and are reactive. This is what the quantitative bar graph is telling us. We can also see some CD8 in this perivascular space. These are the cytotoxic T-cells. I wonder what they are doing there, as they can cross the BBB only during brain injury, as microglial cells will äctivate” these endothelial cells and allow white blood cells to adhere on their surface and cross the BBB into a complicated tango dance.
Figure 2: Here there is an attempt of some matrix correlation. GFAP versus CD8 cells. And we can see there is some (expected) correlation between these two (see linear regression and R2) with ASD brains have higher rates of both compared to controls. Interestingly we see similar pattern between ASD that are genetic versus the idiopathic.
Figure 3: digs in more about the immune cells and some correlations (although the scatter of the ASD brains is less convincing here). Overall it seems we have a higher number of lymphocytes in the ASD brain compared to control, both in the white matter (WM, this is where our cables go through) and grey matter (GM, this is where our processing units are) and lepomeningeal (LM, this is our brain surface protective skin, basically the meninges, pours the CSF into the veinous blood). What seems interesting is that at young age we have lymphocytes sitting in our perivascular space, doing nothing(?) and decrease as we age (thats interesting for the non-neuroimmunologist that I am). However, these number at best slightly increase in ASD brain as we age (and I guess not convincingly enough, otherwise the authors would have reported the R2 value), or at least remain the same. With the exception of the medulla (brain stem) most blood vessels show a higher number in ASD brains versus control brains. Interestingly, cortical blood vessels being the predominant population harboring such feature. Very few NK cells to be honest on the panel.
Figure 4: Again this one makes me cringe a bit as a reviewer, because the author do not show the controls data. Yeah, I am pissed. Anyway. Again, perivascular space. Again immune cells highly present (CD3+), CD8 lymphocytes being the predominant type of T cells, in contrast not many CD4 lymphocytes (usually the T helpers, but my immunology is outdated for 20 years at least). Granzyme staining denotes the presence of natural killer (NK) cells. CD20 is a marker for B cells. What is interesting is mostly not much B-cells in either ASD and control brains, the graph more like a refried version of what we already know (higher number of immune cells and CD8 cells).
Figure 5:  is a bit of a useless graph, I don’t see anything that brings us more information than before.
Figure 6: It shows us a Masson trichrome staining. It is a chemical (histological) staining aimed to make collagen fibers visible under a certain color compared to other tissues. Collagens exist in different forms (based on their alpha-fibrils) but the one you expect to see around the vasculature is Collagen Type IV (COL4A1). This one forms a basement membrane (BM) that is like a net around blood vessels. Think about standing on a trampoline. Thats it. Collagen IV forms the net that supports the BBB. Normally, you would expect the BM to be thinned out, this is the case after stroke as cells secrete protein-degrading enzymes (like matrix metalloproteinases MMP2 and MMP9) that will break it down into pieces. But here it is thickened and hhad a bigger thickness than normally. Why so? What does not mean? I dont know. The only time I have seen such things was in transgenic mice overexpression erythropoietin (EPO). These mice had a such high hematocrit that would make blood be like Aunt Jemima corn syrup. If I remember, my former PhD adviser had a collaboration with an electron microscopist and observed similar thickening. Why this is happening is a good question that is likely the next study.
Figure 7: See Figure 5 comment.
Overall thoughts, limitations and outlook: Overall, it is very interesting study, that has some methodological limitations to be noted. First, we are missing any information about the BBB integrity in general, as I wish the authors would have shown some immunofluorescence to compare changes in tight junction (TJ) proteins expression (claudin-5, occludin) in blood vessels and assess differences in TJ strands. The second problem is the lack of information about microglia activation (that would be done by Iba1 staining. The authors noted they performed it, observed a higher expression in ASD brain but decided not to show the data) and more importantly the status of endothelial cell activation (using ICAM1, VCAM1 staining). Are these residing CD8 T cells freshly migrated or just being duck sitting for a while? Is the inflammation status in the brain (and the BBB) ON or OFF at the time of autopsy? What about pro-inflammatory cytokines levels between ASD and control patients? As usual, studies like that opens much more questions that it answers. The second problem is that the study by itself fairly descriptive and observational. It would be interesting how this would compare to clinical findings done in patients. Do we see flares on the MRI indicating of the BBB opening? How does that data compares to patients with MS?
I would also be very careful on making any claim about a “leaky” or “down-regulated” BBB at this point. There is no data about the barrier integrity (TJ complexes integrity) or assessment of the barrier function (for example an MRI scan with gadolinium as contrasting agent) to support the claim. I have seen this claim floating around in non peer-reviewed articles (including in The Scientist), as a BBB expert I would not jump into that conclusion quickly until I see real data on that
This is the type of interesting study, because it opens 100 questions that incentivize to further look down the road. I hope that the authors were able to prepare RNA and protein samples for transcriptome analysis (RNAseq) and proteome analysis (2D-electrophoresis coupled with MALDI) that could help us learn more.

 

 

Categories
Neurosciences Sciences Stem Cells Uncategorized

[Sciences/Neurosciences] Propionic Acid Induces Gliosis and Neuro-inflammation through Modulation of PTEN/AKT Pathway in Autism Spectrum Disorder (Abdelli et al., Sci. Rep. 2019)

Once a wise man said: “Be always wary of scientific studies trumpeted by mainstream news outlets as groundbreaking. Once the smoke settles down, the study in question is rarely groundbreaking, but rather limited with a lot of caveats”. If I have to summarize this study, that would be within the lines of the wise man. Despite what news outlets have been selling, this is a study that has its own merits, but its methodological limitations and caveats outweighs the novelty and significance. Especially considering the publication occurred in Scientific Reports, the response of Nature Publishing Group to the open-access model, this is an extra layer of concern as Scientific Reports prestige and quality has suffered major setbacks in the last few years due to papers retracted for blatant scientific misconducts that should have been spotted by reviewers.

About the authors: We have three authors. The first author seems to be a postdoc, as she apparently graduated from the same program from another lab. The second author maybe an undergrad, although a faculty with the same family name is listed. Finally the senior author is a faculty with an expertise (based on the publication record) on gastrointestinal (GI) tract physiology and pathophysiology. However, none of them seems to have a history of publication in any field of neurosciences. This is an important point, because it explains a lot of methodological flaws that anyone with neural stem cell biology (and brain development) could pick easily.

