GLUCOCORTICOID RECEPTOR POST-TRANSLATIONAL MODIFICATIONS IN INSULIN RESISTANCE

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Abstract: There is a global epidemic of metabolic syndrome, characterized by insulin resistance, hypertension, and central obesity. Although the etiology of metabolic syndrome is still an active area of investigation, one leading hypothesis is that it is caused by elevated glucocorticoid (GCs) levels in key insulin responsive tissues such as liver and fat. GCs are stress hormones produced by the adrenal gland. GCs bind to the GC receptor (GR) a nuclear hormone receptor that alters transcription of target genes by multiple mechanisms including direct binding to DNA (transactivation) as well as protein-protein mediated repression. GCs are also effective therapies for many inflammatory diseases including chronic obstructive pulmonary disease, inflammatory bowel disease and rheumatoid arthritis, but their use is limited due the adverse metabolic effects including weight gain, insulin resistance and hypertension. Recently, several groups have identified GR post- translational modification (PTM) in cell lines, and these PTM events alter GR transcriptional activity. However, the role of GR PTM in physiologically relevant paradigms in vivo is unknown. Based on preliminary data, I hypothesize that GR PTM, specifically phosphorylation, mediates the complex effects of GC on the liver in vivo. This hypothesis will be tested in three Specific Aims: 1) We will determine the role of GR phosphorylation on hepatocyte metabolism and gene expression. This will be done by adding back wildtype or phosphomutant GR isoforms to GR knockdown hepatoma cells 2) We will determine the role of GR phosphorylation in mediating heaptic metabolism, gene expression and GR occupancy in the livers of mice. This will be done by analyzing metabolism, gene expression and chromatin immunoprecipitation with antibodies to GR. We have created novel GR knockin phosphomutant mice using CRISPRS. These S211A mice have a key phosphorylated serine residue mutated to alanine. We will determine which GC mediated changes in hepatic lipid metabolism, gene expression and GR occupancy are phosphorylation dependent. 3) We will determine if GR phosphorylation is associated with hepatic insulin resistance in samples from obese patients undergoing Roux-en-Y gastic bypass surgery. This will be done by staining liver biopsies from these patients (as well as controls) with phosphoGR specific antibodies. Currently selective GR modulators are being developed for the treatment of metabolic diseases as well as safer anti-inflammatory medications. Therefore, understanding the role of GR PTM in mediating effects of GCs should shed light on novel treatments for metabolic disease as well as common inflammatory conditions.