Wounds Of Wild-type Mice Research Articles

CCL3 Promotes Cutaneous Wound Healing Through Recruiting Macrophages in Mice.

Wound healing is a complex process, which involves three stages: inflammation, proliferation, and remodeling. Inflammation is the first step; thus, immune factors play an important regulatory role in wound healing. In this study, we focused on a chemokine, C-C motif chemokine ligand 3 (CCL3), which is often upregulated for expression during wound healing. We compared cutaneous wound healing at the histological, morphological, and molecular levels in the presence and absence of CCL3. The results showed that the wound healing rate in the wild-type and CCL3-/- + CCL3 mice was faster than that of CCL3-/- mice (P < 0.01), and application of CCL3 to wounds increased the healing rate. In the process of wound healing, the degree of reepithelialization and the rate of collagen deposition in the wound of CCL3-/- mice were significantly lower than those of wild-type mice (P < 0.01). The number of macrophages and the expression levels of tumor necrosis factor(TNF)-α and transforming growth factor (TGF)-β1 in the wounds of wild-type mice were much higher than those of the CCL3-/- mice. Removal of macrophages and CCL3-/- mice share similar phenotypes. Therefore, we infer that the wound healing requires the participation of macrophages, and CCL3 may play an important regulatory role through recruiting macrophages to the wound sites.

QS61. Irradiated Fibroblast Sub-populations Alter Gene Expression to Heal Murine Skin

Introduction: Radiation-induced skin fibrosis is a well-documented and burdensome sequela of radiation therapy, however the exact mechanism behind this effect is not well understood. We aim to better delineate the cellular mechanisms of acute and chronic radiation-induced skin fibrosis. Methods: Thirty adult B6 mice, with equal proportion of males and females underwent 5 Gy of radiation every other day for 12 days, equaling 30 Gy total, of the dorsal skin. At weeks 0, 1, 2, 4, and 8 after radiation, the skin was harvested and analyzed using histology and immunofluorescence. Dorsal skin also underwent single-cell RNA sequencing, data was demultiplexed and underwent dimension reduction to identify transcriptionally distinct subpopulations, cross-referenced with Enrichr to identify relevant genetic pathways. Results: Dermal thickness was noted to progressively, significantly increase from week 0 to 8. Dermal collagen deposition and disorganization also significantly increased throughout the experiment. CD31+ expression increased in the acute phase, but decreased below baseline levels by the chronic phase. Four distinct fibroblast subpopulations were identified, and the genetic expression of these individual subpopulations demonstrated dynamic changes throughout the experiment. Sca, Dlk-1, and CD26+ immunofluorescence staining further confirmed this dynamicity as their expression fluctuated throughout the 8-week course of the experiment. Conclusion: Identification of this dynamic process amongst the various fibroblast subpopulations during the healing process of irradiation wounds in wild-type mice is a novel finding and paramount to better understanding and treatment of radiation-induced skin fibrosis.

Fibroblast Sub-Populations Dynamically Change Composition to Heal Dorsal Skin Radiation Wounds in Wild-Type Mice

Abbas, Darren B. MD; Griffin, Michelle MBChB, PhD; Fahy, Evan J. MB Bch BAO, MCh; Lavin, Christopher MS; Lee, Daniel MD; Mascharak, Shamik BS; King, Megan BS; Januszyk, Michael MD; Longaker, Michael T. MD, MBA, FACS; Wan, Derrick C. MD, FACS Author Information

