Isolation of pluripotent neural crest-derived stem cells from adult human tissues by connexin-43 enrichment

Purinergic Signaling and its Role in the Stem Cell Differentiation

Purinergic signaling is a mechanism in which extracellular purines and pyrimidines interact with specialized cell surface receptors known as purinergic receptors. These receptors are divided into two families of P1 and P2 receptors, each responding to different nucleosides and nucleotides. P1 receptors are activated by adenosine, while P2 receptors are activated by pyrimidine and purines. P2X receptors are ligand-gated ion channels, including seven subunits (P2X1-7). However, P2Y receptors are the G-protein coupled receptors comprising eight subtypes (P2Y1/2/4/6/11/12/13/14). The disorder in purinergic signaling leads to various health-related issues and diseases. In various aspects, it influences the activity of non-neuronal cells and neurons. The molecular mechanism of purinergic signaling provides insight into treating various human diseases. On the contrary, stem cells have been investigated for therapeutic applications. Purinergic signaling has shown promising effect in stem cell engraftment. The immune system promotes the autocrine and paracrine mechanisms and releases the significant factors essential for successful stem cell therapy. Each subtype of purinergic receptor exerts a beneficial effect on the damaged tissue. The most common effect caused by purinergic signaling is the proliferation and differentiation that treat different health-related conditions.

Challenges of Periodontal Tissue Engineering: Increasing Biomimicry through 3D Printing and Controlled Dynamic Environment

In recent years, tissue engineering studies have proposed several approaches to regenerate periodontium based on the use of three-dimensional (3D) tissue scaffolds alone or in association with periodontal ligament stem cells (PDLSCs). The rapid evolution of bioprinting has sped up classic regenerative medicine, making the fabrication of multilayered scaffolds-which are essential in targeting the periodontal ligament (PDL)-conceivable. Physiological mechanical loading is fundamental to generate this complex anatomical structure ex vivo. Indeed, loading induces the correct orientation of the fibers forming the PDL and maintains tissue homeostasis, whereas overloading or a failure to adapt to mechanical load can be at least in part responsible for a wrong tissue regeneration using PDLSCs. This review provides a brief overview of the most recent achievements in periodontal tissue engineering, with a particular focus on the use of PDLSCs, which are the best choice for regenerating PDL as well as alveolar bone and cementum. Different scaffolds associated with various manufacturing methods and data derived from the application of different mechanical loading protocols have been analyzed, demonstrating that periodontal tissue engineering represents a proof of concept with high potential for innovative therapies in the near future.

Neural Crest-Derived Stem Cells (NCSCs) Obtained from Dental-Related Stem Cells (DRSCs): A Literature Review on Current Knowledge and Directions toward Translational Applications

Evidence from dental-related stem cells (DRSCs) suggests an enhanced potential for ectodermal lineage differentiation due to their neural crest origin. Growing evidence that DRSC cultures can produce cells with a neural crest-derived stem cell (NCSC)-like phenotype supports their potential for future therapeutic approaches for neurodegenerative diseases and nerve injuries. However, most of the evidence is limited to the characterization of DRSCs as NCSCs by detecting the expression of neural crest markers. Only a few studies have provided proof of concept of an improved neuro-glial differentiation or direct applicability in relevant models. In addition, a current problem is that several of the existing protocols do not meet manufacturing standards for transferability to a clinical scenario. This review describes the current protocols to obtain NCSCs from DRSCs and their characterization. Also, it provides important considerations from previous work where DRSCs were established and characterized as mesenchymal stromal cells but studied for their neuro-glial differentiation potential. The therapeutic advancement of DRSCs would depend on establishing protocols that can yield a neural crest-like phenotype efficiently, using appropriate manufacturing standards and testing them in relevant models of disease or injury. Achieving these conditions could then facilitate and validate the therapeutic potential of DRSC-NCSCs in regenerative therapies.

Diversified Treatment Options of Adult Stem Cells for Optic Neuropathies

Optic neuropathies refer to a group of ocular disorders with abnormalities or dysfunction of the optic nerve, sharing a common pathophysiology of retinal ganglion cell (RGC) death and axonal loss. RGCs, as the retinal neurons in the central nervous system, show limited capacity in regeneration or recovery upon diseases or after injuries. Critically, there is still no effective clinical treatment to cure most types of optic neuropathies. Recently, stem cell therapy was proposed as a potential treatment strategy for optic neuropathies. Adult stem cells, including mesenchymal stem cells and hematopoietic stem cells, have been applied in clinical trials based on their neuroprotective properties. In this article, the applications of adult stem cells on different types of optic neuropathies and the related mechanisms will be reviewed. Research updates on the strategies to enhance the neuroprotective effects of human adult stem cells will be summarized. This review article aims to enlighten the research scientists on the diversified functions of adult stem cells and consideration of adult stem cells as a potential treatment for optic neuropathies in future clinical practices.

