Multilineage differentiation potential of human dermal skin-derived fibroblasts

Isolation and in vitro expansion of Lgr6-positive multipotent hair follicle stem cells

Hair follicles (HFs) are a well-known niche of multipotent stem cells. Recently, HF cells expressing leucine-rich orphan G protein-coupled receptors (Lgr) have been described as multipotent adult stem cells with a high potential for regenerative therapies. We have now established the conditions for the isolation and long-term expansion of stem cells from HFs (HFSCs) and analyzed their characteristics (reverse transcription with the polymerase chain reaction, immunohistochemistry) and multipotent capacity (differentiation assays). HFSCs possess a high self-renewal capacity and share characteristics of putative HF epithelial stem cells, such as the expression of Lgr6, cytokeratins (Ck18, Ck19), and multipotent stem cell markers (Sca-1, Bcrp1, nestin, P75NTR). Under defined cell culture conditions, HFSCs are able to differentiate into mesenchymal lineages (adipocytes, chondrocytes, muscle cells) or neurons (βIII-tubulin). We report, for the first time, an in vitro culture method to isolate Lgr6-positive stem cells from HFs. HFSCs represent a unique tool for studying the cell characteristics of Lgr6-positive cells and should provide a novel easily accessible source for regenerative therapies.

Adipogenic differentiation of laser-printed 3D tissue grafts consisting of human adipose-derived stem cells

Laser-assisted bioprinting (LaBP) allows the realization of computer-generated 3D tissue grafts consisting of cells embedded in a hydrogel environment. In this study, human adipose-derived stem cells (hASCs) were printed in a free-scalable 3D grid pattern by means of LaBP. We demonstrate that neither the proliferation ability nor the differentiation behaviour of the stem cells was affected by the LaBP procedure. Furthermore, the 3D grafts were differentiated down the adipogenic lineage pathway for 10 days. We verify by quantitative assessments of adipogenic markers that the 3D grafts resemble cell lineages present in natural adipose tissue. Additionally, we provide the proof that even pre-differentiated hASCs could be utilized for the generation of 3D tissue grafts. These results indicate that the biofabrication of living grafts resembling their complex native origin is within reach.

Analysis of cell characterization using cell surface markers in the dermis

BACKGROUND

In recent years, it has been reported that stem cells exist in the mesenchymal tissues of the bone marrow and adipose. These stem cells are thought to express specific cell surface markers such as CD44, CD54, CD105, CD90, and CD271 and have been confirmed to be pluripotent. Furthermore, although it has been reported that stem cells are also present in the dermis, their cell surface markers and characteristics are not fully understood.

OBJECTIVE

To confirm the presence of stem cells in the dermis and their ability, employing the mesenchymal stem cell markers which have previously been reported as an indication.

METHODS

We analyzed the percentages of CD44 (+), CD54 (+), CD90 (+), CD105 (+), and CD271 (+) cells in the dermis of neonatal mice (HR-1 mouse) by performing immunostaining and FACS. Secondly, we isolated each type of marker-positive and -negative cells from dermal tissues and evaluated their proliferation potential and their ability to differentiate into adipocytes, osteoblasts, and chondrocytes.

RESULTS

According to the immunostaining and FACS results, we confirmed that stem cells that express CD44, CD54, CD90, CD105, and CD271 are present in the dermal tissues of neonatal mice. In addition, when we measured the proliferation and differentiation potentials of each type of marker-positive cells, it was revealed that cells expressing CD54 or CD271 have a high proliferation potential and are able to differentiate into adipocytes, osteoblasts, and chondrocytes.

CONCLUSIONS

These results indicated that dermal tissues contain stem cells that express CD44, CD54, CD90, CD105, and CD271 which are stem cell markers. More precisely, it was suggested that both CD54 (+) and CD271 (+) stem cells have high proliferation and differentiation potentials.

