Permanent activation of HMGA2 in lipomas mimics its temporal physiological activation linked to the gain of adipose tissue

Objective: In this study the activation of HMGA2 and overexpression by FGF1-driven stimulation of adipose tissue derived stem cells (ADSCs) in adipose tissue tumors were analyzed. In addition, the expression of HMGA2 and PPAR-gamma mRNA were quantified in canine subcutaneous abdominal adipose tissue from normal and overweight purebred dogs. Design and Methods: ADSCs and adipose tissue explants stimulated with FGF1 followed by gene expression analyses of HMGA2 and p14Arf using Western-blot and qRT-PCR. Furthermore, canine subcutaneous white adipose tissue (WAT) were analyzed by qRT-PCR for their expression of HMGA2 and PPAR-gamma. Results: ADSCs and adipose tissue explants are able to execute a HMGA2 response upon FGF1 stimulation. FGF1 enhances proliferation of ADSCs by a HMGA2-dependent mechanism. In lipomas increase of HMGA2 is accompanied by increased expression of p14Arf. Furthermore, a significantly elevated level of HMGA2 in overweight dogs and a negative correlation between the expression of HMGA2 and PPAR-gamma in subcutaneous cWAT were noted. Conclusions: These results suggest that WAT contains cells that as essential part of adipogenesis up-regulate HMGA2 resulting from growth factor stimulation. In subgroups of lipoma, constitutive activation of HMGA2 due to rearrangements replaces the temporal response triggered by growth factors.