Depot-specific features of adipocyte progenitors revealed by primary cultures plated at low density

Variation in growth across an animal's fat depots derives, at less in part, from inter-depot differences in pre-adipocytes. However, because of technical difficulties that have impeded the study of pre-adipocytes in primary culture, these differences are not well defined. Adipose tissue stromal cell fractions that contain pre-adipocytes grow readily in culture but invariably include cells plated at various stages of maturity. Consequently, crucial events in relatively immature cells are often obscured by activities of cells that are more mature. Therefore, one aim of the present study was to diminish the impact of cells plated near maturity by maximizing the density of immature cells. This was accomplished by the plating of stromal-vascular (SV) cell fractions at low density. Since immature pre-adipocytes proliferate much more rapidly than do mature pre-adipocytes, they become predominant. This approach made it possible for a variety of differences to be seen between cells from retroperitoneal (RP) and epididymal (Epi) tissues: Epi, but not RP, cells were seen to assemble in multi-layer clumps; multiplication was found to remain constant through at least one subculture in RP cells, but not in Epi cells; and, in a variety of ways, RP cells showed more differentiation than Epi cells. The reasons for these differences remain to be determined, but just the fact that they exist suggests that important dissimilarities among pre-adipocytes (including those responsible for nonuniform growth of fat depots) can be revealed and studied in primary cell culture.