Matrix stiffness determines the phenotype of vascular smooth muscle cell in vitro and in vivo: Role of DNA methyltransferase 1.

Cells perceive the physical cues such as perturbations of extracellular matrix (ECM) stiffness, and translate these stimuli into biochemical signals controlling various aspects of cell behavior, which contribute to the physiological and pathological processes of multiple organs. In this study, we tested the hypothesis that during arterial stiffening, vascular smooth muscle cells (SMCs) sense the increase of ECM stiffness, which modulates the cellular phenotype through the regulation in DNA methyltransferases 1 (DNMT1) expression. Moreover, we hypothesized that the mechanisms involve intrinsic stiffening and deficiency in contractility of vascular SMCs. Substrate stiffening was mimicked in vitro with polyacrylamide gels. A contractile-to-synthetic phenotypic transition was induced by substrate stiffening in vascular SMCs through the down-regulation of DNMT1 expression. DNMT1 repression was also observed in the tunica media of mice aortas in an acute aortic injury model and a chronic kidney failure model, as well as in the tunica intima of human carotid arteries with calcified atherosclerotic lesions. DNMT1 inhibition facilitates arterial stiffening in vivo and promotes osteogenic transdifferentiation, calcification and cellular stiffening of vascular SMCs in vitro. These effects may be attributable, at least in part, to the role of DNMT1 in regulating the promoter activities of Transgelin (SM22α) and α-smooth muscle actin (SMA) and the functional contractility of SMCs. We conclude that DNMT1 is a critical regulator that negatively regulates arterial stiffening via maintaining the contractile phenotype of vascular SMCs. This research may facilitate elucidation of the complex crosstalk between vascular SMCs and their surrounding matrix in healthy and in pathological conditions and provide new insights into the implications for potential targeting of the phenotypic regulatory mechanisms in material-related therapeutic applications.

Activation of peroxisome proliferator-activated receptor γ inhibits vascular calcification by upregulating Klotho.

Cardiovascular diseases are common in patients with chronic kidney disease. One of the key symptoms is the calcification of the vascular smooth muscle cells (VSMCs), which is induced by dysregulated mineral metabolism with high circulating levels of inorganic phosphate (Pi) and calcium. Klotho, which was originally identified as an aging suppressor gene, has been shown to be associated with vascular calcification. Since Klotho was recently identified as a target for nuclear receptor peroxisome proliferator-activated receptor (PPAR) γ, the present study aimed to determine whether PPARγ regulates VSMC calcification through modulating the expression levels of Klotho. It was demonstrated that the expression of PPARγ was downregulated during Pi-induced VSMC calcification. In addition, treatment with PPARγ agonists inhibited the calcification and enhanced the expression of Klotho in VSMCs in a PPARγ-dependent manner. Of note, loss of Klotho expression by RNA interference abolished the ability of PPARγ activation to inhibit VSMC calcification. Furthermore, activation of Klotho as well as PPARγ inhibited the expression of Pi transporter 1/2 and reduced Pi influx into VSMCs. To the best of our knowledge, the present study was the first to demonstrate that PPARγ regulates VSMC calcification through activating Klotho.