Extracellular GPX3 drives insulin receptor expression in adipose tissue independent of its peroxidase activity

Obesity-associated insulin resistance is driven in part by adipose tissue dysfunction and oxidative stress, yet the role of extracellular mechanisms in modulating insulin signaling remains poorly understood. Here, we show that extracellular Glutathione Peroxidase 3 (GPX3) enhances adipocyte insulin sensitivity and functionalities independent of its canonical peroxidase function. GPX3, a secreted selenoprotein highly expressed in white adipose tissue (WAT), is suppressed in obesity, but whether it actively regulates insulin sensitivity had not been established. We find that WAT GPX3 expression closely mirrors insulin receptor (InsR) expression across a broad range of metabolic parameters in humans and increases dynamically following weight loss. Prolonged therapeutic selenium supplementation in diet-induced obese mice selectively suppressed epididymal WAT oxidative damage, restored GPX3 and InsR expression, and enhanced insulin-stimulated AKT phosphorylation, improving oral glucose tolerance. Mechanistically, recombinant GPX3 extracellularly administered at physiological concentrations induced InsR expression across multiple adipocyte models, including pre-adipocytes, epididymal WAT explants, and adipocyte organoids, by promoting binding of the transcription factor Specificity Protein 1 (SP1) to the Insr promoter, while knockdown of GPX3 completely blocks SVF adipogenesis. These effects rely on the structural integrity, rather than selenocysteine-dependent activity. Thus, we identify a GPX3-SP1-InsR signaling axis in adipose tissue insulin sensitivity, suggesting GPX3 is a novel paracrine mediator of metabolic health and a potential therapeutic target to reinstate WAT insulin sensitivity in obesity and type 2 diabetes.