NLRP6 governs hippocampal microglial phagocytosis to resist stress-induced depressive-like behaviors in mice and the intervention effect of bezafibrate.

INTRODUCTION

Microglial phagocytosis is crucial for maintaining central nervous system (CNS) homeostasis and is implicated in the development of depression. NOD-like receptor family pyrin domain containing 6 (NLRP6) represents a potential target for depression treatment, but underlying mechanisms remain unclear. Bezafibrate has been shown to exhibit multiple neuroprotective effects.

OBJECTIVES

To investigate the effects of NLRP6 on microglial phagocytosis and depressive-like behaviors, elucidate the potential underlying mechanisms, and evaluate bezafibrate's therapeutic impact.

METHODS

NLRP6 complete gene knockout (Nlrp6-KO), microglia-conditional knockout (Nlrp6-cKO), and chronic restraint stress (CRS) model were established in mice. Behavioral tests (OFT, TST, FST, SPT) were used to assess depressive-like behaviors. Fluorescently labeled cellular debris was stereotactically injected into the hippocampus or co-cultured with the BV2 microglial cell line to assess the microglial phagocytic activity. Underlying mechanisms were investigated using RNA-seq, luciferase assays, flow cytometry, Western blot, qPCR, and ELISA.

RESULTS

Enriched NLRP6 expression in microglia was confirmed by RNAscope experiment. Nlrp6-KO and Nlrp6-cKO mice exhibited significant depressive-like behaviors, accompanied by impaired microglial phagocytic function. In the BV2 cells, NLRP6 regulated phagocytosis of cellular debris by promoting the transactivation of cluster differentiation 36 (CD36). More importantly, corticosterone inhibited NLRP6 and its target gene CD36 expression, thereby reducing microglial phagocytosis. However, bezafibrate treatment restored the NLRP6-CD36 axis, enhanced microglial phagocytosis, and suppressed the inflammatory response to cellular debris in BV2 cells. In CRS mice, bezafibrate alleviated depressive-like behaviors, reversed NLRP6/CD36 downregulation, improved phagocytosis, and reduced hippocampal neuroinflammation. Importantly, bezafibrate failed to alleviate depressive-like behaviors in Nlrp6-KO mice, indicating NLRP6 is essential for its antidepressant effect.

CONCLUSION

NLRP6 critically regulates microglial phagocytosis via CD36, combating depression. Bezafibrate alleviates stress-induced depressive behaviors and neuroinflammation primarily by enhancing NLRP6-dependent phagocytosis. Thus, NLRP6 represents a promising therapeutic target in hippocampal microglia for maintaining CNS homeostasis and treating depression.