MicroRNA-34 Family Enhances Wound Inflammation by Targeting LGR4

Venous ulcers are the most common type of human chronic nonhealing wounds and are stalled in a constant and excessive inflammatory state. The molecular mechanisms underlying the chronic wound inflammation remain elusive. Moreover, little is known about the role of regulatory RNAs, such as microRNAs, in the pathogenesis of venous ulcers. We found that both microRNA (miR)-34a and miR-34c were upregulated in the wound-edge epidermal keratinocytes of venous ulcers compared with normal wounds or the skin. In keratinocytes, miR-34a and miR-34c promoted inflammatory chemokine and cytokine production. In wounds of wild-type mice, miR-34a-mimic treatment enhanced inflammation and delayed healing. To further explore how miR-34 functions, LGR4 was identified as a direct target mediating the proinflammatory function of miR-34a and miR-34c. Interestingly, impaired wound closure with enhanced inflammation was also observed in Lgr4 knockout mice. Mechanistically, the miR-34-LGR4 axis regulated GSK-3β-induced p65 serine 468 phosphorylation, changing the activity of the NF-κB signaling pathway. Collectively, the miR-34-LGR4 axis was shown to regulate keratinocyte inflammatory response, the deregulation of which may play a pathological role in venous ulcers.

Iron Chelation with Transdermal Deferoxamine Accelerates Healing of Murine Sickle Cell Ulcers.

Objective: Sickle cell ulcers (SCUs) are a devastating comorbidity affecting patients with sickle cell disease (SCD). SCUs form over the medial or lateral malleoli of the lower extremity, are slow to heal, and prone to recidivism. Some SCUs may never heal, leading to chronic pain and foot deformities. There is no specific and effective therapy for SCUs. Systemic deferoxamine (DFO) has been demonstrated to prevent some of the sequelae of SCD by chelating iron. In this study, we tested the ability of DFO delivered via a transdermal delivery system (DFO-TDDS) to accelerate healing in a murine model of SCU. Approach: Excisional wounds were created in a transgenic murine model of SCD expressing >99% human sickle hemoglobin, and healing rates were compared with wounds in wild-type mice. Next, excisional wounds in SCD mice were treated with DFO-TDDS, DFO injection, or left untreated. Wound closure rates, histology, and iron in the healed wounds were analyzed. Results: Wounds in SCD mice healed significantly slower than wild-type mice (***p < 0.001). DFO-TDDS-treated wounds demonstrated significantly accelerated time to closure, reduced size, and improved wound remodeling compared with untreated wounds (***p < 0.001) and DFO injection treatment (*p < 0.05). DFO released from the TDDS into wounds resulted in chelation of excessive dermal-free iron. Innovation: DFO-TDDS is a novel therapeutic that is effective in healing wounds in sickle cell mice. Conclusion: DFO-TDDS significantly accelerates healing of murine SCUs by chelation of excessive free iron and is currently manufactured in an FDA-compliant facility to be translated for treating human SCUs.

Pigment Epithelium-Derived Factor (PEDF) as a Regulator of Wound Angiogenesis

Although the inflammatory and proliferative phases of wound healing have been well described, much less is known about how healing resolves. During the resolution phase, pruning of the capillary bed and maturation of capillaries occurs and influences the final strength and fidelity of the wound. PEDF, an endogenous anti-angiogenic factor, is produced in wounds and may contribute to the removal of capillaries during wound resolution. This study utilized PEDF−/− mice to examine how PEDF influences wound angiogenesis, particularly capillary density and permeability. The absence of PEDF led to transient changes in dermal wound closure and collagen content, but caused substantial changes in wound angiogenesis. Compared to wild type (WT) mice, wounds from PEDF−/− mice exhibited a significant increase in capillaries during the proangiogenic phase of repair, and a delay in capillary pruning. Conversely, the addition of rPEDF caused a reduction in capillary density within skin wounds in WT mice. In vitro studies showed that PEDF inhibited migration and tube formation by dermal microvascular endothelial cells, and caused a decrease in the expression of VEGFR2, VCAM-1, and other surface receptors. The results demonstrate that loss of PEDF causes a distinctive wound healing phenotype that is characterized by increased angiogenesis and delayed resolution. The findings suggest that PEDF most likely acts through multiple mechanisms to regulate proper capillary refinement in wounds.

Topical TWEAK Accelerates Healing of Experimental Burn Wounds in Mice.