1. Introduction and hypothesis: The authors are basically using the rationale of changes in metabolomics observed in ASD patients and reported by several studies. In these studies, there are some indications that certain patients on the spectrum (especially those qualified as severely disabled) display an impaired GI function, in particular something we could qualify as something similar to inflammatory bowel diseases. There are studies suggesting that such GI condition is associated in a changes in the gut microbiota, yet with a fairly low resolution (we are able to document changes in a family of bacteria, but not able to pinpoint to the level of Genus species yet). In particular, there is a study that was recently published in Cell Stem Cells (very high impact factor journal) that highlighted changes in mice behavior and gene expression profile of several genes associated to autism following the fecal transplant from patient on the spectrum considered severe (https://www.cell.com/cell/fulltext/S0092-8674(19)30502-1).

In this study, the authors speculate that certain metabolites biosynthesized and/or bio transformed by these class of bacteria are contribution to the symptoms. In particular, the authors consider acetate (AC, CH3-COOH) , propionate (PPA, CH3-CH2-COOH) and butyrate (BA, CH3-CH2-CH2-COOH) as potential culprits, citing studies showing an elevated levels of these small chain fatty acids (SCFA) in fecal cultures of ASD patients compared to control patients. The authors also cite two rare genetic diseases such as neonatal propionic acidemia (PA) and propionyl coA carboxylase (PCC). PA will be very useful to us, because it will help us set what we would consider a pathological level of propionic acid (PPA) in blood. Yet comes the most speculative, and I would say the “jumping the shark” moment of the paper. The authors assume that since processed foods are rich in PPA, such amount of PPA can lead to the development of ASD in the fetal brain during pregnancy. That’s a lot of speculations with little or no layers of evidence. We have here the authors trying to make a statement four to five steps too far from the existing literature for several reasons (and also lakcing the literature backing them up) that be identified as the following:

1.   Where is the literature providing evidence that these SCFA cross the GI tract, at which extent (bioavailability studies)?
2.   What are the levels of PPA (and other SCFA) in the plasma/serum levels of neurotypic patients versus patients on the spectrum? For patients suffering from PA, I have found an old study referring to serum PPA as high as 0.337-1.35mM, with a normal level about 0.00337mM (https://www.jpeds.com/article/S0022-3476(81)80004-2/pdf)
3.   How much of PPA can cross the blood-brain barrier? This is an important question to answer. We can try to build on the analogy of the SCFA to ketone bodies (acetoacetate, beta-hydroxybutyrate) that are formed when someone is fasting or forced into a ketogenic diet. Considering that patients suffering from GLUT1 Deficiency Syndrome are showing improvement when put on a ketogenic diet (with BHB levels around 2-3mM), we can speculate these compounds can cross the BBB readily.
4.   How much of PPA can cross the placental barrier? I don’t have any clue either.

These talking points are important because it will determine if the experimental design of a study is sound or deeply flawed, which eventually will set the quality of the paper and the robustness of the conclusion made. That’s something I should mention by now, is that both the authors and the news outlets have been very fond of superlatives and trying to sell that paper at much higher level that it is meant to. Not only it is scientifically inadequate to make extraordinary conclusions without highly robust data to support them, but also it is nowadays dangerous to do so as such studies will be used by scammers, charlatans and other snakeoil salesmen to promote their supplements claimed to “cure autism” and use these type of studies to claim their products is supported by science.

2. Materials and methods: The authors used neural stem cells (NSCs) derived from fetal tissues (obtained from Life Technologies/Thermofisher) and maintained in a classical medium formulation aimed to maintain these NSCs in their pluripotency stage. The cells were passaged no more than three times, according to the author. This is important, as NSCs/NPCs passaging over time will coax them towards the astrocytes lineage compared to neurons (in terms of development, neurons appear earlier and mature earlier than astrocytes).
Now there is something intriguing. The authors claimed they looked at PPA and BA at concentrations ranging from 0.1mM (that would be physiological), 0.5, 1 and 2mM concentration. Considering such treatment would reproduce the fetal brain, we have to factor in what is the amount capable to cross the three barriers: GI barrier of the mother, the placental barrier and finally the BBB. However, the authors never showed what happened to these concentrations except the 2mM which is limit deadly (remember? This is the one that is detected in newborns having the rare genetic mutation). Are the authors trying to model the effect of PPA to model such diseases or are they assuming that the amount of PPA in processed found will be high enough to put the pregnant women into a severe metabolic acidosis? I don’t know but that like a red flag.
The differentiation of these NSCs into neurons/astrocytes were left to occur in a fairly random fashion, as the authors use the same medium used for NSCs maintenance but without growth factors. I think this is an important issue here as we may have a significant variability in terms of yield between passages in particular when it comes to neurons/astrocytes ratio (personal communication with Clive Svendsen).
Otherwise, nothing else really fancy and classical techniques found in any neurosciences studies: Immunocytochemistry, neurite outgrowth, qPCR…

3. Results:
3.1. Figure 1: I am a bit perplexed from what I see and from what I get when it comes to quantifications. The first issue I have is the lack of scale bar. A scale bar tells you how many pixels equals to a length. For example, a 512×512 pixel image may indicate you that 100 pixels equals to 50 micrometers. Here you have to trust that the experimenter did not fudge the data, crop the pictures and really show you a 10x magnification.
For simplicity, I will focus on the Day 10. My concern is about the health of the neurospheres in some of the groups, in particular the BHB-treated group. You can see in controls; we have nice rosette-shaped neurospheres with a dark core reflecting a dense. In contrast, look at the BHB treated group. These neurospheres are small, frail and lack the morphology observed in control. I wonder if BHB at this concentration is showing signs of toxicity? If yes, the authors were not concerned at all by this issue. And this is something concerning. If BHB is neurotoxic, so how can we make a conclusion to BHB as inhibitor. There are ways to show the viability of these neurospheres: Hoechst staining, propidium iodide staining, Fluorojade staining……..Because of this important issue, I will not consider the BHB treatment as valid.

Slide1

If you compare the data shown in Fig.1B and 1C compared to the quantification made in Fig.1A (and shown in the bottom), you can see we have a certain discrepancy here. I would skip the issue in the y-axis labelling (the correct symbol for micrometers is µ (mu) not n(nu)), but compare the 10 days timepoint to the data we actually obtain from the Fig.1A. In scientific publications, you have to be sure that what your representative blot/micrograph picture shows matches your quantitative analysis. In other words, what I see in the micrograph pictures in Fig.1A should be reflected in Fig.1B and 1C.
Then explain me why the differences in diameter reported is not as different between my quantitation (using ImageJ internal functions) is different from the one displayed. How do the authors justify the use of SEM instead of SD, except for making the graph look nicer (you can see the data actually suggest a much more variability that likely undermine the statistical difference)? How does the authors explain the 3x difference in neurosphere counts between me and them? Did they crop the pictures? If so they should have accounted for, and highlights the importance of having a scale bar in micrographs pictures and normalizing such data to a surface area (e.g. pixels2, µm2, mm2….)

