Impaired Contracture of 3D Collagen Constructs by Fibronectin-Deficient Murine Fibroblasts

Area of Science:

• Extracellular Matrix Biology
• Cellular Mechanotransduction
• Integrin Signaling

Background:

• Fibronectin (FN) is an extracellular matrix glycoprotein crucial for fibroblast functions in wound healing, including cell adhesion, migration, and proliferation.
• FN's ability to bind collagen suggests a role in collagen matrix contracture, potentially mediated by its receptor, integrin α5β1.
• Conflicting reports exist regarding the roles of FN-integrin α5β1 interactions versus collagen-binding integrins (α2β1, α11β1) in collagen contracture.

Purpose of the Study:

• To elucidate the relative contributions of fibronectin-integrin α5β1 interactions and collagen receptors (α2β1, α11β1) in collagen matrix contracture.
• To assess the direct role of cellular fibronectin in mediating collagen gel contracture by mouse fibroblasts.

Main Methods:

• Utilized fibronectin-deficient (FN-null) mouse fibroblasts and wild-type counterparts in *in vitro* collagen gel contracture assays.
• Employed FN-null fibroblast lines with distinct collagen-binding integrin profiles (α11β1 only vs. α2β1 only) to dissect receptor roles.
• Investigated the effects of exogenous FN addition and blocking antibodies/peptides (anti-integrin α5β1, RGD peptide) on contractility.

Main Results:

• FN-null fibroblasts expressing only α11β1 showed minimal spreading and required exogenous FN for integrin α5β1 assembly and matrix contraction.
• FN-suppressed fibroblasts expressing α2β1 could partially contract collagen gels without exogenous FN, but FN addition significantly enhanced contractility.
• Blocking integrin α5β1 or using RGD peptide abolished FN-stimulated collagen contracture in FN-deficient fibroblasts.

Conclusions:

• Collagen-binding integrins, particularly α2β1, can mediate some degree of fibrillar collagen gel contracture by murine fibroblasts.
• Full collagen matrix contracture activity is critically dependent on the presence of pericellular fibronectin and its interaction with integrin α5β1.
• Integrin α5β1 acts as a crucial linker, essential for fibronectin-mediated collagen matrix remodeling.