Abstract P728: Promoting Neuron Survival After Ischemic Stroke via Restoring Astrocytic Endoplasmic Reticulum Function and Glucose Metabolism

Abstract

Stroke-induced reactive astrocytes exhibit abnormal functions and contribute to neurodegeneration. Thus, restoring normal homeostatic astrocyte functions is important for neuroprotection. Overstimulation of Na + /H + exchanger 1 (NHE1) activity after stroke triggers reactive astrocyte formation, which displays abnormal functions. We have shown that targeted deletion of Nhe1 in astrocytes leads to inhibition of reactive astrocytes, reduced infarct volume, and improved neurological function after ischemic stroke. In the present study, we investigated ischemic stroke-mediated endoplasmic reticulum (ER) stress and unfolded protein response (UPR) and its impact on cellular reparative functions. Astrocyte specific deletion of Nhe1 in Gfap-Cre ERT2+/- ;Nhe1 f/f mice ( Nhe1 Astro-KO) was induced by tamoxifen (Tam) treatment. Gfap-Cre ERT2- /- ;Nhe1 f/f mice treated with Tam served as wild-type (WT) controls. In transient middle cerebral artery occlusion (tMCAO) model, ischemic stroke triggered a significant increase in expression of ER stress marker proteins ATF4 and CHOP at 24 h reperfusion (Rp) in WT ischemic brains (p< 0.05), no such elevation was detected in Nhe1 Astro-KO ischemic brains. Immunocytochemical analysis revealed abundant ER chaperone protein GRP78 expression in non-ischemic cortical neurons (NeuN + ) of WT brains, but it was reduced by ~ 70% at 48 h Rp (p < 0.001). In contrast, Nhe1 Astro-KO brains preserved ER chaperone protein GRP78 in NeuN + cells in the ischemic cortex, and their adjacent GFAP + astrocytes showed ~40% increased GRP78 expression compared to WT. These polarized astrocytes with elevated GRP78 expression may provide neuroprotective support. Dysfunctional ER chaperone activity can affect glucose metabolism by decreasing glycolysis and mitochondrial respiration. Consistently, our bulk RNA-Seq analysis of reactive astrocytes shows that Nhe1 Astro-KO astrocytes exhibit significantly stimulated transcriptome profiles for glycolysis ( Hk2, Gpi, and Ldhb) and oxidative phosphorylation (complex I, IV and V). Together, our study demonstrates that restoring astrocytic ER chaperon function and glucose metabolism via specific deletion of Nhe1 promotes neuron survival after ischemic stroke.