The hyperplastic capacity of adipose tissue resides in a group of fibroblast-like adipocyte precursor cells. There is evidence to suggest that their proliferation and differentiation is regulated by insulin-like growth factor-I (IGF-I) and transforming growth factor-β (TGF-β) but there is less information about other growth factors which may also participate in adipocyte precursor cell hyperplasia.
Transforming growth factor-α (TGF-α) is a 50 amino acid polypeptide which has been shown to stimulate proliferation in both neoplastic and normal cell types acting through the epidermal growth factor (EGF) receptor. We have studied the regulation of DNA synthesis and the activity of lipoprotein lipase by TGF-α in chicken adipocyte precursor cells in vitro. Both TGF-α and EGF stimulated incorporation of [3H]thymidine into DNA in a dose-dependent manner. TGF-α was approximately 180-fold more potent than EGF. Addition of TGF-α in combination with IGF-I, TGF-β1 or platelet-derived growth factor produced a synergistic increase in DNA synthesis. Short-term incubation with TGF-α reduced lipoprotein lipase activity by 23%.
These results show that TGF-α is a potent mitogen in these adipocyte precursor cells and can inhibit their differentiation in vitro and may participate in the regulation of adipose tissue development in vivo.