The function of KGF in morphogenesis of epithelium and reepithelialization of wounds

Basic Fibroblast Growth Factor Influences Epidermal Homeostasis of Living Skin Equivalents through Affecting Fibroblast Phenotypes and Functions

AIMS

To elucidate the possible mechanisms of how basic fibroblast growth factor (bFGF) influences epidermal homeostasis in a living skin equivalent (LSE) model.

METHODS

Several wound healing-related growth factors were analyzed at protein and mRNA levels for dermal fibroblasts of induced alpha-smooth muscle actin (α-SMA)-positive or α-SMA-negative phenotypes. During culturing an LSE model by seeding normal human keratinocytes on a fibroblast-populated type I collagen gel, bFGF or neutralizing antibody for keratinocyte growth factor (KGF) was added to investigate its effects on fibroblast phenotypes and, subsequently, epidermal homeostasis by histology and immunohistochemistry.

RESULTS

The α-SMA-positive phenotype of fibroblasts induced by transforming growth factor beta-1 (TGF-β1) markedly suppressed the expression of KGF and hepatocyte growth factor (HGF), and slightly upregulated vascular endothelial growth factor (VEGF) and TGF-β1 at mRNA and protein levels, compared with α-SMA-negative fibroblasts treated with bFGF. α-SMA expression of fibroblasts at the epidermal-mesenchymal junction of the LSEs was suppressed by the addition of bFGF, and a better-differentiated epidermis was presented. The abrogation of KGF from fibroblasts by the addition of the KGF neutralizing antibody disenabled the LSE culturing system to develop an epidermis.

CONCLUSIONS

bFGF, through affecting the phenotypes and functions of fibroblasts, especially KGF expression, influenced epidermal homeostasis in an LSE model.

Fibroblast growth factors: key players in regeneration and tissue repair

Tissue injury initiates a complex repair process, which in some organisms can lead to the complete regeneration of a tissue. In mammals, however, the repair of most organs is imperfect and results in scar formation. Both regeneration and repair are orchestrated by a highly coordinated interplay of different growth factors and cytokines. Among the key players are the fibroblast growth factors (FGFs), which control the migration, proliferation, differentiation and survival of different cell types. In addition, FGFs influence the expression of other factors involved in the regenerative response. Here, we summarize current knowledge on the roles of endogenous FGFs in regeneration and repair in different organisms and in different tissues and organs. Gaining a better understanding of these FGF activities is important for appropriate modulation of FGF signaling after injury to prevent impaired healing and to promote organ regeneration in humans.

Effects of ethyl-α-d-glucoside on human dermal fibroblasts

Ethyl α-d-glucoside (α-EG) is a glycoside present in sake, Japanese rice wine. Previous studies have reported that α-EG suppresses skin roughness after ultraviolet B irradiation, transepidermal water loss, and hepatic function disorder, and has a skin moisturizing effect. In this study, 0.48 μM of α-EG was found to increase the proliferation of normal human dermal fibroblasts (NHDF) by 121.0%, and the amount of collagen I produced by NHDF increased by 159.6% at an α-EG concentration of 0.048 μM, compared to those in cells cultured without α-EG. In NHDF cultured in α-EG-supplemented medium, the expression of fibroblast growth factor I and VII mRNA increased by 148.8 and 153.1%, at an α-EG concentration of 4.8 and 0.048 μM, respectively, as measured by a quantitative reverse transcription-polymerase chain reaction. Transcript levels of type I collagen genes, COL1A1 and COL1A2, increased by 152.4 and 129.7%, respectively, and that of a type III collagen gene, COL3A1, increased by 131.8% at an α-EG concentration of 0.48 μM. These findings supported the possibility that α-EG was involved in the maintenance and improvement of skin homeostasis and moisturizing functions.

Development of Novel Mouse Model of Ulcers Induced by Implantation of Magnets

We developed a novel mouse model of human refractory cutaneous ulcers that more faithfully reflects pathology and evaluated the effects of mixed cell sheets comprising peripheral blood mononuclear cells and fibroblasts, which we previously developed for treating refractory cutaneous ulcers. Model development involved sandwiching the skin between two magnets, one of which was implanted under the skin for 7 consecutive days. This magnet-implanted ulcer model produced persistently large amounts of exudate and induced the infiltration of the ulcer with inflammatory cells. The model mice had a thicker epidermis and impaired transforming growth factor-β (TGF-β) signaling followed by SMAD2 down-regulation, which causes epidermal hyperplasia in chronic ulcers. Impaired TGF-β signaling also occurred in the ulcers of critical limb ischemia patients. Mixed cell implantation in this ulcer model reduced TNF-α and IL-6 levels in the tissues surrounding the mixed cell sheet-treated ulcers compared with controls or mice treated with trafermin (FGF2). Seven days after commencing therapy, the epidermis was thinner in mice treated with the mixed cell sheets than in controls. This model may therefore serve as a clinically relevant model of human ulcers, and our mixed cell sheets may effectively relieve chronic inflammation and inhibit refractoriness mechanisms.

Keratinocyte growth factor and the expression of wound-healing-related genes in primary human keratinocytes from burn patients

PURPOSE

To evaluate the effect of keratinocyte growth factor (KGF) treatment on the expression of wound-healing-related genes in cultured keratinocytes from burn patients.

