Bone marrow cells engraft within the epidermis and proliferate in vivo with no evidence of cell fusion

Emergence and properties of adult mammalian epidermal stem cells

In this review we discuss how the mammalian interfollicular epidermis forms during development, maintains homeostasis, and is repaired following wounding. Recent studies have provided new insights into the relationship between the stem cell compartment and the differentiating cell layers; the ability of differentiated cells to dedifferentiate into stem cells; and the epigenetic memory of epidermal cells following wounding.

Wounds under diabetic milieu: The role of immune cellar components and signaling pathways

A major challenge in the field of diabetic wound healing is to confirm the body's intrinsic mechanism that could sense the immune system damage promptly and protect the wound from non-healing. Accumulating literature indicates that macrophage, a contributor to prolonged inflammation occurring at the wound site, might play such a role in hindering wound healing. Likewise, other immune cell dysfunctions, such as persistent neutrophils and T cell infection, may also lead to persistent oxidative stress and inflammatory reaction during diabetic wound healing. In this article, we discuss recent advances in the immune cellular components in wounds under the diabetic milieu, and the role of key signaling mechanisms that compromise the function of immune cells leading to persistent wound non-healing.

Genes and compounds that increase type VII collagen expression as potential treatments for dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a skin-blistering disease caused by mutations in COL7A1, which encodes type VII collagen (C7). There is no cure for DEB, but previous work has shown potential therapeutic benefit of increased production of even partially functional C7. Genome-wide screens using CRISPR-Cas9 have enabled the identification of genes involved in cancer development, drug resistance, and other genetic diseases, suggesting that they could be used to identify drivers of C7 production. A keratinocyte C7 reporter cell line was created and used in a genome-wide CRISPR activation (CRISPRa) screen to identify genes and pathways that increase C7 expression. The CRISPRa screen results were used to develop a targeted drug screen to identify compounds that upregulate C7 expression. The C7_tdTomato cell line was validated as an effective reporter for detection of C7 upregulation. The CRISPRa screen identified DENND4B and TYROBP as top gene hits plus pathways related to calcium uptake and immune signaling in C7 regulation. The targeted drug screen identified several compounds that increase C7 expression in keratinocytes, of which kaempferol, a plant flavonoid, also significantly increased C7 mRNA and protein in DEB patient cells.

ABCB5+ dermal mesenchymal stromal cells with favorable skin homing and local immunomodulation for recessive dystrophic epidermolysis bullosa treatment

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare, incurable blistering skin disease caused by biallelic mutations in type VII collagen (C7). Advancements in treatment of RDEB have come from harnessing the immunomodulatory potential of mesenchymal stem cells (MSCs). Although human bone marrow-derived MSC (BM-MSC) trials in RDEB demonstrate improvement in clinical severity, the mechanisms of MSC migration to and persistence in injured skin and their contributions to wound healing are not completely understood. A unique subset of MSCs expressing ATP-binding cassette subfamily member 5 (ABCB5) resides in the reticular dermis and exhibits similar immunomodulatory characteristics to BM-MSCs. Our work aimed to test the hypothesis that skin-derived ABCB5+ dermal MSCs (DSCs) possess superior skin homing ability compared to BM-MSCs in immunodeficient NOD-scid IL2rgamma^null (NSG) mice. Compared to BM-MSCs, peripherally injected ABCB5+ DSCs demonstrated superior homing and engraftment of wounds. Furthermore, ABCB5+ DSCs vs BM-MSCs cocultured with macrophages induced less anti-inflammatory interleukin-1 receptor antagonist (IL-1RA) production. RNA sequencing of ABCB5+ DSCs compared to BM-MSCs showed unique expression of major histocompatibility complex class II and Homeobox (Hox) genes, specifically HOXA3. Critical to inducing migration of endothelial and epithelial cells for wound repair, increased expression of HOXA3 may explain superior skin homing properties of ABCB5+ DSCs. Further discernment of the immunomodulatory mechanisms among MSC populations could have broader regenerative medicine implications beyond RDEB treatment.

Leading edge: emerging drug, cell, and gene therapies for junctional epidermolysis bullosa

INTRODUCTION

Junctional epidermolysis bullosa (JEB) is a rare inherited genetic disorder with limited treatments beyond palliative care. A major hallmark of JEB is skin blistering caused by functional loss or complete absence of major structural proteins of the skin. Impaired wound healing in patients with JEB gives rise to chronic cutaneous ulcers that require daily care. Wound care and infection control are the current standard of care for this patient population.

AREAS COVERED

This review covers research and clinical implementation of emerging drug, cell, and gene therapies for JEB. Current clinical trials use topical drug delivery to manipulate the inflammation and re-epithelialization phases of wound healing or promote premature stop codon readthrough to accelerate chronic wound closure. Allogeneic cell therapies for JEB have been largely unsuccessful, with autologous skin grafting emerging as a reliable method of resolving the cutaneous manifestations of JEB. Genetic correction and transplant of autologous keratinocytes have demonstrated persistent amelioration of chronic wounds in a subset of patients.

EXPERT OPINION

Emerging therapies address the cutaneous symptoms of JEB but are unable to attend to systemic manifestations of the disease. Investigations into the molecular mechanism(s) underpinning the failure of systemic allogeneic cell therapies are necessary to expand the range of effective JEB therapies.

A novel role of angiotensin II in epidermal cell lineage determination: Angiotensin II promotes the differentiation of mesenchymal stem cells into keratinocytes through the p38 MAPK, JNK and JAK2 signalling pathways

BACKGROUND

Recent evidence suggests that angiotensin II (Ang II) plays a role in cutaneous wound healing. Mesenchymal stem cells (MSCs) are known as a rich source of cells that re-establish healed skin. However, the potential impact of Ang II on MSC differentiation into keratinocytes is still unknown.

OBJECTIVE

The present study was conducted to explore the effect of Ang II on the differentiation of bone marrow-derived MSCs (BM-MSCs) into keratinocytes.

METHODS

Bone marrow-derived MSCs were isolated from rat bone marrow and cultured. The expression of Ang II type 1 (AT₁ ) and type 2 (AT₂ ) receptors was examined by immunofluorescence staining. The differentiation of BM-MSCs into keratinocytes was investigated by flow cytometry or/and histological observation.

RESULTS

The BM-MSCs constitutively expressed both AT₁ and AT₂ receptors. The differentiation of BM-MSCs into keratinocytes was successfully induced. Interestingly, incubation of BM-MSCs with Ang II further promoted the differentiation of BM-MSCs into keratinocyte, which was abolished by pretreament with losartan, an AT₁ receptor antagonist, but not by PD123319, an AT₂ receptor antagonist. Moreover, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, the c-Jun N-terminal kinase (JNK) inhibitor SP600125 and the Janus-activated kinase (JAK)2 inhibitor AG490 suppressed Ang II-induced differentiation of BM-MSCs into keratinocytes. The phosphoinositide-3 kinase (PI3K) inhibitor wortmannin and MEK1/2 inhibitor U0126 had no effect on BM-MSC differentiation into keratinocytes.

