Dual origin of mesenchymal stem cells contributing to organ growth and repair

Pericytes in the Placenta: Role in Placental Development and Homeostasis

The placenta is the most variable organ, in terms of structure, among the species. Besides it, all placental types have the same function: production of viable offspring, independent of pregnancy length, litter number, or invasion level. The angiogenesis is a central mechanism for placental functionality, due to proper maternal-fetal communication and exchanges. Much is known about the vasculature structure, but little is known about vasculature development and cellular interactions. Pericytes are perivascular cells that were described to control vasculature stability and permeability. Nowadays there are several new functions discovered, such as lymphocyte modulation and activation, macrophage-like phagocytic properties, tissue regenerative and repair processes, and also the ability to modulate stem cells, majorly the hematopoietic. In parallel, placental tissues are known to be a particularly immune microenvironment and a rich stem cell niche. The pericyte function plethora could be similar in the placental microenvironment and could have a central role in placental development and homeostasis.

Higher Pericyte Content and Secretory Activity of Microfragmented Human Adipose Tissue Compared to Enzymatically Derived Stromal Vascular Fraction

Autologous adipose tissue is used for tissue repletion and/or regeneration as an intact lipoaspirate or as enzymatically derived stromal vascular fraction (SVF), which may be first cultured into mesenchymal stem cells (MSCs). Alternatively, transplant of autologous adipose tissue mechanically fragmented into submillimeter clusters has recently showed remarkable efficacy in diverse therapeutic indications. To document the biologic basis of the regenerative potential of microfragmented adipose tissue, we first analyzed the distribution of perivascular presumptive MSCs in adipose tissue processed with the Lipogems technology, observing a significant enrichment in pericytes, at the expense of adventitial cells, as compared to isogenic enzymatically processed lipoaspirates. The importance of MSCs as trophic and immunomodulatory cells, due to the secretion of specific factors, has been described. Therefore, we investigated protein secretion by cultured adipose tissue clusters or enzymatically derived SVF using secretome arrays. In culture, microfragmented adipose tissue releases many more growth factors and cytokines involved in tissue repair and regeneration, noticeably via angiogenesis, compared to isogenic SVF. Therefore, we suggest that the efficient tissue repair/regeneration observed after transplantation of microfragmented adipose tissue is due to the secretory ability of the intact perivascular niche. Stem Cells Translational Medicine 2018;7:876-886.

Molecular Programming of Perivascular Stem Cell Precursors

Pericytes have been shown to act as precursors of resident adult stem cells in stromal tissues in vivo. When expanded in vitro these cells are capable of giving rise to multiple mesenchymal cell types, irrespective of their tissue of origin. This phenomenon of multi-lineage differentiation is only observed in culture, whereas in vivo, stromal stem cell differentiation is restricted to tissue-specific cell types. An important unanswered question is how a single, widely distributed cell type (a pericyte) gives rise to stem cells with tissue-specific functions and attributes. Using a combination of transcriptomics and epigenomics we have compared the molecular status of two populations of stromal stem cell precursors. Using a LacZ transgene insertion that is expressed in pericytes but not in stem cells, we were able to compare pericyte populations from two different tissues, mouse incisors and bone marrow. Pericytes, freshly isolated from mouse incisors and bone marrow, exhibited transcriptomes and epigenetic landscapes that were extensively different, reflecting their tissue of origin and future in vivo differentiation potential. Dspp, an odontoblast differentiation gene, as well as additional odontogenic genes, are shown to be expressed in dental pulp-derived pericytes. These genetic loci are also decorated with histone modifications indicative of a transcriptionally active chromatin state. In bone marrow pericytes, a major osteogenic differentiation gene, Runx2, is not expressed but is marked by both active and repressive histones and therefore primed to be expressed. Polycomb repressor complex 1 analysis showed that key genes involved in the induction of adipogenesis, chondrogenesis, and myogenesis are targeted by Ring1b and therefore stably repressed. This indicates that pericyte populations are molecularly obstructed from differentiating down certain lineages in vivo. Stem Cells 2018;36:1890-15.

Cell Sources for Tissue Engineering Strategies to Treat Calcific Valve Disease

Cardiovascular calcification is an independent risk factor and an established predictor of adverse cardiovascular events. Despite concomitant factors leading to atherosclerosis and heart valve disease (VHD), the latter has been identified as an independent pathological entity. Calcific aortic valve stenosis is the most common form of VDH resulting of either congenital malformations or senile “degeneration.” About 2% of the population over 65 years is affected by aortic valve stenosis which represents a major cause of morbidity and mortality in the elderly. A multifactorial, complex and active heterotopic bone-like formation process, including extracellular matrix remodeling, osteogenesis and angiogenesis, drives heart valve “degeneration” and calcification, finally causing left ventricle outflow obstruction. Surgical heart valve replacement is the current therapeutic option for those patients diagnosed with severe VHD representing more than 20% of all cardiac surgeries nowadays. Tissue Engineering of Heart Valves (TEHV) is emerging as a valuable alternative for definitive treatment of VHD and promises to overcome either the chronic oral anticoagulation or the time-dependent deterioration and reintervention of current mechanical or biological prosthesis, respectively. Among the plethora of approaches and stablished techniques for TEHV, utilization of different cell sources may confer of additional properties, desirable and not, which need to be considered before moving from the bench to the bedside. This review aims to provide a critical appraisal of current knowledge about calcific VHD and to discuss the pros and cons of the main cell sources tested in studies addressing in vitro TEHV.

Tooth Repair and Regeneration

PURPOSE OF REVIEW

Current dental treatments are based on conservative approaches, using inorganic materials and appliances.This report explores and discusses the newest achievements in the field of "regenerative dentistry," based on the concept of biological repair as an alternative to the current conservative approach.

RECENT FINDINGS

The review covers and critically analyzes three main approaches of tooth repair: the re-mineralization of the enamel, the biological repair of dentin, and whole tooth engineering.

SUMMARY

The development of a concept of biological repair based on the role of the Wnt signaling pathway in reparative dentin formation offers a new translational approach into development of future clinical dental treatments.In the field of bio-tooth engineering, the current focus of the researchers remains the establishment of odontogenic cell-sources that would be viable and easily accessible for future bio-tooth engineering.

Evaluation of bone marrow microenvironment could change how myelodysplastic syndromes are diagnosed and treated

Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic disorders. However, the therapies used against the hematopoietic stem cells clones have limited efficacy; they slow the evolution toward acute myeloid leukemia rather than stop clonal evolution and eradicate the disease. The progress made in recent years regarding the role of the bone marrow microenvironment in disease evolution may contribute to progress in this area. This review presents the recent updates on the role of the bone marrow microenvironment in myelodysplastic syndromes pathogenesis and tries to find answers regarding how this information could improve myelodysplastic syndromes diagnosis and therapy.