Mechanotransductive Differentiation of Hair Follicle Stem Cells Derived from Aged Eyelid Skin into Corneal Endothelial-Like Cells

Corneal endothelial insufficiency is one of the leading causes of blindness. The main contemporary treatment for corneal blindness is endothelial keratoplasty, which, however, is unsatisfactory as a medical therapy due to the lack of donor corneas and graft rejection. Therefore, autologous stem cell-based corneal endothelial tissue substitutes may be a promising alternative to conventional grafts in the future. To address the age of most patients suffering from corneal endothelial deficiencies, we investigated the presence and potential of hair-derived stem cells from older tissue donors. Our studies revealed the presence of pluripotency- and neural crest-associated markers in tissue sections from blepharoplasty patients aged 50 to 80 years. In vitro outgrowths from eyelid hair follicles on collagen-coated tissue culture plates revealed a weak decrease in stem-cell potency. In contrast, cells within the spheres that spontaneously formed from the adherent cell layer retained full stem-cell potency and could be differentiated into cells of the ecto- meso and endodermal lineages. Although these highly potent hair follicle derived stem cells (HFSC) were only very slightly expandable, they were able to recognize the biomimicry of the Descemet’s-like topography and differentiate into corneal endothelial-like cells. In conclusion, HFSCs derived from epidermal skin of eyelid biopsies are a promising cell source to provide autologous corneal endothelial replacement for any age group of patients.

Connexins in the development and physiology of stem cells

Connexins (Cxs) form gap junction (GJ) channels linking vertebrate cells. During embryogenesis, Cxs are expressed as early as the 4-8 cell stage. As cells differentiate into pluripotent stem cells (PSCs) and during gastrulation, the Cx expression pattern is adapted. Knockdown of Cx43 and Cx45 does not interfere with embryogenic development until the blastula stage, questioning the role of Cxs in PSC physiology and development. Studies in cultivated and induced PSCs (iPSCs) showed that Cx43 is essential for the maintenance of self-renewal and the expression of pluripotency markers. It was found that the role of Cxs in PSCs is more related to regulation of transcription or cell-cell adherence than to formation of GJ channels. Furthermore, a crucial role of Cxs for the self-renewal and differentiation was shown in cultivated adult mesenchymal stem cells. This review aims to highlight aspects that link Cxs to the function and physiology of stem cell development.

Therapeutic potential of periodontal ligament stem cells

Inflammatory periodontal disease known as periodontitis is one of the most common conditions that affect human teeth and often leads to tooth loss. Due to the complexity of the periodontium, which is composed of several tissues, its regeneration and subsequent return to a homeostatic state is challenging with the therapies currently available. Cellular therapy is increasingly becoming an alternative in regenerative medicine/dentistry, especially therapies using mesenchymal stem cells, as they can be isolated from a myriad of tissues. Periodontal ligament stem cells (PDLSCs) are probably the most adequate to be used as a cell source with the aim of regenerating the periodontium. Biological insights have also highlighted PDLSCs as promising immunomodulator agents. In this review, we explore the state of knowledge regarding the properties of PDLSCs, as well as their therapeutic potential, describing current and future clinical applications based on tissue engineering techniques.

Anti-Inflammatory Effects of Conditioned Medium of Periodontal Ligament-Derived Stem Cells on Chondrocytes, Synoviocytes, and Meniscus Cells

Osteoarthritis (OA) is the most common type of arthritis, afflicting millions of people in the world. Elevation of inflammatory mediators and enzymatic matrix destruction is often associated with OA. Therefore, the objective of this study was to investigate the effects of conditioned medium from periodontal ligament-derived stem cells (PDLSCs) on inflammatory and catabolic gene expressions of chondrocytes, synoviocytes, and meniscus cells under in vitro inflammatory condition. Stem cells were isolated from human periodontal ligaments. Conditioned medium was collected and concentrated 20 × . Chondrocytes, synoviocytes, and meniscus cells were isolated from pig knees and divided into four experimental groups: serum-free media, serum-free media+interleukin-1β (IL-1β) (10 ng/mL), conditioned media (CM), and CM+IL-1β. Protein content and extracellular vesicle (EV) miRNAs of CM were analyzed by liquid chromatography-tandem mass spectrometry and RNA sequencing, respectively. It was found that the IL-1β treatment upregulated the expression of IL-1β, tumor necrosis factor-α (TNF-α), MMP-13, and ADAMTS-4 genes in the three cell types, whereas PDLSC-conditioned medium prevented the upregulation of gene expression by IL-1β in all three cell types. This study also found that there was consistency in anti-inflammatory effects of PDLSC CM across donors and cell subcultures, while PDLSCs released several anti-inflammatory factors and EV miRNAs at high levels. OA has been suggested as an inflammatory disease in which all intrasynovial tissues are involved. PDLSC-conditioned medium is a cocktail of trophic factors and EV miRNAs that could mediate different inflammatory processes in various tissues in the joint. Introducing PDLSC-conditioned medium to osteoarthritic joints could be a potential treatment to prevent OA progression by inhibiting inflammation.

