Orai1-mediated Ca ²⁺ Entry Regulates Lipolysis and Mitochondrial Activation in Brown Adipose Thermogenesis

Cold-induced thermogenesis in brown adipose tissue (BAT) is essential for maintaining energy homeostasis, yet the Ca ²⁺ -dependent mechanisms underlying this process remain incompletely understood. Here, we identify Orai1, a component of the store-operated Ca ²⁺ entry pathway, as a regulator of thermogenic activation in BAT. Using a brown adipocyte-specific Orai1 knockout mouse model, we demonstrate that cold exposure is associated with Orai1-dependent Ca ²⁺ influx through a non-canonical mechanism. Orai1 deficiency leads to impaired cAMP-PKA signaling, reduces the expression of lipolytic enzymes and thermogenic genes, and diminished mitochondrial Ca ²⁺ uptake and uncoupling. These defects culminate in cold intolerance, lipid accumulation, and decreased energy expenditure. Mechanistically, Orai1 facilitates Ca ²⁺ -dependent activation of adenylyl cyclase 3, linking membrane Ca ²⁺ entry to cAMP production, and promotes mitochondrial remodeling and oxidative metabolism. These findings support a key role for Orai1 in coordinating Ca ²⁺ entry to lipolytic and mitochondrial pathways in brown adipocytes and highlight its potential therapeutic target in metabolic diseases characterized by impaired energy metabolism.