ACTIVATION OF ENDOTHELIN-1 PRODUCTION BY TGF-b1 IN ENDOTHELIAL CELLS: IMPLICATION OF THE HYPOXIA-INDUCIBLE TRANSCRIPTION FACTOR HIF-1

Studies in uremic animals have shown that when the relationship between endothelial factors is modified, this leads to the deterioration of renal function and to the development of hypertension and cardiovascular hypertrophy. Transforming growth factor-beta1 (TGF-b1), an important regulator of cell proliferation, cell differentiation and angiogenesis, stimulates the endothelial production of endothelin-1 (ET-1). In uremic rats, TGF-b1 expression is increased in parallel to ET-1 and the neutralization of TGF-b1 causes a decrease in ET-1 production. In this study, we wanted to elucidate the cellular mechanisms involved in endothelial ET-1 production following TGF-b1 stimulation. Bovine aortic and murine pulmonary endothelial cells (EC) were both used as cellular models. Activation of EC by TGF-b1 causes a strong increase in ET-1 excretion in the media by comparison to control cells. This increase of ET-1 excretion resembles that observed in hypoxia (1% oxygen). Since ET-1 is a gene regulated by hypoxia, we then measured hypoxia-inducible factor-1alpha (HIF-1a) protein expression, the active subunit of the hypoxic transcriptional regulator, HIF-1. Interestingly, stimulation of EC by TGF-b1 increases HIF-1alpha protein levels. HIF-1 induced by TGF-b1 in EC is active since it can bind to specific hypoxic response element (HRE) DNA sequences and activate HRE-controlled genes. These results suggest that TGF-b1 regulates endothelial ET-1 expression through the activation of HIF-1a. Comprehension of TGF-b1’s implication in the mechanisms related to endothelial dysfunction could reveal therapeutic targets in the treatment of cardiovascular and renal diseases.