Establishment and neural differentiation of neural crest-derived stem cells from human dental pulp in serum-free conditions

The potential of obtaining cell cultures with neural crest resemblance (neural crest-derived stem cells [NCSCs]) from dental-related tissues, including human dental pulp cells (hDPCs), has been discussed in the literature. However, most reports include the use of serum-rich conditions and do not describe the potential for neural differentiation, slowing translation to the clinic. Therefore, we aimed to culture and characterize NCSCs from the human dental pulp in vitro and evaluate their ability to differentiate into neurons; we also investigated the effectiveness of the addition of BMP4 to enhance this potential. Cultures were established from a varied cohort of patient samples and grown, as monolayers, in serum, serum-free, and also under sphere-aggregation conditions to induce and identify a NCSC phenotype. hDPC cultures were characterized by immunocytochemistry and reverse transcription quantitative polymerase chain reaction. Monolayer cultures expressed stem cell, neural progenitor and neural crest-related markers. Culturing hDPCs as neurospheres (hDPC-NCSCs) resulted in an increased expression of neural crest-related genes, while the addition of BMP4 appeared to produce better NCSC characteristics and neural differentiation. The neural-like phenotype was evidenced by the expression of TUJ1, peripherin, NFH, TAU, SYN1, and GAP43. Our results describe the establishment of hDPC cultures from a large variety of patients in serum-free medium, as NCSC that differentiate into neural-like cells, as well as an important effect of BMP4 in enhancing the neural crest phenotype and differentiation of hDPCs.

Periodontal Ligament Stem Cells: Regenerative Potency in Periodontium

Periodontium is consisted of root cementum, bone lining the tooth socket, gingiva facing the tooth, and periodontal ligament (PDL). Its primary functions are support of the tooth and protection of tooth, nerve, and blood vessels from injury by mechanical loading. Severe periodontitis induces the destruction of periodontium and results in a significant cause of tooth loss among adults. Unfortunately, conventional therapies such as scaling and root planning are often only palliative. Therefore, the ultimate goal of the treatment for periodontitis is to restore disrupted periodontium to its original shape and function. Tissue engineering refers to the process of combining cells, scaffolds, and signaling molecules for the production of functional tissues to restore, maintain, and improve damaged organs. The discovery of periodontal ligament stem cells (PDLSCs) highlighted the possibility for development of tissue engineering technology-based therapeutics for disrupted periodontium. PDLSCs are a kind of somatic stem cells that show potential to differentiate into multiple cell types and undergo robust clonal self-renewal. Therefore, PDLSCs are considered a highly promising stem cell population for regenerative therapy in periodontium; however, their rarity prevents the progression of basic and clinical researches. In this review, we summarize recent research advancement and accumulated information regarding the self-renewal capacity, multipotency, and immunomodulatory effect of PDLSCs, as well as their contribution to repair and regeneration of periodontium and other tissues. We also discuss the possibility of PDLSCs for clinical application of regenerative medicine and provide an outline of the genetic approaches to overcome the issue about the rarity of PDLSCs.

Comparison of responses of melanocyte lineages from p75(+) and p75(-) human scalp-derived neural crest stem cells under phototherapy

Phototherapy is an effective therapeutic option in the treatment of vitiligo; however, responses varied among the different types. The underlying mechanism has scarcely been investigated. To investigate and compare the effects of phototherapy on the mutation of melanocyte lineage differentiated from human scalp-derived neural crest stem cells (HS-NCSCs) with p75 neurotrophin receptor expression positive and p75 neurotrophin receptor expression negative group in vitro, the HS-NCSCs were isolated from fetal scalp tissue, which is identified by immunofluorescent staining. The p75(+) and p75(-) cells from HS-NCSCs were isolated by magnetic cell sorting, respectively. The embryonic neural crest stem cell biomarkers were detected by RT-PCR. Narrow-band UVB (NB-UVB) was used to irradiate the cells. Cell proliferation was evaluated by cell count. Tyrosinase, Tyrp1, and Tyrp2 gene expression were measured by quantitative RT-PCR. Tyrosinase and GRCR protein levels were investigated by Western blot analysis. The electrophoretic strip showed that Sox2, Oct4, Sox10, and Nestin of p75(+) HS-NCSCs were brighter than the p75(-) HS-NCSCs. After the same dose radiation with NB-UVB, the cell proliferation of p75(+) group showed less inhibitory rate compared with the p75(-) HS-NCSCs. The tyrosinase mRNA and protein expression of differentiated melanocytes increased significantly in the group of p75(+) HS-NCSCs compared with the p75(-) group. The melanocytic mutation of p75(+) HS-NCSCs increased significantly compared with the p75(-) HS-NCSCs under NB-UVB, which indicated there were more melanocyte precursors in the differentiated cells from p75(+) HS-NCSCs. This may provide new insights for the different repigmentation efficacy of segmental and non-segmental vitiligo.

Formation, structure, and function of extra-skeletal bones in mammals

This review describes the formation, structure, and function of bony compartments in antlers, horns, ossicones, osteoderm and the os penis/os clitoris (collectively referred to herein as AHOOO structures) in extant mammals. AHOOOs are extra-skeletal bones that originate from subcutaneous (dermal) tissues in a wide variety of mammals, and this review elaborates on the co-development of the bone and skin in these structures. During foetal stages, primordial cells for the bony compartments arise in subcutaneous tissues. The epithelial-mesenchymal transition is assumed to play a key role in the differentiation of bone, cartilage, skin and other tissues in AHOOO structures. AHOOO ossification takes place after skeletal bone formation, and may depend on sexual maturity. Skin keratinization occurs in tandem with ossification and may be under the control of androgens. Both endochondral and intramembranous ossification participate in bony compartment formation. There is variation in gradients of density in different AHOOO structures. These gradients, which vary according to function and species, primarily reduce mechanical stress. Anchorage of AHOOOs to their surrounding tissues fortifies these structures and is accomplished by bone-bone fusion and Sharpey fibres. The presence of the integument is essential for the protection and function of the bony compartments. Three major functions can be attributed to AHOOOs: mechanical, visual, and thermoregulatory. This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals.