The interaction of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor inducible 14 (Fn14) participates in inflammatory responses, fibrosis, and tissue remodeling, which are central in the repair processes of wounds. Fn14 is expressed in main skin cells including dermal fibroblasts. This study was designed to explore the therapeutic effect of TWEAK on experimental burn wounds and the relevant mechanism underlying such function. Third-degree burns were introduced in two BALB/c mouse strains. Recombinant TWEAK was administrated topically, followed by the evaluation of wound areas and histologic changes. Accordingly, the downstream cytokines, inflammatory cell infiltration, and extracellular matrix synthesis were examined in lesional tissue. Moreover, the differentiation markers were analyzed in cultured human dermal fibroblasts upon TWEAK stimulation. The results showed that topical TWEAK accelerated the healing of burn wounds in wild-type mice but not in Fn14-deficient mice. TWEAK strengthened inflammatory cell infiltration, and exaggerated the production of growth factor and extracellular matrix components in wound areas of wild-type mice. Moreover, TWEAK/Fn14 activation elevated the expression of myofibroblastic differentiation markers, including alpha-smooth muscle actin and palladin, in cultured dermal fibroblasts. Therefore, topical TWEAK exhibits therapeutic effect on experimental burn wounds through favoring regional inflammation, cytokine production, and extracellular matrix synthesis. TWEAK/Fn14 activation induces the myofibroblastic differentiation of dermal fibroblasts, partially contributing to the healing of burn wounds.

Elevated Thrombospondin‐2 Contributes to Delayed Wound Healing in Diabetes

Impaired wound healing is a major complication of diabetes and can lead to the development of chronic wounds in a significant portion of diabetes patients. Despite the risks posed by impaired healing, treatment strategies for diabetic wounds remain limited due to an incomplete understanding of the underlying pathological mechanisms. Previous studies have demonstrated that overexpression of thrombospondin‐2 (TSP2), a matricellular protein released after tissue injury, is associated with significant delays in dermal healing in various mouse models. Consistently, wounds lacking TSP2 (TSP2 KO) heal faster than wounds in wild‐type mice or mice with elevated TSP2. Thus, the present study aimed to examine the role of TSP2 in delayed healing in diabetes.First, we evaluated TSP2 expression in human wounds, and found that TSP2 is elevated in wounds from diabetes patients. Then, to determine TSP2's contribution to impaired healing in diabetes, we developed a novel diabetic TSP2 KO mouse model. Though these db/db TSP2 KO mice develop obesity and hyperglycemia comparable to db/db mice, db/db TSP2 KO mice exhibit significantly improved healing. Moreover, primary fibroblasts isolated from db/db TSP2 KO mice exhibit improved migration, providing mechanistic insight into the accelerated healing in these mice. We also studied TSP2 expression in fibroblasts, the major source of TSP2 in the wound, to explore the mechanisms leading to its overexpression in diabetes. Our results showed that TSP2 expression is increased in hyperglycemia, through increased activation of the hexosamine biosynthesis pathway and subsequent O‐GlcNAc modification of transcriptional elements. Overall, the results of this study indicate for the first time that: 1) TSP2 expression is elevated in diabetes and hyperglycemia and 2) TSP2 contributes to impaired healing in diabetes. These results represent a novel role for TSP2 in diabetes complications and a novel target for improving wound healing in diabetes.Support or Funding InformationNIH HL107205, NIH GM 072194, Gruber Science FellowshipThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Silver oxysalts promote cutaneous wound healing independent of infection.

