Age-related differences in the temporal and spatial regulation of matrix metalloproteinases (MMPs) in normal skin and acute cutaneous wounds of healthy humans

Proteolytic events of wound-healing--coordinated interactions among matrix metalloproteinases (MMPs), integrins, and extracellular matrix molecules

During wound-healing, cells are required to migrate rapidly into the wound site via a proteolytically generated pathway in the provisional matrix, to produce new extracellular matrix, and, subsequently, to remodel the newly formed tissue matrix during the maturation phase. Two classes of molecules cooperate closely to achieve this goal, namely, the matrix adhesion and signaling receptors, the integrins, and matrix-degrading and -processing enzymes, the matrix metalloproteinases (MMPs). There is now substantial experimental evidence that blocking key molecules of either group will prevent or seriously delay wound-healing. It has been known for some time now that cell adhesion by means of the integrins regulates the expression of MMPs. In addition, certain MMPs can bind to integrins or other receptors on the cell surface involved in enzyme activation, thereby providing a mechanism for localized matrix degradation. By proteolytically modifying the existing matrix molecules, the MMPs can then induce changes in cell behavior and function from a state of rest to migration. During wound repair, the expression of integrins and MMPs is simultaneously up-regulated. This review will focus on those aspects of the extensive knowledge of fibroblast and keratinocyte MMPs and integrins in biological processes that relate to wound-healing.

Aging and survival of cutaneous microvasculature

The growth and turnover of blood vessels in the skin is fundamental in normal development, wound repair, hair follicle cycling, tumor cell metastasis, and in many different states of cutaneous pathology. Whereas many investigations are focused on mechanisms of angiogenesis in the skin, the influence of cellular aging and replicative senescence (i.e., the inability, after a critical number of population doublings, to replicate) on microvascular remodeling events has received relatively less attention. In this article, we review the clinical and pathologic relationships associated with cutaneous vascular aging and update current knowledge of endothelial cell survival characteristics. A hypothesis is presented in which endothelial cell aging and survival are linked to molecular mechanisms controlling cell proliferation, quiescence, apoptosis, and cellular senescence. We review recent results demonstrating how activation of telomerase in human dermal microvascular endothelial cells affects their durability both in vitro and in vivo and conclude by linking these studies with current concepts involving endothelial cell precursors, control of postnatal somatic cell telomerase activity, and murine model systems.

Regulation of collagenase expression during replicative senescence in human fibroblasts by Akt-forkhead signaling

The expression of collagenase (matrix metalloproteinase 1) in human fibroblasts increases during aging both in vivo and in vitro. This age-associated increase in collagenase expression has been postulated to contribute to the age related decline in tissue function by increasing proteolysis of matrix components, but little is known regarding the regulation of collagenase expression. We examined the role that the serine/threonine kinase Akt plays in collagenase expression during in vitro senescence of WI-38 normal human lung fibroblast cells. Our results indicate that Akt-mediated signals, acting through the forkhead transcription factor FKHRL1, can regulate collagenase expression in WI-38 fibroblasts. Dominant negative forms of Akt increase collagenase promoter activity in early passage WI-38 fibroblasts, whereas an active form of Akt suppresses steady state levels of collagenase mRNA in senescent WI-38 fibroblasts. In addition, the activity of a synthetic promoter containing forkhead-specific binding sites, as measured by luciferase activity, is much higher in senescent cells compared with early passage WI-38 fibroblasts. These results indicate that members of the forkhead family of transcription factors play a role in the regulation of the collagenase promoter and that increased activity of forkhead transcription factors may underlie the increase in collagenase expression observed during replicative senescence.

