LPA-promoted myofibroblast contraction: Role of calcium, myosin light chain phosphatase and Rho-A

• Main Author: Iran-nejad Parizi, Mojgan
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1998
• Subjects: Biochemistry; Cellular biology; Medicine; Surgery
• ISBN: 0599107901; 9780599107908

The purpose of this study was to understand the intracellular signaling pathways leading to myofibroblast contraction. Myofibroblasts generate the contractile force responsible for wound healing and pathological tissue contracture. While it has been proposed that the interaction between actin and myosin within this cell is responsible for force generation, the pathways regulating this interaction are not fully understood, our studies begin elucidate these mechanisms. The stabilized collagen lattice model is a powerful and unique assay suited for studying intracellular signaling mechanisms that generate tension in myofibroblasts. In this assay, myofibroblasts interact with the surrounding stabilized collagen in three dimensions, and within days they develop tension in the collagen lattice. The attached collagen lattice can then be mechanically released from the underlying tissue culture dish with the immediate loss of tension. Upon release of the collagen lattice, quantitative measurements can be made that reflect the amount of contractile force generated by the cells in response to various agonists or inhibitors. In this work we present evidence that LPA promotes myofibroblast contraction by regulating the activity of MLCK and MLCPPase, two enzymes that regulate the phosphoryation of MLC. In direct contrast to smooth muscle cells, where the level of intracellular Ca2+ is the dominant system regulating contraction, we found in myofibroblasts that increasing the level of intracellular Ca2+ was required, but not sufficient to promote contraction. We present evidence that myofibroblast contraction requires activation of the small GTPase Rho and subsequent inactivation of MLCPPase. We believe that there is a fundamental difference between the regulation of smooth muscle contraction and myofibroblast contraction. In smooth muscle cells, elevation of intracellular Ca2+ alone is sufficient to promote contraction; MLCPPase activity regulates the sensitivity of the contractile response to Ca2+ However, in myofibroblasts, MLCPPase activity is the primary regulator of contractility; inhibition of MLCPPase is required before contraction can occur in response to Ca2+ activation of MLCK. An understanding of the intracellular signaling pathways by which myofibroblast contraction occurs is important in distinguishing myofibroblasts from smooth muscle cells, and designing pharamacological therapies which may prevent abnormal wound healing and pathological contractures.