STAT5A expression in Swiss 3T3 cells promotes adipogenesis in vivo in an athymic mice model system.

Many studies from our laboratories and others have shown that STAT5 expression and activity are increased during adipogenesis of murine and human adipocytes. Ectopic expression of STAT5A in fibroblasts or preadipocytes can confer or enhance adipogenesis. To determine whether STAT5A also plays a role in adipogenesis in vivo, we injected athymic mice with Swiss 3T3 cells expressing an empty pBABE retrovirus, Swiss cells expressing a pBABE retrovirus-containing STAT5A, or 3T3-F442A preadipocytes. Athymic mice injected with either 3T3-F442A cells or Swiss 3T3 cells expressing STAT5A resulted in fat pad formation at the site of injection. However, mice injected with Swiss cells containing the parent retroviral vector did not have any observable fat pads. An analysis of the ectopic fat pads obtained from the Swiss 3T3 STAT5A mice revealed abundant expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) and adiponectin. The protein levels of both of these fat cell markers were comparable to expression levels in epididymal fat pads. These results demonstrate that STAT5A can promote adipogenesis in vivo in this model system which supports a role of this transcription factor in adipocyte development in the whole animal.