Region-specific changes in aquaporin 4 induced by hyperglycemia underlie the differences in cell swelling in the cortex and striatum after cerebral ischemia-reperfusion

(S)-roscovitine, a CDK inhibitor, decreases cerebral edema and modulates AQP4 and α1-syntrophin interaction on a pre-clinical model of acute ischemic stroke

Cerebral edema is one of the deadliest complications of ischemic stroke for which there is currently no pharmaceutical treatment. Aquaporin-4 (AQP4), a water-channel polarized at the astrocyte endfoot, is known to be highly implicated in cerebral edema. We previously showed in randomized studies that (S)-roscovitine, a cyclin-dependent kinase inhibitor, reduced cerebral edema 48 h after induction of focal transient ischemia, but its mechanisms of action were unclear. In our recent blind randomized study, we confirmed that (S)-roscovitine was able to reduce cerebral edema by 65% at 24 h post-stroke (t test, p = .006). Immunofluorescence analysis of AQP4 distribution in astrocytes revealed that (S)-roscovitine decreased the non-perivascular pool of AQP4 by 53% and drastically increased AQP4 clusters in astrocyte perivascular end-feet (671%, t test p = .005) compared to vehicle. Non-perivascular and clustered AQP4 compartments were negatively correlated (R = -0.78; p < .0001), suggesting a communicating vessels effect between the two compartments. α1-syntrophin, AQP4 anchoring protein, was colocalized with AQP4 in astrocyte endfeet, and this colocalization was maintained in ischemic area as observed on confocal microscopy. Moreover, (S)-roscovitine increased AQP4/α1-syntrophin interaction (40%, MW p = .0083) as quantified by proximity ligation assay. The quantified interaction was negatively correlated with brain edema in both treated and placebo groups (R = -.57; p = .0074). We showed for the first time, that a kinase inhibitor modulated AQP4/α1-syntrophin interaction, and was implicated in the reduction of cerebral edema. These findings suggest that (S)-roscovitine may hold promise as a potential treatment for cerebral edema in ischemic stroke and as modulator of AQP4 function in other neurological diseases.

Hyperglycemia exacerbates cerebral ischemia/reperfusion injury by up-regulating autophagy through p53-Sesn2-AMPK pathway

Hyperglycemia exacerbates ischemic brain injury by up-regulating autophagy. However, the underlying mechanisms are unknown. This study aims to determine whether hyperglycemia activates autophagy through the p53-Sesn2-AMPK signaling pathway. Rats were subjected to 30-min middle cerebral artery occlusion (MCAO) with reperfusion for 1- and 3-day under normo- and hyperglycemic conditions; and HT22 cells were exposed to oxygen deprivation (OG) or oxygen-glucose deprivation and re-oxygenation (OGD/R) with high glucose. Autophagy inhibitors, 3-MA and ARI, were used both in vivo and in vitro. The results showed that, compared with the normoglycemia group (NG), hyperglycemia (HG) increased infarct volume and apoptosis in penumbra area, worsened neurological deficit, and augmented autophagy. after MCAO followed by 1-day reperfusion. Further, HG promoted the conversion of LC-3I to LC-3II, decreased p62, increased protein levels of aldose reductase, p53, P-p53ser15, Sesn2, AMPK and numbers of autophagosomes and autolysosomes, detected by transmission electron microscopy and mRFP-GFP-LC3 molecular probe, in the cerebral cortex after ischemia and reperfusion injury in animals or in cultured HT22 cells exposed to hypoxia with high glucose content. Finally, experiments with autophagy inhibitors 3-MA and aldose reductase inhibitor (ARI) revealed that while both inhibitors reduced the number of TUNEL positive neurons and reversed the effects of hyperglycemic ischemia on LC3 and p62, only ARI decreased the levels of p53, P-p53ser15. These results suggested that hyperglycemia might induce excessive autophagy to aggravate the brain injury resulted from I/R and that hyperglycemia might activate the p53-Sesn2-AMPK signaling pathway, in addition to the classical PI3K/AKT/mTOR autophagy pathway.

Glial cell alterations in diabetes-induced neurodegeneration

Type 2 diabetes mellitus is a global epidemic that due to its increasing prevalence worldwide will likely become the most common debilitating health condition. Even if diabetes is primarily a metabolic disorder, it is now well established that key aspects of the pathogenesis of diabetes are associated with nervous system alterations, including deleterious chronic inflammation of neural tissues, referred here as neuroinflammation, along with different detrimental glial cell responses to stress conditions and neurodegenerative features. Moreover, diabetes resembles accelerated aging, further increasing the risk of developing age-linked neurodegenerative disorders. As such, the most common and disabling diabetic comorbidities, namely diabetic retinopathy, peripheral neuropathy, and cognitive decline, are intimately associated with neurodegeneration. As described in aging and other neurological disorders, glial cell alterations such as microglial, astrocyte, and Müller cell increased reactivity and dysfunctionality, myelin loss and Schwann cell alterations have been broadly described in diabetes in both human and animal models, where they are key contributors to chronic noxious inflammation of neural tissues within the PNS and CNS. In this review, we aim to describe in-depth the common and unique aspects underlying glial cell changes observed across the three main diabetic complications, with the goal of uncovering shared glial cells alterations and common pathological mechanisms that will enable the discovery of potential targets to limit neuroinflammation and prevent neurodegeneration in all three diabetic complications. Diabetes and its complications are already a public health concern due to its rapidly increasing incidence, and thus its health and economic impact. Hence, understanding the key role that glial cells play in the pathogenesis underlying peripheral neuropathy, retinopathy, and cognitive decline in diabetes will provide us with novel therapeutic approaches to tackle diabetic-associated neurodegeneration.