Neural stem cells for the treatment of disorders of the enteric nervous system: strategies and challenges

Hypoxia-Inducible Factor 1α Stabilization Restores Epigenetic Control of Nitric Oxide Synthase 1 Expression and Reverses Gastroparesis in Female Diabetic Mice

BACKGROUND & AIMS

Although depletion of neuronal nitric oxide synthase (NOS1)-expressing neurons contributes to gastroparesis, stimulating nitrergic signaling is not an effective therapy. We investigated whether hypoxia-inducible factor 1α (HIF1A), which is activated by high O2 consumption in central neurons, is a Nos1 transcription factor in enteric neurons and whether stabilizing HIF1A reverses gastroparesis.

METHODS

Mice with streptozotocin-induced diabetes, human and mouse tissues, NOS1+ mouse neuroblastoma cells, and isolated nitrergic neurons were studied. Gastric emptying of solids and volumes were determined by breath test and single-photon emission computed tomography, respectively. Gene expression was analyzed by RNA-sequencing, microarrays, immunoblotting, and immunofluorescence. Epigenetic assays included chromatin immunoprecipitation sequencing (13 targets), chromosome conformation capture sequencing, and reporter assays. Mechanistic studies used Cre-mediated recombination, RNA interference, and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9)-mediated epigenome editing.

RESULTS

HIF1A signaling from physiological intracellular hypoxia was active in mouse and human NOS1+ myenteric neurons but reduced in diabetes. Deleting Hif1a in Nos1-expressing neurons reduced NOS1 protein by 50% to 92% and delayed gastric emptying of solids in female but not male mice. Stabilizing HIF1A with roxadustat (FG-4592), which is approved for human use, restored NOS1 and reversed gastroparesis in female diabetic mice. In nitrergic neurons, HIF1A up-regulated Nos1 transcription by binding and activating proximal and distal cis-regulatory elements, including newly discovered super-enhancers, facilitating RNA polymerase loading and pause-release, and by recruiting cohesin to loop anchors to alter chromosome topology.

CONCLUSIONS

Pharmacologic HIF1A stabilization is a novel, translatable approach to restoring nitrergic signaling and treating diabetic gastroparesis. The newly recognized effects of HIF1A on chromosome topology may provide insights into physioxia- and ischemia-related organ function.

Genetically engineered neural stem cells (NSCs) therapy for neurological diseases; state-of-the-art

Neural stem cells (NSCs) are multipotent stem cells with remarkable self-renewal potential and also unique competencies to differentiate into neurons, astrocytes, and oligodendrocytes (ODCs) and improve the cellular microenvironment. In addition, NSCs secret diversity of mediators, including neurotrophic factors (e.g., BDNF, NGF, GDNF, CNTF, and NT-3), pro-angiogenic mediators (e.g., FGF-2 and VEGF), and anti-inflammatory biomolecules. Thereby, NSCs transplantation has become a reasonable and effective treatment for various neurodegenerative disorders by their capacity to induce neurogenesis and vasculogenesis and dampen neuroinflammation and oxidative stress. Nonetheless, various drawbacks such as lower migration and survival and less differential capacity to a particular cell lineage concerning the disease pathogenesis hinder their application. Thus, genetic engineering of NSCs before transplantation is recently regarded as an innovative strategy to bypass these hurdles. Indeed, genetically modified NSCs could bring about more favored therapeutic influences post-transplantation in vivo, making them an excellent option for neurological disease therapy. This review for the first time offers a comprehensive review of the therapeutic capability of genetically modified NSCs rather than naïve NSCs in neurological disease beyond brain tumors and sheds light on the recent progress and prospect in this context.

In vitro investigation of the differentiation of enteric neural crest-derived cells following transplantation of aganglionic gut in a mouse model

PURPOSE

Cell therapy is a promising approach to treat enteric neuropathies such as Hirschsprung disease (HD). Recent studies have reported that enteric neurons derived from stem cells (ENCCs) can be grafted into the HD colon. Thus, we investigated the migration and generation of enteric neurospheres from SOX10-VENUS⁺ mice after transplantation into control or Ednrb KO mice, which are a model of HD.

METHODS

Single-cell suspensions were isolated from the fetal guts of SOX10-VENUS⁺ mice E13.5 and dissociated. These cells were cultured for 7 days under non-adherent conditions to generate neurospheres, which were co-cultured with dissociated control or SOX10-VENUS^- Ednrb KO mouse gut on E13.5. 4 days later, these cells were fixed and the expression of the neuronal marker, Tuj1, was evaluated.

RESULTS

Transplanted neurospheres had undergone abundant neuronal migration and differentiation of ENCCs in the control gut compared with the HD gut. The average length and intersections were significantly decreased in HD colon compared with controls (p < 0.05), and a similar pattern was observed in the HD small intestine (p < 0.05).

CONCLUSIONS

We demonstrated that transplanted ENCCs did not differentiate properly in HD gut. These results highlight the importance of the neuronal environment in the recipient gut for enteric nervous system development.

Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Stem cell-based therapy raises hopes for a better approach to promoting tissue repair and functional recovery. However, transplanted stem cells show a high death percentage, creating challenges to successful transplantation and prognosis. Thus, it is necessary to investigate the mechanisms underlying stem cell death, such as apoptotic cascade activation, excessive autophagy, inflammatory response, reactive oxygen species, excitotoxicity, and ischemia/hypoxia. Targeting the molecular pathways involved may be an efficient strategy to enhance stem cell viability and maximize transplantation success. Notably, a more complex network of cell death receives more attention than one crucial pathway in determining stem cell fate, highlighting the challenges in exploring mechanisms and therapeutic targets. In this review, we focus on programmed cell death in transplanted stem cells. We also discuss some promising strategies and challenges in promoting survival for further study.

Resveratrol promotes the survival and neuronal differentiation of hypoxia-conditioned neuronal progenitor cells in rats with cerebral ischemia

Hypoxia conditioning could increase the survival of transplanted neuronal progenitor cells (NPCs) in rats with cerebral ischemia but could also hinder neuronal differentiation partly by suppressing mitochondrial metabolism. In this work, the mitochondrial metabolism of hypoxia-conditioned NPCs (hcNPCs) was upregulated via the additional administration of resveratrol, an herbal compound, to resolve the limitation of hypoxia conditioning on neuronal differentiation. Resveratrol was first applied during the in vitro neuronal differentiation of hcNPCs and concurrently promoted the differentiation, synaptogenesis, and functional development of neurons derived from hcNPCs and restored the mitochondrial metabolism. Furthermore, this herbal compound was used as an adjuvant during hcNPC transplantation in a photothrombotic stroke rat model. Resveratrol promoted neuronal differentiation and increased the long-term survival of transplanted hcNPCs. 18-fluorine fluorodeoxyglucose positron emission tomography and rotarod test showed that resveratrol and hcNPC transplantation synergistically improved the neurological and metabolic recovery of stroke rats. In conclusion, resveratrol promoted the neuronal differentiation and therapeutic efficiency of hcNPCs in stroke rats via restoring mitochondrial metabolism. This work suggested a novel approach to promote the clinical translation of NPC transplantation therapy.