CONCLUSIONS

Our data demonstrated for the first time that Ang II plays a promotive role in the differentiation of BM-MSC into keratinocytes through the AT₁ receptor, and that the p38 MAPK, JNK and JAK2 signalling pathways are involved in this process.

Mesenchymal Stem Cells for Chronic Wound Healing: Current Status of Preclinical and Clinical Studies

Healing skin wounds with anatomic and functional integrity, especially under chronic pathological conditions, remain an enormous challenge. Due to their outstanding regenerative potential, mesenchymal stem cells (MSCs) have been explored in many studies to determine the healing ability for difficult-to-treat diseases. In this article, we review current animal studies and clinical trials of MSC-based therapy for chronic wounds, and discuss major challenges that confront future clinical applications. We found that a wealth of animal studies have revealed the versatile roles and the benefits of MSCs for chronic wound healing. MSC treatment results in enhanced angiogenesis, facilitated reepithelialization, improved granulation, and accelerated wound closure. There are some evidences of the transdifferentiation of MSCs into skin cells. However, the healing effect of MSCs depends primarily on their paracrine actions, which alleviate the harsh microenvironment of chronic wounds and regulate local cellular responses. Consistent with the findings of preclinical studies, some clinical trials have shown improved wound healing after transplantation of MSCs in chronic wounds, mainly lower extremity ulcers, pressure sores, and radiation burns. However, there are some limitations in these clinical trials, especially a small number of patients and imperfect methodology. Therefore, to better define the safety and efficiency of MSC-based wound therapy, large-scale controlled multicenter trials are needed in the future. In addition, to build a robust pool of clinical evidence, standardized protocols, especially the cultivation and quality control of MSCs, are recommended. Altogether, based on current data, MSC-based therapy represents a promising treatment option for chronic wounds. Impact statement Chronic wounds persist as a significant health care problem, particularly with increasing number of patients and the lack of efficient treatments. The main goal of this article is to provide an overview of current status of mesenchymal stem cell (MSC)-based therapy for chronic wounds. The roles of MSCs in skin wound healing, as revealed in a large number of animal studies, are detailed. A critical view is made on the clinical application of MSCs for lower extremity ulcers, pressure sores, and radiation burns. Main challenges that confront future clinical applications are discussed, which hopefully contribute to innovations in MSC-based wound treatment.

Identification of Specific miRNAs in Neutrophils of Type 2 Diabetic Mice: Overexpression of miRNA-129-2-3p Accelerates Diabetic Wound Healing

Neutrophils are involved in the first stage of acute inflammation. After injury, they are mobilized and recruited to the injured tissue. In diabetes, wound healing is delayed and aberrant, leading to excessive recruitment and retention of neutrophils that fail to promote angiogenesis and prolong inflammation. However, the exact pathological mechanisms of diabetic-derived neutrophils in chronic inflammation remain unclear. Here, miRNA profiling of neutrophils from bone marrow in type 2 diabetic mice was performed using a microarray. miRNAs regulate the posttranscriptional expression of target mRNAs and are important in countering inflammation-related diseases. Our study revealed that miRNAs exhibit differential expression in diabetic-derived neutrophils compared with non-diabetic-derived neutrophils, especially miR-129 family members. miR-129-2-3p directly regulated the translation of Casp6 and Ccr2, which are involved in inflammatory responses and apoptosis. Furthermore, miR-129-2-3p overexpression at the wound site of type 2 diabetic mice accelerated wound healing. These results suggest possible involvement of miR-129-2-3p in diabetic-derived neutrophil dysfunction and that retention kinetics of neutrophils and chronic inflammation may be initiated through miR-129-2-3p-regulated genes. This study characterizes changes in global miRNA expression in diabetic-derived neutrophils and systematically identifies critical target genes involved in certain biological processes related to the pathology of diabetic wound healing.

Bone marrow-derived epithelial cells and hair follicle stem cells contribute to development of chronic cutaneous neoplasms

We used allogeneic bone marrow transplantation (BMT) and a mouse multistage cutaneous carcinogenesis model to probe recruitment of bone marrow-derived epithelial cells (BMDECs) in skin tumors initiated with the carcinogen, dimethylbenz[a]anthracene (DMBA), and promoted with 12-O-tetradecanolyphorbol-13-acetate (TPA). BMDECs clustered in the lesional epithelium, expressed cytokeratins, proliferated, and stratified. We detected cytokeratin induction in plastic-adherent bone marrow cells (BMCs) cultured in the presence of filter-separated keratinocytes (KCs) and bone morphogenetic protein 5 (BMP5). Lineage-depleted BMCs migrated towards High Mobility Group Box 1 (HMGB1) protein and epidermal KCs in ex vivo invasion assays. Naive female mice receiving BMTs from DMBA-treated donors developed benign and malignant lesions after TPA promotion alone. We conclude that BMDECs contribute to the development of papillomas and dysplasia, demonstrating a systemic contribution to these lesions. Furthermore, carcinogen-exposed BMCs can initiate benign and malignant lesions upon tumor promotion. Ultimately, these findings may suggest targets for treatment of non-melanoma skin cancers.

Cell recruiting chemokine-loaded sprayable gelatin hydrogel dressings for diabetic wound healing

In this study, we developed horseradish peroxidase (HRP)-catalyzed sprayable gelatin hydrogels (GH) as a bioactive wound dressing that can deliver cell-attracting chemotactic cytokines to the injured tissues for diabetic wound healing. We hypothesized that topical administration of chemokines using GH hydrogels might improve wound healing by inducing recruitment of the endogenous cells. Two types of chemokines (interleukin-8; IL-8, macrophage inflammatory protein-3α; MIP-3α) were simply loaded into GH hydrogels during in situ cross-linking, and then their wound-healing effects were evaluated in streptozotocin-induced diabetic mice. The incorporation of chemokines did not affect hydrogels properties including swelling ratio and mechanical stiffness, and the bioactivities of IL-8 and MIP-3α released from hydrogel matrices were stably maintained. In vivo transplantation of chemokine-loaded GH hydrogels facilitated cell infiltration into the wound area, and promoted wound healing with enhanced re-epithelialization/neovascularization and increased collagen deposition, compared with no treatment or the GH hydrogel alone. Based on our results, we suggest that cell-recruiting chemokine-loaded GH hydrogel dressing can serve as a delivery platform of various therapeutic proteins for wound healing applications.