Identification of protein kinase inhibitors to reprogram breast cancer cells

Direct reversion of cancers into normal-like tissues is an ideal strategy for cancer treatment. Recent reports have showed that defined transcription factors can induce reprogramming of cancer cells into pluripotent stem cells, supporting this notion. Here, we have developed a reprogramming method that uses a conceptually unique strategy for breast cancer cell treatment. We have screened a kinase inhibitor library and found that Rho-associated protein kinase (ROCK) and mammalian target of rapamycin (mTOR) kinase inhibitors can substitute for all transcription factors to be sufficient to reprogram breast cancer cells into progenitor cells. Furthermore, ROCK–mTOR inhibitors could reprogram breast cancer cells to another terminal lineage-adipogenic cells. Genome-wide transcriptional analysis shows that the induced fat-like cells have a profile different from breast cancer cells and similar to that of normal adipocytes. In vitro and in vivo tumorigenesis assays have shown that induced fat-like cells lose proliferation and tumorigenicity. Moreover, reprogramming treatment with ROCK–mTOR inhibitors prevents breast cancer local recurrence in mice. Currently, ROCK–mTOR inhibitors are already used as antitumor drugs in patients, thus, this reprogramming strategy has significant potential to move rapidly toward clinical trials for breast cancer treatment.

Comparative Characterization of Ischemia-Induced Brain Multipotent Stem Cells with Mesenchymal Stem Cells: Similarities and Differences

Mesenchymal stem cells (MSCs) are multipotent stem cells localized to the perivascular regions of various organs, including bone marrow (BM). While MSC transplantation represents a promising stem cell-based therapy for ischemic stroke, increasing evidence indicates that exogenously administered MSCs rarely accumulate in the injured central nervous system (CNS). Therefore, compared with MSCs, regionally derived brain multipotent stem cells may be a superior source to elicit regeneration of the CNS following ischemic injury. We previously identified ischemia-induced multipotent stem cells (iSCs) as likely originating from brain pericytes/perivascular cells (PCs) within poststroke regions. However, detailed characteristics of iSCs and their comparison with MSCs remains to be investigated. In the present study, we compared iSCs with BM-derived MSCs, with a focus on the stemness and neuron-generating activity of each cell type. From our results, stem and undifferentiated cell markers, including c-myc and Klf4, were found to be expressed in iSCs and BM-MSCs. In addition, both cell types exhibited the ability to differentiate into mesoderm lineages, including as osteoblasts, adipocytes, and chondrocytes. However, compared with BM-MSCs, high expression of neural stem cell markers, including nestin and Sox2, were found in iSCs. In addition, iSCs, but not BM-MSCs, formed neurosphere-like cell clusters that differentiated into functional neurons. These results demonstrate that iSCs are likely multipotent stem cells with the ability to differentiate into not only mesoderm, but also neural, lineages. Collectively, our novel findings suggest that locally induced iSCs may contribute to CNS repair by producing neuronal cells following ischemic stroke.

Mesenchymal Stromal/Stem Cells in Regenerative Medicine and Tissue Engineering

As a result of over five decades of investigation, mesenchymal stromal/stem cells (MSCs) have emerged as a versatile and frequently utilized cell source in the fields of regenerative medicine and tissue engineering. In this review, we summarize the history of MSC research from the initial discovery of their multipotency to the more recent recognition of their perivascular identity in vivo and their extraordinary capacity for immunomodulation and angiogenic signaling. As well, we discuss long-standing questions regarding their developmental origins and their capacity for differentiation toward a range of cell lineages. We also highlight important considerations and potential risks involved with their isolation, ex vivo expansion, and clinical use. Overall, this review aims to serve as an overview of the breadth of research that has demonstrated the utility of MSCs in a wide range of clinical contexts and continues to unravel the mechanisms by which these cells exert their therapeutic effects.

MED31 involved in regulating self-renewal and adipogenesis of human mesenchymal stem cells

Regulation of gene expression is critical for the maintenance of cell state and homeostasis. Aberrant regulation of genes can lead to unwanted cell proliferation or misdirected differentiation. Here we investigate the role of MED31, a highly conserved subunit of the Mediator complex, to determine the role this subunit plays in the maintenance of human mesenchymal stem cell (hMSC) state. Using siRNA-mediated knockdown of MED31 we demonstrate a decrease in self-renewal based on cell assays and monitoring of gene expression. In addition, in the absence of MED31, hMSCs also displayed a reduction in adipogenesis as evidenced by diminished lipid vesicle formation and expression of specific adipogenic markers. These data present evidence for a significant role for MED31 in maintaining adult stem cell homeostasis, thereby introducing potential novel targets for future investigation and use in better understanding stem cell behavior and adipogenesis.

Notch-inducing hydrogels reveal a perivascular switch of mesenchymal stem cell fate

The fate of mesenchymal stem cells (MSCs) in the perivascular niche, as well as factors controlling their fate, is poorly understood. Here, we study MSCs in the perivascular microenvironment of endothelial capillaries by modifying a synthetic 3D biomimetic poly(ethylene glycol) (PEG)-hydrogel system in vitro We show that MSCs together with endothelial cells form micro-capillary networks specifically in soft PEG hydrogels. Transcriptome analysis of human MSCs isolated from engineered capillaries shows a prominent switch in extracellular matrix (ECM) production. We demonstrate that the ECM phenotypic switch of MSCs can be recapitulated in the absence of endothelial cells by functionalizing PEG hydrogels with the Notch-activator Jagged1. Moreover, transient culture of MSCs in Notch-inducing microenvironments reveals the reversibility of this ECM switch. These findings provide insight into the perivascular commitment of MSCs by use of engineered niche-mimicking synthetic hydrogels.