Chronic wounds often exist in a heightened state of inflammation whereby excessive inflammatory cells release high levels of proteases and reactive oxygen species (ROS). While low levels of ROS play a fundamental role in the regulation of normal wound healing, their levels need to be tightly regulated to prevent a hostile wound environment resulting from excessive levels of ROS. Infection amplifies the inflammatory response, augmenting levels of ROS which creates additional tissue damage that supports microbial growth. Antimicrobial dressings are used to combat infection; however, the effects of these dressing on the wound environment and healing independent of infection are rarely assessed. Cytotoxic or adverse effects on healing may exacerbate the hostile wound environment and prolong healing. Here we assessed the effect on healing independent of infection of silver oxysalts which produce higher oxidative states of silver (Ag2+ /Ag3+ ). Silver oxysalts had no adverse effect on fibroblast scratch wound closure whilst significantly promoting closure of keratinocyte scratch wounds (34% increase compared with control). Furthermore, dressings containing silver oxysalts accelerated healing of full-thickness incisional wounds in wild-type mice, reducing wound area, promoting reepithelialization, and dampening inflammation. We explored the mechanisms by which silver oxysalts promote healing and found that unlike other silver dressings tested, silver oxysalt dressings catalyze the breakdown of hydrogen peroxide to water and oxygen. In addition, we found that silver oxysalts directly released oxygen when exposed to water. Collectively, these data provide the first indication that silver oxysalts promote healing independent of infection and may regulate oxidative stress within a wound through catalysis of hydrogen peroxide.

Topical Application of Tat-Rac1 Promotes Cutaneous Wound Healing in Normal and Diabetic Mice.

The endogenous small GTPase, Rac1, plays a critical role during normal skin wound healing. It remains to be determined whether endogenous Rac1 can be appropriately activated in chronic wounds; if not, whether exogenous Rac1 has therapeutic effects on wound healing. Here we show that Rac1 protein levels were lower in wounds of db/db diabetic mice than wounds in wild type mice during the healing process. To assess the therapeutic potential of exogenous Rac1 in wound healing, we produced a Tat-Rac1 fusion protein that enters into cells through protein transduction. Tat-Rac1 increased proliferation and migration of keratinocytes and dermal fibroblasts in vitro. Topical application of Tat-Rac1 accelerated cutaneous wound closure in vivo in db/db mice as well as wild type mice. Further analyses revealed that Tat-Rac1 had faster re-epithelialization, higher keratinocyte proliferation and migration without an earlier onset of myofibroblast activation than vehicle treated wounds. Tat-Rac1 also reduced inflammation in wounds. Our findings revealed the failure of diabetic wounds to elevate Rac1 expression and suggested a therapeutic strategy utilizing a Rac1-based biologic to compensate for this defect thereby promoting wound healing.

Plasminogen is a key proinflammatory regulator that accelerates the healing of acute and diabetic wounds

AbstractDespite decades of research on wound healing, effective biologic agents for the treatment of chronic wounds, especially diabetic wounds, are still lacking. In the present study, we report that the inert plasma protein plasminogen (plg) acts as a key regulatory molecule that potentiates wound healing in mice. Early in the healing process, plg bound to inflammatory cells is transported to the wound area, where the level of plg is increased locally, leading to the induction of cytokines and intracellular signaling events and to a potentiation of the early inflammatory response. Systemic administration of additional plg not only accelerates the healing of acute burn wounds in wild-type mice, but also improves the healing of chronic diabetic wounds in a mouse model of diabetes. Our results suggest that the administration of plg may be a novel therapeutic strategy to treat many different types of wounds, especially chronic wounds such as those caused by diabetes.

Combination of stromal cell-derived factor-1 and collagen-glycosaminoglycan scaffold delays contraction and accelerates reepithelialization of dermal wounds in wild-type mice