EMSCs Build an All-in-One Niche via Cell-Cell Lipid Raft Assembly for Promoted Neuronal but Suppressed Astroglial Differentiation of Neural Stem Cells

The therapeutic efficiency of allogenic/intrinsic neural stem cells (NSCs) after spinal cord injury is severely compromised because the hostile niche at the lesion site incurs massive astroglial but not neuronal differentiation of NSCs. Although many attempts are made to reconstruct a permissive niche for nerve regeneration, solely using a living cell material to build an all-in-one, multifunctional, permissive niche for promoting neuronal while inhibiting astroglial differentiation of NSCs is not reported. Here, ectomesenchymal stem cells (EMSCs) are reported to serve as a living, smart material that creates a permissive, all-in-one niche which provides neurotrophic factors, extracellular matrix molecules, cell-cell contact, and favorable substrate stiffness for directing NSC differentiation. Interestingly, in this all-in-one niche, a corresponding all-in-one signal-sensing platform is assembled through recruiting various niche signaling molecules into lipid rafts for promoting neuronal differentiation of NSCs, and meanwhile, inhibiting astrocyte overproliferation through the connexin43/YAP/14-3-3θ pathway. In vivo studies confirm that EMSCs can promote intrinsic NSC neuronal differentiation and domesticating astrocyte behaviors for nerve regeneration. Collectively, this study represents an all-in-one niche created by a single-cell material-EMSCs for directing NSC differentiation.

Cancer Prevention and Therapy of Two Types of Gap Junctional Intercellular Communication⁻Deficient "Cancer Stem Cell"

Early observations showed a lack of growth control and terminal differentiation with a lack of gap junctional intercellular communication (GJIC). Subsequent observations showed that epigenetic tumor promoters and activated oncogenes, which block gap junction function, provide insights into the multi-stage, multi-mechanism carcinogenic process. With the isolation of embryonic induced pluri-potent stem cells and organ-specific adult stem cells, gap junctions were linked to early development. While tumors and tumor cell lines are a heterogeneous mixture of "cancer stem cells" and "cancer non-stem cells", the cancer stem cells seem to be of two types, namely, they express (a) no connexin genes or (b) connexin genes, but do not have functional GJIC. These observations suggest that these "cancer stem cells" originate from normal adult stem cells or from the de-differentiation or re-programming of somatic differentiated cells. This "Concept Paper" provides a hypothesis that "cancer stem cells" either originate from (a) organ-specific adult stem cells before the expression of the connexin genes or (b) organ-specific adult stem cells that just express gap junction genes but that the connexin proteins are rendered dysfunctional by activated oncogenes. Therefore, cancer prevention and therapeutic strategies must account for these two different types of "cancer stem cell".

MicroRNA-132 directs human periodontal ligament-derived neural crest stem cell neural differentiation

Neurogenesis is the basis of stem cell tissue engineering and regenerative medicine for central nervous system (CNS) disorders. We have established differentiation protocols to direct human periodontal ligament-derived stem cells (PDLSCs) into neuronal lineage, and we recently isolated the neural crest subpopulation from PDLSCs, which are pluripotent in nature. Here, we report the neural differentiation potential of these periodontal ligament-derived neural crest stem cells (NCSCs) as well as its microRNA (miRNA) regulatory mechanism and function in NCSC neural differentiation. NCSCs, treated with basic fibroblast growth factor and epidermal growth factor-based differentiation medium for 24 days, expressed neuronal and glial markers (βIII-tubulin, neurofilament, NeuN, neuron-specific enolase, GFAP, and S100) and exhibited glutamate-induced calcium responses. The global miRNA expression profiling identified 60 upregulated and 19 downregulated human miRNAs after neural differentiation, and the gene ontology analysis of the miRNA target genes confirmed the neuronal differentiation-related biological functions. In addition, overexpression of miR-132 in NCSCs promoted the expression of neuronal markers and downregulated ZEB2 protein expression. Our results suggested that the pluripotent NCSCs from human periodontal ligament can be directed into neural lineage, which demonstrate its potential in tissue engineering and regenerative medicine for CNS disorders.

Isolation and Characterization of Neural Crest-Derived Stem Cells From Adult Ovine Palatal Tissue

Adult mammalian craniofacial tissues contain limited numbers of post-migratory neural crest-derived stem cells. Similar to their embryonic counterparts, these adult multipotent stem cells can undergo multi-lineage differentiation and are capable of contributing to regeneration of mesodermal and ectodermal cells and tissues in vivo. In the present study, we describe for the first time the presence of Nestin-positive neural crest-derived stem cells (NCSCs) within the ovine hard palate. We show that these cells can be isolated from the palatal tissue and are able to form neurospheres. Ovine NCSCs express the typical neural crest markers Slug and Twist, exhibit high proliferative and migratory activity and are able to differentiate into α smooth muscle cells and β-III-tubulin expressing ectodermal cells. Finally, we demonstrate that oNCSCs are capable of differentiating into osteogenic, adipogenic and chondrogenic cells. Taken together, our results suggest that oNCSCs could be used as model cells to assess the efficacy and safety of autologous NCSC transplantation in a large animal model.

