Divergent fate and origin of neurosphere-like bodies from different layers of the gut

Updates and Challenges in ENS Cell Therapy for the Treatment of Neurointestinal Diseases

Neurointestinal diseases represent a significant challenge in clinical management with current palliative approaches failing to overcome disease and treatment-related morbidity. The recent progress with cell therapy to restore missing or defective components of the gut neuromusculature offers new hope for potential cures. This review discusses the progress that has been made in the sourcing of putative stem cells and the studies into their biology and therapeutic potential. We also explore some of the practical challenges that must be overcome before cell-based therapies can be applied in the clinical setting. Although a number of obstacles remain, the rapid advances made in the enteric neural stem cell field suggest that such therapies are on the near horizon.

Age-associated changes in lineage composition of the enteric nervous system regulate gut health and disease

The enteric nervous system (ENS), a collection of neural cells contained in the wall of the gut, is of fundamental importance to gastrointestinal and systemic health. According to the prevailing paradigm, the ENS arises from progenitor cells migrating from the neural crest and remains largely unchanged thereafter. Here, we show that the lineage composition of maturing ENS changes with time, with a decline in the canonical lineage of neural-crest derived neurons and their replacement by a newly identified lineage of mesoderm-derived neurons. Single cell transcriptomics and immunochemical approaches establish a distinct expression profile of mesoderm-derived neurons. The dynamic balance between the proportions of neurons from these two different lineages in the post-natal gut is dependent on the availability of their respective trophic signals, GDNF-RET and HGF-MET. With increasing age, the mesoderm-derived neurons become the dominant form of neurons in the ENS, a change associated with significant functional effects on intestinal motility which can be reversed by GDNF supplementation. Transcriptomic analyses of human gut tissues show reduced GDNF-RET signaling in patients with intestinal dysmotility which is associated with reduction in neural crest-derived neuronal markers and concomitant increase in transcriptional patterns specific to mesoderm-derived neurons. Normal intestinal function in the adult gastrointestinal tract therefore appears to require an optimal balance between these two distinct lineages within the ENS.

Adult enteric Dclk1-positive glial and neuronal cells reveal distinct responses to acute intestinal injury

Intestinal ganglionic cells in the adult enteric nervous system (ENS) are continually exposed to stimuli from the surrounding microenvironment and need at times to respond to disturbed homeostasis following acute intestinal injury. The kinase DCLK1 and intestinal Dclk1-positive cells have been reported to contribute to intestinal regeneration. Although Dclk1-positive cells are present in adult enteric ganglia, their cellular identity and response to acute injury have not been investigated in detail. Here, we reveal the presence of distinct Dclk1-tdTom+/CD49b+ glial-like and Dclk1-tdTom+/CD49b- neuronal cell types in adult myenteric ganglia. These ganglionic cells demonstrate distinct patterns of tracing over time yet show a similar expansion in response to elevated serotonergic signaling. Interestingly, Dclk1-tdTom+ glial-like and neuronal cell types appear resistant to acute irradiation injury-mediated cell death. Moreover, Dclk1-tdTom+/CD49b+ glial-like cells show prominent changes in gene expression profiles induced by injury, in contrast to Dclk1-tdTom+/CD49b- neuronal cell types. Finally, subsets of Dclk1-tdTom+/CD49b+ glial-like cells demonstrate prominent overlap with Nestin and p75NTR and strong responses to elevated serotonergic signaling or acute injury. These findings, together with their role in early development and their neural crest-like gene expression signature, suggest the presence of reserve progenitor cells in the adult Dclk1 glial cell lineage.NEW & NOTEWORTHY The kinase DCLK1 identifies glial-like and neuronal cell types in adult murine enteric ganglia, which resist acute injury-mediated cell death yet differ in their cellular response to injury. Interestingly, Dclk1-labeled glial-like cells show prominent transcriptional changes in response to injury and harbor features reminiscent of previously described enteric neural precursor cells. Our data thus add to recently emerging evidence of reserve cellular plasticity in the adult enteric nervous system.

