Fig. 1

Brown adipocyte regulation by exogenous agents. Thyroid hormones act on thermogenesis through interaction with their Thyroid receptors (TR) and the G-protein-coupled receptor (GPCR). TRα promotes an increase in adrenergic signaling while TRβ acts to stimulate uncoupling protein 1 (UCP1). β3 receptor (β3-AR) is expressed constitutively on the surface of the adipocyte and acts to regulate the transcription and activation of genes related to mitochondrial biogenesis, brown adipocyte differentiation, and lipid storage. This receptor can be activated through cold, which is the main mechanism for activating browning, agonist drugs, or diet. Chronic exposure to cold and food intake, such as curcumin and fish oil, promotes thermogenesis by releasing catecholamines from the central nervous system (CNS) that bind to β-AR, thus initiating a signaling cascade. An increase in the concentration of cAMP is elicited which consequently leads to the enhanced activity of protein kinase A (PKA) which promotes the cAMP-response element-binding protein (CREB). This pathway is related to the transcription of thermogenic genes such as peroxisome proliferator-activated receptor γ (PPARγ), Type II iodothyronine deiodinase (DIO2), PR domain containing 16 (PRDM16), Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and Cell death-inducing DNA fragmentation factor-like effector A (CIDEA). The other dietary components can participate in the induction of browning through the modulation of the gut microbiota promoting the increase of the expression of thermogenic genes. The release of growth factor 21 (FGF21) is mediated by the practice of physical exercises and physiological changes. FGF21 will interact with its FGFR receptor and that activation induces a self-phosphorylation of the FGFR that mediates the activation of pathways related to increased expression of UCP1