UCP1-Dependent Thermogenic Adipose Tissue in Human Disease: Adipose-Centered Mechanisms, Biomarker Limitations, and...

Uncoupling protein 1 (UCP1) is a mitochondrial inner-membrane carrier classically recognized as the molecular effector of non-shivering thermogenesis in brown adipose tissue. By dissipating the proton-motive force generated by oxidative phosphorylation, UCP1 converts stored chemical energy into heat and enables adaptive thermogenesis during cold exposure. The rediscovery of metabolically active brown adipose tissue (BAT) and inducible beige adipocytes in adult humans has renewed interest in UCP1-positive thermogenic adipose tissue as a regulator of systemic metabolism and a potential target for therapeutic modulation in obesity and cardiometabolic disease. Beyond thermogenesis, accumulating evidence indicates that UCP1-positive brown/beige adipocytes and thermogenic adipose tissue are involved in lipid and glucose metabolism, mitochondrial redox homeostasis, inflammatory remodeling, organ protection, and tumor-associated metabolic adaptation, mainly through adipocyte-autonomous mechanisms and adipose-organ communication. However, UCP1 biology is complex: BAT activity measured by imaging does not directly quantify UCP1 proton conductance, non-adipose UCP1 expression is often low and technically challenging to validate, local cell-autonomous UCP1 function in non-adipose tissues remains controversial, and UCP1-independent thermogenic pathways may compensate in selected contexts. In this review, we summarize the molecular and structural basis of UCP1 function, its regulation at transcriptional and post-transcriptional levels, and its biological roles in cellular and systemic homeostasis, with explicit distinction between direct adipocyte-autonomous UCP1 functions, indirect systemic effects mediated by thermogenic adipose tissue, and preliminary or incompletely validated evidence of local UCP1 activity in non-adipose cells. We further discuss the association of UCP1-positive thermogenic adipose tissue with obesity, type 2 diabetes mellitus (T2DM), cardiovascular disease, kidney injury, liver disease, neurological disorders, and cancer. Finally, we evaluate UCP1-related thermogenic adipose tissue activity as a biomarker and therapeutic target, highlighting current limitations, safety concerns, and future directions for precision metabolic medicine.