STATEMENT OF SIGNIFICANCE

Despite development of materials combined with therapeutic agents for diabetic wound treatment, impaired wound healing by insufficient chemotactic responses still remain as a significant problem. In this study, we have developed enzyme-catalyzed gelatin (GH) hydrogels as a sprayable dressing material that can deliver cell-attracting chemokines for diabetic wound healing. The chemotactic cytokines (IL-8 and MIP-3α) were simply loaded within hydrogel during in situ gelling, and wound healing efficacy of chemokine-loaded GH hydrogels was investigated in STZ-induced diabetic mouse model. These hydrogels significantly promoted wound-healing efficacy with faster wound closure, neovascularization, and thicker granulation. Therefore, we expect that HRP-catalyzed in situ forming GH hydrogels can serve as an injectable/sprayable carrier of various therapeutic agents for wound healing applications.

Chemically induced skin carcinogenesis: Updates in experimental models (Review)

Skin cancer is one of the most common malignancies affecting humans worldwide, and its incidence is rapidly increasing. The study of skin carcinogenesis is of major interest for both scientific research and clinical practice and the use of in vivo systems may facilitate the investigation of early alterations in the skin and of the mechanisms involved, and may also lead to the development of novel therapeutic strategies for skin cancer. This review outlines several aspects regarding the skin toxicity testing domain in mouse models of chemically induced skin carcinogenesis. There are important strain differences in view of the histological type, development and clinical evolution of the skin tumor, differences reported decades ago and confirmed by our hands‑on experience. Using mouse models in preclinical testing is important due to the fact that, at the molecular level, common mechanisms with human cutaneous tumorigenesis are depicted. These animal models resemble human skin cancer development, in that genetic changes caused by carcinogens and pro‑inflammatory cytokines, and simultaneous inflammation sustained by pro‑inflammatory cytokines and chemokines favor tumor progression. Drugs and environmental conditions can be tested using these animal models. keeping in mind the differences between human and rodent skin physiology.

Microchimeric fetal cells play a role in maternal wound healing after pregnancy

Fetal cells persist in mothers for decades after delivery: in a phenomenon called fetal microchimerism. While persistent fetal cells were first implicated in autoimmune disease, parallel studies in animal and human pregnancy now suggest that microchimeric fetal cells play a role in the response to tissue injury. The aim of this study was to investigate the impact of fetal microchimeric cells in the adult wound, using caesarean section (CS) as a model of wound healing in pregnancy. XY-FISH (fluorescence in situ hybridization) and immunostaining was used in multiple tissue sections from CS skin biopsies from 70 women, to locate, quantitate and characterize microchimeric male presumed-fetal cells. Y-FISH and Nested PCR was used to confirm XY-FISH results. XY-FISH demonstrated the presence of isolated 0-9 male fetal cells per section in the epidermis of the healed CS scars from only those women who had their first male child by CS. Both Y-FISH and Y-PCR confirmed the presence of fetal cells in CS scars. Combined FISH and immunostaining showed all male fetal cells present were keratinocytes, as they expressed cytokeratin, and were almost exclusively located in epidermis. Microchimeric fetal cells also expressed Collagen I, III, and TGF-β3 in healed maternal scars. Identification of male-presumed fetal cells in healed maternal CS scars after pregnancy suggests that, possibly in response to signals produced by maternal skin injury at CS, fetal cells migrate to the site of damage to become involved in maternal tissue repair, or proliferate locally.

Inflammation markers in cutaneous melanoma - edgy biomarkers for prognosis

There is a fine balance between inflammation and tumorigenesis. While environmentally induced inflammatory condition can precede a malignant transformation, in other cases an oncogenic change of unknown origin can induce an inflammatory microenvironment that promotes the development of tumors. Regardless of its origin, maintaining the inflammation milieu has many tumor-promoting effects. As a result, inflammation can aid the proliferation and survival of malignant cells, can promote angiogenesis and metastasis, can down-regulate innate/adaptive immune responses, and can alter responses to hormones and chemotherapeutic agents. There is an abundance of studies unveiling molecular pathways of cancer-related inflammation; this wealth of information brings new insights into biomarkers domain in the diagnosis and treatment improvement pursue. In cutaneous tissue there is an established link between tissue damage, inflammation, and cancer development. Inflammation is a self-limiting process in normal healthy physiological conditions, while tumorigenesis is a complex mechanism of constitutive pathway activation. Once more, in cutaneous melanoma, there is an unmet need for inflammatory biomarkers that could improve prognostication. Targeting inflammation and coping with the phenotypic plasticity of melanoma cells represent rational strategies to specifically interfere with metastatic progression. We have shown that there is a prototype of intratumor inflammatory infiltrate depicting a good prognosis, infiltrate that is composed of numerous T cells CD3+, Langerhans cells, few/absent B cells CD20+ and few/absent plasma cells. Circulating immune cells characterized by phenotype particularities are delicately linked to the stage melanoma is diagnosed in. Hence circulatory immune sub-populations, with activated or suppressor phenotype would give the physician a more detailed immune status of the patient. A panel of tissue/circulatory immune markers can complete the immune status, can add value to the overall prognostic of the patient and, as a result direct/redirect the therapy choice. The future lies within establishing low-cost, affordable/available, easily reproducible assays that will complete the pre-clinical parameters of the patient.

Origin of Vocal Fold Stellate Cells in the Human Macula Flava

Objectives:

There is growing evidence that vocal fold stellate cells (VFSCs) in the human maculae flavae are tissue stem cells of the human vocal fold and that the maculae flavae are a stem cell niche. The origin of the cells in the human maculae flavae (CHMF) and the relationship with bone marrow–derived cells were investigated.

Methods:

Five human adult vocal fold mucosae were investigated. The CHMF were subcultured and morphological features were assessed. Immunoreactivity to antibodies directed to cytokeratin, desmin, GFAP, vimentin, CD34, CD45, and collagen type I was investigated.

Results:

Cultured CHMF formed a colony-forming unit, indicating they are mesenchymal stem cells or stromal stem cells in the bone marrow. The CHMF expressed hematopoietic markers (CD34, CD45) and collagen type I, which are the major makers for bone marrow–derived circulating fibrocytes. The cultured CHMF expressed epithelium-associated, muscle-associated, neural-associated, and mesenchymal cell–associated proteins, indicating the CHMF are undifferentiated and express proteins of all 3 germ layers.

Conclusions:

The CHMF are undifferentiated cells derived from the differentiation of bone marrow cells. The results of this study are consistent with the hypothesis that the VFSCs are tissue stem cells or progenitor cells of the human vocal fold mucosa.

