Geniposide improves repeated restraint stress-induced depression-like behavior in mice by ameliorating neuronal apoptosis via regulating GLP-1R/AKT signaling pathway

Geniposide (GP), a bioactive iridoid glycoside isolated from Gardenia jasminoides Ellis, as well as an agonist of Glucagon-like peptide-1 receptor (GLP-1R), has been reported to exhibit antidepressant-like effects in several rodent models. However, the underlying mechanisms remain obscure. In this study, we mainly investigated the antidepressant-like effects of GP and explored the possible mechanisms associated with GLP-1R signaling by using the repeated restraint stress (RRS)-induced depression model of mice. We found that GP treatment significantly ameliorated depression-like behaviors induced by RRS, such as decreased sucrose preference (SP) in sucrose preference test (SPT), reduced locomotor activity in open field test (OFT) and extended immobility time in tail suspension test (TST) and forced swimming test (FST). In addition, GP suppressed the neuronal apoptosis as well as reduced pro-inflammatory cytokines levels including Interleukin-1 beta (IL-1 beta) and tumor necrosis factor a (TNF-alpha) in the hippocampus of RRS-induced mice. Moreover, GP restored the expression of GLP-1R/protein kinase B (AKT) signaling-related protein. Importantly, these effects were blocked by an antagonist of GLP-1R, Exendin(9-39) (Ex(9-39)), indicating that GLP-1R signaling pathway might be involved in the neuroprotective and antidepressant-like effecacy of GP. In conclusion, GP exerted promising antidepressant-like effects in RRS mice, and the antidepressant-like action of GP might be closely relevant to GLP-1R/AKT signaling.