Ectopic localization of matrix metalloproteinase-9 in chronic cutaneous wounds

It has been hypothesized that excessive activity of matrix metalloproteinases (MMPs), in particular the gelatinases MMP-9 and MMP-2, contributes to poor healing of chronic skin ulcers. We compared MMP-9 and MMP-2 in wound margin biopsies of standardized acute partial-thickness wounds in healthy volunteers (n = 6) and in venous leg ulcer patients (n = 12) with those of chronic wounds of different etiologies (n = 34) by a combination of specific analyses of activity and protein localization. We also studied MMP-14 by immunohistochemistry and in situ hybridization in parallel. Neither MMP-9 (P =.814) nor MMP-2 (P =.742) endogenous activities differed significantly between acute and chronic wound tissues. Acute wound healing was characterized by induction of MMP-9 in the advancing epithelium. In chronic wounds, prominent MMP-9 immunostaining was seen in neutrophils and macrophages in the ulcer bed, but virtually no MMP-9 was detected in wound edge keratinocytes. MMP-2 was increased and activated with acute wound age. MMP-2 was found abundantly in dermal fibroblasts and endothelial cells beneath, but not in new epithelium of acute and chronic wounds. MMP-14 mRNA or protein was detected solely in the stroma of both acute and chronic wounds. In conclusion, the overall activity of gelatinases MMP-9 and MMP-2 was not increased in chronic wounds compared to normally healing wound tissues. Chronic nonhealing wounds may not be caused by excessive gelatinase activity, but are distinguished from healing wounds by an unfavorable distribution and persistance of MMP-9.

Age-related changes in wound healing

Evidence for age-related effects on wound healing have been derived for the most part from empirical observations without adjustment for confounders other than age. Age-related changes in the structure and function of the skin do occur. Some of these changes result from chronic solar radiation exposure rather than chronological age per se. The tensile strength of wounds, accumulation of wound healing factors and rate of wound closure have all been examined in relation to chronological aging. However, the clinical impact of these changes in acute wound healing appears to be small. Poor healing in chronic wounds is more often related to comorbid conditions rather than age alone. Since the majority of these chronic wounds occur in elderly populations, this has contributed to the conclusion that aging itself may influence healing. Progress in understanding the role that growth factors play in wound healing and the ability to synthesise adequate quantities of these factors for clinical use has led to clinical trials evaluating their use in wound healing. The results of these studies, with the possible exception of those in diabetic wounds, have been disappointing. Insight into the wound healing process indicates that growth factors interact during wound healing in a sequential and orderly process. Improved wound healing may require different clinical designs or the use of these factors in a precisely timed sequential administration.

Matrix metalloproteinase inhibitor BB-3103 unlike the serine proteinase inhibitor aprotinin abrogates epidermal healing of human skin wounds ex vivo

Several matrix metalloproteinases and serine proteinases are upregulated in migrating keratinocytes during cutaneous wound repair. Single cell culture studies indicate the necessity for matrix metalloproteinases but not for serine proteinases in keratinocyte locomotion. To account for epithelial-mesenchymal interactions, an ex vivo human skin wound model was used to investigate the contribution of matrix metalloproteinases and serine proteinases to wound healing by treatment with broad-spectrum inhibitors of matrix metalloproteinases (BB-3103) or serine proteinases (aprotinin). Human skin explants with circular 3 mm superficial defects were incubated in culture medium without (controls) or with the proteinase inhibitors for 7 d. BB-3103 abrogated epithelialization (p < 0.001), whereas aprotinin-treated wounds and controls were covered with new epithelium. Lack of epithelialization was unlikely due to cytotoxicity because the matrix metalloproteinase inhibitor did neither influence viability of cultured epidermal keratinocytes nor apoptosis in wounds. Involvement of specific matrix metalloproteinases in epithelialization was analyzed by gelatin zymography, western blotting, immunohistochemistry, and in situ hybridization. Wound healing was accompanied by active matrix metalloproteinase-1 and increased active matrix metalloproteinase-2 but irrespectively of active matrix metalloproteinase-9. BB-3103 blocked activation of matrix metalloproteinase-2 and matrix metalloproteinase-9 but not of matrix metalloproteinase-1. Active matrix metalloproteinase-2 localized solely to the dermis, whereas matrix metalloproteinase-9 was consistently found in new epithelium. Membrane-type 1 matrix metalloproteinase was undetectable in wound keratinocytes. BB-3103 and aprotinin reduced tumor necrosis factor-alpha in media but did not appreciably alter amounts of other soluble regulators of matrix metalloproteinases and epithelialization. Our findings demonstrate that keratinocyte migration is associated with active matrix metalloproteinase-2 but occurs independently of serine proteinases and active matrix metalloproteinase-9 in fibrin-deficient skin wound healing.