Prucalopride might improve intestinal motility by promoting the regeneration of the enteric nervous system in diabetic rats

The present study aimed to investigate whether prucalopride, as a 5-hydroxytryptamine 4 (5-HT4) receptor agonist, improved intestinal motility by promoting the regeneration of the enteric nervous system (ENS) in rats with diabetes mellitus (DM). A rat model of DM was established using an intraperitoneal injection of streptozotocin. The rats were randomly divided into four groups of 6 rats/group: Control, DM (DM model), DM + A (5 µg/kg prucalopride) and DM + B (10 µg/kg prucalopride). The rats in the Control group were given an equal volume of citric acid solvent. After successful model establishment, high blood glucose levels were maintained for 2 weeks before administration of prucalopride. The colonic transit time was measured using the glass bead discharge method. It was revealed that the colonic transit time of diabetic rats was the longest, and this was significantly shortened in the DM + B group. Subsequently, the colons were collected. The expression levels of Nestin, glial fibrillary acidic protein (GFAP), SOX10, RNA-binding protein human antigen D (HuD) and ubiquitin thiolesterase (PGP9.5) were determined via immunohistochemical analysis. Immunofluorescence double staining of 5-HT4 + Nestin and Ki67 + Nestin was performed. The 5-HT level was measured using ELISA. Compared with that in the control group, Nestin expression was significantly increased in the DM and DM + A groups, and it was concentrated in columnar epithelial cells and the mesenchyme. Furthermore, the expression levels of Nestin in the DM + A group were higher than those in the DM group. No difference was observed in the expression levels of Nestin between the DM + B group and the Control group. The expression levels of 5-HT protein were highest in the Control group; however, the expression levels of 5-HT protein in the DM group, DM + A group and DM + B group exhibited an increasing trend. Similar trends in the expression of 5-HT4 and Nestin were not observed; however, similar trends in the expression of Nestin and Ki67 were observed. The expression levels of GFAP, SOX10, PGP9.5 and Ki67 in the DM + A and DM + B groups were higher compared with those in the DM group. In the DM + A group, HuD expression was decreased compared with that in the Control group but it was markedly higher compared with that in the DM group. In conclusion, prucalopride may improve intestinal motility by promoting ENS regeneration in rats with DM.

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.

Age-dependent shift in macrophage polarisation causes inflammation-mediated degeneration of enteric nervous system

OBJECTIVE

The enteric nervous system (ENS) undergoes neuronal loss and degenerative changes with age. The cause of this neurodegeneration is poorly understood. Muscularis macrophages residing in close proximity to enteric ganglia maintain neuromuscular function via direct crosstalk with enteric neurons and have been implicated in the pathogenesis of GI motility disorders like gastroparesis and postoperative ileus. The aim of this study was to assess whether ageing causes alterations in macrophage phenotype that contributes to age-related degeneration of the ENS.

DESIGN

Longitudinal muscle and myenteric plexus from small intestine of young, mid-aged and old mice were dissected and prepared for whole mount immunostaining, flow cytometry, Luminex immunoassays, western blot analysis, enteric neural stem cell (ENSC) isolation or conditioned media. Bone marrow derived macrophages were prepared and polarised to classic (M1) or alternative (M2) activation states. Markers for macrophage phenotype were measured using quantitative RT-PCR.

RESULTS

Ageing causes a shift in macrophage polarisation from anti-inflammatory 'M2' to proinflammatory 'M1' that is associated with a rise in cytokines and immune cells in the ENS. This phenotypic shift is associated with a neural response to inflammatory signals, increase in apoptosis and loss of enteric neurons and ENSCs, and delayed intestinal transit. An age-dependent decrease in expression of the transcription factor FoxO3, a known longevity gene, contributes to the loss of anti-inflammatory behaviour in macrophages of old mice, and FoxO3-deficient mice demonstrate signs of premature ageing of the ENS.

CONCLUSIONS

A shift by macrophages towards a proinflammatory phenotype with ageing causes inflammation-mediated degeneration of the ENS.

Adult enteric nervous system in health is maintained by a dynamic balance between neuronal apoptosis and neurogenesis

According to current dogma, there is little or no ongoing neurogenesis in the fully developed adult enteric nervous system. This lack of neurogenesis leaves unanswered the question of how enteric neuronal populations are maintained in adult guts, given previous reports of ongoing neuronal death. Here, we confirm that despite ongoing neuronal cell loss because of apoptosis in the myenteric ganglia of the adult small intestine, total myenteric neuronal numbers remain constant. This observed neuronal homeostasis is maintained by new neurons formed in vivo from dividing precursor cells that are located within myenteric ganglia and express both Nestin and p75NTR, but not the pan-glial marker Sox10. Mutation of the phosphatase and tensin homolog gene in this pool of adult precursors leads to an increase in enteric neuronal number, resulting in ganglioneuromatosis, modeling the corresponding disorder in humans. Taken together, our results show significant turnover and neurogenesis of adult enteric neurons and provide a paradigm for understanding the enteric nervous system in health and disease.

