HSS2305 Molecular Mechanisms of Disease Lecture 7 PDF

HSS2305: Molecular Mechanisms of Disease Lecture 7 – Interactions Between Cells and Environment Today’s Outline Announcements Interactions Between Cells and Environment Interactions Between Cells and Environment Extracellular Interactions In multicellular organisms, most cells are organ...

HSS2305: Molecular Mechanisms of Disease Lecture 7 – Interactions Between Cells and Environment Today’s Outline Announcements Interactions Between Cells and Environment Interactions Between Cells and Environment Extracellular Interactions In multicellular organisms, most cells are organized into tissues Cells must maintain a defined relationship: With one another With the extracellular materials that lie between the cells Interactions regulate/determine: Cell migration Cell growth Cell differentiation 3-D organization of tissues and organs that emerge during embryo development. Tissue Organization Epithelium refers to a thin layer of tightly packed cells that cover surfaces and line cavities throughout the body. The most well- known examples of epithelium is the epidermis, the outer layer of the skin Endothelium is a specialized type of epithelium found inside blood vessels and lymphatic vessels. It is a single layer of cells that helps control blood flow, regulates blood pressure, and facilitates the exchange of nutrients and waste between the blood and tissues. Epithelium https://rsscience.com/epithelium/ Endothelium https://www.researchgate.net/figure/Overview-of-the-various-endothelial-cells-examined-for-heterogeneity-including-a_fig1_339132939  Tissue Organization- Epithelium Skin – largest organ of the body It serves multiple critical functions, including protection, regulation of body temperature, and sensation Skin Outside 2 main layers: Epidermis: Closely packed epithelial cells Dermis: Dense, irregular connective tissue (extracellular matrix – ECM) Fibroblasts Blood vessels, Hair follicles, Sweat glands, Etc. Separated by: Inside Basement/basal membrane Non-cellular layer Extracellular Matrix (ECM) Contains Basal lamina  Tissue Organization-endothelium Blood vessels are composed of three primary layers, with the endothelium (a layer of endothelial cells) forming the innermost layer. Here's a breakdown: 1.Tunica Intima: 1. The endothelium is a single layer of endothelial cells lining the inner surface of the blood vessel. controls vascular tone, blood flow, and prevents clotting. helps with nutrient and waste exchange between blood and tissues. 2.Tunica Media: 1. This middle layer is made up of smooth muscle cells and elastic fibers. It allows the blood vessel to expand or contract, controlling blood pressure and flow. 3.Tunica Adventitia (or Externa): 1. The outer layer consists of connective tissue, https://www.researchgate.net/figure/Schematic-representation-of-the- providing structural support and protection to three-layers-of-the-blood-vessel-wall-in-an-artery-and-a_fig2_6597677 the vessel. It often contains nerves and small blood vessels (vasa vasorum) that supply the vessel itself. What keeps cells together? Cell-Cell/Cell-ECM Interactions Both endothelial and epithelial cells are involved in cell-cell interactions and cell-extracellular matrix (ECM) interactions  What keeps cells together? Cell-Cell/Cell-ECM Interactions Overview Apical Surface Tight Junctions Seal gap between cells Adherens junctions Connects Actin (a specific protein) filaments between cells Desmosome Connects Intermediate filaments between cells Gap Junction Passage of small water-soluble molecules Hemidesmosome Anchors intermediate filaments to extra cellular matrix (ECM) Focal adhesions Basal Surface Anchors many cell types cells to ECM (not seen in diagram) Extracellular Components Glycocalyx Extracellular Matrix Basement membrane (BM) Glycocalyx Glycocalyx is a cell coat of glycoproteins (carbohydrate containing proteins) and glycolipids (carbohydrate containing lipids) that project outward from the plasma membrane Located at epithelial and endothelial cells Mediate cell-cell and cell-substratum (i.e. cell to basement membrane) interactions Mechanical protection (i.e. endothelial cells) Barrier