Postnatal periodontal ligament as a novel adult stem cell source for regenerative corneal cell therapy

Corneal opacities are a leading cause of global blindness. They are conventionally treated by the transplantation of donor corneal tissue, which is, restricted by a worldwide donor material shortage and allograft rejection. Autologous adult stem cells with a potential to differentiate into corneal stromal keratocytes (CSKs) could offer a suitable choice of cells for regenerative cell therapy. Postnatal periodontal ligament (PDL) contains a population of adult stem cells, which has a similar embryological origin as CSK, that is cranial neural crest. We harvested PDL cells from young adult teeth extracted because of non-functional or orthodontic reason and differentiated them towards CSK phenotype using a two-step protocol with spheroid formation followed by growth factor and cytokine induction in a stromal environment (human amnion stroma and porcine corneal stroma). Our results showed that the PDL-differentiated CSK-like cells expressed CSK markers (CD34, ALDH3A1, keratocan, lumican, CHST6, B3GNT7 and Col8A2) and had minimal expression of genes related to fibrosis and other lineages (vasculogenesis, adipogenesis, myogenesis, epitheliogenesis, neurogenesis and hematogenesis). Introduction of PDL spheroids into the stroma of porcine corneas resulted in extensive migration of cells inside the host stroma after 14-day organ culture. Their quiescent nature and uniform cell distribution resembled to that of mature CSKs inside the native stroma. Our results demonstrated the potential translation of PDL cells for regenerative corneal cell therapy for corneal opacities.

Neural Crest Stem-Like Cells Non-genetically Induced from Human Gingiva-Derived Mesenchymal Stem Cells Promote Facial Nerve Regeneration in Rats

Non-genetic induction of somatic cells into neural crest stem-like cells (NCSCs) is promising for potential cell-based therapies for post-traumatic peripheral nerve regeneration. Here, we report that human gingiva-derived mesenchymal stem cells (GMSCs) could be reproducibly and readily induced into NCSCs via non-genetic approaches. Compared to parental GMSCs, induced NCSC population had increased expression in NCSC-related genes and displayed robust differentiation into neuronal and Schwann-like cells. Knockdown of the expression of Yes-associated protein 1 (YAP1), a critical mechanosensor and mechanotransducer, attenuated the expression of NCSC-related genes; specific blocking of RhoA/ROCK activity and non-muscle myosin II (NM II)-dependent contraction suppressed YAP1 and NCSC-related genes and concurrently abolished neural spheroid formation in NCSCs. Using a rat model of facial nerve defect, implantation of NCSC-laden nerve conduits promoted functional regeneration of the injured nerve. These promising findings demonstrate that induced NCSCs derived from GMSCs represent an easily accessible and promising source of neural stem-like cells for peripheral nerve regeneration.

Neural Crest Stem Cells Can Differentiate to a Cardiomyogenic Lineage with an Ability to Contract in Response to Pulsed Infrared Stimulation

INTRODUCTION

Cellular cardiomyoplasty has rapidly risen to prominence in the clinic following a myocardial infarction; however, low engraftment of transplanted cells limits the therapeutic benefit to these procedures. Recently, lineage-specific stem cells differentiated into cardiomyocytes have gained much attention to assist in the repair of an injured heart tissue; however, questions regarding the ideal cell source remain. In the present study, we have identified a source that is easy to extract stem cells from and show that the cells present have a high plasticity toward the cardiomyogenic lineage. We focused on the recently discovered neural crest stem cells residing in the periodontal ligament that can be easily obtained through dental procedures.

MATERIALS AND METHODS

Neural crest stem cells were obtained from human excised third molars and differentiated in culture using a protocol for directed differentiation into cardiomyocytes. Differentiation of cells was assessed through gene expression and immunostaining studies. Optical stimulation using pulsed infrared radiation (IR) (λ = 1863 nm) was delivered to cell aggregates to study their contractile ability.

RESULTS

We show that neural crest stem cells can be differentiated to a cardiomyogenic lineage, which was verified through immunostaining and gene expression. We observed a significant increase in cardiomyocyte-specific markers, NK2 homeobox 5 (NKX2.5) and troponin T type 2 (TNNT2), with positive changes in tropomyosin I (TPM1), gap junction protein alpha 1/Cx43 (GJA1/Cx43), and myocyte enhancement factor 2C (MEF2C). Furthermore, we were able to elicit and maintain pulse-by-pulse contractile responses in the derived cells, including in cardiospheres, with pulsed IR delivered at various radiant energies. The contractility in responses to IR could be maintained at different frequencies (0.25-2 Hz) and up to 10-min durations. While these cells did not maintain their contractility following cessation of IR, these cells demonstrated responses to the optical stimuli that are consistent with previous reports. We also found no evidence for irreversible mitochondrial depolarization in these cells following the long duration of infrared stimulation, suggesting the robustness of these cells.

CONCLUSIONS

Overall, these results suggest the merit of neural crest-derived stem cells for cardiomyogenic applications and a potential cell source for repair that should contribute to efforts to translate cell-based strategies to the clinic.