Inhibition of ROCK signaling pathway accelerates enteric neural crest cell-based therapy after transplantation in a rat hypoganglionic model

BACKGROUND

Hirschsprung's disease (HSCR) is a congenital gastrointestinal disorder, characterized by enteric ganglia absence in part or entire of the colon, due to abnormal colonization and migration of enteric neural crest cells (ENCCs) during development. Currently, besides surgery which is the main therapy for HSCR, the potential of stem cell-based transplantation was investigated as an alternative option. Although promising, it has limitations, including poor survival, differentiation, and migration of the grafted cells. We hypothesized that modulation of extracellular factors during transplantation could promote ENCCs proliferation and migration, leading to increased transplantation efficiency. Considering that the RhoA/ROCK pathway is highly involved in cytoskeletal dynamics and neurite growth, our study explored the effect of inhibition of this pathway to improve the success of ENCCs transplantation.

METHODS

Enteric neural crest cells were isolated from rat embryos and labeled with a GFP-tag. Cell viability, apoptosis, differentiation, and migration assays were performed with and without RhoA/ROCK inhibition. Labeled ENCCs were transplanted into the muscle layer of an induced hypoganglionic rat model followed by intraperitoneal injections of ROCK inhibitor. The transplanted segments were collected 3 weeks after for histological analysis.

KEY RESULTS

Our results showed that inhibition of ROCK increased viable cell number, differentiation, and migration of ENCCs in vitro. Moreover, transplantation of labeled ENCCs into the hypoganglionic model showed enhanced distribution of grafted ENCCs, upon treatment with ROCK inhibitor.

CONCLUSIONS AND INFERENCES

ROCK inhibitors influence ENCCs growth and migration in vitro and in vivo, and should be considered to improve the efficiency of ENCCs transplantation.

Postnatal human enteric neurospheres show a remarkable molecular complexity

BACKGROUND

The enteric nervous system (ENS), a complex network of neurons and glial cells, coordinates major gastrointestinal functions. Impaired development or secondary aberrations cause severe enteric neuropathies. Neural crest-derived stem cells as well as enteric neuronal progenitor cells, which form enteric neurospheres, represent a promising tool to unravel molecular pathomechanisms and to develop novel therapy options. However, so far little is known about the detailed cellular composition and the proportional distribution of enteric neurospheres. Comprehensive knowledge will not only be essential for basic research but also for prospective cell replacement therapies to restore or to improve enteric neuronal dysfunction.

METHODS

Human enteric neurospheres were generated from three individuals with varying age. For detailed molecular characterization, nCounter target gene expression analyses focusing on stem, progenitor, neuronal, glial, muscular, and epithelial cell markers were performed. Corresponding archived paraffin-embedded individuals' specimens were analyzed accordingly.

KEY RESULTS

Our data revealed a remarkable molecular complexity of enteric neurospheres and archived specimens. Amongst the expression of multipotent stem cell, progenitor cell, neuronal, glial, muscle and epithelial cell markers, moderate levels for the pluripotency marker POU5F1 were observed. Furthermore, besides the interindividual variability, we identified highly distinct intraindividual expression profiles.

CONCLUSIONS & INFERENCES

Our results emphasize the assessment of molecular signatures to be essential for standardized use, optimization of experimental approaches, and elimination of potential risk factors, as the formation of tumors. Our study pipeline may serve as a blueprint implemented into the characterization procedure of enteric neurospheres for various future applications.

Cotransplantation of neuroepithelial stem cells with interstitial cells of Cajal improves neuronal differentiation in a rat aganglionic model

BACKGROUND

Recent advances have raised the possibility of treating Hirschsprung's disease (HSCR) with transplanted neural stem cells. Although these cells have been shown to migrate and differentiate after transplantation, the restoration of intestinal motility by grafted cells is also mediated via the interstitial cells of Cajal (ICCs). We therefore aimed to evaluate the effect of cografting with ICC on neural stem cells after transplanted into aganglionic bowel.

METHODS

Neuroepithelial stem cells (NESCs) and ICCs were isolated from neural tube of embryonic rat (embryonic day 11.5) and colon of neonatal rats respectively. After cotransplantation into the benzalkonium chloride-induced rat aganglionic colon, survival and differentiation of the implanted cells were assessed 8weeks posttransplantation using immunofluorescence and Western blotting. Colonic motility was assessed by measuring the changes of intraluminal pressure responding to inflating stimulation and the response of muscle strips to electrical field stimulation.

RESULTS

Cotransplantation with ICC accelerated neuronal differentiation compared with transplantation of NESCs alone. Moreover, the contractile response to inflation and EFS-induced reaction of the colon after coimplantation were successfully evoked.

CONCLUSIONS

These data indicate that reconstitution of elements in the intestinal environment such as ICC enhances efficacy of NESCs therapy. This may aid development of a stem cell-based treatment for HSCR.

Exposure to GDNF Enhances the Ability of Enteric Neural Progenitors to Generate an Enteric Nervous System

Cell therapy is a promising approach to generate an enteric nervous system (ENS) and treat enteric neuropathies. However, for translation to the clinic, it is highly likely that enteric neural progenitors will require manipulation prior to transplantation to enhance their ability to migrate and generate an ENS. In this study, we examine the effects of exposure to several factors on the ability of ENS progenitors, grown as enteric neurospheres, to migrate and generate an ENS. Exposure to glial-cell-line-derived neurotrophic factor (GDNF) resulted in a 14-fold increase in neurosphere volume and a 12-fold increase in cell number. Following co-culture with embryonic gut or transplantation into the colon of postnatal mice in vivo, cells derived from GDNF-treated neurospheres showed a 2-fold increase in the distance migrated compared with controls. Our data show that the ability of enteric neurospheres to generate an ENS can be enhanced by exposure to appropriate factors.

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Enteric neurospheres are likely to require manipulation for clinical applications

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Exposure to GDNF increased the size and cell number in enteric neurospheres

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GDNF-treated neurospheres showed enhanced migration after transplantation in vivo

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Manipulation of enteric neurospheres can enhance the generation of enteric neurons

Recent advances in regenerative medicine to treat enteric neuropathies: use of human cells

As current options for treating most enteric neuropathies are either non-effective or associated with significant ongoing problems, cell therapy is a potential attractive possibility to treat congenital and acquired neuropathies. Studies using animal models have shown that following transplantation of enteric neural progenitors into the bowel of recipients, the transplanted cells migrate, proliferate, and generate neurons that are electrically active and receive synaptic inputs. Recent studies have transplanted human enteric neural progenitors into the mouse colon and shown engraftment. In this article, we summarize the significance of these recent advances and discuss priorities for future research that might lead to the use of regenerative medicine to treat enteric neuropathies in the clinic.