Transplanted bone marrow-derived circulating PDGFRα+ cells restore type VII collagen in recessive dystrophic epidermolysis bullosa mouse skin graft

Recessive dystrophic epidermolysis bullosa (RDEB) is an intractable genetic blistering skin disease in which the epithelial structure easily separates from the underlying dermis because of genetic loss of functional type VII collagen (Col7) in the cutaneous basement membrane zone. Recent studies have demonstrated that allogeneic bone marrow transplantation (BMT) ameliorates the skin blistering phenotype of RDEB patients by restoring Col7. However, the exact therapeutic mechanism of BMT in RDEB remains unclear. In this study, we investigated the roles of transplanted bone marrow-derived circulating mesenchymal cells in RDEB (Col7-null) mice. In wild-type mice with prior GFP-BMT after lethal irradiation, lineage-negative/GFP-positive (Lin(-)/GFP(+)) cells, including platelet-derived growth factor receptor α-positive (PDGFRα(+)) mesenchymal cells, specifically migrated to skin grafts from RDEB mice and expressed Col7. Vascular endothelial cells and follicular keratinocytes in the deep dermis of the skin grafts expressed SDF-1α, and the bone marrow-derived PDGFRα(+) cells expressed CXCR4 on their surface. Systemic administration of the CXCR4 antagonist AMD3100 markedly decreased the migration of bone marrow-derived PDGFRα(+) cells into the skin graft, resulting in persistent epidermal detachment with massive necrosis and inflammation in the skin graft of RDEB mice; without AMD3100 administration, Col7 was significantly supplemented to ameliorate the pathogenic blistering phenotype. Collectively, these data suggest that the SDF1α/CXCR4 signaling axis induces transplanted bone marrow-derived circulating PDGFRα(+) mesenchymal cells to migrate and supply functional Col7 to regenerate RDEB skin.

Effects of Blocking αvβ₃ integrin by a recombinant RGD disintegrin on remodeling of wound healing after induction of incisional hernia in rats

PURPOSE

Incisional hernia (IH) is characterized by defective wound healing process. Disba-01, a αvb₃ integrin blocker has shown to control the rate of wound repair and therefore it could be a target for new wound healing therapies.The objective of the study was to determine the changes induced by Disba-01 on repair of wound healing after induced IH in rats.

METHODS

Thirty two male albino rats were submitted to IH and divided into 4 experimental groups: G1, placebo control; G2, DisBa-01-treated; G3, anti-αvβ₃ antibodies-treated and G4, anti-α₂ antibodies-treated. Histological. biochemical and extracellular matrix remodeling analysis of abdominal wall were evaluated.

RESULTS

After 14 days, 100% of the G2 did not present hernia, and the hernia ring was closed by a thin membrane. In contrast, all groups maintained incisional hernia. DisBa-01 also increased the number macrophages and fibroblasts and induced the formation of new vessels. Additionally, MMP-2 was strongly activated only in G2 (P<0.05). Anti- αvβ₃-integrin antibodies produced similar results than Disba-01 but not anti-α₂ integrin blocking antibodies.

CONCLUSION

These results strongly indicate that Disba-01 has an important role in the control of wound healing and the blocking of this integrin may be an interesting therapeutical strategy in IH.

Immunohistological localization of endogenous unlabeled stem cells in wounded skin

Various types of endogenous stem cells (SCs) participate in wound healing in the skin at different anatomical locations. SCs need to be identified through multiple markers, and this is usually performed using flow cytometry. However, immunohistological identification of endogenous stem cells in the skin at different anatomical locations by co-staining multiple SC markers has been seldom explored. We examined the immunohistological localization of four major types of SCs in wounded skin by co-staining for their multiple markers. Hematopoietic SCs were co-stained for Sca1 and CD45; mesenchymal SCs for Sca1, CD29, and CD106; adipose SCs for CD34, CD90, and CD105; and endothelial progenitor cells and their differentiated counterparts were co-stained for CD34, Tie2, and von Willebrand factor. We found Sca1(+)CD45(+) SCs in the epidermis, dermis and hypodermis of wounded skin. Sca1(+)CD29(+) and Sca1(+)CD106(+) mesenchymal SCs, CD34(+)CD105(+), CD34(+)CD90(+), and CD90(+)CD105(+) adipose SCs, as well as CD34(+)Tie2(+) endothelial progenitor cells were also located in the epidermis, dermis, and hypodermis. This study demonstrates the feasibility of using immunohistological staining to determine the location of SCs in wounded skin and the intracellular distribution of their molecular markers.

In vivo multimodal microscopy for detecting bone-marrow-derived cell contribution to skin regeneration

Bone-marrow (BM)-derived cells have been shown to be capable of aiding skin regeneration in vivo by differentiating into keratinocytes. However, the conditions under which this occurs are not fully understood. Characterizing innate mechanisms of skin regeneration by stem cells in vivo is important for the area of stem cell biology. In this study, we investigate the use of novel in vivo imaging technology for characterizing the contribution of BM-derived cells to regeneration of the epidermis in mouse skin in vivo. In vivo imaging provides the ability to non-invasively observe the spatial positions and morphology of the BM-derived cells. Using a GFP BM-transplanted mouse model and in vivo multimodal microscopy, BM-derived cells can be observed in the skin. Our in vivo imaging method was used to search for the presence and identify the 3D spatial distribution of BM-derived cells in the epidermis of the skin under normal conditions, following wound healing, and after syngeneic skin grafting. We did not observe any evidence of BM-derived keratinocytes under these conditions, but we did observe BM-derived dendritic cells in the skin grafts. In vivo multimodal imaging has great potential for characterizing the conditions under which BM-derived cells contribute to skin regeneration.

An in vitro skin model to study the effect of mesenchymal stem cells in wound healing and epidermal regeneration

The development of new wound therapies, such as bioengineered skin equivalents, is an ongoing process. Multi-potent mesenchymal stem cells (MSCs) give rise to many tissue lineages and have been implicated in wound healing making them a potential candidate for cell-based bioengineered products for injured tissue. In this study, we investigated the mesenchymal/epithelial interactions of cultured MSCs in comparison to cultured fibroblasts on epidermal proliferation, differentiation, and extracellular matrix (ECM) protein expression using a de-epidermalized dermis (DED) skin model. We also studied whether MSCs can transdifferentiate to keratinocytes using the same model. Keratinocytes were cultured on unseeded DED or DED populated with fibroblasts or MSCs at an air-liquid interface to induce epidermal differentiation. Fibroblasts or MSCs were also seeded on the papillary surface of the DED alone or on the reticular surface. General histology and immunostaining was performed on the skin equivalents to examine the expression of pan keratin (K) (K1, K5, K6, and K18) and protein markers for epidermal differentiation (K10), hyperproliferation (K6), proliferation (PCNA), ECM component (collagen type IV), and mesenchymal marker (vimentin). Keratinocyte-fibroblast skin model and keratinocyte-MSC skin model both displayed an epidermal phenotype similar to epidermis in vivo. Positive expression of proliferation, differentiation and ECM protein markers was observed. MSCs failed to adopt an epithelial phenotype in the DED skin model. Our findings highlight the potential use of MSCs in bioengineered tissue for the treatment of wounds.

