Final Exam Review Slides 7 PDF

CHAPTER 7 The Extracellular Matrix (Basement membrane)  Cells interact with extracellular material to form defined tissues.  These interactions are crucial to the formation of epithelial tissue and connective tissue, which are crucial for various cellular activities.  The best defined extracellu...

CHAPTER 7 The Extracellular Matrix (Basement membrane)  Cells interact with extracellular material to form defined tissues.  These interactions are crucial to the formation of epithelial tissue and connective tissue, which are crucial for various cellular activities.  The best defined extracellular matrices is the basement membrane or basal lamina  It is a continuous sheet 50 to 200 nm thick surrounds nerve fibers, muscles and fat cells. It underlies epithelial tissues and surrounds blood vessels.      It provides the mechanical support for the attached cells Generate signals Serve as a substratum for cell migration Separate adjacent tissues within an organ Forms a barrier to the passage of macromolecules. Image taken: Nature Review. June 2003 Fig 7.4: Scanning electron micrograph of human skin The Extracellular Matrix (Glycocalyx) Fig 7.2 a:Basal surface of an ectodermal cell of an early chick embryo Fig 7.2 c:Basal Molecular model of the glycocalyx. Sugar chains are shown in green, bound to transmembrane protein in red  The glycocalyx (cell coat) is formed from carbohydrate projections form the plasma membrane. • Mediates cell-cell and cell-substratum interactions. • Provides mechanical support • Act as a barrier to macromolecules • Help to bind the regulatory factors on the cell surface The Extracellular Matrix: Collagen  Collagens – fibrous glycoproteins found only in the ECM.  Collagen is the most abundant protein in the human body.  Provide high tensile strength.  It is produced by connective tissues, smooth muscle cells and epithelial cells.  There are 28 different types of human collagen have been characterized on its amino acid composition.  Each collagen is restricted to particular locations in the body. © 2013 John Wiley & Sons, Inc. All rights reserved. https://www.genacol.ca/wpcontent/uploads/2019/03/Collagen _Distribution_Body_EN.png Fibroblast the most common cells of connective tissue in animals and synthesize the extracellular matrix and collagen The Extracellular Matrix: Collagen  The two important structural features are common among all collagen. 1. All collagens are a trimer of polypeptide chains called α chains. 2. These three polypeptide chains wound around each other and form a rod-like triple helix. Collagen molecule: triple helix of three helical alpha chains EM of human collagen fibrils after metal shadowing Collagen I molecules become aligned in staggered rows Atomic force micrograph of a collagen fibril surface A collagen fiber 1 mm in diameter is capable of suspending a weight of 10 kg (22 lb) without breaking The Extracellular Matrix: Collagen Amino acids on the alpha chain proline (PRO), glycine (GLY) and hydroxyproline (HYP) that needs to be hydroxylated and required vitamin C for the enzyme that hydroxylate amino caids and maintain the stability of the triple helix of collagen. Fig taken: Nijhuis et al., 2019 January 2019 Journal of Children s Orthopaedics 13(1):111 Multiple collagen fibrils form into collagen fibres. Vitamin C is essential for the synthesis of stable collagen. Deficiency of vitamin C will affect collagen synthesis and leads to gums diseases, changes to hair and bleeding from the skin (scurvy) Be careful! Don’t copy everything Q) Which vitamin is essential to synthesize collagen? Why? Q) Why our body cannot make vitamin C? Q) What other role vitamin C has in our body? Antioxidant https://www.health2000.co.nz/data/media/images/blog//Free%20radicals.jpg https://resize.hswstatic.com/w_796/gif/free-radical-causes.jpg The Extracellular Matrix: Collagen Types of Collagen: Corneal stroma: layers of collagen fibrils of uniform diameter and spacing arranged at right angles There are four types of collagen Fibrillar collagen 1. Type I Fibrillar collagen 2. Type II Fibrillar collagen 3. Type III Non-fibrillar collagen 4. Type IV Type IV is restricted to the basement membrane and globular domains at the en Type IV collagen network: basement membrane from human amniotic tissue shows an irregular, polygonal lattice The Extracellular Matrix: Collagen Collagen-based diseases results in mutation of genes Type I mutation is characterized by fragile bones, thin skin and weak tendon Example: osteogenesis imperfecta osteogenesis imperfecta Type II mutation is characterized by disproportionate short stature Example: dwarfism and skeletal deformities Type III mutation is characterized by thin translucent skin, wide scars and hyperflexibility Example: Ehler-Danlos syndromes (hyperflexibility) Type IV is characterized by kidney disease, hearing loss and eye abnormalities Example: Alport syndrome- kidney disease of the glomerular basement membrane dwarfism https://creativemeddoses.com/ The Extracellular Matrix: Proteoglycans protein-polysaccharide complex is called a proteoglycan Schematic representations of a single proteoglycan, repeating disaccharide structure of GAGs, and linkage to hyaluronic acid to form a giant complex  A Proteoglycan consists of a core protein molecule to which chains of glycosaminoglycans (GAGs) are covalently attached.  