Cell fate determination from stem cells

Potential Role of AGR2 for Mammalian Skin Wound Healing

The limited ability of mammals to regenerate has garnered significant attention, particularly in regard to skin wound healing (WH), which is a critical step for regeneration. In human adults, skin WH results in the formation of scars following injury or trauma, regardless of severity. This differs significantly from the scarless WH observed in the fetal skin of mammals or anamniotes. This review investigates the role of molecular players involved in scarless WH, which are lost or repressed in adult mammalian WH systems. Specifically, we analyze the physiological role of Anterior Gradient (AGR) family proteins at different stages of the WH regulatory network. AGR is activated in the regeneration of lower vertebrates at the stage of wound closure and, accordingly, is important for WH. Mammalian AGR2 is expressed during scarless WH in embryonic skin, while in adults, the activity of this gene is normally inhibited and is observed only in the mucous epithelium of the digestive tract, which is capable of full regeneration. The combination of AGR2 unique potencies in postnatal mammals makes it possible to consider it as a promising candidate for enhancing WH processes.

Studying Regeneration in Ascidians: An Historical Overview

Ascidians are sessile tunicates, that is, marine animals belonging to the phylum Chordata and considered the sister group of vertebrates. They are widespread in all the seas, constituting abundant communities in various ecosystems. Among chordates, only tunicates are able to reproduce asexually, forming colonies. The high regenerative potentialities enabling tunicates to regenerate damaged body parts, or the whole body, represent a peculiarity of this taxon. Here we review the methodological approaches used in more than a century of biological studies to induce regeneration in both solitary and colonial species. For solitary species, we refer to the regeneration of single organs or body parts (e.g., siphon, brain, gonad, tunic, viscera). For colonial species, we review a plethora of experiments regarding the surgical manipulation of colonies, the regeneration of isolated colonial entities, such as single buds in the tunic, or part of tunic and its circulatory system.

Oral Cavity as a Source of Mesenchymal Stem Cells Useful for Regenerative Medicine in Dentistry

The use of mesenchymal stem cells (MSCs) for regenerative purposes has become common in a large variety of diseases. In the dental and maxillofacial field, there are emerging clinical needs that could benefit from MSC-based therapeutic approaches. Even though MSCs can be isolated from different tissues, such as bone marrow, adipose tissue, etc., and are known for their multilineage differentiation, their different anatomical origin can affect the capability to differentiate into a specific tissue. For instance, MSCs isolated from the oral cavity might be more effective than adipose-derived stem cells (ASCs) for the treatment of dental defects. Indeed, in the oral cavity, there are different sources of MSCs that have been individually proposed as promising candidates for tissue engineering protocols. The therapeutic strategy based on MSCs can be direct, by using cells as components of the tissue to be regenerated, or indirect, aimed at delivering local growth factors, cytokines, and chemokines produced by the MSCs. Here, the authors outline the major sources of mesenchymal stem cells attainable from the oral cavity and discuss their possible usage in some of the most compelling therapeutic frontiers, such as periodontal disease and dental pulp regeneration.

Deciphering transcriptional and functional heterogeneity in hematopoiesis with single-cell genomics

PURPOSE OF REVIEW

Single-cell genomic approaches have uncovered cell fate biases and heterogeneity within hematopoietic subpopulations. However, standard single-cell transcriptomics suffers from high sampling noise, which particularly skews the distribution of lowly expressed genes, such as transcription factors (TFs). This might preclude the identification of rare transcripts that define cell identity and demarcate cell fate biases. Moreover, these studies need to go hand in hand with relevant functional assays to ensure that observed gene expression changes represent biologically meaningful alterations.

RECENT FINDINGS

Single-cell lineage tracing and functional validation studies have uncovered cell fate bias within transcriptionally distinct hematopoietic stem and progenitor subpopulations. Novel markers identified using these strategies have been proposed to prospectively isolate functionally distinct subpopulations, including long-term hematopoietic stem cells for ex vivo applications. Furthermore, the continuous nature of hematopoiesis has prompted the study of the relationship between stochastic transcriptional noise in hematopoietic TFs and cell fate determination.

SUMMARY

An understanding of the limitations of single-cell genomic approaches and follow-up functional assays is critical to discern the technical and biological contribution of noise in hematopoietic heterogeneity, to identify rare gene expression states, and to uncover functionally distinct subpopulations within hematopoiesis.

SUPPLEMENTARY VIDEO

http://links.lww.com/COH/A23.

Malfunctioning CD106-positive, short-term hematopoietic stem cells trigger diabetic neuropathy in mice by cell fusion

Diabetic neuropathy is an incurable disease. We previously identified a mechanism by which aberrant bone marrow-derived cells (BMDCs) pathologically expressing proinsulin/TNF-α fuse with residential neurons to impair neuronal function. Here, we show that CD106-positive cells represent a significant fraction of short-term hematopoietic stem cells (ST-HSCs) that contribute to the development of diabetic neuropathy in mice. The important role for these cells is supported by the fact that transplantation of either whole HSCs or CD106-positive ST-HSCs from diabetic mice to non-diabetic mice produces diabetic neuronal dysfunction in the recipient mice via cell fusion. Furthermore, we show that transient episodic hyperglycemia produced by glucose injections leads to abnormal fusion of pathological ST-HSCs with residential neurons, reproducing neuropathy in nondiabetic mice. In conclusion, we have identified hyperglycemia-induced aberrant CD106-positive ST-HSCs underlie the development of diabetic neuropathy. Aberrant CD106-positive ST-HSCs constitute a novel therapeutic target for the treatment of diabetic neuropathy.

Katagi et al. show that abnormal bone marrow-derived cells originated from hematopoietic stem cells (CD106-positive short-term HSCs) aberrantly fuse with neurons to develop diabetic neuropathy. This study suggests that the pathological abnormality is memorized in the bone marrow and that it cannot be erased by conventional therapy.