Combination of exogenous cell transplantation and 5-HT4 receptor agonism induce endogenous enteric neural crest-derived cells in a rat hypoganglionosis model

Enteric neural crest-derived cells (ENCCs) can migrate into endogenous ganglia and differentiate into progeny cells, and have even partially rescued bowel function; however, poor reliability and limited functional recovery after ENCC transplantation have yet to be addressed. Here, we investigated the induction of endogenous ENCCs by combining exogenous ENCC transplantation with a 5-HT₄ receptor agonist mosapride in a rat model of hypoganglionosis, established by benzalkonium chloride treatment. ENCCs, isolated from the gut of newborn rats, were labeled with a lentiviral eGFP reporter. ENCCs and rats were treated with the 5-HT₄ receptor agonist/antagonist. The labeled ENCCs were then transplanted into the muscular layer of benzalkonium chloride-treated colons. At given days post-intervention, colonic tissue samples were removed for histological analysis. ENCCs and neurons were detected by eGFP expression and immunoreactivity to p75^NTR and peripherin, respectively. eGFP-positive ENCCs and neurons could survive and maintain levels of fluorescence after transplantation. With longer times post-intervention, the number of peripherin-positive cells gradually increased in all groups. Significantly more peripherin-positive cells were found following ENCCs plus mosapride treatment, compared with the other groups. These results show that exogenous ENCCs combined with the 5-HT₄ receptor agonist effectively induced endogenous ENCCs proliferation and differentiation in a rat hypoganglionosis model.

Engraftment of enteric neural progenitor cells into the injured adult brain

Background

A major area of unmet need is the development of strategies to restore neuronal network systems and to recover brain function in patients with neurological disease. The use of cell-based therapies remains an attractive approach, but its application has been challenging due to the lack of suitable cell sources, ethical concerns, and immune-mediated tissue rejection. We propose an innovative approach that utilizes gut-derived neural tissue for cell-based therapies following focal or diffuse central nervous system injury.

Results

Enteric neuronal stem and progenitor cells, able to differentiate into neuronal and glial lineages, were isolated from the postnatal enteric nervous system and propagated in vitro. Gut-derived neural progenitors, genetically engineered to express fluorescent proteins, were transplanted into the injured brain of adult mice. Using different models of brain injury in combination with either local or systemic cell delivery, we show that transplanted enteric neuronal progenitor cells survive, proliferate, and differentiate into neuronal and glial lineages in vivo. Moreover, transplanted cells migrate extensively along neuronal pathways and appear to modulate the local microenvironment to stimulate endogenous neurogenesis.

Conclusions

Our findings suggest that enteric nervous system derived cells represent a potential source for tissue regeneration in the central nervous system. Further studies are needed to validate these findings and to explore whether autologous gut-derived cell transplantation into the injured brain can result in functional neurologic recovery.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-016-0238-y) contains supplementary material, which is available to authorized users.

Transplantation of amniotic fluid-derived neural stem cells as a potential novel therapy for Hirschsprung's disease

BACKGROUND/PURPOSE

We have previously shown that embryonic enteric neural stem cells (NSCs) isolated from the intestine colonize aganglionic intestine upon transplantation, but posttransplantation cell survival limits efficacy. The aims of this study were to investigate whether transplantation of amniotic fluid (AF)-derived NSCs could improve survival of the engrafted cells and promote functional recovery of the diseased colon.

METHODS

AF cells were induced into NSCs with neurogenic medium, and further differentiated into neurons and glial cells. Ednrb knockout mice received an intestinal intramuscular injection of 20,000 AF-derived NSCs into the aganglionic colon. Engrafted cells were visualized and characterized by immunohistochemistry for GFP, neuronal, and glial cell markers. Colonic motility was quantified by colonic bead expulsion time.

RESULTS

AF-derived NSCs had increased expression levels of the NSC marker Nestin and the glial cell marker GFAP compared to enteric NSCs. Transplanted AF-derived NSCs had decreased apoptosis and increased survival compared to enteric NSCs. Colonic motility was significantly improved in Ednrb knockout mice transplanted with AF-derived NSCs, as demonstrated by significantly decreased colonic bead expulsion time.

CONCLUSION

AF-derived NSCs have enhanced survival upon transplantation into a defective enteric nervous system. Transplantation of AF-derived NSCs may represent a potential novel future therapy for the treatment of Hirschsprung's disease.

In Vitro Conditioned Bone Marrow-Derived Mesenchymal Stem Cells Promote De Novo Functional Enteric Nerve Regeneration, but Not Through Direct-Transdifferentiation

Injury or neurodegenerative disorders of the enteric nervous system (ENS) cause gastrointestinal dysfunctions for which there is no effective therapy. This study, using the benzalkonium chloride-induced rat gastric denervation model, aimed to determine whether transplantation of bone marrow-derived mesenchymal stem cells (BMSC) could promote ENS neuron regeneration and if so, to elucidate the mechanism. Fluorescently labeled BMSC, isolated from either WT (BMSC labeled with bis-benzimide [BBM]) or green fluorescent protein (GFP)-transgenic rats, were preconditioned in vitro using fetal gut culture media containing glial cell-derived neurotrophic factor (GDNF), and transplanted subserosally into the denervated area of rat pylorus. In the nerve-ablated pylorus, grafted BMSC survived and migrated from the subserosa to the submucosa 28 days after transplantation, without apparent dedifferentiation. A massive number of PGP9.5/NSE/HuC/D/Tuj1-positive (but GFP- and BBM-negative) neurons were effectively regenerated in denervated pylorus grafted with preconditioned BMSC, suggesting that they were regenerated de novo, not originating from trans-differentiation of the transplanted BMSC. BMSC transplantation restored both basal pyloric contractility and electric field stimulation-induced relaxation. High levels of GDNF were induced in both in vitro-preconditioned BMSC as well as the previously denervated pylorus after transplantation of preconditioned BMSC. Thus, a BMSC-initiated GDNF-positive feedback mechanism is suggested to promote neuron regeneration and growth. In summary, we have demonstrated that allogeneically transplanted preconditioned BMSC initiate de novo regeneration of gastric neuronal cells/structures that in turn restore gastric contractility in pylorus-denervated rats. These neuronal structures did not originate from the grafted BMSC. Our data suggest that preconditioned allogeneic BMSC may have therapeutic value in treating enteric nerve disorders.

