Unit 3 - Inflammation and Tissue Repair PDF

Chapter 3: Inflammation and Repair Unit 3 Dr. Angela LI School of MHS  Inflammation is the second line of defense. Is one of the nonspecific defense....

Chapter 3: Inflammation and Repair Unit 3 Dr. Angela LI School of MHS  Inflammation is the second line of defense. Is one of the nonspecific defense. Figure 3.1 Lines of defense. Dr. Angela LI, School of MHS, Tung Wah College 2  Dr. Angela LI, School of MHS, 3 Tung Wah College Inflammatory response Inflammation: the host response that accomplished following goals after injury ▫ Get rid of damaged or necrotic tissues and foreign invaders Inflammatory response ▫ Acute inflammation: is considered an expected body response to injury. ▫ Chronic inflammation: is presented as an altered inflammatory response due to unrelenting injury.  4 Dr. Angela LI, School of MHS, Sequential steps of inflammation Tung Wah College The typical inflammatory reaction develops through a series of sequential steps: 1. Recognition of the offending agent 2. Recruitment of leukocytes and plasma proteins 3. Activation of leukocytes and plasma proteins and elimination of the offending substances 4. Reaction is controlled and terminated 5. Tissue repair  5 Dr. Angela LI, School of MHS, Tung Wah College Recognition of the offending agent Recruitment of leukocytes and plasma proteins Activation of leukocytes and plasma proteins and elimination of the offending substances Tissue repair  6 Dr. Angela LI, School of MHS, Cause of inflammation Tung Wah College Inflammatory reactions may be triggered by a variety of stimuli: ▫ Infections ▫ Tissue necrosis: some molecules released from necrotic cells are known to trigger inflammation  Ischemia  Trauma  Physical and chemical injury ▫ Foreign bodies ▫ Immune reactions  7 Dr. Angela LI, School of MHS, Tung Wah College Part I ACUTE INFLAMMATION  8 Dr. Angela LI, School of MHS, Tung Wah College Features of acute inflammation Cardinal Signs: ▫ Rubor – Redness ▫ Tumor – Swelling ▫ Calor – Heat ▫ Dolor – Pain ▫ Functio laesa – Loss of function  9 Dr. Angela LI, School of MHS, Tung Wah College Manifestation of Acute Inflammation Manifestation Rationale Redness Vasodilation; increased blood flow to the injured area Heat Vasodilation; increased blood flow to the injured area Pain Chemical mediators directly elicit pain receptor; Accumulated fluid (Edema) causes compression in the tissue Edema and/or Exudate Increased vascular permeability; fluid accumulation in extracellular space Loss of function Tissue damage from injury; Pain and swelling at the site limit the function  10 Dr. Angela LI, School of MHS, Tung Wah College Part I A. Major Components of Acute Inflammation  11 Three major components of Acute Dr. Angela LI, School of MHS, Tung Wah College Inflammation: 1. Increase blood flow to site of injury (vascular response) 2. Permit plasma protein and leukocytes to leave the circulation (vascular response) 3. Leukocytes emigration and accumulation in the site of injury (cellular response)  To remove injured tissue and prepare for tissue repair  12 Dr. Angela LI, School of MHS, Tung Wah College The major local manifestations of acute inflammation, compared to normal. (1) vascular dilation and increased blood flow (causing erythema and warmth); (2) extravasation and extravascular deposition of plasma fluid and proteins (edema); (3) leukocyte emigration and accumulation in the site of injury  13 Dr. Angela LI, School of MHS, Tung Wah College Vascular Cellular response response  14 1. Vascular Response Dr. Angela LI, School of MHS, Tung Wah College Vascular reactions consist of changes in: 1. Increase blood flow  Blood vessels dilate (vasodilation):  by chemical mediators, notably histamine.  Vascular congestion: stasis of blood flow  Caused by increased permeability of the capillaries → loss of fluid  Heat and redness at the site 2. Increase of permeability of the blood vessel  Endothelial retraction induced by mediators.  Endothelium injury, resulting in endothelial cell necrosis and detachment. ▫ E.g. burns, microbial toxins, or leukocyte adhesion  Edema (exudate) or swelling at the site of injury  15 Dr. Angela LI, School of MHS, Tung Wah College (1) vascular dilation and increased blood flow (causing erythema and warmth);  16 Dr. Angela LI, School of MHS, Tung Wah College 2) Increase of permeability of the blood vessel (causing swelling)  17 Dr. Angela LI, School of MHS, Tung Wah College Response of lymphatic vessels and Lymph nodes Lymphatic participate in acute inflammation ▫ Lymph flow increase, helping to drain extravascular fluid ▫ Secondarily inflamed when leukocytes, cell debris and microbes go into the system  Lymphangitis  Lymphadenitis (inflamed lymph node)  18 2. Cellular Response Dr. Angela LI, School of MHS, Tung Wah College Deliver leukocytes to the site of injury and to activate the leukocytes to eliminate the offending agents. Most important leukocytes: neutrophils and macrophages. Three steps for a successful cellular recruitment: 1. Adhesion to endothelium: attraction and binding  Leukocytes adhere to endothelial cells near the site of injury 2. Migration through endothelium: move across endothelial cells. 