A cold-inducible phospholipid-protein interaction in brown fat mitochondria optimizes thermogenic capacity

Cold stress elicits dynamic remodeling of the mitochondrial lipidome in brown adipose tissue (BAT), marked by an increase in arachidonoyl-phosphatidylethanolamine (AA-PE). However, the function of membrane lipid rewiring in thermoregulatory physiology has been a longstanding mystery. Here, we identify LPCAT3 as a cold-regulated O-acyltransferase driving the highly selective accrual of AA-PE in BAT mitochondria. Lipid-based proteomics, molecular dynamics simulations, and bioenergetic analyses reveal that AA-PE partitions at the COX4I1 interface of the Cytochrome c oxidase complex, enhancing electron transport chain (ETC) efficiency. Accordingly, fat-specific Lpcat3 -knockout mice have defects in respiratory-dependent BAT thermogenesis and cold tolerance, despite intact β-adrenergic signaling and UCP1 function. Under cold acclimation, Lpcat3 ^-/- BAT exhibits ETC dysfunction and activation of the integrated stress-response. Thus, our study illuminates a cold-regulated lipid-protein interaction as a gating factor in UCP1-dependent thermogenesis.