The extracellular matrix (ECM) regulates cell behavior by influencing cell proliferation, survival, shape, migration and differentiation. Far from being a static structure, the ECM is constantly undergoing remodeling--i.e. assembly and degradation--particularly during the normal processes of development, differentiation and wound repair. When misregulated, this can contribute to disease. ECM assembly is regulated by the 3D environment and the cellular tension that is transmitted through integrins. Degradation is controlled by complex proteolytic cascades, and misregulation of these results in ECM damage that is a common component of many diseases. Tissue engineering strives to replace damaged tissues with stem cells seeded on synthetic structures designed to mimic the ECM and thus restore the normal control of cell function. Stem cell self-renewal and differentiation is influenced by the 3D environment within the stem cell niche. For tissue-engineering strategies to be successful, the intimate dynamic relationship between cells and the ECM must be understood to ensure appropriate cell behavior.

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Extracellular matrix dynamics in development and regenerative medicine.

Significance: Fibroblasts play a critical role in normal wound healing. Various extracellular matrix (ECM) components, including collagens, fibrin, fibronectin, proteoglycans, glycosaminoglycans, and matricellular proteins, can be considered potent protagonists of fibroblast survival, migration, and metabolism. Recent Advances: Advances in tissue culture, tissue engineering, and ex vivo models have made the examination and precise measurements of ECM components in wound healing possible. Likewise, the development of specific transgenic animal models has created the opportunity to characterize the role of various ECM molecules in healing wounds. In addition, the recent characterization of new ECM molecules, including matricellular proteins, dermatopontin, and FACIT collagens (Fibril-Associated Collagens with Interrupted Triple helices), further demonstrates our cursory knowledge of the ECM in coordinated wound healing. Critical Issues: The manipulation and augmentation of ECM components in the healing wound is emerging in patient care, as demonstrated by the use of acellular dermal matrices, tissue scaffolds, and wound dressings or topical products bearing ECM proteins such as collagen, hyaluronan (HA), or elastin. Once thought of as neutral structural proteins, these molecules are now known to directly influence many aspects of cellular wound healing. Future Directions: The role that ECM molecules, such as CCN2, osteopontin, and secreted protein, acidic and rich in cysteine, play in signaling homing of fibroblast progenitor cells to sites of injury invites future research as we continue investigating the heterotopic origin of certain populations of fibroblasts in a healing wound. Likewise, research into differently sized fragments of the same polymeric ECM molecule is warranted as we learn that fragments of molecules such as HA and tenascin-C can have opposing effects on dermal fibroblasts.

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Extracellular Matrix and Dermal Fibroblast Function in the Healing Wound

The salmon louse (SL) is an ectoparasitic caligid crustacean infecting salmonid fishes in the marine environment. SL represents one of the major challenges for farming of salmonids, and veterinary intervention is necessary to combat infection. This study addressed gene expression responses of Atlantic salmon infected with SL, which may account for its high susceptibility. The effects of SL infection on gene expression in Atlantic salmon were studied throughout the infection period from copepodids at 3 days post infection (dpi) to adult lice (33 dpi). Gene expression was analyzed at three developmental stages in damaged and intact skin, spleen, head kidney and liver, using real-time qPCR and a salmonid cDNA microarray (SFA2). Rapid detection of parasites was indicated by the up-regulation of immunoglobulins in the spleen and head kidney and IL-1 receptor type 1, CD4, beta-2-microglobulin, IL-12β, CD8α and arginase 1 in the intact skin of infected fish. Most immune responses decreased at 22 dpi, however, a second activation was observed at 33 dpi. The observed pattern of gene expression in damaged skin suggested the development of inflammation with signs of Th2-like responses. Involvement of T cells in responses to SL was witnessed with up-regulation of CD4, CD8α and programmed death ligand 1. Signs of hyporesponsive immune cells were seen. Cellular stress was prevalent in damaged skin as seen by highly significant up-regulation of heat shock proteins, other chaperones and mitochondrial proteins. Induction of the major components of extracellular matrix, TGF-β and IL-10 was observed only at the adult stage of SL. Taken together with up-regulation of matrix metalloproteinases (MMP), this classifies the wounds afflicted by SL as chronic. Overall, the gene expression changes suggest a combination of chronic stress, impaired healing and immunomodulation. Steady increase of MMP expression in all tissues except liver was a remarkable feature of SL infected fish. SL infection in Atlantic salmon is associated with a rapid induction of mixed inflammatory responses, followed by a period of hyporesponsiveness and delayed healing of injuries. Persistent infection may lead to compromised host immunity and tissue self-destruction.

