Suppressed recruitment of alternatively activated macrophages reduces TGF-β1 and impairs wound healing in streptozotocin-induced diabetic mice

BackgroundDiabetes mellitus inhibits wound-induced angiogenesis, impairing the wound healing process and leading to the development of chronic wounds. Impaired healing of diabetic wounds is caused by persistent pro-inflammatory macrophages recruited to the granulation tissue; however, little is known about the phenotype of the macrophages involved in diabetic wound healing. The present study was conducted to examine the involvement of macrophages in impaired wound healing using streptozotocin (STZ)-induced diabetic mice.MethodsFull-thickness skin wounds were created on the backs of mice treated with STZ or vehicle.ResultsCompared with controls, wound healing and angiogenesis were suppressed in STZ-treated mice, with attenuated expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)-2 in wound granulation tissue. STZ-treated mice exhibited enhanced recruitment of classically activated macrophages (M1) expressing inducible nitric oxide synthase (iNOS) and suppressed recruitment of alternatively activated macrophages (M2) expressing transforming growth factor-beta-1 (TGF-β1). Treatment of diabetic mice with TGF-β1 restored wound healing and angiogenesis and normalized M1/M2 macrophage polarization in the granulation tissue.ConclusionsThese results suggest that an imbalance of macrophage phenotypes contributes to impaired wound healing in STZ-induced diabetic mice, and treatment with cytokines derived from M2 macrophages may be an effective therapeutic strategy to increase angiogenesis and promote healing of diabetic wounds.     

Manganese superoxide dismutase expression in endothelial progenitor cells accelerates wound healing in diabetic mice

Amputation as a result of impaired wound healing is a serious complication of diabetes. Inadequate angiogenesis contributes to poor wound healing in diabetic patients. Endothelial progenitor cells (EPCs) normally augment angiogenesis and wound repair but are functionally impaired in diabetics. Here we report that decreased expression of manganese superoxide dismutase (MnSOD) in EPCs contributes to impaired would healing in a mouse model of type 2 diabetes. A decreased frequency of circulating EPCs was detected in type 2 diabetic (db/db) mice, and when isolated, these cells exhibited decreased expression and activity of MnSOD. Wound healing and angiogenesis were markedly delayed in diabetic mice compared with normal controls. For cell therapy, topical transplantation of EPCs onto excisional wounds in diabetic mice demonstrated that diabetic EPCs were less effective than normal EPCs at accelerating wound closure. Transplantation of diabetic EPCs after MnSOD gene therapy restored their ability to mediate angiogenesis and wound repair. Conversely, siRNA-mediated knockdown of MnSOD in normal EPCs reduced their activity in diabetic wound healing assays. Increasing the number of transplanted diabetic EPCs also improved the rate of wound closure. Our findings demonstrate that cell therapy using diabetic EPCs after ex vivo MnSOD gene transfer accelerates their ability to heal wounds in a mouse model of type 2 diabetes.     

Recombinant human erythropoietin improves angiogenesis and wound healing in experimental burn wounds

OBJECTIVE: Erythropoietin interacts with vascular endothelial growth factor (VEGF) and stimulates endothelial cell mitosis and motility; thus it may be of importance in the complex phenomenon of wound healing. The purpose of this study was to investigate the effect of recombinant human erythropoietin (rHuEPO) on experimental burn wounds. DESIGN: Randomized experiment. SETTING: Research laboratory. SUBJECTS: C57BL/6 male mice weighing 25-30 g. INTERVENTIONS: Mice were immersed in 80 degrees C water for 10 secs to achieve a deep-dermal second degree burn. Animals were randomized to receive either rHuEPO (400 units/kg/day for 14 days in 100 microL subcutaneously) or its vehicle alone (100 microl/day distilled water for 14 days subcutaneously). On day 14 the animals were killed. Burn areas were used for histologic examination, evaluation of neoangiogenesis by immunohistochemistry, and expression (Western blot) of the specific endothelial marker CD31 as well as quantification of microvessel density, measurement of VEGF wound content (enzyme-linked immunosorbent assay), expression (Western blot) of endothelial and inducible nitric oxide synthases, and determination of wound nitric oxide (NO) products. MEASUREMENTS AND MAIN RESULTS: rHuEPO increased burn wound reepithelialization and reduced the time to final wound closure. These effects were completely abated by a passive immunization with specific antibodies against erythropoietin. rHuEPO improved healing of burn wound through increased epithelial proliferation, maturation of the extracellular matrix, and angiogenesis. The hematopoietic factor augmented neoangiogenesis as suggested by the marked increase in microvessel density and by the robust expression of the specific endothelial marker CD31. Furthermore, rHuEPO enhanced the wound content of VEGF caused a marked expression of endothelial and inducible nitric oxide synthases and increased wound content of nitric oxide products. CONCLUSIONS: Our study suggests that rHuEPO may be an effective therapeutic approach to improve clinical outcomes after thermal injury.     