Expression of matrix metalloproteinase (MMP-1) and tissue inhibitor of MMP in serosal tissue of intraperitoneal organs and adhesions

OBJECTIVE

To compare expression of matrix metalloproteinase (MMP-1) and tissue inhibitor of MMP (TIMP-1) in serosal tissue of intraperitoneal organs and adhesions.

DESIGN

Prospective and cross-sectional study.

SETTING

Academic research centers.

PATIENT(S)

Patients undergoing abdominal or pelvic surgery.

INTERVENTION(S)

MMP-1 and TIMP-1 expression.

MAIN OUTCOME MEASURE(S)

Expression of messenger ribonucleic acid (mRNA) and protein was measured by using quantitative reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay.

RESULT(S)

Serosal tissue of intraperitoneal organs and adhesions express MMP-1 and TIMP-1 mRNA and protein at levels that are consistently varied with 10- to 10,000-fold and 2- to 10-fold higher TIMP, mRNA and protein, respectively. Parietal peritoneum, fallopian tubes and ovaries express higher MMP-1 mRNA levels compared with uterus and adhesions; the lowest expression is found in small and large bowels, subcutaneous tissue. and omentum. Expression of TIMP-1 mRNA was less variable; the highest level was found in the uterus and the lowest in subcutaneous tissue and small bowels. There was less variability in MMP-1 and TIMP-1 protein content than mRNA expression; ovaries and adhesions contained the highest MMP-1 and TIMP-1 levels, respectively, and peritoneum contained the lowest. The MMP-1 and TIMP-1 content and ratios further indicate limited MMP-1 proteolytic activity. Although tissues from premenopausal women express more MMP-1 and TIMP-1, expression did not differ by sex or age.

CONCLUSION(S)

Because MMP-1 and TIMP-1 expression varies consistently among the serosal tissues of peritoneal organs and adhesions, and because tissue injury alters their expression, site-specific variations in expression of these substances may predispose a particular organ to develop more adhesions.

Topical synthetic inhibitor of matrix metalloproteinases delays epidermal regeneration of human wounds

Matrix metalloproteinases (MMPs) degrade extracellular proteins during epithelialization of wounds. To evaluate the biological significance of MMPs in epidermal healing, the synthetic broad-spectrum MMP inhibitor GM 6001 (also called Galardin and Ilomastat) was applied topically to standardized human wounds. GM 6001 (10 microg/microl) or vehicle alone was applied every second day onto 4 de-roofed 6 mm suction blister wounds on the volar forearm of healthy male volunteers for 12 days. GM 6001 delayed healing by 2-4 days as assessed macroscopically and microscopically. In situ hybridization or immunohistochemistry showed that MMP-1 (interstitial collagenase) was present in and MMP-2 (gelatinase A) close to laterally migrating keratinocytes whereas MMP-9 (gelatinase B) was seen during maturation of new epidermis. MMP-1 was undetectable in blister roofs (normal epidermis) and found in low levels in normal skin. Total MMP-1 activities increased about 100-fold in wounds, independent of treatment, compared to normal skin as analyzed by specific ELISA-based activity assay. By gelatin zymography, MMP-2, but not MMP-9, was detected in blister roofs and wound healing was associated with increased active MMP-2 and latent MMP-9 levels. GM 6001 prevented activation of MMP-2 and increased latent MMP-9 levels. GM 6001 delayed re-appearance of laminin-5, the synthesis of which correlated with epidermal regeneration. Restoration of stratum corneum, measured indirectly by transepidermal water loss, was also impaired (P<0.05) in the GM 6001 group. In conclusion, pharmacological MMP inhibition delayed epidermal regeneration in vivo, suggesting that MMPs are required to restore epidermis after epidermal ablation in humans.