Specific age-associated DNA methylation changes in human dermal fibroblasts

Epigenetic modifications of cytosine residues in the DNA play a critical role for cellular differentiation and potentially also for aging. In mesenchymal stromal cells (MSC) from human bone marrow we have previously demonstrated age-associated methylation changes at specific CpG-sites of developmental genes. In continuation of this work, we have now isolated human dermal fibroblasts from young (<23 years) and elderly donors (>60 years) for comparison of their DNA methylation profiles using the Infinium HumanMethylation27 assay. In contrast to MSC, fibroblasts could not be induced towards adipogenic, osteogenic and chondrogenic lineage and this is reflected by highly significant differences between the two cell types: 766 CpG sites were hyper-methylated and 752 CpG sites were hypo-methylated in fibroblasts in comparison to MSC. Strikingly, global DNA methylation profiles of fibroblasts from the same dermal region clustered closely together indicating that fibroblasts maintain positional memory even after in vitro culture. 75 CpG sites were more than 15% differentially methylated in fibroblasts upon aging. Very high hyper-methylation was observed in the aged group within the INK4A/ARF/INK4b locus and this was validated by pyrosequencing. Age-associated DNA methylation changes were related in fibroblasts and MSC but they were often regulated in opposite directions between the two cell types. In contrast, long-term culture associated changes were very consistent in fibroblasts and MSC. Epigenetic modifications at specific CpG sites support the notion that aging represents a coordinated developmental mechanism that seems to be regulated in a cell type specific manner.

Dermal fibroblasts display similar phenotypic and differentiation capacity to fat-derived mesenchymal stem cells, but differ in anti-inflammatory and angiogenic potential

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem cells able to differentiate into different cell lineages. However, MSCs represent a subpopulation of a more complex cell composition of stroma cells contained in mesenchymal tissue. Due to a lack of specific markers, it is difficult to distinguish MSCs from other more mature stromal cells such as fibroblasts, which, conversely, are abundant in mesenchymal tissue. In order to find more distinguishing features between MSCs and fibroblasts, we studied the phenotypic and functional features of human adipose-derived MSCs (AD-MSCs) side by side with normal human dermal fibroblasts (HNDFs) in vitro

METHODS

AD-MSCs and HNDFs were cultured, expanded and phenotypically characterized by flow cytometry (FC). Immunofluorescence was used to investigate cell differentiation. ELISA assay was used to quantify angiogenic factors and chemokines release. Cultures of endothelial cells (ECs) and a monocyte cell line, U937, were used to test angiogenic and anti-inflammatory properties.

RESULTS

Cultured AD-MSCs and HNDFs display similar morphological appearance, growth rate, and phenotypic profile. They both expressed typical mesenchymal markers-CD90, CD29, CD44, CD105 and to a minor extent, the adhesion molecules CD54, CD56, CD106 and CD166. They were negative for the stem cell markers CD34, CD146, CD133, CD117. Only aldehyde dehydrogenase (ALDH) was expressed. Neither AD-MSCs nor HNDFs differed in their multi-lineage differentiation capacity; they both differentiated into osteoblast, adipocyte, and also into cardiomyocyte-like cells. In contrast, AD-MSCs, but not HNDFs, displayed strong angiogenic and anti-inflammatory activity. AD-MSCs released significant amounts of VEGF, HGF and Angiopoietins and their conditioned medium (CM) stimulated ECs proliferation and tube formations. In addition, CM-derived AD-MSCs (AD-MSCs-CM) inhibited adhesion molecules expression on U937 and release of RANTES and MCP-1. Finally, after priming with TNFα, AD-MSCs enhanced their anti-inflammatory potential; while HNDFs acquired pro-inflammatory activity.

CONCLUSIONS

AD-MSCs cannot be distinguished from HNDFs in vitro by evaluating their phenotypic profile or differentiation potential, but only through the analysis of their anti-inflammatory and angiogenic properties. These results underline the importance of evaluating the angiogenic and anti-inflammatory features of MSCs preparation. Their priming with inflammatory cytokines prior to transplantation may improve their efficacy in cell-based therapies for tissue regeneration.

Derivation of functional smooth muscle cells from multipotent human hair follicle mesenchymal stem cells