Isolation and establishment of skin-derived and mesenchymal cells from south American bat Artibeus planirostris (Chiroptera - Phyllostomidae)

Animal models represent a crucial tool for biological research, so the establishment of new cultures is fundamental for the discovery of new therapies and the understanding of mechanisms of cell development in the most diverse animals. Here, we report the successful establishment of two new primary cell cultures derived from a South American bat (Artibeus planirostris). The establishment of a new bat culture can help in the investigation of new zoonoses since bats have been proposed as carriers of these diseases. We evaluated the chromosomal stability of cells from different passages. Primary cultures were collected from ear tissues and bone marrow of A. planirostris. Cultures were expanded, and osteogenic and adipogenic inductions were conducted for 21 days. For osteogenic differentiation, the medium was supplemented with 0.1 μM dexamethasone, 3 mM β-glycerophosphate, and 10 μM L-ascorbic acid 2-phosphate. For adipogenic differentiation, the medium was supplemented with 5 μM rosiglitazone, 0.4 μM insulin, 0.1 mM indomethacin, and 0.1 μM dexamethasone. After the induction period, the cells were stained with Alizarin Red to assess osteogenic differentiation and Oil Red O to assess adipogenic differentiation. We observed the appearance of lipid droplets in adipocytes and the extracellular deposition of calcium matrix by osteocytes, indicating that bone marrow-derived cells and skin-derived cells of A. planirostris could successfully differentiate into these lineages. Also, the number of chromosomes remained stable for both primary cultures during passages 2, 4, 6, and 8.

Reconstituting neurovascular unit with primary neural stem cells and brain microvascular endothelial cells in three-dimensional matrix

Neurovascular dysfunction is a primary or secondary cause in the pathogenesis of several cerebrovascular and neurodegenerative disorders, including stroke. Therefore, the overall protection of the neurovascular unit (NVU) is a promising therapeutic strategy for various neurovascular diseases. However, the complexity of the NVU limits the study of the pathological mechanisms of neurovascular dysfunction. Reconstituting the in vitro NVU is important for the pathological study and drug screening of neurovascular diseases. In this study, we generated a spontaneously assembled three‐dimensional NVU (3D NVU) by employing the primary neural stem cells and brain microvascular endothelial cells in a Matrigel extracellular matrix platform. This novel model exhibits the fundamental structures and features of the NVU, including neurons, astrocytes, oligodendrocytes, vascular‐like structures, and blood–brain barrier‐like characteristics. Additionally, under oxygen‐glucose deprivation, the 3D NVU exhibits the neurovascular‐ or oxidative stress‐related pathological characteristics of cerebral ischemia and the injuries can be mitigated, respectively, by supplementing with the vascular endothelial growth factor or edaravone, which demonstrated that the availability of 3D NVU in ischemic stroke modeling. Finally, the 3D NVU promoted the angiogenesis and neurogenesis in the brain of cerebral ischemia rats. We expect that the proposed in vitro 3D NVU model will be widely used to investigate the relationships between angiogenesis and neurogenesis and to study the pathology and pharmacology of neurovascular diseases.

Orthogonal tuning of gene expression noise using CRISPR-Cas

The control of gene expression noise is important for improving drug treatment and the performance of synthetic biological systems. Previous work has tuned gene expression noise by changing the rate of transcription initiation, mRNA degradation, and mRNA translation. However, these methods are invasive: they require changes to the target genetic components. Here, we create an orthogonal system based on CRISPR-dCas9 to tune gene expression noise. Specifically, we modulate the gene expression noise of a reporter gene in Escherichia coli by incorporating CRISPR activation and repression (CRISPRar) simultaneously in a single cell. The CRISPRar uses a single dCas9 that recognizes two different single guide RNAs (sgRNA). We build a library of sgRNA variants with different expression activation and repression strengths. We find that expression noise and mean of a reporter gene can be tuned independently by CRISPRar. Our results suggest that the expression noise is tuned by the competition between two sgRNAs that modulate the binding of RNA polymerase to promoters. The CRISPRar may change how we tune expression noise at the genomic level. Our work has broad impacts on the study of gene functions, phenotypical heterogeneity, and genetic circuit control.

Distinct Origins of Restricted Progenitors in Postnatal Mouse Blood

Background

Most researchers have accepted that unipotent progenitors are the predominant components in bone marrow for tissue regeneration. However, the unipotent progenitors for blood components are still unclear. We previously found that erythrocytes are derived from a distinct unipotent progenitors, or erythrocyte sacs.

Methods

In the current study, we investigated if the other types of unipotent blood cell progenitors existed, what was their original morphologies, and the mechanism of their generation in mouse blood.

Results

We found two morphologically distinct structures that released spore-like small progenitors in mouse blood. One structure was filamentary-like, contained inclusions, widened due to differentiation of the inclusions, and eventually, released spore-like DNA+ and cluster of differentiation 34 (CD34)⁺ spore-like small progenitors. Another structure was bud-like, contained inclusion, enlarged from less than 10 µm to more than 30 µm, and also released many spore-like small progenitors. Each type of these spore-like progenitors was approximately 1 µm in diameter and could continue to transdifferentiate in circulation.

Conclusions

Our data provide evidence that two types of blood cell restricted progenitors are produced from either filamentary structures or bud-like structures. Both filamentary and bud-like structures were originally released from morphologically distinct, or lineage predetermined tube-shaped structures, or specific niches. Thus, distinct lineages of blood unipotent progenitors are newly produced.