to molecules Bind regulatory factors Adsorption of nutrients Environment for enzymes Protective lining on all blood vessels  Glycocalyx in Disease Kidney - Glomerulus Blood Vessels Glycocalyx damaged in: Kidney disease Atherosclerosis  Extracellular Matrix The extracellular matrix (ECM) It’s an organized network of extracellular material Provides physical and biochemical signals Regulates shape and activities of tissues ECM of cartilage cells It’s removal alters synthetic and secretory activity of cells It’s a dynamic structure Degraded and reformed Mammary gland epithelial cells  Extracellular Matrix Basement Membrane Basement membrane (includes basal lamina): Part of extracellular matrix 50-200 nm Underlies epithelial tissue Also Surrounds: Blood vessels (i.e. endothelial tissue) Nerve fibers (with connective tissue – not epi or endo) Muscles (with connective tissue – not epi or endo) Fat cells (with connective tissue – not epi or endo) Separates adjacent tissues within an organ Mechanical support Generates signals to maintain cell survival Serves as substratum for cell migration barrier to macromolecules i.e. keeps proteins in blood  Extracellular Matrix Basement Membrane – Summary of roles: For Epithelium: Anchorage: Anchors epithelial cells to the underlying connective tissue, maintaining tissue structure. Filtration: Acts as a filter, controlling the exchange of substances between the epithelium and adjacent tissues. Compartmentalization: Separates epithelial tissue from connective tissue, ensuring distinct tissue boundaries. Cell differentiation and regeneration: Provides cues for epithelial cell differentiation and helps guide tissue repair. For Endothelium: Structural support: Provides a foundation for endothelial cells, maintaining the integrity of blood vessels. Selective barrier: Regulates the passage of molecules between the bloodstream and surrounding tissues. Cell migration and repair: Aids in endothelial cell migration and proliferation, especially during angiogenesis and wound healing. Maintains separation: Prevents mixing of endothelial cells with underlying tissues, ensuring functional compartmentalization.  Extracellular Matrix Basement Membrane in Disease The glomerular endothelium lines the blood vessels within the kidney glomerulus and works with the Glomerular basement membrane (GBM) to filter blood while retaining cells and large proteins. Abnormal GBM can impair the kidneys' ability to filter blood. Some examples: Diabetes: GBM becomes very thick Basement membrane disease: GBM becomes thin GoodPasture’s syndrome: GBM is disrupted and is thin Thin Basement Membrane Disease: Goodpasture’s Syndrome (Attack of Genetically inherited →collagen glomerular basement membrane): issue Autoimmune disease →Ab against Blood and protein in urine collagen Kidneys and lungs Extracellular Matrix Proteins found in the ECM Extracellular Matrix Collagen  Extracellular Matrix Collagens Collagens Main structural proteins in the ECM Most abundant protein in the human body (>25%) High tensile strength fiber of 1 mm diameter can suspend ~ 22lbs Produced by fibroblasts, smooth muscle cells, epithelial cells, and a few other cells 28 types of collagen fibers Each restricted to particular locations Collagen is a trimer of polypeptide chains (α chains) wound around each other in a helix  Extracellular Matrix Collagen - Structure α chains of collagen: Lots of hydroxylated proline residues (amino acid) Maintains stability as a triple helix Vitamin C (Ascorbic acid) adds hydroxyl groups to: lysine and proline amino acids - both help maintain the structure of collagen Vitamin C Deficiency: Scurvy Poor wound healing Changes to hair Skin bleeding Extracellular Matrix Collagen - Types Fibrillar collagens assemble into rigid, cable-like fibrils which get packaged into thicker fibers as a helical lattice Collagen type I, II, III Mechanical framework Skin, tendons, vasculature, cornea, bone, organs Non-Fibrillar collagens Non-helical lattice arrangement of collagens with globular domains Found in basement membranes Collagen type IV Mechanical support with flexibility  Extracellular Matrix Collagen Collagen type Genetic mutations Type I most