We investigated the potential of human hair follicle cells for multilineage differentiation and as a source of functional smooth muscle cells (SMCs). We report that human hair follicle stem cells (HFCs) isolated from individual follicles expressed surface markers that are characteristic of mesenchymal stem cells such as CD44, CD49b, CD73, CD90, and CD105 but lacked hematopoietic markers CD45 and CD34. In addition, HFCs differentiated toward adipocytes, chondrocytes, osteoblasts, or SMCs in the appropriate induction medium. Treatment with basic fibroblast growth factor increased proliferation and prevented myogenic differentiation, suggesting that basic fibroblast growth factor can be used to expand the population of undifferentiated HFCs to the large numbers needed for therapeutic applications. SMCs were isolated from HFCs using tissue-specific promoters and flow cytometry sorting. Cylindrical vascular constructs engineered with HF-SMCs showed remarkable contractility in response to receptor and nonreceptor agonists such KCl, endothelin-1, and the thromboxane mimetic, U46619, as well as superior mechanical properties compared to their counterparts with human vascular SMCs. Our results suggest that HF is a rich source of mesenchymal stem cells with great potential for myogenic differentiation providing functional SMCs for tissue regeneration and cell therapies.

Human dermal fibroblasts exhibit delayed adipogenic differentiation compared with mesenchymal stem cells

Human dermal fibroblasts (FBs) express mesenchymal stem cell (MSC)-specific cell surface markers and differentiate into several cell types under appropriate conditions. Molecular mechanisms controlling the early stages of differentiation of dermal FBs and MSCs isolated from different sources have not been well studied. Here, we have analyzed the cell type-specific changes of adipose tissue-derived mesenchymal stem cells (AdMSCs) and dermal FBs in the process of differentiation into adipocytes and osteoblasts. Analysis of gene expression in the course of adipogenic differentiation of AdMSCs and FBs isolated from the same individuals revealed a time lag in the induction of adipogenesis-related genes in FBs compared with AdMSCs, a phenomenon not previously described. Further, preliminary evidence suggests that delayed adipogenesis of FBs is related to the delayed induction of preadipocyte transcription factor ZNF423 in FBs. These findings clearly show that AdMSCs and FBs have similar developmental potential but different molecular control mechanisms of initial stages of adipogenic differentiation.

Effect of honey and its major royal jelly protein 1 on cytokine and MMP-9 mRNA transcripts in human keratinocytes

Honey has been used since ancient times as a remedy in wound healing. However, even though the results from randomized clinical trials document that honey accelerates wound healing, no study dealing with its influence on human skin cells (epidermal keratinocytes and dermal fibroblast) has been performed. We demonstrate that keratinocytes, which are known to be involved in wound healing, are responsible for elevated production of mediators including cytokines (TNF-alpha, IL-1beta and TGF-beta) and matrix metalloproteinase-9 (MMP-9) after incubation with honey. Real-time PCR was performed for the quantification of mRNA level of selected cytokines and MMP-9. Furthermore, we show that the increased level of MMP-9 in the epidermis following incubation with honey leads to degradation of type IV collagen in the basement membrane. These data indisputably demonstrate that honey activates keratinocytes and support the findings that honey may accelerate wound healing process.

Differential surface antigen expression and 1α,25-dihydroxyvitamin D3 responsiveness distinguish human dermal fibroblasts with age-dependent osteogenic differentiation potential from marrow-derived stromal cells in vitro

BACKGROUND AIMS

Recent studies have demonstrated that cells committed to a fibroblastic lineage, including dermal fibroblasts, may undergo osteoblastic differentiation when treated with steroid hormones. However, stem cells have also been isolated from the dermis, making it unclear whether osteoinduction of dermal fibroblasts is the result of transdifferentiation of committed fibroblasts or differentiation of resident multipotent stromal cells, which are morphologically indistinguishable.

METHODS

Flow cytometry was used to characterize the expression of CD26, CD90 and CD105 on neonatal and adult human dermal fibroblasts and adult human bone marrow-derived stromal cells. These cells were then cultured with the steroid hormones 1α,25-dihydroxyvitamin D(3) and dexamethasone, and evaluated for protein expression and mineral deposition typical of an osteoblastic phenotype.

RESULTS

The surface peptidase, dipeptidyl peptidase IV (CD26), was differentially expressed between human neonatal (98.22 ± 1.47%) and adult (90.73 ± 7.97%) dermal fibroblasts and adult bone marrow-derived stromal cells (6.84 ± 5.07%). In addition, neonatal dermal fibroblasts treated with vitamin D(3) expressed alkaline phosphatase, osteocalcin and bone sialoprotein, and deposited mineral, which is consistent with an osteoblastic phenotype. Such differentiation was not observed in adult dermal fibroblasts. In contrast, marrow-derived stromal cells required dexamethasone in order to undergo osteoblastic differentiation.

