Transforming growth factor β1-regulated xylosyltransferase I activity in human cardiac fibroblasts and its impact for myocardial remodeling

In cardiac fibrosis remodeling of the failing myocardium is associated with a complex reorganization of the extracellular matrix (ECM). Xylosyltransferase I and Xylosyltransferase II (XT- I and XT- II) are the key enzymes in proteoglycan biosynthesis, which are an important fraction of the ECM. XT- I was shown to be a measure for the proteoglycan biosynthesis rate and a biochemical fibrosis marker. Here, we investigated the XT- I and XT- II expression in cardiac fibroblasts and in patients with dilated cardiomyopathy and compared our findings with nonfailing donor hearts. We analyzed XT- I and XT- II expression and the glycosaminoglycan ( GAG) content in human cardiac fibroblasts incubated with transforming growth factor (TGF)- beta 1 or exposed to cyclic mechanical stretch. In vitro and in vivo no significant changes in the XT- II expression were detected. For XT- I we found an increased expression in parallel with an elevated chondroitin sulfate-GAG content after incubation with TGF-beta(1) and after mechanical stretch. XT- I expression and subsequently increased levels of GAGs could be reduced with neutralizing anti-TGF- beta 1 antibodies or by specific inhibition of the activin receptor-like kinase 5 or the p38 mitogen-activated protein kinase pathway. Usage of XT- I small interfering RNA could specifically block the increased XT- I expression under mechanical stress and resulted in a significantly reduced chondroitin sulfate-GAG content. In the left and right ventricular samples of dilated cardiomyopathy patients, our data show increased amounts of XT- I mRNA compared with nonfailing controls. Patients had raised levels of XT- I enzyme activity and an elevated proteoglycan content. Myocardial remodeling is characterized by increased XT- I expression and enhanced proteoglycan deposition. TGF-beta(1) and mechanical stress induce XT- I expression in cardiac fibroblasts and have impact for ECM remodeling in the dilated heart. Specific blocking of XT- I expression confirmed that XT- I catalyzes a rate-limiting step during fibrotic GAG biosynthesis.