abundant Osteogenesis Imperfecta: also found in tendons, skin, vessel walls, fibrocartilage, known as brittle bone disease bones, teeth (main component of the organic part of bone) Type II makes up 50% of all cartilage protein Dwarfism: short stature that results from a genetic or medical condition Type III wound healing, often found alongside type I Ehlers-Danlos Syndrome (type 4): vessel walls, skin, intestines and the uterus typically present with acrogeria (distinctive facial appearance), bruising, thin skin, and vascular or visceral rupture. Also have hypermobility of joints and elastic skin. Type IV primary collagen of basement membrane in Alport Syndrome: characterized glomerulus, capillaries, eye lens by progressive kidney disease, hearing loss, and eye abnormalities. Type V cell surfaces, hair, and placenta Ehlers Danlos- Syndrome (classical type):  Extracellular Matrix Collagen Case Study: 30 year old male Elevated blood pressure Blood in urine (hematuria) Urinalysis demonstrates elevated levels of protein (proteinurea) Gradual bilateral hearing loss, particularly at high tones. Family history of end-stage kidney disease (maternal grandfather). Ultrasound No major structural abnormalities detected Urinary tract and kidney infections are ruled out. Kidney biopsy profound thickening and splitting of the glomerular basement membrane Extracellular Matrix Collagen Case Study - Alport Syndrome Characterized by: Glomerulonephritis End-stage kidney disease Hearing loss Some instances can affect the eyes Blood in the urine (hematuria) is almost always found in this condition Mutations in collagen type IV biosynthesis genes Prevents proper production or assembly of the type IV collagen network Important structural component of basement membranes in the kidney, inner ear, and eye X-linked, predominantly affects males. Treatment: Dialysis Kidney transplant Hearing aids Extracellular Matrix Fibronectin  Extracellular Matrix Fibronectin Fibronectin Glycoprotein of ECM Secreted primarily by fibroblasts Initially soluble protein Cells use it to make insoluble matrix Plays a major role: Cell adhesion Growth Migration Differentiation Wound healing Embryonic development Waves of cell migration guided by fibronectin https://youtu.be/XFjIaTfJpaw Extracellular Matrix Fibronectin - Structure Binds to: Integrins (membrane- spanning receptor proteins on cells) Via Arg-Gly-Asp sequence Binds to ECM via collagen, fibrin, and proteoglycans It is a protein dimer: 2 nearly identical monomers linked by a pair of disulfide bonds The Monomer is composed of distinct modules organized into different functional units (Fn) Arginine-glycine-aspartic acid Extracellular Matrix Laminin  Extracellular Matrix Laminin Laminin Family of extracellular glycoproteins (>15) Consist of 3 polypeptide chains linked by di- sulfide bonds organized into molecule resembling a cross Extracellular Matrix Laminin Binds to: Cell-surface receptors Other laminin molecules Proteoglycans (heparin) Collagen of basement membrane Important for cell: Migration Growth Differentiation Collagen IV Laminin Entactin molecules (BM) Extracellular Matrix Laminin Plays a pivotal role in the migration of primordial germ cells (PGCs) (ie sperm or eggs) PGCs eventually form gametes PGCs arise in the yolk sac Outside the embryo Travel through bloodstream and embryonic tissues to the developing gonad Via regions rich in laminin. Cell surface protein adheres strongly to a subunit of laminin primordial germ cells (in green; second image) migrating along a tract of laminin (in red) from the PGC to the developing gonad  Extracellular Matrix Proteoglycans greatly influence a cell’s potential for migration, growth and differentiation pivotal role in the migration of primordial germ cells primordial germ cells migrating along a tract of laminin from the dorsal mesentery to the developing gonad  Extracellular Matrix Proteoglycans Proteoglycans ECM protein-polysaccharide GAGs complex Composed of a core protein and Glycosaminoglycans (GAGs) covalently attached to it Highly acidic due to sulfate and carboxyl groups of GAGs (Negatively charged) As a result, they bind cations and H2O Forms porous, hydrated