CONCLUSIONS

Taken together, the differential surface antigen expression and disparate response to steroid hormones suggest that committed neonatal dermal fibroblasts are distinct from mesenchymal stromal cells and possess osteogenic differentiation potential.

Age-related changes in proliferation, the numbers of mast cells, eosinophils, and cd45-positive cells in human dermis

Skin aging is an extremely important medical and social problem in the modern world. Therefore, a goal of the present work was to estimate changes in the numbers of fibroblast-like cells, proliferating cells nuclear antigen-positive cells, CD45-positive cells, mast cells, and eosinophils in human dermis at different ages. Skin specimens from human fetuses that died antenatally from 20 to 40 weeks of pregnancy and humans who died from different causes from 1 day to 85 years of life were used for the study. Results showed a decrease in a total number and the number of proliferating cells nuclear antigen-positive fibroblast-like cells in dermis with progression of age. The numbers of CD45-positive cells and mast cells are gradually increased with aging. Eosinophils are almost absent in dermis independently on age. Mast cells are probably a main factor that potentially can be involved in tissue damage and aging changes in skin. Mast cells should be regarded as an important target for anti-aging therapy.

Markers distinguishing mesenchymal stem cells from fibroblasts are downregulated with passaging

Expansion of plastic-adherent bone marrow-derived mesenchymal stem cells (MSCs) results in gradual loss of osteogenic potential after passage 5-6. One explanation is contamination of MSC cultures with mature cells including fibroblasts. Identification and elimination of fibroblasts from MSC cultures could improve MSC yield and differentiation potential and also prevent tumor formation after MSC transplantation. However, no specific markers currently exist that can reliably discriminate between MSCs and fibroblasts. Flow cytometry analysis demonstrated that markers currently used to define MSCs, such as CD105, CD166, CD90, CD44, CD29, CD73, and CD9, are also expressed on human skin or lung fibroblasts. However, the level of expression of CD166 was significantly higher and that of CD9 was significantly lower in MSCs than in fibroblasts. CD146 was expressed only in MSCs. Using small focused microarrays, new markers differentially expressed in MSCs and fibroblasts were identified. Real-time polymerase chain reaction confirmed that expression of CD106, integrin alpha 11, and insulin-like growth factor-2 in MSCs was at least 10-fold higher than in fibroblasts; whereas expression of matrix metalloproteinase 1 and matrix metalloproteinase 3 was almost 100-fold lower. Flow cytometry and immunostaining demonstrated that CD106 protein expression on cell surface could be upregulated in MSCs but not in fibroblasts by the treatment with tumor necrosis factor-alpha. Comparison of surface expression of commonly used and newly identified MSC markers in MSCs cultures of passage 2 and passage 6 demonstrated that CD106 (with and without tumor necrosis factor-alpha treatment), integrin alpha 11, and CD146 were downregulated in MSCs of passage 6, and CD9 was upregulated; whereas all other markers did not change. Newly identified markers that have robust differences of expression in MSCs and fibroblasts on gene and protein level could be used for quality control of MSC cultures after expansion, cryopreservation, gene transfection, and other manipulations.

Human umbilical cord-derived mesenchymal stromal cells differentiate into functional Schwann cells that sustain peripheral nerve regeneration

Human umbilical cord-derived mesenchymal stromal cells (UC-MSCs) that are available from cell banks can be induced to differentiate into various cell types, thereby making them practical potential sources for cell-based therapies. In injured peripheral nerves, Schwann cells (SCs) contribute to functional recovery by supporting axonal regeneration and myelin reconstruction. Here, we first demonstrate a system to induce UC-MSCs to differentiate into cells with SC properties (UC-SCs) by treatment with β-mercaptoethanol followed by retinoic acid and a set of specific cytokines. The UC-SCs are morphologically similar to SCs and express SC markers, including P0, as assessed by immunocytochemistry and reverse transcription polymerase chain reaction. Transplantation of UC-SCs into transected sciatic nerves in adult rats enhanced nerve regeneration. The effectiveness of UC-SCs for axonal regeneration was comparable to that of authentic human SCs based on histological criteria and functional recovery. Immunohistochemistry and immunoelectron microscopy also demonstrated myelination of regenerated axons by UC-SCs. These findings indicate that cells with SC properties and with the ability to support axonal regeneration and reconstruct myelin can be successfully induced from UC-MSCs to promote functional recovery after peripheral nerve injury. This system may be applicable for the development of cell-based therapies.

