Early Studies on Role of Stearoyl-CoA Desaturase During Preadipocyte Differentiation

Abstract

Having extensively investigated the catalytic mechanism of action of acetyl-CoA carboxylase (ACC) (Polakis et al. 1972, 1974; Guchhait et al. 1971, 1974a, b; Moss and Lane 1971) and its allosteric regulation by citrate (Moss and Lane 1972; Gregolin et al. 1966; Ryder et al. 1967; Beaty and Lane 1983a, b), in the late 1970s and early 1980s, our lab decided to determine how expression of ACC is controlled. To conduct such studies we needed a lipogenic cell line that could be cultured for extended periods of time (i.e., greater than a week), during which gene expression and protein translation could be assessed. About this time Howard Green and colleagues, who had recently moved from the New York University Medical School to the Massachusetts Institute of Technology (MIT), had established several preadipocyte cell lines—notably the 3T3-L1 and 3T3F442 cell lines (Green and Kehinde 1974, 1975, 1976)—for the study of adipocyte biology. These lines could be induced to differentiate into cells with the phenotype of adipocytes including high rates of lipogenesis (Mackall et al. 1976; Mackall and Lane 1977; Coleman et al. 1978; Student et al. 1980) and responsiveness to insulin (Reed et al. 1977, 1981; Reed and Lane 1980). Since then the 3T3-L1 preadipocyte line has become the “gold standard” for studies on adipocyte differentiation. We (Student et al. 1980) and others (Lai et al. 1982) developed protocols to induce differentiation and demonstrated that expression of fatty acid synthase (FAS), ACC, and numerous other lipogenic proteins paralleled the acquisition of adipocyte morphology. These early observations verified the system and established the primary parameters linked to the utilization of the 3T3-L1 model including (1) an accumulation of cytoplasmic fat as revealed by Oil Red O staining (Mackall et al. 1976), (2) a dramatic increase in the rate of fatty acid synthesis (Mackall et al. 1976; Student et al. 1980), (3) a coordinate increase in the enzymatic activities of ACC (Mackall et al. 1976), FAS, and complex lipids synthesis (triacylglycerol and phospholipids) (Coleman et al. 1978), and (4) hormonally regulated lipid metabolism including insulin-stimulated glucose uptake and lipogenesis and catecholamine-stimulated lipolysis (Reed et al. 1977, 1981; Reed and Lane 1980).