Impaired migration, integrin function, and actin cytoskeletal organization in dermal fibroblasts from a subset of aged human donors

Deficits in the motility of fibroblasts contribute to age-related impairment of wound healing. We analyzed 'young' fibroblasts from four healthy donors 22-30 years old and 'aged' fibroblasts from six healthy donors 81-92 years old for migratory ability on type I collagen, secretion of matrix metalloproteases (MMPs), attachment to matrices and, expression and function of integrin alpha2beta1. Cells from each donor were analyzed separately in each experiment. Whereas migration of young fibroblasts was uniformly robust, three aged lines migrated well and three migrated poorly. Synthesis of MMP1 and TIMP1, but not MMP2 or MMP9, was increased in the aged fibroblasts relative to the young fibroblast lines irrespective of their motility. All lines of young and aged fibroblasts attached to plastic or collagen with similar efficiency. Although young and aged fibroblasts expressed comparable levels of the alpha2 integrin; the lines of aged fibroblasts that were poor migrators exhibited a significant reduction in alpha2beta1 function relative to fibroblasts with normal migratory capacities. Moreover, the lines of aged fibroblasts that exhibited poor migration demonstrated a disordered actin cytoskeleton and a reduced ability to contract collagen gels. In conclusion, aged fibroblasts, unlike young fibroblasts, displayed variable migratory capacities. Deficient migration by specific lines of aged fibroblasts was not related to the capacity to attach, express alpha2 integrin, or secrete MMPs and TIMP1, but was characterized by disorganized cytoskeletal actin and reduced alpha2beta1 function.

Delayed wound healing in aged rats is associated with increased collagen gel remodeling and contraction by skin fibroblasts, not with differences in apoptotic or myofibroblast cell populations

Aging has been anecdotally reported to result in prolonged wound healing. Measurement of punch biopsy wound closure in young (4 month old) and old (36 month old) rats indicated there was a significant delay in wound closure by old rats during the early phase of repair, after which closure rates were equivalent. The delay in granulation tissue accumulation in older animals could involve premature programmed cell death (apoptosis); however, apoptotic fibroblasts in sponge granulation tissue and tissue culture were less abundant in samples from old rats relative to young rats. Myofibroblasts express alpha-smooth muscle actin, and they are believed to be important in wound contraction. There were no significant differences in overall abundance or distribution of alpha-smooth muscle actin containing myofibroblasts in granulation tissue and in cultured granulation tissue fibroblasts regardless of the age of the donor rat. The spatial distribution of myofibroblasts and apoptotic cells was distinct. Fibroblasts from granulation tissue and skin explants were placed in a collagen gel contraction assay prior to the 5th passage to determine their in vitro contractility. While granulation tissue fibroblasts from young and old rats showed similar collagen gel contractility, skin fibroblasts from old rats displayed greater collagen gel contractile behavior than young skin fibroblasts. Greater gel contractility of fibroblasts from old rats appeared to result, in large part, from the ability of those cells to cause generalized gel degradation. Gelatin zymography indicated a greater abundance of matrix metalloproteinase-2 in supernatants from gels containing skin fibroblasts from old rats. Taken together, these results suggest that the age-associated healing delay in the rat may not be related to the appearance or abundance of distinct myofibroblast or apoptotic cell populations. Proteolysis may have a significant role in delayed wound healing in aged animals.