3.2. Figure2: These are immunofluorescence pictures of plated neurospheres allowed to differentiate by their own on Matrigel-coated plates (Cultrex). The pictures are okay, although not very convincing for some and certainly not suitable for quantification. The use of flow cytometer is definitively a go-to when it comes to assessing cell populations.

Slide2

We are also here having a mixed results and missing important cell markers. First, the authors should have performed a nestin staining, as nestin is one of the markers present in NSCs/NPCs. Second, the use of GFAP as astrocytes marker has to be taken with a big grain of salt. I am not sure experts in the field would have let this fly with just one marker. GFAP can be expressed by NSCs and NPCs. Showing at least two markers per cell lineages (NeuN/bIII tubulin for neurons, S100B/GLAST1 for astrocytes) would have been much more convincing. bIII tubulin antibody (in particular the one used in this paper) is known to have a very strong non-specific staining. A good bIII tubulin would show nice neurites. I have attached a picture of an iPSC line developed by Sigma-Aldrich. You can use it to compare so you can see what a good bIII tubulin and a good GFAP staining should look like in NPC-derived astrocytes. Here we have just some blobs (that indicates a possible non-specific immunoreactivity) that dangerously overlap with GFAP. Technically, you cannot have a neuron that express both GFAP or bIII tubulin. It is either or but not both. R&D Systems has a nice interactive map that shows you the different cell markers expressed by the neural lineage as its differentiate into neurons and astrocytes here: https://www.rndsystems.com/pathways/neural-stem-cell-differentiation-pathways-lineage-specific-markers

What I am supposed to do with that?

3.3. Figure 3: The authors looked at both GFAP and bIII tubulin at mRNA levels (PCR) and protein levels (by ELISA). I would have personally put the PCR data first, followed by the ELISA data. The PCR data was normalized to GAPDH and the DeltaDeltaCt method was used, which is good, the authors also have represented the apparent bIII tubulin or GFAP/GAPDH ratio, which is good.  However, I am more skeptical on the ELISA data. The reason why? The data is represented as micrograms of protein/microliters of cell extract. I am skeptical why the authors did not run a Western-blot analysis for these two housekeeping genes, since you expect a lot of proteins being expressed. The authors also forgot to mention if they have diluted the samples or just added the crude extract at is. This is important because you can easily blunt the accuracy of your ELISA. LSBio is honestly a cheapskate when it comes to showing a standard curve, unlike more established ELISA kits manufacturer such as R&D Systems or Abcam, that will show you their standard curves and tell you the coefficient of variation in them. The maximum concentration of the standard curve is 1000pg/mL or 1ng/mL, with a detection range of 15.63-1000pg/mL and a sensitivity of 9.38pg/mL. The authors reported concentrations for GFAP was 0.8-3 pg/ml according to their graphs. Something is wrong here, and we have at least 2 reviewers that completely miss that. Are the authors telling me that they were able to detect GFAP and bIII tubulin below the sensitivity level (9.38 and 313pg/mL respectively)? Give me a break! I would also have advised the authors to normalize their concentrations into something meaningful like mg of proteins. It is easy to take a fraction of the cell lysate and measure the total protein concentration by BCA. I ask my students whenever they use an ELISA for quantifying a cellular protein to normalize their amount detected (pg/mL) to a total protein concentration (mg/mL) which allows us to normalize the data. Failure to do this normalization is like showing a Western-blot without a proper loading control (e.g. actin, GAPDH….).

3.4. Figure 4: In this figure, the authors are trying to show the expression of GPR41 (aka free fatty acid receptor 3 or FFAR3) in those cells. Honestly, this is my breaking point of tolerance. First, the authors underwent some cherry-picking of the data, showing you only the PPA treatment in astrocytes (where is the BA treatment? Where are the BHB treatments?) and only the BA treatment in neurons (where is PPA? Where are BHB?).
I am also very skeptical that what the authors call astrocytes are really astrocytes looking. What we see in Fig.4A looks very similar to 4B: very thin cytoplasmic projections looking like neurites. Only neurons form neurites in cultures. Astrocytes have more a flat-shaped feature, sometimes a bit fusiform like shape. Again, the GPR41 protein expression is really up when you have tons of PPA given (mM and more). How come this went through peer-review unabated and have at least 2 reviewers did not notice this gross conundrum in the data?

4. Rest of the figures and conclusion: I can go further with this paper. It was looking very interesting and promising, but the lack of expertise from the authors quickly percolated into loose and inconclusive data. This is the kind of paper you wish the authors would seek feedback from across the street, from some faculty with a neuroscience background and give them an honest feedback to make this paper good and scientifically sound. What we have indeed is a half-baked study, served as the next big thing since sliced bread. Not only the data is far from convincing of the claims made my authors (I would probably accept as a possible model for modelling PA or PCC, but this paper IS ABSOLUTELY NOT SHOWING THAT PPA IS CAUSING AUTISM for several reasons below:

1.   It does not account for the PPA levels found in normal persons, even less provide a study showing PPA levels in people eating processed foods (if such dietary habit even lead to such outcome).
2.   It does not consider that in order to be valid the authors have to show that you have a 100% bioavailability of PPA across the GI barrier, the placental barrier and the BBB, which are not reported or cited by the authors in any credible form.
3.   It does not account that the levels used as so ridiculously high that a pregnant mother would deal with a possibly deadly metabolic acidosis.
4.   It also ignored that BHB was showing signs of neurotoxicity.
5.   There is a worrisome pattern of data cherry-picking, with groups popping in and out intermittently, sometimes even in a complacent manner. This is a no-no and an unacceptable behavior that has no place in any respected peer-reviewed journals. Why did the reviewers overlooked that issue?
6.   There are several inconsistencies in the data, especially whether the axis labels are botched or if the authors really provided measurements that were nornally impossible to reach (below detection limit).

This paper should at least had a “major revision” to fill the gaps. Yet, it went through at least 2 reviewers and none of them were able to see the obvious methodological flaws. As a reviewer for Sci Rep on a seldom basis, I am very concerned about the quality of review provided by the journal in the recent years, especially in light of series of retraction. Conclusions? The news outlets have been trying to sell an overhyped paper that does not live much under scrutiny. This is just “same old, same old” when it comes to journalistic reporting on science (trying to fudge it as groundbreaking), but also opens a dangerous precedent. I will bet that within 12 months, there will be some quack doctors and snake oilsalesmen that will claim they can cure autism by selling you supplements aimed to reduce the PPA or by selling you a dietary fad book, claiming it will cure your child autism by dietary restriction. I guess the keto diet will soon join the casein-free/gluten-free diet as outdated and have another fad being served as dietary torture to children on the spectrum.