Inspired by Nature: Hydrogels as Versatile Tools for Vascular Engineering

Significance: Diseases related to vascular malfunction, hyper-vascularization, or lack of vascularization are among the leading causes of morbidity and mortality. Engineered, vascularized tissues as well as angiogenic growth factor-releasing hydrogels could replace defective tissues. Further, treatments and testing of novel vascular therapeutics will benefit significantly from models that allow for the study of vascularized tissues under physiological relevant in vitro conditions. Recent Advances: Inspired by fibrin, the provisional matrix during wound healing, naturally derived and synthetic hydrogel scaffolds have been developed for vascular engineering. Today, engineers and biologists use commercially available hydrogels to pre-vascularize tissues, to control the delivery of angiogenic growth factors, and to establish vascular diseases models. Critical Issue: For clinical translation, pre-vascularized tissue constructs must be sufficiently large and stable to substitute function-relevant tissue defects and integrate with host vascular perfusion. Moreover, the continuous integration of knowhow from basic vascular biology with innovative, tailorable materials and advanced manufacturing technologies is key to achieving near-physiological tissue models and new treatments to control vascularization. Future Directions: For transplantation, engineered tissues must comprise hierarchically organized vascular trees of different caliber and function. The development of novel vascularization-promoting or -inhibiting therapeutics will benefit from physiologically relevant vessel models. In addition, tissue models representing treatment-relevant vascular tissue functions will increase the capacity to screen for therapeutic compounds and will significantly reduce the need for animals for their validation.

Tissue Specific Origin, Development, and Pathological Perspectives of Pericytes

Pericytes are mural cells surrounding blood vessels, adjacent to endothelial cells. Pericytes play critical roles in maturation and maintenance of vascular branching morphogenesis. In the central nervous system (CNS), pericytes are necessary for the formation and regulation of the blood-brain barrier (BBB) and pericyte deficiency accompanies CNS diseases including multiple sclerosis, diabetic retinopathy, neonatal intraventricular hemorrhage, and neurodegenerative disorders. Despite the importance of pericytes, their developmental origins and phenotypic diversity remain incompletely understood. Pericytes express multiple markers and the origin of pericytes differs by tissue, which may cause difficulty for the identification and understanding of the ontogeny of pericytes. Also, pericytes have the potential to give rise to different tissues in vitro but this is not clear in vivo. These studies indicate that pericytes are heterogeneous in a tissue- and context- dependent manner. This short review focuses on recent studies about identification of pericytes, heterogeneous origin of pericytes during development and in adults, and the differentiation capacity of pericytes, and pericytes in pathological settings.

The controversial origin of pericytes during angiogenesis - Implications for cell-based therapeutic angiogenesis and cell-based therapies

Pericytes reside within the basement membrane of small vessels and are often in direct cellular contact with endothelial cells, fulfilling important functions during blood vessel formation and homeostasis. Recently, these pericytes have been also identified as mesenchymal stem cells. Mesenchymal stem cells, and especially their specialized subpopulation of pericytes, represent promising candidates for therapeutic angiogenesis applications, and have already been widely applied in pre-clinical and clinical trials. However, cell-based therapies of ischemic diseases (especially of myocardial infarction) have not resulted in significant long-term improvement. Interestingly, pericytes from a hematopoietic origin were observed in embryonic skin and a pericyte sub-population expressing leukocyte and monocyte markers was described during adult angiogenesis in vivo. Since mesenchymal stem cells do not express hematopoietic markers, the latter cell type might represent an alternative pericyte population relevant to angiogenesis. Therefore, we sourced blood-derived angiogenic cells (BDACs) from monocytes that closely resembled hematopoietic pericytes, which had only been observed in vivo thus far. BDACs displayed many pericytic features and exhibited enhanced revascularization and functional tissue regeneration in a pre-clinical model of critical limb ischemia. Comparison between BDACs and mesenchymal pericytes indicated that BDACs (while resembling hematopoietic pericytes) enhanced early stages of angiogenesis, such as endothelial cell sprouting. In contrast, mesenchymal pericytes were responsible for blood vessel maturation and homeostasis, while reducing endothelial sprouting.Since the formation of new blood vessels is crucial during therapeutic angiogenesis or during integration of implants into the host tissue, hematopoietic pericytes (and therefore BDACs) might offer an advantageous addition or even an alternative for cell-based therapies.

Regenerative endodontics: a comprehensive review

The European Society of Endodontology and the American Association for Endodontists have released position statements and clinical considerations for regenerative endodontics. There is increasing literature on this field since the initial reports of Iwaya et al. (Dental Traumatology, 17, 2001, 185) and Banchs & Trope (Journal of Endodontics, 30, 2004, 196). Endogenous stem cells from an induced periapical bleeding and scaffolds using blood clot, platelet rich plasma or platelet-rich fibrin have been utilized in regenerative endodontics. This approach has been described as a 'paradigm shift' and considered the first treatment option for immature teeth with pulp necrosis. There are three treatment outcomes of regenerative endodontics; (i) resolution of clinical signs and symptoms; (ii) further root maturation; and (iii) return of neurogenesis. It is known that results are variable for these objectives, and true regeneration of the pulp/dentine complex is not achieved. Repair derived primarily from the periodontal and osseous tissues has been shown histologically. It is hoped that with the concept of tissue engineering, namely stem cells, scaffolds and signalling molecules, that true pulp regeneration is an achievable goal. This review discusses current knowledge as well as future directions for regenerative endodontics. Patient-centred outcomes such as tooth discolouration and possibly more appointments with the potential for adverse effects needs to be discussed with patients and parents. Based on the classification of Cvek (Endodontics and Dental Traumatology, 8, 1992, 45), it is proposed that regenerative endodontics should be considered for teeth with incomplete root formation although teeth with near or complete root formation may be more suited for conventional endodontic therapy or MTA barrier techniques. However, much is still not known about clinical and biological aspects of regenerative endodontics.

Regulation of Mesenchymal Stem to Transit-Amplifying Cell Transition in the Continuously Growing Mouse Incisor

In adult tissues and organs with high turnover rates, the generation of transit-amplifying cell (TAC) populations from self-renewing stem cells drives cell replacement. The role of stem cells is to provide a renewable source of cells that give rise to TACs to provide the cell numbers that are necessary for cell differentiation. Regulation of the formation of TACs is thus fundamental to controlling cell replacement. Here, we analyze the properties of a population of mesenchymal TACs in the continuously growing mouse incisor to identify key components of the molecular regulation that drives proliferation. We show that the polycomb repressive complex 1 acts as a global regulator of the TAC phenotype by its direct action on the expression of key cell-cycle regulatory genes and by regulating Wnt/β-catenin-signaling activity. We also identify an essential requirement for TACs in maintaining mesenchymal stem cells, which is indicative of a positive feedback mechanism.

A role for pericytes in chronic pain?

PURPOSE OF REVIEW

The importance of the blood-brain barrier (BBB) and neuroinflammation in neurodegenerative conditions is becoming increasingly apparent, yet very little is known about these neurovascular functions in nonmalignant disease chronic pain. Neural tissue pericytes play critical roles in the formation and maintenance of the BBB. Herein, we review the important roles of neural pericytes and address their potential role in chronic pain.

