Fluid shear stress induces endothelial transforming growth factor beta-1 transcription and production. Modulation by potassium channel blockade.

Abstract

The endothelium has the capacity to modulate vascular structure in response to hemodynamic stimuli.We tested the hypothesis that exposure of the endothelium to increased laminar shear stress induces the expression of TGFp1 via a signal transduction pathway modulated by K+ channel currents.Although TGFp1 is normally secreted in a latent, inactive form, exposure of cultured endothelial cells to steady laminar shear stress (20 dynes/cm2) induced in- creased generation of biologically active TGFfi1.This in- crease in active TGFp1 was associated with a sustained increase in TGFB1 mRNA expression within 2 h of stimula- tion.TGFI31 mRNA levels increased in direct proportion to the intensity of the shear stress within the physiologic range.The effect of shear stress on TGFp1 mRNA expression was regulated at the transcriptional level as defined by nuclear run-off studies and transient transfection of a TGF,1 promoter-reporter gene construct.Blockade of endothelial K+ channels with tetraethylammonium significantly inhibited: activation of TGFfJ1 gene transcription; increase in steady state mRNA levels; and generation of active TGFp1 in re- sponse to shear stress.These data suggest that endothelial K+ channels and autocrine-paracrine TGF,B1 may be in- volved in the mechanotransduction mechanisms mediating flow-induced vascular remodeling.(J.Clin.Invest.1995.95:1363-1369.)Key words: flow * mechanical stress * cyto- kine * ion channel * gene expression MethodsCell culture Bovine aortic endothelial cells (BAEC)' were harvested and passaged by trypsinization as previously described ( 16).These cells have been characterized as endothelial cells based upon morphology, acetylated-LDL binding, angiotensin-converting enzyme measurements, and Factor VIII antigen analysis.The cells were grown on tissue culture plates ( 150 cm2) in 10% calf serum in DME/F12 supplemented with L-glutamine (4 mM), Hepes buffer pH 7.4, penicillin (100 U/ml), and streptomycin (100 i.g/ml).Studies were conducted on cells between passages 4 and 11 that were maintained at a confluent state for 2 d.Before exposure to shear stress, the medium was switched to a defined serum-free medium without ATP, that contains insulin (1 yM), transferrin (5 mg/ml), and ascorbate (0.2 mM). 1. Abbreviations used in this paper.BAEC, bovine aortic endothelial cells; CAT, chloramphenicol acetyltransferase; SSRE, shear stress re- sponsive element; TEA, tetraethylammonium.