Neuregulin 4 and the Erb-B2 Receptor Promote Hypoxia-Induced Adipose Tissue Browning in Mice
Hypoxic conditions in high-altitude environments present unique physiological stressors that drive metabolic adaptations, including adipose tissue browning. In this study, we investigated whether hypoxia (11.6% O2, simulating 5,300 m altitude) could independently induce browning of adipose tissue in mice, apart from cold-induced mechanisms. Hypoxia significantly promoted the formation of multilocular adipocytes in inguinal white adipose tissue (iWAT) and upregulated thermogenic genes (UCP1, PGC-1a, Cox4i1, VEGF), glucose metabolism-related genes (IRS1/2, PDK2, PPARa), and beige adipocyte markers (Car4, UCP1). In contrast, interscapular brown adipose tissue (iBAT) showed minimal response to hypoxia, with no significant change in UCP1 expression. Notably, hypoxia elevated both Nrg4 and phosphorylated ErbB4 in iWAT. In vitro, Nrg4 overexpression in 3T3-L1 adipocytes increased the expression of PKAca, PGC-1a, and UCP1, while pharmacological inhibition of ErbB4 phosphorylation using Dacomitinib attenuated Nrg4- and hypoxia-induced browning and lipolysis. In vivo, Dacomitinib treatment impaired hypoxia-mediated improvements in WAT browning and glucose tolerance. To explore the structural basis of this interaction, molecular docking and 100-ns molecular dynamics simulations were conducted, revealing strong and stable binding between Nrg4 and ErbB4, with calculated binding energies of -174.26 kcal/mol (MM/GBSA) and -19.5 kcal/mol (PRODIGY). These findings collectively demonstrate that the Nrg4–ErbB4 axis plays a central role in mediating hypoxia-induced browning and metabolic reprogramming of WAT, providing mechanistic insight into adipose tissue plasticity under low-oxygen conditions. Overall design: Thirty male C57BL/6J mice, aged 11 weeks, were obtained from Air Force Medical University. Of these, 15 mice were maintained in a normoxic environment (simulated altitude of 399 m, 20.9% O2) as the control group, while the remaining 15 were acclimatized to a hypoxic environment (simulated altitude of 3,000 m, 15.4% O2) for 3 days. Following this acclimatization, they were exposed to 11.6% O2 (simulated altitude of 5,300 m) for a duration of 4 weeks. During the hypoxic treatment, all mice had unrestricted access to food and water, with a light-dark cycle maintained at 12 hours each.after the hypoxia treatment, the mice were anesthetized with sodium pentobarbital (1.5%, 40 mg/kg) and euthanized by cervical dislocation.Subcutaneous inguinal white adipose tissue (iWAT), and interscapular brown adipose tissue (iBAT) were subsequently isolated for analysis.RNA extraction and sequencing of isolated adipose tissue