Long-term time-lapse multimodal intravital imaging of regeneration and bone-marrow-derived cell dynamics in skin

A major challenge for translating cell-based therapies is understanding the dynamics of cells and cell populations in complex in vivo environments. Intravital microscopy has shown great promise for directly visualizing cell behavior in vivo. However, current methods are limited to relatively short imaging times (hours), by ways to track cell and cell population dynamics over extended time-lapse periods (days to weeks to months), and by relatively few imaging contrast mechanisms that persist over extended investigations. We present technology to visualize and quantify complex, multifaceted dynamic changes in natural deformable skin over long time periods using novel multimodal imaging and a non-rigid image registration method. These are demonstrated in green fluorescent protein (GFP) bone marrow (BM) transplanted mice to study dynamic skin regeneration. This technology provides a novel perspective for studying dynamic biological processes and will enable future studies of stem, immune, and tumor cell biology in vivo.

Composite tissue allotransplantation and dysregulation in tissue repair and regeneration: a role for mesenchymal stem cells

Vascularized composite tissue allotransplantation is a rapidly evolving area that has brought technological advances to the forefront of plastic surgery, hand surgery, and transplant biology. Composite tissue allografts (CTAs) may have profound functional, esthetic, and psychological benefits, but carry with them the risks of life-long immunosuppression and the inadequate abilities to monitor and prevent rejection. Allografts may suffer from additional insults further weakening their overall benefits. Changes in local blood flow, lack of fully restored neurologic function, infection, inflammation with subsequent dysregulated regenerative activity, and paucity of appropriate growth factors may all be involved in reducing the potential of CTAs and therefore serve as new therapeutic targets to improve outcomes. Strategies involving minimized immunosuppression and pro-regenerative therapy may provide a greater path to optimizing long-term CTA function. One such strategy may include mesenchymal stem cells (MSCs), which can provide unique anti-inflammatory and pro-regenerative effects. Insights gained from new studies with MSCs on composite allografts, advances in tissue regeneration reported in other MSC-based clinical studies, as well as consideration of newly described capacities of MSCs, may provide new regenerative based strategies for the care of CTAs.

Bone marrow transplantation in epidermolysis bullosa

Epidermolysis bullosa (EB) is a heterogeneous group of inherited blistering skin diseases. Severe forms of EB are associated with increased morbidity and mortality, and there is currently no effective treatment. To combat severe complications of EB, such as chronic erosions, scarring and malignancy, effective therapy needs to be given systemically and at an early age. One recent therapeutic advancement has been a clinical trial of whole bone marrow (BM) transplantation in children with the dystrophic form of EB. This led to correction of the inherent skin basement membrane defect and better skin integrity in some individuals. The challenge now is to precisely identify which BM cells contribute to skin recovery and what mechanisms are involved in tissue regeneration. An improved understanding of the key aspects of BM skin repair is likely to lead to significant health improvements for patients with EB and other skin diseases.

Stem cell application in acute burn care and reconstruction

Burn injuries have a consistently high rate of mortality and morbidity, principally due to sepsis and systemic inflammation. Furthermore, wound closure is often troubled by a limited supply of autologous skin graft availability. Researchers are now looking at augmenting alternative sources for tissues engineering, including stem cells in the bone marrow, fat and hair follicles. Many studies suggest that the ability of stem cells to augment the clinical care of thermally-injured patients shows great potential; however, while our understanding of stem-cell biology has expanded dramatically over the last two decades, significant insight is still required so the full potential of these cells can be safely harnessed and transferred to patient care. This article provides a commentary on the evidence supporting a role for stem-cell therapy in acute burn care and tissue reconstruction, with particular reference to those in the bone marrow, adipose tissue and hair follicle.

Imaging and tracking of bone marrow-derived immune and stem cells

Bone marrow (BM)-derived stem and immune cells play critical roles in maintaining the health, regeneration, and repair of many tissues. Given their important functions in tissue regeneration and therapy, tracking the dynamic behaviors of BM-derived cells has been a long-standing research goal of both biologists and engineers. Because of the complex cellular-level processes involved, real-time imaging technologies that have sufficient spatial and temporal resolution to visualize them are needed. In addition, in order to track cellular dynamics, special attention is needed to account for changes in the microenvironment where the cells reside, for example, tissue contraction, stretching, development, etc. In this chapter, we introduce methods for real-time imaging and longitudinal tracking of BM-derived immune and stem cells in in vivo three-dimensional (3-D) tissue environments with an integrated optical microscope. The integrated microscope combines multiple imaging functions derived from optical coherence tomography (OCT) and multiphoton microscopy (MPM), including optical coherence microscopy (OCM), microvasculature imaging, two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) microscopy. Short- and long-term tracking of the dynamic behavior of BM-derived cells involved in cutaneous wound healing and skin grafting in green fluorescent protein (GFP) BM-transplanted mice is demonstrated. Methods and algorithms for nonrigid registration of time-lapse images are introduced, which allows for long-term tracking of cell dynamics over several months.

Epithelial stem cells and implications for wound repair

Activation of epithelial stem cells and efficient recruitment of their proliferating progeny plays a critical role in cutaneous wound healing. The reepithelialized wound epidermis has a mosaic composition consisting of progeny that can be traced back both to epidermal and several types of hair follicle stem cells. The contribution of hair follicle stem cells to wound epidermis is particularly intriguing as it involves lineage identity change from follicular to epidermal. Studies from our laboratory show that hair follicle-fated bulge stem cells commit only transient amplifying epidermal progeny that participate in the initial wound re-epithelialization, but eventually are outcompeted by other epidermal clones and largely disappear after a few months. Conversely, recently described stem cell populations residing in the isthmus portion of hair follicle contribute long-lasting progeny toward wound epidermis and, arguably, give rise to new interfollicular epidermal stem cells. The role of epithelial stem cells during wound healing is not limited to regenerating stratified epidermis. By studying regenerative response in large cutaneous wounds, our laboratory uncovered that epithelial cells in the center of the wound can acquire greater morphogenetic plasticity and, together with the underlying wound dermis, can engage in an embryonic-like process of hair follicle neogenesis. Future studies should uncover the cellular and signaling basis of this remarkable adult wound regeneration phenomenon.

Bioengineering the hair follicle

The hair follicle develops from the primitive embryonic epidermis as a result of complex epithelial-mesenchymal interactions. The full follicle, consisting of epithelial cylinders under control of a proximal lying mesenchymal papilla, grows in cycles giving rise to a new hair shaft during each cycle. The ability to cycle endows the follicle with regenerative properties. The evolution of hair follicle engineering began with the recognition in the early 1960's that hair follicles could be transplanted clinically into a foreign site and still grow a shaft typical of the donor site. Since that time, it has been found that the follicular papilla has hair follicle inducing properties and that the hair follicle houses within it epithelial stem cells that can respond to hair inductive signals. These findings have laid the foundation for isolating hair-forming cells, for expanding the cells in culture, and for forming new follicles in vivo.