Each GAG is composed of a repeating disaccharide structure (A-B-A-B).  GAGs are highly acidic due to the presence of sulfate and carboxyl groups attached to the sugar rings. The Extracellular Matrix: Proteoglycans  Negatively charged GAGs attract lots of cations, which in turn attract water forming a porous, hydrated gel that fills the extracellular space like packing material and resist crushing forces; cushion cells.  Nonsulfated GAG attachment to the core protein resulted in hyaluronic acid Electron micrograph of a proteoglycan complex isolated from cartilage matrix. The Extracellular Matrix: Fibronectin  Fibronectin (Fn) – a linear array of distinct polypeptides giving it a modular structure.  Each polypeptide is about 30 Fn modules. RGD is a tripeptide sequence in fibronectin that consists of Arginine, Glycine and Aspartate and mediates cell attachment.  The 30 or so Fn domains combine to form five or six larger functional units  Fn modules are found in other proteins too.  Fn has binding sites for other components of the ECM.  Fn guides migrating cells during embryogenesis. Fig 7.10 a: Human fibronectin molecule consists of two similar polypeptides joined by disulfide bonds. They are organized into several larger functional units, each containing one or more binding sites for a component of the ECM or for the surface of cells. Remember? RGD motif(Fibronectin) RGD is a tripeptide sequence in fibronectin that consists of Arginine, Glycine and Aspartate and mediates cell attachment. Interactions of Cells with Extracellular Materials • Integrins  Linkage between integrins and their ligands mediates adhesion between cells and their environment.  Binding of proteins to integrins is facilitated by tripeptide (amino acid sequence, argininie-glycine-aspartic acid) called RGD.  RGD is present in the cell binding sites of proteoglycans, fibronectin, laminin and various other extracellular proteins  RGD sequence opened the new doors for the treatment of medical conditions © 2013 John Wiley & Sons, Inc. All rights reserved. Interactions of Cells with Extracellular Materials Fibrinogen Fibrin Clotting  RGD required for platelet aggregation.  Fibrinogen binds to Integrin in “gluing” platelets together  Clot Buster Drugs (antithrombotic agents)  RGD peptide acts as competitive inhibitor to Fibrinogen/Integrin interaction and can inhibit blood clot formation.  Aggrastat (RGD peptide)  ReoPro (anti-RGDAb) Blood clot forms when platelets adhere to one another through fibrinogen bridges that binds to platelet integrin RGB synthetic peptide inhibits blood clot formation Fig 7.14:a, b Q) Which of the following contains RGD? a) b) c) d) e) Fibronectin Proteoglycans Laminin Other extracellular proteins All of the above All of the above The Extracellular Matrix: Laminin  Laminins – extracellular glycoproteins consisting of three polypeptide chains linked by disulfide bonds. – More than 15 types found – Help cell migration during development. – Components of basement membranes lining tissues. – Domains for interaction with other proteins (proteoglycans) 7.12: A model of the basement membrane scaffold. Basement membranes contain two network-forming molecules, collagen IV (pink), and laminin (green) that are connected by entactin molecules (purple). Dynamic Properties of the Extracellular Matrix  The ECM fibrils can be stretched during tension.  The ECM can be stretch several times their normal length.  ECM is Not static, constant remodeling by degradation and reconstruction. How ECM degrade? – ECM materials degraded by matrix metalloproteinases (MMPs). – MMPs are enzymes that are secreted into the ECM or anchored to the plasma membrane. – MMPs possibly involved in tissue remodeling, embryonic cell migration, wound healing , and formation of blood vessels. © 2013 John Wiley & Sons, Inc. All rights reserved. Dynamic Properties of the Extracellular Matrix – Disease states associated with MMPs • Arthritis, tumor progression, blood clots, and heart attacks. – MMPs regulated by TIMPs (tissue inhibitor of metalloproteinases) Life Sci.2019, 1 (234) A balance between MMP and TIMP control the removal and assembly of the ECM a painful swelling that can eventually result in bone erosion and joint deformity is caused by increase in MMPs production that can degrade all components of the ECM Integrins  The name “integrin” was suggested for an integral membrane protein complex.  It is an integral protein that integrate the extracellular and intracellular environments.  