3. Chemotaxis: moving cells to the site of injury.  Migration in the tissues toward chemotactic factors They are then free to participate in: (function) ▫ Removal of the offending agents ▫ Leukocyte-induced tissue injury  19 Dr. Angla LI, School of MHS, Tung Wah College Chemotaxis  20 1. Adhesion to Endothelium Dr. Angela LI, School of MHS, Tung Wah College Margination and Rolling and Adhesion Margination: ▫ Stasis of blood flow causing leukocytes to settle-out of the central flow column and “marginate” along the endothelial surface Rolling: ▫ Endothelial cells and leukocytes have complementary surface adhesion molecules which briefly stick and release causing the leukocyte to roll along the endothelium like a tumbleweed until it eventually comes to a stop as mutual adhesion reaches a peak ▫ Mediated by selectins ▫ Regulated by cytokines Adhesion: ▫ Rolling comes to a stop and adhesion results ▫ Mediated by integrins  21 Dr. Angela LI, School of MHS, Tung Wah College 2. Migration through Endothelium (diapedesis) Move across endothelial cells. Adhesion molecules in intercellular junctions are involved. Cross basement membrane by secreting collagenases Migrate toward the chemotactic gradient Genetic deficiencies in leukocyte adhesion molecules result in recurrent bacterial infections  22 3. Chemotaxis Dr. Angela LI, School of MHS, Tung Wah College Leukocytes follow chemical gradient to site of injury (chemotaxis) ▫ Chemotactic agents bind surface receptors inducing calcium mobilization and assembly of cytoskeletal contractile elements Endogenous chemoattractants: chemical mediators: ▫ Cytokines; components of complement system; AA metabolites The nature of the leukocyte infiltrate varies with the age of the inflammatory response and the type of stimulus ▫ Early in inflammatory: mostly neutrophils. ▫ Progression of inflammation: monocytes, lymphocytes, etc.  Neutrophil: short-lived  Monocytes: long-lived. Dominant in chronic inflammation Figure 03-06C. Nature of leukocyte infiltrates in inflammatory reactions. The photomicrographs show an inflammatory reaction in the myocardium after ischemic necrosis (infarction). A, Early (neutrophilic) infiltrates and congested blood vessels. B, Later (mononuclear) cellular infiltrates. C, The approximate kinetics of edema and cellular infiltration. For simplicity, edema is shown as an acute transient response, although secondary waves of delayed edema and neutrophil infiltration can also occur.  23 Dr. Angela LI, School of MHS, Tung Wah College Phagocytosis and clearance of the offending agent Once leukocytes have been recruited to a site of infection or cell death, the must be activated to perform their functions. Recognition and activation of leukocyte ▫ The responses of leukocytes in site of infection or cell death include two sequential sets of events ▫ Recognition  Express several receptors then deliver signals to initiate activation ▫ Activation  Increases cytosolic Ca2+ and activation of enzymes  Important for phagocytosis and intracellular killing  24 Dr. Angela LI, School of MHS, Tung Wah College  25 Dr. Angela LI, School of MHS, Tung Wah College Phagocytosis and clearance of the offending agent Phagocytosis – Removal of the offending agents Once at site of injury, leukocytes: ▫ Recognize and attach ▫ Engulfment  Formation of vacuole which fuses with lysosomal granule membrane (phagolysosome) ▫ Kill (degrade)  Destruction of ingested particles with phagolysosome by lysosomal enzyme and by reactive oxygen and nitrogen species.  26 Dr. Angela LI, School of MHS, Tung Wah College  27 Dr. Angela LI, School of MHS, Tung Wah College Other functional responses of activated leukocytes. Play role in wound repair and anti-inflammation.  28 Dr. Angela LI, School of MHS, Termination of the Acute inflammatory Tung Wah College Response Inflammation declines after the offending agents are removed. ▫ Mediators are produced in rapid bursts  Short half-lives  Degraded after release ▫ Neutrophils have short half-lives ▫ Inflammation process triggers a variety of stop signals  Switch AA metabolite from proinflammatory leukotriens to anti-inflammatory lipoxins  Release anti-inflammatory cytokines  29 Dr. Angela LI, School of MHS, Tung Wah College Part I B. Chemical Mediators  30 Chemical mediators Dr. Angela LI, School of MHS, Tung Wah College Are the substances that initiate and regulate inflammatory reactions Come from cells or plasma Produced in response to various stimuli One can stimulate the release of other one Mediators vary in their range of cellular targets Short-lived: ▫ Quickly decay (AA metabolites), are inactivated enzymatically (kininase), or are scavenged (antioxidants) Most important mediator of acute inflammation: ▫ Vasoactive amines, lipid products (prostaglandins and leukotrienes), cytokines and products of complement activation Vascular Cellular response response Figure 3.3 Concept map. An overview of the importance of chemical mediators in the vascular and cellular responses of inflammation. PMNs, polymorphonuclear neutrophils.  