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Board of Directors

Dr. Dariush Honardoust, President & cheif director Prof._Honar.jpg

MSc: Anatomy and Cell Biology, Faculty of Medicine, University of Western Ontario, Canada

Doctorate: Craniofacial / Dental SC, Dentistry, University of British Columbia Canada

Post-Doctorate: Surgery Division, University of Alberta, Canada

Dr. Honardoust's Research Publications - Pubmed

Articles: Dermal Wound Healing | Hypertrophic Scar  | Collagen Fibrilogenesis | Small Leucine-rich Proteoglycans

 

 

CAMACS Representative in IRAN

Hossein_Lotfi.jpg Hossein Lotfi, MBA., MHE. International Educational Affairs & Seminars

Office Address: Unit 10 - 4 42-Street, Yousif Abad, Tehran, Iran. Tel: 011 98 (021) 88060414 / 88061718

 

 

Dr._Jennifer_Dean.jpg-Dr. Jeniffer Deana, Training & Certification

 

Ali_asi.jpg- Dr. Ali Asi, Financial Advisor and Legal Consultant
                          

Alice_Xu_pic.jpg- Alice Dan Xu, Representative of CAMACS in China & Asia

 

 

Kirnel_Hunt.jpg Kornel Hunt, Aesthetic Medicine Specialist & Consultant

 

 

 CarolAnn Kellar, Certified Medical Aesthetic NurseCarolAnn_Kellar.jpg

 

Representative of the CAMACS Eastern Canada (ON, QC, NS)

Dr._Khalifeh.jpg- Ali Khalifeh, MD

Board Certified Dermatologist,YSMU

Licensed Holistic Health Practitioner, NAHHP

Dermatologic & Laser Surgery, Medical Aesthetics

Member of World Association for Laser Therapy, WALT

Member of European Society for Cosmetic and Aesthetic Dermatology, ESCAD

Member of National Association of Holistic Health Practitioner NAHHP, Canada

Teaching Professor, Canadian Association of Medical Spas and Aesthetic Surgeons

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A Review on dermal wound healing by Dr. Dariush Honardoust

Overview of wound healing

The process of wound healing is comprised of overlapping phases of inflammation and repair in which platelets, fibroblasts, epithelial, endothelial and inflammatory cells interact with each other and extracellular matrix (ECM) molecules, growth factors and cytokines. Aberrations in this process may result in chronic non-healing wounds or deposition of excess collagen and scar formation. Wound healing consists of three partially overlapping phases: a) haemostasis and inflammation, b) re-epithelialization and granulation tissue formation, and c) maturation and tissue remodeling. Figure 3 summarizes major wound healing events over time.

Early wound healing events and inflammatory phase

Haemostasis Soon after wounding, glycoproteins expressed on the cell surface of platelets mediate their adhesion and aggregation to form hemostasis plaque. Activation of prothrombin to the serine protease thrombin leads to converting fibrinogen into fibrin. Fibrin is then cross-linked by factor XIII to form blood clot. Fibrin and fibronectin cross-link together and form a network that traps proteins and platelets, prevents further blood loss, facilitates cell migration and provides matrix scaffold for collagen deposition. Platelets also release large amount of growth factors, cytokines and pro- inflammatory factors such as serotonin, bradykinin, prostaglandins, prostacyclins, thromboxane and histamine. Thromboxanes and prostaglandins promote vasoconstriction to minimize blood loss, followed by vasodilation

Inflammatory response

Cytokines present in the blood clot attract inflammatory cells including polymorphonuclear leukocytes (PMNs) and macrophages into the wound. PMNs are involved in phagocytosis and clearance of debris, damaged cells and bacteria. They also release large amount of inflammatory cytokines and growth factors. About two days after injury, macrophages replace PMNs and become predominant cell type in the wound and continue to secrete major growth factors such as transforming growth factor-b1 (TGF-b1) and platelet drive growth factor (PDGF). In addition to phagocytosis and immune response, macrophages have been proposed to influence re- epithelialization, granulation tissue formation, matrix deposition and angiogenesis. During inflammatory phase, fibroblasts and endothelial cells release anti- bacterial superoxide in order to protect the wound from infection. In addition, superoxidase induces cell signaling for further stimulation of growth factor release. Taken together, the inflammatory response during wound healing provides pivotal conditions for resistance to wound infections and a bridge between earlier phases of wound healing and later stages when wound is repaired and stabilized.

