Remote Ischemic Post-Conditioning Modulates Brain Expression of PIWI Proteins After Experimental Cerebral Ischemia

This study explores the involvement of PIWI family proteins in cerebral ischemia and their potential contribution to the neuroprotective effects of remote ischemic post-conditioning (RIC), a promising intervention for ischemic stroke whose underlying mechanisms remain to be fully elucidated. Using a mouse model of transient middle cerebral artery occlusion (MCAo), we evaluated the effects of RIC induced by femoral artery occlusion (FAo) on brain injury, inflammation, and PIWI proteins expression in the brain. RIC significantly reduced infarct volume, cerebral edema, and neurological deficits, while attenuating the ischemia-induced upregulation of pro-inflammatory cytokines, including IL-1β and TNF-α, in the brain cortex. The ischemic insult induced a robust upregulation of PIWIL2 and PIWIL4 in the ipsilateral cortex, primarily in neurons, with PIWIL4 also detected in astrocytes, few microglia and numerous infiltrating myeloid cells. Notably, RIC suppressed this cortical upregulation, suggesting a potential link between PIWI proteins and ischemic damage. By contrast, in neurogenic regions of the hippocampus, RIC selectively enhanced PIWIL4 expression, particularly in neurons of the CA3 region and dentate gyrus. This increase was associated with elevated expression of the neurogenic and repair-related factors TGF-β1 and TREM2. Accordingly, in the subventricular zone of post-conditioned mice, PIWIL4 was localized in SOX2-positive neural progenitor cells that also express the proliferation marker Ki67. These findings reveal a region- and cell-specific modulation of PIWILs expression in cerebral ischemia and RIC, strongly supporting the concept that PIWI pathways may represent promising targets for neuroprotection and recovery following stroke.