MM517 Lecture 3 - The ECM PDF

MEC1052 - Advanced Biomechanics & Tissue Engineering Lecture 3 – The Extracellular Matrix Lecture Content －Overview of organ and tissue structure －The role of vasculature －The extracellular matrix (ECM) －Cell adhesion molecules －Protein fibres Main Organs and their functions －Huma...

MEC1052 - Advanced Biomechanics & Tissue Engineering Lecture 3 – The Extracellular Matrix Lecture Content －Overview of organ and tissue structure －The role of vasculature －The extracellular matrix (ECM) －Cell adhesion molecules －Protein fibres Main Organs and their functions －Human body consists of 10 organ systems －Nervous, cardiovascular, respiratory, digestive, musculoskeletal, endocrine, immune/lymphatic, urinary, reproductive and integumentary (i.e. skin, hair, nails) Main Organs and their functions －Each system is affected by the functions of all other organ systems in the body －Failure of any system disrupts haemostasis (i.e. balance) in the body and can lead to death －Organ transplantation －healthy organs from another individual e.g. heart, kidney, liver and even lungs －Limitations －shortage of donor organs, risk of rejection and requirement for life-long immunosuppressive drugs Tissue Ultrastructure －Organs are made of several tissues, the most important are: －epithelial, connective, muscle and nervous tissues －Each organ contains cells specific to its function: －Hepatocytes in the liver, cardiac myocyte in the heart, keratinocytes and fibroblasts in skin and chondrocytes in cartilage. Tissue Ultrastructure －Each organ has its own very complex 3D architecture composed of smaller functional units. －Replicating these complex structures remains a challenge in the TERM field. Importance of Vasculature －Ability to provide nutrients and remove waste presents a further challenge. －In the body, a network of tiny blood vessels (capillaries) surround almost every cell in the body. －Red blood cells containing haemoglobin travel through the blood vessels carrying oxygen and carbon dioxide. －Achieving continuous perfusion with fluids containing sufficient oxygen is challenging to recreate in vitro The Extracellular Matrix －All tissues consist of cells and the extracellular matrix (ECM) that surrounds them. －The ECM is composed of a network of fibres (collagen, elastin) and ground substance. －Ground substance has a high water content in addition to other components depending on the tissue type e.g. proteoglycans, glycosaminoglycans and glycoproteins. Protein Fibres -Collagen －Most prevalent structure in the extracellular matrix －Composed on collagen fibrils of different lengths and widths －Collagen molecule consists of a triple helix of three alpha polypeptide chains －Currently 25 type of collagen －Type I collagen is most abundant Protein Fibres －Reticular fibres －Consist of type III collagen －Found in liver, bone marrow and lymphatic system －Elastin fibres －Ability to stretch and return to shape once loading removed －Main component of vertebral ligaments, epiglottis, elastic arteries The Extracellular Matrix －ECM functions: －Physical barrier －an anchorage site －a movement track for cell migration －provides mechanical strength to tissue －and enables cell communication.  ECM remodelling and modulation －ECM is constantly undergoing remodelling. －Intermolecular cross-linking by the enzyme lysyl oxidases (LOX) is a key modification for collagens and elastin, leading to increased tissue tensile strength and matrix stiffness, thereby affecting cellular behaviours. －Cellular responses to changing mechanical stimuli is called mechanobiology. －ECM is also modulated by exogenous stimuli such as cytokines, glucocorticoids, oxidative stress, pressure and mechanical stretch. Yue B. Biology of the extracellular matrix: an overview. J Glaucoma. 2014 Oct-Nov;23(8 Suppl 1):S20-3. ECM as a reservoir for bioactive molecules －ECM can store and sequester growth factors and cytokines, establishing concentration gradients and regulating spatially and temporally their bioavailability. －In particular, the fibroblast growth factor (FGF) family strongly binds to heparan sulfate chains of proteoglycans, involved in binding, transporting, and activating developmental control factors including Wnt factors and hedgehog.  ECM provides chemical and physical cues －The biochemical properties of the ECM allow cells to sense and interact with their extracellular environment using various signal transduction pathways. －The chemical cues are provided by ECM components, especially the adhesive proteins such as fibronectin, integrin and non-integrin receptors, as well as growth factors and associated signaling molecules. －The physical properties of the ECM, including its rigidity, density, porosity, insolubility and topography (spatial arrangement and orientation), provide physical cues to the cells. Yue B. Biology of the extracellular matrix: an overview. J Glaucoma. 2014 Oct-Nov;23(8 Suppl 1):S20-3. Protein attachment －The ECM anchors cells and other components such as growth factors through adhesion molecules －Ability of cells to adhere is critical for differentiation, growth, migration and survival －Specialized cell junctions occur at points of cell- cell and cell-matrix contact in all tissues －Tight/occluding junctions －Desmosome/anchoring junctions －Gap/communicating junctions Tight/occluding Desmosome/anchoring Gap/communicating junctions junctions junctions Cell Junctions －Tight/occluding junctions －seal cells together in a way that prevents even small molecules from leaking from one side of the sheet to the other. Cell Junctions －Desmosome/anchoring junctions －mechanically attach cells (and their cytoskeletons) to their neighbors or to the extracellular matrix －provide mechanical stability Cell Junctions －Gap/communicating junctions －mediate the passage of chemical or electrical signals from one interacting cell to its partner. －allow small molecules to diffuse in and out of cells and between connected cells – critical in regulation of homeostasis Cell adhesion molecules －Cell surface proteins that mediate the interaction between cells, or between cells and the ECM. －Four main families: －Cadherins - Bind to the actin filaments through catenins. Failure of cadherin-cadherin interaction can be involved in cancer development due to disruption of the pathway called contact- inhibition, which limits growth of cells connected to their neighbours －Immunoglobulin super-family - Role in inflammation and immune response －Selectins - Mostly found in white blood cells, endothelial cells and platelets －Integrins - Facilitate cell-extracellular matrix adhesion. Attach to components of ECM e.g. collagen Attachment Glycoproteins －Glycoproteins are surface proteins that help identify cells and facilitate cell communication, transportation and interaction with extracellular molecules and other cells. －Fibronectin －Several domains, one binds to ECM molecules, another to cell surface receptors. Play a role in blood clot formation and wound healing －Laminin －Integral part of structural scaffolding in almost every tissue of an organism. Bind to cell membrane through integrin receptors and other plasma membrane molecules －Tenascin －Mostly present during embryogenesis, reactivates during regenerative processes such as wound healing －Osteopontin －Mainly present in bones, plays an important role in calcification of ECM Adhesion molecules in Tissue Engineering －Adhesion molecules can be used to coat surfaces to improve cell attachment －Type I collagen isolated from rat tail －Gelatin – produced by hydrolysis of collagen to breakup of protein fibrils into a mixture of smaller peptides －Other protein adhesion molecules include laminin and fibronectin －Negatively charged synthetic peptides, such as polylysine, also serve as efficient coating agents Key lessons learned －Understand the complexity of each organ and main differences between them. －Name the key components of the extracellular matrix －Describe the function of the ECM －Distinguish between occluding, anchoring and communicating junctions －Identify the main classes of cell adhesion molecules