RECENT FINDINGS

Pericytes are implicated in the function of neural microvasculature, including BBB permeability, neuroimmune factor secretion and leukocyte transmigration. In addition, the multipotent stem cell nature of pericytes affords pericytes the ability to migrate into neural parenchyma and differentiate into pain-associated cell types. These recent findings indicate that pericytes are key players in pathological BBB disruption and neuroinflammation, and as such pericytes may be key players in chronic pain states.

SUMMARY

Pericytes play key roles in pathological processes associated with chronic pain. We propose that pericytes may be a therapeutic target for painful diseases that have associated neural vascular dysfunction. Given the paucity of new pharmacotherapies for chronic pain conditions, we hope that this review inspires researchers to unearth the potential role(s) of pericytes in chronic pain sowing the seeds for future new chronic pain therapies.

Dental Mesenchymal Stem Cell-Based Translational Regenerative Dentistry: From Artificial to Biological Replacement

Dentistry is a continuously changing field that has witnessed much advancement in the past century. Prosthodontics is that branch of dentistry that deals with replacing missing teeth using either fixed or removable appliances in an attempt to simulate natural tooth function. Although such "replacement therapies" appear to be easy and economic they fall short of ever coming close to their natural counterparts. Complications that arise often lead to failures and frequent repairs of such devices which seldom allow true physiological function of dental and oral-maxillofacial tissues. Such factors can critically affect the quality of life of an individual. The market for dental implants is continuously growing with huge economic revenues. Unfortunately, such treatments are again associated with frequent problems such as peri-implantitis resulting in an eventual loss or replacement of implants. This is particularly influential for patients having co-morbid diseases such as diabetes or osteoporosis and in association with smoking and other conditions that undoubtedly affect the final treatment outcome. The advent of tissue engineering and regenerative medicine therapies along with the enormous strides taken in their associated interdisciplinary fields such as stem cell therapy, biomaterial development, and others may open arenas to enhancing tissue regeneration via designing and construction of patient-specific biological and/or biomimetic substitutes. This review will overview current strategies in regenerative dentistry while overviewing key roles of dental mesenchymal stem cells particularly those of the dental pulp, until paving the way to precision/translational regenerative medicine therapies for future clinical use.

Homeobox C10 inhibits the osteogenic differentiation potential of mesenchymal stem cells

PURPOSE

Mesenchymal stem cells (MSCs) are a reliable cell source for tissue regeneration. However, the molecular mechanisms underlying the directed differentiation of MSCs remain unclear which impedes potential clinical applications. Recent studies have discovered that Homeobox (HOX) genes are involved in the differentiation regulation of MSCs and bone formation. In this study, we investigate the HOXC10 function in the osteogenic differentiation potential of MSCs.

MATERIALS AND METHODS

Stem cells from apical papilla (SCAPs) and adipose-derived stem cells (ADSCs) were used in this study. Alkaline phosphatase (ALP) activity assays, ALP staining, Alizarin red staining, quantitative calcium analysis, osteogenesis-associated gene expression, and in vivo transplantation experiments were used to study osteogenic differentiation potential.

RESULTS

Our results showed that overexpression of HOXC10 in SCAPs inhibited ALP activity and mineralization in vitro and decreased the mRNA expression of collagen alpha-1 (I) chain, bone sialoprotein, osteocalcin, and a key transcription factor, runt-related transcription factor 2, in SCAPs. Depletion of HOXC10 promoted osteogenic differentiation in SCAPs in vitro. In addition, in vivo transplantation experiments in nude mice confirmed that SCAPs osteogenesis was triggered when HOXC10 was downregulated. Furthermore, depletion of HOXC10 also enhanced osteogenic differentiation in ADSCs.

CONCLUSIONS

Taken together, these results indicated that HOXC10 decreased the MSC osteogenic differentiation potential. Thus, inhibition of HOXC10 in MSCs might have the potential to improve tissue regeneration and provide insight into the mechanism underlying the directed differentiation of MSCs.

FGF2 Enhances Odontoblast Differentiation by αSMA+ Progenitors In Vivo

The goal of this study was to examine the effects of early and limited exposure of perivascular cells expressing α (αSMA) to fibroblast growth factor 2 (FGF2) in vivo. We performed in vivo fate mapping by inducible Cre-loxP and experimental pulp injury in molars to induce reparative dentinogenesis. Our results demonstrate that early delivery of exogenous FGF2 to exposed pulp led to proliferative expansion of αSMA-tdTomato⁺ cells and their accelerated differentiation into odontoblasts. In vivo lineage-tracing experiments showed that the calcified bridge/reparative dentin in FGF2-treated pulps were lined with an increased number of Dspp⁺ odontoblasts and devoid of BSP⁺ osteoblasts. The increased number of odontoblasts derived from αSMA-tdTomato⁺ cells and the formation of reparative dentin devoid of osteoblasts provide in vivo evidence for the stimulatory effects of FGF signaling on odontoblast differentiation from early progenitors in dental pulp.

The physiological functions of central nervous system pericytes and a potential role in pain

Central nervous system (CNS) pericytes regulate critical functions of the neurovascular unit in health and disease. CNS pericytes are an attractive pharmacological target for their position within the neurovasculature and for their role in neuroinflammation. Whether the function of CNS pericytes also affects pain states and nociceptive mechanisms is currently not understood. Could it be that pericytes hold the key to pain associated with CNS blood vessel dysfunction? This article reviews recent findings on the important physiological functions of CNS pericytes and highlights how these neurovascular functions could be linked to pain states.

Biology Explaining Tooth Repair and Regeneration: A Mini-Review

The tooth is an intricate composition of precisely patterned, mineralized matrices and soft tissues. Mineralized tissues include enamel (produced by the epithelial cells called ameloblasts), dentin and cementum (produced by mesenchymal cells called odontoblasts and cementoblasts, respectively), and soft tissues, which include the dental pulp and the periodontal ligament along with the invading nerves and blood vessels. It was perceived for a very long time that teeth primarily serve an esthetical function. In recent years, however, the role of healthy teeth, as well as the impact of oral health on general well-being, became more evident. Tooth loss, caused by tooth decay, congenital malformations (tooth agenesis), trauma, periodontal diseases, or age-related changes, is usually replaced by artificial materials which lack many of the important biological characteristics of the natural tooth. Human teeth have very low to almost absent regeneration potential, due to early loss of cell populations with regenerative capacity, namely stem cells. Significant effort has been made in recent decades to identify and characterize tooth stem cells, and to unravel the developmental programs which these cells follow in order to generate a tooth.