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Local and systemic gene expression responses of Atlantic salmon (Salmo salar L.) to infection with the salmon louse (Lepeophtheirus salmonis)

Delayed wound healing is one of the complications of diabetes mellitus. The present study was performed to investigate the effect of Aloe vera oral administration on open wounds in type 2 diabetic rats. Full thickness open wounds (1.5 × 1.5 cm) were created under general anesthesia on the backs of the rats. These rats were divided into two group, a control group (Group C) and an Aloe vera oral administration group (Group A). Each wound area was measured on days 1, 2, 4 and 8 postwounding. The stages of wound granulation tissues were evaluated histopathologically. The expression of transforming growth factor (TGF)-β1 and vascular endothelial growth factor (VEGF) were determined by immunohistochemically. The wounds were significantly contracted in Group A on days 2, 4 and 8 postwounding. Histological results revealed that the inflammatory cell infiltration, angiogenesis, extracellular matrix deposition and epithelialization were promoted in Group A, respectively. The immunohistochemical results revealed that both TGF-β1 and VEGF protein-positive cells increased in Group A on day 4 postwounding. We concluded that Aloe vera oral administration accelerated wound healing in type 2 diabetic rats.

The Effect of Aloe Vera Oral Administration on Cutaneous Wound Healing in Type 2 Diabetic Rats

Production-scale fibronectin nanofibers promote wound closure and tissue repair in a dermal mouse model.

Plasma fibronectin (FN) has a broad range of biological functions involved in cellular adhesion, motility, differentiation, apoptosis, hemostasis, wound healing, reticuloendothelial system function, and ischemic injury. In this study, we examined the effects of FN on D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced fulminant liver failure in mice. Female Balb/c mice received intraperitoneal injection of 50 mug/kg of LPS and 400 mg/kg of GalN simultaneously. Thirty minutes before GalN/LPS administration, human plasma FN (FN group) or the same dose of human serum albumin (control group) was given intravenously. GalN/LPS induced a marked decrease in plasma FN, which was reversed by FN pretreatment. The survival rate of the FN group was markedly improved in a dose-dependent manner compared with that of the control group (survival rate 0%). FN prevented increases in the concentrations of serum enzymes and total bilirubin related to liver injury. FN pretreatment significantly suppressed tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and interleukin (IL)-6 levels, and enhanced IL-10 levels in serum and liver tissue compared with the control group. Moreover, TUNEL staining, caspase 3 and 8 activities, and necrosis in the remnant liver were significantly decreased in the FN-treated rats compared with the controls. Furthermore, FN pretreatment inhibited the activation of nuclear factor (NF)-kappaB and increased the expression of Bcl-xL protein in liver tissue. These results suggest that FN protected against GalN/LPS-induced liver failure by a mechanism involving inhibition of NF-kappaB activation, which caused down-regulation of TNF-alpha and involved up-regulation of IL-10, and elevation of Bcl-xL induced a blockage of apoptotic signals, by which apoptosis of hepatocytes caused by GalN/LPS was suppressed.

Fibronectin prevents D-galactosamine/lipopolysaccharide-induced lethal hepatic failure in mice.

Fibronectin (Fn) has been shown to play an important role in wound healing because it appears to be the stimulus for migration of fibroblasts and epidermal cells. The purpose of this study was to investigate whether topical application of plasma Fn (pFn) improves healing of full-thickness skin wounds in rats. A round section of full-thickness skin (diameter of approximately 15 mm) was resected in rats. Animals were then divided into two groups, and wounds were treated topically with a single application of human plasma albumin (control group) or human pFn (FN group). Wound closure rate, hydroxyproline concentration, and histologic features (immunohistochemical staining) were evaluated. The FN group had a significantly higher wound closure rate and hydroxyproline level in the skin than the control group. Histologic analysis of macrophage and fibroblast migration, collagen regeneration, and epithelialization were significantly increased in the FN group compared with the control group. A single topical application of pFn increased the migration of macrophages, myofibroblasts, and fibroblasts. Moreover, further release of transforming growth factor-beta1 from activated fibroblasts, keratinocytes, and epithelial cells may also contribute to the beneficial effect of pFn on wound healing.

Yutaka Hirao

Papers

Fibronectin prevents D-galactosamine/lipopolysaccharide-induced lethal hepatic failure in mice.

Topical Application of Plasma Fibronectin in Full-Thickness Skin Wound Healing in Rats