Topical S-nitrosoglutathione-releasing hydrogel improves healing of rat ischaemic wounds

Topical application of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) is known to exert beneficial effects on wound healing. The aim of this study was to evaluate, for the first time, the effect of topical application of GSNO on the healing of ischaemic wounds. Wistar rats were submitted to two parallels incisions on their backs; the skin was separated from the underlying tissue, the incisions were sutured and an excisional wound was made between the parallel incisions to create an ischaemic condition surrounding the wound. The animals were separated into a control group, which received a hydrogel vehicle without GSNO, and a GSNO-treated group, which received a GSNO-containing hydrogel. The animals were treated for 7 days consecutively with one daily application. The GSNO-treated group displayed higher rates of wound contraction and re-epithelization, lower amounts of inflammatory cells, an increase in collagen fibre density and organization and a decrease in the neovascularization compared to control. These results show that topical application of GSNO is effective in the treatment of ischaemic wounds, leading to a significant improvement in the wound healing. Therefore, topical GSNO-containing hydrogels have potential for the therapeutic treatment of ischaemic diabetic and venous ulcers.     

Progress and expectation of stem cell therapy for diabetic wound healing

Impaired wound healing presents great health risks to diabetics. Encouragingly, the current clinical successfully found out meaningful method to repair wound tissue, and stem cell therapy could be an effective method for diabetic wound healing with its ability to accelerate wound closure and avoid amputation. This minireview aims at introducing stem cell therapy for facilitating tissue repair in diabetic wounds, discussing the possible therapeutic mechanism and clinical application status and problems.     

Expression of the oxygen-regulated protein ORP150 accelerates wound healing by modulating intracellular VEGF transport

Expression of angiogenic factors such as VEGF under conditions of hypoxia or other kinds of cell stress contributes to neovascularization during wound healing. The inducible endoplasmic reticulum chaperone oxygen-regulated protein 150 (ORP150) is expressed in human wounds along with VEGF. Colocalization of these two molecules was observed in macrophages in the neovasculature, suggesting a role of ORP150 in the promotion of angiogenesis. Local administration of ORP150 sense adenovirus to wounds of diabetic mice, a treatment that efficiently targeted this gene product to the macrophages of wound beds, increased VEGF antigen in wounds and accelerated repair and neovascularization. In cultured human macrophages, inhibition of ORP150 expression caused retention of VEGF antigen within the endoplasmic reticulum (ER), while overexpression of ORP150 promoted the secretion of VEGF into hypoxic culture supernatants. Taken together, these data suggest an important role for ORP150 in the setting of impaired wound repair and identify a key, inducible chaperone-like molecule in the ER. This novel facet of the angiogenic response may be amenable to therapeutic manipulation.     

Skin Electroporation of a Plasmid Encoding hCAP-18/LL-37 Host Defense Peptide Promotes Wound Healing

Host defense peptides, in particular LL-37, are emerging as potential therapeutics for promoting wound healing and inhibiting bacterial growth. However, effective delivery of the LL-37 peptide remains limiting. We hypothesized that skin-targeted electroporation of a plasmid encoding hCAP-18/LL-37 would promote the healing of wounds. The plasmid was efficiently delivered to full-thickness skin wounds by electroporation and it induced expression of LL-37 in the epithelium. It significantly accelerated reepithelialization of nondiabetic and diabetic wounds and caused a significant VEGFa and interleukin (IL)-6 induction. IL-6 was involved in LL-37–mediated keratinocyte migration in vitro and IL-6 neutralizing antibodies delivered to mice were able to suppress the wound healing activity of the hCAP-18/LL-37 plasmid. In a hindlimb ischemia model, electroporation of the hCAP-18/LL-37 plasmid increased blood perfusion, reduced muscular atrophy, and upregulated the angiogenic chemokines VEGFa and SDF-1a, and their receptors VEGF-R and CXCR-4. These findings demonstrate that a localized gene therapy with LL-37 is a promising approach for the treatment of wounds.     