Integrins are the principal receptors used by animal cells to bind to the extracellular matrix. Integrins  A large “head” on two “legs,” with the head containing the sites for ligand binding and subunit association. Fig 7.13  Integrins – family of membrane proteins composed of heterodimers with α and β subunits, that are noncovalently linked.  Eighteen different α subunits and eight different β subunits have been identified  Have a major role in integrating extracellular and intracellular environments.  Another role is adhesion of cells to their substratum or other cells. Signaling:  The essential role of integrins in tissue organization and cell development, their signal transduction mechanisms (from outside to in and inside to out!) Interactions of Cells with Extracellular Materials Model of integrin activation Inside-out signaling: Inactive confirmation (bent state) active confirmation (upright conformation) Inside-out signaling: In the inactive stage, the two subunits of integrin are in Fig 7.13: close proximity. Talin binding to cytoplasmic tails separates  and  chains, inducing conformational change that allows Integrin to bind extracellular matrix ligands © 2013 John Wiley & Sons, Inc. All rights reserved. Interactions of Cells with Extracellular Materials Model of integrin activation outside-in signaling:  Ligand binding to external domain causes conformational in talin on the inside of the membrane. https://www.mechanobio.info/wp-content/uploads/2017/06/integrin-activation.jpg Signaling can also occur in the opposite direction, a phenomenon known as “outside-in” signaling  This triggers the activation of cytoplasmic protein kinases that control many aspects of cell behaviour such as differentiation, mobility, growth and even the cell survival.  In some cases, activation leads all the way to the nucleus and change gene Q) What is the bent state confirmation of integrin indicates? Inactive and shows that no ligand binding Q) What is the upright confirmation of integrin indicates? Active and shows that it binds to ligand Interactions of Cells with Extracellular Materials Hemidesmosomes Hemidesmosomes: Electron micrograph and schematic showing binding of intermediate filaments. Fig 7.19: Hemidesmosomes  Hemidesmosomes –are the special adhesive structure- basal attachments of epithelial cells to the basement membrane in vivo. – Contain a dense plaque with filaments consisting of keratin. – Keratin filaments are linked to the ECM by membrane-spanning integrins. © 2013 John Wiley & Sons, Inc. All rights reserved. Interactions of Cells with Extracellular Materials Hemidesmosomes • Human diseases: Bullous pemphigoid: is a rare skin condition that causes large, fluid-filled blisters, most common in older adults  Bullous pemphigoid is an autoimmune disease (antibodies produced against plaque proteins). Epidermolysis bullosa: leakage of fluid into the space beneath the epidermis results in severe blistering of the skin.  Epidermolysis bullosa a genetic alteration in any one of a number of hemidesmosomal proteins. Bullous pemphigoid https://www.medsafe.govt.jpg Epidermolysis bullosa https://www.merckmanuals.com Interaction of Cells with Other Cells Cadherins and the EMT epithelial– mesenchymal transition: epithelial cells lose their cell polarity and cell-cell adhesion and acquire invasive properties. Development of the neural tube: E-cadherin expression in epithelium. N-cadherin expression in neural tube cells. Fig 7.22a © 2013 John Wiley & Sons, Inc. All rights reserved. The Human Perspective: The Role of Cell Adhesion in Inflammation and Metastasis  Cancer is the result of abnormal cell proliferation.  The spread of a tumor to other parts of the body is called metastasis.  Changes in the numbers and types of cell-adhesion molecules lead to promote metastasis.  Metastatic cells have special cell adhesion properties:     Are less adhesive. Are able to penetrate several barriers. Are able to invade normal tissues. Changes in the numbers and types of celladhesion molecules lead to promote metastasis.  During growth and development of a tumor there is loss of E-cadherin leading to less Steps leading to metastatic spread Interaction of Cells with Other Cells 1. Adherens Junctions Anchoring Cells to Other Cells – Adherens junctions – they form “belts” near apical surface called junctional complex. 2. Desmosomes – disk-shaped adhesive junctions between cells. Anchoring Cells to Other Cells Found in a variety of tissues (areas of mechanical stress, e.g. skin, gum, cervix). 3. Tight junctions (TJs) – specialized contacts between epithelial cells. Fig 7.24 Diagram showing the junctional complex on the lateral surfaces of a simple columnar epithelial cell • TJs form the blood-brain barrier. Claudin-16: expressed in kidney tubule; abnormal claudin-16 makes tubule impermeable to Mg+2; excreted not reabsorbed Claudin-1: KO mice die from dehydration from uncontrolled water loss Intercellular junction complex 4. Gap junctions – sites between animal cells for intercellular communication