Facilitating microglia M2 polarization alleviates p-Synephrine-induced depressive-like behaviours in CSDS mice via the 5-HT6R-FYN-ERK1/2 pathway
Shanshan Wang, Qianbin Li, Di Deng, Zedan Xie, Kerun Cao, Fan Zhang, Qingying Yu, Zizheng Li, Yunn‐Hwa Ma, Shasha Bai, Jinlan Zhao, Lei Yang, Liang Qi, Lin An, Rong Zhang
Abstract
p-Synephrine alleviated depressive-like behaviors in CSDS mice by facilitating microglia M2 polarization through the 5-HT6R-FYN-ERK1/2 signaling pathway. • p-Synephrine significantly improved social interaction deficits and depressive-like behaviors in CSDS mice. • p-Synephrine inhibits the expression of pro-inflammatory factors and promotes microglial M2 polarization through the 5-HT6R-FYN-ERK1/2 pathway. • 5-HT6R is a potential target for p-Synephrine to exert its antidepressant effects. In recent years, modulation of microglial phenotype transformation has emerged as a promising strategy for treating central nervous system disorders. Aurantii Fructus Immaturus (Zhishi), a traditional Chinese medicine with versatile applications, contains p-Synephrine (p-SYN) as its principal bioactive compound, recognized for its anti-inflammatory efficacy. However, the molecular mechanisms underlying these effects remain unclear. This study aimed to elucidate the mechanisms through which p-SYN modulates the microglial phenotype and alleviates neuroinflammation using both a chronic social defeat stress (CSDS) model and a lipopolysaccharide-induced human microglial cell (HMC-3) system. The antidepressant effects of p-SYN were assessed using various behavioural tests including social interaction, three-chambered social interaction, sucrose preference, tail suspension, forced swimming, open field, and novelty-suppressed feeding tests. Additionally, brain penetration of p-SYN was determined using LC-MS. The results indicated that p-SYN mitigated CSDS-induced social deficits and depressive-like behaviours, and lowered inflammatory responses, as evidenced by decreased levels of TNF-α and IL-6 and increased IL-10 levels. Moreover, p-SYN reduced the expression of M1 markers CD86 and iNOS, while increasing that of M2 markers Arg-1 and CD206. Cellular thermal shift assay, drug affinity reaction target stabilization technology, and co-immunoprecipitation demonstrated that p-SYN directly binds to the 5-hydroxytryptamine 6 receptor (5-HT6R), leading to weakening 5-HT6R and tyrosine kinase FYN interaction and inhibiting the 5-HT6R-FYN-ERK1/2 pathway. This enhances the production of anti-inflammatory factors, subsequently shifts microglia to the M2 phenotype, and eventually mitigates neuroinflammation, thereby exhibiting antidepressant properties.