Role of the Inferior Alveolar Nerve in Rodent Lower Incisor Stem Cells

In developing teeth, the sequential and reciprocal interactions between epithelial and mesenchymal tissues promote stem/progenitor cell differentiation. However, the origin of the stem/progenitor cells has been the subject of considerable debate. According to recent studies, mesenchymal stem cells originate from periarterial cells and are regulated by neurons in various organs. The present study examined the role of innervation in tooth development and rodent incisor stem/progenitor cell homeostasis. Rodent incisors continuously grow throughout their lives, and the lower incisors are innervated by the inferior alveolar nerve (IAN). In this study, we resected the IAN in adult rats, and the intact contralateral side served as a nonsurgical control. Sham control rats received the same treatment as the resected rats, except for the resection process. The extent of incisor eruption was measured, and both mesenchymal and epithelial stem/progenitor cells were visualized and compared between the IAN-resected and sham-operated groups. One week after surgery, the IAN-resected incisors exhibited a chalky consistency, and the eruption rate was decreased. Micro–computed tomography and histological analyses performed 4 wk after surgery revealed osteodentin formation, disorganized ameloblast layers, and reduced enamel thickness in the IAN-resected incisors. Immunohistochemical analysis revealed a reduction in the CD90- and LRIG1-positive mesenchymal cell ratio in the IAN-resected incisors. However, the p40-positive epithelial stem/progenitor cell ratio was comparable between the 2 groups. Thus, mesenchymal stem/progenitor cell homeostasis is more related to IAN innervation than to epithelial stem/progenitor cells. Furthermore, sensory nerve innervation influences subsequent incisor growth and formation.

Early Immunomodulatory Effects of Implanted Human Perivascular Stromal Cells During Bone Formation

Human perivascular stem/stromal cells (PSC) are a multipotent mesodermal progenitor cell population defined by their perivascular residence. PSC are most commonly derived from subcutaneous adipose tissue, and recent studies have demonstrated the high potential for clinical translation of this fluorescence-activated cell sorting-derived cell population for bone tissue engineering. Specifically, purified PSC induce greater bone formation than unpurified stroma taken from the same patient sample. In this study, we examined the differences in early innate immune response to human PSC or unpurified stroma (stromal vascular fraction [SVF]) during the in vivo process of bone formation. Briefly, SVF or PSC from the same patient sample were implanted intramuscularly in the hindlimb of severe combined immunodeficient (SCID) mice using an osteoinductive demineralized bone matrix carrier. Histological examination of early inflammatory infiltrates was examined by hematoxylin and eosin and immunohistochemical staining (Ly-6G, F4/80). Results showed significantly greater neutrophilic and macrophage infiltrates within and around SVF in comparison to PSC-laden implants. Differences in early postoperative inflammation among SVF-laden implants were associated with reduced osteogenic differentiation and bone formation. Similar findings were recapitulated with PSC implantation in immunocompetent mice. Exaggerated postoperative inflammation was associated with increased IL-1α, IL-1β, IFN-γ, and TNF-α gene expression among SVF samples, and conversely increased IL-6 and IL-10 expression among PSC samples. These data document a robust immunomodulatory effect of implanted PSC, and an inverse correlation between host inflammatory cell infiltration and stromal progenitor cell-mediated ossification.

HMGA2 sustains self-renewal and invasiveness of glioma-initiating cells

Glioblastoma multiforme (GBM) is the most common type of brain tumors with dismal outcomes. The mesenchymal phenotype is the hallmark of tumor aggressiveness in GBMs. Perivascular smooth muscle cells (pericytes) are essential in homeostasis of normal and glioma tissues. Here we found HMGA2, an architectural transcription factor that promotes mesenchymal phenotypes in a number of solid tumors, is highly expressed in mesenchymal subtype of GBMs and labels both glioma pericytes and glioma-initiating cells (GICs). Accordingly, depletion of HMGA2 in GICs resulted in compromised self-renewal and tumorigenic capability, as well as undermined mesenchymal or pericyte differentiation. We further showed HMGA2 allows expressions of FOXM1 and PLAU to maintain GIC propagation, gliomagenesis and aggressiveness both in vitro and in vivo. Therefore, suppressing HMGA2-mediated GIC self-renewal and invasiveness might be a promising means to treat GBMs.

Advanced 3D Models Cultured to Investigate Mesenchymal Stromal Cells of the Human Dental Follicle

The human dental follicle (hDF) contains the developing tooth and is involved in regulating tooth maturation and eruption. To investigate the mesenchymal stromal cells of the dental follicle, 2 three-dimensional (3D) culture models were used, based on a dynamic bioreactor: the Rotary Cell Culture System (RCCS™) and the 3D culture of precursor cells isolated from follicular tissue (human dental follicle cells [hDFCs]). The hDFCs were obtained from impacted third molars of 20 patients. Two 3D culture models were tested. In the first model, intact hDF explants were cultured in 3D conditions, preserving the original tissue architecture; they were studied using histomorphological and molecular analyses. The second model involved the 3D culture of hDFCs, which were characterized to evaluate their multipotency in terms of differentiation capability. Of the biomarkers known to characterize hDFCs, hDF precursors were selected for our study. The immunophenotype and in situ immunocytochemistry were evaluated for markers CD44, CD90, CD146, CD105, CD31, CD34, and CD45 Ag. The results show that the conditions provided by the RCCS preserve the original organizational architecture of the cells. The 3D conditions of the model enhanced differentiation in response to adipogenic, osteogenic, and chondrogenic inductive growth media. The immunophenotype and the immunocytochemistry showed generally high expression of CD90, CD44, and CD105, while CD146 expression was more restricted to ∼30% of cells. No expression was observed for CD31, CD34, and CD45 Ags. Two 3D tissue- and cell-based ex vivo models of the hDF supported the long-term maintenance of hDF-specific cell phenotypes and their ability to recapitulate typical cellular differentiation states. As such, these ex vivo models could be used to study the physiopathology of human odontogenesis. In addition, in a therapeutic context, they could be used to examine the role of specific chemical signals (e.g., new therapeutic agents) in the processes of dental tissue repair and regeneration.

A quiescent cell population replenishes mesenchymal stem cells to drive accelerated growth in mouse incisors

The extent to which heterogeneity within mesenchymal stem cell (MSC) populations is related to function is not understood. Using the archetypal MSC in vitro surface marker, CD90/Thy1, here we show that 30% of the MSCs in the continuously growing mouse incisor express CD90/Thy1 and these cells give rise to 30% of the differentiated cell progeny during postnatal development. In adulthood, when growth rate homeostasis is established, the CD90/Thy1+ MSCs decrease dramatically in number. When adult incisors are cut, the growth rate increases to rapidly re-establish tooth length and homeostasis. This accelerated growth rate correlates with the re-appearance of CD90/Thy+ MSCs and re-establishment of their contribution to cell differentiation. A population of Celsr1+ quiescent cells becomes mitotic following clipping and replenishes the CD90/Thy1 population. A sub-population of MSCs thus exists in the mouse incisor, distinguished by expression of CD90/Thy1 that plays a specific role only during periods of increased growth rate.