Modulation of inflammation by cicaderma ointment accelerates skin wound healing

Skin wound healing is a natural and intricate process that takes place after injury, involving different sequential phases such as hemostasis, inflammatory phase, proliferative phase, and remodeling that are associated with complex biochemical events. The interruption or failure of wound healing leads to chronic nonhealing wounds or fibrosis-associated diseases constituting a major health problem where, unfortunately, medicines are not very effective. The objective of this study was to evaluate the capacity of Cicaderma ointment (Boiron, Lyon, France) to accelerate ulcer closure without fibrosis and investigate wound healing dynamic processes. We used a necrotic ulcer model in mice induced by intradermal doxorubicin injection, and after 11 days, when the ulcer area was maximal, we applied Vaseline petroleum jelly or Cicaderma every 2 days. Topical application of Cicaderma allowed a rapid recovery of mature epidermal structure, a more compact and organized dermis and collagen bundles compared with the Vaseline group. Furthermore, the expression of numerous cytokines/molecules in the ulcer was increased 11 days after doxorubicin injection compared with healthy skin. Cicaderma rapidly reduced the level of proinflammatory cytokines, mainly tumor necrosis factor (TNF)-α and others of the TNF pathway, which can be correlated to a decrease of polymorphonuclear recruitment. It is noteworthy that the modulation of inflammation through TNF-α, macrophage inflammatory protein-1α, interleukin (IL)-12, IL-4, and macrophage-colony-stimulating factor was maintained 9 days after the first ointment application, facilitating the wound closure without affecting angiogenesis. These cytokines seem to be potential targets for therapeutic approaches in chronic wounds. Our results confirm the use of Cicaderma for accelerating skin wound healing and open new avenues for sequential treatments to improve healing.     

PKCδ inhibition normalizes the wound-healing capacity of diabetic human fibroblasts

Abnormal fibroblast function underlies poor wound healing in patients with diabetes; however, the mechanisms that impair wound healing are poorly defined. Here, we evaluated fibroblasts from individuals who had type 1 diabetes (T1D) for 50 years or more (Medalists, n = 26) and from age-matched controls (n = 7). Compared with those from controls, Medalist fibroblasts demonstrated a reduced migration response to insulin, lower VEGF expression, and less phosphorylated AKT (p-AKT), but not p-ERK, activation. Medalist fibroblasts were also functionally less effective at wound closure in nude mice. Activation of the δ isoform of protein kinase C (PKCδ) was increased in postmortem fibroblasts from Medalists, fibroblasts from living T1D subjects, biopsies of active wounds of living T1D subjects, and granulation tissues from mice with streptozotocin-induced diabetes. Diabetes-induced PKCD mRNA expression was related to a 2-fold increase in the mRNA half-life. Pharmacologic inhibition and siRNA-mediated knockdown of PKCδ or expression of a dominant-negative isoform restored insulin signaling of p-AKT and VEGF expression in vitro and improved wound healing in vivo. Additionally, increasing PKCδ expression in control fibroblasts produced the same abnormalities as those seen in Medalist fibroblasts. Our results indicate that persistent PKCδ elevation in fibroblasts from diabetic patients inhibits insulin signaling and function to impair wound healing and suggest PKCδ inhibition as a potential therapy to improve wound healing in diabetic patients.     

