Culture of porcine stromal-vascular cells in serum-free medium: Differential action of various hormonal agents on adipose conversion

We developed a strictly controlled serum-free culture system and tested the effects of adipogenic and antiadipogenic agents on the proliferation and(or) adipose conversion of porcine stromal-vascular cells. To avoid any interference with serum components, stromal-vascular cells were isolated, plated, and grown in absence of serum. In these culture conditions, a very limited growth phase and the absence of cell confluence were observed. However, when compared with continuous culture in serum-containing medium, the serum-free conditions were significantly more adipogenic as assessed by increased lipid content and increased enzymatic activities for lipoprotein lipase, glycerol 3-phosphate dehydrogenase, and malic enzyme. In serum-free medium, physiological concentrations of insulin or IGF-I were sufficient to significantly increase the percentage of lipid-containing cells, whereas triiodothyronine (T(sub 3)) and GH had no effect. Insulin, IGF-I, and, more moderately, T(sub 3) also accelerated the lipid filling in the lipid-containing cells. In the presence of insulin, stimulation by T(sub 3) or hydrocortisone alone had no effect on glycerol 3-phosphate dehydrogenase activity, whereas their concomitant addition significantly increased it. Chronic exposure to tumor necrosis factor-(alpha) dose-dependently stimulated cell proliferation but clearly inhibited differentiation. Epidermal growth factor, another known antiadipogenic agent, also significantly increased the proliferation of stromal-vascular cells, but, surprisingly, this was not correlated with inhibition of adipocyte differentiation. Indeed, epidermal growth factor treatment did not decrease lipid filling and significantly improved lipoprotein lipase and malic enzyme activities. Taken together, the results obtained in these strictly controlled serum-free culture conditions point out functions for insulin, IGF-I, hydrocortisone, and T(sub 3) during early and(or) later steps of porcine adipose conversion. In addition, this study reports a positive activity of epidermal growth factor on porcine adipocyte differentiation that is in clear contrast with previous works performed with rodent cells. Key Words: Pigs, Adipocytes, Hormones, Growth Factors, Cytokines