METHODS

Keratinocytes were cultured and divided into 4 groups (n=4 in each group): TKB (KGF-treated keratinocytes from burn patients), UKB (untreated keratinocytes from burn patients), TKC (KGF-treated keratinocytes from controls), and UKC (untreated keratinocytes from controls). Gene expression analysis using quantitative polymerase chain reaction (qPCR) array was performed to compare (1) TKC versus UKC, (2) UKB versus UKC, (3) TKB versus UKC, (4) TKB versus UKB, (5) TKB versus TKC, and (6) UKB versus TKC.

RESULTS

Comparison 1 showed one down-regulated and one up-regulated gene; comparisons 2 and 3 resulted in the same five down-regulated genes; comparison 4 had no significant difference in relative gene expression; comparison 5 showed 26 down-regulated and 7 up-regulated genes; and comparison 6 showed 25 down-regulated and 11 up-regulated genes.

CONCLUSION

There was no differential expression of wound-healing-related genes in cultured primary keratinocytes from burn patients treated with keratinocyte growth factor.

Explant culture: An advantageous method for isolation of mesenchymal stem cells from human tissues

Mesenchymal stem cell (MSC) research progressively moves towards clinical phases. Accordingly, a wide range of different procedures were presented in the literature for MSC isolation from human tissues; however, there is not yet any close focus on the details to offer precise information for best method selection. Choosing a proper isolation method is a critical step in obtaining cells with optimal quality and yield in companion with clinical and economical considerations. In this concern, current review widely discusses advantages of omitting proteolysis step in isolation process and presence of tissue pieces in primary culture of MSCs, including removal of lytic stress on cells, reduction of in vivo to in vitro transition stress for migrated/isolated cells, reduction of price, processing time and labour, removal of viral contamination risk, and addition of supporting functions of extracellular matrix and released growth factors from tissue explant. In next sections, it provides an overall report of technical highlights and molecular events of explant culture method for isolation of MSCs from human tissues including adipose tissue, bone marrow, dental pulp, hair follicle, cornea, umbilical cord and placenta. Focusing on informative collection of molecular and methodological data about explant methods can make it easy for researchers to choose an optimal method for their experiments/clinical studies and also stimulate them to investigate and optimize more efficient procedures according to clinical and economical benefits.

Tissue-scale coordination of cellular behaviour promotes epidermal wound repair in live mice

Tissue repair is fundamental to our survival as tissues are challenged by recurrent damage. During mammalian skin repair, cells respond by migrating and proliferating to close the wound. However, the coordination of cellular repair behaviours and their effects on homeostatic functions in a live mammal remains unclear. Here we capture the spatiotemporal dynamics of individual epithelial behaviours by imaging wound re-epithelialization in live mice. Differentiated cells migrate while the rate of differentiation changes depending on local rate of migration and tissue architecture. Cells depart from a highly proliferative zone by directionally dividing towards the wound while collectively migrating. This regional coexistence of proliferation and migration leads to local expansion and elongation of the repairing epithelium. Finally, proliferation functions to pattern and restrict the recruitment of undamaged cells. This study elucidates the interplay of cellular repair behaviours and consequent changes in homeostatic behaviours that support tissue-scale organization of wound re-epithelialization.

Conditional knockout of N-WASP in mouse fibroblast caused keratinocyte hyper proliferation and enhanced wound closure

Neural-Wiskott Aldrich Syndrome Protein (N-WASP) is expressed ubiquitously, regulates actin polymerization and is essential during mouse development. We have previously shown that N-WASP is critical for cell-ECM adhesion in fibroblasts. To characterize the role of N-WASP in fibroblast for skin development, we generated a conditional knockout mouse model in which fibroblast N-WASP was ablated using the Cre recombinase driven by Fibroblast Specific Protein promoter (Fsp-Cre). N-WASP^FKO (N-WASP^fl/fl; Fsp-cre) were born following Mendelian genetics, survived without any visible abnormalities for more than 1 year and were sexually reproductive, suggesting that expression of N-WASP in fibroblast is not critical for survival under laboratory conditions. Histological sections of N-WASP^FKO mice skin (13 weeks old) showed thicker epidermis with higher percentage of cells staining for proliferation marker (PCNA), suggesting that N-WASP deficient fibroblasts promote keratinocyte proliferation. N-WASP^FKO mice skin had elevated collagen content, elevated expression of FGF7 (keratinocyte growth factor) and TGFβ signaling proteins. Wound healing was faster in N-WASP^FKO mice compared to control mice and N-WASP deficient fibroblasts were found to have enhanced collagen gel contraction properties. These results suggest that N-WASP deficiency in fibroblasts improves wound healing by growth factor-mediated enhancement of keratinocyte proliferation and increased wound contraction in mice.

Cellular and Molecular Responses to Mechanical Expansion of Tissue

The increased use of tissue expander in the past decades and its potential market values in near future give enough reasons to sum up the consequences of tissue expansion. Furthermore, the patients have the right to know underlying mechanisms of adaptation of inserted biomimetic, its bioinspired materials and probable complications. The mechanical strains during tissue expansion are related to several biological phenomena. Tissue remodeling during the expansion is highly regulated and depends on the signal transduction. Any alteration may lead to tumor formation, necrosis and/or apoptosis. In this review, stretch induced cell proliferation, apoptosis, the roles of growth factors, stretch induced ion channels, and roles of second messengers are organized. It is expected that readers from any background can understand and make a decision about tissue expansion.