32 Dr. Angela LI, School of MHS, Chemical mediators Tung Wah College Cell-derived: ▫ Preformed, sequestered and released (mast cell histamine) ▫ Synthesized as needed (prostaglandin) ▫ Including: vasoactive amines, AA metabolite, cytokines and chemokines and others ▫ Major cell type produce these mediators are:  macrophages, dendritic cells and mast cells Plasma-derived: ▫ Complement, kinins, coagulation factors ▫ Many in “pro-form” requiring activation (enzymatic cleavage)  33 Dr. Angela LI, School of MHS, Tung Wah College Cell-derived Chemical mediators Vasoactive amines, AA metabolite, cytokines and chemokines  34 Dr. Angela LI, School of MHS, Tung Wah College Vasoactive amines Histamine and serotonin are the two major vasoactive amines, having important actions on blood vessels. Stored in the cell and are the first mediators released. ▫ Histamine:  Riches in mast cells.  Released in response to variety of stimulus.  Cause dilation of arterioles and increase the permeability of venules. ▫ Serotonin:  Present in platelet and neuroendocrine cells in GI tract;  Release triggered by platelet aggregation  Vasodilator (mainly) and vasoconstrictor (unclear in inflammation)  35 Arachidonic Acid Metabolites Dr. Angela LI, School of MHS, Tung Wah College The lipid mediators, prostaglandins and leukotrienes, are produced from AA. Stimulating vascular and cellular reactions in acute inflammation. ▫ Prostaglandins and thromboxane:  Produced by mast cells, macrophages, endothelial cells and others  In AA pathway, generated via cyclooxygenase (COX) pathway;  Involve in the vascular and systemic reaction of inflammation.  Prostaglandins :Vasodilation (PGI2, PGD2, PGE2) and systemic reactions (fever, pain);  Thromboxane: Vasoconstriction and aggregation of platelet  But also protective (gastric mucosa);  COX blocked by aspirin and NSAIDS (anti-inflammatory drug)  36 Dr. Angela LI, School of MHS, Tung Wah College Arachidonic Acid Metabolites (Cont.) lipid mediators: (Cont.) ▫ Leukotrienes:  Produced by leukocytes and mast cells by lipoxygenase pathway;  Involved in vascular and smooth muscle reactions and leukocyte recruitment.  Functions:  Attract neutrophils (5-HETE),  Vasoconstriction, bronchospasm, and increased permeability of venules (LTC4, LTD4, and LTE4)  Effect of bronchospasm and increasing vascular permeability is more potent than histamine.  Inhibit by leukotriene receptor antagonist ▫ Lipoxins  Produced by leukocytes by lipoxygenase pathway;  Suppress inflammation by inhibiting the recruitment of WBC  37 Dr. Angela LI, School of MHS, Tung Wah College  38 Dr. Angela LI, School of MHS, Tung Wah College Table 3-5 Principal Inflammatory Actions of Arachidonic Acid Metabolites (Eicosanoid) Action Eicosanoid Vasodilation PGI2 (prostacyclin), PGE1, PGE2, PGD2 Vasoconstriction Thromboxane A2, leukotrienes C4, D4, E4 Increased vascular permeability Leukotrienes C4, D4, E4 Chemotaxis, leukocyte adhesion Leukotrienes B4, HETE  39 Cytokines and chemokines: Dr. Angela LI, School of MHS, Tung Wah College Cytokines ▫ Proteins produced by many cell types (principally activated lymphocytes, macrophages, and dendritic cells. Also by endothelial cells and connective tissue cells) ▫ Act as a message to other cells, telling them how to behave. Mediate and regulate immune and inflammatory reactions ▫ Tumor necrosis factor (TNF) and interleukin-1 (IL-1)  Mainly produced by activated macrophages and dendritic cells  Contribute to the local and systemic reaction of inflammation:  Increase endothelial cell adhesion molecule expression,  Activation and aggregation of PMNs, etc.  Systemic acute-phase response: fever  TNF antagonists used to treat chronic inflammatory disease Chemokines ▫ Family of small proteins ▫ Act primarily as chemoattractants for specific type of WBC  40 Dr. Angela LI, School of MHS, Tung Wah College  41 Dr. Angela LI, School of MHS, Tung Wah College Principal local and systemic actions of tumor necrosis factor (TNF) and interleukin-1 (IL-1)  42 Dr. Angela LI, School of MHS, Tung Wah College Plasma protein-derived mediators Complement Clotting system Kinins  43 Dr. Angela LI, School of MHS, Complement system Tung Wah College Function mainly in host defense against microbes and in pathologic inflammatory reactions ▫ Complement proteins are in inactive forms in the plasma, and activated by different pathways. ▫ Then to further degrade other complement proteins to produce the active enzymes. Three main function of the complement system:  Inflammation  Stimulate histamine release from mast cells: vasodilation, vascular permeability  Chemotactic agents for WBC, e.g. neutrophils, monocytes, etc.  