α-Endosulfine (ARPP-19e) Expression in a Rat Model of Stroke

In nutrient restricted environments, the yeast endosulfines Igo1/2 are activated via TORC1 inhibition and function critically to initiate and coordinate the cellular stress response that promotes survival. We examined expression of αEnsa, the mammalian homolog of yeast endosulfines, in rat stroke. Prominent neuronal upregulation of αEnsa was identified in 3 patterns within the ischemic gradient: (1) neurons in GFAP-/HSF1+ cortex showed upregulation and near-complete nuclear translocation of αEnsa protein within hours of ischemic onset; (2) neurons in GFAP+/HSF1+ cortex showed upregulation in cytoplasm and nuclei that persisted for days; (3) neurons in GFAP+/HSF1- cortex showed delayed cytosolic-only upregulation that persisted for days. Findings were corroborated using in situ hybridization for ENSA mRNA. Rapamycin treatment was found to reduce infarct size and behavioral deficits and, in GFAP+/HSF1+ zones, enhance αEnsa neuronal nuclear translocation and mitigate cell death, relative to controls. Based on the conservation of TOR signaling across species, and on the finding that the Rim15-Igo1/2-PP2A module is triggered by substrate deprivation in eukaryotic yeast, we speculate that αEnsa is activated by substrate deprivation, functioning through the homologous MASTL-αEnsa/ARPP19-PP2A module to promote neuronal survival. In conjunction with recent studies suggesting a neuroprotective role, our data highlight a potential function for αEnsa within ischemic brain.