A total of four wells were treated for each condition as follows: vehicle, 1 nM leptin, 10 M DEX, 10 M DEX with 0.1 nM, 1 nM or 3 nM leptin, and grown for 48 h. of cultured neural stem/progenitor cells from adult hippocampus. Further mechanistic analysis revealed that leptin and DEX converged on GSK3 and -catenin. DEX decreased Ser9 phosphorylation and increased Tyr216 phosphorylation of GSK3, while leptin increased Ser9 phosphorylation and attenuated the effects of DEX at both Ser9 and Tyr216 phosphorylation sites of GSK3. Moreover, leptin increased total level and nuclear translocation of -catenin, a primary substrate of GSK3 and a key regulator in controlling neural progenitor proliferation, and reversed the inhibitory effects of DEX on -catenin. Together, our results suggest that adult neurogenesis is usually involved in the delayed long-lasting antidepressant-like behavioral effects of leptin, and leptin treatment counteracts chronic stress and glucocorticoid-induced suppression of hippocampal neurogenesisviaactivating the GSK3/-catenin signaling pathway. Keywords:leptin, chronic unpredictable stress, glucocorticoids, neurogenesis, depressive disorder, glycogen synthase kinase 3, -catenin == INTRODUCTION == New neurons are constantly generated throughout adulthood from a pool of neural stem/progenitor cells in the subgranular zone of the dentate gyrus of the hippocampus. In a tightly regulated process, these cells divide and give rise to granule cells that Rabbit Polyclonal to KLF extend axons along the mossy fiber pathway and are capable of integrating into functional hippocampal circuitry35. These processes are modulated both positively or negatively by neurotransmitters612, hormones1322, neurotrophic factors6,21,2329, pharmacological brokers and environmental factors3032. Among the regulatory factors of hippocampal neurogenesis, stress, a participating and precipitating factor of depression, potently inhibits neurogenesis in adult animals18,3337. For example, chronic stress paradigms including chronic unpredictable stress (CUS), chronic mild stress, and chronic interpersonal defeat stress that can induce depression-like behaviors, have been reported to decrease proliferation of neural progenitor cells in the dentate gyrus3849. Also, a decrease in hippocampal neurogenesis has been demonstrated in other rodent models of stress such as repeated restraint stress50,51, predator odor5255, and footshock stress5659. These findings suggest that reduction of hippocampal neurogenesis is usually a common feature of various types of stress. The mechanisms underlying stress-induced decrease of neurogenesis is most likely to be mediated by activation of the hypothalamic-pituitary-adrenal axis and subsequent elevation of glucocorticoid stress hormones during stress. Indeed, elevation of glucocorticoid stress hormones or administration of exogenous glucocorticoids decreases hippocampal neurogenesis14,15,49,6066, and depletion of glucocorticoids by adrenalectomy attenuates stress-reduced neurogenesis52. Chronic treatment with a variety of antidepressants, including selective serotonin reuptake inhibitors, norepinephrine reuptake inhibitors, monoamine oxidase inhibitors, increases basal adult hippocampal neurogenesis, and reverses the inhibitory effects of stress and glucocorticoids on neurogenesis10,28,35,49,56,63,64,6769. Further studies indicate that some behavioral effects of antidepressants are neurogenesis-dependent under chronic stress or glucocorticoid treatment conditions49,64. Our earlier studies demonstrate that leptin, an adipocyte-derive hormone with antidepressant-like efficacy1, promotes adult hippocampal neurogenesis under basal conditions2. This obtaining provides evidence for adipostatic control of adult neurogenesis. However, it remains unknown whether leptin can reverse or oppose the reduction of neurogenesis Dibutyl phthalate induced by stress. Leptin is known to enter the brain by a saturable transport system70, where it exerts its biological functionsviainteracting with leptin receptors. Among six isoforms of the leptin receptor (af) that have been identified71,72, LepRb is the only functional isoform as Dibutyl phthalate it possesses all the intracellular motifs required for signal transduction. We have previously shown that LepRb is usually expressed in neural stem/progenitor cells of adult hippocampus2. The glucocorticoid receptor (GR) has also Dibutyl phthalate been reported to be present in neural stem/progenitor cells73,74, suggesting a possible conversation between leptin signaling and glucocorticoid signaling in the regulation of neurogenesis. In the present study, we examined the effects of leptin on hippocampal neurogenesis and actions in a chronic unpredictable stress (CUS) model of depression and the involvement of hippocampal neurogenesis in the antidepressant-like behavioral effects of leptin. Furtherin vitromechanistic studies investigated the effects of leptin on glucocorticoid-induced inhibition of neurogenesis and the underlying molecular mechanisms involving the GSK3/-catenin signaling pathway. == MATERIALS AND METHODS == == Animals == Male Sprague Dawley rats, weighing 250300 g, were purchased from Charles River Laboratories (Wilmington, MA). Rats were housed in groups of three. All animals were maintained on a 12-h light/dark cycle (lights on at 0700 h) withad libitumaccess to food and water. Animals were habituated to housing conditions for 710 days prior to the beginning of experimental procedures. All procedures were carried out in accordance with the National Institutes of Health Guide. == Drug treatment == Recombinant rat leptin (R&D Systems, Minneapolis, MN) was dissolved in sterile saline at a concentration of 1 1 mg/ml and intraperitoneally (i.p.) injected into animals.