Can hematopoietic stem cells be an alternative source for skin regeneration?

Epigenetic regulation of embryonic ectoderm development in stem cell differentiation and transformation during ontogenesis

Dynamic chromatin accessibility regulates stem cell fate determination and tissue homeostasis via controlling gene expression. As a histone-modifying enzyme that predominantly mediates methylation of lysine 27 in histone H3 (H3K27me1/2/3), Polycomb repressive complex 2 (PRC2) plays the canonical role in targeting developmental regulators during stem cell differentiation and transformation. Embryonic ectoderm development (EED), the core scaffold subunit of PRC2 and as an H3K27me3-recognizing protein, has been broadly implicated with PRC2 stabilization and allosterically stimulated PRC2. Accumulating evidences from experimental data indicate that EED-associating epigenetic modifications are indispensable for stem cell maintenance and differentiation into specific cell lineages. In this review, we discuss the most updated advances to summarize the structural architecture of EED and its contributions and underlying mechanisms to mediating lineage differentiation of different stem cells during epigenetic modification to expand our understanding of PRC2.

The Therapeutic Potential of Hematopoietic Stem Cells in Bone Regeneration

The repair process of bone fractures is a complex biological mechanism requiring the recruitment and in situ functionality of stem/stromal cells from the bone marrow (BM). BM mesenchymal stem/stromal cells have been widely explored in multiple bone tissue engineering applications, whereas the use of hematopoietic stem cells (HSCs) has been poorly investigated in this context. A reasonable explanation is the fact that the role of HSCs and their combined effect with other elements of the hematopoietic niches in the bone-healing process is still elusive. Therefore, in this review we intend to highlight the influence of HSCs in the bone repair process, mainly through the promotion of osteogenesis and angiogenesis at the bone injury site. For that, we briefly describe the main biological characteristics of HSCs, as well as their hematopoietic niches, while reviewing the biomimetic engineered BM niche models. Moreover, we also highlighted the role of HSCs in translational in vivo transplantation or implantation as promoters of bone tissue repair.

Stem cell therapy for chronic skin wounds in the era of personalized medicine: From bench to bedside

With the significant financial burden of chronic cutaneous wounds on the healthcare system, not to the personal burden mention on those individuals afflicted, it has become increasingly essential to improve our clinical treatments. This requires the translation of the most recent benchtop approaches to clinical wound repair as our current treatment modalities have proven insufficient. The most promising potential treatment options rely on stem cell-based therapies. Stem cell proliferation and signaling play crucial roles in every phase of the wound healing process and chronic wounds are often associated with impaired stem cell function. Clinical approaches involving stem cells could thus be utilized in some cases to improve a body's inhibited healing capacity. We aim to present the laboratory research behind the mechanisms and effects of this technology as well as current clinical trials which showcase their therapeutic potential. Given the current problems and complications presented by chronic wounds, we hope to show that developing the clinical applications of stem cell therapies is the rational next step in improving wound care.

Advances of Stem Cell Therapeutics in Cutaneous Wound Healing and Regeneration

Cutaneous wound healing is a complex multiple phase process, which overlaps each other, where several growth factors, cytokines, chemokines, and various cells interact in a well-orchestrated manner. However, an imbalance in any of these phases and factors may lead to disruption in harmony of normal wound healing process, resulting in transformation towards chronic nonhealing wounds and abnormal scar formation. Although various therapeutic interventions are available to treat chronic wounds, current wound-care has met with limited success. Progenitor stem cells possess potential therapeutic ability to overcome limitations of the present treatments as it offers accelerated wound repair with tissue regeneration. A substantial number of stem cell therapies for cutaneous wounds are currently under development as a result of encouraging preliminary findings in both preclinical and clinical studies. However, the mechanisms by which these stem cells contribute to the healing process have yet to be elucidated. In this review, we emphasize on the major treatment modalities currently available for the treatment of the wound, role of various interstitial stem cells and exogenous adult stem cells in cutaneous wound healing, and possible mechanisms involved in the healing process.

Specific disruption of Lnk in murine endothelial progenitor cells promotes dermal wound healing via enhanced vasculogenesis, activation of myofibroblasts, and suppression of inflammatory cell recruitment

BACKGROUND

Although endothelial progenitor cells (EPCs) contribute to wound repair by promoting neovascularization, the mechanism of EPC-mediated wound healing remains poorly understood due to the lack of pivotal molecular targets of dermal wound repair.

METHODS AND RESULTS

We found that genetic targeting of the Lnk gene in EPCs dramatically enhances the vasculogenic potential including cell proliferation, migration, and tubule-like formation as well as accelerates in vivo wound healing, with a reduction in fibrotic tissue and improved neovascularization via significant suppression of inflammatory cell recruitment. When injected into wound sites, Lnk ^-/- EPCs gave rise to a significant number of new vessels, with remarkably increased survival of transplanted cells and decreased recruitment of cytotoxic T cells, macrophages, and neutrophils, but caused activation of fibroblasts in the wound-remodeling phase. Notably, in a mouse model of type I diabetes, transplanted Lnk ^-/- EPCs induced significantly better wound healing than Lnk ^+/+ EPCs did.

