Role of transcriptional coregulator GRIP1 in control of macrophage polarization and metabolic homeostasis

Diet-induced obesity is characterized by macrophage (MF) infiltration and low-grade chronic inflammation in white adipose tissue (WAT) leading to insulin resistance. WAT MF are highly heterogeneous in their origin, patterns of gene expression and activities: unlike infiltrating monocyte-derived MF that promote inflammation and metabolic dysfunction, tissue-resident WAT MF originally described as ‘M2’ are phenotypically anti-inflammatory and counteract obesity and insulin resistance. Despite the critical role of the balance between these MF populations in metabolic homeostasis, the molecular mechanisms and key players that establish the resident MF transcription program are poorly understood. We recently reported that glucocorticoid receptor (GR)-interacting protein (GRIP)1 - a nuclear receptor coactivator - cooperates with GR to repress transcription of inflammatory genes. Here, using mice conditionally lacking GRIP1 in MF (cKO), we show that GRIP1 promotes MF polarization in response to IL4 (M2(IL4)) via a nuclear receptor-independent pathway by serving as a coactivator for Kruppel-like factor (KLF)4 – a critical driver of tissue MF differentiation. Interestingly, in vivo, GRIP1 cKO mice challenged with high-fat diet develop massive MF infiltration and chronic inflammation in WAT and liver, fatty livers, hyperglycemia, hyperinsulinemia and glucose intolerance consistent with metabolic syndrome phenotype. Together, our findings identify GRIP1 as a critical regulator of immunometabolism, which relies on distinct transcriptional mechanisms to coordinate the balance between MF populations in vivo thereby protecting mice from obesity-induced metabolic disease. Overall design: 1. Examination of IL4 induced transcriptome in in vitro differentiated primary bone marrow-derived macrophages. 2. Examination of macrophage transcriptome in macrophages isolated from the white adipose tissue of the WT and GRIP1(cKO) conditional KO animals