Type 2 diabetes mellitus (T2D) is a chronic condition affecting nearly half a billion people worldwide. Symptoms of T2D include impaired glucose tolerance, decreased insulin secretion and significant weight gain. While the symptoms of T2D are well-documented, the underlying pathology remains unclear. Recent research has indicated the critical role of the nuclear receptor Nr4a3 in the development of glucose intolerance and weight gain. In individuals with T2D, the Nr4a3 promoter is hypermethylated, leading to decreased Nr4a3 expression. Elucidating the role of Nr4a3 in mitochondrial respiration in adipose will help define the mechanism of T2D onset and treatment. Here we demonstrate the effect of systemic Nr4a3 loss. Full body Nr4a3 KO animals were fed a standard diet. Male, but not female, Nr4a3 KO mice demonstrate impaired glucose and insulin tolerance. Male Nr4a3 KO mice have normal muscle, liver, and kidney respiration rates, while adipose tissue respiration is impaired. The impaired adipose respiration corresponds with increased mass of all adipose depots, increased adipocyte size, and increased lipid droplet size. The analysis of electron transport chain and tricarboxylic acid complex proteins did not reveal significant differences. Instead, the altered respiration is attributed to a decreased Mek1 protein level, and decreased phosphorylation and activation of its downstream target DRP1. Our data demonstrate the critical role of Nr4a3 in adipose tissue through regulating mitochondrial function. NIH R15DK124835-01A1. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.