CONCLUSIONS

The specific targeting of Lnk may be a promising EPC-based therapeutic strategy for dermal wound healing via improvement of neovascularization but inhibition of excessive inflammation as well as activation of myofibroblasts during dermal tissue remodeling.

Subcutaneous Suture Can Accelerate Wound Healing of Lower Midline Incision: A Randomized Controlled Trial

Poor wound healing is one of the most common complications after laparotomy, especially in lower abdominal midline incisions. The aims of this trial are to assess the value of subcutaneous suture and identify risk factors to prevent poor wound healing. From October 2010 to October 2011, a total of 180 patients were randomized to the subcutaneous suture group (n = 89) or control group (n = 91) after laparotomy with a lower midline incision. Univariate and multivariate analyses were performed to determine the predictive significance of variables of poor wound healing. Patients’ demographics, preoperative laboratory values, and operative details were comparable between the two groups. The overall rate of poor wound healing was 16.7 per cent (30 of 180). Patients randomized to subcutaneous suture group (n = 89) had poor healing in 10.1 per cent (nine of 89) and those without suture (n = 91) in 23.1 per cent (21 of 91) ( P = 0.020). Multivariate logistic regression analysis revealed that American Society of Anesthesiologists (ASA) score (3 to 4) (odds ratio [OR], 2.933), subcutaneous suture (OR, 0.323), and blood loss (greater than 200 mL) (OR, 5.995) were independent risk factors for poor wound healing. Subcutaneous suture can effectively accelerate wound healing. Nonsubcutaneous suture, ASA score (3 to 4), and blood loss (greater than 200 mL) are independent risk factors for poor would healing.

Active ingredients against human epidermal aging

The decisive role of the epidermis in maintaining body homeostasis prompted studies to evaluate the changes in epidermal structure and functionality over the lifetime. This development, along with the identification of molecular mechanisms of epidermal signaling, maintenance, and differentiation, points to a need for new therapeutic alternatives to treat and prevent skin aging. In addition to recovering age- and sun-compromised functions, proper treatment of the epidermis has important esthetic implications. This study reviews active ingredients capable of counteracting symptoms of epidermal aging, organized according to the regulation of specific age-affected epidermal functions: (1) several compounds, other than retinoids and derivatives, act on the proliferation and differentiation of keratinocytes, supporting the protective barrier against mechanical and chemical insults; (2) natural lipidic compounds, as well as glycerol and urea, are described as agents for maintaining water-ion balance; (3) regulation of immunological pathogen defense can be reinforced by natural extracts and compounds, such as resveratrol; and (4) antioxidant exogenous sources enriched with flavonoids and vitamin C, for example, improve solar radiation protection and epidermal antioxidant activity. The main objective is to provide a functional classification of active ingredients as regulatory elements of epidermal homeostasis, with potential cosmetic and/or dermatological applications.

Patient-specific naturally gene-reverted induced pluripotent stem cells in recessive dystrophic epidermolysis bullosa

Spontaneous reversion of disease-causing mutations has been observed in some genetic disorders. In our clinical observations of severe generalized recessive dystrophic epidermolysis bullosa (RDEB), a currently incurable blistering genodermatosis caused by loss-of-function mutations in COL7A1 that results in a deficit of type VII collagen (C7), we have observed patches of healthy-appearing skin on some individuals. When biopsied, this skin revealed somatic mosaicism resulting from the self-correction of C7 deficiency. We believe this source of cells could represent an opportunity for translational “natural” gene therapy. We show that revertant RDEB keratinocytes expressing functional C7 can be reprogrammed into induced pluripotent stem cells (iPSCs) and that self-corrected RDEB iPSCs can be induced to differentiate into either epidermal or hematopoietic cell populations. Our results give proof in principle that an inexhaustible supply of functional patient-specific revertant cells can be obtained—potentially relevant to local wound therapy and systemic hematopoietic cell transplantation. This technology may also avoid some of the major limitations of other cell therapy strategies, e.g., immune rejection and insertional mutagenesis, which are associated with viral- and nonviral- mediated gene therapy. We believe this approach should be the starting point for autologous cellular therapies using “natural” gene therapy in RDEB and other diseases.

Cell therapy for multiple sclerosis: an evolving concept with implications for other neurodegenerative diseases