Dermal-Epidermal Cross-Talk: Differential Interactions With Microvascular Endothelial Cells

The biological importance of circulatory blood supply and angiogenesis for hair growth is now well recognized, but the their regulatory mechanisms require more mechanistic investigation. In vitro cocultures and tricultures can be successfully employed to greatly improve our knowledge on paracrine crosstalk between cell types that populate the dermal-epidermal interface and cutaneous vasculature. Here we report that human dermal fibroblasts (NHDF) promote viability and proliferation of microvascular endothelial cells (HMVEC), while HMVEC are not mitogenic for NHDF. In triculture setup, conditioned media (CM) obtained by cocultures (HMVEC/NHDF or HMVEC/follicle fibroblasts) differently modulate growth and proliferation of keratinocytes and alter the expression of metabolic and pro-inflammatory markers. In conclusion, tricultures were successfully employed to characterize in vitro dermal-epithelial and endothelial interactions and could integrate ex vivo and in vivo approaches by the use of high-throughput and standardized protocols in controlled conditions. J. Cell. Physiol. 232: 897-903, 2017. © 2016 Wiley Periodicals, Inc.

Mesenchymal Stem/Stromal Cells under Stress Increase Osteosarcoma Migration and Apoptosis Resistance via Extracellular Vesicle Mediated Communication

Studies have shown that mesenchymal stem/stromal cells (MSCs) from bone marrow are involved in the growth and metastasis of solid tumors but the mechanism remains unclear in osteosarcoma (OS). Previous studies have raised the possibility that OS cells may receive support from associated MSCs in the nutrient deprived core of the tumors through the release of supportive macromolecules and growth factors either in vesicular or non-vesicular forms. In the present study, we used stressed mesenchymal stem cells (SD-MSCs), control MSCs and OS cells to examine the hypothesis that tumor-associated MSCs in nutrient deprived core provide pro-proliferative, anti-apoptotic, and metastatic support to nearby tumor cells. Assays to study of the effects of SD-MSC conditioned media revealed that OS cells maintained proliferation when compared to OS cells grown under serum-starved conditions alone. Furthermore, OS cells in MSCs and SD-MSC conditioned media were significantly resistant to apoptosis and an increased wound healing rate was observed in cells exposed to either conditioned media or EVs from MSCs and SD-MSCs. RT-PCR assays of OS cells incubated with extracellular vesicles (EVs) from SD-MSCs revealed microRNAs that could potentially target metabolism and metastasis associated genes as predicted by in silico algorithms, including monocarboxylate transporters, bone morphogenic receptor type 2, fibroblast growth factor 7, matrix metalloproteinase-1, and focal adhesion kinase-1. Changes in the expression levels of focal adhesion kinase, STK11 were confirmed by quantitative PCR assays. Together, these data indicate a tumor supportive role of MSCs in osteosarcoma growth that is strongly associated with the miRNA content of the EVs released from MSCs under conditions that mimic the nutrient deprived core of solid tumors.

The role of Rho kinase (Rock) in re-epithelialization of adult zebrafish skin wounds

Complete re-epithelialization of full-thickness skin wounds in adult mammals takes days to complete and relies on numerous signaling cues and multiple overlapping cellular processes that take place both within the epidermis itself and in other participating tissues. We have previously shown that re-epithelialization of full-thickness skin wounds of adult zebrafish, however, is extremely rapid and largely independent of the other processes of wound healing allowing for the dissection of specific processes that occur in, or have a direct effect on, re-epithelializing keratinocytes. Recently, we have shown that, in addition to lamellipodial crawling at the leading edge, re-epithelialization of zebrafish partial- and full-thickness wounds requires long-range epithelial rearrangements including radial intercalations, flattening and directed elongation and that each of these processes involves Rho kinase (Rock) signaling. Our studies demonstrate how these coordinated signaling events allow for the rapid collective cell migration observed in adult zebrafish wound healing. Here we discuss the particular contribution of Rock to each of these processes.

Concise Review: The Use of Adipose-Derived Stromal Vascular Fraction Cells and Platelet Rich Plasma in Regenerative Plastic Surgery

Tissue engineering has emerged at the intersection of numerous disciplines to meet a global clinical need for technologies to promote the regeneration of tissues. Recently, many authors have focused their attention on mesenchymal stem/stromal cells (MSCs) for their capacity to differentiate into many cell lineages. The most widely studied cell types are bone marrow mesenchymal stem cells and adipose-derived stem cells (ASCs), which display similar results. Biomaterials, cells, and growth factors are needed to design a regenerative plastic surgery approach in the treatment of organ and tissue defects, but not all tissues are created equal. The aim of this article is to describe the advances in tissue engineering through the use of ASCs, platelet rich plasma, and biomaterials to enable regeneration of damaged complex tissue. Stem Cells 2017;35:117-134.