Activate lipoxygenase pathway of AA metabolism, cause further releasing of inflammatory mediators  Opsonization and phagocytosis  Cell lysis  44 Dr. Angela LI, School of MHS, Tung Wah College  45 Dr. Angela LI, School of MHS, Clotting system Tung Wah College Inflammation and blood clotting are often intertwined, with each promoting the other. ▫ Hageman factor (factor XII): collagen, basement membrane, activated platelets converts XII to XIIa (active form). Ultimately converts soluble fibrinogen to insoluble fibrin clot (blood clotting) ▫ XIIa initiates four systems involved in the inflammatory responses:  Kinin system: vasoactive  Clotting system: induces formation of thrombin  Fibrinolytic system: to prevent continuous clot propagation  Complement system: produces anaphylatoxins and other mediators.  46 Dr. Angela LI, School of MHS, Tung Wah College  47 Dr. Angela LI, School of MHS, Tung Wah College Kinins Kinins are vasoactive peptides derived from plasma proteins called kiniogens. Leads to formation of bradykinin from cleavage of precursor Functions of bradykinin: ▫ Increase vascular permeability ▫ Non-vascular smooth muscle contraction (e.g., bronchial smooth muscle) ▫ Arteriolar dilation ▫ Causes pain ▫ Rapidly inactivated (kininases)  48 Table 3-7 Role of Mediators in Different Reactions of inflammation Dr. Angela LI, School of MHS, Tung Wah College Role in Inflammation Mediators Vasodilation Prostaglandins Nitric oxide Histamine Increased vascular Histamine and serotonin permeability C3a and C5a (by liberating vasoactive amines from mast cells, other cells) Bradykinin Leukotrienes C4, D4, E4 PAF Substance P Chemotaxis, TNF, IL-1 leukocyte recruitment and Chemokines activation C3a and C5a Leukotrienes B4 (bacterial products) Fever IL-1, TNF Prostaglandin Pain Prostaglandin Bradykinin Tissue damage Lysosomal enzymes of leukocytes Reactive oxygen species Nitric oxide  49 Dr. Angela LI, School of MHS, Tung Wah College Morphologic Patterns of Acute Inflammation Serous inflammation ▫ Watery fluid with small amounts proteins and cells ▫ Causes: allergic chemicals, burns Fibrinous inflammation ▫ Thick, sticky, increase cell fibrin content ▫ Increase risk of scar tissue Purulent inflammation: abscess ▫ Thick, yellow-green (pus); increase leukocytes, cell debris, microbes. Indicates bacterial infection. Ulcers ▫ Ulcers are circumscribed, open, craterlike lesion of the skin or mucous membranes.  50 Dr. Angela LI, School of MHS, Tung Wah College Serous inflammation  51 Dr. Angela LI, School of MHS, Tung Wah College Fibrinous inflammation  52 Dr. Angela LI, School of MHS, Tung Wah College Purulent inflammation: abscess  53 Dr. Angela LI, School of MHS, Tung Wah College Ulcers  54 Dr. Angela LI, School of MHS, Tung Wah College Part I C. Systemic effects of inflammations  55 Dr. Angela LI, School of MHS, Tung Wah College Systemic effects of inflammations Inflammation, even if it is localized, is associated with cytokine-induced systemic reactions that are collectively called the acute-phase responses. Cytokines, TNF, IL-1 and IL-6 are important mediators of the acute-phase reaction.  56 Acute-phase responses Dr. Angela LI, School of MHS, Tung Wah College Clinical and pathologic changes: Fever ▫ Most prominent manifestations, especially infective injury ▫ Pyrogens: substances that induce fever  Exogenous pyrogens: LPS – bacterial product  Endogenous pyrogens: Cytokines (IL-1 and TNF) and PGE2 Leukocytosis: Elevated white blood cell count ▫ Bacterial infection (neutrophilia) ▫ Parasitic infection (eosinophilia) ▫ Viral infection (lymphocytosis) Acute-phase proteins: ▫ Plasma proteins: C-reactive protein (CRP), Fibrinogen, serum amyloid A (SAA)  57 Dr. Angela LI, School of MHS, Possible outcomes of acute inflammation Tung Wah College All acute inflammatory reactions typically have one of three outcomes below. Complete resolution ▫ The acute inflammatory response is self-limited. ▫ Once the offending agent has been destroyed and removed, the inflammatory response will be deactivated, allowing the tissue to heal. ▫ Little tissue damage ▫ Capable of regeneration Scarring or fibrosis (fibrosis occurs in chronic condition) ▫ In tissues unable to regenerate ▫ Excessive fibrin deposition organized into fibrous tissue Chronic inflammation  58 Dr. Angela LI, School of MHS, Tung Wah College  59 Dr. Angela LI, School of MHS, Tung Wah College Part II CHRONIC INFLAMMATION  60 Chronic inflammation Dr. Angela LI, School