Enteric nervous system abnormalities are present in human necrotizing enterocolitis: potential neurotransplantation therapy

Introduction

Intestinal dysmotility following human necrotizing enterocolitis suggests that the enteric nervous system is injured during the disease. We examined human intestinal specimens to characterize the enteric nervous system injury that occurs in necrotizing enterocolitis, and then used an animal model of experimental necrotizing enterocolitis to determine whether transplantation of neural stem cells can protect the enteric nervous system from injury.

Methods

Human intestinal specimens resected from patients with necrotizing enterocolitis (n = 18), from control patients with bowel atresia (n = 8), and from necrotizing enterocolitis and control patients undergoing stoma closure several months later (n = 14 and n = 6 respectively) were subjected to histologic examination, immunohistochemistry, and real-time reverse-transcription polymerase chain reaction to examine the myenteric plexus structure and neurotransmitter expression. In addition, experimental necrotizing enterocolitis was induced in newborn rat pups and neurotransplantation was performed by administration of fluorescently labeled neural stem cells, with subsequent visualization of transplanted cells and determination of intestinal integrity and intestinal motility.

Results

There was significant enteric nervous system damage with increased enteric nervous system apoptosis, and decreased neuronal nitric oxide synthase expression in myenteric ganglia from human intestine resected for necrotizing enterocolitis compared with control intestine. Structural and functional abnormalities persisted months later at the time of stoma closure. Similar abnormalities were identified in rat pups exposed to experimental necrotizing enterocolitis. Pups receiving neural stem cell transplantation had improved enteric nervous system and intestinal integrity, differentiation of transplanted neural stem cells into functional neurons, significantly improved intestinal transit, and significantly decreased mortality compared with control pups.

Conclusions

Significant injury to the enteric nervous system occurs in both human and experimental necrotizing enterocolitis. Neural stem cell transplantation may represent a novel future therapy for patients with necrotizing enterocolitis.

Neural stem cell therapies for enteric nervous system disorders

The enteric nervous system is vulnerable to a range of congenital and acquired disorders that disrupt the function of its neurons or lead to their loss. The resulting enteric neuropathies are some of the most challenging clinical conditions to manage. Neural stem cells offer the prospect of a cure given their potential ability to replenish missing or dysfunctional neurons. This article discusses diseases that might be targets for stem cell therapies and the barriers that could limit treatment application. We explore various sources of stem cells and the proof of concept for their use. The critical steps that remain to be addressed before these therapies can be used in patients are also discussed. Key milestones include the harvesting of neural stem cells from the human gut and the latest in vivo transplantation studies in animals. The tremendous progress in the field has brought experimental studies exploring the potential of stem cell therapies for the management of enteric neuropathies to the cusp of clinical application.

In vivo transplantation of neurosphere-like bodies derived from the human postnatal and adult enteric nervous system: a pilot study

Recent advances in the in vitro characterization of human adult enteric neural progenitor cells have opened new possibilities for cell-based therapies in gastrointestinal motility disorders. However, whether these cells are able to integrate within an in vivo gut environment is still unclear. In this study, we transplanted neural progenitor-containing neurosphere-like bodies (NLBs) in a mouse model of hypoganglionosis and analyzed cellular integration of NLB-derived cell types and functional improvement. NLBs were propagated from postnatal and adult human gut tissues. Cells were characterized by immunohistochemistry, quantitative PCR and subtelomere fluorescence in situ hybridization (FISH). For in vivo evaluation, the plexus of murine colon was damaged by the application of cationic surfactant benzalkonium chloride which was followed by the transplantation of NLBs in a fibrin matrix. After 4 weeks, grafted human cells were visualized by combined in situ hybridization (Alu) and immunohistochemistry (PGP9.5, GFAP, SMA). In addition, we determined nitric oxide synthase (NOS)-positive neurons and measured hypertrophic effects in the ENS and musculature. Contractility of treated guts was assessed in organ bath after electrical field stimulation. NLBs could be reproducibly generated without any signs of chromosomal alterations using subtelomere FISH. NLB-derived cells integrated within the host tissue and showed expected differentiated phenotypes i.e. enteric neurons, glia and smooth muscle-like cells following in vivo transplantation. Our data suggest biological effects of the transplanted NLB cells on tissue contractility, although robust statistical results could not be obtained due to the small sample size. Further, it is unclear, which of the NLB cell types including neural progenitors have direct restoring effects or, alternatively may act via 'bystander' mechanisms in vivo. Our findings provide further evidence that NLB transplantation can be considered as feasible tool to improve ENS function in a variety of gastrointestinal disorders.

Review article: the assessment and management of chronic severe gastrointestinal dysmotility in adults

BACKGROUND

The characterisation and management of chronic severe gastrointestinal (GI) dysmotility are challenging. It may cause intestinal failure requiring home parenteral nutrition (HPN).

AIMS

To review the presentation, aetiology, characterisation, management and outcome of chronic severe GI dysmotility, and to suggest a pragmatic management algorithm.

METHODS

PubMed search was performed up to December 2012 using appropriate search terms, restricted to human articles and reviewed for relevance. Segmental dysmotility, acute ileus, functional syndromes and non-English articles were excluded. Evidence and recommendations were evaluated using the GRADE system.

RESULTS

In total, 721 relevant articles were reviewed. A coherent and definitive picture is hampered by overlapping classification systems using multi-modal characterisation methods, subject to pitfalls and some requiring further validation. The literature is confined to case series with no randomised trials. Fewer than 20% undergo full thickness jejunal biopsy, which are otherwise labelled idiopathic. However, in studies with up to 80% biopsy rates, neuromuscular abnormalities may be found in 90%. Between 14% and 50% will require HPN, comprising 8-14% of all HPN patients, of which 2/3 are primary/idiopathic and 1/3 secondary, with scleroderma being the leading secondary cause. Ten-year  mortality ranges from 13% to 35% and is worst in elderly scleroderma patients. Management includes limited treatments for secondary causes, prokinetics, symptom palliation, psychological support, nutrition, hydration and judicious surgery.

CONCLUSIONS

Severe dysmotility often remains idiopathic. It is rarely possible to alter disease trajectory; consequently, prognosis may be poor. Multi-disciplinary teams in a specialist setting can improve outcomes. Graded recommendations are enumerated and a pragmatic algorithm is suggested.

