Limb Remote Ischemic Conditioning Promotes Neurogenesis after Cerebral Ischemia by Modulating miR-449b/Notch1 Pathway in Mice

Neurogenesis plays an important role in the prognosis of stroke patients and is known to be promoted by the activation of the Notch1 signaling pathway. Studies on the airway epithelium have shown that miR-449b represses the Notch pathway. The study aimed to investigate whether limb remote ischemic conditioning (LRIC) was able to promote neurogenesis in cerebral ischemic mice, and to investigate the role of the miR-449b/Notch1 pathway in LRIC-induced neuroprotection. Male C57BL/6 mice (22-25 g) were subjected to transient middle cerebral artery occlusion (MCAO), and LRIC was performed in the bilateral lower limbs immediately after MCA occlusion. Immunofluorescence staining was performed to assess neurogenesis. The cell line NE-4C was used to elucidate the proliferation of neuronal stem cells in 8% O-2. After LRIC treatment on day 28, mice recovered neurological function. Neuronal precursor proliferation was enhanced in the SVZ, and neuronal precursor migration was enhanced in the basal ganglia on day 7. LRIC promoted the improvement of neurological function in mice on day 28, promoted neuronal precursor proliferation in the SVZ, and enhanced neuronal precursor migration in the basal ganglia on day 7. The neurological function score was negatively correlated with the number of BrdU-positive/DCX-positive cells in the SVZ and striatum. LRIC promoted activated Notch1 protein expression in the SVZ and substantially down-regulated miR-449b levels in the SVZ and plasma. In vitro, miR-449b was found to target Notch1. Lentivirus-mediated miR-449b knockdown increased Notch1 levels in NE-4C cells and increased proliferation in the cells. The effects of miR-449b inhibition on neurogenesis were ablated by the application of Notch1 shRNA. Our study showed that LRIC promoted the proliferation and migration of neural stem cells after MCAO, and these effects were modulated by the miR-449b/Notch1 pathway.