Formation of keratinocyte multilayers on filters under airlifted or submerged culture conditions in medium containing calcium, ascorbic acid, and keratinocyte growth factor

Three-dimensional (3D) cell culture is a powerful in vitro technique to study the stratification and differentiation of keratinocytes. However, culture conditions, including culture media, supplements, and scaffolds (e.g., collagen gels with or without fibroblasts), can vary considerably. Here, we evaluated the roles of calcium, L-ascorbic acid phosphate magnesium salt n-hydrate (APM), and keratinocyte growth factor (KGF) in a chemically defined medium, EpiLife, in 3D cultures of primary human epidermal keratinocytes directly plated on polycarbonate filter inserts under airlifted or submerged conditions. Eight culture media containing various combinations of these three supplements were examined. Calcium was necessary for the stratification and differentiation of keratinocytes based on the localization of keratins and involucrin. However, the localization patterns of keratins and integrin β4 were partially disrupted and Ki67-positive basal cells almost disappeared 3 weeks after airlift. The addition of KGF, but not APM, prevented these changes. Further addition of APM markedly improved the tissue architecture, including basal cell morphology and the appearance of keratohyalin granules and localized involucrin in the upper suprabasal cells, even after 1 week. Although the submerged culture also formed cornified epithelium-like multilayers, involucrin was localized in the cornified layer, where nuclei were often found. Based on these results, it is most effective to culture keratinocytes at the air-liquid interface in EpiLife medium supplemented with calcium, APM, and KGF to form well-organized and orthokeratinized multilayers as skin analogues.

Cutaneous Wound Healing: Myofibroblastic Differentiation and in Vitro Models

Wound healing is an interactive, dynamic 3-phased process. During the formation of granulation tissue, many fibroblastic cells acquire some morphological and biochemical smooth muscle features and are called myofibroblasts. Myofibroblasts participate in both granulation tissue formation and remodeling phases. Excessive scarring, which is a feature of impaired healing, is a serious health problem that may affect the patient's quality of life. The treatment costs of such lesions are high, and often, the results are unsatisfactory. To understand the wound healing process better and to promote improvement in human healing, models are needed that can predict the in vivo situation in humans. In vitro models allow the study of cell behavior in a controlled environment. Such modeling partitions and reduces to small scales behavior perceived in vivo. This article is focused on `fibroblasts.' In vitro models to study wound healing, the role of (myo)fibroblasts, and skin reconstruction in tissue replacement and promotion of wound healing are discussed.

N-Cadherin and Fibroblast Growth Factor Receptors crosstalk in the control of developmental and cancer cell migrations

Cell migrations are diverse. They constitutemajor morphogenetic driving forces during embryogenesis, but they contribute also to the loss of tissue homeostasis and cancer growth. Capabilities of cells to migrate as single cells or as collectives are controlled by internal and external signalling, leading to the reorganisation of their cytoskeleton as well as by the rebalancing of cell-matrix and cell-cell adhesions. Among the genes altered in numerous cancers, cadherins and growth factor receptors are of particular interest for cell migration regulation. In particular, cadherins such as N-cadherin and a class of growth factor receptors, namely FGFRs cooperate to regulate embryonic and cancer cell behaviours. In this review, we discuss on reciprocal crosstalk between N-cadherin and FGFRs during cell migration. Finally, we aim at clarifying the synergy between N-cadherin and FGFR signalling that ensure cellular reorganization during cell movements, mainly during cancer cell migration and metastasis but also during developmental processes.

Re-epithelialization of cutaneous wounds in adult zebrafish combines mechanisms of wound closure in embryonic and adult mammals

Re-epithelialization of cutaneous wounds in adult mammals takes days to complete and relies on numerous signalling cues and multiple overlapping cellular processes that take place both within the epidermis and in other participating tissues. Re-epithelialization of partial- or full-thickness skin wounds of adult zebrafish, however, is extremely rapid and largely independent of the other processes of wound healing. Live imaging after treatment with transgene-encoded or chemical inhibitors reveals that re-epithelializing keratinocytes repopulate wounds by TGF-β- and integrin-dependent lamellipodial crawling at the leading edges of the epidermal tongue. In addition, re-epithelialization requires long-range epithelial rearrangements, involving radial intercalations, flattening and directed elongation of cells - processes that are dependent on Rho kinase, JNK and, to some extent, planar cell polarity within the epidermis. These rearrangements lead to a massive recruitment of keratinocytes from the adjacent epidermis and make re-epithelialization independent of keratinocyte proliferation and the mitogenic effect of FGF signalling, which are only required after wound closure, allowing the epidermis outside the wound to re-establish its normal thickness. Together, these results demonstrate that the adult zebrafish is a valuable in vivo model for studying and visualizing the processes involved in cutaneous wound closure, facilitating the dissection of direct from indirect and motogenic from mitogenic effects of genes and molecules affecting wound re-epithelialization.

Aberrant Wound Healing in an Epidermal Interleukin-4 Transgenic Mouse Model of Atopic Dermatitis

Wound healing in a pre-existing Th2-dominated skin milieu was assessed by using an epidermal specific interleukin-4 (IL-4) transgenic (Tg) mouse model, which develops a pruritic inflammatory skin condition resembling human atopic dermatitis. Our results demonstrated that IL-4 Tg mice had delayed wound closure and re-epithelialization even though these mice exhibited higher degrees of epithelial cell proliferation. Wounds in IL-4 Tg mice also showed a marked enhancement in expression of inflammatory cytokines/chemokines, elevated infiltration of inflammatory cells including neutrophils, macrophages, CD3+ lymphocytes, and epidermal dendritic T lymphocytes. In addition, these mice exhibited a significantly higher level of angiogenesis as compared to wild type mice. Furthermore, wounds in IL-4 Tg mice presented with larger amounts of granulation tissue, but had less expression and deposition of collagen. Taken together, an inflamed skin condition induced by IL-4 has a pronounced negative influence on the healing process. Understanding more about the pathogenesis of wound healing in a Th2- dominated environment may help investigators explore new potential therapeutic strategies.