Differential activation of migration by hypoxia in keratinocytes isolated from donors of increasing age: implication for chronic wounds in the elderly

Chronic wound healing conditions are often observed in elderly patients with poor tissue oxygenation. Impaired re-epithelialization is a hallmark of these wounds, which is seen in both clinical studies and in our animal models of impaired healing. To investigate the pathogenic mechanism of chronic wounds, we studied the effect of hypoxia on migration of keratinocytes isolated from human donors of increasing age. Keratinocytes from elderly donors had depressed migratory activity when exposed to hypoxia, as opposed to an increase in migration in young cells. Analysis of underlying biochemical changes demonstrated a differential activation of matrix metalloproteinases by hypoxia in keratinocytes isolated from the young and the old. Matrix metalloproteinases-1 and -9 and tissue inhibitor of matrix metalloproteinase-1 were strongly upregulated by hypoxia in young cells, whereas no induction was observed in aged cells. Furthermore, transforming growth factor-beta 1 signaling appears to be involved in the keratinocyte differential response to hypoxia, as transforming growth factor-beta type I receptor was upregulated by hypoxia in young cells, while there was no induction in aged cells. Transforming growth factor-beta neutralizing reagents blocked hypoxia-induced matrix metalloproteinase-1, matrix metalloproteinase-9 expression, and hypoxia-induced cell migration as well. Our results suggest that an age-related decrease in response to hypoxia plays a crucial part in the pathogenesis of retarded re-epithelialization in wound.

Defective extracellular matrix reorganization by chronic wound fibroblasts is associated with alterations in TIMP-1, TIMP-2, and MMP-2 activity

Chronic leg wounds are characterized by defective remodeling of the extracellular matrix, failure of reepithelialization, and prolonged inflammation. The hypothesis that this defective extracellular matrix remodeling is associated with phenotypic differences in the activity of the matrix metalloproteinases and tissue inhibitors of metalloproteinases was studied in chronic wound and patient-matched normal fibroblasts in three-dimensional collagen lattice systems. Chronic wound fibroblasts exhibited no differences in morphology or proliferation (p > 0.1) compared with patient-matched uninvolved dermal fibroblasts. The ability of chronic wound fibroblasts to reorganize extracellular matrix was significantly impaired, however, in comparison to the uninvolved dermal fibroblasts (p < 0.01). This difference in extracellular matrix reorganization was not related to differences in proliferation within the collagen lattices (p > 0.05) or attachment to type I collagen (p > 0.1). Marked differences were evident in matrix metalloproteinase-2 activity between chronic wound and patient-matched normal fibroblasts. Whereas levels of pro-matrix metalloproteinase-2 were similar between the two fibroblast populations (p > 0.1), the chronic wound fibroblasts exhibited significantly decreased levels of the 62 kDa active form of matrix metalloproteinase-2 (p < 0.01). Reverse zymography and enzyme-linked immunosorbent assay demonstrated that the decreased matrix metalloproteinase-2 activity was associated with increased production of tissue inhibitors of metalloproteinase-1 and -2 by the chronic wound fibroblasts (p < 0.05). Increased production of tissue inhibitors of metalloproteinases in chronic wound fibroblasts was also reflected in decreased levels of matrix metalloproteinase-1 (p < 0.005). These data suggest that the impaired ability of chronic wound fibroblasts to reorganize extracellular matrix in vitro is related to decreased levels of active matrix metalloproteinase-2 and matrix metalloproteinase-1 resulting from increased production of tissue inhibitors of metalloproteinase-1 and -2 by chronic wound fibroblasts. These findings provide a mechanism to explain the impaired cellular responses and extracellular matrix reorganization observed in chronic leg wounds in vivo.

Loss of Smad3 modulates wound healing

TGF-beta plays a central and critical role in tissue repair. The recent identification of TGF-beta signal transduction pathways involving Smad proteins has now made it possible to explore their contribution to the activities of TGF-beta in vivo. Both Smad3 and its closely related homolog Smad2 act as latent nuclear transcriptional activators and mediate intracellular signaling by TGF-betas and activin, each of which regulates cellular functions pivotal to cutaneous wound healing. Mice null for Smad3 (Smad3(ex8/ex8)) survive into adulthood and show accelerated cutaneous wound healing characterized by an increased rate of re-epithelialization and a reduced local inflammatory infiltrate. These data implicate Smad3 in specific pathways of tissue repair and suggest that it could be a target for the development of therapeutic strategies to modulate wound healing.

