Preferential expression of cholesteryl ester transfer protein mRNA by stromal-vascular cells of human adipose tissue

Cholesteryl ester transfer protein (CETP) mRNA is more abundantly expressed in small mature adipocytes as compared to large, lipid-rich adipocytes [Radeau et al., J. Lipid Res. 36 (1995) 2552-2561]. In the present study, the stromal vascular fraction (SVF) of human adipose tissue was isolated and the presence of very small fat cells in this fraction confirmed by electron microscopy and by demonstrating the presence of mRNA for adipsin and for CCAAT enhancer binding protein alpha (C/EBPalpha), a marker of adipocyte differentiation. sn-Glycerol 3-phosphate dehydrogenase (GPDH) activity was present in the SVF but not in the preadipocyte fraction. Northern blot analysis of human adipose tissue demonstrated that CETP mRNA expression was significantly greater (+96%, P<0.03) in stromal-vascular cells (SVC) as compared to mature fat cells. By comparison, lipoprotein lipase mRNA expression was lower (-75%, P<0.03) in SVC while apolipoprotein E mRNA expression was not significantly different in SVC as compared to isolated adipocytes. By RT-PCR analysis, we demonstrated that CETP mRNA was expressed by human pre-adipocytes at levels less than those of SVC and adipocytes. The absence of monocytes/macrophages in SVC was confirmed by the absence of FcgammaRIII (CD16) mRNA in these fractions. These data demonstrate that CETP mRNA is most highly expressed in the immature fat cells of human adipose tissue, consistent with other experiments from this laboratory demonstrating that CETP plays an important local role in adipocyte cholesterol accumulation.