Role of fibroblast growth factors in organ regeneration and repair

In its broad sense, regeneration refers to the renewal of lost cells, tissues or organs as part of the normal life cycle (skin, hair, endometrium etc.) or as part of an adaptive mechanism that organisms have developed throughout evolution. For example, worms, starfish and amphibians have developed remarkable regenerative capabilities allowing them to voluntarily shed body parts, in a process called autotomy, only to replace the lost parts afterwards. The bizarre myth of the fireproof homicidal salamander that can survive fire and poison apple trees has persisted until the 20th century. Salamanders possess one of the most robust regenerative machineries in vertebrates and attempting to draw lessons from limb regeneration in these animals and extrapolate the knowledge to mammals is a never-ending endeavor. Fibroblast growth factors are potent morphogens and mitogens that are highly conserved among the animal kingdom. These growth factors play key roles in organogenesis during embryonic development as well as homeostatic balance during postnatal life. In this review, we provide a summary about the current knowledge regarding the involvement of fibroblast growth factor signaling in organ regeneration and repair. We also shed light on the use of these growth factors in previous and current clinical trials in a wide array of human diseases.

Control of hepatocyte proliferation and survival by Fgf receptors is essential for liver regeneration in mice

OBJECTIVE

Fibroblast growth factors (Fgfs) are key orchestrators of development, and a role of Fgfs in tissue repair is emerging. Here we studied the consequences of inducible loss of Fgf receptor (Fgfr) 4, the major Fgf receptor (Fgfr) on hepatocytes, alone or in combination with Fgfr1 and Fgfr2, for liver regeneration after PH.

DESIGN

We used siRNA delivered via nanoparticles combined with liver-specific gene knockout to study Fgfr function in liver regeneration. Liver or blood samples were analysed using histology, immunohistochemistry,real-time RT-PCR, western blotting and ELISA.

RESULTS

siRNA-mediated knockdown of Fgfr4 severely affected liver regeneration due to impairment of hepatocyte proliferation combined with liver necrosis.Mechanistically, the proliferation defect resulted from inhibition of an Fgf15-Fgfr4-Stat3 signalling pathway,which is required for injury-induced expression of the Foxm1 transcription factor and subsequent cell cycle progression, while elevated levels of intrahepatic toxicbile acids were identified as the likely cause of the necrotic damage. Failure of liver mass restoration in Fgfr4 knockdown mice was prevented at least in part by compensatory hypertrophy of hepatocytes. Most importantly, our data revealed partially redundant functions of Fgf receptors in the liver, since knock down of Fgfr4 in mice lacking Fgfr1 and Fgfr2 in hepatocytes caused liver failure after PH due to severe liver necrosis and a defect in regeneration.

CONCLUSIONS

These results demonstrate that Fgfr signalling in hepatocytes is essential for liver regeneration and suggest activation of Fgfr signalling asa promising approach for the improvement of the liver's regenerative capacity.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Cellular and molecular mechanisms of repair in acute and chronic wound healing

Summary

A considerable understanding of the fundamental cellular and molecular mechanisms underpinning healthy acute wound healing has been gleaned from studying various animal models, and we are now unravelling the mechanisms that lead to chronic wounds and pathological healing including fibrosis. A small cut will normally heal in days through tight orchestration of cell migration and appropriate levels of inflammation, innervation and angiogenesis. Major surgeries may take several weeks to heal and leave behind a noticeable scar. At the extreme end, chronic wounds – defined as a barrier defect that has not healed in 3 months – have become a major therapeutic challenge throughout the Western world and will only increase as our populations advance in age, and with the increasing incidence of diabetes, obesity and vascular disorders. Here we describe the clinical problems and how, through better dialogue between basic researchers and clinicians, we may extend our current knowledge to enable the development of novel potential therapeutic treatments.

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Extract of Allium tuberosum Rottler ex Spreng Promoted the Hair Growth through Regulating the Expression of IGF-1

Allium tuberosum Rottler ex Spreng (ATRES) has been used as a traditional medicine for the treatment of abdominal pain, diarrhea, and asthma. In this study, we investigated the hair growth promoting activities of ATRES on telogenic C57BL6/N mice. Hair growth was significantly increased in the dorsal skin of ethanol extract of ATRES treated mouse group compared with the control mouse group. To enrich the hair promoting activity, an ethanol-insoluble fraction was further extracted in sequence with n-hexane, dichloromethane, ethyl acetate, n-butanol, and distilled water. Interestingly, we found that extraction with n-butanol is most efficient in producing the hair promoting activity. In addition, the soluble fraction of the n-butanol extract was further separated by silica gel chromatography and thin layer chromatography (TLC) resulting in isolating four single fractions which have hair growth regeneration potential. Furthermore, administration of ATRES extracts to dorsal skin area increased the number of hair follicles compared with control mouse group. Interestingly, administration of ATRES extract stimulated the expression of insulin-like growth factor-1 (IGF-1) but not of keratin growth factor (KGF) or vascular endothelial growth factor (VEGF). Taken together, these results suggest that ATRES possesses strong hair growth promoting potential which controls the expression of IGF-1.