Transplanted progenitors generate functional enteric neurons in the postnatal colon

Cell therapy has the potential to treat gastrointestinal motility disorders caused by diseases of the enteric nervous system. Many studies have demonstrated that various stem/progenitor cells can give rise to functional neurons in the embryonic gut; however, it is not yet known whether transplanted neural progenitor cells can migrate, proliferate, and generate functional neurons in the postnatal bowel in vivo. We transplanted neurospheres generated from fetal and postnatal intestinal neural crest-derived cells into the colon of postnatal mice. The neurosphere-derived cells migrated, proliferated, and generated neurons and glial cells that formed ganglion-like clusters within the recipient colon. Graft-derived neurons exhibited morphological, neurochemical, and electrophysiological characteristics similar to those of enteric neurons; they received synaptic inputs; and their neurites projected to muscle layers and the enteric ganglia of the recipient mice. These findings show that transplanted enteric neural progenitor cells can generate functional enteric neurons in the postnatal bowel and advances the notion that cell therapy is a promising strategy for enteric neuropathies.

Evaluation of ES-derived neural progenitors as a potential source for cell replacement therapy in the gut

Background

Stem cell-based therapy has recently been explored for the treatment of disorders of the enteric nervous system (ENS). Pluripotent embryonic stem (ES) cells represent an attractive cell source; however, little or no information is currently available on how ES cells will respond to the gut environment. In this study, we investigated the ability of ES cells to respond to environmental cues derived from the ENS and related tissues, both in vitro and in vivo.

Methods

Neurospheres were generated from mouse ES cells (ES-NS) and co-cultured with organotypic preparations of gut tissue consisting of the longitudinal muscle layers with the adherent myenteric plexus (LM-MP).

Results

LM-MP co-culture led to a significant increase in the expression of pan-neuronal markers (βIII-tubulin, PGP 9.5) as well as more specialized markers (peripherin, nNOS) in ES-NS, both at the transcriptional and protein level. The increased expression was not associated with increased proliferation, thus confirming a true neurogenic effect. LM-MP preparations exerted also a myogenic effect on ES-NS, although to a lesser extent. After transplantation in vivo into the mouse pylorus, grafted ES-NS failed to acquire a distinct phenotype al least 1 week following transplantation.

Conclusions

This is the first study reporting that the gut explants can induce neuronal differentiation of ES cells in vitro and induce the expression of nNOS, a key molecule in gastrointestinal motility regulation. The inability of ES-NS to adopt a neuronal phenotype after transplantation in the gastrointestinal tract is suggestive of the presence of local inhibitory influences that prevent ES-NS differentiation in vivo.

The microenvironment in the Hirschsprung's disease gut supports myenteric plexus growth

INTRODUCTION

The transplantation of neural crest derived stem cells (NCSC) is a potent alternative for the treatment of Hirschsprung's disease (HSCR). Cells to be transplanted should find an appropriate microenvironment to survive and differentiate. Influences of HSCR-smooth-muscle-protein extracts upon isolated myenteric plexus cells, dissociated dorsal root ganglia and NCSC were studied in vitro to investigate the quality of this microenvironment effects.

METHODS

Postnatal human gut from children undergoing colonic resection due to HSCR was divided in segments. Smooth muscle was dissected and homogenized. Glial-cell-line-derived-neurotrophic-factor (GDNF) and transforming-growth-factor-β-1 (TGFβ-1) concentration were measured in the homogenates from the individual segment using ELISA. Myenteric plexus and dissociated dorsal root ganglia (DRG) cultures, as well as NCSCs were exposed to protein extracts derived from ganglionic and aganglionic HSCR segments, and their effect upon neurite outgrowth, survival, and branching was evaluated.

RESULTS AND CONCLUSIONS

The amount of the factors varied considerably between the individual segments and also from patient to patient. Four major expression patterns could be detected. While all extracts tested lead to a significant increase in neurite outgrowth compared to the control, extracts from proximal segments tended to have more prominent effects. In one experiment, extracts from all individual segments of a single patient were tested. Neurite outgrowth, neuronal survival, and branching pattern varied from segment to segment, but all HSCR-muscle-protein extracts increased neuronal survival and network formation. Smooth muscle protein from aganglionic bowel supports the survival and outgrowth of myenteric neurons and NCSCs and is so an appropriate target for neural stem cell treatment.

Neuroprotection of VEGF-expression neural stem cells in neonatal cerebral palsy rats

Cerebral palsy (CP) is a very common neural system development disorder that can cause physical disability in human. Here, we studied the neuroprotective effect of vascular endothelial growth factor (VEGF)-transfected neural stem cells (NSCs) in newborn rats with cerebral palsy (CP). Seven-day-old Sprague-Dawley rats were randomly divided into four groups: sham operation (control group), PBS transplantation (PBS group), VEGF+NSCs transplantation (transgene NSCs group) and NSCs transplantation groups (NSCs group). PBS, Transgene NSCs and NSCs groups respectively received stereotactic injections of PBS, lentiviral vector (pGC-FU-VEGF) infected NSCs or a NSCs suspension in the left sensory-motor cortex 3 days after CP model was established. The NSCs activity, their impacts on neural cell growth and apoptosis, brain development and animal behaviors were examined on the animals up to age 35-days. As expected, unilateral carotid artery occlusion plus hypoxia (cerebral palsy model) resulted in severe neural developmental disorders, including slowed growth, increased in cortical neuron apoptosis, decreased cerebral cortex micro-vessel density and retarded behavior developments. Transplantation of NSCs not only resulted in increases in VEGF protein expression in rat brains, but also largely prevented the behavioral defects and brain tissue pathology that resulted from cerebral palsy procedure, with animals received VEGF transfected NSCs always being marginally better than these received un-transfected cells. In conclusion, NSCs transplantation can partially prevent/slow down the brain damages that are associated with CP in the newborn rats, suggesting a new possible strategy for CP treatment.

Smooth muscle proteins from Hirschsprung's disease facilitates stem cell differentiation

BACKGROUND AND AIMS

The transplantation of neural crest derived stem cells (NCSC's) is a potent alternative for the treatment of Hirschsprung's disease (HSCR). Cells to be transplanted should find an appropriate microenvironment to survive and differentiate. To investigate the quality of this microenvironment, effects of HSCR-smooth-muscle-protein extracts upon NCSC's were studied in vitro.

METHODS

Postnatal human gut from children undergoing colonic resection due to HSCR was divided in segments. Smooth muscle was dissected and homogenized. Glial-cell-line-derived-neurotrophic-factor (GDNF) concentration was measured in the homogenates from the individual segment using ELISA. NCSC's were exposed to protein extracts derived from ganglionic and aganglionic HSCR segments, and their effect upon neurite outgrowth, survival and branching was evaluated.

RESULTS

The amount of the factors varied considerably between the proximal and distal segments, and also from patient to patient. While extracts from proximal segments tended to have more prominent effects, all HSCR-muscle-protein extracts increased neuronal survival and network formation.