Wound healing action of nitric oxide‐releasing self‐expandable collagen sponge

Mounting evidence showing that local nitric oxide (NO) delivery may significantly improve the wound healing process has stimulated the development of wound dressings capable of releasing NO topically. Herein, we describe the preparation of a self‐expandable NO‐releasing hydrolyzed collagen sponge (CS), charged with the endogenously found NO donor, S‐nitrosoglutathione (GSNO). We show that cold pressed and GSNO‐charged CS (CS/GSNO) undergo self‐expansion to its original 3D shape upon water absorption to a swelling degree of 2,300 wt%, triggering the release of free NO. Topical application of compressed CS/GSNO on wounds in an animal model showed that exudate absorption by CS/GSNO leads to the release of higher NO doses during the inflammatory phase and progressively lower NO doses at later stages of the healing process. Moreover, treated animals showed significant increase in the mRNA expression levels of monocyte chemoattractant protein‐1 (MCP‐1), murine macrophage marker (F4/80), transforming growth factor beta (TGF‐β), stromal cell‐derived factor 1 (SDF‐1), insulin‐like growth factor‐1 (IGF‐1), nitric oxide synthase(iNOS), and matrix metalloproteinase(MMP‐9). Cluster differentiation 31 (CD31), vascular endothelial growth factor (VEGF), and F4/80 were measured on Days 7 and 12 by immunohistochemistry in the cicatricial tissue. These results indicate that the topical delivery of NO enhances the migration and infiltration of leucocytes, macrophages, and keratinocytes to the wounded tissue, as well as the neovascularization and collagen deposition, which are correlated with an accelerated wound closure. Thus, self‐expandable CS/GSNO may represent a novel biocompatible and active wound dress for the topical delivery of NO on wounds.     

Adenovirus-mediated VEGF(165) gene transfer enhances wound healing by promoting angiogenesis in CD1 diabetic mice

It has been previously shown that vascular endothelial growth factor (VEGF) plays a central role in promoting angiogenesis during wound repair and that healing-impaired diabetic mice show decreased VEGF expression levels. In order to investigate the potential benefits of gene therapy with growth factors on wound repair, a replication-deficient recombinant adenovirus vector carrying the human VEGF(165) gene (AdCMV.VEGF(165)) was topically applied on excisional wounds of streptozotocin-induced diabetic mice. Treatment with AdCMV.VEGF(165) significantly accelerated wound closure when compared with AdCMV.LacZ-treated, as well as saline-treated control mice, by promoting angiogenesis at the site of injury. Our findings suggest that AdCMV.VEGF(165) may be regarded as a therapeutic tool for the treatment of diabetic ulcers.     

Discordant effects of a soluble VEGF receptor on wound healing and angiogenesis

Soluble receptors to vascular endothelial growth factor (VEGF) can inhibit its angiogenic effect. Since angiogenesis is involved in wound repair, we hypothesized that adenovirus-mediated gene transfer of a soluble form of VEGF receptor 2 (Flk-1) would attenuate wound healing in mice. C57Bl/6J and genetically diabetic (db/db) mice (each n=20) received intravenous (i.v.) injections of recombinant adenoviruses (10(9) PFU) encoding the ligand-binding ectodomain of VEGF receptor 2 (Flk-1) or cDNA encoding the murine IgG2alpha Fc fragment (each n=10). At 4 days after gene transfer, two full-thickness skin wounds (0.8 cm) were created on the dorsum of each animal. Wound closure was measured over 9-14 days after which wounds were resected for histological analysis. Prior to killing, fluorescent microspheres were systemically injected for quantitation of wound vascularity. Single i.v. injections of adenoviruses encoding soluble Flk-1 significantly decreased wound angiogenesis in both wild-type and diabetic mice. Fluorescence microscopy revealed a 2.0-fold (wild type) and 2.9-fold (diabetic) reduction in wound vascularity in Flk-1-treated animals (p<0.05). Impairment of angiogenesis was confirmed by CD31 immunohistochemistry. Interestingly, despite significant reductions in wound vascularity, wound closure was not grossly delayed. Our data indicates that while VEGF function is essential for optimal wound angiogenesis, it is not required for wound closure.     

不同换药方式对糖尿病模型小鼠和正常小鼠创面愈合影响的实验研究

[目的]比较生理盐水、4%硼酸溶液、0.5%碘伏＋3%过氧化氢3种临床常用护理换药方式对糖尿病小鼠和正常小鼠创面愈合的影响,以期探索最适合糖尿病难愈性创面的护理换药方式。[方法]取雄性8周龄C57BL/6J小鼠30只,设糖尿病组与对照组小鼠各15只,糖尿病小鼠以链脲佐菌素（STZ诱导）在背部制作3个同等大小的全层皮肤创面后,每日1次分别以生理盐水（A处理）、4%硼酸溶液（B处理）和0.5%碘伏＋3%过氧化氢溶液（C处理）对创面换药,记录创面结痂及感染情况并计算创面愈合率。[结果]在同一时相点、A处理换药方式下,糖尿病组小鼠的创面愈合率明显低于对照组小鼠;对照组小鼠在3种不同换药处理方式下,其创面愈合率差异无统计学意义（P〉0.05）;糖尿病小鼠应用B处理的创面愈合率显著高于应用A和C处理法（P〈0.05）。[结论]正常小鼠创面应用3种换药方式对创面的愈合率无显著影响;糖尿病小鼠创面使用硼酸溶液换药较其他换药方式更有利于伤口愈合。     