Bone marrow mesenchymal stem cells can differentiate and assume corneal keratocyte phenotype

It remains elusive as to what bone marrow (BM) cell types infiltrate into injured and/or diseased tissues and subsequently differentiate to assume the phenotype of residential cells, for example, neurons, cardiac myocytes, keratocytes, etc., to repair damaged tissue. Here, we examined the possibility of whether BM cell invasion via circulation into uninjured and injured corneas could assume a keratocyte phenotype, using chimeric mice generated by transplantation of enhanced green fluorescent protein (EGFP)⁺ BM cells into keratocan null (Kera^−/−) and lumican null (Lum^−/−) mice. EGFP⁺ BM cells assumed dendritic cell morphology, but failed to synthesize corneal-specific keratan sulfate proteoglycans, that is KS-lumican and KS-keratocan. In contrast, some EGFP⁺ BM cells introduced by intrastromal transplantation assumed keratocyte phenotypes. Furthermore, BM cells were isolated from Kera-Cre/ZEG mice, a double transgenic mouse line in which cells expressing keratocan become EGFP⁺ due to the synthesis of Cre driven by keratocan promoter. Three days after corneal and conjunctival transplantations of such BM cells into Kera^−/− mice, green keratocan positive cells were found in the cornea, but not in conjunctiva. It is worthy to note that transplanted BM cells were rejected in 4 weeks. MSC isolated from BM were used to examine if BM mesenchymal stem cells (BM-MSC) could assume keratocyte phenotype. When BM-MSC were intrastromal-transplanted into Kera^−/− mice, they survived in the cornea without any immune and inflammatory responses and expressed keratocan in Kera^−/− mice. These observations suggest that corneal intrastromal transplantation of BM-MSC may be an effective treatment regimen for corneal diseases involving dysfunction of keratocytes.

Biochemistry of epidermal stem cells

BACKGROUND

The epidermis is an important protective barrier that is essential for maintenance of life. Maintaining this barrier requires continuous cell proliferation and differentiation. Moreover, these processes must be balanced to produce a normal epidermis. The stem cells of the epidermis reside in specific locations in the basal epidermis, hair follicle and sebaceous glands and these cells are responsible for replenishment of this tissue.

SCOPE OF REVIEW

A great deal of effort has gone into identifying protein epitopes that mark stem cells, in identifying stem cell niche locations, and in understanding how stem cell populations are related. We discuss these studies as they apply to understanding normal epidermal homeostasis and skin cancer.

MAJOR CONCLUSIONS

An assortment of stem cell markers have been identified that permit assignment of stem cells to specific regions of the epidermis, and progress has been made in understanding the role of these cells in normal epidermal homeostasis and in conditions of tissue stress. A key finding is the multiple stem cell populations exist in epidermis that give rise to different structures, and that multiple stem cell types may contribute to repair in damaged epidermis.

GENERAL SIGNIFICANCE

Understanding epidermal stem cell biology is likely to lead to important therapies for treating skin diseases and cancer, and will also contribute to our understanding of stem cells in other systems. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Therapeutic potential of bone marrow-derived mesenchymal stem cells for cutaneous wound healing

Despite advances in wound care, many wounds never heal and become chronic problems that result in significant morbidity and mortality to the patient. Cellular therapy for cutaneous wounds has recently come under investigation as a potential treatment modality for impaired wound healing. Bone marrow-derived mesenchymal stem cells (MSCs) are a promising source of adult progenitor cells for cytotherapy as they are easy to isolate and expand and have been shown to differentiate into various cell lineages. Early studies have demonstrated that MSCs may enhance epithelialization, granulation tissue formation, and neovascularization resulting in accelerated wound closure. It is currently unclear if these effects are mediated through cellular differentiation or by secretion of cytokines and growth factors. This review discusses the proposed biological contributions of MSCs to cutaneous repair and their clinical potential in cell-based therapies.

Hematological abnormalities and the use of granulocyte-colony-stimulating factor in patients with Stevens-Johnson syndrome and toxic epidermal necrolysis

BACKGROUND

Derangements in blood cell counts have been described in patients with Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) but are not well characterized. We aim to describe the relationship between our patients' hematological results and the evolution of disease and hypothesize on the possible roles of granulocyte-colony-stimulating factor (G-CSF) in the management of these conditions.

MATERIALS AND METHODS

Clinical records of our patients with SJS and TEN from January 2005 to 2010 were analyzed.

RESULTS

Anemia and lymphopenia were most commonly seen, while thrombocytopenia was uncommon. Leukopenia and neutropenia were seen in patients with more severe disease, and the trend of leukopenia and neutropenia followed the evolution of disease. Two patients received G-CSF for febrile neutropenia and had a rapid recovery of their neutrophil counts as well as a shorter time to re-epithelialization.

CONCLUSION

Our patients tended to have leukopenia and neutropenia that followed a predictable trend of decline and subsequent improvement depending on the stage of disease. This may be of pathogenic significance, and G-CSF may be used in these cases to manage febrile neutropenia and aid re-epithelialization. Further basic science research is required to prove our hypotheses.

25 years of epidermal stem cell research

This is a chronicle of concepts in the field of epidermal stem cell biology and a historic look at their development over time. The past 25 years have seen the evolution of epidermal stem cell science, from first fundamental studies to a sophisticated science. The study of epithelial stem cell biology was aided by the ability to visualize the distribution of stem cells and their progeny through lineage analysis studies. The excellent progress we have made in understanding epidermal stem cell biology is discussed in this article. The challenges we still face in understanding epidermal stem cells include defining molecular markers for stem and progenitor sub-populations, determining the locations and contributions of the different stem cell niches, and mapping regulatory pathways of epidermal stem cell proliferation and differentiation. However, our rapidly evolving understanding of epidermal stem cells has many potential uses that promise to translate into improved patient therapy.

Epithelial stem cells, wound healing and cancer

It is well established that tissue repair depends on stem cells and that chronic wounds predispose to tumour formation. However, the association between stem cells, wound healing and cancer is poorly understood. Lineage tracing has now shown how stem cells are mobilized to repair skin wounds and how they contribute to skin tumour development. The signalling pathways, including WNT and Hedgehog, that control stem cell behaviour during wound healing are also implicated in tumour formation. Furthermore, tumorigenesis and wound repair both depend on communication between epithelial cells, mesenchymal cells and bone marrow-derived cells. These studies suggest ways to harness stem cells for wound repair while minimizing cancer risk.

Mesenchymal stem cell therapy and delivery systems in nonhealing wounds

OBJECTIVE

The objective of the study was to inform wound care practitioners of mesenchymal stem cell application for nonhealing wounds. Recent advances in delivery systems are also discussed in order to highlight potential improvements toward clinical application of stem cell therapy for chronic wounds.

DATA SOURCES

MEDLINE and PubMed Central were searched for scientific studies regarding the use of mesenchymal stem cells and delivery systems in wound healing.

STUDY SELECTION

Preclinical studies using stem cells as therapeutic modality for chronic wounds were selected for this review.

DATA EXTRACTION

Information on study design, sample size and characteristics, stem cell source, type of delivery systems, and rate and time of wound closure was abstracted.