Re-epithelialization

Immediately after injury, cytokines released from platelets activate keratinocytes. Migration of keratinocytes and hence re-epithelialization starts as early as two hours after wounding. Growth factors such as keratinocytes growth factor (KGF) and epidermal growth factor (EGF) induce proliferation and migration of keratinocytes. The main sources of migrating keratinocytes during re-epithelialization process are basal keratinocytes from the wound edges, dermal appendages such as hair follicles, sweat glands and sebacious glands and bone marrow derived keratinocyte stem cells. Keratinocytes secrete proteases and plasminogen activator that activates plasmin, which dissolves the clot, debris, and parts of the ECM and promote cell migration. Migration of keratinocytes over the wound site is also enhanced by lack of contact inhibition and nitric oxide released from PMNs, keratinocytes and fibroblasts. Epithelial cells continue migrating across the wound bed until cells from different sides meet in the middle, at which point contact between keratinocytes inhibits further migration. Subsequently, new layers of keratinocytes differentiate and give rise to a stratified epidermis. Additionally, wound contraction by myofibroblasts present in the granulation tissue accelerates wound closure by bringing wound edges closer together. Fast keratinocyte migration and re-epithelialization often leads to better wound healing outcomes and decreased scar formation. In contrast, exposure to air and / or lack of moisture retards healing process. Keratinocytes are also involved in angiogenesis, matrix production, chemoattraction and mitogenic activity by releasing vascular endothelial growth factor (VEGF), PDGF, and transforming growth factor-a (TGF-a).

Figure 1
Summary of inflammation showing key inflammatory cells - mast cells and neutrophils
Courtesy of Birmingham City University - Faculty of Health Physiology
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Granulation tissue formation
The granulation tissue formation phase is characterized by fibroplasia in which the number of fibroblasts is increased in the wound. Soon after injury, local resident fibroblasts migrate into the wound site, undergo proliferation and constitute the granulation tissue. The number of fibroblasts that are involved in phagocytosis and deposition of new ECM in the wounded area peaks at one to two weeks post-wounding making them the dominant cells type in the granulation tissue. Depending on their origin, fibroblasts in the wound granulation tissue show phenotypically and functionally distinct characteristics that determine how they respond to wound healing stimulation. Cells involved in the granulation tissue formation and wound healing are originated from different sources. For example, stem cells derived from muscle and adipose tissue, mesenchymal stem cell-like cells from surrounding healthy, unwounded tissue, perivascular cells and cells form the dermal sheath of the hair follicles have been suggested to contribute to granulation tissue formation. Granulation tissue is also populated by circulating blood-borne cells such as fibrocytes that can differentiate into myofibroblasts. Fibrocytes also secrete angiogenic factors that induce neovascularization during wound healing. Pericytes and bone marrow-derived endothelial progenitor cells that enter to the blood circulation in response to cytokine released from the injury also integrate into the granulation tissue at the sites of new blood vessel growth. In addition, newly discovered relatively poorly characterized blood-derived Dot cells that are believed to promote scarless dermal wound healing also migrate to wound, differentiate and reside in the granulation tissue. Similarities in the structure and cell populations of both skin and oral mucosa suggest that in both tissues progenitor cells involved in wound healing may be recruited from similar origins with the exception that oral mucosa obviously lacks hair follicle-derived cells. Granulation tissue also contains increased number of inflammatory cells such as macrophages and a provisional ECM that is mainly composed of fibronectin, type III collagen, glycosaminoglycans, proteoglycans and hyaluronan. The provisional matrix provides hydrated matrix that facilitates migration of cells to the granulation tissue. In addition, low oxygen environment stimulates neovascularization by inducing macrophages and platelets to secrete angiogenic factors such as fibronectin and increase growth factors that attract endothelial cells to the granulation tissue. Endothelial cells themselves secrete collagenases and plasminogen activator to degrade the clot ECM to facilitate their motility. Formation of new blood vessels continues increasingly in granulation tissue until after three to four weeks when their number decreases through apoptosis. Upon changes in ECM microenvironment caused by wounding, fibroblasts evolve into the proto-myofibroblasts that will subsequently differentiate to myofibroblasts characterized by the expression of a-smooth muscle actin (a-SMA). Transition of fibroblasts to proto-myofibroblasts and to a-SMA expressing myofibroblasts is thought to be regulated by extra domain A (EDA) fibronectin, growth factors such as TGF-b and PDGF and by mechanical tension incurred from wounding and contraction. Myofibroblasts use a2b1 integrin to attach to collagen and pull collagen using actin-rich cytoskeleton that is linked to the cytoplasmic tail of a2b1 integrin. Therefore, in addition to synthesis of ECM components, particularly type I collagen, myofibroblasts regulate wound contraction and ECM reorganization. Around after two weeks, soon after the formation of new epithelium over the granulation tissue, the number of myofibroblasts starts to decrease through apoptosis.