Categories
Neurosciences Sciences Stroke Uncategorized

[Sciences] Restoration of brain circulation and cellular functions hours post-mortem (Vrselja et al., Nature 2019)

You may have heard about that groundbreaking story last on “pig brains being revived” sounding almost like a scenario of a zombie movie. Let’s say science journalism love to use superlatives and sensationalistic headlines to grab few more clicks and views.
As usual, my skepticism was to first look at the paper and see how the claims hold on. The publication behind that “pig zombie paper” is the study from Vrselja and colleagues published in Nature last week and available here: https://www.nature.com/articles/s41586-019-1099-1
So what is about this story? First it is published in Nature, a top-tier peer-review journal. Second it is a huge paper, coming from Yale University. The paper was initially submitted on February 22, 2018 and got accepted March 1st. You can say a bit more than a year and that suggest that this paper likely went at least two rounds of review and probably more than three peer-reviews (three were named as well as other anonymous). One of the peer-reviewer was Pr. Constantino Iadeccola (Cornell University, NY), a “rock star” in the field of cerebral blood flow (which nicely match for the paper).
Overall, it is a very good paper with some reservations on the greater impact that I will explain later.
To understand the paper, you need to understand first that as until now we consider the brain highly dependent on continuous cerebral perfusion with blood flow to survive. The brain is highly dependent on oxygen and glucose (at least 20% of our daily uptake is taken by this tissue that only represent less than 2% of the human body weight).
We assume that if you stop flowing the brain with blood (e.g. cardiac arrest), you will die within minutes from massive and irreversible brain damage. The whole idea of this paper was: “what if we could maintain a blood flow for 24 hours, can we maintain some neurological function?”. In particular, the authors have developed a kind of artificial blood, cell-free, called BEx. It contains a hemoglobin carrier called Hemopure(R), glucose/pyruvate, as well as a cocktail of neuroprotective agents, antibiotics and some echogenic agents (to measure blood flow). The caveat is that as a control the authors used a simple saline solution without glucose and pyruvate (see supplementary tables below). Considering the importance of glucose for the brain tissue, and the absence of glycogen storage in that tissue, I would argue that this is a non-negligible flaw in the experimental design, giving a serious advantage to the BEx and maybe even overestimating the BEx activity.
Screen Shot 2019-04-17 at 2.06.26 PM

Nethertheless, let’s continue the discussion. Pig brains were not obtained from pigs euthanized for the sole purpose of the experiments, but rather obtained as waste from the slaughterhouse. Thats ethically much more acceptable, even 3R-friendly (as it valorize animal tissues considered as waste) and much more easy for obtaining an IACUC approval. About 300 post-mortem brains were used, I guess mostly for the development and optimization of the technique. The sample size (N) appears to be 32 pigs/group, which is very good for statistical power of analysis.
The surgical procedure (to connect these brain to the system) was about 10 minutes of warm anoxia, which would probably represent a severe cardiac arrest in which CPR is not performed immediately. They exposed these brain to either 1 hour or 10 hours post-mortem interval (PMI) without flow, with control perfusate or with BEx. Note that the perfusion to occur happened about 3 hours since the initial brain flush, the surgical preparation appears indeed tidious, but reproduce a pulsate blood flow similar to what would happen in animals. They also cooled down the brain to 25ºC, which is known that cooler temperature improve the chance of reducing brain damage (the common sense is that drowning in an hypothermic environment (frozen lake) increase your chance of resuscitation compared to drawing in a normothermic environment (swimming pool). The experiment lasted 10 hours for all groups, except the 1 hour PMI group.
The first results shown demonstrated the presence of a functional flow inside the brain tissue, and some vascular reactivity, using nimodipine infusion (a Ca channel blocker commonly used to reduce blood flow) and showing changes in blood flows. In other words, there is a proof of principle that it works.
The second result looked at changes in cerebral edema as a crude estimation of the blood-brain barrier (BBB) function. The control perfusate showed an increased water content, which is not surprising as some of our in-house data (and other studies) suggesting that the BBB function has a greater dependence to glucose than to oxygen when it comes to maintaining the barrier integrity. Since the CP is glucose-free, that is not surprising. The BEx group of course fare better (same level than 1 hour PMI group) but wonder how it would have fared if the CP contained the same amount of glucose and pyruvate. My personal thought is why did not the authors performed a gadolinium imaging of these two brains? They provide some T1 scans, which are nice but confirming changes in the BBB leakiness using gadolinium as contrasting agent would have been better.
Figure 3 show us a series of tissue staining of these brain, in particular from the hippocampal region. As expected, the Nissl staining worsened in the PMI, the presence of CP partially improved the situation and the BEx was similar to the 1 hour PMI and has the lowest cell death (as imaged by active caspase-3). When you look between CP and BEx, the difference is not that dramatic and makes me wonder that if we had the right CP formulation (with same glucose/lactate content), we would unlikely have a difference between CP and BEx, suggesting that perfusion with a saline solution oxygenated and with the correct amount of glucose can do as well than a more complex one.
Figure 4 show that the perfusion with BEx help to maintain astrocytes and microglial cells alive and functional (as measured by the secretion of pro-inflammatory cytokines following treatment with LPS).
Figure 5 show that there are some functional neurons present in BEx, capable to show electrophysiological activity. Small activity (not enough to be detected by EEG) but measurable by patch-clamp analysis.
Overall, it is a nice paper, considering it got published in Nature. There are some interesting stuff, but there are also some questionable limitations and caveats that I would have pointed as a reviewer and expected reviewers from Nature to have pointed it before letting it accepted. It shows that no matter what, never blindly trust a paper even if published in Nature.
The idea is very interesting and can help us better understand the post-mortem brain. It also raises the importance of CPR or any procedure aimed to keep a steady flow in the brain after injury or cardiac arrest and maybe worth considering it.

