Title: Adipocyte-specific Tribbles-1 Regulates Plasma Adiponectin and Lipoprotein Metabolism in Mice
Description: Multiple GWAS have identified SNPs in the 8q24 locus near the TRIB1 gene that significantly associate with plasma lipids and coronary artery disease. While subsequent studies have uncovered roles for hepatic and myeloid Trib1 in contributing to plasma lipids or atherosclerosis, eQTLs linking TRIB1 expression to the 8q24 GWAS SNPs have not been identified in any metabolic tissue, making the causal tissue for these GWAS associations unclear. The same 8q24 SNPs significantly associate with plasma adiponectin levels in humans as well, suggesting a role for TRIB1 in adipose tissue. To investigate the role of adipocyte-specific TRIB1 in plasma adiponectin and lipid regulation, we generated adipocyte-specific Trib1 knockout mice (Trib1_ASKO) and show that they have increased plasma adiponectin levels and decreased plasma cholesterol and triglycerides. We demonstrate that loss of Trib1 increases adipocyte production and secretion of adiponectin independent of the known TRIB1 function of regulating proteasomal degradation.

RNA-seq analysis of adipocytes and livers from Trib1_ASKO mice suggests that alterations in adipocyte function underlie the plasma lipid changes observed in these mice. Secretomics and RNA-seq analysis reveal that Trib1_ASKO mice have increased production of LPL and decreased production of ANGPTL4 in adipose tissue, and fluorescent substrate assays confirm an increase in adipose tissue LPL activity, which likely underlies the observed triglyceride phenotype. To better understand the role of the 8q24 SNPs in regulation of TRIB1 expression, we also present a short study of putative enhancer regions identified through DNA accessibility and ChIP-seq enhancer marks in Huh-7 cells. CRISPRi and CRISPRa perturbation of these regions do not affect TRIB1 expression, but instead affect the expression of a lncRNA that overlaps with the GWAS signal. In summary, we demonstrate here a novel role for adipocyte TRIB1 in regulating plasma adiponectin, total cholesterol, and triglycerides in mice, confirming previous genetic associations observed in humans and providing a novel avenue through which TRIB1 regulates plasma lipids and coronary artery disease.