HMGB1 Regulates Adipocyte Lipolysis via Caveolin-1 Signaling: Implications for Metabolic and Cardiovascular Diseases.

High-mobility group box 1 (HMGB1) is a nuclear protein that can be secreted or released into the extracellular environment during cellular stress, functioning as a damage-associated molecular pattern molecule. This study investigates the role of HMGB1 in adipocyte development and metabolism, explicitly examining its interaction with β3-adrenergic receptor-mediated lipolysis and caveolin-1 (CAV1) regulation, which may influence cardiovascular risk factors. Using 3T3-L1 preadipocytes and mouse embryonic fibroblasts, we demonstrated that HMGB1 expression increases progressively during adipogenesis, reaching peak levels in mature adipocytes. While exogenous HMGB1 treatment did not affect preadipocyte proliferation or differentiation, it inhibited lipolysis in mature adipocytes. Mechanistically, HMGB1 suppressed β3-adrenergic receptor agonist CL-316,243-induced hormone-sensitive lipase activation by reducing protein kinase A-mediated phosphorylation and attenuating extracellular signal-regulated kinase signaling without affecting upstream cyclic AMP levels. We discovered a novel regulatory mechanism wherein CAV1 physically interacts with HMGB1 in mature adipocytes, with c-Src-dependent CAV1 phosphorylation functioning as a negative regulator of HMGB1 secretion. This finding was confirmed in CAV1-deficient models, which displayed increased HMGB1 secretion and diminished lipolytic activity both in vitro and in vivo. Furthermore, administering HMGB1-neutralizing antibodies to wild-type mice enhanced fasting-induced lipolysis, establishing circulating HMGB1 as a crucial antilipolytic factor. These findings reveal HMGB1's previously uncharacterized role in adipose tissue metabolism as a negative regulator of lipolysis through CAV1-dependent mechanisms. This work provides new insights into adipose tissue metabolism regulation and identifies potential therapeutic targets for obesity-related metabolic disorders and cardiovascular diseases.