Human nasal mucosa contains tissue-resident immunologically responsive mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MSC) are present in bone marrow and other tissues such as adipose tissue, muscle, pancreas, liver, and so on. Recent evidence suggests that MSC migrate to sites of infection, inflammation, and cancer, and interact with different immune cell subsets. Here, we report for the first time on the isolation and characterization of multipotent nasal mucosa-derived mesenchymal stromal cells (nm-MSC). nm-MSC showed a plastic adherent and fibroblast-like morphology and were able to form colonies. They expressed the typical bone marrow MSC marker antigens CD29, CD44, CD73, CD90, and CD105 and were able to differentiate along the adipogenic, chondrogenic, and osteogenic pathways. nm-MSC produced a set of inflammatory cytokines, expressed chemokine receptors, and were responsive to stimulation with cytokines, chemokines, and TLR4 ligand LPS. Thus, these cells may serve as an alternative adult stromal cell resource for regenerative tissue repair and may represent important regulators of local mucosal immunity.

Keratinocyte proximity and contact can play a significant role in determining mesenchymal stem cell fate in human tissue

Bone marrow-derived human mesenchymal stem cells (hMSCs) possess multipotent differentiation capabilities and are a potent source of paracrine factors. We show how the epidermal keratinocyte can direct hMSC differentiation selectively. Keratinocytes and hMSCs were either cocultured in physical contact (contact cocultures), or separated without physical contact using a transwell insert (noncontact cocultures). We also delivered hMSCs into an ex vivo human excisional wound where subpopulations of the hMSCs were either in contact or were physically separated from the epidermal keratinocytes. In comparison to control hMSCs that were not cocultured, contact cocultured hMSCs adopted an epithelial morphology and expressed keratinocyte markers while noncontact cocultured hMSCs, surprisingly, adopted phenotypes that resembled myofibroblast and early neural lineage, both of which are of dermal origin. Cell fusion was not a requirement in in vitro contact cocultures, as determined by fluorescence-activated cell sorting (FACS) and fluorescence in situ hybridization analysis (FISH). To the best of our knowledge, this work provides the first example of hMSC differentiation into different lineages depending on their proximity to a single cell type.

[Cutaneous mesenchymal stem cells. Current status of research and potential clinical applications]

Within the next decade stem cell-based therapies can be expected to be part of clinical medicine. In regard to the skin, the focus of stem cell research is on the epidermis and the hair follicle. In 2001, mesenchymal stem cells residing within the dermis were first isolated which have the capacity to differentiate into adipocytes, smooth muscle cells, osteocytes, chondrocytes and even neurons and glia as well as hematopoietic cells of myeloid and erythroid lineage. The perifollicular connective tissue sheath and the papilla represent the likely anatomical niche for these multipotent dermal cells. They have the potential to function as an easily accessible, autologous source for future stem cell transplantation. Potential therapeutic applications include the treatment of acute and steroid-refractory graft-versus-host disease, systemic lupus erythematosus, idiopathic pulmonary fibrosis and arthritis. The neuronal differentiation potential of cutaneous mesenchymal stem cells may also be exploited in the treatment of neurodegenerative disorders and traumatic spinal injury. The most immediate impact can be expected in the field of wound healing.

Isolation and characterization of endosteal niche cell populations that regulate hematopoietic stem cells

The endosteal niche is critical for the maintenance of hematopoietic stem cells (HSCs). However, it consists of a heterogeneous population in terms of differentiation stage and function. In this study, we characterized endosteal cell populations and examined their ability to maintain HSCs. Bone marrow endosteal cells were subdivided into immature mesenchymal cell-enriched ALCAM(-)Sca-1(+) cells, osteoblast-enriched ALCAM(+)Sca-1(-), and ALCAM(-)Sca-1(-) cells. We found that all 3 fractions maintained long-term reconstitution (LTR) activity of HSCs in an in vitro culture. In particular, ALCAM(+)Sca-1(-) cells significantly enhanced the LTR activity of HSCs by the up-regulation of homing- and cell adhesion-related genes in HSCs. Microarray analysis showed that ALCAM(-)Sca-1(+) fraction highly expressed cytokine-related genes, whereas the ALCAM(+)Sca-1(-) fraction expressed multiple cell adhesion molecules, such as cadherins, at a greater level than the other fractions, indicating that the interaction between HSCs and osteoblasts via cell adhesion molecules enhanced the LTR activity of HSCs. Furthermore, we found an osteoblastic marker(low/-) subpopulation in ALCAM(+)Sca-1(-) fraction that expressed cytokines, such as Angpt1 and Thpo, and stem cell marker genes. Altogether, these data suggest that multiple subsets of osteoblasts and mesenchymal progenitor cells constitute the endosteal niche and regulate HSCs in adult bone marrow.