gel resistant to crushing Gives cartilage and other ECM strength and resistance to deformation  Extracellular Matrix Proteoglycans Form gigantic complexes Proteoglycans bind together forming larger complex Linked by hyaluronic acid Nonsulfated GAG  Extracellular Matrix Proteoglycans - Supplements Sulfated and nonsulfated GAGs taken as health supplements to maintain skin and joint health  Extracellular Matrix Remodeling Dynamic, components are continuously subject to degradation and reconstruction Renewal of the ECM and remodelling is important for: Embryonic development Wound healing Cancer metastasis  Extracellular Matrix Remodeling: MMPs Matrix metalloproteinases (MMPs): Zinc containing enzymes that degrade the ECM Secreted into the ECM or anchored to plasma membranes Digest nearly all ECM components Actively involved in: Tissue remodeling Cell migration/invasion Wound healing Neovasculogenesis  Extracellular Matrix MMPs Matrix metalloproteinases (MMPs): Interaction of cells with extracellular materials Interaction of cells with extracellular materials: Integrins Integrins Bind Arginine-glycine-aspartic acid 2 membrane-spanning polypeptide chains (α and ß) Non-covalently linked 18 different α subunits and 8 different ß subunits >100 different pairings (~ 24 identified) Integrate extracellular and intracellular environments Bind fibronectin, laminin, proteoglycans, collagen For example, they can bind Arg-Gly-Asp (RGD) sequences (see Fibronectin) Interaction of cells with extracellular materials: Integrins “Inside-Out signalling” Active Internal cell signals to external environment “upright” (i.e. ECM) to affect: ECM Assembly conformation Cell migration Inactive “bent” Adhersion process conformation “Outside-in signalling” External environment signals to internal cell to affect: Signaling Differentiation Motility Growth Survival Cytoskeletal rearrangements Proliferation Gene Expression Cell Polarity Uniquely Cancer cells depend less on integrin signalling so that they can migrate. Normal cells need integrin interaction with ECM. Cancer cells do not. Inside-out signalling  Cell-Cell/Cell-ECM Interactions Focal Adhesions Apical Surface Tight Junctions Seal gap between cells Adherens junctions Connects Actin (a specific protein) filaments between cells Desmosome Connects Intermediate filaments between cells Gap Junction Passage of small water-soluble molecules Hemidesmosome Anchors intermediate filaments to ECM in epithelial cells Focal adhesions Basal Surface Anchors many cell types cells to ECM Cell – ECM Interactions Focal Adhesions Focal adhesions Anchor a cell to a substratum large clusters of integrins (most commonly seen in vitro but found in muscle and tendons). Disassembled for movement or cell replication Sensory structure Senses Extracellular environment Focal adhesions Focal adhesions are known to sense both chemical and physical properties of their matrix environment. Chemical sensing is mediated by the different types of receptors that may function additively, synergistically or antagonistically Overall focal adhesions can sense and affect : Cell adhesion https://www.mechanobio.info/what-is-mechanobiology/how- Proliferation do-focal-adhesions-facilitate- Survival mechanosensing/#:~:text=Focal%20adhesions%20are%20kno Locomotion wn%20to,3%5D%2C%5B4%5D  Cell – ECM Interactions Hemidesmesomes Hemidesmosome This is a specialized integrin adhesive structure in epithelial cells in vivo More permanent anchor to basement membrane Laminin of the ECM bound to integrins which are bound to dense collection of keratin intermediate filaments on a plaque of plectin Keratin inside the cell Cell – ECM Interactions Hemidesmesomes- disease Bullous pemphigoid is a rare skin condition that causes large, fluid-filled blisters Chronic, autoimmune, sub-epidermal, blistering skin disease Occurs at the space between the epidermis and dermis skin layers Auto-antibodies attack a hemidesmosomal protein (called bullous pemphigoid antigen 1) Cell – ECM Interactions Focal Adhesions vs Hemidesmosomes Interactions Between Cells to Be Covered Next Lecture Questions? Next Lecture Interactions between Cells and Gene Transcription and Translation (Ch. 11)