Strategies for derivation of endothelial lineages from human stem cells

Accumulating evidence demonstrates that pre-vascularization of tissue-engineered constructs can significantly enhance their survival and engraftment upon transplantation. Endothelial cells (ECs), the basic component of vasculatures, are indispensable to the entire process of pre-vascularization. However, the source of ECs still poses an issue. Recent studies confirmed that diverse approaches are available in the derivation of ECs for tissue engineering, such as direct isolation of autologous ECs, reprogramming of somatic cells, and induced differentiation of stem cells in typology. Herein, we discussed a variety of human stem cells (i.e., totipotent, pluripotent, multipotent, oligopotent, and unipotent stem cells), which can be induced to differentiate into ECs and reviewed the multifarious approaches for EC generation, such as 3D EB formation for embryonic stem cells (ESCs), stem cell-somatic cell co-culture, and directed endothelial differentiation with growth factors in conventional 2D culture.

Role of Extracellular Matrix in Cardiac Cellular Therapies

The extracellular matrix (ECM) is an essential regulator of homeostasis at the cellular, tissue, and organ level. It is now very well known that ECM dynamic remodeling is indispensable not only for normal growth and development but also recovery from tissue injuries. Indeed, abnormal remodeling of the ECM plays a major role in many pathophysiological processes and contributes to many different pathologies including cardiovascular disorders. Recently, cellular therapies have emerged as a potential therapeutic strategy for restoration of lost cardiomyocytes or their rejuvenation after cardiac damage and injuries. Harnessing the biological properties of ECM could be a viable strategy to enhance the therapeutic effects of cellular therapies by improving the engraftment, integration, survival, and functional adaptation of newly transplanted cells in many different platforms. Conversely, transplanted cells could restore the functionality and original composition of damaged ECM by secreting and depositing new ECM or stimulating normal ECM production by cardiac tissue native cells. Although the ultimate role of cell therapy in treatment of cardiac disorders is still a matter of great debate, the potential utility of ECM in improving the therapeutic effect of transplanted cells and vice versa the potential role of cell therapy as a means to restore the structure and functionality of damaged ECM should be carefully considered in implementation of future clinical cardiovascular cell therapy trials.

Determining the control networks regulating stem cell lineages in colonic crypts

The question of stem cell control is at the center of our understanding of tissue functioning, both in healthy and cancerous conditions. It is well accepted that cellular fate decisions (such as divisions, differentiation, apoptosis) are orchestrated by a network of regulatory signals emitted by different cell populations in the lineage and the surrounding tissue. The exact regulatory network that governs stem cell lineages in a given tissue is usually unknown. Here we propose an algorithm to identify a set of candidate control networks that are compatible with (a) measured means and variances of cell populations in different compartments, (b) qualitative information on cell population dynamics, such as the existence of local controls and oscillatory reaction of the system to population size perturbations, and (c) statistics of correlations between cell numbers in different compartments. Using the example of human colon crypts, where lineages are comprised of stem cells, transit amplifying cells, and differentiated cells, we start with a theoretically known set of 32 smallest control networks compatible with tissue stability. Utilizing near-equilibrium stochastic calculus of stem cells developed earlier, we apply a series of tests, where we compare the networks' expected behavior with the observations. This allows us to exclude most of the networks, until only three, very similar, candidate networks remain, which are most compatible with the measurements. This work demonstrates how theoretical analysis of control networks combined with only static biological data can shed light onto the inner workings of stem cell lineages, in the absence of direct experimental assessment of regulatory signaling mechanisms. The resulting candidate networks are dominated by negative control loops and possess the following properties: (1) stem cell division decisions are negatively controlled by the stem cell population, (2) stem cell differentiation decisions are negatively controlled by the transit amplifying cell population.

Epithelial stem cells are formed by small-particles released from particle-producing cells

Recent spatiotemporal report demonstrated that epidermal stem cells have equal potential to divide or differentiate, with no asymmetric cell division observed. Therefore, how epithelial stem cells maintain lifelong stem-cell support still needs to be elucidated. In mouse blood and bone marrow, we found a group of large cells stained strongly for eosin and containing coiled-tubing-like structures. Many were tightly attached to each other to form large cellular clumps. After sectioning, these large cell-clumps were composed of not cells but numerous small particles, however with few small "naked" nuclei. The small particles were about 2 to 3 μm in diameter and stained dense red for eosin, so they may be rich in proteins. Besides the clumps composed of small particles, we identified clumps formed by fusion of the small particles and clumps of newly formed nucleated cells. These observations suggest that these small particles further fused and underwent cellularization. E-cadherin was expressed in particle-fusion areas, some "naked" nuclei and the newly formed nucleated cells, which suggests that these particles can form epithelial cells via fusion and nuclear remodeling. In addition, we observed similar-particle fusion before epithelial cellularization in mouse kidney ducts after kidney ischemia, which suggests that these particles can be released in the blood and carried to the target tissues for epithelial-cell regeneration. Oct4 and E-cadherin expressed in the cytoplasmic areas in cells that were rich in protein and mainly located in the center of the cellular clumps, suggesting that these newly formed cells have become tissue-specific epithelial stem cells. Our data provide evidence that these large particle-producing cells are the origin of epithelial stem cells. The epithelial stem cells are newly formed by particle fusion.

Role of Endogenous Bone Marrow Stem Cells Mobilization in Repair of Damaged Inner Ear in Rats

Background and Objectives

The utilization of the stem cells is widely used in the last few years in different fields of medicine, either by external transplantation or endogenous mobilization, most of these studies still experimental on animals; few were tried on human as in the spinal cord injury or myocardial infarction. As regard its use in the inner ear, stem cell transplantation was examined in many previous studies, while the mobilization idea is a new method to be experimented in inner ear hair cell regeneration. The present work assessed the possibility of mobilizing endogenous bone marrow derived stem cells (SCs) in rats using granulocyte colony stimulating factor (G-CSF) to induce regeneration and repair to experimentally damaged inner ear hair cells by Amikacin injection.