of MHS, Tung Wah College Recurrent or persistent inflammation lasting several weeks or longer Inflammation, tissue injury and attempts of repair coexist, in varying combinations. ▫ Causes: when acute phase cannot be resolved  Persistent injury or infection (ulcer, TB)  Prolonged toxic agent exposure (silica)  Autoimmune disease states (RA, SLE) Leukocyte-induced tissue injury in acute and chronic inflammation ▫ Important causes of injury to normal cells and tissues under several circumstances  Injure to adjacent tissues as part of normal reaction  Inappropriately against host tissue, such as autoimmune disease  Excessively reaction, such as allergic  61 Dr. Angela LI, School of MHS, Tung Wah College Chronic inflammation Morphologic Features: ▫ Mononuclear cell infiltration, e.g. lymphocyte, macrophage, plasma cell ▫ Tissue destruction: by inflammatory cells ▫ Attempts at repair with fibrosis and angiogenesis (new vessel formation)  62 Dr. Angela LI, School of MHS, Tung Wah College destruction of epithelium collection of chronic inflammatory cells * fibrosis * leukocyte recruitment Congestion caused by vasodilation  63 Dr. Angela LI, School of MHS, Tung Wah College Cells and Mediators of Chronic inflammation Macrophages The dominant cells in most chronic inflammatory reactions. ▫ Derived from blood monocytes. Scattered all over (microglia, Kupffer cells, lymph nodes, alveolar macrophages, etc.) ▫ Circulate as monocytes and reach site of injury within 24 – 48 hrs and transform ▫ Become activated by:  Classical pathways: microbicidal action and inflammation  Alternative pathways: tissue repair, fibrosis and anti-inflammation T cell- derived cytokines, endotoxins, and other products of inflammation  64 Dr. Angela LI, School of MHS, Macrophages Tung Wah College Productions of macrophages helps to eliminate injurious agents and initiate the process of repair, but also responsible for the tissue injury in chronic inflammation Functions: ▫ Phagocytosis and destruction of debris & bacteria ▫ Initiate the process of tissue repair and involve in scar formation and fibrosis ▫ Secrete mediators of inflammation,  Synthesis; not only cytokines, but also complement components, blood clotting factors, proteases ▫ Processing and presentation of antigen to immune system.  65 Dr. Angela LI, School of MHS, Tung Wah College Granulomatous Inflammation A form of chronic inflammation characterized by collections of activated macrophages, often with T cells, and sometimes associated with central necrosis. Cellular attempt to contain an offending agent that is difficult to eradicate. Granuloma: wall outside, macrophages and harmful substances inside. ▫ Macrophages develop and begin to resemble squamous cells, therefore called “epithelioid” cells ▫ Some activated macrophages fuse, forming multinucleate “giant cells” Dr. Angela LI, School of MHS, Tung Wah College 66 epithelioid cell central necrosis * giant cell Dr. Angela LI, School of MHS, Tung Wah College 67  68 Consequences of defective or excessive Dr. Angela LI, School of MHS, Tung Wah College inflammation Defective inflammation ▫ Increased susceptibility to infections ▫ Delayed wound healing Excessive inflammation ▫ Cause the abnormal reaction of body, e.g., allergies, autoimmune diseases ▫ Prolonged inflammation induces fibrosis and tissue injuries.  69 Dr. Angela LI, School of MHS, Tung Wah College Part III Tissue Repair  70 Tissue Repair Dr. Angela LI, School of MHS, Tung Wah College Repair, also called healing, refers to the restoration of tissue architecture and function after an injury ▫ Tissue healing can only occur with an effective inflammatory response Two types of reactions in healing: ▫ Regeneration: restores normal tissue  Proliferation of cells and tissues to replace lost structures ▫ Connective tissue deposition (scar formation):  Repair by laying down of connective (fibrous) tissue, and may result in scar formation. ▫ Both reactions contribute in varying degrees to ultimate repair.  71 Dr. Angela LI, School of MHS, Tung Wah College  72 Dr. Angela LI, School of MHS, Cell and Tissue Regeneration Tung Wah College The regeneration of injured cells and tissues involves cell proliferation, which driven by growth factors and is critically dependent on the integrity of the extracellular matrix (ECM) and by the development of mature cells from stems cells. Repair to injured tissue depends on: ▫ Ability of regeneration of injured parenchymal cells (cell types) ▫ Degree of injury (the original framework remains or not)  73 Dr. Angela LI, School of MHS, Tung Wah College Figure 3-2 Role of the extracellular matrix in regeneration and repair. Liver regeneration with restoration of normal tissue after injury requires an intact cellular matrix. If the matrix is damaged, the injury is repaired by fibrous tissue deposition and scar formation  