Moving towards in situ tracheal regeneration: the bionic tissue engineered transplantation approach

In June 2008, the world's first whole tissue-engineered organ - the windpipe - was successfully transplanted into a 31-year-old lady, and about 18 months following surgery she is leading a near normal life without immunosuppression. This outcome has been achieved by employing three groundbreaking technologies of regenerative medicine: (i) a donor trachea first decellularized using a detergent (without denaturing the collagenous matrix), (ii) the two main autologous tracheal cells, namely mesenchymal stem cell derived cartilage-like cells and epithelial respiratory cells and (iii) a specifically designed bioreactor that reseed, before implantation, the in vitro pre-expanded and pre-differentiated autologous cells on the desired surfaces of the decellularized matrix. Given the long-term safety, efficacy and efforts using such a conventional approach and the potential advantages of regenerative implants to make them available for anyone, we have investigated a novel alternative concept how to fully avoid in vitro cell replication, expansion and differentiation, use the human native site as micro-niche, potentiate the human body's site-specific response by adding boosting, permissive and recruitment impulses in full respect of sociological and regulatory prerequisites. This tissue-engineered approach and ongoing research in airway transplantation is reviewed and presented here.

Differentiation of dermal multipotent cells into odontogenic lineage induced by embryonic and neonatal tooth germ cell-conditioned medium

Stem cell-based therapy represents a novel and more advantageous modality of treatment for tooth defect or loss. However, this strategy is challenged in the circumstances where tooth-derived stem cells are not readily accessible. In present study we sought to explore the possibility of utilizing dermal multipotent cells (DMCs) easily available from skin tissue for odontogenic induction. Using the limiting dilution technique, colony-forming cell population was isolated and characterized by proliferative activity and multilineage differentiation potential. By exposure to conditioned medium of embryonic and neonatal tooth germ cells in culture, the proliferation and mineralization activity of DMCs was elevated, while the embryonic tooth germ cell-conditioned medium (ETGC-CM) produced more significant effects. Meanwhile, ETGC-CM-treated DMCs phenocopied the odontoblasts in vitro as indicated by specific lineage markers. Following in vivo transplantation as cell pellet, ETGC-CM-treated DMCs were capable of producing blocks of mineralized tissues, which resembled those of dental pulp stem cell (DPSC) explants in the same subcutaneous pockets environment. These observations suggest that although more sufficient and continuous inductive microenvironment may be needed for undifferentiated DMCs to perform as odontoblasts, ETGC-CM-treated DMCs indeed acquire properties as those of DPSCs. Our work highlights the potential utility of DMCs as an alternative candidate cell source in hopes of developing more practical strategy of tooth regeneration research and offering promising opportunities for therapeutic approach.

Mesenchymal stem cells derived from human gingiva are capable of immunomodulatory functions and ameliorate inflammation-related tissue destruction in experimental colitis

Aside from the well-established self-renewal and multipotent differentiation properties, mesenchymal stem cells exhibit both immunomodulatory and anti-inflammatory roles in several experimental autoimmune and inflammatory diseases. In this study, we isolated a new population of stem cells from human gingiva, a tissue source easily accessible from the oral cavity, namely, gingiva-derived mesenchymal stem cells (GMSCs), which exhibited clonogenicity, self-renewal, and multipotent differentiation capacities. Most importantly, GMSCs were capable of immunomodulatory functions, specifically suppressed peripheral blood lymphocyte proliferation, induced expression of a wide panel of immunosuppressive factors including IL-10, IDO, inducible NO synthase (iNOS), and cyclooxygenase 2 (COX-2) in response to the inflammatory cytokine, IFN-gamma. Cell-based therapy using systemic infusion of GMSCs in experimental colitis significantly ameliorated both clinical and histopathological severity of the colonic inflammation, restored the injured gastrointestinal mucosal tissues, reversed diarrhea and weight loss, and suppressed the overall disease activity in mice. The therapeutic effect of GMSCs was mediated, in part, by the suppression of inflammatory infiltrates and inflammatory cytokines/mediators and the increased infiltration of regulatory T cells and the expression of anti-inflammatory cytokine IL-10 at the colonic sites. Taken together, GMSCs can function as an immunomodulatory and anti-inflammatory component of the immune system in vivo and is a promising cell source for cell-based treatment in experimental inflammatory diseases.

