Gregory S. Schultz

Keratinocyte Collagenase-1 Expression Requires an Epidermal Growth Factor Receptor Autocrine Mechanism

In response to cutaneous injury, expression of collagenase-1 is induced in keratinocytes via α2β1 contact with native type I collagen, and enzyme activity is essential for cell migration over this substratum. However, the cellular mechanism(s) mediating integrin signaling remain poorly understood. We demonstrate here that treatment of keratinocytes cultured on type I collagen with epidermal growth factor receptor (EGFR) blocking antibodies or a specific receptor antagonist inhibited cell migration across type I collagen and the matrix-directed stimulation of collagenase-1 production. Additionally, stimulation of collagenase-1 expression by hepatocyte growth factor, transforming growth factor-β1, and interferon-γ was blocked by EGFR inhibitors, suggesting a required EGFR autocrine signaling step for enzyme expression. Collagenase-1 mRNA was not detectable in keratinocytes isolated immediately from normal skin, but increased progressively following 2 h of contact with collagen. In contrast, EGFR mRNA was expressed at high steady-state levels in keratinocytes isolated immediately from intact skin but was absent following 2 h cell contact with collagen, suggesting down-regulation following receptor activation. Indeed, tyrosine phosphorylation of the EGFR was evident as early as 10 min following cell contact with collagen. Treatment of keratinocytes cultured on collagen with EGFR antagonist or heparin-binding (HB)-EGF neutralizing antibodies dramatically inhibited the sustained expression (6–24 h) of collagenase-1 mRNA, whereas initial induction by collagen alone (2 h) was unaffected. Finally, expression of collagenase-1 in ex vivo wounded skin and re-epithelialization of partial thickness porcine burn wounds was blocked following treatment with EGFR inhibitors. These results demonstrate that keratinocyte contact with type I collagen is sufficient to induce collagenase-1 expression, whereas sustained enzyme production requires autocrine EGFR activation by HB-EGF as an obligatory intermediate step, thereby maintaining collagenase-1-dependent migration during the re-epithelialization of epidermal wounds.

Epidermal Growth Factor in Wound Healing: A Model for the Molecular Pathogenesis of Chronic Wounds

Wound healing in the skin is a complex biological process that has been extensively characterized at the light microscope level. However, regulation of skin wound healing is only partially understood at the molecular level. Skin wound healing can be divided into three general phases: (a) the inflammatory phase, (b) the repair phase, and (c) the remodeling phase. There is considerable temporal overlap of these stages of healing and the entire process lasts for several months (1, 2).

Mechanisms of Vascular Disease: Principles of wound healing

INTRODUCTION Acute wounds normally heal in an orderly and efficient manner, and progress smoothly through the four distinct, but overlapping phases of wound healing: haemostasis, inflammation, proliferation and remodelling (Figure 23.1). In contrast, chronic wounds will similarly begin the healing process, but will have prolonged inflammatory, proliferative, or remodelling phases, resulting in tissue fibrosis and in non-healing ulcers. The process of wound healing is complex and involves a variety of specialized cells, such as platelets, macrophages, fibroblasts, epithelial and endothelial cells. These cells interact with each other and with the extracellular matrix. In addition to the various cellular interactions, healing is also influenced by the action of proteins and glycoproteins, such as cytokines, chemokines, growth factors, inhibitors, and their receptors. Each stage of wound healing has certain milestones that must occur in order for normal healing to progress. In order to identify the differences inherent in chronic wounds that prevent healing, it is important to review the process of healing in normal wounds PHASES OF ACUTE WOUND HEALING Haemostasis Haemostasis occurs immediately following an injury. To prevent exsanguination, vasoconstriction occurs and platelets undergo activation, adhesion and aggregation at the site of injury. Platelets become activated when exposed to extravascular collagen (such as type I collagen), which they detect via specific integrin receptors, cell surface receptors that mediate a cells interactions with the extracellular matrix. Once in contact with collagen, platelets release the soluble mediators (growth factors and cyclic AMP) and adhesive glycoproteins, which signal them to become sticky and aggregate.