Human bone marrow harbors cells with neural crest-associated characteristics like human adipose and dermis tissues

Adult neural crest stem-derived cells (NCSC) are of extraordinary high plasticity and promising candidates for use in regenerative medicine. Several locations such as skin, adipose tissue, dental pulp or bone marrow have been described in rodent, as sources of NCSC. However, very little information is available concerning their correspondence in human tissues, and more precisely for human bone marrow. The main objective of this study was therefore to characterize NCSC from adult human bone marrow. In this purpose, we compared human bone marrow stromal cells to human adipose tissue and dermis, already described for containing NCSC. We performed comparative analyses in terms of gene and protein expression as well as functional characterizations. It appeared that human bone marrow, similarly to adipose tissue and dermis, contains NESTIN⁺ / SOX9⁺ / TWIST⁺ / SLUG⁺ / P75^NTR+/ BRN3A⁺/ MSI1⁺/ SNAIL1⁺ cells and were able to differentiate into melanocytes, Schwann cells and neurons. Moreover, when injected into chicken embryos, all those cells were able to migrate and follow endogenous neural crest migration pathways. Altogether, the phenotypic characterization and migration abilities strongly suggest the presence of neural crest-derived cells in human adult bone marrow.

p75 Neurotrophin Receptor in the Skin: Beyond Its Neurotrophic Function

p75 neurotrophin receptor (p75^NTR), also known as CD271, is the low-affinity receptor that, together with the tyrosine kinase receptor tropomyosin-receptor kinase (Trk), mediate neurotrophin (NT) functions. Beside their classic role in skin innervation, NT and their receptors constitute a complex cutaneous network associated with a number of autocrine and paracrine activities. In this context, the role of p75^NTR is becoming more and more important. This review will focus on the intriguing functions of p75^NTR in healthy and diseased skin. First, p75^NTR counterbalances the proliferative and survival activities of its cognate receptor Trk by inducing keratinocyte apoptosis. In addition, p75^NTR identifies an early transit-amplifying (TA) keratinocyte population and plays a critical role in keratinocyte stem cell transition to its progeny as well as in epidermal differentiation. p75^NTR is absent in psoriatic TA cells, thus rendering these cells resistant to apoptosis. On the other hand, p75^NTR infection restores NT-induced apoptosis in psoriatic keratinocytes. Taken together, these results provide evidence for a critical role of p75^NTR in epidermal homeostasis, while its lack may account for the TA defect in psoriasis. While the issue of p75^NTR as a marker of melanoma initiating cells is still to be solved, there is strong evidence that downregulation of this receptor is a precondition to melanoma invasion and metastasis in vitro and in vivo. All in all, this review points to p75^NTR as a major actor in both physiologic and pathologic conditions at the skin level.

Role of connexins and pannexins during ontogeny, regeneration, and pathologies of bone

Electron micrographs revealed the presence of gap junctions in osteoblastic cells over 40 years ago. These intercellular channels formed from connexins are present in bone forming osteoblasts, bone resorbing osteoclasts, and osteocytes (mature osteoblasts embedded in the mineralized bone matrix). More recently, genetic and pharmacologic studies revealed the role of connexins, and in particular Cx43, in the differentiation and function of all bone types. Furthermore, mutations in the gene encoding Cx43 were found to be causally linked to oculodentodigital dysplasia, a condition that results in an abnormal skeleton. Pannexins, molecules with similar structure and single-membrane channel forming potential as connexins when organized as hemichannels, are also expressed in osteoblastic cells. The function of pannexins in bone and cartilage is beginning to be uncovered, but more research is needed to determine the role of pannexins in bone development, adult bone mass and skeletal homeostasis. We describe here the current knowledge on the role of connexins and pannexins on skeletal health and disease.

An Overview of Protocols for the Neural Induction of Dental and Oral Stem Cells In Vitro

To date, various adult stem cells have been identified within the oral cavity, including dental pulp stem cells, dental follicle stem cells, stem cells from apical papilla, stem cells from human exfoliated deciduous teeth, periodontal ligament stem cells, and mesenchymal stem cells from the gingiva. All of these possess neurogenic potential due to their common developmental origin from the embryonic neural crest. Besides the relative ease of isolation of these adult stem cells from readily available biological waste routinely produced during dental treatment, these cells also possess the advantage of immune compatibility in autologous transplantation. In recent years, much interest has been focused on the derivation of neural lineages from these adult stem cells for therapeutic applications in the brain, spinal cord, and peripheral nerve regeneration. In addition, there are also promising nontherapeutic applications of stem cell-derived neurons in pharmacological and toxicological screening of neuroactive drugs, and for in vitro modeling of neurodevelopmental and neurodegenerative diseases. Hence, this review will critically examine the diverse array of in vitro neural induction protocols that have been devised for dental and oral-derived stem cells. These protocols are defined not only by the culture milieu comprising the basal medium plus growth factors, small molecules, and other culture supplements but also by the substrata/surface coatings utilized, the presence of multiple culture stages, the total culture duration, the initial seeding density, and whether the spheroid/neurosphere formation is being utilized to recapitulate the three-dimensional neural differentiation microenvironment that is naturally present physiologically in vivo.