Optogenetic Demonstration of Functional Innervation of Mouse Colon by Neurons Derived From Transplanted Neural Cells

BACKGROUND & AIMS

Cell therapy offers the potential to treat gastrointestinal motility disorders caused by diseased or absent enteric neurons. We examined whether neurons generated from transplanted enteric neural cells provide a functional innervation of bowel smooth muscle in mice.

METHODS

Enteric neural cells expressing the light-sensitive ion channel, channelrhodopsin, were isolated from the fetal or postnatal mouse bowel and transplanted into the distal colon of 3- to 4-week-old wild-type recipient mice. Intracellular electrophysiological recordings of responses to light stimulation of the transplanted cells were made from colonic smooth muscle cells in recipient mice. Electrical stimulation of endogenous enteric neurons was used as a control.

RESULTS

The axons of graft-derived neurons formed a plexus in the circular muscle layer. Selective stimulation of graft-derived cells by light resulted in excitatory and inhibitory junction potentials, the electrical events underlying contraction and relaxation, respectively, in colonic muscle cells. Graft-derived excitatory and inhibitory motor neurons released the same neurotransmitters as endogenous motor neurons-acetylcholine and a combination of adenosine triphosphate and nitric oxide, respectively. Graft-derived neurons also included interneurons that provided synaptic inputs to motor neurons, but the pharmacologic properties of interneurons varied with the age of the donors from which enteric neural cells were obtained.

CONCLUSIONS

Enteric neural cells transplanted into the bowel give rise to multiple functional types of neurons that integrate and provide a functional innervation of the smooth muscle of the bowel wall. Circuits composed of both motor neurons and interneurons were established, but the age at which cells are isolated influences the neurotransmitter phenotype of interneurons that are generated.

Postnatal human enteric neuronal progenitors can migrate, differentiate, and proliferate in embryonic and postnatal aganglionic gut environments

BACKGROUND

Enteric neural stem/progenitor cells (ENSCs) offer an innovative approach to treating Hirschsprung disease (HSCR) and other enteric neuropathies. However, postnatal-derived human ENSCs have not been thoroughly characterized and their behavior in the embryonic and postnatal intestinal environment is unknown.

METHODS

ENSCs were isolated from the intestines of 25 patients undergoing bowel resection, including 7 children with HSCR. Neuronal differentiation and proliferation of ENSCs from submucosal and myenteric plexuses from patients with and without HSCR were characterized. ENSC migration and differentiation were studied following transplantation into embryonic chick neural crest, embryonic chick hindgut, and postnatal mouse aganglionic colon.

RESULTS

The proliferative and neurogenic potential of ENSCs from HSCR intestine is equivalent to that of non-HSCR controls. Similarly, no difference was observed between myenteric- and submucosal-derived ENSCs. Postnatal ENSCs transplanted to embryonic neural crest pathways and to aneural hindgut migrate normally and differentiate into appropriate neural crest-derived cell types. ENSCs in postnatal mouse aganglionic colon differentiate into neurons and glia both ex vivo and in vivo.

CONCLUSIONS

ENSCs isolated from the postnatal intestine of patients with and without HSCR can behave like embryonic neural crest-derived cells. These results support the feasibility of cell-based therapy for future treatment of neurointestinal disease.

Cell therapy for GI motility disorders: comparison of cell sources and proposed steps for treating Hirschsprung disease

Cell therapeutic approaches to treat a range of congenital and degenerative neuropathies are under intense investigation. There have been recent significant advancements in the development of cell therapy to treat disorders of the enteric nervous system (ENS), enteric neuropathies. These advances include the efficient generation of enteric neural progenitors from pluripotent stem cells and the rescue of a Hirschsprung disease model mouse following their transplantation into the bowel. Furthermore, a recent study provides evidence of functional innervation of the bowel muscle by neurons derived from transplanted ENS-derived neural progenitors. This mini-review discusses these recent findings, compares endogenous ENS-derived progenitors and pluripotent stem cell-derived progenitors as a cell source for therapy, and proposes the key steps for cell therapy to treat Hirschsprung disease.

