Multiethnic genome-wide meta-analysis of ectopic fat depots identifies loci associated with adipocyte development and differentiation

Abstract

Variation in body fat distribution contributes to the metabolic sequelae of obesity. The genetic determinants of body fat distribution are poorly understood. The goal of this study was to gain new insights into the underlying genetics of body fat distribution by conducting sample-size-weighted fixed-effects genome-wide association meta-analyses in up to 9,594 women and 8,738 men of European, African, Hispanic and Chinese ancestry, with and without sex stratification, for six traits associated with ectopic fat (hereinafter referred to as ectopic-fat traits). In total, we identified seven new loci associated with ectopic-fat traits (ATXN1, UBE2E2, EBF1, RREB1, GSDMB, GRAMD3 and ENSA; P < 5 × 10^-8; false discovery rate < 1%). Functional analysis of these genes showed that loss of function of either Atxn1 or Ube2e2 in primary mouse adipose progenitor cells impaired adipocyte differentiation, suggesting physiological roles for ATXN1 and UBE2E2 in adipogenesis. Future studies are necessary to further explore the mechanisms by which these genes affect adipocyte biology and how their perturbations contribute to systemic metabolic disease.

Figure 1. Functional characterization of Atxn1, Ebf1, Rreb1 and Ube2e2

(a,b,e) Data is displayed as box/whisker plots where the center line represents the median, box limits contain the 25^th–75^th percentiles, and whiskers span max/min values. (a) Gene expression measured by qPCR in murine subcutaneous (SAT), perigonadal visceral (VAT), and pericardial (PAT) adipose tissues (n=6 mice). Statistical significance was assessed using ANOVA and Sidak’s correction for multiple comparisons. (b) Gene expression measured by qPCR in murine adipose tissues after 8 weeks of high fat feeding compared to normal chow fed controls (n=5 mice per group). Statistical significance was assigned using a two-sided T-test. (c) Gene expression measured by qPCR in cultured adipocyte progenitors isolated from the subcutaneous (SAT) or perigonadal visceral (VAT) depots (n=4 replicates). Cells were expanded to confluence and then collected at intervals after induction of adipogenic differentiation. Data displayed as mean, error bar=s.e.m. Statistical significance was assessed using ANOVA and Sidak’s correction for multiple comparisons to time 0. (d) Oil-red-o staining of progenitors isolated from subcutaneous adipose and exposed to retroviral delivery of shRNA constructs during ex vivo expansion and induction of adipogenesis. Relative to control vector carrying a scramble sequence, shRNA constructs specific for Atxn1 and Ube2e2 impaired adipogenic differentiation. Scale=1mm. (e) Oil-red-o stain was alcohol extracted and quantified at OD₅₂₀ (n=9 technical replicates). Statistical significance was assessed using ANOVA and Sidak’s correction for multiple comparisons to control (Scramble). Data representative of 3 independent experiments.