Dental stem cells: a future asset of ocular cell therapy

Regenerative medicine using patient's own stem cells (SCs) to repair dysfunctional tissues is an attractive approach to complement surgical and pharmacological treatments for aging and degenerative disorders. Recently, dental SCs have drawn much attention owing to their accessibility, plasticity and applicability for regenerative use not only for dental, but also other body tissues. In ophthalmology, there has been increasing interest to differentiate dental pulp SC and periodontal ligament SC (PDLSC) towards ocular lineage. Both can commit to retinal fate expressing eye field transcription factors and generate rhodopsin-positive photoreceptor-like cells. This proposes a novel therapeutic alternative for retinal degeneration diseases. Moreover, as PDLSC shares similar cranial neural crest origin and proteoglycan secretion with corneal stromal keratoctyes and corneal endothelial cells, this offers the possibility of differentiating PDLSC to these corneal cell types. The advance could lead to a shift in the medical management of corneal opacities and endothelial disorders from highly invasive corneal transplantation using limited donor tissue to cell therapy utilizing autologous cells. This article provides an overview of dental SC research and the perspective of utilizing dental SCs for ocular regenerative medicine.

Differential Properties of Human ALP+ Periodontal Ligament Stem Cells vs Their ALP- Counterparts

Characterizing subpopulations of stem cells is important to understand stem cell properties. Tissue-nonspecific alkaline phosphatase (ALP) is associated with mineral tissue forming cells as well as stem cells. Information regarding ALP subpopulation of human periodontal ligament stem cells (hPDLSCs) is limited. In the present study, we examined ALP⁺ and ALP⁻ hPDLSC subpopulations, their surface markers STRO-1 and CD146, and the expression of stemness genes at various cell passages. We found that ALP⁺ subpopulation had higher levels of STRO-1 (30.6 ± 5.6%) and CD146 (90.4 ± 3.3%) compared to ALP⁻ (STRO-1: 0.5 ± 0.1%; CD146: 75.3 ± 7.2%). ALP⁺ cells expressed significantly higher levels of stemness associated genes, NANOG, OCT4 and SOX than ALP⁻ cells at low cell passages of 2-3 (p<0.05). ALP⁺ and ALP⁻ cells had similar osteogenic, chondrogenic and neurogenic potential while ALP⁻, not ALP⁺ cells, lacked adipogenic potential. Upon continuous culturing and passaging, ALP⁺ continued to express higher stemness genes and STRO-1 and CD146 than ALP⁻ cells at ≥passage 19. Under conditions (over-confluence and vitamin C treatment) when ALP⁺ subpopulation was increased, the stemness gene levels of ALP⁺ was no longer significantly higher than those in ALP⁻ cells. In conclusion, ALP⁺ hPDLSCs possess differential properties from their ALP⁻ counterparts.

Concise Review: Are Stimulated Somatic Cells Truly Reprogrammed into an ES/iPS-Like Pluripotent State? Better Understanding by Ischemia-Induced Multipotent Stem Cells in a Mouse Model of Cerebral Infarction

Following the discovery of pluripotent stem (PS) cells such as embryonic stem (ES) and induced pluripotent stem (iPS) cells, there has been a great hope that injured tissues can be repaired by transplantation of ES/iPS-derived various specific types of cells such as neural stem cells (NSCs). Although PS cells can be induced by ectopic expression of Yamanaka's factors, it is known that several stimuli such as ischemia/hypoxia can increase the stemness of somatic cells via reprogramming. This suggests that endogenous somatic cells acquire stemness during natural regenerative processes following injury. In this study, we describe whether somatic cells are converted into pluripotent stem cells by pathological stimuli without ectopic expression of reprogramming factors based on the findings of ischemia-induced multipotent stem cells in a mouse model of cerebral infarction.

Cigarette smoking hinders human periodontal ligament-derived stem cell proliferation, migration and differentiation potentials

Cigarette smoking contributes to the development of destructive periodontal diseases and delays its healing process. Our previous study demonstrated that nicotine, a major constituent in the cigarette smoke, inhibits the regenerative potentials of human periodontal ligament-derived stem cells (PDLSC) through microRNA (miRNA) regulation. In this study, we hypothesized that the delayed healing in cigarette smokers is caused by the afflicted regenerative potential of smoker PDLSC. We cultured PDLSC from teeth extracted from smokers and non-smokers. In smoker PDLSC, we found significantly reduced proliferation rate and retarded migration capabilities. Moreover, alkaline phosphatase activity, calcium deposition and acidic polysaccharide staining were reduced after BMP2-induced differentiation. In contrast, more lipid deposition was observed in adipogenic-induced smoker PDLSC. Furthermore, two nicotine-related miRNAs, hsa-miR-1305 (22.08 folds, p = 0.040) and hsa-miR-18b (15.56 folds, p = 0.018), were significantly upregulated in smoker PDLSC, suggesting these miRNAs might play an important role in the deteriorative effects on stem cells by cigarette smoke. Results of this study provide further evidences that cigarette smoking affects the regenerative potentials of human adult stem cells.

The role of purinergic receptors in stem cell differentiation

A major challenge modern society has to face is the increasing need for tissue regeneration due to degenerative diseases or tumors, but also accidents or warlike conflicts. There is great hope that stem cell-based therapies might improve current treatments of cardiovascular diseases, osteochondral defects or nerve injury due to the unique properties of stem cells such as their self-renewal and differentiation potential. Since embryonic stem cells raise severe ethical concerns and are prone to teratoma formation, adult stem cells are still in the focus of research. Emphasis is placed on cellular signaling within these cells and in between them for a better understanding of the complex processes regulating stem cell fate. One of the oldest signaling systems is based on nucleotides as ligands for purinergic receptors playing an important role in a huge variety of cellular processes such as proliferation, migration and differentiation. Besides their natural ligands, several artificial agonists and antagonists have been identified for P1 and P2 receptors and are already used as drugs. This review outlines purinergic receptor expression and signaling in stem cells metabolism. We will briefly describe current findings in embryonic and induced pluripotent stem cells as well as in cancer-, hematopoietic-, and neural crest-derived stem cells. The major focus will be placed on recent findings of purinergic signaling in mesenchymal stem cells addressed in in vitro and in vivo studies, since stem cell fate might be manipulated by this system guiding differentiation towards the desired lineage in the future.