Mast cells are dispensable in a genetic mouse model of chronic dermatitis

Chronic inflammatory skin diseases, such as atopic dermatitis, affect a large percentage of the population, but the role of different immune cells in the pathogenesis of these disorders is largely unknown. Recently, we found that mice lacking fibroblast growth factor receptor 1 (Fgfr1) and Fgfr2 (K5-R1/R2 mice) in the epidermis have a severe impairment in the epidermal barrier, which leads to the development of a chronic inflammatory skin disease that shares many features with human atopic dermatitis. Using Fgfr1-/Fgfr2-deficient mice, we analyzed the consequences of the loss of mast cells. Mast cells accumulated and degranulated in the skin of young Fgfr1-/Fgfr2-deficient mice, most likely as a consequence of increased expression of the mast cell chemokine Ccl2. The increase in mast cells occurred before the development of histological abnormalities, indicating a functional role of these cells in the inflammatory skin phenotype. To test this hypothesis, we mated the Fgfr1-/Fgfr2-deficient mice with mast cell-deficient CreMaster mice. Surprisingly, loss of mast cells did not or only mildly affect keratinocyte proliferation, epidermal thickness, epidermal barrier function, accumulation and activation of different immune cells, or expression of different proinflammatory cytokines in the skin. These results reveal that mast cells are dispensable for the development of chronic inflammation in response to a defect in the epidermal barrier.

Clinical implication of perioperative inflammatory cytokine alteration

Cytokines are key modulators of inflammatory responses, and play an important role in the defense and repair mechanisms following trauma. After traumatic injury, an immuno-inflammatory response is initiated immediately, and cytokines rapidly appear and function as a regulator of immunity. In pathologic conditions, imbalanced cytokines may provide systemic inflammatory responses or immunosuppression. Expression of perioperative cytokines vary by different intensities of surgical trauma and types of anesthesia and anesthetic agents. Inflammatory cytokines play important roles in postoperative organ dysfunction including central nervous system, cardiovascular, lung, liver, and kidney injury. Inhibition of cytokines could protect against traumatic injury in some circumstances, therefore cytokine inhibitors or antagonists might have the potential for reducing postoperative tissue/organ dysfunction. Cytokines are also involved in wound healing and post-traumatic pain. Application of cytokines for the improvement of surgical wound healing has been reported. Anesthesia-related immune response adjustment might reduce perioperative morbidity because it reduces proinflammatory cytokine expression; however, the overall effects of anesthetics on postoperative immune-inflammatory responses needs to be further investigated.

Physiological functions and underlying mechanisms of fibroblast growth factor (FGF) family members: recent findings and implications for their pharmacological application

Despite their name, fibroblast growth factors (FGFs) are multifunctional regulators affecting a wide variety of physiological events. This review summarizes our recent studies on FGFs from mechanistic, physiological and application-oriented viewpoints. These include studies on the importance of βKlotho and glycosaminoglycans for the signaling of hormonal FGFs (FGF21 and FGF19); the physiological role of a paracrine FGF (FGF18) in hair cycle regulation; and the development of a stable, chimeric FGF protein composed of FGF1 and FGF2 domains suitable for radioprotection.

Wound repair and regeneration: mechanisms, signaling, and translation

The cellular and molecular mechanisms underpinning tissue repair and its failure to heal are still poorly understood, and current therapies are limited. Poor wound healing after trauma, surgery, acute illness, or chronic disease conditions affects millions of people worldwide each year and is the consequence of poorly regulated elements of the healthy tissue repair response, including inflammation, angiogenesis, matrix deposition, and cell recruitment. Failure of one or several of these cellular processes is generally linked to an underlying clinical condition, such as vascular disease, diabetes, or aging, which are all frequently associated with healing pathologies. The search for clinical strategies that might improve the body's natural repair mechanisms will need to be based on a thorough understanding of the basic biology of repair and regeneration. In this review, we highlight emerging concepts in tissue regeneration and repair, and provide some perspectives on how to translate current knowledge into viable clinical approaches for treating patients with wound-healing pathologies.

Careless talk costs lives: fibroblast growth factor receptor signalling and the consequences of pathway malfunction

Since its discovery 40 years ago, fibroblast growth factor (FGF) receptor (FGFR) signalling has been found to regulate fundamental cellular behaviours in a wide range of cell types. FGFRs regulate development, homeostasis, and repair and are implicated in many disorders and diseases; and indeed, there is extensive potential for severe consequences, be they developmental, homeostatic, or oncogenic, should FGF-FGFR signalling go awry, so careful control of the pathway is critically important. In this review, we discuss the recent developments in the FGF field, highlighting how FGFR signalling works in normal cells, how it can go wrong, how frequently it is compromised, and how it is being targeted therapeutically.

Ecklonia cava promotes hair growth

BACKGROUND

Previous studies have reported the protective effects on skin elasticity of the edible marine seaweed Ecklonia cava, which acts through regulation of both antioxidative and anti-inflammatory responses.

AIM

We evaluated the effect of E. cava and one of its components, dioxinodehydroeckol, on hair-shaft growth in cultured human hair follicles and on hair growth in mice.

