Transforming growth factor-β 1 increases lysyl oxidase enzyme activity and mRNA in rat aortic smooth muscle cells

Purpose: This investigation was designed to test the hypothesis that transforming growth factor-β 1 (TGF-β 1) regulates lysyl oxidase secretion from vascular smooth muscle cells. Lysyl oxidase is an enzyme that catalyzes an essential step in collagen and elastin cross-linking in the extracellular matrix, and TGF-β 1 has been implicated in the pathogenesis of restenosis after vascular injury. The effect of TGF-β 1 on lysyl oxidase in vascular smooth muscle cells has not been previously defined. Methods: Rat aortic smooth muscle cells were grown in culture to confluence. Cells in passage 2 to 6 were incubated for 24 hours in media containing 0.1, 0.5, 1.0, or 10.0 ng/ml of TGF-β 1. Lysyl oxidase activity in the media was quantitated with a tritium-release bioassay against an insoluble 3H-labeled aortic elastin substrate. Northern blot analyses were performed to determine steady-state levels of lysyl oxidase mRNA in the smooth muscle cells. Results: Lysyl oxidase activity in the media increased 1.5-fold above control levels after exposure to 10 ng/ml of TGF-β 1 ( p < 0.01). This increase in lysyl oxidase activity was associated with a concentration-dependent increase in steady-state levels of lysyl oxidase mRNA, being 4.3- and 6.2-fold above control levels after exposure to 1 and 10 ng/ml TGF-β 1, respectively ( p < 0.01). The observed increase in steady-state lysyl oxidase mRNA after exposure to TGF-β 1 was also time-dependent over the 24-hour experimental period. Conclusions: TGF-β 1 appears to regulate lysyl oxidase in cultured rat aortic smooth muscle cells. Increases in lysyl oxidase activity may be one of the mechanisms by which TGF-β 1 contributes to arterial restenosis after vascular injury. (J Vasc Surg 1997;25:446-52.)