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

Characterization of p75 neurotrophin receptor expression in human dental pulp stem cells

Human adult dental pulp stem cells (DPSC) are a heterogeneous stem cell population, which are able to differentiate down neural, chondrocyte, osteocyte and adipocyte lineages. We studied the expression pattern of p75 neurotrophin receptors (p75NTR), a marker of neural stem cells, within human DPSC populations from eight donors. p75NTR are expressed at low levels (<10%) in DPSC. Importantly, p75(+) DPSC represent higher expression levels of SOX1 (neural precursor cell marker), SOX2 (cell pluripotency marker) and nestin (neural stem cell marker) in comparison to p75(-) DPSC. Our results suggest that p75(+) hDPSC may denote a subpopulation with greater neurogenic potential.

Simultaneous optical and electrical in vivo analysis of the enteric nervous system

The enteric nervous system (ENS) is a major division of the nervous system and vital to the gastrointestinal (GI) tract and its communication with the rest of the body. Unlike the brain and spinal cord, relatively little is known about the ENS in part because of the inability to directly monitor its activity in live animals. Here, we integrate a transparent graphene sensor with a customized abdominal window for simultaneous optical and electrical recording of the ENS in vivo. The implanted device captures ENS responses to neurotransmitters, drugs and optogenetic manipulation in real time.

The enteric nervous system (ENS) plays a key role in regulating gut motility and homeostasis yet it remains a challenging system to record from. Here, the authors develop a novel abdominal window permitting simultaneous optical and electrical recording of mouse ENS system activity over prolonged time periods.

Isogenic enteric neural progenitor cells can replace missing neurons and glia in mice with Hirschsprung disease

BACKGROUND

Transplanting autologous patient-derived enteric neuronal stem/progenitor cells (ENSCs) is an innovative approach to replacing missing enteric neurons in patients with Hirschsprung disease (HSCR). Using autologous cells eliminates immunologic and ethical concerns raised by other cell sources. However, whether postnatal aganglionic bowel is permissive for transplanted ENSCs and whether ENSCs from HSCR patients can be successfully isolated, cultured, and transplanted in vivo remains unknown.

METHODS

ENSCs isolated from the ganglionic intestine of Ednrb(-/-) mice (HSCR-ENSCs) were characterized immunohistochemically and evaluated for their capacity to proliferate and differentiate in vitro. Fluorescently labeled ENSCs were co-cultured ex vivo with aganglionic Ednrb(-/-) colon. For in vivo transplantation, HSCR-ENSCs were labeled with lentivirus expressing green fluorescent protein (GFP) and implanted into aganglionic embryonic chick gut in ovo and postnatal aganglionic Ednrb(-/-) rectum in vivo.

KEY RESULTS

HSCR-ENSCs maintain normal capacity self-renewal and neuronal differentiation. Moreover, the Ednrb(-/-) aganglionic environment is permissive to engraftment by wild-type ENSCs ex vivo and supports migratrion and neuroglial differentiation of these cells following transplantation in vivo. Lentiviral GFP-labeled HSCR-ENSCs populated embryonic chick hindgut and postnatal colon of Ednrb(-/-) HSCR, with cells populating the intermuscular layer and forming enteric neurons and glia.

CONCLUSIONS & INFERENCES

ENSCs can be isolated and cultured from mice with HSCR, and transplanted into the aganglionic bowel of HSCR littermates to generate enteric neuronal networks. These results in an isogenic model establish the potential of using autologous-derived stem cells to treat HSCR and other intestinal neuropathies.

Stem cell therapy for GI neuromuscular disorders

The enteric nervous system is the intrinsic innervation of the gut. Several neuromuscular disorders affect the neurons and glia of the enteric nervous system adversely, resulting in disruptions in gastrointestinal motility and function. Pharmacological interventions to remedy gastrointestinal function do not address the underlying cause of dysmotility arising from lost, absent, or damaged enteric neuroglial circuitry. Cell-based therapies have gained traction in the past decade, following the discovery of several adult stem cell niches in the human body. Adult neural stem cells can be isolated from the postnatal and adult intestine using minimally invasive biopsies. These stem cells retain the ability to differentiate into several functional classes of enteric neurons and enteric glia. Upon identification of these cells, several groups have also established that transplantation of these cells into aganglionic or dysganglionic intestine rescues gastrointestinal motility and function. This chapter highlights key studies performed in the field of stem cell transplantation therapies that are targeted towards the remedy of gastrointestinal motility and function.

