Capsaicin induces ATP-dependent thermogenesis via the activation of TRPV1/β3-AR/α1-AR in 3T3-L1 adipocytes and mouse model

Capsaicin (CAP) is a natural bioactive compound in chili pepper that activates the transient receptor potential vanilloid subfamily 1 (TRPV1) and is known to stimulate uncoupling protein 1 (UCP1)-dependent thermogenesis. However, its effect on ATP-dependent thermogenesis remains unknown. In this study, we employed qRT-PCR, immunoblot, staining method, and assay kit to investigate the role of CAP on ATP-dependent thermogenesis and its modulatory roles on the TRPV1, β3-adrenergic receptor (β3-AR), and α1-AR using in vitro and in vivo models. The studies showed that CAP treatment in high-fat diet-induced obese mice resulted in lower body weight gain and elevated ATP-dependent thermogenic effectors' protein and gene expression through ATP-consuming calcium and creatine futile cycles. In both in vitro and in vivo experiments, CAP treatment elevated the protein and gene expressions of sarcoendoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2), ryanodine receptor 2 (RYR2), creatine kinase B (CKB), and creatine kinase mitochondrial 2 (CKMT2) mediated by the activation of β3-AR, α1-AR, and TRPV1. Our study showed that CAP increased intracellular Ca2+ levels and the expression of voltage-dependent anion channel (VDAC) and mitochondrial calcium uniporter (MCU) which indicates that increased mitochondrial Ca2+ levels lead to increased expression of oxidative phosphorylation protein complexes as a result of ATP-futile cycle activation. A mechanistic study in 3T3-L1 adipocytes revealed that CAP induces UCP1- and ATP-dependent thermogenesis mediated by the β3-AR/PKA/p38MAPK/ERK as well as calcium-dependent α1-AR/TRPV1/CaMKII/AMPK/SIRT1 pathway. Taken together, we identified CAP's novel functional and modulatory roles in UCP1- and ATP-dependent thermogenesis, which is important for developing therapeutic strategies for combating obesity and metabolic diseases.