Rewiring Adipocyte Plasticity: The Redox–Mitochondrial Axis as a Driver of Beige Fat Immunometabolism and Adipose Inflammation

Figures

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  Figure 1. Posttranslational import of UCP1 and ER–mitochondrial proteostasis. UCP1 is synthesized on cytosolic ribosomes and imported directly into the inner mitochondrial membrane (IMM) via the TIM22 carrier translocase, bypassing the ER–Golgi pathway. This spatial segregation prevents ER luminal overload and ER-derived ROS, thereby preserving physiological Ca2+ flux. Low ER stress supports mitochondrial expansion and thermogenesis, whereas high ER stress leads to Ca2+ overload and ROS, which disrupt UCP1 function. The direct import of UCP1 is an evolutionary adaptation for high-flux thermogenesis.

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  Figure 2. Metabolic and redox integration in white-to-beige adipocyte reprogramming. Under hypoxic/inflammatory stress, white adipocytes increase glucose uptake and lactate exchange via MCT1, while BCAA catabolism supplies nitrogen for proteostasis. Carbon and nitrogen fluxes converge on the TCA cycle. Citrate synthase (CS) condenses oxaloacetate (OXA) with acetyl-CoA, and isocitrate dehydrogenase (IDH) converts isocitrate to α-ketoglutarate, generating NADH/FADH2 for the electron transport chain. Balanced redox promotes mitochondrial biogenesis, ketogenesis, and TCA efficiency. Fasting (NAD+ → sirtuins) and exercise (ROS → mitophagy) enhance quality control. In beige adipocytes, UCP1-mediated proton leak uncouples ATP synthesis from the ETC, enabling thermogenesis while maintaining redox balance.

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  Figure 3. Comparison of the adipose tissue microenvironment under normoxia and hypoxia. Normoxia (left) promotes beige adipocytes and M2 macrophage polarization (Th2 response: IL-13, IL-10, IL-4). Hypoxia (right) induces an inflammatory state with white adipocyte development and M1 macrophage polarization (Th1 response: TNF-α, MCP-1, IL-6).

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  Figure 4. Orchestration of the redox–mitochondrial axis in adipocyte plasticity and thermogenesis. β-adrenergic signaling and electrophiles (SFN, RSV) activate AMPK (Thr172), promoting PGC-1α-dependent mitochondrial biogenesis and autophagy. Nrf2 dissociates from KEAP1, translocates to the nucleus, and induces ARE-driven antioxidant enzymes (SOD, GSH, and CAT), thereby preserving redox homeostasis. In contrast, excessive ROS/RNS enhances KEAP1/Cul3-mediated Nrf2 degradation, leading to mitochondrial dysfunction and thermogenesis impairment. UCP1-mediated H+ leakage uncouples oxidative phosphorylation from ATP synthesis to generate heat. Arrows indicate activation and/or phosphorylation of molecular flux.