Polysaccharides and Glycosides from Aralia echinocaulis Modulate Succinate Levels in the Gut to Target Intestinal Dendritic Cells via the Receptor GPR91 in the Treatment of Rheumatoid Arthritis

Background: Aralia echinocaulis has therapeutic effects on rheumatoid arthritis (RA), with total polysaccharide and glycoside (TPGs) as main active components. RA pathogenesis involves gut microbiota dysbiosis and immune-metabolic crosstalk, but the role of microbiota-derived succinate in RA remains unclear. Objective: This study explored the role of succinate-GPR91 signaling in intestinal dendritic cells (DCs) in the context of RA and the therapeutic mechanism of A. echinocaulis TPGs. Methods: Collagen-induced arthritis (CIA) mice were treated with TPGs or exogenous succinate. Paw edema, inflammation, gut succinate levels, the Th17/regulatory T (Treg) balance, and DC activation via succinate-GPR91 were detected, and GPR91-targeting siRNA and CD4+ T-cell coculture assays for verification. Results: TPGs alleviated symptoms in CIA mice and restored the Th17/Treg balance by reducing intestinal succinate levels. Succinate activated DCs via GPR91 to promote Th17 differentiation, while TPGs suppressed DC maturation and Th17-driven inflammation, supporting the involvement of a gut-centric immunometabolic axis in RA. Conclusions: TPGs ameliorate RA by targeting the succinate-GPR91-Th17 pathway, identifying succinate as a novel RA target and TPGs as a potential microbiota-modulating agent.