Intradermal Delivery of Plasmid VEGF165 by Electroporation Promotes Wound Healing

Skin flaps are extensively used in reconstructive surgeries to repair large defects and deep wounds, but severe ischemia and necrosis often results in loss of the transplanted tissue. Thus, skin flap models are often used to study the biology of healing and necrosis of acute ischemic wounds. Delivery of exogenous vascular endothelial growth factor (VEGF) to areas of ischemia has shown promise for promoting therapeutic angiogenesis, but its expression must be tightly regulated to avoid adverse effects. In this study, plasmid DNA encoding VEGF₁₆₅ (pVEGF) was delivered to the ischemic skin of a rat skin flap model by intradermal injection followed by electroporation (EP) (pVEGFE+). Treatment with pVEGFE+ significantly increased VEGF expression for 5 days after delivery compared to injection of pVEGF without EP (pVEGFE−). The short-term increase in VEGF was sufficient to mediate an upregulation of endothelial nitric oxide synthase, an angiogenic factor that increases vascular permeability. pVEGFE+ significantly increased skin flap perfusion at both days 10 and 14 postoperatively. The observed increase in perfusion with pVEGFE+ correlated with an increase in skin flap healing and survival. Our results demonstrate that pVEGFE+ is a potential nonviral noninvasive therapy to increase perfusion and healing of skin flaps and ischemic wounds.     

The dipeptidyl peptidase-4 inhibitor linagliptin attenuates inflammation and accelerates epithelialization in wounds of diabetic ob/ob mice

In recent years, new and effective therapeutic agents for blood glucose control have been added to standard diabetes therapies: dipeptidyl peptidase-4 (DPP-4) inhibitors, which prolong the bioavailability of the endogenously secreted incretin hormone glucagon-like peptide-1 (GLP-1). Full-thickness excisional wounding was performed in wild-type (C57BL/6J) and diabetic [C57BL/6J-obese/obese (ob/ob)] mice. DPP-4 activity was inhibited by oral administration of linagliptin during healing. Wound tissue was analyzed by using histological, molecular, and biochemical techniques. In healthy mice, DPP-4 was constitutively expressed in the keratinocytes of nonwounded skin. After skin injury, DPP-4 expression declined and was lowest during the most active phase of tissue reassembly. In contrast, in ob/ob mice, we observed increasing levels of DPP-4 at late time points, when delayed tissue repair still occurs. Oral administration of the DPP-4 inhibitor linagliptin strongly reduced DPP-4 activity, stabilized active GLP-1 in chronic wounds, and improved healing in ob/ob mice. At day 10 postwounding, linagliptin-treated ob/ob mice showed largely epithelialized wounds characterized by the absence of neutrophils. In addition, DPP-4 inhibition reduced the expression of the proinflammatory markers cyclooxygenase-2 and macrophage inflammatory protein-2, but enhanced the formation of myofibroblasts in healing wounds from ob/ob mice. Our data suggest a potentially beneficial role of DPP-4 inhibition in diabetes-affected wound healing.     

Wound pathophysiology,infection and therapeutic options

Wound healing is a complex and highly regulated process that can be compromised by both endogenous factors (pathophysiological) and exogenous factors (micro-organisms). Microbial colonisation of both acute and chronic wounds is inevitable, and in most situations endogenous bacteria predominate, many of which are potentially pathogenic in the wound environment. The risk of wound infection increases as local conditions favour bacterial growth rather than host defence. Consequently a primary objective in wound management is to redress the host-bacterial balance, and this is most effectively achieved by ensuring that the wound is cleared of devitalised tissue and foreign bodies, the bacterial load and inflammation are controlled, and that adequate tissue perfusion is maintained. Although surgical debridement is the most rapid and effective technique for removing devitalised tissue, topical enzymes, moisture-retentive dressings, biosurgical therapy and vacuum therapy have been used as alternative approaches to wound cleansing and preparation. Topical antimicrobial agents continue to be used widely for preventing wound infection and current interest is focused on alternatives to antibiotics, such as antimicrobial moisture-retentive dressings, honey, essential oils and cationic peptides. In addition to the need to control wound microflora, unregulated inflammation caused by both micro-organisms and underlying abnormal pathophysiological conditions is a major factor associated with poor healing in chronic wounds. Consequently, therapeutic strategies that target chronic inflammatory processes are critical to wound progression. The success of future therapies will be dependent on a growing understanding of the pathophysiological processes and the host-bacterial interactions that significantly influence wound healing.     

