Autocrine production and TGF-β1-mediated effects on metabolism and viability in renal cells

Transforming growth factor-β1 (TGF-β1) treatment (0.2-2.0 ng/ml, 8-80 pM) of confluent primary cultures of rabbit renal proximal tubular cells (RPTC) for 6 consecutive days resulted in both a phenotypic transformation of the monolayer into solid clusters of cells and apoptosis. TGF-β1 treatment stimulated glycolysis before any effect on monolayer DNA content or morphology. TGF-β1 treatment also resulted in a 35% decrease in oxygen consumption, 50% inhibition of Na+-K+ATPase activity, and a 57% decrease in gluconeogenesis. A concentration of 0.06 ng/ml TGF-β1 decreased oxygen consumption and induced glycolysis but had no effect on morphology and viability of RPTC. Endogenous production of TGF-β1 by RPTC increased 2.6-fold during 10 days of culture. Control RPTC treated with anti-TGF-β antibodies exhibited decreased glycolysis, and lactate metabolism shifted from net production to net consumption. These results show that TGF-β1 stimulates glycolysis, decreases respiration, and, at higher concentrations, induces RPTC apoptosis and phenotypic changes. Inhibition of net lactate production in cells grown in the presence of anti-TGF-β antibodies suggests that increased endogenous production of TGF-β is responsible for the stimulation of glycolysis in long-term cultures of RPTC.