Methods

The study included thirty adult Sprague Dawley male rats. Experimental induction of inner ear damage was done by repeated intratympanic injection of amikacin sulfate. Mobilization of bone marrow SCs was provoked by subcutaneous injection of GCSF. Cochlear integrity, induction of hearing loss and functional recovery of sensory hearing loss were assessed using Distortion Product Otoacoustic Emission (DPOAEs). The morphological alteration and recovery of the organ of Corti was assessed histologically using the light and scanning electron microscopes.

Results

After six month duration, there was improvement in 50% of the sensorineural DPOAE results. Functional recovery coincided with the repair of structural components of organ of Corti.

Conclusions

SCs mobilization by G-CSF is a promising alternative method for replacement therapy in sensorineural hearing loss.

Evaluation of CD44 variant expression in oral, head and neck squamous cell carcinomas using a triple approach and its clinical significance

Cancer stem cells possess the qualities of self-renewal, tumorigenesis and the ability to recapitulate a heterogeneous tumor. Our group was the first to isolate head and neck squamous cell carcinoma (HNSCC) stem cells using the cell surface marker CD44. CD44 is a trans-membrane glycoprotein with a multitude of key-functions that regulate cancer cell proliferation and metastasis. The variety of CD44 functions is due to tissue-specific patterns of glycosylation of the extracellular portion, and to the multiple protein isoforms (CD44 variants, CD44v) generated by alternative splicing. This study investigates the expression pattern of CD44 variants in HNSCC. Ten cell lines from the most common HNSCC locations and representative of various clinical outcomes were assayed by quantitative realtime PCR, flow cytometry and immunofluorescence comparatively with normal oral keratinocytes. The CD44 v4 and v6 were exclusively abundant in HNSCC while the isoform v1,2 was expressed in normal oral keratinocytes. Of interest, the highest level of CD44v6 expression was detected in advanced metastatic HNSCC, suggesting a link between CD44v6 expression and HNSCC metastasis, while the highest CD44v4 was detected in a stage IV HNSCC refractory to chemotherapy which developed recurrence. Oral-derived HNSCC expressed the highest CD44v4 and v6, and levels corresponded with staging, showing also an increasing tendency with recurrence and metastasis. CD44v were detected predominantly in smaller cells (a characteristic that has been associated with stem cell properties) or cells with mesenchymal morphology (a characteristic that has been associated with the migratory and invasive potential of epithelial tumor cells), suggesting that CD44v differential expression in HNSCC may be representative of the morphological changes inherent during tumor progression towards a more aggressive potential, and thus contributing to the individual tumor biology. The mechanism of CD44 variant involvement in HNSCC progression and metastasis is under investigation.

Skin wound healing and scarring: fetal wounds and regenerative restitution

The adverse physiological and psychological effects of scars formation after healing of wounds are broad and a major medical problem for patients. In utero, fetal wounds heal in a regenerative manner, though the mechanisms are unknown. Differences in fetal scarless regeneration and adult repair can provide key insight into reduction of scarring therapy. Understanding the cellular and extracellular matrix alterations in excessive adult scarring in comparison to fetal scarless healing may have important implications. Herein, we propose that matrix can be controlled via cellular therapy to resemble a fetal-like matrix that will result in reduced scarring.

Stem cells as potential targeted therapy for inflammatory bowel disease

The incidence and prevalence of inflammatory bowel disease is increasing in Western countries. Current therapies, ranging from anti-inflammatory drugs, immunosuppressive regimens to new biological therapies, remain inadequate. Advances in our understanding of the pathophysiological mechanisms underlying the pathogenetic disease process and the recent findings on the regenerative and immunoregulatory potential of stem cells open new opportunities in the therapy of inflammatory bowel disease. Therapeutic modalities, including hematopoietic stem cells, adult mesenchymal stem/stromal cells, and the recently identified amniotic origin stem cells, attracted much attention in the recent years. The current review highlights the recent pivotal findings for stem cell-based approaches to inflammatory bowel disease therapy.

Advances in tissue engineering through stem cell-based co-culture

Stem cells are the future in tissue engineering and regeneration. In a co-culture, stem cells not only provide a target cell source with multipotent differentiation capacity, but can also act as assisting cells that promote tissue homeostasis, metabolism, growth and repair. Their incorporation into co-culture systems seems to be important in the creation of complex tissues or organs. In this review, critical aspects of stem cell use in co-culture systems are discussed. Direct and indirect co-culture methodologies used in tissue engineering are described, along with various characteristics of cellular interactions in these systems. Direct cell-cell contact, cell-extracellular matrix interaction and signalling via soluble factors are presented. The advantages of stem cell co-culture strategies and their applications in tissue engineering and regenerative medicine are portrayed through specific examples for several tissues, including orthopaedic soft tissues, bone, heart, vasculature, lung, kidney, liver and nerve. A concise review of the progress and the lessons learned are provided, with a focus on recent developments and their implications. It is hoped that knowledge developed from one tissue can be translated to other tissues. Finally, we address challenges in tissue engineering and regenerative medicine that can potentially be overcome via employing strategies for stem cell co-culture use.

Pre-stem cell formation by non-platelet RNA-containing particle fusion

We found a group of non-platelet RNA-containing particles (NPRCP) in human umbilical cord blood. To understand the origin, characterization and differentiation of NPRCP, we examined cord blood-isolated NPRCP in vitro. The NPRCP range in size from < 1 to 5 μm, have a thin bilayer membrane and various morphological features, contain short RNA and microRNA and express octamer-binding transcription factor 4 (OCT4), sex-determining region Y 2 (SOX2) and DEAD box polypeptide 4 (DDX4). On coculture with nucleated cells from umbilical cord blood, NPRCP fuse to small, active, non-nucleated cells called 'particle fusion-derived non-nucleated cells' (PFDNC). The PFDNC are approximately 8 μm in diameter and are characterized by their twisting movement in culture plates. They can easily move into and out of nucleated cells and finally differentiate into mesenchymal-like cells. In addition, the larger non-nucleated cellular structures that are derived from the aggregation and fusion of multiple NPRCP can further differentiate into large stem cells that also release OCT4- and SOX2-positive non-nucleated small cells. Our data provide strong evidence that NPRCP can fuse into PFDNC, which further differentiate into mesenchymal-like cells. Multiple NPRCP also fuse into other types of large stem cells. We believe that stem cells are derived from NPRCP fusion. There is considerable potential for the use of NPRCP in clinical therapy.