74 Dr. Angela LI, School of MHS, Cell Proliferation Tung Wah College The ability of tissues to repair themselves depends on their intrinsic proliferative capacity. Classification of cells by their proliferative potential ▫ Labile (continuous dividing)  epithelium of skin, respiratory tract, gastrointestinal tract and urinary tract, hematopoietic cells, et al ▫ Stable (quiescent)  parenchymal cells in liver, kidney, pancreas, salivary gland, et al ▫ Permanent (nondividing)  myocardium, skeletal muscle, neuron  75 Dr. Angela LI, School of MHS, Tung Wah College  76 Dr. Angela LI, School of MHS, Tung Wah College Regulation of cell proliferation Cell proliferation is driven by signals provided by growth factors and from the ECM. Mechanisms of cell growth and tissue repair ▫ Growth factors (soluble factors)  Signal transduction pathways (ligand-receptor with intrinsic tyrosine kinase activity) ▫ Signal from ECM (insoluble)  77 Dr. Angela LI, School of MHS, Tung Wah College Regulation of cell proliferation Growth factors are polypeptide molecules causing an expansion of cell populations which include an increase in cell size, mitotic activity and protection from apoptotic death (survival). Growth factors induce the synthesis or activity of transcription factors In addition to stimulating cellular proliferation, they promote cellular migration, differentiation, contractibility, as well as enhancing the synthesis of special proteins such as collagen by fibroblasts.  78 Dr. Angela LI, School of MHS, Tung Wah College  79 Dr. Angela LI, School of MHS, Tung Wah College  80 Table 1-1 Growth factors and Cytokines Involved in Regeneration and Wound Healing Dr. Angela LI, School of MHS, Growth Factor Symbol sources Function Tung Wah College Epidermal growth α EGF Platelets, macrophages, saliva, Mitogenic for keratinocytes and fibroblasts; stimulates urine, milk, plasma keratinocyte migration and granulation tissue formation Transforming growth TGF-α Macrophages, T lymphocytes, Similar to EGF; stimulates replication of hepatocytes factor α keratinocytes, and many tissues and most epithelial cells Hepatocyte growth HGF Mesenchymal cells Enhances proliferation of hepatocytes, epithelial factor/ scatter factor cells, and endothelial cells; increases cell motility, keratinocyte replication Vascular endothelial VEGF Many types of cells Increases vascular permeability; mitogenic for cell growth factor endothelial cells (see table 3-3); angiogenesis Platelet-derived growth PDGF Platelets, macrophages, Chemotactic for PMNs, macrophages, fibroblasts, factor endothelial cells, keratinocytes, and smooth muscle cells; activates PMNs, smooth muscle cells macrophages, and fibroblasts; mitogenic for fibroblasts, endothelial cells, and smooth muscle cells; stimulates production of MMPs, fibronectin, and HA; stimulates angiogenesis and wound contraction Fibroblast growth factor FGF Macrophages, mast cells, T Chemotactic for fibroblasts; mitogenic for fibroblasts 1, 2, and family lymphocytes, endothelial cells, and keratinocytes; stimulates keratinocyte migration, fibroblasts angiogenesis, wound contraction, and matrix deposition Transforming growth TGF- β Platelets, T lymphocytes, Chemotactic for PMNs, macrophages, lymphocytes, factor β macrophages, endothelial cells, fibroblasts, and smooth muscle cells; stimulates TIMP keratinocytes, smooth muscle synthesis, angiogenesis, and fibroplasia; inhibits cells, fibroblasts production of MMPs and keratinocyte proliferation Keratinocyte growth KGF fibroblasts Stimulates keratinocyte migration, proliferation, and factor differentiation  81 Dr. Angela LI, School of MHS, Tung Wah College Regulation of cell proliferation Tissue repair and regeneration depend not only on the activity of soluble factors, but also on interactions between cells and the components of the extracellular matrix (ECM) Roles of ECM ▫ Mechanical support for cell anchorage ▫ Determination of cell orientation (polarity) ▫ Control cell growth ▫ Maintenance of cell differentiation ▫ Scaffolding for tissue renewal ▫ Establishment of tissue microenvironments, storage and presentation of regulatory molecules  82 Dr. Angela LI, School of MHS, Tung Wah College The Extracellular Matrix A dynamic, constantly, remodeling, macromolecular complex ▫ Interstitial matrix ▫ Basement membrane (BM) Three types of macromolecules 1. Fibrous structural proteins: ▫ Collagens and Elastin ▫ Provide framework, tensile strength and recoil 2. Adhesive proteins (cell adhesion molecules, CAM) ▫ Four main families: immunoglobulin family CAM, cadherins, integrins, and selectins ▫ Connect the matrix elements to one another and to cells 3. Proteoglycans and hyaluronan ▫ Provide resilience and lubrication  83 Dr. Angela LI, School of MHS, Tung Wah College  84 Dr. Angela LI, School of MHS, Tung Wah College The Extracellular Matrix The Cell-Matrix Interactions Cell growth and differentiation involve at least two types of signals acting in concert. One derives from soluble molecules such as polypeptide growth factors and growth inhibitors. The other involves insoluble elements of the ECM interacting with cellular integrins.  