Figure 2

Proliferative phase of wound healing showing fibroblasts producing extracellular matrix and re-epithelialisation by keratinocytes
Courtesy of Birmingham City University - Faculty of Health Physiology
wound_healing2-_proliferative_phase.bmp
Maturation and tissue remodeling
During wound healing, ECM components undergo substantial changes that include transition from clot of fibrin and fibronectin to a mixture of hyaluronate, proteoglycans and collagen. Initially, collagen is deposited as a thin and randomly organized network that gradually is increased in thickness, rearranged, cross-linked and aligned. This leads to replacement of provisional matrix with collagen fiber bundles that more closely resembles to normal unwounded tissue. During wound maturation and tissue remodeling phase, type III collagen, that is abundant during granulation tissue formation, is gradually degraded and type I collagen becomes dominant. During several weeks to few months, as the remodeling phase progresses, the tensile strength of the wound increases with the strength reaching about 80% that of normal tissue. Depending on the size and location of the wound the maturation phase can last from months to years after the injury. However, balance in synthesis and degradation of collagen appears to be critical for a normal connective tissue remodeling and ECM reorganization. For example, in gingiva the degradation and remodeling of collagen-rich ECM are essential in maintaining normal oral mucosal connective tissue composition. In vitro studies suggest that the uptake and lysosomal degradation of collagen by fibroblasts comprises a major pathway in the turnover of collagen and connective tissue remodeling. The uptake of collagen by fibroblasts involves binding of collagen fibrils to the specific cell surface receptors. For example, phagocytosis of collagen by fibroblasts is mediated mostly by a2b1 integrin. In addition, urokinase-type plasminogen activator receptor-associated protein (uPARAP)/Endol80(CD280), an endocytic receptor expressed on the cell surface, also binds to and mediates endocytosis of collagen for lysosomal degradation but its expression during wound healing is not known. Matrix metalloproteinases (MMPs) released by fibroblasts cleave most of the ECM molecules and are also involved in the breakdown and remodeling during wound healing. Collagenases such as MMP1, MMP2, MMP8, MMP9, MMP13 and MMP14 that degrade connective tissue collagen, gelatinases such as MMP2 and MMP9 that degrade basement membrane collagens and stromelysins such as MMP3, MMP10, and MMP11 that degrade ECM proteoglycans, laminin, fibronectin, and gelatin play an important role in ECM turnover and remodeling during wound healing. Thus, abnormalities in MMP activity and/or endocytosis or phagocytosis of ECM components may be associated with accumulation of excess collagen and scar formation.

Figure 3

Summary of wound healing events illustrating different phases and cells involved.

Wound_hualing_phases.jpg

Scar formation after skin wound

Hypertrophic Scar Formation

In skin, abnormalities in wound healing process may lead to delayed healing or excess fibrosis and scar formation. Scars are fibrous tissues that replace normal tissue at the site of injury. When scaring occurs in skin it may result in significant cosmetic, functional and psychological impairments. Minor scars of skin are usually flat and pale with a trace of the original wound. Compared to other type of scars, they contain less collagen and connective tissue cells. In contrast, over-healing results in excessive collagen deposition and formation of keloids or hypertrophic scars. They are characterized by excess amounts of thick unorganized collagen fibers that are randomly aligned as compared to normal basket-wave orientation in unwounded tissue. Hypertrophic scars are red, raised and itchy lumps on the skin and are limited in the boundaries of the original wound. Keloids that occur in about 10% of population are larger and grow beyond the original wound zone. Analysis of scar-inducing factors has been the center of attention in many studies. Excess activity of TGF-b1 released from platelets and inflammatory cells in the first phase of wound healing, failure to eliminate myofibroblasts from granulation tissue and reduced collagen breakdown at later time points have been considered as conditions that lead to formation of hypertrophic scars. Although some observations did not detect changes in the population of myofibroblasts in hypertrophic scars, increased number of myofibroblasts has been observed in other studies. Furthermore, increased inflammatory response resulting in excess release of cytokines and fibrotic growth factors has been shown to promote keloid and hypertrophic scar formation.