Categories
Drug Delivery Neurosciences Sciences Uncategorized

[Sciences/BBB/Drug Delivery] Red blood cell-hitchhiking boosts delivery of nanocarriers to chosen organs by orders of magnitude (Brenner et al., Nat Comm 2018)

I know, I know I have been fairly quiet. I have to tell that between attending a scientific meeting, teaching a summer course, taking care of two grants proposals and finally handling three manuscripts. However, sometimes I also like to share some papers published in the field that are interesting or bringing novel ideas or concepts. This one has been suggested by one of the author and this is his quick summary:
We bind nanoparticles to the surface of red blood cells. These nanoparticles are going to be released from the red cells once they pass the first capillary bed. Therefore we can concentrate the nanoparticles in the target tissue. In addition, these nanoparticles potentially can carry one or multiple selected drug(s). So if we inject intravenously the particles are going to be release in the lungs but if we inject through the brain arteries the nanoparticles will be release into the brain vasculature.
It is a very nice of work here published in Nature Communication (I consider this is one of the top OA journal to get published in) and you can download the full-text here.
You can also appreciate this paper likely went into at least one round of review, with a time period of about 7 months between it got accepted for review and accepted for publications.

In this paper, the authors have been working on trying to develop alternative drug delivery carrier, in that case use red blood cells as “piggyback” cells to enhance drug delivery. They tried different formulations on isolated RBCs and identified some suitable for carrying antibodies or proteins.  They called these piggybacking RBCs as RBC-Hitchiking (RH) (I wonder if it is some Easter egg towards the “Hitchiking Guide to Galaxy”).

Upon identification of the right nanoparticle materials, the authors investigated the distribution and the delivery of the conjugates in different organs, as liver and lungs. What is interesting is the amount of injected dose recovered is much higher in the RH than the free-circulating one, in particular in lungs, whether they are bare-naked or bound with a protein. These nano-carriers can be delivered to endothelial cells.

But the interesting snack-bite from this paper is the intra-arterial injection in the carotid artery, in which there was a significant increase in nano carriers delivery in the brain.  Nano-carriers alone show a %ID lesser than 1% (that is about what you expect from delivering antibodies from an IV route towards the brain)  to over 10%.   The delivery was also maintaining the ipsilateral injection site, which is good considering you are likely to treat one brain hemisphere.

Now, time for me to be picky and kind of wish we had information on the PK profile, especially if this approach increased the stability of the nanocarriers. It would be also interesting to see how this technique fare in a experimental disease model (for instance a xenograft brain tumor and see if you can deliver targeted chemotherapy in mice).

Nevertheless it is a good paper that take us out from the classical nanoparticles formulation and try here an innovative and novel approach in drug delivery.

 

Categories
Neurosciences Uncategorized

[Neurosciences/Cancer] About Sen. McCain brain tumor……and glioblastoma multiforme

You may have heard the tragic news that broke hell under the feet of Senator McCain (R-AZ) and his family on Wednesday. According to several sources, Senator McCain biopsy taken from his recent medical examination revealed to be classified as “glioblastoma multiform” (or GBM) for short.
I am not a brain cancer specialist but I have been doing some collaboration with a research group focused on GBM and I know all too well what does it mean and what is the prognosis. This is a type of tumor I would not wish my fiercest archenemy to get. I thought it would maybe help me to make a lay summary on GBM and explain why the BBB in that case is one of our fiercest challenge for drug delivery.

1. What is glioblastoma multiforme?
Glioblastoma multiforme (aka GBM) is a primary brain tumor characterized by its heterogeneity. However, we assume that GBM is originating from tumor astrocytes. Astrocytes are an important cell type of the macroglia, outnumbering neurons from 3:1 to 5:1. For a long time, astrocytes were considered as “glue cells”, playing only a function of scaffold and nourishing cells to neurons.
However, in the last 50 years, astrocytes have been shown to play much more important roles including the induction of the blood-brain barrier phenotype, regulation of the cerebral blood flow, modulation of neuronal cell activity, ability to form a parallel signaling network and also to play an important function in terms of protection of the brain during diseases.
The World Health Organization (WHO) classify GBM as a grade IV brain tumor (https://link.springer.com/article/10.1007/s00401-016-1545-1), meaning this type of cancer is classify as highly aggressive. Because the brain is a very soft tissue, tumor cells can easily proliferate, migrate and invade the surrounding healthy tissues.
The cause of GBM remains unclear, however we know that some GBMs are evolved from other types of brain tumors that have a lesser malignancy like lower-grade astrocytomas (grade II) or anaplastic astrocytomas (grade III). GBM is considered the most common type of primary tumor (not caused by metastatic cells) but also remains pretty rare with a case of 2-3 new patients diagnosed with the condition for every 100’000 inhabitants. There is a possible sexual dimorphism, as men are more likely to be affected than women (3:2 ratio), with an increased risk with age (https://www.ncbi.nlm.nih.gov/pubmed/17373878).
There is no particular risk factor associated with GBM. So far, we assume it has a strong genetic background, as several genes have been associated with GBM including some abnormalities (including loss of DNA in a chromosome domain) on the chromosome 10, mutations in various genes including TP53 (tumor suppressor gene, its function is to repair cell DNA or to induce cell death by apoptosis if it fails to repair), MDM2 (pro-survival gene, its function is to promote cell survival), EFGR and PDGFRα (these are two receptors that induce cell growth, cell proliferation and cell survival upon stimulation by growth factors).
Also noteworthy, there has been speculation and a perpetuated myth that wireless cell phones activity are associated with an increased risk of developing brain tumors. There is no reliable studies (both on epidemiological standpoint and on animal models) that can show an association between the use of cell phones with increased risk of brain tumors.

2. What are the treatments and prognosis for patients with GBMs?

This is where I cannot have much optimism. GBM is a very aggressive type of cancer. The average survival rate is about 18 months, with less than 5% of patients making through the 5-year milestone.
Like any type of cancer, there are different options proposed: radiation therapy, surgery and chemotherapy.
Surgery is commonly practiced but have several challenges: Firstly, it is very hard to identify GBM tissue from the healthy tissue by naked eye during surgery. The neurosurgeon has to rely on the MRI cliches to resect the tumor tissue. Secondly, the neurosurgeon wants to maximize the removal of tumor tissue but also he/she wants to limit the damage to the surrounding healthy tissue to not induce further brain damage. Thirdly, GBM is prone to form glioblastoma stem cell-like cells (GSCs) that share several features with stem cells. These cells can tolerate very aggressive environment and can rapidly proliferate. This is one of the common complication occurring in GBM patients. After you remove the tumor and see no trace of it under the MRI, you conclude it got eliminated. Only to find out three months later that the tumor grew back in size and started to invade more brain tissues.
Chemotherapy arsenal for GBM is very limited. So far, temozolomide is the way to go for GBM. However, 50% of the patients will not respond to temozolomide due to a mutation in the MGMT gene capable to inactivate it (http://www.sciencedirect.com/science/article/pii/S2352304216300162). Other anti cancerous agents including EGFR inhibitors (e.g. lapatinib) fail to show any activity to the presence of a pathological form of the blood-brain barrier (BBB) called “brain-tumor barrier” (BTB). This abnormal form of the BBB involve interactions with brain tumor cells. For a long time, the scientific community thought that BBB surrounding brain tumors was leaky and therefore accessible to chemotherapeutics. However, we know that indeed there is a BTB that can act as a barrier for the penetration and delivery of drugs into the tumor region.