DATA SYNTHESIS

Application of mesenchymal stem cells improved wound healing in experimental and clinical settings. Advances in stem cell therapy and delivery vehicles offer promising alternatives to current limited therapeutic modalities for chronic wounds.

CONCLUSIONS

Stem cell therapy has recently emerged as a promising therapeutic strategy for nonhealing wounds. Further research is needed to evaluate the relationship between the various delivery systems and stem cells in order to maximize their therapeutic effects. Development of novel delivery vehicles for stem cells can open new opportunities for more effective cell therapy of chronic wounds.

From keratinocyte to cancer: the pathogenesis and modeling of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common human cancer with over 250,000 new cases annually in the US and is second in incidence only to basal cell carcinoma. cSCC typically manifests as a spectrum of progressively advanced malignancies, ranging from a precursor actinic keratosis (AK) to squamous cell carcinoma (SCC) in situ (SCCIS), invasive cSCC, and finally metastatic SCC. In this Review we discuss clinical and molecular parameters used to define this range of cutaneous neoplasia and integrate these with the multiple experimental approaches used to study this disease. Insights gained from modeling cSCCs have suggested innovative therapeutic targets for treating these lesions.

Chemically-induced cancers do not originate from bone marrow-derived cells

BACKGROUND

The identification and characterization of cancer stem cells (CSCs) is imperative to understanding the mechanism of cancer pathogenesis. Growing evidence suggests that CSCs play critical roles in the development and progression of cancer. However, controversy exists as to whether CSCs arise from bone marrow-derived cells (BMDCs).

METHODOLOGY AND PRINCIPAL FINDINGS

In the present study, n-nitrosodiethylamine (DEN) was used to induce tumor formation in female mice that received bone marrow from male mice. Tumor formation was induced in 20/26 mice, including 12 liver tumors, 6 lung tumors, 1 bladder tumor and 1 nasopharyngeal tumor. Through comparison of fluorescence in situ hybridization (FISH) results in corresponding areas from serial tumor sections stained with H&E, we determined that BMDCs were recruited to both tumor tissue and normal surrounding tissue at a very low frequency (0.2-1% in tumors and 0-0.3% in normal tissues). However, approximately 3-70% of cells in the tissues surrounding the tumor were BMDCs, and the percentage of BMDCs was highly associated with the inflammatory status of the tissue. In the present study, no evidence was found to support the existence of fusion cells formed form BMDCs and tissue-specific stem cells.

CONCLUSIONS

In summary, our data suggest that although BMDCs may contribute to tumor progression, they are unlike to contribute to tumor initiation.

Bone marrow cells in murine colitis: multi-signal analysis confirms pericryptal myofibroblast engraftment without epithelial involvement

Background

The contribution of bone marrow-derived cells to epithelial tissues in the inflamed gut remains controversial. Recent reports have suggested that cell fusion between bone marrow-derived cells and the intestinal epithelium takes place in inflammatory conditions.

Methods

In attempts to confirm this, we have undertaken gender mis-matched bone marrow (BM) transplants from male Swiss Webster (SWR) mice to B and T cell-deficient female Rag2 KO mice which, 4 weeks later, were given 5% dextran sodium sulphate in drinking water to induce acute colitis. A further BM-treated group of animals with a graft versus host-like condition was also studied. We developed a new method to combine up to three brightfield or fluorescent lectin- or immuno-histochemical signals with fluorescent in situ hybridisation for the Y and X chromosomes to enable us unequivocally to identify BM-derived male cells which presented as different cell types in the gastrointestinal tract.

Principal Findings

In rolled preparations of whole intestines we scanned around 1.5 million crypts at many tissue levels. In no instance did we see a Y chromosome-positive cell in the epithelial compartment, which was not also CD45-positive. We saw no evidence of cell fusion, based on combined X and Y chromosome analysis. Levels of CD45-positive stromal and lymphoid cells and pericryptal myfibroblasts (positive for α-smooth muscle actin) increased with time up to a plateau, which resembled the level seen in untreated control grafted animals. We saw very few Y chromosome-positive endothelial cells in intestinal stromal vessels.

Conclusions

We conclude that whole BM transplantation does not result in intestinal epithelial engraftment in this model. Our new methods can usefully assist in multi-signal analyses of cell phenotypes following BM transplant and in models of chimaerism and regenerative medicine.

Preferential recruitment of bone marrow-derived cells to rat palatal wounds but not to skin wounds

OBJECTIVE

To investigate the contribution of bone marrow-derived cells to oral mucosa wounds and skin wounds.

BACKGROUND

Bone marrow-derived cells are known to contribute to wound healing, and are able to differentiate in many different tissue-specific cell types. As wound healing in oral mucosa generally proceeds faster and with less scarring than in skin, we compared the bone marrow contribution in these two tissues.

DESIGN

Bone marrow cells from GFP-transgenic rats were transplanted to irradiated wild-type rats. After recovery, 4-mm wounds were made in the mucoperiosteum or the skin. Two weeks later, wound tissue with adjacent normal tissue was stained for GFP-positive cells, myofibroblasts (a-smooth muscle actin), activated fibroblasts (HSP47), and myeloid cells (CD68).

RESULTS

The fraction of GFP-positive cells in unwounded skin (19%) was larger than in unwounded mucoperiosteum (0.7%). Upon wounding, the fraction of GFP-positive cells in mucoperiosteum increased (8.1%), whilst it was unchanged in skin. About 7% of the myofibroblasts in both wounds were GFP-positive, 10% of the activated fibroblasts, and 25% of the myeloid cells.

CONCLUSIONS

The results indicate that bone marrow-derived cells are preferentially recruited to wounded oral mucosa but not to wounded skin. This might be related to the larger healing potential of oral mucosa.

The recruitment of bone marrow-derived cells to skin wounds is independent of wound size

Wounded skin recruits progenitor cells, which repair the tissue defect. These cells are derived from stem cells in several niches in the skin. In addition, bone marrow-derived cells (BMDCs) are recruited and contribute to wound repair. We hypothesized that larger wounds recruit more cells from the bone marrow. Wild-type rats were lethally irradiated and transplanted with bone marrow cells from green fluorescent protein (GFP)-transgenic rats. Seven weeks later, 4, 10, and 20 mm wounds were created. The wound tissue was harvested after 14 days. The density of GFP-positive cells in the wounds and the adjacent tissues was determined, as well as in normal skin from the flank. Bone marrow-derived myofibroblasts, activated fibroblasts, and macrophages were also quantified. After correction for cell density, the recruitment of BMDCs (23±11%) was found to be independent of wound size. Similar fractions of GFP-positive cells were also detected in nonwounded adjacent tissue (29±11%), and in normal skin (26±19%). The data indicate that BMDCs are not preferentially recruited to skin wounds. Furthermore, wound size does not seem to affect the recruitment of BMDCs.

