Adipose tissue fatty acid storage factors: Effects of depot, sex and fat cell size

Background/Objectives: Patterns of postabsorptive adipose tissue fatty acid storage correlate with sex-specific body fat distribution. Some proteins and enzymes participating in this pathway include CD36 (facilitated transport), acyl-CoA synthetase (ACS; the first step in fat metabolism) and diacylglycerol acetyltransferase (DGAT; the final step of triglyceride synthesis). Our aim was to better define CD36, ACS and DGAT in relation to sex, subcutaneous fat depots and adipocyte size. Subjects/Methods: Data were collected from studies conducted at Mayo Clinic between 2004 and 2012. Abdominal and femoral subcutaneous fat biopsy samples must have been collected in the postabsorptive state from healthy males and premenopausal females. Body composition was measured with dual-energy X-ray absorptiometry and abdominal computerized tomography scans. Adipocyte size (microscopy), CD36 protein content (enzyme-linked immunosorbent assay) and ACS and DGAT enzyme activities were measured. Data are presented as medians and 25th, 75th quartiles. Results: Males (n = 60) and females (n = 78) did not differ by age (37; 28, 46 years), body mass index (28.4; 24.6, 32.1 kg m^-2) or abdominal (0.60; 0.45, 0.83 μg lipid per cell) and femoral adipocyte size (0.76; 0.60, 0.94 μg lipid per cell). Femoral ACS and DGAT were greater in females than males when expressed per mg lipid (ACS: 73 vs 55 pmol/mg lipid/min; DGAT: 5.5 vs 4.0 pmol/mg lipid/min; P < 0.0001 for both) and per 1000 adipocytes (ACS: 59 vs 39 pmol per min per 1000 adipocytes; DGAT: 4.3 vs 3.1 pmol per min per 1000 adipocytes; P ≤ 0.0003 for both). There were no differences in abdominal fat storage factors between sexes. ACS and DGAT decreased as a function of adipocyte size (P < 0.0001 for both). The decrease in ACS was greater in males and abdominal subcutaneous fat. There were no sex differences in CD36 in either fat depot, nor did it vary across adipocyte size. Conclusions: Facilitated transport of fatty acids by CD36 under postabsorptive conditions would not be different in those with large vs small adipocytes in either depot of both sexes. However, intracellular trafficking of fatty acids to triglyceride storage by ACS and DGAT may be less efficient in larger adipocytes.