There are some new avenues and approaches to target GBM but they are still very experimental. Amongst them, the possibility to use oncolytic viruses like a modified form of the polio virus capable to set brain tumor cells into “auto-destruction” mode. The second avenue explored is possible use of immunotherapy. The rationale behind is to help the immune system “to learn” about the tumor cells as foreign agents and strike them. There are some success using antibodies targeting tumors and also by reprogramming patients own cells (CAR-T cell therapy).

The diagnosis of GBM is probably one of the most difficult one a neurologist or neurosurgeon has to set, as it has a very poor prognosis. Let’s be honest, it is not looking good and for someone like Senator McCain that has been facing death several times during his military duties this is probably the toughest one to overcome.

3. Concluding remarks

This is why we need to foster research in brain tumors, this is why we need funding to help research findings, this is why we need clinical trials to pick the most promising drug candidate to fight this type of cancer, this is why we need to have a public health policy that ensure healthcare coverage for everyone can have access to treatment to beat the odds and not have to decline treatment because of the huge costs associated that health insurance may simply refuse to share the burden.

I am so embarrassed to say that right now the only thing we can provide Senator McCain and anyone with GBM and their relatives are our sympathies and our wishful thinking. This is why I have colleagues, peers working days and nights, weekends to bring on a “silver bullet” capable to annihilate such condition.

If you are looking to help, the best I can advise is to support research by donating to association like ABTA (http://www.abta.org) that focuses on funding research on brain tumors. Also considerate to let your voice heard and support healthcare policies that ensure an universal coverage of the population regardless of their age, gender, socio-economic status. Because refusing treatment by fear of letting your most loved ones with a humongous amount of debt should be the last of your worry.

 

 

 

 

 

 

Categories
Blood-Brain Barrier glut1 deficiency syndrome Uncategorized

[Neurosciences/BBB] 8th GLUT1 Deficiency Conference – Summary

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Today wrapped the second and last day of the 8th GLUT1 Deficiency conference that was held in Nashville, TN this year. It was my second time I am attending this conference and honored to be a guest speaker this year.

 

The whole conference took place at the Inn at Opryland, part of the Gaylord Resort at Opryland. It is a fairly impressive complex with shuttle to the Opry Mills outlet shopping center and, the Gaylord Resort & Convention Center (in which the AACP is also holding a meeting starting today but I am just attending one day meeting there).

According to the organizers, we had about 220 attendees, with 68 families present. What I liked this year was the blending between parents, healthcare providers and scientists. In the previous conference, the first day was family and healthcare providers and the second day was the professional day. This allowed a unique interactions, questions & answers and discussion.

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It was also a very good time for updating my knowledge on the disease. Not much on the basic science, but more on the current treatment and dietary intervention with various experts of the field including Pr. Jorg Klepper (University of Essen, Germany); Pr. Juan Pascual (UT Southwestern, Dallas, TX); Pr. Eric Kossoff (John Hopkins University, Baltimore, MD) and other scientific experts.
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My learning from the conference is that the disease in an evolutive disorder. We learn more about the disease as we learn from the patients growing in. As the patient grows, he or she displays different symptoms: “funny eyes movements” during infancy, presence of absence seizures during toddler times and learning attention and deficit during early school age, presence of movement disorders in both during childhood and adulthood and migraines, hemiplegia and “writers hand fatigue” syndrome. This seems to be linked by an impaired glucose uptake in the cerebral cortex and the thalamus.  It also seems that there is at some point in the disease the presence of a sexual dimorphism, as female patients seems to experience in their teenage years a “paroxysmal dystonia” that seems triggered by moderate and vigorous exercise. So, the GLUT1DS is not a static disorder. It is a disorder evolving over time with its clinical manifestations evolving as well.
The second thing I learned is the variety of “ketogenic diets”. There is not one single “keto diet” but several variants with different dosages and variety, including a Modified Atkins Diet.

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It seems there is not a “one size fits all” but rather different types of diets that also seems to vary with age.

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The younger age appears to need the following of a strict keto diet and as the patients age, some softening and flexibility can be introduced. It seems the critical time for the keto diet is infancy and childhood. The earlier the child is introduced, the better. There are also several companies providing cookbooks, supplements like keto powders or kets-friendly products aimed for patients.

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In terms of diagnosis, some interesting news came from a French biotech startup that can measure GLUT1 levels in RBC within 24 hours using a proprietary cell assay (that looks like an antibody assay) using a flow cytometry-based approach.
Another interesting result is the outcome of the ketogenic diet for GLUT1DS patients. For the vast majority of GLUT1DS patients (95% of patients), the keno diet significantly decrease the number of seizures by at least 50%. In contrast, other types of epilepsies combined only show a 50% of patients showing a responsive outcome to keto diet. Still, 5% of GLUT1DS do not respond to keto diet and there is a fraction of patients that show a normal glucose CSF levels and/or GLUT1 expression. We certainly have a lot of patients that undergo undiagnosed or misdiagnosed for years as “drug-refractory epilepsies”. But it seems that some patients maybe falsely diagnosed as GLUT1DS. Hopefully, with the decrease in price for DNA testing (it seems 23andMe can detect some GLUT1 SNPs) may help to broaden the diagnosis and identification of patients.
Some interesting topics presented at the conference was some possible drug adverse effects reported in G1D heterozygous mice in particular to diazepam and phenobarbital but also other drugs. Some parents noted the anecdotical adverse reactions following certain treatment. However, the absence of studies directly investigating such drug adverse effects in G1D patients most of the time go under the radar, with the health practitioner attributing it to the disease condition rather than some particular drug adverse effects. Having from screening tools can greatly help.
Another interesting presentation is the study of G1D heterozygous mice. These mice seems to display a lower brain vascular density compared to wild-type. This is not surprising considering the recent work of Pr. Peter Carmeliet (Universidaed Leuwen, Belgium) on endothelial cell metabolism. According to Pr. Carmeliet, brain endothelial cells highly depend on glycolysis to function despite being in presence of plenty amount of oxygen levels.
There have been also discussion of trying to setup a comprehensive guide for parents for a consensus on GLUT1DS diagnosis and management that can help them as a source for documentation during their visit with their doctors. There is also a discussion of improving the community outreach to professionals and politicians to improve the funding and the recognition of GLUT1DS as a condition, discussing about supporting open-access options for certain papers allowing parents a free-access to these new studies and also finding ways to support GLUT1DS awareness and management among minority populations and in other geographic areas (especially South America).
The person missing at this meeting by his presence was certainly Pr. Daryl DeVivo (Columbia University, New York, NY). Little patients left him some very kind words and their name on a paper board. I found it was a very cute gesture and remembered us that his absence was felt.
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The interesting silver lining comes from Europe, as they have set now a sister association that held their first European GLUT1 meeting last fall and plan to hold it in London in 2018 and in Paris in 2020.
For me, I am looking forward to attend the 2019 meeting in Washington DC and hopefully bring on some more breaking news from my lab there.

