A couple of days ago, I attended the second full-day of the American Heart Association International Stroke Conference (#ISC20) that held in Los Angeles, CA from February 19th until February 21st.
Considering this is a meeting mostly driven towards clinical science (physicians, nurses….), it was a very good year for basic sciences as I had a pretty well loaded schedule of scientific sessions.
My goal is not to provide a detailed description of the findings but really try to keep this summary succint and easy to understand for the layman language. Here are some of the highlights that caught my attention:
* We knew that age is an important predictor of stroke severity and recovery outcome. What we did not knew about is one of these parameters involved is inflammation. A study presented data suggesting that the infusion of young plasma in aged mice undergoing stroke fared better than infusion of old plasma , in terms of infarct size and outcomes. A probable mechanism of action seems to involve a shift of balance in the microglia population (pro-inflammatory vs. anti-inflammatory microglia) and seems to involve exosomes (30-40nm sizes) diffusion from plasma into the brain.
* Further work on the gut-brain axis and stroke, especially this one on the effect of ischemic stroke on the gut. What is interesting is that an ischemic stroke may have a ripple effect on the gut lining in mice, as it can significantly alter the colon integrity. What was interesting is the sex dimorphism observed, as young female were showing an intact GI lining compared to other group, aligning with the well-established finding that young females fared better than other groups in terms of stroke severity and outcome. Two possible gene candidates identified: MUC4 and CD44, as well as mucin-related genes. Changes in intraepithelial cells (IECs) seems a key factor in such changes.
* Microglia is an important type of immune cells, resident cells inside the brain in resting state. However following injury (DAMPs) or infection (PAMPs), these microglial cells can become activated and trigger the first steps of neuroinflammation. In particular, aging seems to increase the microglial cells population secreting TNF-alpha (a well-known pro-inflammatory factor) suggesting that microglia activation maybe inherently bad for stroke severity and outcome. Therefore, blocking or targeting microglial cell population (by depleting them) would be considered beneficial no? Well turns out maybe not. A study targeted microglia by depleting these cells in both young and old animals using PLX-5622 for 21 days. Interestingly, such treatment resulted in worsened stroke outcome, as the infarct size noted in MCAO group was bigger versus the vehicle group. What was also interesting was such animals showed an increased numbers of monocytes and neutrophils, and an increase in reactive astrocytes in aged animals. There was also changes in the gut microbiota as two genus (Verrucombroia and Akkermansia) were increased in this group, as well as a decrease in Iba1+ gut macrophages.
* Ischemic brain has an effect on the macrophage transcriptome. A study looked at macrophage gene expression profile between circulating monocytes/macrophages in the periphery versus macrophages that migrated into the ischemic injury site. More than 3000 genes were identified as differentially expressed, with an important clustering of genes associated with the peroxisome proliferator-activated receptors (PPARs) including PPAR-delta and PPAR-gamma.
* MicroRNAs (mIR) play an important role in ischemic stroke injury. In particular a study showed that inhibition of mIR-15a and mIR-16-1 following MCAO (for up to 21 days) resulted in an increased post-stroke angiogenesis (using conditional KO animals). Treatment with AZD0530 resulted in a worsening outcome. A possible mechanism of action may occur via Src-dependent mechanism, that still need some brush-up (is Src activation or inhibition needed?).
* This year, the Thomas Willis award and lecture went to Pr. Maiken Nedergaard (University of Rochester) on the contribution of the glymphatic system. I have to say this is still a very controversial topic that remains highly contested within the BBB field (especially from those interested in fluids movements inside and outside the brain). I have been following as a bystander so I just really keep it on what I have seen presented (and not coming with a knowledge of her papers). According to Pr. Nedergaard, it is a “highly polarized” pumping system, pumping the CSF down to the arterial system, pumped by the glia endfeet processes and clearing in the venous system. According to her, meninges and dura have lymphatic vessels. Amongst things exchanged are ions, lactates and she was also able to observe movements of microspheres up to 1 micron size (aggregates moved to same speed than single ones).
The CSF tracer diffusion was much more present when animals were in sleeping state or under anesthesia, all into the cortex. Similar observations were done in patients as well. The flow is fast and occurs from central to periphery. The CSF accounts about 10% of the brain. According to her findings, tracer was flowing in despite reduced blood flow, all along the cerebral arteries and increase observed mainly in the ipsilateral side.
She also reported a decrease in the volume of CSF after stroke, suggesting that the CSF maybe the source of acute edema. Interestingly, she reported an increase of intracellular calcium influx (known to occur during the ischemic depolarization) preceding the CSF flux, and would still occur later after stroke as the post-stroke vasoconstrictions would drive such CSF flux.
The rest of the day was marked by some other sessions, meeting old collaborators and friends in the stroke field (an opportunity to meet beyond the emails) and by the visit of some posters.
Overall, it was a good stroke conference this year, and hopefully next year would allow me to spend more time (it is always tenuous to attend it as it falls right in my busiest semester). Next year? It will take place in the (very) mildly hypoxic mile-high city (Denver, CO), allowing me to drive (or maybe just an hour fly away whichever will be the cheapest option). See you in ISC2021 in Denver!