Multiple sclerosis is a major cause of neurological disability, and particularly occurs in young adults. It is characterised by conspicuous patches of damage throughout the brain and spinal cord, with loss of myelin and myelinating cells (oligodendrocytes), and damage to neurons and axons. Multiple sclerosis is incurable, but stem-cell therapy might offer valuable therapeutic potential. Efforts to develop stem-cell therapies for multiple sclerosis have been conventionally built on the principle of direct implantation of cells to replace oligodendrocytes, and therefore to regenerate myelin. Recent progress in understanding of disease processes in multiple sclerosis include observations that spontaneous myelin repair is far more widespread and successful than was previously believed, that loss of axons and neurons is more closely associated with progressive disability than is myelin loss, and that damage occurs diffusely throughout the CNS in grey and white matter, not just in discrete, isolated patches or lesions. These findings have introduced new and serious challenges that stem-cell therapy needs to overcome; the practical challenges to achieve cell replacement alone are difficult enough, but, to be useful, cell therapy for multiple sclerosis must achieve substantially more than the replacement of lost oligodendrocytes. However, parallel advances in understanding of the reparative properties of stem cells--including their distinct immunomodulatory and neuroprotective properties, interactions with resident or tissue-based stem cells, cell fusion, and neurotrophin elaboration--offer renewed hope for development of cell-based therapies. Additionally, these advances suggest avenues for translation of this approach not only for multiple sclerosis, but also for other common neurological and neurodegenerative diseases.

Primary progressive multiple sclerosis: progress and challenges

Primary progressive multiple sclerosis (MS) has long been recognised as presenting great difficulties to our management of what is increasingly a treatable neurological disease. Here we review some basic and clinical aspects of primary progressive MS, and describe how the disorder in fact offers powerful insights and opportunities for better understanding multiple sclerosis, and from a practical perspective an invaluable clinical substrate for studying and treating progressive disability in MS. Difficult hurdles remain, however, and these too are reviewed.

Melanocyte stem cells: biology and current aspects

Epidermal stem cells have become an object of intensive research. The epidermis constitutes one of the main sources of stem cells and is a tissue of choice for use in exploring their biology.

Stratified squamous epithelium (epidermis) possesses the capacity for self-renewal and repair due to the presence of epidermal stem cells (ESC). They have been identified within basal layer of the interfollicular epidermis (IFE), in the “bulge” of the hair follicles of rodents, and also in the human follicular bulge. Melanocyte stem cells (MSC) from hair follicles (precisely from the bulge region, which also contains epidermal stem cells) provide an attractive model for the study of stem cells and their regulation at the niche.

This review summarizes the rapidly developing field of epidermal stem cell research and their application in regenerative medicine, paying particular attention to melanocyte stem cells, their biology and some of the processes that occur during hair graying and regeneration of the pigmentary system, as well as discussing how aged-associated changes in the melanocyte stem cells compartment impact hair graying. This review also includes differentiation of human skin stem cells into functional epidermal melanocytes.

Dedifferentiation of human terminally differentiating keratinocytes into their precursor cells induced by basic fibroblast growth factor

Reprogramming differentiated cells toward stem cells may have long-term applications in stem-cell research and regenerative medicine. Here we report on the dedifferentiation of human epidermal keratinocytes into their precursor cells in vitro with basic fibroblast growth factor (bFGF) but not external gene intervention. After incubation of human terminally differentiating keratinocytes, some of the surviving keratinocytes reverted from a differentiated to a dedifferentiated state, as evidenced by re-expression of biological markers of native keratinocyte stem cells (nKSCs), including β(1)-integrin, CK19 and CK14. Moreover, these dedifferentiation-derived KSCs (dKSCs) showed an ability for high colony formation correlated with cell cycle analysis showing a marked accumulation in S phases, acquired a similar regional distribution of both α(6)-integrin and CD71 expression at the ultrastructural level, and had a increased proliferative capacity by releasing telomerase from nucleolar sites to nucleoplasmic distribution. However, on comparing dKSCs with nKSCs, 2 points seem noteworthy: (1) the proportion of transit amplifying cells in dKSCs treated with bFGF is much higher than that in nKSCs and (2) regional differences exist in the subcellular localization of telomerase in nKSCs and dKSCs. Most nKSCs showed a prominent nucleolar concentration of human telomerase reverse transcriptase expression, whereas most dKSCs showed a more diffuse intranuclear distribution of telomerase or even signal depletion at nucleoli relative to the general nucleoplasm. These results indicate that bFGF could induce the terminally differentiating epidermal keratinocytes to convert into their precursor cells, which offers a new approach for generating residual healthy stem cells for wound repair and regeneration.

Genetically-manipulated adult stem cells as therapeutic agents and gene delivery vehicle for wound repair and regeneration

Wound therapy remains a clinical challenge and much effort has been focused on the development of novel therapeutic approaches for wound management. New knowledge about the way in which signals control wound cellular and molecular behavior has promoted the topical application of multipotent stem cells and bioactive molecules to injured tissue, for skin regeneration with less scar formation. However, limited clinical success indicates that the effective delivery of polypeptides and therapeutic cells, with controlled releasing profile, is a major challenge which is yet to be overcome. Recently, a technique in which the genetically-manipulated stem cells were used both as the therapeutic agents and the vehicle for gene delivery for wound treatment - a method which serves to provide regenerative cells and bioactive genes within an optimal environment of regulatory molecular expression for wound sites - has emerged as a promising strategy for wound regenerative therapy. In this article, the roles of adult stem cells - as the therapeutics and the vehicles in these advanced biomimetic drug delivery systems for wound regeneration medicine - are scrutinized to indicate their mechanisms, characteristics, broad applicability and future lines of investigation.