CREB1 and obesity due to melanocortin 4 receptor deficiency: The exact mechanisms responsible for the obesity-related BCAA dysregulation remain poorly understood, but may be attributed to the following two reasons: 1) the impaired central nerves system insulin signaling under obesity (28); 2) HFD-induced hyperglycemia which inhibits CREB-stimulated KLF15 transcription resulting in downregulation of enzymes in the BCAA catabolism pathway (29).