Use of conditionally immortalized mouse cardiac fibroblasts to examine theeffect of mechanical stretch on alpha-smooth muscle actin

Mechanical stretch regulates alpha -smooth muscle actin (SMA) expression in myofibroblasts but limited replication and cellular heterogeneity have ham pered definitive studies in vitro. We examined the role of applied force in regulating SMA expression in conditionally immortalized cardiac fibroblast lines derived from H-2K(b)-tsA58 transgenic mice. When plated in different iating conditions (37 degreesC without interferon-gamma), transgenic myofib roblasts exhibited vimentin staining, no desmin staining and abundant SMA i n well-developed stress fibers that were indistinguishable from controls, M agnetically-generated tensile forces (similar to 500 pN/cell) applied throu gh collagen-coated magnetite beads selectively reduced SMA but not beta -ac tin mRNA and protein content in both cell types. The early loss of SMA was due in part to selective leakage into the cell culture medium. Depolymeriza tion of actin filaments with cytochalasin D blocked the force-induced reduc tion of SMA. Cardiac fibroblast lines established from H-2K(b)-tsA58 transg enic mice provide a phenotypically stable source of cells for studying the role of physical forces in regulating SMA. (C) 2001 Harcourt Publishers Ltd .