Immunohistochemical localization of the STRO-1 antigen in developing rat teeth by light microscopy and electron microscopy

STRO-1 is a cell-surface antigen. A cell population that is positive for the anti-STRO-1 antibody has been shown to contain mesenchymal stem cells. STRO-1-positive cells have been reported to reside in dental pulp and periodontal ligaments as well as in bone marrow. However, the tissue localization of STRO-1 in developing teeth is not clear. The present study was designed to investigate the spatiotemporal localization of STRO-1 in developing rat teeth by immunohistochemistry using light microscopy and electron microscopy. Wistar rats at ages 2, 3, 6 and 12 weeks postnatum and embryos at 18 days postcoitum were fixed with 4% paraformaldehyde. Mandibles and maxillae were resected and decalcified in 10% EDTA. The specimens were embedded in paraffin, and sections were cut and processed for immunohistochemistry using the anti-STRO-1 antibody. Selected specimens were frozen, sectioned and processed for immunoelectron microscopy. Immunoreactions for STRO-1 were identified in some bone marrow cells. Some odontoblasts and dental pulp cells showed positive immunoreactivity in developing rat tooth crowns and roots. Alveolar osteoblasts, cementoblasts and periodontal ligament cells were also immunoreactive. Electron microscopy localized the antigen in plasma membrane and some vesicles in dental pulp cells and odontoblasts. The study suggests that the STRO-1 antigen is involved in the differentiation of mesenchymal cell lineages and formation of the matrix in dental tissues.

Cutaneous mesenchymal stem cells: status of current knowledge, implications for dermatopathology

Stem cell biology is currently making its impact on medicine, which will probably increase over the next decades. It not only influences our therapeutic thinking caused by the enormous plasticity of stem cells but also affects diagnostic and conceptual aspects of dermatopathology. Although our knowledge of the keratinocytic stem cells located within the follicular bulge has exploded exponentially since their discovery in 1990, the concept of cutaneous mesenchymal stem cells (MSCs) is new. Described initially in 2001 in mice, MSCs later were also found in the human dermis. The connective tissue sheath and the papilla of the hair follicle probably represent the anatomical niche for cutaneous MSCs. In line with the cancer stem cell hypothesis, mutations of these cells may be the underlying basis of mesenchymal skin neoplasms, such as dermatofibrosarcoma protuberans. Furthermore, research on cutaneous MSCs may impact our thinking on the interaction of the epithelial component of skin neoplasms with their surrounding stroma. We are only in the early stages to recognize the importance of the potential contributions of cutaneous MSC research to dermatopathology, but it is not inconceivable to assume that they could be tremendous, paralleling the early discovery of the follicular bulge as a stem cell niche.

Expression of mesenchymal stem cell marker CD90 on dermal sheath cells of the anagen hair follicle in canine species

The dermal sheath (DS) of the hair follicle is comprised by fibroblast-like cells and extends along the follicular epithelium, from the bulb up to the infundibulum. From this structure, cells with stem characteristics were isolated: they have a mesenchymal origin and express CD90 protein, a typical marker of mesenchymal stem cells. It is not yet really clear in which region of hair follicle these cells are located but some experimental evidence suggests that dermal stem cells are localized prevalently in the lower part of the anagen hair follicle.

As there are no data available regarding DS stem cells in dog species, we carried out a morphological analysis of the hair follicle DS and performed both an immunohistochemical and an immunocytochemical investigation to identify CD90⁺ cells. We immunohistochemically evidenced a clear and abundant positivity to CD90 protein in the DS cells located in the lower part of anagen hair follicle. The positive cells showed a typical fibroblast-like morphology. They were flat and elongated and inserted among bundles of collagen fibres.The whole structure formed a close and continuous sleeve around the anagen hair follicle. Our immunocytochemical study allowed us to localize CD90 protein at the cytoplasmic membrane level.