METHODS

The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to check cell viability of human dermal papilla cells (DPCs) and outer root sheath (ORS) cells after treatment with E. cava and its metabolite, dioxinodehydroeckol. Hair-shaft growth was measured using the in vitro hair-follicle organ-culture system, in the presence or absence of E. cava and dioxinodehydroeckol. Anagen induction activity was examined by topical application of E. cava to the dorsal skin of C57BL/6 mice. Insulin-like growth factor (IGF)-1 expression was measured by reverse transcriptase PCR and ELISA.

RESULTS

The proliferation activity was found to be highest for the ethyl acetate-soluble fraction of E. cava (EAFE) in DPCs and in ORS cells. Treatment with EAFE resulted in elongation of the hair shaft in cultured human hair follicles, and promoted transition of the hair cycle from the telogen to the anagen phase in the dorsal skin of C57BL/6 mice. In addition, EAFE induced an increase in IGF-1 expression in DPCs. Dioxinodehydroeckol, a component of E. cava, induced elongation of the hair shaft, an increase in proliferation of DPCs and ORS cells, and an increase in expression of IGF-1 in DPCs.

CONCLUSIONS

These results suggest that E. cava containing dioxinodehydroeckol promotes hair growth through stimulation of DPCs and ORS cells.

Recombinant Human Keratinocyte Growth Factor Induces Akt Mediated Cell Survival Progression in Emphysematous Mice

INTRODUCTION

Emphysema has been associated with decreased VEGF and VEGFR-2 expression and the presence of high numbers of apoptotic alveolar cells. Keratinocyte growth factor stimulates VEGF synthesis which in turn confers normal lung structure maintenance via the Akt pathway. In this study the potential role of rHuKGF in the improvement of deregulated Akt mediated cell survival pathway in emphysematous mice was investigated.

METHODS

Three experimental groups, i.e., emphysema, treatment and control groups, were prepared. Lungs of mice were treated on 3 occasions by oropharyngeal instillation of 10mg rHuKGF per kg body weight after induction of emphysema with porcine pancreatic elastase. Subsequently, lung tissues from mice were collected for histopathology and molecular biology studies.

RESULTS AND DISCUSSION

Histopathology photomicrographs and destructive index analysis have shown that elastase-induced airspace enlargement and loss of alveoli recovered in the treatment group. rHuKGF stimulates VEGF production which in turn induces the Akt mediated cell survival pathway in emphysematous lungs. mRNA expression of VEGF, VEGFR, PI3K and Akt was significantly increased while Pten, Caspase-9 and Bad was notably decreased in treatment group when compared with emphysema group, being comparable with the control group. Moreover, VEGF protein expression was in accordance with that found for mRNA.

CONCLUSION

Therapeutic rHuKGF supplementation improves the deregulated Akt pathway in emphysema, resulting in alveolar cell survival through activation of the endogenous VEGF-dependent cell survival pathway. Hence rHuKGF may prove to be a potential drug in the treatment of emphysema.

Epithelialization in Wound Healing: A Comprehensive Review

Significance: Keratinocytes, a major cellular component of the epidermis, are responsible for restoring the epidermis after injury through a process termed epithelialization. This review will focus on the pivotal role of keratinocytes in epithelialization, including cellular processes and mechanisms of their regulation during re-epithelialization, and their cross talk with other cell types participating in wound healing. Recent Advances: Discoveries in epidermal stem cells, keratinocyte immune function, and the role of the epidermis as an independent neuroendocrine organ will be reviewed. Novel mechanisms of gene expression regulation important for re-epithelialization, including microRNAs and histone modifications, will also be discussed. Critical Issues: Epithelialization is an essential component of wound healing used as a defining parameter of a successful wound closure. A wound cannot be considered healed in the absence of re-epithelialization. The epithelialization process is impaired in all types of chronic wounds. Future Directions: A comprehensive understanding of the epithelialization process will ultimately lead to the development of novel therapeutic approaches to promote wound closure.

Palifermin for the protection and regeneration of epithelial tissues following injury: new findings in basic research and pre-clinical models

Keratinocyte growth factor (KGF) is a paracrine-acting epithelial mitogen produced by cells of mesenchymal origin, that plays an important role in protecting and repairing epithelial tissues. Pre-clinical data initially demonstrated that a recombinant truncated KGF (palifermin) could reduce gastrointestinal injury and mortality resulting from a variety of toxic exposures. Furthermore, the use of palifermin in patients with hematological malignancies reduced the incidence and duration of severe oral mucositis experienced after intensive chemoradiotherapy. Based upon these findings, as well as the observation that KGF receptors are expressed in many, if not all, epithelial tissues, pre-clinical studies have been conducted to determine the efficacy of palifermin in protecting different epithelial tissues from toxic injury in an attempt to model various clinical situations in which it might prove to be of benefit in limiting tissue damage. In this article, we review these studies to provide the pre-clinical background for clinical trials that are described in the accompanying article and the rationale for additional clinical applications of palifermin.

