Mechanistic Drivers of Thermogenic Adipose Tissue Dysfunction in Aging and Obesity

Population aging is accelerating worldwide, and is accompanied by a growing burden of chronic metabolic diseases. Adipose tissue dysfunction represents a central mechanism linking aging and obesity to metabolic decline, contributing to chronic low-grade inflammation, impaired adipokine signaling, ectopic lipid deposition, and the whitening of thermogenic fat depots. Brown adipose tissue (BAT) plays a key role in adaptive thermogenesis through UCP1 mediated mitochondrial uncoupling, however, its activity progressively declines with advancing age and excess adiposity. This narrative review synthesizes emerging biomolecular mechanisms that underlie impaired thermogenic function in the context of aging and obesity. We integrate evidence across three major regulatory domains: (1) intracellular thermogenic signaling, highlighting salt-inducible kinases (SIK2/3), as transcriptional repressors that limit UCP1 expression when ß3-adrenergic/PKA signaling is impaired, (2) autophagy-dependent secretion of acyl-CoA binding protein (ACBP), which suppresses lipolysis, ß-oxidation, and thermogenic signaling and may contribute to BAT whitening, and (3) immune mediated regulation of thermogenic adipose tissue, with macrophage modulating sympathetic signaling, inflammatory tone, and extracellular matrix remodeling through pathways involving NLRP3-MAOA, SLIT3/ETS1, prolidase (PEPD) and immunoglobulin G (IgG). Collectively, these convergent mechanisms illustrate how aging and obesity impose coordinated constraints on brown and beige adipose tissue activation. By framing thermogenic decline as a regulated process, this review provides a conceptual basis for future studies aimed at preserving metabolic flexibility and promoting healthier aging.