CONCLUSION

Muscle protein from aganglionic bowel supports the survival and outgrowth of NCSC's and is so an appropriate target for neural stem cell treatment.

Enteric nervous system specific deletion of Foxd3 disrupts glial cell differentiation and activates compensatory enteric progenitors

The enteric nervous system (ENS) arises from the coordinated migration, expansion and differentiation of vagal and sacral neural crest progenitor cells. During development, vagal neural crest cells enter the foregut and migrate in a rostro-to-caudal direction, colonizing the entire gastrointestinal tract and generating the majority of the ENS. Sacral neural crest contributes to a subset of enteric ganglia in the hindgut, colonizing the colon in a caudal-to-rostral wave. During this process, enteric neural crest-derived progenitors (ENPs) self-renew and begin expressing markers of neural and glial lineages as they populate the intestine. Our earlier work demonstrated that the transcription factor Foxd3 is required early in neural crest-derived progenitors for self-renewal, multipotency and establishment of multiple neural crest-derived cells and structures including the ENS. Here, we describe Foxd3 expression within the fetal and postnatal intestine: Foxd3 was strongly expressed in ENPs as they colonize the gastrointestinal tract and was progressively restricted to enteric glial cells. Using a novel Ednrb-iCre transgene to delete Foxd3 after vagal neural crest cells migrate into the midgut, we demonstrated a late temporal requirement for Foxd3 during ENS development. Lineage labeling of Ednrb-iCre expressing cells in Foxd3 mutant embryos revealed a reduction of ENPs throughout the gut and loss of Ednrb-iCre lineage cells in the distal colon. Although mutant mice were viable, defects in patterning and distribution of ENPs were associated with reduced proliferation and severe reduction of glial cells derived from the Ednrb-iCre lineage. Analyses of ENS-lineage and differentiation in mutant embryos suggested activation of a compensatory population of Foxd3-positive ENPs that did not express the Ednrb-iCre transgene. Our findings highlight the crucial roles played by Foxd3 during ENS development including progenitor proliferation, neural patterning, and glial differentiation and may help delineate distinct molecular programs controlling vagal versus sacral neural crest development.

Stem cells for GI motility disorders

Currently available therapies for gastrointestinal motility conditions are often inadequate. Recent scientific advances, however, have facilitated the identification of neural stem cells as novel tools for cellular replenishment. Such cells can be generated from a number of tissue sources including the gut itself. Neural stem cells can readily be harvested from postnatal human gut including by conventional endoscopy, and in experimental transplantation studies appear capable of generating a neo-Enteric Nervous System. Current initiatives are addressing pre-clinical proof of concept studies in vivo utilising animal models of disease. Although definitive cell replenishment therapies for gut motility disorders appear to be an exciting and realistic prospect, even in the short-term, a number of challenges remain to be addressed before definitive clinical application.

Gut-derived factors promote neurogenesis of CNS-neural stem cells and nudge their differentiation to an enteric-like neuronal phenotype

Recent studies have explored the potential of central nervous system-derived neural stem cells (CNS-NSC) to repopulate the enteric nervous system. However, the exact phenotypic fate of gut-transplanted CNS-NSC has not been characterized. The aim of this study was to investigate the effect of the gut microenvironment on phenotypic fate of CNS-NSC in vitro. With the use of Transwell culture, differentiation of mouse embryonic CNS-NSC was studied when cocultured without direct contact with mouse intestinal longitudinal muscle-myenteric plexus preparations (LM-MP) compared with control noncocultured cells, in a differentiating medium. Differentiated cells were analyzed by immunocytochemistry and quantitative RT-PCR to assess the expression of specific markers and by whole cell patch-clamp studies for functional characterization of their phenotype. We found that LM-MP cocultured cells had a significant increase in the numbers of cells that were immune reactive against the panneuronal marker β-tubulin, neurotransmitters neuronal nitric oxide synthase (nNOS), choline acetyltransferase (ChAT), and neuropeptide vasoactive intestinal peptide (VIP) and showed an increase in expression of these genes, compared with control cells. Whole cell patch-clamp analysis showed that coculture with LM-MP decreases cell excitability and reduces voltage-gated Na(+) currents but significantly enhances A-current and late afterhyperpolarization (AHP) and increases the expression of the four AHP-generating Ca(2+)-dependent K(+) channel genes (KCNN), compared with control cells. In a separate experiment, differentiation of LM-MP cocultured CNS-NSC produced a significant increase in the numbers of cells that were immune reactive against the neurotransmitters nNOS, ChAT, and the neuropeptide VIP compared with CNS-NSC differentiated similarly in the presence of neonatal brain tissue. Our results show that the gut microenvironment induces CNS-NSC to produce neurons that share some of the characteristics of classical enteric neurons, further supporting the therapeutic use of these cells for gastrointestinal disorders.

Transplantation of enteric cells into the aganglionic rodent small intestines

BACKGROUND

Enteric cells, a mixture of cells isolated from the longitudinal and circular muscle of the gut, may contain neural crest stem cells (NCSCs) and therefore may be a potential source to regenerate the enteric nervous system.

MATERIALS AND METHODS

Benzylalkonium chloride (BAC) was employed to ablate the myenteric and submucosal plexi of the rodent jejunum. Enteric cells were then injected into this BAC-treated segment of the jejunum either with or without basic fibroblast growth factor (bFGF) mixed in collagen.

RESULTS

Expression of peripherin, S100, and synaptophysin were found in all of the cell injection sites. Peripherin and S100 expression appeared in close proximity in ganglion-like structures when bFGF was injected simultaneously with enteric cells. Synapses that were formed in the presence of bFGF were elongated compared with those formed in the absence of exogenously delivered bFGF. A small percentage of enteric cells expressed peripherin in the injection site after transplantation.

CONCLUSIONS

Enteric cells transplanted with collagen and bFGF in an aganglionic segment of jejunum regenerated ganglion-like structures and may hold potential as a cellular therapeutic for various motility disorders of the gastrointestinal tract.

Enteric nervous system neuropathy: repair and restoration

PURPOSE OF REVIEW

Disordered neurobiology of the enteric nervous system (ENS) underlies a broad assortment of idiopathic, acquired, and congenital pathophysiologies up and down the digestive tract. Progress in two major areas of regenerative medicine related to enteric neuropathy is summarized: new insight into how everyday damage to the ENS might be corrected by indwelling stem cells and prospects for patient-specific replacement of damaged or diseased intestine with one reproduced from pluripotent stem cells derived from embryos or reprogrammed adult cells.