Cardiac stem cells in patients with heart disease

The heart has been regarded as a terminally differentiated organ for decades. There are numerous indicators for the potency of myocardial regeneration, which opens up new avenues for the treatment of heart disease. Cardiac stem cells (CSCs) have been discovered in the human heart and they play a vital role in myocardial regeneration. This review discusses the distribution, properties and proliferation of CSCs in the myocardium of patients with heart disease. Additionally, the potency of myocardial regeneration in patients with heart disease is discussed.

Wound repair and regeneration

The skin is the biggest organ of the human being and has many functions. Therefore, the healing of a skin wound displays an extraordinary mechanism of cascading cellular functions which is unique in nature. As healing and regeneration processes take place in all parts of the human body, this review focuses on the healing processes of the skin and highlights the classical wound healing phases. While regeneration describes the specific substitution of the tissue, i.e. the superficial epidermis, mucosa or fetal skin, skin repair displays an unspecific form of healing in which the wound heals by fibrosis and scar formation. The first stage of acute wound healing is dedicated to hemostasis and the formation of a provisional wound matrix, which occurs immediately after injury and is completed after some hours. Furthermore, this phase initiates the inflammatory process. The inflammatory phase of the wound healing cascade gets activated during the coagulation phase and can roughly be divided into an early phase with neutrophil recruitment and a late phase with the appearance and transformation of monocytes. In the phase of proliferation the main focus of the healing process lies in the recovering of the wound surface, the formation of granulation tissue and the restoration of the vascular network. Therefore, next to the immigration of local fibroblasts along the fibrin network and the beginning of reepithelialization from the wound edges, neovascularization and angiogenesis get activated by capillary sprouting. The formation of granulation tissue stops through apoptosis of the cells, characterizing a mature wound as avascular as well as acellular. During the maturation of the wound the components of the extracellular matrix undergo certain changes. The physiological endpoint of mammalian wound repair displays the formation of a scar, which is directly linked to the extent of the inflammatory process throughout wound healing.

Acute inducible ablation of GRP78 reveals its role in hematopoietic stem cell survival, lymphogenesis and regulation of stress signaling

GRP78, a master regulator of the unfolded protein response (UPR) and cell signaling, is required for inner cell mass survival during early embryonic development. However, little is known about its role in adult hematopoietic stem cells (HSCs) and hematopoiesis. Here we generated a conditional knockout mouse model that acutely deletes Grp78 in the adult hematopoietic system. Acute GRP78 ablation resulted in a significant reduction of HSCs, common lymphoid and myeloid progenitors, and lymphoid cell populations in the mutant mice. The GRP78-null induced reduction of the HSC pool could be attributed to increased apoptosis. Chimeric mice with Grp78 deletion only in the hematopoietic cells also showed a loss of HSCs and lymphopenia, suggesting a cell intrinsic effect. Analysis of GRP78 deficient bone marrow (BM) cells showed constitutive activation of all the major UPR signaling pathways, including activation of eIF2α, ATF6, xbp-1 splicing, as well as caspase activation. A multiplex cytokine assay further revealed alteration in select cytokine and chemokine serum levels in the mutant mice. Collectively, these studies demonstrate that GRP78 plays a pleiotropic role in BM cells and contributes to HSC survival and the maintenance of the lymphoid lineage.

Pluripotent and multipotent stem cells in adult tissues

One of the most intriguing questions in stem cell biology is whether pluripotent stem cells exist in adult tissues. Several groups of investigators employing i) various isolation protocols, ii) detection of surface markers, and iii) experimental in vitro and in vivo models, have reported the presence of cells that possess a pluripotent character in adult tissues. Such cells were assigned various operational abbreviations and names in the literature that added confusion to the field and raised the basic question of whether these are truly distinct or overlapping populations of the same primitive stem cells. Unfortunately, these cells were never characterized side-by-side to address this important issue. Nevertheless, taking into consideration their common features described in the literature, it is very likely that various investigators have described overlapping populations of developmentally early stem cells that are closely related. These different populations of stem cells will be reviewed in this paper.

Reusing and composing models of cell fate regulation of human bone precursor cells

In order to treat osteoporosis and other bone mass disorders it is necessary to understand the regulatory processes that control the cell fate decisions responsible for going from bone precursor cells to bone tissue. Many processes interact to regulate cell division, differentiation and apoptosis. There are models for these basic processes, but not for their interactions. In this work we use the theory of switched systems, reuse and composition of validated models to describe the cell fate decisions leading to bone and fat formation. We describe the differentiation of osteo-adipo progenitor cells by composing its model with differentiation stimuli. We use the activation of the Wnt pathway as stimulus to osteoblast lineage, including regulation of cell division and apoptosis. This model is our first step to simulate physiological responses in silico to treatments for bone mass disorders.

