Orthopedia regulates Melanocortin 4 Receptor transcription and energy homeostasis

Disruption of hypothalamic melanocortin 4 receptors (MC4Rs) causes obesity in mice and humans. Here, we investigate the transcriptional regulation of MC4R in the hypothalamus. In mice, we show that the homeodomain transcription factor Orthopedia (Otp) is enriched in Mc4r neurons in the paraventricular nucleus of the hypothalamus (PVN) and directly regulates Mc4r transcription. Deletion of Otp in PVN neurons during development or adulthood reduces Mc4r expression, causing increased food intake and obesity. In humans, four of five carriers of rare predicted functional OTP variants in UK Biobank had obesity. To explore a causal role for human OTP variants, we generated mice with a loss-of-function OTP mutation identified in a child with severe obesity. Heterozygous knock-in mice exhibit hyperphagia and obesity, reversed by treatment with an MC4R agonist. Our findings demonstrate that OTP regulates mammalian energy homeostasis and enable the diagnosis and treatment of people with obesity due to OTP deficiency. Overall design: To determine whether Otp can directly bind to the Mc4r promoter, we performed a CUT&RUN (Cleavage Under Targets and Release Using Nuclease) assay in the adult PVN.