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Extracellular Matrix lecture

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I give this lecture in the Cell Biology and Genetics course for first-year veterinary students. The core material comes from Alberts' Molecular Biology of the Cell, Fifth Edition. I have added multiple clinical examples, both human and veterinary.

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Extracellular Matrix lecture

  1. 1. Extracellular Matrix Antonia Jameson Jordan, D.V.M., Ph.D. November 21, 2008 Outline: •  Overview of structural and signaling roles of ECM •  Two main classes of ECM molecules –  Glycosaminoglycan polysaccharide chains •  Structure and function –  Fibrous proteins •  Structure and function •  Basal lamina (basement membrane) •  Integrins 1
  2. 2. ECM has structural and signaling roles: Organized in two main ways: connective tissue basal lamina (basement membranes) Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 14 October 2008 08:50 PM) © 2007 Elsevier ECM consists of two main classes of molecules: •  Glycosaminoglycan polysaccharide chains –  Form hydrated gels •  Fibrous proteins –  Organize and strengthen Figure 19-41 Molecular Biology of the Cell (© Garland Science 2008) 2
  3. 3. Glycosaminoglycans (GAGs) are unbranched polysaccharide chains: •  Composed of repeating disaccharide units •  Too stiff to fold into compact globular shape •  Highly negatively charged due to sulfate or carboxyl groups on the sugars •  Highly hydrophilic –  High density of negative charge attracts osmotically active cations Figure 19-55 Molecular Biology of the Cell (© Garland Science 2008) GAG chains occupy large amounts of space and form hydrated gels: •  Turgor –  Withstand compressive forces •  Allow rapid diffusion of nutrients, metabolites, hormones between blood and tissues Figure 19-56 Molecular Biology of the Cell (© Garland Science 2008) 3
  4. 4. Hyaluronan is a major polysaccharide component of the ECM: •  Present in all tissues and body fluids •  Simplest GAG –  Regular repeating sequence of up to 25,000 disaccharide units –  No sulfated sugars –  Not linked to a core protein Figure 19-57 Molecular Biology of the Cell (© Garland Science 2008) Functions of hyaluronan: •  Resists compressive forces in joints and tissues –  Important constituent of joint fluid •  In osteoarthritis, decreased concentration and decreased molecular weight of intra-articular HA 4
  5. 5. Role of HA in morphogenesis: •  Acts as space filler and facilitator of cell migration –  If synthesized on the basal side of an epithelium, creates a cell-free space into which other cells can migrate The role of HA in atrioventricular canal morphogenesis: Itano, N. J Biochem 2008 144:131-137; doi:10.1093/jb/mvn046 Copyright restrictions may apply. 5
  6. 6. FDA approved HA for cosmetic use in humans – 2003: Proteoglycans are composed of GAG chains covalently linked to a core protein: •  Classified by sugar composition –  Keratan sulfate, chondroitin sulfate, dermatan sulfate, heparan sulfate •  Modification of sugar residues allows for enormous diversity •  Associate with each other and with other ECM components to make complex meshworks Figure 19-58 Molecular Biology of the Cell (© Garland Science 2008) 6
  7. 7. Examples of proteoglycans found in ECM: •  Decorin “decorates” collagen fibrils –  Decorin knock-out mouse has irregular collagen fibril formation •  skin – lax and fragile •  tendons have abnormal structure •  Aggrecan has serine-rich core protein and chondroitin sulfate and keratan sulfate chains Figure 19-59 Molecular Biology of the Cell (© Garland Science 2008) Aggrecan is the major glycoprotein of articular cartilage: •  Provides hydrated gel structure that endows cartilage with load-bearing properties •  Chondroskeletal morphogenesis during development Figure 19-60a Molecular Biology of the Cell (© Garland Science 2008) 7
  8. 8. Skin turgor test to assess hydration status: Blowey & Weaver, Diseases and Disorders of Cattle (Mosby, 1997) Signaling roles of proteoglycans: •  Proteoglycans can regulate the activities of secreted proteins –  Gels formed by GAG chains act as “sieves” that regulate passage of molecules by size and charge –  Bind secreted signaling molecules •  Control diffusion, range of action, lifetime, modify signaling activity –  e.g.,heparan sulfate immobilizes chemokines on the endothelial surface of a blood vessel at a site of inflammation •  Cell-surface proteoglycans act as co-receptors 8
  9. 9. Table 19-6 Molecular Biology of the Cell (© Garland Science 2008) Collagens are the major proteins of animal connective tissues: Figure 19-63 Molecular Biology of the Cell (© Garland Science 2008) 9
  10. 10. Collagen chains undergo a series of post-translational modifications: •  Hydroxylation of selected prolines and lysines •  Self-assembly of three pro-α chains Figures 19-64 and 19-65 Molecular Biology of the Cell (© Garland Science 2008) Vitamin C is necessary for proline hydroxlation: •  Defective pro-α chains fail to form triple helix •  Failure of collagen synthesis •  Guinea pigs need vitamin C! Figure 9-30 Pathologic Basis of Disease (© Elsevier 1995) 10
  11. 11. Intracellular and extracellular events of collagen fibril formation: Figure 19-66 Molecular Biology of the Cell (© Garland Science 2008) Different classes of collagen are organized in different ways: •  Secreted fibril-associated collagens help organize the fibrils •  Fibrillar (fibril-forming) –  Types I, II, III, V –  Long, rope-like structures –  principal collagen of bone and skin •  Fibril-associated –  Type IX, Type XII –  link fibrils to one another and to other components of ECM •  Network-forming –  Type IV –  major component of basal lamina •  Anchoring –  Type VI •  Resistance to tensile forces 11