Wound pathophysiology,infection and therapeutic options

Wound healing is a complex and highly regulated process that can be compromised by both endogenous factors (pathophysiological) and exogenous factors (micro-organisms). Microbial colonisation of both acute and chronic wounds is inevitable, and in most situations endogenous bacteria predominate, many of which are potentially pathogenic in the wound environment. The risk of wound infection increases as local conditions favour bacterial growth rather than host defence. Consequently a primary objective in wound management is to redress the host-bacterial balance, and this is most effectively achieved by ensuring that the wound is cleared of devitalised tissue and foreign bodies, the bacterial load and inflammation are controlled, and that adequate tissue perfusion is maintained. Although surgical debridement is the most rapid and effective technique for removing devitalised tissue, topical enzymes, moisture-retentive dressings, biosurgical therapy and vacuum therapy have been used as alternative approaches to wound cleansing and preparation. Topical antimicrobial agents continue to be used widely for preventing wound infection and current interest is focused on alternatives to antibiotics, such as antimicrobial moisture-retentive dressings, honey, essential oils and cationic peptides. In addition to the need to control wound microflora, unregulated inflammation caused by both micro-organisms and underlying abnormal pathophysiological conditions is a major factor associated with poor healing in chronic wounds. Consequently, therapeutic strategies that target chronic inflammatory processes are critical to wound progression. The success of future therapies will be dependent on a growing understanding of the pathophysiological processes and the host-bacterial interactions that significantly influence wound healing.     

Role of nitric oxide in wound healing

Chronic wounds mainly affect elderly individuals and persons with comorbid diseases due to a compromised immune status. An age-related decline in immune function deters proper healing of wounds in an orderly and timely manner. Thus, older adults with 1 or more concomitant illnesses are more likely to experience and sufferfrom a nonhealing wound, which may drastically decrease their quality of life and financial resources. Novel therapies in wound care management rely heavily on our current knowledge of wound healing physiology. It is well established that normal wound healing occurs sequentially and is strictly regulated by pro-inflammatory cytokines and growth factors. A multitude of commercial products such as growth factors are available; however, their effectiveness in healing chronic wounds has yet to be proven. Recently, investigators have implicated nitric oxide (NO) in the exertion of regulatoryforces on various cellular activities of the inflammatory and proliferative phases of wound healing. Gene therapy in animal studies has shown promising results and is furthering our understanding of impaired wound healing. The purpose of this article is to review the literature on NO and its role in wound healing. A discussion of the physiology of normal healing and the pathophysiology of chronic wounds is provided.     

A fragment of secreted Hsp90α carries properties that enable it to accelerate effectively both acute and diabetic wound healing in mice

Wounds that fail to heal in a timely manner, for example, diabetic foot ulcers, pose a health, economic, and social problem worldwide. For decades, conventional wisdom has pointed to growth factors as the main driving force of wound healing; thus, growth factors have become the center of therapeutic developments. To date, becaplermin (recombinant human PDGF-BB) is the only US FDA-approved growth factor therapy, and it shows modest efficacy, is costly, and has the potential to cause cancer in patients. Other molecules that drive wound healing have therefore been sought. In this context, it has been noticed that wounds do not heal without the participation of secreted Hsp90α. Here, we report that a 115-aa fragment of secreted Hsp90α (F-5) acts as an unconventional wound healing agent in mice. Topical application of F-5 peptide promoted acute and diabetic wound closure in mice far more effectively than did PDGF-BB. The stronger effect of F-5 was due to 3 properties not held by conventional growth factors: its ability to recruit both epidermal and dermal cells; the fact that its ability to promote dermal cell migration was not inhibited by TGF-β; and its ability to override the inhibitory effects of hyperglycemia on cell migration in diabetes. The discovery of F-5 challenges the long-standing paradigm of wound healing factors and reveals a potentially more effective and safer agent for healing acute and diabetic wounds.