While dermal substitutes can mitigate scarring and wound contraction, a significant drawback of current dermal replacement technologies is the apparent delay in vascular ingrowth compared with conventional skin grafts. Herein, we examined the effect of the chemokine stromal cell-derived factor-1 (SDF-1) on the performance of a porous collagen-glycosaminoglycan dermal analog in excisional wounds in mice. C57BL/6 mice with 1 cm × 1 cm dorsal full-thickness wounds were covered with a collagen-glycosaminoglycan scaffold, followed by four daily topical applications of 1 μg SDF-1 or phosphate-buffered saline vehicle. Some animals were also pretreated with five daily doses of 300 mg/kg granulocyte colony-stimulating factor. Animals treated with SDF-1 and no granulocyte colony-stimulating factor reepithelialized 36% faster than vehicle controls (16 vs. 25 days), and exhibited less wound contraction on postwounding day 18 (∼ 35% greater wound area) plus three-fold longer neoepidermis formed than controls. Conversely, granulocyte colony-stimulating factor promoted contraction and no epidermal regeneration. Early (postwounding Day 3) inflammatory cell infiltration in the SDF-1-treated group was 86% less, while the fraction of proliferating cells (positive Ki67 staining) was 32% more, when compared with controls. These results suggest that SDF-1 simultaneously delays contraction and promotes reepithelialization and may improve the wound-healing performance of skin substitutes.

Germ plasm‐like Dot cells maintain their wound regenerative function after in vitro expansion

1. Wounds in fetal skin heal without scarring; however, the mechanism for this is unknown. We have identified a novel group of protein and nucleotides-positive particles in fetal and adult mouse blood and in human blood, and termed them 'Dot cells'. Freshly isolated Dot cells regenerate wounds with less scarring and can be cultured without feeder layers. 2. Because the morphology of Dot cells has never been described, in the present study we describe the specific characterizations of Dot cells, including their growth pattern in vitro, and their expressions of stem cell markers using fluorescent cell sorting analyses and immunofluorescent histology. Our data indicates that cultured Dot cells express stem cell surface markers and embryonic stem cell transcription markers, such as Oct4, Nanog and Sox-2. In addition, Dot cells express VASA, the germ plasm specific marker. 3. To confirm whether Dot cells maintain their wound regenerative activity after in vitro expansion, in vitro cultured Dot cells were transplanted to wounded mice. Dot cells from albino mice maintain their wound regenerative activities after intravenous transplantation to black-background diabetic mice. In addition, Dot cells regenerate both the epithelial and dermal cells in the wounds of wild-type mice. The regenerated hair follicles, smooth muscle and dermal tissues express transiently to VASA. 4. Our data demonstrate that Dot cells are newly identified organisms located in the blood and bone marrow of mammals. They express germ cell, embryonic stem cell and adult stem cell markers. Dot cells maintain their regenerative function after in vitro expansion.

Germ plasm-like Dot cells maintain the wound regenerative function after in vitro expansion

1. Wounds in fetal skin heal without scarring; however, the mechanism for this is unknown. We have identified a novel group of protein and nucleotides-positive particles in fetal and adult mouse blood and in human blood, and termed them ‘Dot cells’. Freshly isolated Dot cells regenerate wounds with less scarring and can be cultured without feeder layers. 2. Because the morphology of Dot cells has never been described, in the present study we describe the specific characterizations of Dot cells, including their growth pattern in vitro, and their expressions of stem cell markers using fluorescent cell sorting analyses and immunofluorescent histology. Our data indicates that cultured Dot cells express stem cell surface markers and embryonic stem cell transcription markers, such as Oct4, Nanog and Sox-2. In addition, Dot cells express VASA, the germ plasm specific marker. 3. To confirm whether Dot cells maintain their wound regenerative activity after in vitro expansion, in vitro cultured Dot cells were transplanted to wounded mice. Dot cells from albino mice maintain their wound regenerative activities after intravenous transplantation to black-background diabetic mice. In addition, Dot cells regenerate both the epithelial and dermal cells in the wounds of wild-type mice. The regenerated hair follicles, smooth muscle and dermal tissues express transiently to VASA. 4. Our data demonstrate that Dot cells are newly identified organisms located in the blood and bone marrow of mammals. They express germ cell, embryonic stem cell and adult stem cell markers. Dot cells maintain their regenerative function after in vitro expansion.