  12. 12. Collagen type IV forms a fine meshwork: •  More flexible structure than fibrillar collagens •  Interruptions of triple- helical structure •  Not cleaved after secretion •  Interact via uncleaved terminal domains to assemble into a flexible network Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 17 November 2008 03:08 PM) Type 1 collagen diseases (Osteogenesis imperfecta): Downloaded from: Resident & Staff Physician (on 10 November 2008 05:31 PM) Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 10 November 2008 05:31 PM) 12
  13. 13. Type 1 collagen diseases (Osteogenesis imperfecta): Clinical signs and diagnosis of osteogenesis imperfecta in three dogs (Ron Minor et al,1997) Seeliger et al: Osteogenesis imperfecta in two litters of Dachsunds. Vet Pathol 40: 530-539, 2003 Ehlers-Danlos syndrome: •  Defect in synthesis or structure of fibrillar collagen (mutations have been found in collagen types I, III, V) –  Skin hyperextensibility, joint laxity, fragile skin and vessels, poor wound healing 13
  14. 14. Collagen VII defects cause blistering skin diseases: Table 19-7 Molecular Biology of the Cell (© Garland Science 2008) 14
  15. 15. Importance of collagen in wound healing: Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 14 October 2008 08:53 PM) © 2007 Elsevier Elastin gives tissues their elasticity: Figures 19-70 and 19-71 Molecular Biology of the Cell (© Garland Science 2008) 15
  16. 16. Fibronectin is an extracellular protein that helps cells attach to the matrix: Figure 19-72 Molecular Biology of the Cell (© Garland Science 2008) Basal laminae underly all epithelia and surround some nonepithelial cell types: •  Critical role in determining the architecture of the body •  Thin: 4-120 nanometers thick •  Synthesized by cells on each side of it Figures 19-39 and 19-40 Molecular Biology of the Cell (© Garland Science 2008) 16
  17. 17. Molecular structure of the basal lamina: •  Glycosaminoglycans –  perlecan •  Fibrous proteins –  Laminin, type IV collagen, nidogen Figure 19-43 Molecular Biology of the Cell (© Garland Science 2008) Laminin is a primary component of the basal lamina: •  Primary organizer of the sheet structure •  Composed of 3 chains held together by disulfide bonds •  Self-assembles through interactions of the head groups Figure 19-42a Molecular Biology of the Cell (© Garland Science 2008) 17
  18. 18. Basal laminae have diverse functions: •  Structural –  Critical role in the architecture of an organ –  Mechanical connection between epithelia and underlying connective tissue •  Scaffold for tissue regeneration Basal laminae have diverse functions: •  Selective filtration –  Glomerulus •  Selective barrier to cell movement •  Spatial organization of the components of the neuromuscular junction Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 17 November 2008 03:08 PM) 18
  19. 19. Interactions between cells and the ECM: •  Cells synthesize, organize, and degrade ECM •  Matrix influences cellular behavior –  Tissue architecture •  Cells interact with ECM via matrix receptors –  Integrins –  Transmembrane proteoglycans Integrins are transmembrane heterodimers that link to the cytoskeleton: Figure 19-45 Molecular Biology of the Cell (© Garland Science 2008) 19
  20. 20. Change in conformation of an integrin molecule when it binds a ligand: Figure 19-48 Molecular Biology of the Cell (© Garland Science 2008) Attachment to the ECM via integrins affects cell proliferation and survival: •  Anchorage dependence for cellular survival and growth –  Way to ensure that cell survives and proliferates only in the appropriate environment •  Cell spreading on matrix promotes survival and growth 20
  21. 21. Activation of integrins by cross-talk from other signaling pathways: Figure 19-49 Molecular Biology of the Cell (© Garland Science 2008) Integrin defects are responsible for many different genetic diseases: Table 19-4 Molecular Biology of the Cell (© Garland Science 2008) 21
  22. 22. Integrins involved in pathogenesis of other diseases: •  Cancer –  Tumor progression •  Role in infectious diseases –  Can provide a means for viral entry •  Foot and mouth disease •  Autoimmune diseases –  Recruitment of leukocytes •  Multiple sclerosis, Crohn’s disease Interaction of cells with ECM via integrins leads to a variety of critical behaviors: Downloaded from: Robbins & Cotran Pathologic Basis of Disease (on 14 October 2008 08:53 PM) © 2007 Elsevier 22
  23. 23. Conclusion: 23
  24. 24. Integrins recruit intracellular signaling proteins at sites of cell-substratum adhesion: •  Focal adhesion kinase (FAK) –  Cytoplasmic tyrosine kinase 24
  25. 25. Figure 19-47 Molecular Biology of the Cell (© Garland Science 2008) 25
  26. 26. Figure 19-48a Molecular Biology of the Cell (© Garland Science 2008) 26
  27. 27. Figure 19-46 Molecular Biology of the Cell (© Garland Science 2008) 27
  28. 28. Hyaluronan acts as a space filler and facilitator of cell migration: •  Simplest GAG –  Regular repeating sequence of up to 25,000 disaccharide units –  No sulfated sugars –  Not linked to a core protein •  Present in all tissues and body fluids •  Resists compressive forces in joints and tissues –  Important constituent of joint fluid •  Roles in morphogenesis –  If synthesized on the basal side of an epithelium, creates a cell-free space into which other cells can migrate Figure 19-57 Molecular Biology of the Cell (© Garland Science 2008) 28

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