Morgan-Bathke M, Chen L, Oberschneider E, Harteneck D, Jensen MD. Sex and depot differences in ex vivo adipose tissue fatty acid storage and glycerol-3-phosphate acyltransferase activity. Am J Physiol Endocrinol Metab 308: E830 -E846, 2015. First published March 3, 2015 doi:10.1152/ajpendo.00424.2014.-Adipose tissue fatty acid storage varies according to sex, adipose tissue depot, and degree of fat gain. However, the mechanism(s) for these variations is not completely understood. We examined whether differences in adipose tissue glycerol-3-phosphate acyltransferase (GPAT) might play a role in these variations. We optimized an enzyme activity assay for total GPAT and GPAT1 activity in human adipose tissue and measured GPAT activity. Omental and subcutaneous adipose tissue was collected from obese and nonobese adults for measures of GPAT and GPAT1 activities, ex vivo palmitate storage, acyl-CoA synthetase (ACS) and diacylglycerol-acyltransferase (DGAT) activities, and CD36 protein. Total GPAT and GPAT1 activities decreased as a function of adipocyte size in both omental (r ϭ Ϫ0.71, P ϭ 0.003) and subcutaneous (r ϭ Ϫ0.58, P ϭ 0.04) fat. The relative contribution of GPAT1 to total GPAT activity increased as a function of adipocyte size, accounting for up to 60% of GPAT activity in those with the largest adipocytes. We found strong, positive correlations between ACS, GPAT, and DGAT activities for both sexes and depots (r values 0.58 -0.91) and between these storage factors and palmitate storage rates into TAG (r values 0.55-0.90). We conclude that: 1) total GPAT activity decreases as a function of adipocyte size; 2) GPAT1 can account for over half of adipose GPAT activity in hypertrophic obesity; and 3) ACS, GPAT, and DGAT are coordinately regulated. omental fat; subcutaneous fat; fat distribution; glycerol-3-phosphate acyltransferase 1 BODY FAT DISTRIBUTION PLAYS an important role in the development of the comorbidities associated with obesity. In general, adults with greater amounts of visceral fat have more risk for chronic disease than those with a lesser proportion of visceral fat (14). Although regional balances of fatty acids (uptake vs. release) should determine whether one depot expands at the expense of another, interindividual differences in regional lipolysis (8,13,24) and meal fat storage (21, 26, 31) do not appear to explain differences in body fat distribution. We found that direct free fatty acid (FFA) storage rates in subcutaneous fat are greater in women than men and that the sex-specific variations in direct FFA storage into adipocyte triacylglycerol (TAG) are consistent with body fat distribution patterns (16,18,28). On average, the protein content (CD36 and fatty acid transport protein 1) and enzyme activity [acyl-

Adipose tissue fatty acid storage varies according to sex, adipose tissue depot and degree of fat gain. However, the mechanism(s) for these variations is not completely understood. We recently published findings based on the glycerol 3-phosphate acyltransferase (GPAT) enzyme activity assay we optimized for use with human adipose tissue. These findings include a decrease in total GPAT and GPAT1 as a function of adipocyte size in both omental and subcutaneous adipose tissue and a strong, positive correlations between ACS, GPAT, and DGAT activities for both sexes and depots and between these storage factors and palmitate storage rates into TAG. The aim of this commentary is to expand upon the data from our recent publication. We describe here additional details on the optimization of the GPAT enzyme activity assay, a correlation between DGAT and percentage palmitate in the diacylglycerol fraction, and sex differences in fatty acid storage factors and storage rates into TAG at high palmitate concentrations.