Mesenchymal Stem Cells as Endogenous Regulators of Inflammation

This chapter discusses the regulatory role of endogenous mesenchymal stem cells (MSC) during an inflammatory response. MSC are a heterogeneous population of multipotent cells that normally contribute towards tissue maintenance and repair but have garnered significant scientific interest for their potent immunomodulatory potential. It is through these physicochemical interactions that MSC are able to exert an anti-inflammatory response on neighbouring stromal and haematopoietic cells. However, the impact of the chronic inflammatory environment on MSC function remains to be determined. Understanding the relationship of MSC between resolution of inflammation and autoimmunity will both offer new insights in the use of MSC as a therapeutic, and also their involvement in the pathogenesis of inflammatory disorders.

Mesenchymal stromal cell plasticity and the tumor microenvironment

Mesenchymal stem cells or mesenchymal stromal cells (MSCs) are a multipotent, heterogeneous population of cells that play a critical role in wound healing and tissue regeneration. MSCs, found in the tumor microenvironment, support tumor growth through the production of angiogenic factors, growth factors and extracellular matrix proteins. They also have immunomodulatory properties, and since they produce indoleamine 2,3-dioxygenase (IDO), prostaglandin E2 (PGE2) and transforming growth factor β (TGF-β), they have been thought to have primarily immunosuppressive effects. However, their role in the tumor microenvironment is complex and demonstrates plasticity depending on location, stimulatory factors and environment. The presence of melanoma-activated tumor-infiltrating lymphocytes (TILs) has been shown to produce pro-inflammatory changes with TH1 (type 1T helper)-like phenotype in MSCs via activated-TIL released cytokines such as interferon γ (IFN-γ), tumor necrosis factor α (TNF-α) and interleukin-1α (IL-1α), while simultaneously producing factors, such as IDO1, which have been traditionally associated with immunosuppression. Similarly, the combination of IFN-γ and TNF-α polarizes MSCs to a primarily TH1-like phenotype with the expression of immunosuppressive factors. Ultimately, further studies are encouraged and needed for a greater understanding of the role of MSCs in the tumor microenvironment and to improve cancer immunotherapy.

Expression and regulation of long noncoding RNAs during the osteogenic differentiation of periodontal ligament stem cells in the inflammatory microenvironment

Although long noncoding RNAs (lncRNAs) have been emerging as critical regulators in various tissues and biological processes, little is known about their expression and regulation during the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in inflammatory microenvironment. In this study, we have identified 63 lncRNAs that are not annotated in previous database. These novel lncRNAs were not randomly located in the genome but preferentially located near protein-coding genes related to particular functions and diseases, such as stem cell maintenance and differentiation, development disorders and inflammatory diseases. Moreover, we have identified 650 differentially expressed lncRNAs among different subsets of PDLSCs. Pathway enrichment analysis for neighboring protein-coding genes of these differentially expressed lncRNAs revealed stem cell differentiation related functions. Many of these differentially expressed lncRNAs function as competing endogenous RNAs that regulate protein-coding transcripts through competing shared miRNAs.

Local application of IGFBP5 protein enhanced periodontal tissue regeneration via increasing the migration, cell proliferation and osteo/dentinogenic differentiation of mesenchymal stem cells in an inflammatory niche

Background

Periodontitis is a widespread infectious disease ultimately resulting in tooth loss. The number of mesenchymal stem cells (MSCs) in patients with periodontitis is decreased, and MSC functions are impaired. Rescuing the impaired function of MSCs in periodontitis is the key for treatment, especially in a manner independent of exogenous MSCs. Our previous study found that overexpressed insulin-like growth factor binding protein 5 (IGFBP5) could promote exogenous MSC-mediated periodontal tissue regeneration. Here, we investigate the role of IGFBP5 protein in MSCs and periodontal tissue regeneration independent of exogenous MSCs in an inflammatory niche.

Methods

TNFα was used to mimic the inflammatory niche. Lentiviral IGFBP5 shRNA was used to silence IGFBP5 and recombinant human IGFBP5 protein (rhIGFBP5) was used to stimulate the periodontal ligament stem cells (PDLSCs) and bone marrow stem cells (BMSCs). The effects of IGFBP5 on PDLSCs were evaluated using the scratch-simulated wound migration, Transwell chemotaxis, alkaline phosphatase (ALP) activity, Alizarin red staining, Cell Counting Kit-8, Western blot, Real-time PCR, Co-IP and ChIP assays. The swine model of periodontitis was used to investigate the functions of IGFBP5 for periodontal regeneration and its anti-inflammation effect.

Results

We discovered that 0.5 ng/ml rhIGFBP5 protein enhanced the migration, chemotaxis, osteo/dentinogenic differentiation and cell proliferation of MSCs under the inflammatory condition. Moreover, 0.5 ng/ml rhIGFBP5 application could rescue the impaired functions of IGFBP5-silenced-MSCs in the inflammatory niche. Furthermore, local injection of rhIGFBP5 could promote periodontal tissue regeneration and relieve the local inflammation in a minipig model of periodontitis. Mechanistically, we found that BCOR negatively regulated the expression of IGFBP5 in MSCs. BCOR formed a protein complex with histone demethylase KDM6B and raised histone K27 methylation in the IGFBP5 promoter.

Conclusions

This study revealed that rhIGFBP5 could activate the functions of MSCs in an inflammatory niche, provided insight into the mechanism underlying the activated capacities of MSCs, and identified IGFBP5 as a potential cytokine for improving tissue regeneration and periodontitis treatment independent of exogenous MSCs and its potential application in dental clinic.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0663-6) contains supplementary material, which is available to authorized users.

Pericytes and their potential in regenerative medicine across species

The discovery that pericytes are in vivo counterparts of Mesenchymal Stem/Stromal Cells (MSCs) has placed these perivascular cells in the research spotlight, bringing up hope for a well-characterized cell source for clinical applications, alternative to poorly defined, heterogeneous MSCs preparations currently in use. Native pericytes express typical MSC markers and, after isolation by fluorescence-activated cell sorting, display an MSC phenotype in culture. These features have been demonstrated in different species, including humans and horses, the main targets of regenerative treatments. Significant clinical potential of pericytes has been shown by transplantation of human cells into rodent models of tissue injury, and it is hoped that future studies will demonstrate clinical potential in veterinary species. Here, we provide an overview of the current knowledge on pericytes across different species including humans, companion and large animal models, in relation to their identification in different body tissues, methodology for prospective isolation, characterization, and potential for tissue regeneration. © 2017 International Society for Advancement of Cytometry.