Hypertrophic Scar
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A Fibroblast Cell
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In the skin, fibroblasts are major cell types that regulate wound healing and collagen synthesis. Excess production of collagen by fibroblasts leads to hypertorphic scar formation.

Collagen fibrillogenesis and its role in skin

What is collagen?

Collagen is one of the most plentiful proteins present in the bodies of mammals. Collagen is fibrous in nature, connects and supports tissues and organs such as skin, bone, tendons, muscles, and cartilage. Generally it is referred to be as the glue that holds the body together. It means that without collagen that provides tensile strength and attachment for the tissues, the body would, relatively, fall apart. There are more than 25 types of collagens that naturally occur in the body. Collagen can be found both inside and outside of cells. Collagen fibers are important in contributing to the external structure of cells. However, they are present on the inside of some cells as well.

Molecular Structure of Collagen

Cross sectional view of tendon looks white and shiny. This is how type I collagen, a typical structural collagen, looks like. Microscopic examination of tendon shows long, wavy bundles of fibers 10 microns thick (a human hair is 50 to 100 microns). Like the fibers of a rope, collagen fibers are made up of smaller structures, namely fibrils. These fibrils appear long, smooth and uniform in a regular pattern in which smaller units are joined together. Collagen fibrils are made of many individual collagen molecules packed together. Each collagen molecule is a triple helix formed from three protein chains twisted together in a specific shape resulting in a robust, steady protein string. Collagen molecules are mass-produced by the cells called fibroblasts identical in composition and size which is 300 nanometers long by 1.5 nanometers wide. To form collagen fibrils, the collagen molecules are stacked in bundles with the ends offset. The gaps between sets of individual collagen molecules appear as bands in the fibrils. Collagens are composed of hundreds of amino acids linked together through amide bonds. Two kinds of amino acid in particular, play a major role in collagen's structure: proline and glycine. The proline is modified into the more polar hydroxyproline after it has been incorporated into the chain. Glycine is the smallest amino acid, and it appears as every third amino acid in the sequence. Glycine's small size gives it the flexibility to accommodate the twists and turns of the chain as it forms a helix.

Collagen and skin health

Abnormalities to collagen in the skin may results in lack of tensile strength and fragility. Unfortunately, due to many factors, skin begins looking less and less healthy as people age. Particularily, sun exposure damages the skin's collagen and affects connective tissues normal constituents. As a result, facial veins, wrinkles on the face, sagging skin, and thinning of lips may appear as people age. The skin begins to lose its elasticity and the fibrous protein matrix made of collagen and elastin in the skin becomes rigid as the harmful UV radiation of sun doe's more and more damage.

Collagen fiber anatomy

Small Leucine-rich Proteoglycan

The small leucine-rich proteoglycans (SLRPs) are a family of proteins that are present in extracellular matrix and that share in common multiple repeats of a leucine-rich structural motif, flanked by cysteine residues. These proteins appear to interact in many cases with collagen, modifying the deposition and arrangement of collagen fibers in the extracellular matrix, and also with cells and with soluble growth factors. The interaction of SLRPs with cells and with growth factors like TGF-beta may affect the proliferation of cells in addition to modifying the extracellular environment. Postranslational modification of SLRPs with carbohydrates and sulfate-containing groups appears to modify the function of SLRPs. Changes in SLRP expression and modification in cornea, atherosclerotic plaque, joints, bone, tendons, and kidney may be associated with disease progression in those tissues. Decorin is one SLRP expressed throughout the body that stabilizes collagen fibrils and that also antagonizes the action of the cytokine TGF-beta, blocking cell cycle progression, and potentially playing a role in cancer and wound healing. The SLRP biglycan is expressed in bone and other connective tissues and genetic disruption of biglycan in mice causes low bone mass similar to osteoporosis.