🦠Regenerative Medicine Engineering Unit 4 – ECM and Cell-Matrix Interactions in Regen Med

Key Concepts and Definitions

• Extracellular matrix (ECM) complex network of proteins, glycoproteins, and proteoglycans that provides structural and biochemical support to cells
• Integrins transmembrane receptors that mediate cell-ECM interactions and play a crucial role in cell adhesion, migration, and signaling
• Mechanotransduction process by which cells convert mechanical stimuli from the ECM into biochemical signals that regulate cell behavior and function
• Matrix metalloproteinases (MMPs) enzymes that degrade ECM components and play a key role in ECM remodeling during tissue repair and regeneration
• Tissue engineering interdisciplinary field that combines principles of biology, engineering, and materials science to develop functional tissue substitutes
• Biomaterials synthetic or natural materials designed to interact with biological systems for therapeutic purposes, such as scaffolds for tissue regeneration
• Cell signaling complex network of communication pathways that allow cells to respond to external stimuli and coordinate their behavior within tissues

ECM Composition and Structure

• ECM composed of a diverse array of macromolecules, including collagen, elastin, fibronectin, laminin, and proteoglycans
  • Collagen most abundant protein in the ECM, provides tensile strength and structural support to tissues
  • Elastin highly elastic protein that allows tissues to stretch and recoil, particularly important in blood vessels and skin
• ECM organization varies depending on tissue type and function
  • Basement membrane specialized ECM that separates epithelial and endothelial cells from underlying connective tissue
  • Interstitial matrix ECM surrounding cells in connective tissues, such as bone, cartilage, and tendons
• ECM structure and composition dynamically regulated by cells through synthesis, degradation, and remodeling of ECM components
• Mechanical properties of ECM (stiffness, elasticity) influence cell behavior, such as differentiation, migration, and proliferation
• ECM acts as a reservoir for growth factors and cytokines, which can be released upon ECM degradation or remodeling

Cell-ECM Interactions

• Cells interact with the ECM through cell surface receptors, primarily integrins
• Integrins bind to specific ECM ligands (fibronectin, collagen) and link the ECM to the cell's cytoskeleton
  • Integrin-ECM interactions trigger intracellular signaling cascades that regulate cell adhesion, migration, proliferation, and differentiation
• Focal adhesions specialized protein complexes that form at sites of integrin-ECM engagement, serving as signaling hubs and mechanical linkages
• Cell-ECM interactions guide cell migration during development, wound healing, and tissue regeneration
  • Cells can sense and respond to ECM stiffness and topography through mechanotransduction pathways
• ECM provides essential survival signals to cells, and disruption of cell-ECM interactions can lead to apoptosis (anoikis)

ECM in Tissue Regeneration

• ECM plays a critical role in tissue regeneration by providing structural support, signaling cues, and a microenvironment conducive to cell growth and differentiation
• During tissue injury, ECM undergoes remodeling to facilitate cell infiltration, proliferation, and differentiation
  • Inflammatory cells (macrophages) secrete cytokines and growth factors that stimulate ECM production and remodeling
  • Fibroblasts synthesize new ECM components (collagen, fibronectin) to replace damaged tissue
• ECM composition and organization influence stem cell fate and differentiation during tissue regeneration
  • Stem cells can sense and respond to ECM stiffness, topography, and biochemical cues to guide their differentiation into specific cell types
• Decellularized ECM scaffolds (derived from native tissues) can be used to promote tissue regeneration by providing a natural microenvironment for cell growth and differentiation
• Tissue-specific ECM (bone, cartilage) contains unique composition and properties that guide the regeneration of those tissues

Biomaterials and ECM Mimetics

• Biomaterials designed to mimic the structure and function of native ECM to support tissue regeneration
  • Scaffolds provide a 3D structure for cell attachment, growth, and differentiation
  • Hydrogels (collagen, alginate) can be used to encapsulate cells and provide a hydrated environment similar to native ECM
• Biomaterials can be functionalized with ECM-derived proteins (collagen, fibronectin) or peptides (RGD) to enhance cell adhesion and signaling
• Biomaterial properties (stiffness, porosity, degradation rate) can be tuned to match the requirements of specific tissues and guide cell behavior
• Incorporation of growth factors (BMP, VEGF) or small molecules into biomaterials can further stimulate tissue regeneration
• Decellularized ECM-derived biomaterials (porcine small intestinal submucosa) have been used clinically for wound healing and soft tissue repair

Cell Signaling and Mechanotransduction

• Cell signaling pathways (MAPK, PI3K/Akt) are activated by integrin-ECM interactions and regulate cell behavior
  • Focal adhesion kinase (FAK) key signaling protein that is activated upon integrin clustering and mediates downstream signaling events
• Mechanotransduction allows cells to convert mechanical stimuli from the ECM into biochemical signals
  • Integrins and focal adhesions act as mechanosensors, detecting changes in ECM stiffness and tension
  • Mechanical forces can induce conformational changes in proteins (talin, vinculin) that expose cryptic binding sites and activate signaling pathways
• Mechanotransduction regulates gene expression and cell fate through transcription factors (YAP/TAZ) that shuttle between the cytoplasm and nucleus in response to mechanical cues
• Mechanical loading (stretch, compression) can influence ECM synthesis and remodeling by cells
  • Mechanical stimulation of osteoblasts promotes bone matrix production and mineralization
  • Cyclic stretching of vascular smooth muscle cells induces ECM protein synthesis and alignment

ECM Remodeling in Disease

• Dysregulation of ECM remodeling contributes to various pathological conditions, such as fibrosis, cancer, and cardiovascular diseases
• Fibrosis excessive accumulation of ECM (collagen) leading to tissue stiffening and loss of function
  • Myofibroblasts key cell type involved in fibrosis, characterized by increased ECM synthesis and contractility
  • Transforming growth factor-beta (TGF-β) major pro-fibrotic cytokine that stimulates ECM production and myofibroblast differentiation
• Cancer cells can modify the ECM to create a permissive microenvironment for tumor growth and metastasis
  • Increased ECM stiffness promotes cancer cell invasion and metastasis
  • Cancer-associated fibroblasts (CAFs) secrete ECM proteins and proteases that remodel the tumor microenvironment
• Cardiovascular diseases (atherosclerosis, hypertension) involve ECM remodeling in blood vessels
  • Vascular calcification pathological process characterized by the deposition of calcium phosphate minerals in the ECM of blood vessels

Applications in Regenerative Medicine

• ECM-based therapies aim to harness the regenerative potential of the ECM for tissue repair and regeneration
• Decellularized ECM scaffolds used for various applications, such as cardiac patch for myocardial infarction, nerve guidance conduits for peripheral nerve repair, and dermal substitutes for wound healing
  • Decellularization process removes cells while preserving ECM composition and structure
  • Recellularization of decellularized ECM scaffolds with patient-specific cells can create personalized tissue constructs
• Injectable ECM hydrogels can be used for minimally invasive delivery of cells and bioactive factors to promote in situ tissue regeneration
  • Hydrogels can be designed to undergo gelation in response to physiological stimuli (temperature, pH) for targeted delivery
• ECM-mimetic biomaterials can be engineered to provide specific signaling cues and mechanical properties to guide tissue regeneration
  • Incorporation of ECM-derived peptides (GFOGER, IKVAV) can promote cell adhesion, migration, and differentiation
  • Biomaterials with gradient properties (stiffness, porosity) can mimic the native tissue interface and guide cell behavior
• ECM-based bioinks can be used for 3D bioprinting of complex tissue structures with precise control over cell and ECM distribution