Pericytes or Mesenchymal Stem Cells: Is That the Question?

For almost a decade, mesenchymal stem cells (MSCs) were believed to reside as perivascular cells in vivo. In this issue of Cell Stem Cell, Guimarães-Camboa et al. (2017) challenge this idea and use lineage tracing to demonstrate that perivascular cells do not behave as tissue-specific progenitors in various organs, despite showing MSC potential in vitro.

Dental mesenchymal stem cells

Mammalian teeth harbour mesenchymal stem cells (MSCs), which contribute to tooth growth and repair. These dental MSCs possess many in vitro features of bone marrow-derived MSCs, including clonogenicity, expression of certain markers, and following stimulation, differentiation into cells that have the characteristics of osteoblasts, chondrocytes and adipocytes. Teeth and their support tissues provide not only an easily accessible source of MSCs but also a tractable model system to study their function and properties in vivo In addition, the accessibility of teeth together with their clinical relevance provides a valuable opportunity to test stem cell-based treatments for dental disorders. This Review outlines some recent discoveries in dental MSC function and behaviour and discusses how these and other advances are paving the way for the development of new biologically based dental therapies.

Novel Regenerative Therapies Based on Regionally Induced Multipotent Stem Cells in Post-Stroke Brains: Their Origin, Characterization, and Perspective

Brain injuries such as ischemic stroke cause severe neural loss. Until recently, it was believed that post-ischemic areas mainly contain necrotic tissue and inflammatory cells. However, using a mouse model of cerebral infarction, we demonstrated that stem cells develop within ischemic areas. Ischemia-induced stem cells can function as neural progenitors; thus, we initially named them injury/ischemia-induced neural stem/progenitor cells (iNSPCs). However, because they differentiate into more than neural lineages, we now refer to them as ischemia-induced multipotent stem cells (iSCs). Very recently, we showed that putative iNSPCs/iSCs are present within post-stroke areas in human brains. Because iNSPCs/iSCs isolated from mouse and human ischemic tissues can differentiate into neuronal lineages in vitro, it is possible that a clearer understanding of iNSPC/iSC profiles and the molecules that regulate iNSPC/iSC fate (e.g., proliferation, differentiation, and survival) would make it possible to perform neural regeneration/repair in patients following stroke. In this article, we introduce the origin and traits of iNSPCs/iSCs based on our reports and recent viewpoints. We also discuss their possible contribution to neurogenesis through endogenous and exogenous iNSPC/iSC therapies following ischemic stroke.

How Plastic Are Pericytes?

Pericytes are defined by both their anatomical location and molecular markers. Numerous publications have reported their role as stem cells, contributing to the formation of tissues other than blood vessels. However, using cell-lineage tracing in a new transgenic mouse model, a recent study shows that in the context of aging and some pathologies, Tbx18+ pericytes do not function as stem cells in vivo. This study challenges the current view that pericytes can differentiate into other cells and reopen questions about their plasticity. This emerging knowledge is important not only for our understanding of development but may also inform treatments for diseases.

Spatial and temporal expression of Sox9 during murine incisor development

Mouse incisors are capable of continuously growing due to the renewal of dental epithelium stem cells and mesenchymal stem cells residing at the proximal ends. The transcription factor Sox9 plays important roles in maintaining the stem cells of hair follicles, retinal progenitor cells and neural crest stem cells. Whether Sox9 is involved during mouse incisor development is not reported yet. In this study, we examined the expression pattern of Sox9 during mouse incisor development by in situ hybridization and immunohistochemistry. Sox9 mRNA and protein showed similar expression pattern from embryonic day (E) 13.5 to postnatal (PN) day 10. At E13.5 and E14.5, Sox9 was strongly expressed in the dental epithelium. At E16.5, Sox9 started to be detected in the mesenchymal cells within the dental pulp, especially the dental pulp cells that adjacent to the labial cervical loop. Similarly with E14.5, Sox9 was strongly detected in the labial cervical loop, including the basal epithelium, the stellate reticulum and the outer enamel epithelium from E16.5 to PN10. The mesenchyme adjacent to the labial cervical loop also showed strong signal of Sox9. The spatiotemporal expression of Sox9 suggested its possible involvement during mouse incisor development.

Pericytes are heterogeneous in their origin within the same tissue

Pericytes heterogeneity is based on their morphology, distribution, and markers. It is well known that pericytes from different organs may have distinct embryonic sources. Yamazaki et al. (2017) using several transgenic mouse model reveal by cell-lineage tracing that pericytes are even more heterogeneous than previously appreciated. This study shows that pericytes from within the same tissue may be heterogeneous in their origin. Remarkably, a subpopulation of embryonic dermal pericytes derives from the hematopoietic lineage, an unexpected source. Reconstructing the lineage of pericytes is central to understanding development, and also for the diagnosis and treatment of diseases in which pericytes play important roles.

Axin2-expressing cells differentiate into reparative odontoblasts via autocrine Wnt/β-catenin signaling in response to tooth damage

In non-growing teeth, such as mouse and human molars, primary odontoblasts are long-lived post-mitotic cells that secrete dentine throughout the life of the tooth. New odontoblast-like cells are only produced in response to a damage or trauma. Little is known about the molecular events that initiate mesenchymal stem cells to proliferate and differentiate into odontoblast-like cells in response to dentine damage. The reparative and regenerative capacity of multiple mammalian tissues depends on the activation of Wnt/β-catenin signaling pathway. In this study, we investigated the molecular role of Wnt/β-catenin signaling pathway in reparative dentinogenesis using an in vivo mouse tooth damage model. We found that Axin2 is rapidly upregulated in response to tooth damage and that these Axin2-expressing cells differentiate into new odontoblast-like cells that secrete reparative dentine. In addition, the Axin2-expressing cells produce a source of Wnt that acts in an autocrine manner to modulate reparative dentinogenesis.