Recapitulation of morphogenetic cell shape changes enables wound re-epithelialisation

Wound repair is a fundamental, conserved mechanism for maintaining tissue homeostasis and shares many parallels with embryonic morphogenesis. Small wounds in simple epithelia rapidly assemble a contractile actomyosin cable at their leading edge, as well as dynamic filopodia that finally knit the wound edges together. Most studies of wound re-epithelialisation have focused on the actin machineries that assemble in the leading edge of front row cells and that resemble the contractile mechanisms that drive morphogenetic episodes, including Drosophila dorsal closure, but, clearly, multiple cell rows back must also contribute for efficient repair of the wound. Here, we examine the role of cells back from the wound edge and show that they also stretch towards the wound and cells anterior-posterior to the wound edge rearrange their junctions with neighbours to drive cell intercalation events. This process in anterior-posterior cells is active and dependent on pulses of actomyosin that lead to ratcheted shrinkage of junctions; the actomyosin pulses are targeted to breaks in the cell polarity protein Par3 at cell vertices. Inhibiting actomyosin dynamics back from the leading edge prevents junction shrinkage and inhibits the wound edge from advancing. These events recapitulate cell rearrangements that occur during germband extension, in which intercalation events drive the elongation of tissues.

Pten loss induces autocrine FGF signaling to promote skin tumorigenesis

Inactivation of the Pten tumor suppressor negatively regulates the PI3K-mTOR pathway. In a model of cutaneous squamous cell carcinoma (SCC), we demonstrate that deletion of Pten strongly elevates Fgf10 protein levels without increasing Fgf10 transcription in vitro and in vivo. The translational activation of Fgf10 by Pten deletion is reversed by genetic disruption of the mTORC1 complex, which also prevents skin tumorigenesis in Pten mutants. We further show that ectopic expression of Fgf10 causes skin papillomas, whereas Pten deletion-induced skin tumors are inhibited by epidermal deletion of Fgfr2. Collectively, our data identify autocrine activation of FGF signaling as an essential mechanism in promoting Pten-deficient skin tumors.

The effects of social isolation on wound healing mechanisms in female mice

Various stressors impair wound healing in humans and rodents. For example, social isolation delays wound closure in rodents, but the healing mechanisms that underlie this delay have yet to be identified. Here, the effects of three weeks of social isolation on hypothalamic-pituitary-adrenal axis responses and healing factors involved in the inflammatory and proliferative phases of wound healing were assessed in adult female hairless mice. Social isolation reduced basal circulating corticosterone concentrations and increased body and thymus weights compared with group-housed controls. Isolation impaired dermal wound closure by up to 30% and reduced initial total wound bacterial load relative to controls. Inflammatory gene expression in the wounds was not affected by the observed differences in wound bacterial load. However, isolation reduced wound gene expression of keratinocyte growth factor and vascular endothelial growth factor, which are involved in keratinocyte proliferation/migration and angiogenesis during the proliferative phase of healing. These data indicate that social isolation induces healing impairments that may be attributed to reductions in growth factors necessary for proper skin cell proliferation and blood vessel growth during healing. This healing impairment occurred in the absence of both high wound bacterial load and elevated circulating glucocorticoids, which have previously been hypothesized to be required for stress-impaired healing in mice.

Strengthening the skin with topical delivery of keratinocyte growth factor-1 using a novel DNA plasmid

Fragile skin, susceptible to decubitus ulcers and incidental trauma, is a problem particularly for the elderly and for those with spinal cord injury. Here, we present a simple approach to strengthen the skin by the topical delivery of keratinocyte growth factor-1 (KGF-1) DNA. In initial feasibility studies with the novel minimalized, antibiotic-free DNA expression vector, NTC8385-VA1, the reporter genes luciferase and enhanced green fluorescent protein were delivered. Transfection was documented when luciferase expression significantly increased after transfection. Microscopic imaging of enhanced green fluorescent protein-transfected skin showed green fluorescence in hair follicles, hair shafts, and dermal and superficial epithelial cells. With KGF-1 transfection, KGF-1 mRNA level and protein production were documented with quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry, respectively. Epithelial thickness of the transfected skin in the KGF group was significantly increased compared with the control vector group (26 ± 2 versus 16 ± 4 µm) at 48 hours (P = 0.045). Dermal thickness tended to be increased in the KGF group (255 ± 36 versus 162 ± 16 µm) at 120 hours (P = 0.057). Biomechanical assessment showed that the KGF-1-treated skin was significantly stronger than control vector-transfected skin. These findings indicate that topically delivered KGF-1 DNA plasmid can increase epithelial thickness and strength, demonstrating the potential of this approach to restore compromised skin.

Mast cells are dispensable for normal and activin-promoted wound healing and skin carcinogenesis

The growth and differentiation factor activin A is a key regulator of tissue repair, inflammation, fibrosis, and tumorigenesis. However, the cellular targets, which mediate the different activin functions, are still largely unknown. In this study, we show that activin increases the number of mature mast cells in mouse skin in vivo. To determine the relevance of this finding for wound healing and skin carcinogenesis, we mated activin transgenic mice with CreMaster mice, which are characterized by Cre recombinase-mediated mast cell eradication. Using single- and double-mutant mice, we show that loss of mast cells neither affected the stimulatory effect of overexpressed activin on granulation tissue formation and reepithelialization of skin wounds nor its protumorigenic activity in a model of chemically induced skin carcinogenesis. Furthermore, mast cell deficiency did not alter wounding-induced inflammation and new tissue formation or chemically induced angiogenesis and tumorigenesis in mice with normal activin levels. These findings reveal that mast cells are not major targets of activin during wound healing and skin cancer development and also argue against nonredundant functions of mast cells in wound healing and skin carcinogenesis in general.