Isolation of Enteric Nervous System Progenitor Cells from the Aganglionic Gut of Patients with Hirschsprung's Disease

Enteric nervous system progenitor cells isolated from postnatal human gut and cultured as neurospheres can then be transplanted into aganglionic gut to restore normal patterns of contractility. These progenitor cells may be of future use to treat patients with Hirschprung’s disease, a congenital condition characterized by hindgut dysmotility due to the lack of enteric nervous system ganglia. Here we demonstrate that progenitor cells can also be isolated from aganglionic gut removed during corrective surgery for Hirschsprung’s disease. Although the enteric nervous system marker calretinin is not expressed in the aganglionic gut region, de novo expression is initiated in cultured neurosphere cells isolated from aganglionic Hirschsprung bowel. Furthermore, expression of the neural markers NOS, VIP and GFAP also increased during culture of aganglionic gut neurospheres which we show can be transplantation into cultured embryonic mouse gut explants to restore a normal frequency of contractility. To determine the origin of the progenitor cells in aganglionic region, we used fluorescence-activated cell sorting to demonstrate that only p75-positive neural crest-derived cells present in the thickened nerve trunks characteristic of the aganglionic region of Hirschsprung gut gave rise to neurons in culture. The derivation of enteric nervous system progenitors in the aganglionic gut region of Hirschprung’s patients not only means that this tissue is a potential source of cells for future autologous transplantation, but it also raises the possibility of inducing the differentiation of these endogenous cells in situ to compensate for the aganglionosis.

Enteric neurospheres are not specific to neural crest cultures: implications for neural stem cell therapies

Objectives

Enteric neural stem cells provide hope of curative treatment for enteric neuropathies. Current protocols for their harvesting from humans focus on the generation of ‘neurospheres’ from cultures of dissociated gut tissue. The study aims to better understand the derivation, generation and composition of enteric neurospheres.

Design

Gut tissue was obtained from Wnt1-Cre;Rosa26^Yfp/Yfp transgenic mice (constitutively labeled neural crest cells) and paediatric patients. Gut cells were cultured either unsorted (mixed neural crest/non-neural crest), or following FACS selection into neural crest (murine-YFP+ve/human-p75+ve) or non-neural crest (YFP-ve/p75-ve) populations. Cultures and resultant neurospheres were characterized using immunolabelling in vitro and following transplantation in vivo.

Results

Cultures of (i) unsorted, (ii) neural crest, and (iii) non-neural crest cell populations generated neurospheres similar in numbers, size and morphology. Unsorted neurospheres were highly heterogeneous for neural crest content. Neural crest-derived (YFP+ve/p75+ve) neurospheres contained only neural derivatives (neurons and glia) and were devoid of non-neural cells (i.e. negative for SMA, c-Kit), with the converse true for non-neural crest-derived (YFP-ve/p75-ve) ‘neurospheres’. Under differentiation conditions only YFP+ve cells gave rise to neural derivatives. Both YFP+ve and YFP-ve cells displayed proliferation and spread upon transplantation in vivo, but YFP-ve cells did not locate or integrate within the host ENS.

Conclusions

Spherical accumulations of cells, so-called ‘neurospheres’ forming in cultures of dissociated gut contain variable proportions of neural crest-derived cells. If they are to be used for ENS cell replacement therapy then improved protocols for their generation, including cell selection, should be sought in order to avoid inadvertent transplantation of non-therapeutic, non-ENS cells.

Anti-inflammatory activity of Wnt signaling in enteric nervous system: in vitro preliminary evidences in rat primary cultures

Background

In the last years, Wnt signaling was demonstrated to regulate inflammatory processes. In particular, an increased expression of Wnts and Frizzled receptors was reported in inflammatory bowel disease (IBD) and ulcerative colitis to exert both anti- and pro-inflammatory functions regulating the intestinal activated nuclear factor κB (NF-кB), TNFa release, and IL10 expression.

Methods

To investigate the role of Wnt pathway in the response of the enteric nervous system (ENS) to inflammation, neurons and glial cells from rat myenteric plexus were treated with exogenous Wnt3a and/or LPS with or without supporting neurotrophic factors such as basic fibroblast growth factor (bFGF), epithelial growth factor (EGF), and glial cell-derived neurotrophic factor (GDNF). The immunophenotypical characterization by flow cytometry and the protein and gene expression analysis by qPCR and Western blotting were carried out.