Age-related changes in the proteoglycans of human skin

Skin undergoes dramatic age-related changes in its mechanical properties, including changes in tissue hydration and resiliency. Proteoglycans are macromolecular conjugates of protein and carbohydrate (glycosaminoglycan) which are involved in these tissue properties. In order to examine whether age-related changes in skin proteoglycans may contribute to the age-related changes in the mechanical properties of skin, proteoglycans from human skin of various ages were extracted and analyzed. Samples were obtained from two different fetal ages, from mature skin, and from senescent skin. As a function of age, there is a decrease in the proportion of large chondroitin sulfate proteoglycans (versican) and a concomitant increase in the proportion of small dermatan sulfate proteoglycans (decorin). Based on reactivity with antibodies to various chondroitin sulfate epitopes, fetal versican differs from the versican found in older skin with respect to the chondroitin sulfate chains. Also, the decorin of fetal skin is slightly larger, while the decorin of older skin shows greater polydispersity in both its size and its charge to mass ratio. There are also age-related differences in the size and polydispersity of the core proteins of decorin. The most pronounced change in skin proteoglycans is the appearance in mature skin of a proteoglycan which is smaller than decorin, but which has the same amino terminal amino acid sequence as decorin. This small proteoglycan is abundant in mature skin and may be a catabolic fragment of decorin or an alternatively spliced form of decorin. In light of the known ability of decorin to influence collagen fibrillogenesis and fibril diameter, the appearance of this small decorin-related proteoglycan may have a significant effect on skin elasticity. The observation that proteoglycans in skin show dramatic age-related differences suggests that these changes may be involved in the age-related changes in the physical properties of skin.

Topical estrogen accelerates cutaneous wound healing in aged humans associated with an altered inflammatory response

The effects of intrinsic aging on the cutaneous wound healing process are profound, and the resulting acute and chronic wound morbidity imposes a substantial burden on health services. We have investigated the effects of topical estrogen on cutaneous wound healing in healthy elderly men and women, and related these effects to the inflammatory response and local elastase levels, an enzyme known to be up-regulated in impaired wound healing states. Eighteen health status-defined females (mean age, 74.4 years) and eighteen males (mean age, 70.7 years) were randomized in a double-blind study to either active estrogen patch or identical placebo patch attached for 24 hours to the upper inner arm, through which two 4-mm punch biopsies were made. The wounds were excised at either day 7 or day 80 post-wounding. Compared to placebo, estrogen treatment increased the extent of wound healing in both males and females with a decrease in wound size at day 7, increased collagen levels at both days 7 and 80, and increased day 7 fibronectin levels. In addition, estrogen enhanced the strength of day 80 wounds. Estrogen treatment was associated with a decrease in wound elastase levels secondary to reduced neutrophil numbers, and decreased fibronectin degradation. In vitro studies using isolated human neutrophils indicate that one mechanism underlying the altered inflammatory response involves both a direct inhibition of neutrophil chemotaxis by estrogen and an altered expression of neutrophil adhesion molecules. These data demonstrate that delays in wound healing in the elderly can be significantly diminished by topical estrogen in both male and female subjects.

Differential expression of tissue inhibitors of metalloproteinases (TIMP-1, -2, -3, and -4) in normal and aberrant wound healing

Wound healing is characterized by hemostasis, re-epithelialization, granulation tissue formation, and remodeling of the extracellular matrix. Matrix metalloproteinases and their specific inhibitors, TIMPs, contribute to these events. We investigated a total of 47 samples of normally healing wounds, chronic venous ulcers, ulcerative vasculitis, and suction blisters using immunohistochemistry and in situ hybridization, to clarify the role of TIMPs in normal and aberrant wound repair. Expression of TIMP-1 and -3 mRNAs was found in proliferating keratinocytes in 3- to 5-day-old normally healing wounds, whereas no epidermal expression was detected in chronic ulcers. However, TIMP-3 protein was found in the proliferating epidermis in 20 of 24 samples representing both full-thickness acute and chronic wounds. TIMP-1 and TIMP-3 also were abundantly expressed by spindle-shaped, fibroblast-like, and plump, macrophage-like stromal cells, as well as by endothelial cells. In normally healing wounds, TIMP-2 protein localized under the migrating epithelial tip and to the stromal tissue under the eschar more frequently than in chronic ulcers. Occasional staining for TIMP-4 protein was detected in stromal cells of chronic ulcers near blood vessels. Our results indicate that TIMP-1 and TIMP-3 may be involved both in the regeneration of the epidermis by stabilizing the basement membrane zone and in the regulation of stromal remodeling and angiogenesis of the wound bed. Lack of TIMP-2 near the migrating epithelial wound edges might contribute to uncontrolled activity of MMP-2 in chronic ulcers. We conclude also that TIMPs are temporally and spatially tightly regulated and that the imbalance between metalloproteinases and TIMPs-1, -2, and -3 may lead to delayed wound healing.