Disruption of Interleukin-1 Signaling Improves the Quality of Wound Healing

In this study, we investigated the role of interleukin (IL)-1 signaling in wound healing. IL-1 receptor type I (IL-1R) knockout (KO) mice showed reduced fibrosis in both cutaneous and deep tissue wounds, which was accompanied by a reduction in inflammatory cellular infiltration in cutaneous but not in deep tissue wounds. There were no differences in either total collagenolytic activity or in the expression of selected matrix metalloproteinases or tissue inhibitors of metalloproteinases between the wound fluids from wild-type or IL-1R KO mice. However, wound fluids from IL-1R KO mice contained lower levels of IL-6 compared with wild-type controls. In addition, the infusion of IL-6 into wounds in IL-1R KO mice did not increase fibrosis. Skin wounds in IL-1R KO animals had lower levels of collagen and improved restoration of normal skin architecture compared with skin wounds in wild-type mice. However, neither the tensile strength of incisional skin wounds nor the rate of closure of excisional wounds differed between IL-1R KO and wild-type animals. The reduced fibrotic response in wounds from IL-1R KO mice could be reproduced by the administration of an IL-1R antagonist. These findings suggest that pharmacological interference with IL-1 signaling could have therapeutic value in the prevention of hypertrophic scarring and in the treatment of fibrotic diseases.

Loss of dioxin-receptor expression accelerates wound healing in vivo by a mechanism involving TGFβ

Delayed wound healing caused by inefficient re-epithelialization underlines chronic skin lesions such as those found in diabetes. The dioxin receptor (AhR) modulates cell plasticity and migration and its activation by occupational polycyclic aromatic hydrocarbons (PAHs) results in severe skin lesions such as contact hypersensitivity, dermatitis and chloracne. Using wild-type (Ahr+/+) and AhR-null (Ahr-/-) mouse primary keratinocyte cultures and tissue explants, we show that lack of AhR increases keratinocyte migration and accelerates skin re-epithelialization without affecting cell proliferation or recruitment of inflammatory cells. Wounds in Ahr-/- animals had elevated numbers of fibroblasts and increased collagen content in their granulation tissue. Importantly, Ahr-/- dermal fibroblasts secreted higher levels of active TGFbeta that increased keratinocyte migration in culture and that could account for over-activation of the TGFbeta pathway and for faster wound healing in the AhR-null neo-epithelium. Consistently, a TGFbeta neutralizing antibody decreased keratinocyte migration in culture and halted re-epithelialization in Ahr-/- mice. Moreover, in vivo treatment with an antisense oligonucleotide for AhR increased TGFbeta signaling and improved re-epithelialization in wounds of wild-type mice. These data indicate that AhR is relevant for wound repair and suggest that AhR downmodulation might be a potential new tool for the treatment of chronic, surgical or accidental wounds.

Nitric oxide elicits functional MMP‐13 protein‐tyrosine nitration during wound repair

Nitric oxide (NO) plays a critical role in wound healing, in part by promoting angiogenesis. However, the precise repair pathways affected by NO are not well defined. We now show that NO regulates matrix metalloproteinase-13 (MMP-13) release during wound repair. We find that normally MMP-13 is kept inside endothelial cells by an association with caveolin-1. However, nitration of MMP-13 on tyrosine residue Y338 causes it to dissociate from caveolin-1 and be released from endothelial cells. We next explored the functional significance of MMP-13 nitration in vivo. Skin injury increases nitration of MMP-13 in mice. Skin wounds in inducible nitric oxide synthase knockout mice release less MMP-13 and heal more slowly than skin wounds in wild-type mice. Conversely, skin wounds in caveolin-1 knockout mice have increased NO production, increased MMP-13 nitration, and accelerated wound healing. Collectively, our data reveal a new pathway through which NO modulates wound repair: nitration of MMP-13 promotes its release from endothelial cells, where it accelerates angiogenesis and wound healing.

