Direct and Indirect Effects of Leptin on Preadipocyte

Leptin has been shown to reduce body fat in vivo. Adipocytes express the leptin receptor, so it is realistic to expect a direct effect of leptin on adipocyte growth and metabolism. However, in vitro studies examining the effect of leptin on adipocyte metabolism require supraphysiologic doses of the protein to see a decrease in lipogenesis or stimulation of lipolysis, implying an indirect action of leptin. It is also possible that leptin reduces adipose mass by inhibiting preadipocyte proliferation (increase in cell number) and/or differentiation (lipid filling). Thus, we determined direct and indirect effects of leptin on preadipocyte proliferation and differentiation in vitro. We determined the effect of leptin (0-500 ng/ml), serum from leptin infused rats (0.25% by volume), and adipose conditioned media from leptin infused rats (0-30% by volume) on preadipocyte proliferation and differentiation in a primary culture of cells from male Sprague-Dawley rat adipose tissue. Leptin (50 ng/ml) stimulated proliferation of preadipocytes, but 250 and 500 ng leptin/ml inhibited proliferation of both preadipocyte and stromal vascular fractions, as measured by 3H-thymidine incorporation. Serum from leptin infused rats inhibited proliferation of the adipose (p< 0.06) and stromal vascular (p< 0.05) fractions, but conditioned media had no effect on proliferation of either cell fraction. None of the treatments changed preadipocyte differentiation as measured by GPDH activity. These results suggest that leptin could inhibit preadipocyte proliferation by modifying release of a factor from tissue other than adipose tissue.