Recent advances on skin-resident stem/progenitor cell functions in skin regeneration, aging and cancers and novel anti-aging and cancer therapies

Recent advances in skin-resident adult stem/progenitor cell research have revealed that these immature and regenerative cells with a high longevity provide critical functions in maintaining skin homeostasis and repair after severe injuries along the lifespan of individuals. The establishment of the functional properties of distinct adult stem/progenitor cells found in skin epidermis and hair follicles and extrinsic signals from their niches, which are deregulated during their aging and malignant transformation, has significantly improved our understanding on the etiopathogenesis of diverse human skin disorders and cancers. Particularly, enhanced ultraviolet radiation exposure, inflammation and oxidative stress and telomere attrition during chronological aging may induce severe DNA damages and genomic instability in the skin-resident stem/progenitor cells and their progenies. These molecular events may result in the alterations in key signalling components controlling their self-renewal and/or regenerative capacities as well as the activation of tumour suppressor gene products that trigger their growth arrest and senescence or apoptotic death. The progressive decline in the regenerative functions and/or number of skin-resident adult stem/progenitor cells may cause diverse skin diseases with advancing age. Moreover, the photoaging, telomerase re-activation and occurrence of different oncogenic events in skin-resident adult stem/progenitor cells may also culminate in their malignant transformation into cancer stem/progenitor cells and skin cancer initiation and progression. Therefore, the anti-inflammatory and anti-oxidant treatments and stem cell-replacement and gene therapies as well as the molecular targeting of their malignant counterpart, skin cancer-initiating cells offer great promise to treat diverse skin disorders and cancers.

Exploring the role of stem cells in cutaneous wound healing

The skin offers a perfect model system for studying the wound healing cascade, which involves a finely tuned interplay between several cell types, pathways and processes. The dysregulation of these factors may lead to wound healing disorders resulting in chronic wounds, as well as abnormal scars such as hypertrophic and keloid scars. As the contribution of stem cells towards tissue regeneration and wound healing is increasingly appreciated, a rising number of stem cell therapies for cutaneous wounds are currently under development, encouraged by emerging preliminary findings in both animal models and human studies. However, we still lack an in-depth understanding of the underlying mechanisms through which stem cells contribute to cutaneous wound healing. The aim of this review is, therefore, to present a critical synthesis of our current understanding of the role of stem cells in normal cutaneous wound healing. In addition to summarizing wound healing principles and related key molecular and cellular players, we discuss the potential participation of different cutaneous stem cell populations in wound healing, and list corresponding stem cells markers. In summary, this review delineates current strategies, future applications, and limitations of stem cell-based or stem cell-targeted therapy in the management of acute and chronic skin wounds.

A role for pericytes as microenvironmental regulators of human skin tissue regeneration

The cellular and molecular microenvironment of epithelial stem and progenitor cells is poorly characterized despite well-documented roles in homeostatic tissue renewal, wound healing, and cancer progression. Here, we demonstrate that, in organotypic cocultures, dermal pericytes substantially enhanced the intrinsically low tissue-regenerative capacity of human epidermal cells that have committed to differentiate and that this enhancement was independent of angiogenesis. We used microarray analysis to identify genes expressed by human dermal pericytes that could potentially promote epidermal regeneration. Using this approach, we identified as a candidate the gene LAMA5, which encodes laminin alpha5, a subunit of the ECM component laminin-511/521 (LM-511/521). LAMA5 was of particular interest as we had previously shown that it promotes skin regeneration both in vitro and in vivo. Analysis using immunogold localization revealed that pericytes synthesized and secreted LAMA5 in human skin. Consistent with this observation, coculture with pericytes enhanced LM-511/521 deposition in the dermal-epidermal junction of organotypic cultures. We further showed that skin pericytes could also act as mesenchymal stem cells, exhibiting the capacity to differentiate into bone, fat, and cartilage lineages in vitro. This study suggests that pericytes represent a potent stem cell population in the skin that is capable of modifying the ECM microenvironment and promoting epidermal tissue renewal from non-stem cells, a previously unsuspected role for pericytes.