Loss of CXC chemokine receptor 3 signaling cause a delay in epidermal and dermal maturation and leads to hypertrophic scarring

CXCR3 and its ligands modulate the timing of keratinocytes migration, fibroblasts and endothelial cell immigration into the wound and epidermal and matrix maturation during wound healing. To investigated the long term effects of CXCR3 in wound healing full thickness excisional wounds were created on CXCR3−/− or wildtype mice and examined at 180 days. Grossly the CXCR3−/− mice presented a thick keratinized eschar compared to the wildtype mice that had a scarcely noticeable scar. Histological analysis of the CXCR3−/− mice also revealed a thicker epidermis that was hyperproliferative, dermal layers that were disorganized with thick and long collagen fibrils, and contained excessive collagen content in comparison to the wildtype mice. Interestingly, the CXCR3−/− wounds results in a weaker tensile strength as a result of decreased cross‐linking of collagen fibers. A lack of ECM turnover was shown by the elevated expression of matrix proteins tenascin C, fibronectin, and an imbalance of MMP‐9 expression; these were noted as late as 180 days postwounding, whereas these markers of an immature dermis are long gone in wounds in wildtype mice. These in vivo studies establish that the absence of the CXCR3 signaling network results in hypertrophic scarring by delaying maturation and altering the synthesis and degradation of collagen in addition to other matrix components during wound healing. Supported by grants from the NIH

Wound Healing in Tenascin-X Deficient Mice Suggests that Tenascin-X is Involved in Matrix Maturation Rather than Matrix Deposition

Tenascin-X (TNX) is an extracellular matrix glycoprotein whose absence in humans leads to a recessive form of Ehlers-Danlos Syndrome (EDS). TNX deficient patients have hypermobile joints and fragile skin, but unlike the classical type of EDS, no atrophic scars were observed. Anecdotal evidence suggested that wound healing in TNX deficient patients is abnormal, but no detailed study has been performed so far. To address the role of TNX in wound healing, we analyzed skin wound morphology and mechanical properties of scars in TNX knockout (KO) mice. Breaking strength of unwounded skin of KO mice is significantly lower (<50%) than that of wild-type (WT) mice. In the early stage of wound healing when TNX is hardly expressed in WT wounds (day 7), WT and KO skin are of similar strength. After 14 days, when TNX starts to be expressed at moderate levels in wounds of WT mice, the WT scars gain a further increase in breaking strength, whereas KO scars do not progress beyond the mechanical strength of uninjured KO skin. No obvious differences between KO and WT mice were noted in the rate of wound closure, or in expression of fibrillar collagens during wound healing. We conclude that TNX is unlikely to be involved in matrix deposition in the early phase of wound healing, but it is required in the later phase when remodeling and maturation of the matrix establishes and improves its biomechanical properties.

Plasminogen activation independent of uPA and tPA maintains wound healing in gene-deficient mice

Simultaneous ablation of the two known activators of plasminogen (Plg), urokinase-type (uPA) and the tissue-type (tPA), results in a substantial delay in skin wound healing. However, wound closure and epidermal re-epithelialization are significantly less impaired in uPA;tPA double-deficient mice than in Plg-deficient mice. Skin wounds in uPA;tPA-deficient mice treated with the broad-spectrum matrix metalloproteinase (MMP) inhibitor galardin (N-[(2R)-2-(hydroxamido-carbonylmethyl)-4-methylpentanoyl]-L-tryptophan methylamide) eventually heal, whereas skin wounds in galardin-treated Plg-deficient mice do not heal. Furthermore, plasmin is biochemically detectable in wound extracts from uPA;tPA double-deficient mice. In vivo administration of a plasma kallikrein (pKal)-selective form of the serine protease inhibitor ecotin exacerbates the healing impairment of uPA;tPA double-deficient wounds to a degree indistinguishable from that observed in Plg-deficient mice, and completely blocks the activity of pKal, but not uPA and tPA in wound extracts. These findings demonstrate that an additional plasminogen activator provides sufficient plasmin activity to sustain the healing process albeit at decreased speed in the absence of uPA, tPA and galardin-sensitive MMPs and suggest that pKal plays a role in plasmin generation.