[Therapy for skin disease using bone marrow cells]

Attempts to treat congenital protein deficiencies using bone marrow-derived cells have been reported. These efforts have been based on the concepts of stem cell plasticity. We aimed to clarify whether bone marrow transplantation (BMT) treatment can rescue epidermolysis bullosa (EB) caused by defects in keratinocyte structural proteins. BMT treatment of adult collagen XVII (Col17) knockout mice induced donor-derived keratinocytes and Col17 expression associated with the recovery of hemidesmosomal structure and better skin manifestations, as well improving the survival rate. Furthermore, human cord blood CD34+ cells also differentiated into keratinocytes and expressed human skin component proteins in transplanted immunocompromised mice. The current conventional BMT techniques have significant potential as a systemic therapeutic approach for the treatment of human EB.

Hox transcription factor regulation of adult bone-marrow-derived cell behaviour during tissue repair and regeneration

INTRODUCTION

Bone marrow offers a valuable source of stem/progenitor cells that contribute to the repair of injured tissues. Failure in the function of these cells results in delayed or reduced tissue repair. Identification of factors that can correct these defects is critical to treating the underlying dysfunction. Notably, homeobox (Hox) transcription factors have been identified as having significant effects on BMDC behaviour, including differentiation, migration and adhesion in injured tissue, and may provide a basis for future therapies.

AREAS COVERED

Hox protein regulation of bone-marrow-derived cell (BMDC) differentiation, factors that influence BMDC behaviour in response to injury, the effects of the diabetic environment on BMDCs, methods that can be used to reprogramme BMDCs, and the use of Hox transcription factors to correct BMDC behaviour.

EXPERT OPINION

Hox gene therapy has been successfully employed to change cell behaviour using ex vivo 'reprogramming' strategies overexpressing selected Hox genes in BMDCs to direct the fate of these cells to the desired cell type, promoting tissue repair.

Analyses of donor-derived keratinocytes in hairy and nonhairy skin biopsies of female patients following allogeneic male bone marrow transplantation

Skin samples taken from 6 female patients receiving allogeneic bone marrow transplants (BMT) from male siblings (n=5) or from unrelated human leukocyte antigen (HLA)-matched male donor (n=1) due to hematological malignancies were studied for the presence of donor cells. One nontransplanted male and 1 female control that received female BM were used as further controls of the technique. Skin biopsies were taken from the scalp and the back from each patient 12-16 years after the successful BMT. We have found donor chimerism in all of the 6 patients in both of their biopsies. Using single and double immunostainings in combination with Y chromosome hybridization, we observed that there are cytokeratin-expressing donor-derived cells in the epidermis of all the 6 patients, the numbers being slightly higher in the scalp (0.37%-1.78%) than in the back (0.32%-1.08%) biopsies. The indication for BMT, and the age of the patient did not seem to have any effect on the numbers found. A few of the double-labeled cells also stained for Ki67, a marker of cellular proliferation, suggesting that the engrafted cells were able to further divide in the epidermis. In 2 patients we observed patches of donor keratinocytes within the epidermis, suggesting a clonal origin. We conclude that in agreement with some and in contrast to other published studies, BM-derived circulating cells are able to engraft in the human skin and to further proliferate there and thus contribute to tissue renewal. These data raise the possibility to use BM cells in regenerative medicine to help in extended injuries, large surface burns, or lack of skin due to other reasons.

Bone marrow-derived cells in palatal wound healing

OBJECTIVE

Myofibroblasts are responsible for contraction and scarring after cleft palate repair. This leads to growth disturbances in the upper jaw. We hypothesized that cells from the bone marrow are recruited to palatal wounds and differentiate into myofibroblasts.

METHODS

We transplanted bone marrow from green fluorescent protein (GFP)-transgenic rats into lethally irradiated wild-type rats. After recovery, experimental wounds were made in the palatal mucoperiosteum, and harvested 2 weeks later. GFP-expressing cells were identified using immunostaining. Myofibroblasts, activated fibroblasts, endothelial cells, and myeloid cells were quantified with specific markers.

RESULTS

After transplantation, 89 ± 8.9% of mononuclear cells in the blood expressed the GFP and about 50% of adherent cells in the bone marrow. Tissue obtained during initial wounding contained only minor numbers of GFP-positive cells, like adjacent control tissue. Following wound healing, 8.1 ± 5.1% of all cells in the wound area were positive, and 5.0 ± 4.0% of the myofibroblasts, which was significantly higher than in adjacent tissue. Similar percentages were found for activated fibroblasts and endothelial cells, but for myeloid cells it was considerably higher (22 ± 9%).

CONCLUSIONS

Bone marrow-derived cells contribute to palatal wound healing, but are not the main source of myofibroblasts. In small wounds, the local precursor cells are probably sufficient to replenish the defect.

Microchimerism in labial salivary glands of hematopoietic stem cell transplanted patients

OBJECTIVE

Microchimerism has been extensively investigated in autoimmune diseases, which display similarities with graft-vs-host disease. This study was conducted to investigate the presence of microchimerism in minor salivary glands of hematopoietic stem cell transplanted patients, one of the targets of graft-vs-host disease.

METHODS

Labial salivary glands biopsy specimens from 11 stem cell transplanted patients were analysed. The samples were grouped in control (five specimens from a female-to-female transplantation) and study group (five glands from male-to-female transplantation). One male transplanted patient was used as a positive control. Fluorescence in situ hybridization with Y-chromosome probe and immunofluorescence with anticytokeratin AE1/AE3 and CD45 were used to identify Y-chromosome positive glandular epithelial cells from allogeneic hematopoietic stem cell transplanted patients.

RESULTS

In the study group, all samples were positive to Y-chromosome and cytokeratin AE1/AE3, in agreement with the pattern exhibited by male labial salivary gland. None of the samples from control group were positive to Y-chromosome despite being positive to cytokeratin AE1/AE3. Positivity to CD45 was not relevant.

CONCLUSION

Microchimerism in the labial salivary glands of sex-mismatched stem cell transplanted patients is a real phenomenon. Further studies are necessary to elucidate the impact of this phenomenon on the clinical status of stem cell transplanted patients.

Concise review: bone marrow-derived stem/progenitor cells in cutaneous repair and regeneration

Our understanding of the role of bone marrow (BM)-derived cells in cutaneous homeostasis and wound healing had long been limited to the contribution of inflammatory cells. Recent studies, however, suggest that the BM contributes a significant proportion of noninflammatory cells to the skin, which are present primarily in the dermis in fibroblast-like morphology and in the epidermis in a keratinocyte phenotype; and the number of these BM-derived cells increases markedly after wounding. More recently, several studies indicate that mesenchymal stem cells derived from the BM could significantly impact wound healing in diabetic and nondiabetic animals, through cell differentiation and the release of paracrine factors, implying a profound therapeutic potential. This review discusses the most recent understanding of the contribution of BM-derived noninflammatory cells to cutaneous homeostasis and wound healing.