RECENT FINDINGS

Germinal centers with undifferentiated stem cells are in position outside ENS ganglia. Messages, which might be released after damage to the ENS or when neurons are lost, direct migration of stem cells into ENS ganglia where they differentiate into one or the other of the specialized classes of interneurons or motor neurons and become 'wired' into the synaptic circuits as neuronal replacements. Action of serotonin and the 5-hydroxytryptamine (HT)4 receptor subtype is a message that initiates the neuronal replacement and circuit restoration process. A reasonable facsimile of a functional intestine can be derived from pluripotent stem cells.

SUMMARY

Emerging knowledge of cell and molecular biology of indwelling stem cells in the gut and strategies for application of pluripotential stem cells in patient-specific organ transplantation reflect an emergent revolution in understanding and treating disordered gut function when the underlying cause is ENS neuropathy.

Transplantation of neonatal gut neural crest progenitors reconstructs ganglionic function in benzalkonium chloride-treated homogenic rat colon

BACKGROUND

To value the possibility and the future feasibility of the use of autograft cells transplantation in disorders of the enteric neural system, we postulate that isolated neonatal nongenetically modified neural crest progenitors could survive and differentiate into neurons and glia in homogenic denervated rats and, therefore, restore partial intestinal function after transplantation.

METHODS

Neural crest progenitors were isolated from neonatal rats. After passages, the cells were labeled with CM-DiI. The labeled cells were then delivered into the muscular distal denervated colon of rats whose neural plexuses were eliminated using benzalkonium chloride. The treated colons of recipients were harvested at 1, 4, and 8 wk, and identified by immunofluorescent staining. The physiologic and functional improvements on treated colons were well examined after transplantation 8 wk.

RESULTS

Progenitors could generate neurospheres and differentiate into neurons and glia in vitro. After transplantation, red fluorescent cells were observed in the injected tissue for up to 8 wk, and they differentiated into neurons and glia in the host colon. Functional examinations indicated that symptoms and intestinal dysfunction of the denervated model were reversed.

CONCLUSIONS

We provide herein further evidence that autologous cell transplantation is a feasible therapy for enteric nervous system disorders.

Transplantation of enteric cells expressing p75 in the rodent stomach

BACKGROUND

Neural crest stem cells may hold potential as a cellular therapeutic to repopulate the enteric nervous system. The expression of the low-affinity nerve growth factor receptor, p75, may enrich enteric cells isolated from the neonatal rodent intestinal tract for neural crest stem cells. While these cells have shown tremendous promise in vitro, it remains to be determined whether they will survive and differentiate after in vivo transplantation.

MATERIALS AND METHODS

Cells isolated from the neonatal rodent intestinal muscularis were sorted according to their degree of p75 expression. The parent, p75-high, and p75-low expressing populations were injected into the rodent stomach for 7 d in vivo.

RESULTS

Cells that expressed high levels of p75 also expressed high levels of nestin. Evaluation of the parent, p75-high, and p75-low populations of cells showed 420-, 130-, and 20-fold growth, respectively, after 11 d of culture. Transplantation of these populations of cells into syngeneic rodent stomachs showed cell survival in the injection site after 7 d. Cells expressing either the neuronal marker, peripherin, or the glial marker, S100, were present in and around the injection site when the parent and the p75-high populations were transplanted.

CONCLUSIONS

Enteric cells survive transplantation into the rodent stomach and induce the expression of differentiation markers in and around the injection site. Based on these results, enteric cells may hold potential as a cellular therapeutic in a variety of gastrointestinal disorders.

Long-term MR cell tracking of neural stem cells grafted in immunocompetent versus immunodeficient mice reveals distinct differences in contrast between live and dead cells

Neural stem cell (NSC)-based therapy is actively being pursued in preclinical and clinical disease models. Magnetic resonance imaging (MRI) cell tracking promises to optimize current cell transplantation paradigms, however, it is limited by dilution of contrast agent during cellular proliferation, transfer of label from dying cells to surrounding endogenous host cells, and/or biodegradation of the label. Here, we evaluated the applicability of magnetic resonance imaging for long-term tracking of transplanted neural stem cells labeled with superparamagnetic iron oxide and transfected with the bioluminescence reporter gene luciferase. Mouse neural stem cells were transplanted into immunodeficient, graft-accepting Rag2 mice or immunocompetent, graft-rejecting Balb/c mice. Hypointense voxel signals and bioluminescence were monitored over a period of 93 days. Unexpectedly, in mice that rejected the cells, the hypointense MR signal persisted throughout the entire time-course, whereas in the nonrejecting mice, the contrast cleared at a faster rate. In immunocompetent, graft-rejecting Balb/c mice, infiltrating leukocytes, and microglia were found surrounding dead cells and internalizing superparamagnetic iron oxide clusters. The present results indicate that live cell proliferation and associated label dilution may dominate contrast clearance as compared with cell death and subsequent transfer and retention of superparamagnetic iron oxide within phagocytes and brain interstitium. Thus, interpretation of signal changes during long-term MR cell tracking is complex and requires caution.

Small-molecule induction of neural crest-like cells derived from human neural progenitors

Neural crest (NC) cells are stem cells that are specified within the embryonic neuroectodermal epithelium and migrate to stereotyped peripheral sites for differentiation into many cell types. Several neurocristopathies involve a deficit of NC-derived cells, raising the possibility of stem cell therapy. In Hirschsprung's disease the distal bowel lacks an enteric nervous system caused by a failure of colonization by NC-derived cells. We have developed a robust method of producing migrating NC-like cells from human embryonic stem cell-derived neural progenitors using a coculture system of mouse embryonic fibroblasts. Significantly, subsequent exposure to Y27632, a small-molecule inhibitor of the Rho effectors ROCKI/II, dramatically increased the efficiency of differentiation into NC-like cells, identified by marker expression in vitro. NC-like cells derived by this method were able to migrate along NC pathways in avian embryos in ovo and within explants of murine bowel, and to differentiate into cells with neuronal and glial markers. This is the first study to report the use of a small molecule to induce cells with NC characteristics from embryonic stem cells that can migrate and generate neurons and support cells in complex tissue. Furthermore, this study demonstrates that small-molecule regulators of ROCKI/II signaling may be valuable tools for stem cell research aimed at treatment of neurocristopathies.

