Fibronectin is a high-molecular-weight glycoprotein found in the extracellular matrix (ECM) and plasma. It plays a key role in cell adhesion, migration, growth, wound healing, and tissue repair by connecting cells to the surrounding matrix and helping organize the ECM.
Definition:
Fibronectin is a multifunctional adhesive glycoprotein that binds to integrins on the cell surface and to other ECM components like collagen, fibrin, and heparan sulfate proteoglycans.
Key Characteristics:
- Exists as a dimer, with two similar subunits linked by disulfide bonds.
- Contains multiple binding domains for:
- Integrins (via the RGD motif – arginine-glycine-aspartic acid)
- Collagen
- Heparin
- Fibrin
- Present in two major forms:
- Plasma fibronectin – Soluble; circulates in the blood.
- Cellular (or matrix) fibronectin – Insoluble; part of the ECM.
Functions of Fibronectin:
- Cell adhesion: Acts as a bridge between cells and the ECM by binding to integrins.
- Cell migration: Crucial during embryonic development, wound healing, and cancer metastasis.
- Tissue repair: Helps form a temporary matrix for cells during wound healing.
- Blood clotting: Binds fibrin in blood clots to stabilize the clot structure.
- ECM organization: Helps align and arrange other ECM proteins like collagen.
Where It’s Found:
- Extracellular matrix of connective tissues
- Blood plasma
- Wounds and healing tissue
- Basement membranes
- Embryonic tissues (especially during development)
How It Works:
- Fibronectin is secreted by cells (e.g., fibroblasts).
- It binds to integrins on the cell surface and simultaneously to ECM components.
- This dual binding supports:
- Anchorage of cells to the matrix.
- Signaling into the cell to regulate shape, movement, and survival.
- Fibronectin fibrils can assemble into networks that guide cell behavior.
Role in Health and Disease:
- Wound Healing: Fibronectin provides a scaffold for migrating cells like fibroblasts and keratinocytes.
- Cancer: Abnormal fibronectin expression can promote tumor growth and metastasis.
- Fibrosis: Excess fibronectin contributes to excessive tissue scarring.
- Development: Essential for embryonic development (e.g., blood vessel and heart formation).
Summary Table:
| Feature | Description |
|---|---|
| Structure | Dimeric glycoprotein |
| Major Forms | Plasma fibronectin (soluble), cellular fibronectin (insoluble) |
| Binds To | Integrins, collagen, fibrin, heparan sulfate |
| Functions | Cell adhesion, migration, ECM assembly, wound healing |
| Found In | ECM, plasma, wound sites, developing tissues |