Investigating the impact of GPx3 on selenite induced insulin action in adipocytes.

Glutathione peroxidase 3 (GPx3) is a protein belonging to the selenoprotein family. Selenoproteins, which contain the essential trace element selenium as a key component, play a significant role in regulating cellular redox homeostasis and metabolic processes by participating in antioxidative and redox reactions. Our previous work indicated that GPx3, canonically known as the circulating GPx, enhances adipocyte insulin receptor (IR) expression and sensitivity. However, it is unclear, whether GPx3 improves adipocyte differentiation and whether endogenous (by selenite treatment) or exogenous GPx3 (recombinant) impacts IR signalling and adipocyte functions. Insulin action in 3T3L1 preadipocytes was investigated in untreated (10nM selenium in media, low Se) or 200nM selenite supplemented conditions (high Se, as inducer of endogenous GPx3 expression), and/ or extracellular application of 500 ng/ml recombinant GPx3. Importantly, the concentration of 500 ng/ml GPx3 has been found in mouse plasma, and can therefore be considered physiological. We analysed the effect of GPx3 on insulin dependent processes: Insulin signalling, mitochondrial respiration and lipid accumulation in undifferentiated 3T3L1 preadipocytes and during differentiation over 14 days. After 5 min stimulation with 100nM insulin, GPx3 treated 3T3L1 cells exhibited increased level of pIRY1135 (65%) only in the high Se conditions, indicating increased insulin sensitivity in the presence of elevated extracellular GPx3 levels. Since insulin serves as the signal for lipogenesis, we further investigated how GPx3 and selenite impact the differentiation of adipocytes. Vital requirement for adequate adipocyte differentiation is increased mitochondrial respiration capacity. Here, GPx3 treatment in high Se increased mitochondrial function during adipogenesis. Specifically, starting 36 hours after induction of differentiation we observed a 5% increase in O2 consumption that persists until the end of differentiation at day 14. However, although GPx3 increases acute insulin signalling and mitochondrial function during adipogenesis, lipid accumulation, observed by oil red O staining showed no additional effect of GPx3 in high Se conditions at the final timepoint. Therefore, we believe that GPx3 treatment in high Se conditions does not lead to an overall increase in differentiation capacity, but rather acceleration of the differentiation process. Strikingly, incubating gonadal white adipose tissue explants from B6N mice in media containing 500ng/ml GPx3 for 24h increased adipocyte IR mRNA levels by 92%. In summary, we identify GPx3 as a regulator of insulin receptor expression and insulin sensitivity in white adipocytes in vitro and ex vivo This modulation potentially occurs through paracrine or autocrine mechanism and is responsive to trace element intervention. Publication History Article published online: 18 April 2024 © 2024. Thieme. All rights reserved. Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany