Vascular smooth muscle mechanotransduction and plasticity-the role of microRNA, calcium signaling and actin polymerization

Smooth muscle cells residing in the blood vessel media are constantly exposed to mechanical forces exerted by the intraluminal pressure. The smooth muscle senses and adapts to mechanical forces by activation of multiple signaling pathways and cytoskeletal rearrangements. Stretch of the vascular wall is therefore an important factor that controls smooth muscle cell phenotype and function. The goal of this thesis was to study the role of microRNAs and calcium-sensitive proline-rich tyrosine kinase (PYK 2) in stretch-induced signaling as well as to characterize genes whose expression is regulated by actin polymerization in smooth muscle. Murine portal vein cultured ex vivo under longitudinally applied load was used to study the effects of stretch. Spontaneous activity as well as stretch-induced synthesis of contractile/cytoskeletal proteins was diminished in portal vein lacking functional microRNAs (Dicer KO). In wild type portal vein, stretch down-regulated miR-144/451 cluster expression, which inversely correlated with increased activation of AMP-kinase and contractile differentiation of smooth muscle. Stretch increased phosphorylation of PYK 2 at Tyr402 in rat portal vein. The PYK 2 inhibitor, PF-4594755 reduced DNA and total protein synthesis, whereas stretch-induced mRNA expression of smooth muscle contractile markers was maintained. Stabilization of actin filaments in smooth muscle cells resulted in increased expression of a number of genes encoding proteins involved in cytoskeletal and contractile function, including dystrophin and synaptopodin 2. The expression of dystrophin and synaptopodin 2 was down-regulated in phenotypically modulated smooth muscle cells and after balloon-injury of human mammary artery. Furthermore, loss of dystrophin resulted in decreased smooth muscle contractile function. In summary, this study provides novel evidence for the role of microRNAs and calcium-sensitive PYK 2 in stretch-induced signaling in smooth muscle. Moreover, the data show that dystrophin and synaptopodin 2 are regulated by actin polymerization and that their expression is altered in models of vascular disease