The extracellular matrix (ECM) is a complex network of proteins and molecules surrounding cells. It provides structural support, regulates cell behavior, and plays a crucial role in tissue function. Understanding ECM components and structure is essential for grasping how cells interact with their environment.

ECM functions go beyond mere scaffolding. It influences cell behavior, mediates signaling, and contributes to tissue-specific properties. From basement membranes to interstitial matrices, the ECM's diverse organization and interactions shape cellular responses and tissue function in health and disease.

Extracellular Matrix Components and Structure

Components of extracellular matrix

• Collagen forms fibrous structures providing tensile strength to tissues most abundant protein in ECM (Types I, II, III, IV, V, and XI)
• Elastin confers elasticity and resilience to tissues forms elastic fibers with fibrillin (blood vessels, skin)
• Proteoglycans consist of core protein with attached glycosaminoglycan (GAG) chains retain water and provide compressive strength (aggrecan, versican, perlecan)
• Glycoproteins facilitate cell-matrix interactions and tissue organization fibronectin promotes cell adhesion and migration laminin organizes basement membrane tenascin supports tissue remodeling and wound healing

Organization of extracellular matrix

• Interstitial matrix surrounds cells in connective tissues composed of fibrous proteins and ground substance (tendons, ligaments)
• Pericellular matrix immediately adjacent to cell surface facilitates cell-matrix interactions (chondrocytes in cartilage)
• Tissue-specific ECM organization:
  • Bone contains mineralized collagen fibrils for strength and rigidity
  • Cartilage features highly hydrated proteoglycan-rich matrix for shock absorption
  • Skin exhibits layered structure with distinct ECM composition for barrier function
• Fiber arrangement:
  • Parallel alignment in tendons and ligaments for directional strength
  • Basket-weave pattern in skin for multidirectional flexibility
  • Random orientation in loose connective tissue for adaptability

Extracellular Matrix Function and Interactions

Role of basement membrane

• Structure thin, sheet-like specialized ECM composed primarily of type IV collagen and laminin
• Functions:
  1. Separates epithelial/endothelial cells from underlying connective tissue
  2. Provides structural support and anchorage
  3. Regulates cell polarity and differentiation
• Cell-basement membrane interactions mediated by integrins transmembrane receptors linking cells to ECM dystroglycan complex connects cytoskeleton to basement membrane
• Tissue-specific roles:
  • Filtration in kidney glomeruli selectively allows passage of molecules
  • Blood-brain barrier formation restricts passage of substances into brain tissue
  • Neuromuscular junction organization facilitates synaptic transmission

Matrix influence on cell behavior

• Mechanical properties matrix stiffness influences cell differentiation and behavior elasticity affects tissue resilience and function (soft brain tissue vs. rigid bone)
• Biochemical signaling growth factors sequestered and released by ECM matricellular proteins modulate cell-matrix interactions (thrombospondins, CCN proteins)
• Cell adhesion and migration ECM proteins provide attachment sites for cells proteases remodel ECM to facilitate cell movement (wound healing, cancer metastasis)
• Tissue homeostasis and regeneration dynamic remodeling of ECM in response to stimuli ECM composition changes during development and aging
• Pathological alterations fibrosis results from excessive ECM deposition altered ECM promotes tumor progression in cancer
• Tissue engineering applications designing scaffolds with specific ECM compositions modulating cell behavior through engineered matrices (3D printed scaffolds, hydrogels)