Interaction of plasma lipoprotein subfractions with differentiating 3T3-L1 and human mammary preadipocytes in culture

Abstract

Differentiating 3T3-L1 preadipocytes (murine fatty fibroblasts) and human preadipocytes interact with human lipoprotein subfractions (HDL2 and LDLII/III) at all stages of the differentiation program, displaying saturable binding behavior. Both cell types interact similarly with LDLII/III as differentiation proceeds, showing increased binding affinities and capacities and maximal rates of uptake in the mature cells, as compared with the preadipocyte stage. These changes coincide with the intracellular appearance of lipid droplets. However, with regard to HDL2, a markedly different pattern of interaction is evident in both cell types. For 3T3-L1 cells, lowered binding and uptake affinities and capacities are apparent in the fully differentiated state for HDL2, as compared with LDLII/III. Human preadipocytes displayed two distinct affinity binding sites for HDL2 during the early stages of differentiation (days 2 and 3), as compared with a single affinity site for LDLII/III at all stages. However, in the fully differentiated human cells, only a single affinity site, indistinguishable from the high-affinity site present on day 2, is evident, and probably represents the only binding site of physiological significance in these cells. All the cellular developments appear to be largely unaffected by exposure of both preadipocyte types to added lipoproteins (HDL + LDL) in the medium during the early stages of the conversion process.