Leptin restores adult hippocampal neurogenesis suppressed by chronic unpredictable stress and reverses glucocorticoid-induced inhibition of GSK3β/β-catenin signaling

Stress and glucocorticoid stress hormones inhibit neurogenesis, whereas antidepressants increase neurogenesis and block stress-induced decrease of neurogenesis. Our previous studies have shown leptin, an adipocyte-derived hormone with antidepressant-like properties (1), promotes baseline neurogenesis in the adult hippocampus (2). The present study aimed to determine whether leptin is able to restore stress-induced suppression of neurogenesis in a rat chronic unpredictable stress (CUS) model of depression. Chronic treatment with leptin reversed the CUS-induced reduction of hippocampal neurogenesis and depression-like behaviors. Leptin treatment elicited delayed long-lasting antidepressant-like effects in the behavioral despair test, and this effect was blocked by ablation of neurogenesis with X-irradiation. The functional isoform of the leptin receptor, LepRb, and the glucocorticoid receptor (GR) were colocalized in hippocampal neural stem/progenitor cells in vivo and in vitro. Leptin treatment reversed the GR agonist dexamethasone (DEX)-induced reduction of proliferation of cultured neural stem/progenitor cells from adult hippocampus. Further mechanistic analysis revealed that leptin and DEX converged on GSK3β and β-catenin. DEX decreased Ser9 phosphorylation and increased Tyr216 phosphorylation of GSK3β, while leptin increased Ser9 phosphorylation and attenuated the effects of DEX at both Ser9 and Tyr216 phosphorylation sites of GSK3β. Moreover, leptin increased total level and nuclear translocation of β-catenin, a primary substrate of GSK3 β and a key regulator in controlling neural progenitor proliferation, and reversed the inhibitory effects of DEX on β-catenin. Together, our results suggest that adult neurogenesis is involved in the delayed long-lasting antidepressant-like behavioral effects of leptin, and leptin treatment counteracts chronic stress and glucocorticoid-induced suppression of hippocampal neurogenesis via activating the GSK3β/β-catenin signaling pathway.