Characterization of the collagen types synthesized by human and rat adipocyte precursors in vitro

The types of collagen molecules synthesized by newly confluent rat and human adipocyte precursor cells were studied and compared with those synthesized by fibroblasts in culture. For this the cells were incubated in the presence of [2]3H]L-glycine and [5-3H]L-proline and the newly synthesized radiolabelled collagen produced was purified and analysed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. This analysis revealed that the ratio of Types I and III collagen produced by four adipocyte precursor cell strains, each of distinct origin, was identical to that found with two different strains of lung fibroblasts. The mean ratio of Type I: Type III collagen in all cases was approximately 3.5:1. Because mature fat cells do not synthesize collagen and the adipocyte precursor cells lose their capacity for collagen synthesis during their post-confluent differentiation in vitro these data provide a biochemical basis to substantiate previous suggestions, based on morphology only, that the adipocyte stem cell is fibroblastic in nature.