Osthol ameliorates obesity-associated lipid metabolic disorders by inhibiting ADRA1D-dependent Th17 cell differentiation.

Osthol (OST), a natural coumarin, exhibits anti-inflammatory and metabolism-regulating potential. This study investigated whether OST ameliorates obesity-associated metabolic dysregulation and inflammation by targeting ADRA1D-mediated T helper 17 (Th17) differentiation. High-fat diet (HFD)-induced obese mice were treated with OST. Metabolic parameters including body/organ weights, serum lipids, hepatic enzymes, and histopathology were assessed. Th17-related and inflammatory markers were evaluated via flow cytometry, ELISA, RT-qPCR, and Western blot. In vitro Th17 differentiation (primary murine CD4⁺ T cells) and lipid metabolism (3T3-L1 adipocytes) models were used. ADRA1D was identified as a key target via bioinformatics and validated through overexpression in cells and mice. OST significantly reduced HFD-induced weight gain, liver and fat mass, serum triglycerides (TG), free fatty acids (FFA), alanine aminotransferase (ALT), aspartate aminotransferase (AST), hepatic lipid deposition, and adipocyte hypertrophy. OST suppressed Th17 differentiation, CD4⁺IL-17A⁺ and CD4⁺RORγt⁺ cell proportions, and pro-inflammatory cytokines (IL-17A, IL-6, TNF-α), while elevating anti-inflammatory cytokines (IL-10, TGF-β). OST downregulated IL-17RA, TRAF6, and Act1 expression and inhibited ERK1/2 and PI3K phosphorylation. In vitro studies confirmed the dose-dependent inhibitory effect of OST on Th17 polarization. Mechanistically, OST modulated Th17-related signaling via ADRA1D. ADRA1D overexpression partially reversed OST-mediated suppression of Th17 differentiation, expression of lipogenic genes (FASN, PPARγ), and lipid droplet accumulation. In vivo, ADRA1D overexpression attenuated the beneficial effects of OST on metabolic parameters and tissue inflammation, confirming ADRA1D dependence. OST ameliorates obesity-related metabolic dysregulation and inflammation by inhibiting ADRA1D-mediated Th17 differentiation, highlighting ADRA1D as a key mediator and potential therapeutic target for immunometabolic disorders.