Journal of Biomedical and Engineering Research

Cold-Induced Activation of Brown Adipose Tissue: Molecular Mechanisms of Non-Shivering Thermogenesis in Adult Humans

Abstract

Danish Sadiq Dar

Brown adipose tissue (BAT) is a specialised thermogenic organ that plays a central role in maintaining human body temperature through non-shivering thermogenesis (NST). In contrast to white fat that stores energy, brown fat has a high concentration of mitochondria with a special protein called uncoupling protein 1 (UCP1). UCP1 helps in converting the proton gradient from oxidative phosphorylation into heat rather than ATP production. While BAT was thought to be important only in infants in the past, modern imaging techniques have shown that active BAT is present in adults, especially in specific regions like the neck, chest, and back. Cold exposure is the strongest trigger for activating BAT, which involves a coordinated response from the brain, nerves, hormones, and cell signals to increase heat production. This review examines the molecular and physiological mechanisms underlying cold-induced BAT activation in adult humans, with particular emphasis on the regulation of nonshivering thermogenesis. The review covers how the body senses temperature, activates the nervous system, uses specific signals, and relies on UCP1 for producing heat in BAT. Additionally, the metabolic adaptations supporting thermogenesis—including intracellular lipolysis, fatty acid oxidation, glucose uptake, mitochondrial biogenesis, and enhanced oxidative metabolism—are comprehensively evaluated. The review also looks at important regulators like PPARγ, PRDM16, PGC-1α, and other molecules that control how BAT develops and functions. Additionally, the review talks about how thyroid hormones, insulin, fibroblast growth factor 21 (FGF21), irisin, and environmental factors affect BAT activity to regulate its function. Current evidence demonstrates that BAT functions as a highly dynamic endocrine and metabolic organ rather than merely a site of heat production. Through coordinated neural, hormonal, and cellular mechanisms, cold-induced BAT activation contributes significantly to energy expenditure, metabolic flexibility, glucose homeostasis, and thermal adaptation. By synthesising recent experimental and clinical findings, this review provides a comprehensive overview of the physiological processes governing BAT activation and identifies important gaps in current knowledge regarding the variability of BAT function among adults. A deeper understanding of these molecular mechanisms may enhance future investigations into human thermoregulation and metabolic physiology while providing a robust foundation for subsequent translational research. This study may pave the way for developing novel treatments for metabolic disorders and related conditions, offering new therapeutic options.

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