85 Dr. Angela LI, School of MHS, Tung Wah College  86 Dr. Angela LI, School of MHS, Tung Wah College Repair by Connective Tissue Deposition If repair cannot be accomplished by regeneration alone, it occurs by replacement of the injured cells with connective tissues, leading scar formation. Steps of Scar formation: ▫ Angiogenesis ▫ Formation of granulation tissue ▫ Remodeling of connective tissue  87 Dr. Angela LI, School of MHS, Tung Wah College  88 Dr. Angela LI, School of MHS, Tung Wah College Cutaneous Wound Healing First intention: the usual case with a surgical wound, in which there is a clean wound with well-apposed edges, and minimal clot formation Second intention: when wound edges cannot be apposed, (e.g., following wound infection), then the wound slowly fills with granulation tissue from the bottom up. A large scar usually results.  89 Dr. Angela LI, School of MHS, Tung Wah College Healing by first Intention When the injury involves only the epithelia layer, the primary mechanism of repair is epithelial regeneration. Sequence of events in wound healing ▫ Inflammation ▫ Proliferation of epithelial and other cells ▫ Maturation of the connective tissue scar  90 Dr. Angela LI, School of MHS, Tung Wah College Cutaneous Wound Healing Stages of Wound Healing Inflammatory phase ▫ Clot formation ▫ Chemotaxis Proliferative phase ▫ Angiogenesis and granulation tissue formation, Proliferation, migration of connective tissue, re- epithelialization of wound Maturational or remodeling phase ▫ ECM deposition, tissue remodeling, and wound contraction  91 Dr. Angela LI, School of MHS, Tung Wah College  92 Dr. Angela LI, School of MHS, Tung Wah College 1. Formation of blood clot Coagulation pathway activated Blood clot serves to cover the wound, stop bleeding, and as a scaffold for migrating cells (neutrophil) ▫ Neutrophil appear in 24 hours ▫ Release proteolytic enzymes that clean out debris and invading bacteria  93 Dr. Angela LI, School of MHS, Tung Wah College 2. Formation of Granulation Tissue 1. 24 to 72 hours, the induction of fibroblast and endothelial cell proliferation form granulation tissue, which is a hallmark of tissue repair. 2. Granulation tissue which is pink and soft, with a granular appearance such as seen underneath the scab of an injured skin. 3. Reach to peak around day 5. 4. Histologically, it is composed of proliferating fibroblasts, newly formed thin capillaries and loose ECM. 5. Amount of granulation tissue depends on the size of tissue deficit and the intensity of inflammation.  94 Dr. Angela LI, School of MHS, Tung Wah College  95 Angiogenesis Dr. Angela LI, School of MHS, Tung Wah College The process of new blood vessel development from existing vessels. Steps of angiogenesis ▫ Vasodilation and increased permeability induced by VEGF ▫ Proteolytic degradation of the parent vessel basement membrane (BM), allowing formation of a capillary sprout ▫ Migration of endothelial cells from the original capillary toward an angiogenetic stimulus ▫ Proliferation of the endothelial cells behind the leading edge of migrating cells ▫ Maturation of endothelial cells with inhibition of growth and organization into capillary tubes ▫ Recruitment of periendothelial cells to for the mature vessel VEGF is the most important growth factor in adult angiogenesis. Secreted by many types of cells.  96 Dr. Angela LI, School of MHS, Tung Wah College Steps in the process of angiogenesis  97 Dr. Angela LI, School of MHS, Tung Wah College  98 Dr. Angela LI, School of MHS, Tung Wah College Roles of Granulation Tissue in Fibrous Repair Growth into the necrotic tissue, hemorrhage, thrombi, inflammatory exudate and replace them(organization) Connect the separated tissue, restore the lost tissue and support them to keep the integrity of body Protect the wound and anti-infection  99 Dr. Angela LI, School of MHS, Tung Wah College 3. Cell proliferation and collagen deposition Macrophages replace neutrophils by 48-96 hours. ▫ Key cellular constituents of tissue repair ▫ Cleaning extracellular debris, fibrin and foreign materials; promoting angiogenesis and ECM deposition ▫ Main resource for chemokines and growth factors in this process Migration and proliferation of fibroblasts at the injury site, and deposition of collagen fibers by fibroblasts. Epithelial cells proliferate from edge to center of wound from 24- 48 hours after injury  100 Dr. Angela LI, School of MHS, Tung Wah College  101 Dr. Angela LI, School of MHS, Tung Wah College 4. Scar formation During the second week The granulation