Stability of neural differentiation in human adipose derived stem cells by two induction protocols

There are some evidences for suggesting that adipose derived stem cells (ADSCs) can be differentiated to the fate of neural cell type. ADSCs can be expanded rapidly in vitro and can be obtained by a less invasive method. In this study, we attempted to compare the stability of neural differentiation in human ADSCs by using two induction protocols. Isolated ADSCs were induced into neural-like cells using diverse effects of two specific procedures. For protocol 1, ADSCs were induced by chemical induction. In protocol 2, ADSCs were treated for sphere formation. Then, the singled cells were cultured in neurobasal media supplemented with special components. Differentiated ADSCs were evaluated for Nestin, MAP2 and GFAP expression by immunocytochemistry and semi quantitative RT-PCR techniques. Moreover, MTT assay was employed to detect cell viability and proliferation. Immunocytochemical analysis of both protocols demonstrated that ADSCs had large expression of the neural-specific markers. In RT-PCR, protocol 1 showed the highest percentage of MAP2 expression, but with time passing, the neural like state was reversible. Protocol 2 found with express of Nestin at week 1, however MAP2 and GFAP expression increased after 3 weeks. The neural-like cells produced by protocol 1 led to the further cell death. Comparative analysis showed that neural-like cell differentiation of ADSCs in chemical induction protocol was rapid but transitory, while it was approximately steady in neurosphere formation protocol.

A novel composition for in vitro and in vivo regeneration of skin and connective tissues

The particular combination of polydeoxyribonucleotides, l-carnitine, calcium ions, proteolytic enzyme and other ingredients acts in a synergetic way in the regeneration of skin and connective tissues. This new formulation of active principles was tested in vitro as a cell and tissue culture medium and in vivo for various preparations in support of tissue regeneration. In vitro, the new blend allowed the maintenance of skin biopsies for more than 1 year in eutrophic conditions. Immunocytochemical analyses of fibroblasts isolated from these biopsies confirmed a significant increase of the epidermal and connective wound-healing markers such as collagen type I, collagen type IV, cytokeratin 1 (CK1), CK5, CK10 and CK14 versus controls. To examine the effects of the new compound in vivo, we studied impaired wound healing in genetically diabetic db/db mice. At day 18, diabetic mice treated with the new composition showed 100% closure of wounds and faster healing than mice treated with the other solutions. This complex of vital continuity factors or life-keeping factors could be used as a tissue-preserving solution or a cosmetic/drug/medical device to accelerate wound healing in the treatment of patients with deficient wound repair to promote the regeneration of cutaneous and connective tissues (injuries-wound, dermatitis) and prevent the recurrent relapses.

Adult peripheral blood mononuclear cells transdifferentiate in vitro and integrate into the retina in vivo

Adult peripheral blood-derived cells are able to differentiate into a variety of cell types, including nerve cells, liver-like cells and epithelial cells. However, their differentiation into retina-like cells is controversial. In the present study, transdifferentiation potential of human adult peripheral blood mononuclear cells into retina-like cells and integration into the retina of mice were investigated. Freshly isolated adult peripheral blood mononuclear cells were divided into two groups: cells in group I were cultured in neural stem cell medium, and cells in group II were exposed to conditioned medium from rat retinal tissue culture. After 5 days, several distinct cell morphologies were observed, including standard mononuclear, neurons with one or two axons and elongated glial-like cells. Immunohistochemical analysis of neural stem cell, neuron and retina cell markers demonstrated that cells in both groups were nestin-, MAP2 (microtubule-associated protein)- and GFAP (glial fibrillary acidic protein)-positive. Flow cytometry results suggested a significant increase in nestin-, MAP2- and CD16-positive cells in group I and nestin-, GFAP-, MAP2-, vimentin- and rhodopsin-positive cells in group II. To determine survival, migration and integration in vivo, cell suspensions (containing group I or group II cells) were injected into the vitreous or the peritoneum. Tissue specimens were obtained and immunostained 4 weeks after transplantation. We found that cells delivered by intravitreal injection integrated into the retina. Labelled cells were not detected in the retina of mice receiving differentiated cells by intraperitoneal injection, but cells (groups I and II) were detected in the liver and spleen. Our findings revealed that human adult peripheral blood mononuclear cells could be induced to transdifferentiate into neural precursor cells and retinal progenitor cells in vitro, and the differentiated peripheral blood mononuclear cells can migrate and integrate into the retina in vivo.

Stability analysis of multi-compartment models for cell production systems

We study two- and three-compartment models of a hierarchical cell production system with cell division regulated by the level of mature cells. We investigate the structure of equilibria with respect to parameters as well as local stability properties for the equilibria. To interpret the results we adapt the concept of reproduction numbers, which is well known in ecology, to stem cell population dynamics. In the two-compartment model, the positive equilibrium is stable wherever it exists. In the three-compartment model, we find that the intermediate stage of differentiation is responsible for the emergence of an instability region in the parameter plane. Moreover, we prove that this region shrinks as the mortality rate for mature cells increases and discuss this result.

Notch signaling in mammalian hematopoietic stem cells

Notch is a crucial cell signaling pathway in metazoan development. By means of cell-cell interactions, Notch signaling regulates cellular identity, proliferation, differentiation and apoptosis. Within the last decade, numerous studies have shown an important role for this pathway in the development and homeostasis of mammalian stem cell populations. Hematopoietic stem cells (HSCs) constitute a well-defined population that shows self-renewal and multi-lineage differentiation potential, with the clinically relevant capacity to repopulate the hematopoietic system of an adult organism. Here, we review the emergence, development and maintenance of HSCs during mammalian embryogenesis and adulthood, with respect to the role of Notch signaling in hematopoietic biology.