Expression and activation of matrix metalloproteinases in wounds: modulation by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+

We investigated the expression and activation of matrix metalloproteinases in a model of experimental wounds in rats, and their modulation by glycyl-L-histidyl-L-lysine-Cu(II), a potent activator of wound repair. Wound chambers were inserted under the skin of Sprague-Dawley rats and received serial injections of either 2 mg glycyl-L-histidyl-L-lysine-Cu(II) or the same volume of saline. The wound fluid and the neosynthetized connective tissue deposited in the chambers were collected and analyzed for matrix metalloproteinase expression and/or activity. Interstitial collagenase increased progressively in the wound fluid throughout the experiment. Glycyl-L-histidyl-L-lysine-Cu(II) treatment did not alter its activity. Matrix metalloproteinase-9 (gelatinase B) and matrix metalloproteinase-2 (gelatinase A) were the two main gelatinolytic activities expressed during the healing process. Pro-matrix metalloproteinase (pro-form of matrix metalloproteinase)-9 was strongly expressed during the early stages of wound healing (day 3). In the wound fluid, it decreased rapidly and disappeared after day 18, whereas in the wound tissue, matrix metalloproteinase-9 expression persisted in the glycyl-L-histidyl-L-lysine-Cu(II) injected chamber until day 22. Pro-matrix metalloproteinase-2 was expressed at low levels at the beginning of the healing process, increased progressively until day 7, then decreased until day 18. Activated matrix metalloproteinase-2 was present in wound fluid and wound tissue. It increased until day 12, then decreased progressively. Glycyl-L-histidyl-L-lysine-Cu(II) injections increased pro-matrix metalloproteinase-2 and activated matrix metalloproteinase-2 during the later stages of healing (days 18 and/or 22). These results demonstrate that various types of matrix metalloproteinases are selectively expressed or activated at the various periods of wound healing. Glycyl-L-histidyl-L-lysine-Cu(II) is able to modulate their expression and might significantly alter wound remodeling.

A novel in-situ-zymography technique localizes gelatinolytic activity in human skin to mast cells

Matrix-metallo-proteinases play a key role in cutaneous tissue remodeling and wound healing, and have been implicated as the rate-limiting factor in cutaneous tumor invasion and metastasis. We here describe a novel in-situ-zymographic method, which allows to directly localize sites of gelatinolytic activity in human skin. Gelatinolysis was detected through protein-hydrolysis in a 200 microm thick polyacrylamide gel underlying tissue sections. The lysis was substrate-dependent, demonstrated time- and temperature-dependent kinetics, and was inhibited by both EDTA and 1,10-phenanthroline. Normal and diseased skin sections demonstrated multiple focal points of gelatinolysis which co-localized with individual cells. Histochemically, these were shown to represent most likely mast cells (via AS-d-chloroacetate esterase staining and metachromasia). However, immunohistochemical staining for gelatinases A and B showed no immunoreactivity patterns that corresponded to the identified foci of gelatinolysis. The reported in-situ-zymographic technique offers a decisive advantage over immunohistochemistry, since it detects only the activated and catabolically relevant proteases, and provides further evidence for a role of mast cells in extracellular matrix remodeling.