 

 

 

Categories
Neurosciences Sciences Uncategorized

[Science/Neurosciences] Mole rats running on…..fructose!

You may have heard about this paper from Park TJ and colleagues (Park TJ et al., Science 2017) on how mole rats were showing extreme compliance to anoxic (0% oxygen) level, no? It made the news these last couple of weeks and finally was able to put my hand on. You can access to it here (need to have a Science subscription though) but I read it and it is really interesting for many reasons, especially because I try to think how can we translate it as a therapeutical strategies for hypoxemic pre-terms babies or even as a stroke fighting-drug.

First, mole rats. Oh mole rats! Not the prettiest mammals out there. They are naked, they have long teeth and look all wrinkled. But they are underground dwelling animals like moles. Underneath, oxygenation is scarce and these animals have developed formidable adaption to hypoxia. We as humans can barely survive 8% oxygen (thats about the Mount Everest). At 6% oxygen (thats what would happen if a aircraft cabin undergo a depressurization), you die within minutes.

In this experiment, they went fairly extreme, they put the animals into anoxia (0% O2) and looked how long the animals would survive. They used a common mouse strain as a control. Mice rapidly died at 100% rate at 5% O2 and died twice faster (based on the number of breaths) at 0% O2. In opposite, mole rats went 30 times longer than mice and still were doing fine (0% deaths). Were mice died within 60 seconds, molerats died over 1000 seconds of anoxia. One possible reason is their ability of their heart to beat much longer than mice.

Now what is interesting is how the authors came to fructose. Mammalian cells run on glucose through the following biochemical pathway (see below):

glycolysis-10-steps-explained-steps-by-steps-with-diagram

I will spare you the Krebs cycle but this is what every since healthcare and life scientist have to learn. Glucose is broken down into many intermediates and at the end becomes pyruvate. From pyruvate, you can enter the Krebs Cycle and produce a significant amount of ATP (the fuel cell of every living organism) needed to provide energy for any biological process. Krebs cycle is very good at it and provides an ATP yield of 36ATP/glucose consumed. However, the Krebs cycle stall under hypoxia and forces the cell to adapt. In particular, it needs to regenerate NAD+ (from NADH) in order to keep the system flowing and producing energy. One way mammalian cells solved it is by converting pyruvate into lactate. Thats allow cells to produce some energy (2ATP/glucose) and regenerate its NAD+. However lactate has tendency to accumulate and develop adverse effect (the famous muscle cramps any runners have experienced).

Fructose is not much different from glucose, it has the same composition but just a little difference in the molecular structure.  We get fructose from our daily diet made of fruits and vegetables, but also from refined sugar (sucrose or HFCS, same deal).

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Now fructose can bypass and feed the glycolysis at different steps:
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Fructose can produce glyceraldehyde-3-P (GA3P) and dihydroxyacetone-P (DHAP) and enter the rest of the glycolysis. Now like glucose, fructose needs a transporter to enter inside the cells. Glucose has a myriad of glucose transporters (GLUTs and SGLTs) that can provide glucose inside the cells. But not fructose. These transporters have very poor affinity for fructose. In that case, fructose has one transporter called GLUT5 that prefers fructose over glucose.
Now this is where it becomes interesting, mole rats show much higher levels of fructose than mice during anoxia in many organs and in blood. Now the interesting fact is the high prevalence of it as fructose-1-P in the brain, only this form. How it goes in? I don’t know but mole rat brains have a higher GLUT5 expression than mice. Where this transporter is expressed? I don’t know either but it would interesting to look at this transporter at the BBB.

What is interesting is the difference in how mole rats  brain and heart differ from mice in terms of fructose activity. When administered fructose over glucose, mole rats organs know to switch between the two sugars to gets its energy. In the other hand, mice organs fail to switch and result in decrease their activity.

Now the question I have (since I am working on glucose transport across the BBB and its impact in kids suffering from GLUT1 deficiency) is: does human express GLUT5? If yes, which brain cells express it and if these cells can adopt fructose as a source of energy?

Categories
Alzheimer's Disease Neurodegenerative diseases Neurosciences Sciences

[Neurosciences/Alzheimer] Structural variation in amyloid-β fibrils from Alzheimer’s disease clinical subtypes

Interesting study published in Nature about how differences in Abeta fibrils have an implication on the clinical symptoms.
A quick refresher for those not much familiar (it is also a bit of a headache as I just dive in the Alzheimer’s research). Alzheimer’s disease is characterized by the formation of senile plaques and tangles, such structures have been considered as the causative agents in neuronal cell death.
These plaques are clumps of a peptide called Abeta (for amyloid beta) peptides. We know how these peptides are formed (by cleavage of the amyloid precursor protein or APP) and we know there are different “flavors” of Abeta that have been described: Abeta 1-40, Abeta 1-42…..
We also know that these peptides are “sticky”. They are released as monomers (single peptide) and because they are hydrophobic (hates water, like oil hates water) they will try to bind together and form oligomers (think about little sticky balls). These oligomers then can form fibrils.
It is a very “dry” study because it is heavy on structural biology and computational biology but in the same time very interesting.
It shows us that plaque formation is not a linear processes, there are different combinations possible (imagine like comparing snowflakes) that have a direct impact on the clinical presentation and outcomes in patients.
That’s maybe providing another way of thinking in targeting Abeta that can help us learn from the failure of previous clinical trials.