tissue becomes a scar composed of inactive spindle-shaped fibroblasts, dense collagen, fragments of elastic tissue, and other ECM components. A progressive vascular regression results in a pale avascular scar. By the end of the first month, the scar is made up of acellular connective tissue devoid of inflammatory infiltrate, covered by intact epidermis  102 Dr. Angela LI, School of MHS, 5. Connective tissue Remodeling Tung Wah College The balance between ECM synthesis and degradation results in remodeling of the connective tissue framework A scar after surgical operation or trauma will become softer, smaller because of degradation of collagens and other elements of ECM by matrix metalloproteinases (MMPs) After 3 months, the skin reaches about 70-80% of the tensile strength of unwounded skin. And lower tensile strength in the healed wound area may persist for life.  103 Dr. Angela LI, School of MHS, Tung Wah College Phase of wound healing. Wound contraction occurs only in healing by the second intension  104 Healing by Second Intention Dr. Angela LI, School of MHS, Tung Wah College When cell or tissue loss is more extensive, such as in large wounds, abscesses, ulceration, and ischemic necrosis (infarction), the repair process involves a combination of regeneration and scaring. Features: ▫ Inflammatory reaction is more intense ▫ Abundant granulation tissue ▫ Accumulation of ECM ▫ Formation of a large scar  The dermal appendage that have been destroyed are permanently lost ▫ Sound contraction by the action of myofibroblasts  105 Dr. Angela LI, School of MHS, Healing by Second Intention Tung Wah College Wound Contraction ▫ Generally occurs in large surface wounds, an important feature in healing by secondary union. ▫ Helps to close the wound by decreasing the gap between its dermal edges and by reducing the wound area. ▫ Myofibroblasts account for contraction, and represent an intermediate type of cell, between a fibroblast and a myocyte.  106 Dr. Angela LI, School of MHS, Tung Wah College The Healing in second intension-- Skin Ulcer  107 Healing by Second Intention Dr. Angela LI, School of MHS, Tung Wah College Fibrosis Excessive deposition of collagen in a tissue in chronic disease Is a pathologic process induced by persistent injurious stimuli. ▫ Chronic infection ▫ Immunologic reaction Is typically associated with loss of tissue.  108 Dr. Angela LI, School of MHS, Tung Wah College  109 Dr. Angela LI, School of MHS, Tung Wah College  110 Factors that Influence Wound Healing Dr. Angela LI, School of MHS, Tung Wah College Systemic factors Overall nutrition: ▫ Vitamin and protein deficiencies lead to poor wound healing, especially vitamin C, which is involved in collagen synthesis Metabolic status: ▫ Vascular supply (diabetics heal poorly) Circulatory status: ▫ Poor blood supply Hormones ▫ Corticosteroids drastically impair wound healing, because of their profound effect on inflammatory cells Age: younger is definitely better!  111 Dr. Angela LI, School of MHS, Tung Wah College Factors that Influence Wound Healing Local factors Infection ▫ Delays wound healing and leads to more granulation tissue and scarring Type, size, and location of the wound Movement ▫ Wounds over joints do not heal well due to traction Foreign bodies  112 Abnormalities in Tissue Repair Dr. Angela LI, School of MHS, Tung Wah College Defective granulation tissue or scar formation ▫ Dehiscence or ulceration ▫ Usually due to:  Wound infection (common); malnutrition (rare); hypoxia with ulceration, usually due to inadequate vascularity in a skin flap (common) Excessive scar formation (keloid) ▫ Keloids (hypertrophic scars) are the result of over-exuberant production of scar tissue, primarily composed of type III collagen.  Thought to be due to genetic factors, perhaps due to lack of the proper metalloproteinases to degrade type III collagen Contraction ▫ Excessive contraction of a wound is known as a contracture. They are a special problem in the treatment of extensive burns ▫ Limit joint movement.  113 Dr. Angela LI, School of MHS, Tung Wah College Ulcer Dehiscence Keloids Excessive scar formation  114 Dr. Angela LI, School of MHS, Tung Wah College Fixed joint Figure 3-24 Wound contracture. Severe contracture of a wound after deep burn injury.  115 Dr. Angela LI, School of MHS, Tung Wah College  116 Content Dr. Angela LI, School of MHS, Tung Wah College Part I: Acute inflammation Part III: Tissue Repair ▫ Cardinal signs ▫ Regeneration A. Major Components of Acute  Cell proliferation and regulation of Inflammation cell proliferation  Vascular response ▫ Scar formation  Cellular response ▫ Cutaneous wound healing B. Chemical Mediators ▫ Factors that Influence Wound  Cell-derived Healing  Plasma-derived ▫ Abnormalities in Tissue Repair C. Systemic effects of inflammations Part II: Chronic inflammation