How is UCP1 measured?

How is UCP1 measured?

UCP1 — uncoupling protein 1, also written as UCP-1, thermogenin, or SLC25A7 — is a member of the mitochondrial carrier family (SLC25 family) of inner-membrane anion transporters. It is the canonical marker of brown adipose tissue (BAT) and of beige (brite) adipocytes arising in white adipose tissue depots. The gene symbol is UCP1 in humans and Ucp1 in mice; the protein is a proton-conducting inner mitochondrial membrane carrier whose activity dissipates the proton gradient generated by the electron transport chain, uncoupling substrate oxidation from ATP synthesis and producing heat. Measurement in the research literature is therefore not a single assay but a family of approaches — transcript abundance, protein abundance, and functional proton-leak or respiration readouts — each with different tissue requirements and different sensitivity to contaminating cell types.

The work described below centres on the TGF-β superfamily and its downstream SMAD signalling, together with adrenergic receptor signalling, as the pathways most often manipulated when UCP1 or browning is being measured in adipose tissue models.

Research Studies

Follistatin and adipose browning in the Hybrid Mouse Diversity Panel

Follistatin (FST) binds and neutralises members of the transforming growth factor-beta (TGF-β) superfamily and regulates skeletal muscle, adipose, and bone homeostasis. In mice, FST promotes adipose browning and improves plasma lipid profiles. Transcriptomic and metabolomic analysis of the Hybrid Mouse Diversity Panel found that Fst expression was negatively correlated with aortic lesion area, and the study reported that FST mitigates atherosclerosis through activation of arginine metabolism and adipose browning [1]. Browning in that work was assessed in mouse tissue, so the readouts are animal-derived.

GDF-11 and cold-induced browning of white adipose tissue

Growth differentiation factor 11 (GDF-11) is a circulating TGF-β superfamily member. In mice exposed to cold to induce browning, GDF-11 expression and SMAD2/3 activation were assessed in brown adipose tissue, visceral and subcutaneous white adipose tissue, and skeletal muscle, with in vivo results combined with in vitro approaches in 3T3-L1 cells [2]. The study reported that GDF-11 triggers cold-induced browning and metabolic activation of adipose tissue. Because the design pairs mouse tissue with a murine cell line, the findings are animal and in vitro rather than human.

Finerenone and epicardial adipose tissue in a cardiac trial

Finerenone is a nonsteroidal mineralocorticoid receptor antagonist with anti-inflammatory, antifibrotic, and metabolic effects. Preclinical studies suggest it promotes browning of adipose tissue and improves epicardial adipose tissue (EAT) characteristics, and prior large trials associated it with a lower incidence of atrial fibrillation. A single-centre, randomised, investigator-blinded pilot trial is enrolling 40 patients after catheter ablation with pulmonary vein isolation to test whether finerenone reduces atrial fibrillation recurrence [3]. Adipose endpoints in that protocol are secondary to the rhythm outcome; the browning rationale rests on preclinical work.

Exercise and Mediterranean diet in metabolic syndrome volunteers

A study in middle-aged volunteers with the metabolic syndrome is testing whether physical exercise and/or a Mediterranean diet preserve adipose tissue functionality and retard skeletal muscle ageing, assessed by mitochondrial biogenesis and accumulation of reactive oxygen species, through pathways homologous to caloric restriction [4]. The design uses a cross-sectional model alongside the intervention. Adipose functionality here is a human physiological endpoint rather than a direct UCP1 measurement.

Syringaresinol and the skeletal muscle SIRT1–FNDC5/irisin axis

Syringaresinol (SYR) is a plant-derived lignan. A study examined whether SYR modulates skeletal muscle SIRT1-related FNDC5/irisin signalling and high-fat-diet-associated metabolic outcomes, treating differentiated C2C12 myotubes with SYR alongside the SIRT1 activator SRT1720 and the SIRT1 inhibitor EX-527 to assess irisin signalling [5]. The model is a murine myoblast line, so the mechanism is in vitro and the tissue is skeletal muscle rather than adipose.

Time-restricted feeding and HIIT in diabetic rat white adipose tissue

A study evaluated the independent and combined effects of time-restricted feeding (TRF) and high-intensity interval training (HIIT) on thermogenesis-related protein abundance in white adipose tissue of diabetic rats. Forty male Wistar rats were divided into normal and diabetic groups [6]. Thermogenesis-related protein abundance in WAT is the readout of interest; the work is animal-only and in a disease model.

β2-adrenergic stimulation of human adipose-derived stem cells

β-adrenergic receptors drive induction of beige adipocytes in rodents and humans, but whether β2-AR or β3-AR is the dominant human subtype remains debated. A study aimed to confirm whether human adipose-derived mesenchymal stem cell (hADSC)-derived adipocytes can serve as a beiging-competent model under human-relevant conditions, using β2-adrenergic receptor stimulation to drive differentiation into beige adipocytes [7]. This is a human cell model, but it is in vitro and does not establish an in vivo human response.

Bombesin receptor-activated protein homolog deficiency in high-fat-diet mice

Bombesin receptor-activated protein (BRAP) and its mouse homolog BC004004 are expressed in the central nervous system. In feeding experiments, BRAP homolog knockout mice (BC004004^-/-) showed reduced preference for a high-fat diet, and the study reported reduced food intake and alleviated metabolic dysfunction in high-fat-diet-treated mice [8]. The model is a mouse knockout, so the findings are animal-only.

Comparison of measurement approaches

Across the studies above, browning is inferred from combinations of these readouts rather than from any single assay, and the species and model system determine how far a result can be generalised.

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Sources

• [1] Follistatin Mitigates Atherosclerosis Through Activation of Arginine Metabolism and Adipose Browning — https://pubmed.ncbi.nlm.nih.gov/42439678/
• [2] GDF-11 triggers cold-induced browning and metabolic activation of adipose tissue — https://pubmed.ncbi.nlm.nih.gov/42296290/
• [3] Finerenone After Catheter Ablation to Reduce Atrial Fibrillation Recurrence — https://clinicaltrials.gov/study/NCT07799519
• [4] Beneficial Effects of Exercise and Healthy Diets on Muscle and Adipose Tissue — https://clinicaltrials.gov/study/NCT01793896
• [5] Syringaresinol activates the skeletal muscle SIRT1-FNDC5/irisin axis to enhance weight management — https://pubmed.ncbi.nlm.nih.gov/42733416/
• [6] Effects of time-restricted feeding and high-intensity interval training on thermogenesis-related protein abundance in white adipose tissue of diabetic rats — https://pubmed.ncbi.nlm.nih.gov/42572539/
• [7] β2-adrenergic receptor stimulation drives differentiation of human adipose-derived mesenchymal stem cells into beige adipocytes — https://europepmc.org/article/PMC/PMC13336291
• [8] Bombesin receptor-activated protein homolog deficiency reduces food intake and alleviates metabolic dysfunction in high-fat diet treated mice — https://pubmed.ncbi.nlm.nih.gov/41932562/