Effects of tissue age, presence of neurones and endothelin-3 on the ability of enteric neurone precursors to colonize recipient gut: implications for cell-based therapies

BACKGROUND Most enteric neurones arise from neural crest cells that originate in the post-otic hindbrain, and migrate into and along the developing gastrointestinal tract. There is currently great interest in the possibility of cell therapy to replace diseased or absent enteric neurones in patients with enteric neuropathies, such as Hirschsprung's disease. However, it is unclear whether neural crest stem/progenitor cells will be able to colonize colon (i) in which the mesenchyme has differentiated into distinct layers, (ii) that already contains enteric neurones or (iii) that lacks a gene expressed by the gut mesenchyme, such as endothelin-3 (Et-3). METHODS Co-cultures were used to examine the ability of enteric neural crest-derived cells (ENCCs) from E11.5 mouse gut to colonize a variety of recipient hindguts. KEY RESULTS Enteric neural crest-derived cells migrated and gave rise to neurones in E14.5 and E16.5 aneural colon in which the external muscle layers had differentiated, but they did not migrate as far as in younger colon. There was no evidence of altered ENCC proliferation, cell death or neuronal differentiation in older recipient explants. Enteric neural crest-derived cells failed to enter most recipient E14.5 and E16.5 colon explants already containing enteric neurones, and the few that did showed very limited migration. Finally, ENCCs migrated a shorter distance and a higher proportion expressed the pan-neuronal marker, Hu, in recipient E11.5 Et-3(-/-) colon compared to wild-type recipient colon. CONCLUSIONS & INFERENCES Age and an absence of Et-3 from the recipient gut both significantly reduced but did not prevent ENCC migration, but the presence of neurones almost totally prevented ENCC migration.

Potential of cell therapy to treat pediatric motility disorders

Gut motility disorders represent a significant challenge in clinical management with current palliative approaches failing to overcome disease and treatment-related morbidity. The recent progress with stem cells to restore missing or defective elements of the gut neuromusculature offers new hope for potential cure. Focusing on enteric neuropathies such as Hirschsprung's disease, the review discusses the progress that has been made in the sourcing of putative stem cells and the studies into their biology and therapeutic potential. It also explores the practical challenges that must be overcome before stem cell-based therapies can be applied in the clinical arena. Although many obstacles remain, the speed of advancement of the enteric stem cell field suggests that such therapies are on the horizon.

Cancer stem cells: the other face of Janus

Advances in the field of stem cell biology have provided renewed hopes that stem cells can be used to treat a wide range of genetic diseases and traumatic injuries. However, advances in the field of cancer cell biology have led to formulation of the cancer stem cell hypothesis, which posits that cancers arise from mutant stem cells. Further, this hypothesis proposes that these stem cells account for cancer recurrence, metastasis, and resistance to conventional treatments. Thus, although normal stem cells represent potential effective solutions to numerous clinical problems, when mutated, they may also represent the cause of many human malignancies.

Neural stem cell transplantation in the enteric nervous system: roadmaps and roadblocks

The enteric nervous system (ENS) is vulnerable to a variety of genetic, metabolic or environmental threats, resulting in clinical disorders characterized by loss or malfunction of neuronal elements. These disorders have been difficult to treat and there is much enthusiasm for novel therapies such as neural stem cell (NSC) transplantation to restore ENS function in diseased segments of the gut. Recent research has indicated the potential for a variety of innovative approaches to this effect using NSC obtained from the central nervous system (CNS) as well as gut derived enteric neuronal progenitors. The main goal of this review is to summarize the current status of NSC research as it applies to the ENS, delineate a roadmap for effective therapeutic strategies using NSC transplantation and point out the numerous challenges that lie ahead.

The enteric nervous system: normal functions and enteric neuropathies

Most aspects of the normal organisation and functioning of the enteric nervous system have been resolved in recent years, especially for the small and large intestines, where the ENS has essential roles in controlling bowel movement and transmucosal fluid exchange. The roles of the ENS in the esophagus are not understood, and the relative roles of intrinsic reflexes in relation to extrinsic control of the stomach require clarification. In the small intestine and colon, it needs to be understood how neural activity is orchestrated to subserve different functional outcomes, for example propulsion, mixing and retrograde movement. However, the most important future challenges are to properly understand the molecular and cellular changes that underlie enteric neuropathies, to utilise knowledge of the normal neurochemistry, pharmacology and physiology of the ENS to devise strategies to treat disorders of motility and secretion, and to develop effective therapeutic compounds. It is suggested that ion channels of enteric neurons have been under-investigated as therapeutic targets. Other future challenges lie in the identification of biomarkers for functional bowel disorders and in the use of neural stem cells for restitution of ENS function.

Functional development of the enteric nervous system--from migration to motility

The enteric nervous system (ENS) consists of many different types of enteric neurones forming complex reflex circuits that underlie or regulate many gut functions. Studies of humans with Hirschsprung's disease (distal aganglionosis), and of animal models of Hirschsprung's disease, have led to the identification of many of the genetic, molecular and cellular mechanisms responsible for the colonization of the gut by enteric neurone precursors. However, later events in the ENS development are still poorly understood, including the development of functioning ENS circuits. This article is a personal view of the current state of play in our understanding of the ENS development and of the future of the field.

Neural progenitors from isolated postnatal rat myenteric ganglia: expansion as neurospheres and differentiation in vitro

Identification of the stem cell niche is crucial for understanding the factors that regulate these cells. Rodent enteric neural crest-derived stem cells have previously been isolated by flow cytometry and culture of cell suspensions from the outer smooth muscle layers or the entire gut wall from postnatal and adult animals. Such cell suspensions contain a mixture of cell types, including smooth muscle, fibroblasts and cells associated with the vasculature and extrinsic innervation. Thus these preparations may be contaminated by stem cells associated with extrinsic sensory and autonomic nerves and by other types of stem cell that reside in the gut. Here we describe a different approach, similar to that recently used for infant human gut, to obtain enteric ganglion-derived cells, with properties of neural progenitor cells, using isolated myenteric ganglia from postnatal rat ileum. Myenteric ganglia were separated from the gut wall, dispersed and resulting cell dissociates were plated in non-adherent culture conditions with EGF and FGF-2. Under these conditions neurosphere-like bodies (NLB) developed. Cells in NLB incorporated BrdU and expressed the stem cell marker nestin but not the pan-neuronal marker PGP 9.5. Upon growth factor withdrawal some BrdU-immunopositive cells assumed the morphology of neurons and expressed PGP 9.5; others were flattened and expressed the glial cell marker GFAP. This work therefore provides evidence that neural crest-derived progenitors in the postnatal rat gut are located in the myenteric plexus, and shows that these cells can be expanded and differentiated in NLB in vitro.

Enteric nervous system development and Hirschsprung's disease: advances in genetic and stem cell studies

The enteric nervous system (ENS) has been explored by developmental neurobiologists and medical researchers for decades. Whereas developmental biologists have been unravelling the molecular mechanisms underlying the migration, proliferation and differentiation of the neural crest derivatives that give rise to the ENS, human geneticists have been uncovering the genetic basis for diseases of the ENS, notably Hirschsprung's disease. Here we discuss the exciting recent advances, including novel transgenic and genetic tools, a broadening range of model organisms, and the pursuit of ENS stem cells as a therapeutic tool, that are bringing these fields closer together.