Mitochondrial dynamics, elimination and biogenesis during post-ischemic recovery in ischemia-resistant and ischemia-vulnerable gerbil hippocampal regions.

Transient ischemic attacks (TIA) result from a temporary blockage in blood circulation in the brain. As TIAs cause disabilities and often precede full-scale strokes, the effects of TIA are investigated to develop neuroprotective therapies. We analyzed changes in mitochondrial network dynamics, mitophagy and biogenesis in sections of gerbil hippocampus characterized by a different neuronal survival rate after 5-minute ischemia-reperfusion (I/R) insult. Our research revealed a significantly greater mtDNA/nDNA ratio in CA2-3, DG hippocampal regions (5.8 ± 1.4 vs 3.6 ± 0.8 in CA1) that corresponded to a neuronal resistance to I/R. During reperfusion, an increase of pro-fission (phospho-Ser616-Drp1/Drp1) and pro-fusion proteins (1.6 ± 0.5 and 1.4 ± 0.3 for Mfn2 and Opa1, respectively) was observed in CA2-3, DG. Selective autophagy markers, PINK1 and SQSTM1/p62, were elevated 24-96 h after I/R and accompanied by significant elevation of transcription factors proteins PGC-1α and Nrf1 (1.2 ± 0.4, 1.78 ± 0.6, respectively) and increased respiratory chain proteins (e.g., 1.5 ± 0.3 for complex IV at I/R 96 h). Contrastingly, decreased enzymatic activity of citrate synthase, reduced Hsp60 protein level and electron transport chain subunits (0.88 ± 0.03, 0.74 ± 0.1 and 0.71 ± 0.1 for complex IV at I/R 96 h, respectively) were observed in I/R-vulnerable CA1. The phospho-Ser616-Drp1/Drp1 was increased while Mfn2 and total Opa1 reduced to 0.88 ± 0.1 and 0.77 ± 0.17, respectively. General autophagy, measured as LC3-II/I ratio, was activated 3 h after reperfusion reaching 2.37 ± 0.9 of control. This study demonstrated that enhanced mitochondrial fusion, followed by late and selective mitophagy and mitochondrial biogenesis might together contribute to reduced susceptibility to TIA.

Increase of aquaporin 9 expression in astrocytes participates in astrogliosis.

Here we assess the potential functional role of increased aquaporin 9 (APQ9) in astrocytes. Increased AQP9 expression was achieved in primary astrocyte cultures by transfection of a plasmid-containing green fluorescent protein fused to either wild-type or mutated human AQP9. Increased AQP9 expression and phosphorylation at Ser222 were associated with a significant change in astrocyte morphology, mainly with a higher number of processes. Similar phenotypic changes are observed in astrogliosis processes after injury. In parallel, we observed that in vivo, thrombin preconditioning before ischemic stroke induced an early increase in AQP9 expression in the male mouse brain. This increased AQP9 expression was also associated with astrocyte morphological changes, especially in the white matter tract. Astrocyte reactivity is debated as being either beneficial or deleterious. As thrombin preconditioning leads to a decrease in lesion size after stroke, our data suggest that the early increase in AQP9 concomitant with astrocyte reactivity leads to a beneficial effect. © 2017 Wiley Periodicals, Inc.

Molecular and Cellular Responses to Interleukin-4 Treatment in a Rat Model of Transient Ischemia.

Within hours after stroke, potentially cytotoxic pro-inflammatory mediators are elevated within the brain; thus, one potential therapeutic strategy is to reduce them and skew the brain toward an anti-inflammatory state. Because interleukin-4 (IL-4) treatment induces an anti-inflammatory, "alternative-activation" state in microglia and macrophages in vitro, we tested the hypothesis that early supplementation of the brain with IL-4 can shift it toward an anti-inflammatory state and reduce damage after transient focal ischemia. Adult male rat striata were injected with endothelin-1, with or without co-injection of IL-4. Inflammation, glial responses and damage to neurons and white matter were quantified from 1 to 7 days later. At 1 day, IL-4 treatment increased striatal expression of several anti-inflammatory markers (ARG1, CCL22, CD163, PPARγ), increased phagocytic (Iba1-positive, CD68-positive) microglia/macrophages, and increased VEGF-A-positive infiltrating neutrophils in the infarcts. At 7 days, there was evidence of sustained, propagating responses. IL-4 increased CD206, CD200R1, IL-4Rα, STAT6, PPARγ, CD11b, and TLR2 expression and increased microglia/macrophages in the infarct and astrogliosis outside the infarct. Neurodegeneration and myelin damage were not reduced, however. The sustained immune and glial responses when resolution and repair processes have begun warrant further studies of IL-4 treatment regimens and long-term outcomes.