Abstract and link to the original paper

Aggregation of amyloid-β peptides into fibrils or other self-assembled states is central to the pathogenesis of Alzheimer’s disease. Fibrils formed in vitro by 40- and 42-residue amyloid-β peptides (Aβ40 and Aβ42) are polymorphic, with variations in molecular structure that depend on fibril growth conditions. Recent experiments suggest that variations in amyloid-β fibril structure in vivo may correlate with variations in Alzheimer’s disease phenotype, in analogy to distinct prion strains that are associated with different clinical and pathological phenotypes. Here we investigate correlations between structural variation and Alzheimer’s disease phenotype using solid-state nuclear magnetic resonance (ssNMR) measurements on Aβ40 and Aβ42 fibrils prepared by seeded growth from extracts of Alzheimer’s disease brain cortex. We compared two atypical Alzheimer’s disease clinical subtypes—the rapidly progressive form (r-AD) and the posterior cortical atrophy variant (PCA-AD)—with a typical prolonged-duration form (t-AD). On the basis of ssNMR data from 37 cortical tissue samples from 18 individuals, we find that a single Aβ40 fibril structure is most abundant in samples from patients with t-AD and PCA-AD, whereas Aβ40 fibrils from r-AD samples exhibit a significantly greater proportion of additional structures. Data for Aβ42 fibrils indicate structural heterogeneity in most samples from all patient categories, with at least two prevalent structures. These results demonstrate the existence of a specific predominant Aβ40 fibril structure in t-AD and PCA-AD, suggest that r-AD may relate to additional fibril structures and indicate that there is a qualitative difference between Aβ40 and Aβ42 aggregates in the brain tissue of patients with Alzheimer’s disease.

Source: Structural variation in amyloid-β fibrils from Alzheimer’s disease clinical subtypes : Nature : Nature Research

Categories
Blood-Brain Barrier Neurodegenerative diseases Neurosciences Uncategorized

[Neurosciences/BBB] Alpha-Synuclein pre-formed fibrils impair tight junction protein expression without affecting cerebral endothelial function

Hi everyone, today I am experimenting a journal club on a blog, sharing my thought on some recent publications in the BBB field.
The paper I will be discussing today is a study recently published by Dr. Roger A Barker (University of Cambridge, Cambridge, UK) in the journal Experimental Neurology (IF=4.5) titled “Alpha-Synuclein pre-formed fibrils impair tight junction protein expression without affecting cerebral endothelial function” (http://www.sciencedirect.com/science/article/pii/S0014488616302710).
Why did I choose this paper? Because this paper is investigating the interaction between alpha-synuclein (aSyn) and the blood-brain barrier. I have recently developed interests to see how the BBB behave in neurodegenerative disorders such as Alzheimer’s, Parkinson’s and Huntington’s disease and in particular how the BBB let peptides involved in such diseases go in and out. In this study, they have used the hCMEC/D3 immortalized human brain endothelial cell line (Weksler et al., FASEB 2005) as well as primary human neurons and astrocytes co-cultures. For the hypothesis, they have used monomeric aSyn as well as what they referred as preformed fibrils (pff).
One of the caveat of this study is the use of hCMEC/D3 cells that are notoriously known for their poor barrier properties. This poor barrier properties was indeed displayed in the paper as the authors reported values of only 15 Ohms*cm2 that is very low. I was also surprised that the authors reported the use of FITC-dextran of 10kDa size as this compound is big enough to poorly cross the BBB. But the use of such tracer also make sense as it can also a comparison to aSyn. aSyn (as pff) did not have much effect on the barrier function, we can even observe an increase in the TEER and decrease in the permeability suggesting a possible induction of the barrier. Another piece of data presented purposively show a immunostaining for ZO1, a protein adapter for tight junction complexes. The immunolocalization of ZO1 was suboptimal, making difficult the interpretation of the negative effect of pff on ZO1. There is a increase  in immunoreactivity following pff treatment. Astrocytes co-cultures improved the barrier function and again no effect of pff was noted on the barrier function. The authors also showed no effects of pff on astrocytes GFAP expression.
The interesting but also the data that raised some skepticism is the experiments involving hCMEC/D3 cells co-cultured with primary neurons. The TEER is lower than the monocultures and astrocyte co-cultures (~8 Ohms.cm2) yet they display permeability values for FITC-dextran 10kDa that are 200X lower than the monoculture. Aside from this issue (that should have been noted by the peer-reviewers), there were also disprecancies between TEER and permeability. If we consider the relative permeability to untreated group accurate, we can note a 50% increase in permeability following treatment with pff or aSyn monomers. Again the immunostaining was pointless as the staining for ZO1 looked poor but also the representative pictures are displaying different cell densities (as noted by  DAPI-cell nuclei density per field).
To better understand the impact of pff on neurons, the authors treated some fetal cortical cells with aSyn monomers or pff using a TUNEL assay (a common technique to observe cell death in vitro) but this was using an immunohistochemistry approach (HRP with DAB stain) instead of the classical immunofluorescence.
Finally, the authors showed some quantitative protein expression analysis from the in vitro cultures and from post-mortem tissues obtained from PD patients. An interesting feature observed was the increase in ZO1, claudin-5 expression following neuronal co-culture, but also a very strong regulation of tricellulin and MarvelD3 proteins (their detection was weak if not negative in monocultures). Surprisingly, the pff treatment decreased occludin and ZO-1 expression at protein levels. The PD Western blots were showing much inter-individuals variability that makes hard to translate from in vitro to in vivo.
In conclusion, the title was very attracting and interesting but I felt the data was poorly supporting the claims. The hCMEC/D3 model is not the best model for modeling the BBB in vitro, especially considering the barrier values reported were below what are commonly reported. I was left on my hunger, it had some interesting data but also some data with lesser quality and foremost did not address if aSyn, as its monomeric or pff form can cross or not the BBB.

 

Categories
Neurosciences Uncategorized

[Neurosciences/BBB/ASD] Impaired Amino Acid Transport at the Blood Brain Barrier Is a Cause of Autism Spectrum Disorder

Very interesting study that came out, maybe the first study that directly link the blood-brain barrier dysfunction to a certain form of autism spectrum disorder (at least in a rodent model).
In this study, Tarlungeanu and colleagues identified the solute carrier SLC7A5, encoding for the large aminoacid transporter-1 (LAT1) as the causative agent. LAT1 usually transport branched aminoacids (BCAA) like valine, leucine and isoleucine inside the brain.
The first piece of interesting data is the aminoacid temporal profile compared to wt mice at different developmental stages (embryonic vs. postnatal versus adulthood. BCAA levels went down, but surprisingly phenylalanine and histidine levels went up.
SLC7A5 KO mice had a neurological signature similar to other autism models. They also validated their findings by whole-genome sequencing genes from patients (from Lybia and Turkey) from co-sanguine marriages displaying various neurological disorders and identified two key mutations impairing SLC7A5 activity.
You can find more about this study by clicking to the source: Impaired Amino Acid Transport at the Blood Brain Barrier Is a Cause of Autism Spectrum Disorder