Fibroblast expression of α-smooth muscle actin, α2β1 integrin and αvβ3 integrin: Influence of surface rigidity

Abstract

Open wound contraction necessitates cells and connective tissue interactions, that produce tension. Investigating fibroblasts responses to tension utilizes collagen coated polyacrylamide gels with differences in stiffness. Human foreskin fibroblasts were plated on native type I collagen-coated polyacrylamide gels coverslips with different rigidities, which was controlled by bis-acrylamide concentrations. Changes in alpha smooth muscle actin (αSMA), α2β1 integrin (CD49B) and αvβ3 integrin (CD-51) were documented by Immuno-histology and Western blot analysis. Cells plated on rigid gels were longer, expressed αvβ3 integrin and αSMA within cytoplasmic stress fibers. In contrast, cells on flexible gels were shorter, expressed α2β1 integrin and had fine cytoskeletal microfilaments without αSMA. Increased tension changed the actin makeup of the cytoskeleton and the integrin expressed on the cell’s surface. These in vitro findings are in agreement with the tension buildup as an open wound closes by wound contraction. It supports the notion cells under minimal tension in early granulation tissue express α2β1 integrin, required for organizing fine collagen fibrils into thick collagen fibers. Thicker fibers create a rigid matrix, generating more tension. With increased tension cytoskeletal stress fibers develop that contain αSMA and αvβ3 integrin replaces α2β1 integrin, consistent with cell switching from collagen to non-collagen proteins interactions.

Palladin Mediates Stiffness-Induced Fibroblast Activation in the Tumor Microenvironment

“…We found that fibroblasts acquire a myofibroblast-like phenotype when cultured in collagen-I 3D hydrogels with a stiffness that mimics the tumor-associated stroma. Although others have shown that increased stiffness plays a role in fibroblast activation, these experiments were performed with models in which the stiffness was unknown or increased 10-fold or more greater than normal stroma (4,15,61). In this study we have shown that a fourfold increase in stiffness, which is more physiologically appropriate, is sufficient to lead to fibroblast activation.…”

Extracellular Matrix and Dermal Fibroblast Function in the Healing Wound

“…The same fibroblasts also show simultaneous decreased expression of a 2 b 1 integrin, which is recognized as the fibroblast-collagen binding integrin and is required for fibroblast migration. 50,53 Conceptually, this correlates with the idea that as an open wound contracts and builds up tension through tightening of collagen fibrils, myofibroblasts transition away from a 2 b 1 integrin-mediated organization of collagen fibers, and toward a v b 3 integrin-mediated migration along the noncollagen proteins present in acute wounds. This wound contraction and subsequent reorganization of collagen fibers can be seen histologically (Fig.…”

“…[42][43][44][45][46][47][48] Even a 15% increase in cell stretch is capable of altering a fibroblast's orientation in relation to the ECM, inducing alterations in focal adhesion kinase signaling, or up-regulating expression of alpha smooth muscle actin (aSMA), consistent with differentiation into the contractile myofibroblast. 49,50 Some clinicians have theorized that reducing the tension on wound fibroblasts by paralyzing local muscle fibers may reduce myofibroblast proliferation and collagen production, thereby decreasing scarring. Botulinum A toxin is an injectable neurotoxin that causes flaccid paralysis of muscles, and if injected around a wound would thus lessen the mechanical stretch on nearby fibroblasts.…”

Integrins in Wound Healing

“…Cells under minimal tension in early granulation tissue express a 2 b 1 integrin that regulates fine collagen fibril organization into thick collagen fibers. 140 Thicker fibers create a rigid matrix, generating more tension, which leads to cell switching to a v b 3 integrin and noncollagen ECM interactions. 140 However, fibroblast differentiation into myofibroblasts and wound contraction are not affected by a v b 3 integrin deficiency at least in the mouse skin wound healing model (Table 2), 50 suggesting that compensatory mechanisms exist in vivo.…”