Mechanical signals regulating extracellular matrix gene expression in fibroblasts

Abstract

Mechanical forces are essential for connective tissue homeostasis. The extracellular matrix (ECM) plays a key role in the transmission of forces generated by the organism (e.g. muscle contraction) and externally applied (e.g. gravity). The expression of specific ECM proteins such as collagens and tenascin-C, as well as of matrix metalloproteinases, involved in their turnover, is influenced by mechanical stimuli. The precise mechanisms by which mechanical strains are translated into chemical signals and lead to differential gene expression are however not fully understood. Cell-matrix adhesion sites are good candidates for hosting a "mechanosensory switch", as they transmit forces from the ECM to the cytoskeleton and vice versa by physically linking the cytoskeleton to the ECM. Integrins, transmembrane proteins located to these adhesion sites, have been shown to trigger a set of internal signaling cascades after mechanical stimulation. We have shown that the expression level of tenascin-C directly correlates with externally applied mechanical stress, as well as with RhoA/RhoA-dependent kinase-mediated cytoskeletal tension. Presumably other genes are regulated in a similar manner. The changes in ECM composition and mechanical properties derived from mechanical stress are relevant in medical intervention after ligament and tendon injury.

Mechanoregulation of gene expression in fibroblasts

“…Mechanical stress stimulates the release of TGF-β (Lindahl et al, 2002;Nakatani et al, 2002;Yang et al, 2004) as described in the previous section, as well as enhances its gene transcription through activation of EGR-1 . These indirect mechanotransduction mechanisms have been explained in detail previously (Chiquet, 1999;Sarasa-Renedo and Chiquet, 2005).…”

“…When cyclic equibiaxial tensile stretch was applied (15%, 0.3 Hz) to these fibroblasts, tenascin-C mRNA was induced 2-to 4-fold compared to non-stretched cells within 3-6 h (Chiquet et al, 2003). When cells were pretreated with cytochalasin-B, an actin depolymerizing drug, and latrunculin A, an actin cytoskeleton disrupting drug, the stretching-induced tenascin-C mRNA expression was abolished, indicating that an intact cytoskeleton is required for stretching-induced tenascin-C mRNA expression (Chiquet et al, 2003;Sarasa-Renedo and Chiquet, 2005). Collagen XII has an expression pattern similar to that of tenascin-C and has been shown to co-assemble with collagen I during fibril formation (Koch et al, 1995).…”

“…Mechanoregulation of gene expression has been widely studied in chicken skin fibroblasts, and various mechanisms have been proposed for the mechanoregulation of ECM genes (Chiquet-Ehrismann et al, 1994;Chiquet et al, 1996Chiquet et al, , 2003Chiquet et al, , 2004Sarasa-Renedo and Chiquet, 2005;Sarasa-Renedo et al, in press). The genes of focus in these studies are tenascin-C and collagen fibril-associated type XII collagen.…”

“…The maturation of focal complexes requires externally applied mechanical force or internal actin cytoskeletal contractile force (Balaban et al, 2001;Hinz and Gabbiani, 2003). For instance, cyclic equibiaxial stretching of fibroblasts induce the formation of large matrix adhesions containing vinculin along their margins (Sarasa-Renedo and Chiquet, 2005). Moreover, after stretching, the actin stress fibers assume a crescent morphology and are aligned parallel to the long axis of the cell body; while in cells at rest, the stress fibers are straight and randomly oriented.…”

Articular Cartilage Increases Transition Zone Regeneration in Bone-tendon Junction Healing

“…Mechanical loading plays an important role in the development, function, and repair of all tissues in the musculoskeletal system, including bone, tendon, ligament, and muscle. Connective tissue cells change their extracellular matrix according to the mechanical stress received [6,28]. The exact mechanism and signaling pathways by which these adaptive changes occur are unknown.…”