A nuclear ERK-ATF5 axis coordinates mitochondrial metabolism and thermogenic gene expression in brown adipocytes

Obesity and diabetes arise from disrupted energy homeostasis, underscoring the need to identify mechanisms that enhance energy expenditure. Brown adipose tissue dissipates energy through mitochondria-dependent non-shivering thermogenesis; however, the transcriptional regulators coordinating this process remain incompletely defined. Here, we investigated the role of activating transcription factor 5 in thermogenic programming and mitochondrial metabolism in brown adipocytes using in vivo and in vitro models. Cold exposure and β3-adrenergic stimulation induced activating transcription factor 5 expression in brown adipose tissue and differentiated adipocytes, accompanied by activation of thermogenic gene programs. Mechanistically, activating transcription factor 5 functioned downstream of a nuclear protein kinase A-extracellular signal-regulated kinase pathway, whose nuclear activation was required for its induction and for upregulation of uncoupling protein 1. Loss of activating transcription factor 5 impaired thermogenic gene expression, reduced mitochondrial stress response and lipolytic programs, diminished mitochondrial oxidative capacity, and suppressed fatty acid oxidation, including reduced incorporation of fatty acid-derived carbons into the tricarboxylic acid cycle. Transcriptomic analysis revealed coordinated repression of pathways related to fatty acid oxidation, oxidative phosphorylation, and thermogenesis in activating transcription factor 5-deficient adipocytes. Live-cell imaging further confirmed that β3-adrenergic stimulation selectively enhanced nuclear kinase activity, establishing a nuclear-localized signaling axis. Together, these findings identify activating transcription factor 5 as a key transcriptional regulator linking mitochondrial metabolism and thermogenic gene expression, supporting its potential as a therapeutic target for enhancing energy expenditure in metabolic disease.