The endoplasmic reticulum chaperone protein GRP94 is required for maintaining hematopoietic stem cell interactions with the adult bone marrow niche

Hematopoietic stem cell (HSC) homeostasis in the adult bone marrow (BM) is regulated by both intrinsic gene expression products and interactions with extrinsic factors in the HSC niche. GRP94, an endoplasmic reticulum chaperone, has been reported to be essential for the expression of specific integrins and to selectively regulate early T and B lymphopoiesis. In GRP94 deficient BM chimeras, multipotent hematopoietic progenitors persisted and even increased, however, the mechanism is not well understood. Here we employed a conditional knockout (KO) strategy to acutely eliminate GRP94 in the hematopoietic system. We observed an increase in HSCs and granulocyte-monocyte progenitors in the Grp94 KO BM, correlating with an increased number of colony forming units. Cell cycle analysis revealed that a loss of quiescence and an increase in proliferation led to an increase in Grp94 KO HSCs. This expansion of the HSC pool can be attributed to the impaired interaction of HSCs with the niche, evidenced by enhanced HSC mobilization and severely compromised homing and lodging ability of primitive hematopoietic cells. Transplanting wild-type (WT) hematopoietic cells into a GRP94 null microenvironment yielded a normal hematology profile and comparable numbers of HSCs as compared to WT control, suggesting that GRP94 in HSCs, but not niche cells, is required for maintaining HSC homeostasis. Investigating this, we further determined that there was a near complete loss of integrin α4 expression on the cell surface of Grp94 KO HSCs, which showed impaired binding with fibronectin, an extracellular matrix molecule known to play a role in mediating HSC-niche interactions. Furthermore, the Grp94 KO mice displayed altered myeloid and lymphoid differentiation. Collectively, our studies establish GRP94 as a novel cell intrinsic factor required to maintain the interaction of HSCs with their niche, and thus regulate their physiology.

Purified hematopoietic stem cell transplantation: the next generation of blood and immune replacement

Replacement of disease-causing stem cells with healthy ones has been achieved clinically via hematopoietic cell transplantation (HCT) for the last 40 years, as a treatment modality for a variety of cancers and immunodeficiencies with moderate, but increasing, success. This procedure has traditionally included transplantation of mixed hematopoietic populations that include hematopoietic stem cells (HSC) and other cells, such as T cells. This article explores and delineates the potential expansion of this technique to treat a variety of inherited diseases of immune function, the current barriers in HCT and pure HSC transplantation, and the up-and-coming strategies to combat these obstacles.

Epigenetic regulation of aging stem cells

The function of adult tissue-specific stem cells declines with age, which may contribute to the physiological decline in tissue homeostasis and the increased risk of neoplasm during aging. Old stem cells can be 'rejuvenated' by environmental stimuli in some cases, raising the possibility that a subset of age-dependent stem cell changes is regulated by reversible mechanisms. Epigenetic regulators are good candidates for such mechanisms, as they provide a versatile checkpoint to mediate plastic changes in gene expression and have recently been found to control organismal longevity. Here, we review the importance of chromatin regulation in adult stem cell compartments. We particularly focus on the roles of chromatin-modifying complexes and transcription factors that directly impact chromatin in aging stem cells. Understanding the regulation of chromatin states in adult stem cells is likely to have important implications for identifying avenues to maintain the homeostatic balance between sustained function and neoplastic transformation of aging stem cells.

Scarless fetal wound healing: a basic science review

SUMMARY

Scar formation is a major medical problem that can have devastating consequences for patients. The adverse physiological and psychological effects of scars are broad, and there are currently no reliable treatments to prevent scarring. In contrast to adult wounds, early gestation fetal skin wounds repair rapidly and in the absence of scar formation. Despite extensive investigation, the exact mechanisms of scarless fetal wound healing remain largely unknown. For some time, it has been known that significant differences exist among the extracellular matrix, inflammatory response, cellular mediators, and gene expression profiles of fetal and postnatal wounds. These differences may have important implications in scarless wound repair.

Purified hematopoietic stem cell transplantation: the next generation of blood and immune replacement

Replacement of disease-causing stem cells with healthy ones has been achieved clinically via hematopoietic cell transplantation (HCT) for the last 40 years, as a treatment modality for a variety of cancers and immunodeficiencies with moderate, but increasing, success. This procedure has traditionally included transplantation of mixed hematopoietic populations that include hematopoietic stem cells (HSC) and other cells, such as T cells. This article explores and delineates the potential expansion of this technique to treat a variety of inherited diseases of immune function, the current barriers in HCT and pure HSC transplantation, and the up-and-coming strategies to combat these obstacles.

Biological characteristics of stem cells from foetal, cord blood and extraembryonic tissues

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacity in vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.

Germ plasm-like Dot cells maintain their wound regenerative function after in vitro expansion

1. Wounds in fetal skin heal without scarring; however, the mechanism for this is unknown. We have identified a novel group of protein and nucleotides-positive particles in fetal and adult mouse blood and in human blood, and termed them 'Dot cells'. Freshly isolated Dot cells regenerate wounds with less scarring and can be cultured without feeder layers. 2. Because the morphology of Dot cells has never been described, in the present study we describe the specific characterizations of Dot cells, including their growth pattern in vitro, and their expressions of stem cell markers using fluorescent cell sorting analyses and immunofluorescent histology. Our data indicates that cultured Dot cells express stem cell surface markers and embryonic stem cell transcription markers, such as Oct4, Nanog and Sox-2. In addition, Dot cells express VASA, the germ plasm specific marker. 3. To confirm whether Dot cells maintain their wound regenerative activity after in vitro expansion, in vitro cultured Dot cells were transplanted to wounded mice. Dot cells from albino mice maintain their wound regenerative activities after intravenous transplantation to black-background diabetic mice. In addition, Dot cells regenerate both the epithelial and dermal cells in the wounds of wild-type mice. The regenerated hair follicles, smooth muscle and dermal tissues express transiently to VASA. 4. Our data demonstrate that Dot cells are newly identified organisms located in the blood and bone marrow of mammals. They express germ cell, embryonic stem cell and adult stem cell markers. Dot cells maintain their regenerative function after in vitro expansion.

