Naren, Q. | Search bioRxiv

bioRxiv2026

Differential Nucleotide Inhibition Profile of Mouse and Human UCP1 Expressed in Liver Mitochondria Is Associated with an F88S Mutation

Uncoupling protein 1 (UCP1) mediates thermogenesis in brown adipose tissue. Whether human-UCP1 shares the bioenergetic properties established for rodent UCP1 (innate uncoupling, GDP sensitivity, fatty acid (re)activation) is not known. Therefore, we expressed human and mouse UCP1 in mouse liver, using adeno-associated viral vectors, and characterized their properties in isolated liver mitochondria. Both UCP1s induced marked innate uncoupling, characterized by increased substrate-supported respiration and decreased membrane potential, in the absence of exogenous fatty acids. Mouse-UCP1 in liver retained the classical regulatory properties of native brown-fat UCP1, including potent inhibition by GDP and reactivation by oleate. In contrast, human-UCP1 was only weakly inhibited by GDP but was strongly responsive to fatty acids. However, ATP potently inhibited human-UCP1, with an apparent IC of {approx}0.4 mM compared with {approx}1.4 mM for GDP, and ATP markedly decreased the sensitivity of human-UCP1 to oleate (re)activation. Despite substantial UCP1-mediated uncoupling, oxidative phosphorylation capacity and mitochondrial OXPHOS protein levels were preserved. Molecular dynamics simulations suggested a structural basis for the species difference. GDP formed persistent interactions with F88 in mouse-UCP1, an interaction absent at the corresponding S88 residue in human-UCP1. In-silico substitution of F88 by serine reduced GDP interaction at this site. Thus, human and mouse UCP1 share innate thermogenic activity but differ fundamentally in nucleotide regulation. The F88/S88 difference may contribute to the preferential GDP sensitivity of mouse-UCP1, whereas ATP provides effective nucleotide control of human-UCP1.

biochemistry↗

bioRxiv2026

Only a fraction of UCP1 is required to sustain adaptive nonshivering thermogenesis in the cold

To address the long-standing question of the respective physiological contributions of classical brown versus beige adipocytes to adaptive nonshivering thermogenesis, we generated mice with lineage-specific ablation of UCP1 in thermogenic adipocytes of myogenic origin. This selectively targeted the major classical brown adipocyte lineage while preserving UCP1 expression in the remaining thermogenic adipocytes, reducing total UCP1 content by approximately 80 %. Unexpectedly, despite this profound reduction in UCP1 abundance, cold acclimation-recruited thermogenic capacity, assessed by adrenergic stimulation, remained largely preserved. In contrast, complete UCP1 deficiency abolished the adrenergically induced thermogenic response, demonstrating that UCP1 is indispensable for adaptive nonshivering thermogenesis. These findings indicate that in cold-acclimated mice only a fraction of the UCP1 normally present is required to sustain maximal thermogenic capacity. We further establish that the capacity to support UCP1-dependent oxidative metabolism, rather than UCP1 abundance, is the principal constraint on maximal thermogenic output under these conditions.

physiology↗