Epigenetic regulation of brown fat thermogenesis by the histone demethylase KDM6A

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Obesity is a disorder of energy homeostasis due to energy intake over energy expenditure. Adaptive thermogenesis, in which brown adipose tissue (BAT) functions to dissipate energy as heat, is an integral part of overall energy expenditure. Obesity is a complex disease resulting from gene and environment interactions. One of the mechanisms that environmental factors such as diets affect gene expression patterns involves their capacity to reprogram the epigenome. Evidence converges to suggest that epigenetic events, including histone methylation, figure prominently in the development of obesity. Lysine (K) specific demethylase 6A (KDM6A) is a histone demethylase that preferentially demethylates tri-methylated histone lysine 27 (H3K27me3) and therefore relieves its ability to silence the genes, leading to activation of the gene transcription. Our published and preliminary data suggest that KDM6A is important in regulating brown fat thermogenic program, energy metabolism and diet-induced obesity (DIO), and that KDM6A overexpression increases the expression and secretion of a BAT-derived neurotrophic factor neurotrophin 3 (NT3), which enhances sympathetic nervous system (SNS) innervation into adipose tissue. Therefore, we hypothesize that KDM6A plays an important role in regulating brown fat thermogenesis, energy metabolism and obesity, and that KDM6A-stimulated NT3, a BAT-derived neurotropic factor, promotes brown/beige cell thermogenesis via enhanced SNS innervation. Aim 1 will determine the role of KDM6A in cold-induced thermogenesis, energy metabolism and diet-induced obesity in genetic models. We will use brown fat KDM6A deficient or overexpressing mice (named AKO and AOE mice, respectively) to determine whether specific deletion of KDM6A in brown fat impairs brown fat thermogenesis during cold exposure and promotes diet-induced obesity, whereas specific overexpression of KDM6A in brown fat does the opposite. O-GlcNAcylation has emerged as a key nutrient sensor that regulates cellular metabolic pathways in response to overnutritional cues (e.g. excess glucose and fatty acids). We will determine whether KDM6A O-GlcNAcylation by excess nutrients (glucose and fatty acids) decreases its ability to demethylate H3K27me3 at the thermogenic gene promoters, thereby compromising diet-induced thermogenesis. Aim 2 will investigate the role of KDMK6A-stimulated NT3, a brown fat-derived neurotropic factor, in regulating adaptive thermogenesis, energy metabolism and diet-induced obesity, via sympathetic innervation into adipose tissue. We have generated mice with adipocyte-specific overexpression of NT3. We will determine 1) whether adipose overexpression of NT3 promotes cold-induced thermogenesis and prevents diet-induced obesity; 2) whether NT3 stimulates SNS innervation into adipose tissue and sympathetic neuron axonal growth via activating its receptor tropomyosin receptor kinase C (TRKC); 3) whether or to what extent NT3 mediates the effect of KDM6A in promoting brown/beige cell thermogenesis and preventing DIO. Completion of this project could help guide the development of KDM6A and NT3 as new therapeutic targets in the treatment of obesity.