Comparison of the efficiencies of three neural induction protocols in human adipose stromal cells

The aim of this study was to compare the neural differentiation potential and the expression of neurotrophic factors (NTFs) in differentiated adipose-derived stem cells (ADSCs) using three established induction protocols, serum free (Protocol 1), chemical reagents (Protocol 2), and spontaneous (Protocol 3) protocols. Protocol 1 produced the highest percentage of mature neural-like cells (MAP2ab(+)). Protocol 2 showed the highest percentage of immature neural-like cells (beta-tubulin III(+)), but the neural-like state was transient and reversible. Protocol 3 caused ADSCs to differentiate spontaneously into immature neural-like cells, but not into mature neural cell types. The neural-like cells produced by Protocol 1 lived the longest in culture with little cell death, but Protocol 2 and 3 led to the significant cell death. Therefore, Protocol 1 is the most efficient among these protocols. Additionally, soon after differentiation, the mRNA levels of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in dADSCs were sharply decreased by Protocol 1 and 2 (acute induction protocol), but not by Protocol 3 (chronic induction protocol). The results indicate that NTFs played an important role in neural differentiation via acute responses to NGF and BDNF, but not chronically during the transdifferentiation process.

Tissue-derived stem and progenitor cells

The characterization and isolation of various stem cell populations, from embryonic through tissue-derived stem cells, have led a rapid growth in the field of stem cell research. These research efforts have often been interrelated as to the markers that identify a select cell population are frequently analyzed to determine their expression in cells of distinct organs/tissues. In this review, we will expand the current state of research involving select tissue-derived stem cell populations including the liver, central nervous system, and cardiac tissues as examples of the success and challenges in this field of research. Lastly, the challenges of clinical therapies will be discussed as it applies to these unique cell populations.

Fetal skin wound healing

The developing fetus has the ability to heal wounds by regenerating normal epidermis and dermis with restoration of the extracellular matrix (ECM) architecture, strength, and function. In contrast, adult wounds heal with fibrosis and scar. Scar tissue remains weaker than normal skin with an altered ECM composition. Despite extensive investigation, the mechanism of fetal wound healing remains largely unknown. We do know that early in gestation, fetal skin is developing at a rapid pace and the ECM is a loose network facilitating cellular migration. Wounding in this unique environment triggers a complex cascade of tightly controlled events culminating in a scarless wound phenotype of fine reticular collagen and abundant hyaluronic acid. Comparison between postnatal and fetal wound healing has revealed differences in inflammatory response, cellular mediators, cytokines, growth factors, and ECM modulators. Investigation into cell signaling pathways and transcription factors has demonstrated differences in secondary messenger phosphorylation patterns and homeobox gene expression. Further research may reveal novel genes essential to scarless repair that can be manipulated in the adult wound and thus ameliorate scar.

Mesenchymal stem cells: emerging therapy for Duchenne muscular dystrophy

Multipotent cells that can give rise to bone, cartilage, fat, connective tissue, and skeletal and cardiac muscle are termed mesenchymal stem cells. These cells were first identified in the bone marrow, distinct from blood-forming stem cells. Based on the embryologic derivation, availability, and various pro-regenerative characteristics, research exploring their use in cell therapy shows great promise for patients with degenerative muscle diseases and a number of other conditions. In this review, the authors explore the potential for mesenchymal stem cell therapy in the emerging field of regenerative medicine with a focus on treatment for Duchenne muscular dystrophy.

Coherent activation of a synthetic mammalian gene network

A quantitative analysis of naturally-occurring regulatory networks, especially those present in mammalian cells, is difficult due to their high complexity. Much simpler gene networks can be engineered in model organisms and analyzed as isolated regulatory modules. Recently, several synthetic networks have been constructed in mammalian systems. However, most of these engineered mammalian networks have been characterized using steady-state population level measurements. Here, we use an integrated experimental-computational approach to analyze the dynamical response of a synthetic positive feedback network in individual mammalian cells. We observe a switch-like activation of the network with variable delay times in individual cells. In agreement with a stochastic model of the network, we find that increasing the strength of the positive feedback results in a decrease in the mean delay time and a more coherent activation of individual cells. Our results are important for gaining insight into biological processes which rely on positive feedback regulation.

Human cord blood CD133+ stem cells transplanted to nod-scid mice provide conditions for regeneration of olfactory neuroepithelium after permanent damage induced by dichlobenil

The herbicide dichlobenil selectively causes necrosis of the dorsomedial part of olfactory neuroepithelium (NE) with permanent damage to the underlying mucosa, whereas the lateral part of the olfactory region and the nasal respiratory mucosa remain undamaged. We investigated here whether human umbilical cord blood CD133(+) stem cells (HSC) injected intravenously to nod-scid mice pretreated with dichlobenil may engraft the olfactory mucosa and contribute to the regeneration of the damaged NE. We tested HLA-DQalpha1 DNA and three human microsatellites (Combined DNA Index System) as indicators of engrafted cells, finding polymerase chain reaction evidence of chimaerism in various tissues of the host, including the olfactory mucosa and bulb, at 7 and 31 days following HSC transplantation. Histology, immunohistochemistry, and lectin staining revealed the morphological recovery of the dorsomedial region of the NE in dichlobenil-treated mice that received HSC, contrasting with the lack of regeneration in similarly injured areas as these remained damaged in control nontransplanted mice. FISH analysis, to detect human genomic sequences from different chromosomes, confirmed persistent engraftment of the regenerating olfactory area with chimeric cells. Electro-olfactograms in response to odorants, to test the functionality of the olfactory NE, confirmed the functional damage of the dorsomedial area in dichlobenil-treated mice and the functional recovery of the same area in transplanted mice. These findings support the concept that transplanted HSC migrating to the damaged olfactory area provide conditions facilitating the recovery from olfactory receptor cell loss.