Heterogeneity and Developmental Connections between Cell Types Inhabiting Teeth

Every tissue is composed of multiple cell types that are developmentally, evolutionary and functionally integrated into the unit we call an organ. Teeth, our organs for biting and mastication, are complex and made of many different cell types connected or disconnected in terms of their ontogeny. In general, epithelial and mesenchymal compartments represent the major framework of tooth formation. Thus, they give rise to the two most important matrix–producing populations: ameloblasts generating enamel and odontoblasts producing dentin. However, the real picture is far from this quite simplified view. Diverse pulp cells, the immune system, the vascular system, the innervation and cells organizing the dental follicle all interact, and jointly participate in transforming lifeless matrix into a functional organ that can sense and protect itself. Here we outline the heterogeneity of cell types that inhabit the tooth, and also provide a life history of the major populations. The mouse model system has been indispensable not only for the studies of cell lineages and heterogeneity, but also for the investigation of dental stem cells and tooth patterning during development. Finally, we briefly discuss the evolutionary aspects of cell type diversity and dental tissue integration.

Mesenchymal stem cells and their therapeutic applications in inflammatory bowel disease

Mesenchymal stem or stromal cells (MSCs) are non-hematopoietic stem cells that facilitate tissue regeneration through mechanisms involving self-renewal and differentiation, supporting angiogenesis and tissue cell survival, and limiting inflammation. MSCs were originally identified and expanded in long-term cultures of cells from bone marrow and other organs; and their native identity was recently confined into pericytes and adventitial cells in vascularized tissue. The multipotency, as well as the trophic and immunosuppressive effects, of MSCs have prompted the rapid development of clinical applications for many diseases involving tissue inflammation and immune disorders, including inflammatory bowel disease. Although standard criteria have been established to define MSCs, their therapeutic efficacy has varied significantly among studies due to their natural heterogenicity. Thus, understanding the biological and immunological features of MSCs is critical to standardize and optimize MSCs-based therapy. In this review, we highlight the cellular and molecular mechanisms involved in MSCs-mediated tissue repair and immunosuppression. We also provide an update on the current development of MSCs-based clinical trials, with a detailed discussion of MSC-based cell therapy in inflammatory bowel disease.

BMP signaling orchestrates a transcriptional network to control the fate of mesenchymal stem cells in mice

Signaling pathways are used reiteratively in different developmental processes yet produce distinct cell fates through specific downstream transcription factors. In this study, we used tooth root development as a model with which to investigate how the BMP signaling pathway regulates transcriptional complexes to direct the fate determination of multipotent mesenchymal stem cells (MSCs). We first identified the MSC population supporting mouse molar root growth as Gli1⁺ cells. Using a Gli1-driven Cre-mediated recombination system, our results provide the first in vivo evidence that BMP signaling activity is required for the odontogenic differentiation of MSCs. Specifically, we identified the transcription factors Pax9, Klf4, Satb2 and Lhx8 as being downstream of BMP signaling and expressed in a spatially restricted pattern that is potentially involved in determining distinct cellular identities within the dental mesenchyme. Finally, we found that overactivation of one key transcription factor, Klf4, which is associated with the odontogenic region, promotes odontogenic differentiation of MSCs. Collectively, our results demonstrate the functional significance of BMP signaling in regulating MSC fate during root development and shed light on how BMP signaling can achieve functional specificity in regulating diverse organ development.

Resolving stem and progenitor cells in the adult mouse incisor through gene co-expression analysis

Investigations into stem cell-fueled renewal of an organ benefit from an inventory of cell type-specific markers and a deep understanding of the cellular diversity within stem cell niches. Using the adult mouse incisor as a model for a continuously renewing organ, we performed an unbiased analysis of gene co-expression relationships to identify modules of co-expressed genes that represent differentiated cells, transit-amplifying cells, and residents of stem cell niches. Through in vivo lineage tracing, we demonstrated the power of this approach by showing that co-expression module members Lrig1 and Igfbp5 define populations of incisor epithelial and mesenchymal stem cells. We further discovered that two adjacent mesenchymal tissues, the periodontium and dental pulp, are maintained by distinct pools of stem cells. These findings reveal novel mechanisms of incisor renewal and illustrate how gene co-expression analysis of intact biological systems can provide insights into the transcriptional basis of cellular identity.

Microencapsulation of Lefty-secreting engineered cells for pulmonary fibrosis therapy in mice

Idiopathic pulmonary fibrosis (IPF) is a progressive disease that causes unremitting deposition of extracellular matrix proteins, thus resulting in distortion of the pulmonary architecture and impaired gas exchange. Associated with high morbidity and mortality, IPF is generally refractory to current pharmacological therapies. Lefty A, a potent inhibitor of transforming growth factor-β signaling, has been shown to have promising antifibrotic ability in vitro for the treatment of renal fibrosis and other potential organ fibroses. Here, we determined whether Lefty A can attenuate bleomycin (BLM)-induced pulmonary fibrosis in vivo based on a novel therapeutic strategy where human embryonic kidney 293 (HEK293) cells are genetically engineered with the Lefty A-associated GFP gene. The engineered HEK293 cells were encapsulated in alginate microcapsules and then subcutaneously implanted in ICR mice that had 1 wk earlier been intratracheally administered BLM to induce pulmonary fibrosis. The severity of fibrosis in lung tissue was assessed using pathological morphology and collagen expression to examine the effect of Lefty A released from the microencapsulated cells. The engineered HEK293 cells with Lefty A significantly reduced the expression of connective tissue growth factor and collagen type I mRNA, lessened the morphological fibrotic effects induced by BLM, and increased the expression of matrix metalloproteinase-9. This illustrates that engineered HEK293 cells with Lefty A can attenuate pulmonary fibrosis in vivo, thus providing a novel method to treat human pulmonary fibrotic disease and other organ fibroses.

Identification of Multipotent Stem Cells in Human Brain Tissue Following Stroke

Perivascular regions of the brain harbor multipotent stem cells. We previously demonstrated that brain pericytes near blood vessels also develop multipotency following experimental ischemia in mice and these ischemia-induced multipotent stem cells (iSCs) can contribute to neurogenesis. However, it is essential to understand the traits of iSCs in the poststroke human brain for possible applications in stem cell-based therapies for stroke patients. In this study, we report for the first time that iSCs can be isolated from the poststroke human brain. Putative iSCs were derived from poststroke brain tissue obtained from elderly stroke patients requiring decompressive craniectomy and partial lobectomy for diffuse cerebral infarction. Immunohistochemistry showed that these iSCs were localized near blood vessels within poststroke areas containing apoptotic/necrotic neurons and expressed both the stem cell marker nestin and several pericytic markers. Isolated iSCs expressed these same markers and demonstrated high proliferative potential without loss of stemness. Furthermore, isolated iSCs expressed other stem cell markers, such as Sox2, c-myc, and Klf4, and differentiated into multiple cells in vitro, including neurons. These results show that iSCs, which are likely brain pericyte derivatives, are present within the poststroke human brain. This study suggests that iSCs can contribute to neural repair in patients with stroke.