Excess glucocorticoids contribute to the development of diabetes and metabolic syndrome, which includes: obesity, hyperglycemia, hypercholesterolemia, insulin resistance, and liver steatosis. Glucocorticoids exert their physiological effects via the glucocorticoid receptor (GR), a transcription factor that binds chromatin at GRE motifs leading to gene activation or repression. Our published work identified a previously unrecognized mechanism for GR-mediated gene regulation through its collaboration with the SET domain-containing protein, SETDB2, to activate a select subset of GR gene targets in the liver associated with diabetes. We showed livers of mice deficient in SETDB2 have a significantly blunted glucocorticoid response as demonstrated by fasting hypoglycemia and lack of induction of key GR target genes. Since inhibition of glucocorticoid action in liver can prevent the negative metabolic effects of glucocorticoid-induced diabetes, we hypothesize that liver-specific SETDB2-knockout (DB2-LKO) mice will be partially protected from metabolic dysfunction when exposed to conditions that lead to elevated glucocorticoids. Fundamental mechanisms associated with glucocorticoid-induced metabolic disease are studied by evaluating the effects of liver-specific DB2-LKO and liver-specific GR-LKO on glucose/lipid homeostasis under conditions of elevated endogenous glucocorticoids (diet- induced obesity) or exogenous glucocorticoid administration. Metabolic parameters associated with diabetes will be measured: weight gain, glucose-intolerance, insulin-resistance, hyperlipidemia, and hepatic steatosis. Additionally, the molecular mechanism for the combined action of SETDB2 and GR will be characterized within these experimental paradigms and novel gene targets and chromatin targeting will be identified by RNA-seq, ChIP-seq and Hi-ChIP. Integrating the proposed experiments will provide a better understanding of how SETDB2 affects the positive and negative actions of GR that are relevant to metabolic disease in the liver. The fundamental mechanism studied may provide a pathway to target SETDB2?s role in GR action as a new therapeutic target for glucocorticoid-induced diabetes and metabolic disease. The experiments a balance of mechanistic and exploratory studies in mouse models to investigate the regulation of hepatic metabolic processes that are directly relevant to human disease. The results from both aims will be integrated together to reveal the overlapping and unique mechanisms by which the SETDB2-GR regulatory axis contributes to the adaptation of the liver to acute nutritional (Aim 1), chronic nutritional and hormonal (Aim 2) states of metabolic stress.
Our preliminary published and unpublished studies support a role for the SET-domain containing protein, SETDB2, in glucocorticoid receptor (GR)-dependent gene expression essential to liver metabolism during metabolic stress. We hypothesize liver SETDB2 deficiency will be protective to the metabolic adverse effects of excess endogenous or exogenous glucocorticoids. Successful execution of this proposal will result in mechanistic insight into the genomic regulation behind glucocorticoid- induced diabetes through a potential unique SETDB2-GR regulatory node, which may open new therapeutic strategies for multiple glucocorticoid associated diseases in humans.
