Vitamin A regulates neural stem cell proliferation in rats after hypoxic-ischemic brain damage via RARɑ-mediated modulation of the β-catenin pathway

Our previous experiments found that a suitable dose of vitamin A (VA) can affect neuronal apoptosis after hypoxic-ischemic brain damage (HIBD) by binding to RARα to activate the PI3K/AKT signaling pathway; however, the other neuroprotective effects of VA after HIBD, for example, whether it promotes neural stem cell (NSC) proliferation, remain unclear. In this study, in vivo and in vitro experiments revealed that VA regulates β-catenin signaling through RARɑ to affect NSC proliferation after HIBD and to improve neurocognitive outcomes. Because of the accumulation and suspended growth characteristics of NSCs, we performed in vitro experiments with PC12 cells to mimic NSCs. Flow cytometry, CCK8, EdU staining, immunofluorescence and behavioral tests were performed to explore the effects of retinoic acid (RA) on NSC proliferation and post-HIBD function. The expression of RARα and β-catenin pathway components were measured by real-time PCR and Western blotting. We found that the learning and memory of the VA-deficient (VAD) group was more seriously damaged than that of the VA normal (VAN) group. The proliferation of hippocampal NSCs was significantly decreased in the VAD group compared with the VAN group. The mRNA and protein expression of RARɑ, AKT, GSK-3β, β-catenin and Cyclin D1 were significantly lower in the VAD group than in the VAN group. In vitro, too high and too low of an RA intervention resulted in decreased proliferation, while an appropriate RA concentration (1−5 μmol/L) significantly promoted proliferation, S phase cells and high β-catenin pathway expression. These results suggested that VA can exert a neuroprotective effect by promoting the proliferation of hippocampal NSCs after neonatal HIBD injury at the appropriate concentration. VA activates RARɑ, which regulates the β-catenin signaling pathway, which in turn upregulates Cyclin D1 expression, promotes NSC proliferation, and finally plays a role in the neuroprotective effect.