Cranial neural crest cell contribution to craniofacial formation, pathology, and future directions in tissue engineering

This review provides an overview of the state and future directions of development and pathology in the craniofacial complex in the context of Cranial Neural Crest Cells (CNCC). CNCC are a multipotent cell population that is largely responsible for forming the vertebrate head. We focus on findings that have increased the knowledge of gene regulatory networks and molecular mechanisms governing CNCC migration and the participation of these cells in tissue formation. Pathology due to aberrant migration or cell death of CNCC, termed neurocristopathies, is discussed in addition to craniosynostoses. Finally, we discuss tissue engineering applications that take advantage of recent advancements in genome editing and the multipotent nature of CNCC. These applications have relevance to treating diseases due directly to the failure of CNCC, and also in restoring tissues lost due to a variety of reasons.

miR-21 promotes the differentiation of hair follicle-derived neural crest stem cells into Schwann cells

Hair follicle-derived neural crest stem cells can be induced to differentiate into Schwann cells in vivo and in vitro. However, the underlying regulatory mechanism during cell differentiation remains poorly understood. This study isolated neural crest stem cells from human hair follicles and induced them to differentiate into Schwann cells. Quantitative RT-PCR showed that microRNA (miR)-21 expression was gradually increased during the differentiation of neural crest stem cells into Schwann cells. After transfection with the miR-21 agonist (agomir-21), the differentiation capacity of neural crest stem cells was enhanced. By contrast, after transfection with the miR-21 antagonist (antagomir-21), the differentiation capacity was attenuated. Further study results showed that SOX-2 was an effective target of miR-21. Without compromising SOX2 mRNA expression, miR-21 can down-regulate SOX protein expression by binding to the 3′-UTR of miR-21 mRNA. Knocking out the SOX2 gene from the neural crest stem cells significantly reversed the antagomir-21 inhibition of neural crest stem cells differentiating into Schwann cells. The results suggest that miR-21 expression was increased during the differentiation of neural crest stem cells into Schwann cells and miR-21 promoted the differentiation through down-regulating SOX protein expression by binding to the 3′-UTR of SOX2 mRNA.

Neural crest-derived dental stem cells--where we are and where we are going

OBJECTIVES

There are five types of post-natal human dental stem cells that have been identified, isolated and characterized. Here, we review the information available on dental stem cells as well as their potential applications in dentistry, regenerative medicine and the development of other therapeutic approaches.

DATA

Data pertinent to dental stem cells and their applications, published in peer-reviewed journals from 1982 to 2013 in English were reviewed.

SOURCES

Sources were retrieved from PubMed databases as well as related references that the electronic search yielded.

STUDY SELECTION

Manuscripts describing the origin, retrieval, characterization and application of dental stem cells were obtained and reviewed.

CONCLUSIONS

Dental stem cell populations present properties similar to those of mesenchymal stem cells, such as the ability to self-renew and the potential for multilineage differentiation. While they have greater capacity to give rise to odontogenic cells and regenerate dental pulp and periodontal tissue, they have the capacity to differentiate into all three germ line cells, proving that a population of pluripotent stem cells exists in the dental tissues.

CLINICAL SIGNIFICANCE

Dental stem cells have the capacity to differentiate into endoderm, mesoderm and ectoderm tissues. Consequently they do not only have applications in dentistry, but also neurodegenerative and ischemic diseases, diabetes research, bone repair, and other applications in the field of tissue regeneration.

Neurogenesis of neural crest-derived periodontal ligament stem cells by EGF and bFGF

Neuroregenerative medicine is an ever-growing field in which regeneration of lost cells/tissues due to a neurodegenerative disease is the ultimate goal. With the scarcity of available replacement alternatives, stem cells provide an attractive source for regenerating neural tissue. While many stem cell sources exist, including: mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells, the limited cellular potency, technical difficulties, and ethical considerations associated with these make finding alternate sources a desirable goal. Periodontal ligament stem cells (PDLSCs) derived from the neural crest were induced into neural-like cells using a combination of epidermal growth factor, and basic fibroblast growth factor. Morphological changes were evident in our treated group, seen under both light microscopy and scanning electron microscopy. A statistically significant increase in the expression of neuron-specific β-tubulin III and the neural stem/progenitor cell marker nestin, along with positive immunohistochemical staining for glial fibrillary acidic protein, demonstrated the success of our treatment in inducing both neuronal and glial phenotypes. Positive staining for synaptophysin demonstrated neural connections and electrophysiological recordings indicated that when subjected to whole-cell patch clamping, our treated cells displayed inward currents conducted through voltage-gated sodium (Na(+) ) channels. Taken together, our results indicate the success of our treatment in inducing PDLSCs to neural-like cells. The ease of sourcing and expansion, their embryologic neural crest origin, and the lack of ethical implications in their use make PDLSCs an attractive source for use in neuroregenerative medicine.