Enriched housing promotes post-stroke neurogenesis through calpain 1-STAT3/HIF-1α/VEGF signaling

Abstract

Enriched environment (EE) has been shown to promote neurogenesis and functional recovery after ischemic stroke. However, the underlying molecular mechanisms are not fully understood. In this study, C57BL/6 mice underwent middle cerebral artery occlusion (60 min) followed by reperfusion, after which mice were housed in either standard environment (SE) or EE and allowed to survive for 3, 4, 6 or 10 weeks. Ipsilateral subventricular zone (SVZ) or striatum cells were dissociated from ischemic hemispheric brains of enriched mice at 14 days post-ischemia (dpi) and cultured in vitro. Our data showed that post-ischemic EE inhibited calpain 1 activity, and increased the expression of phosphorylated signal transducer and activator of transcription 3 (p-STAT3) in the ischemic hemisphere of enriched mice at 21 dpi. Calpain 1-specific inhibitor PD151746 further increased p-STAT3 expression and augmented the promoting effects of EE on post-stroke SVZ neural precursor cells (NPCs) proliferation and functional recovery. EE also increased the expression of hypoxia-inducible factor 1-alpha (HIF-1α) and vascular endothelial growth factor (VEGF) in the ischemic hemisphere at 21 dpi. Inhibition of the JAK/STAT3 pathway with AG490 decreased the expression of HIF-1α and VEGF. Furthermore, inhibition of HIF-1α with 2-methoxyestradiol robustly abolished EE-induced elevation of VEGF l expression. Furthermore, VEGF-A promoted the production and secretion of high mobility group box-1 protein (HMGB1) from reactive astrocytes in vitro. Culture supernatant from reactive astrocytes treated with VEGF-A promoted the proliferation and differentiation of NPCs. Glycyrrhizin reversed the promoting effects of EE on post-stroke neurorepair and functional recovery in vivo. Taken together, our data indicate that EE promotes post-stroke functional recovery through the inhibition of calpain 1 activity, and subsequent STAT3-HIF-1α-VEGF-mediated neurogenesis.