Results

Flow cytometry and immunofluorescence staining evidenced that enteric neurons coexpressed Frizzled 9 and toll-like receptor 4 (TLR4) while glial cells were immunoreactive to TLR4 and Wnt3a suggesting that canonical Wnt signaling is active in ENS.

Under in vitro LPS treatment, Western blot analysis demonstrated an active cross talk between canonical Wnt signaling and NF-кB pathway that is essential to negatively control enteric neuronal response to inflammatory stimuli. Upon costimulation with LPS and Wnt3a, a significant anti-inflammatory activity was detected by RT-PCR based on an increased IL10 expression and a downregulation of pro-inflammatory cytokines TNFa, IL1B, and interleukin 6 (IL6). When the availability of neurotrophic factors in ENS cultures was abolished, a changed cell reactivity by Wnt signaling was observed at basal conditions and after LPS treatment.

Conclusions

The results of this study suggested the existence of neuronal surveillance through FZD9 and Wnt3a in enteric myenteric plexus. Moreover, experimental evidences were provided to clarify the correlation among soluble trophic factors, Wnt signaling, and anti-inflammatory protection of ENS.

Erythropoietin production in neuroepithelial and neural crest cells during primitive erythropoiesis

Erythropoietin (Epo) supports both primitive erythropoiesis in the yolk sac and definitive erythropoiesis in the fetal liver and bone marrow. Although definitive erythropoiesis requires kidney- and liver-secreted Epo, it is unclear which cells produce Epo for primitive erythropoiesis. Here we find neural Epo-producing (NEP) cells in mid-gestational stage embryos using mouse lines that express green fluorescent protein (GFP) under the Epo gene regulation. In these mice, GFP is expressed exclusively in a subpopulation of neural and neural crest cells at embryonic day 9.0 when Epo-deficient embryos exhibit abnormalities in primitive erythropoiesis. The GFP-positive NEP cells express Epo mRNA and the ex vivo culture of embryonic day 8.5 neural tubes results in the secretion of Epo, which is able to induce the proliferation and differentiation of yolk sac-derived erythroid cells. These results thus suggest that NEP cells secrete Epo and might support the development of primitive erythropoiesis.

Role of p75 neurotrophin receptor in stem cell biology: more than just a marker

p75(NTR), the common receptor for both neurotrophins and proneurotrophins, has been widely studied because of its role in many tissues, including the nervous system. More recently, a close relationship between p75(NTR) expression and pluripotency has been described. p75(NTR) was shown to be expressed in various types of stem cells and has been used to prospectively isolate stem cells with different degrees of potency. Here, we give an overview of the current knowledge on p75(NTR) in stem cells, ranging from embryonic to adult stem cells, and cancer stem cells. In an attempt to address its potential role in the control of stem cell biology, the molecular mechanisms underlying p75(NTR) signaling in different models are also highlighted. p75(NTR)-mediated functions include survival, apoptosis, migration, and differentiation, and depend on cell type, (pro)neurotrophin binding, interacting transmembrane co-receptors expression, intracellular adaptor molecule availability, and post-translational modifications, such as regulated proteolytic processing. It is therefore conceivable that p75(NTR) can modulate cell-fate decisions through its highly ramified signaling pathways. Thus, elucidating the potential implications of p75(NTR) activity as well as the underlying molecular mechanisms of p75(NTR) will shed new light on the biology of both normal and cancer stem cells.

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.

Expression and function of NIK- and IKK2-binding protein (NIBP) in mouse enteric nervous system

BACKGROUND

NIK- and IKK2-binding protein (NIBP)/TRAPPC9 is expressed in brain neurons, and human NIBP mutations are associated with neurodevelopmental disorders. The cellular distribution and function of NIBP in the enteric nervous system (ENS) remain unknown.

METHODS

Western blot and reverse transcription-polymerase chain reaction analysis were used respectively to identify the protein and mRNA expression of NIBP and other neuronal markers. Multi-labeled immunofluorescent microscopy and confocal image analysis were used to examine the cellular distribution of NIBP-like immunoreactivity (IR) in whole mount intestine. Enteric neuronal cell line (ENC) was infected with lentivirus carrying NIBP or its shRNA expression vectors and treated with vehicle or tumor necrosis factor (TNF)α.

KEY RESULTS

NIBP is expressed at both mRNA and protein levels in different regions and layers of the mouse intestine. NIBP-like-IR was co-localized with various neuronal markers, but not with glial, smooth muscular, or interstitial cells of Cajal markers. A small population of NIBP-expressing cells and fibers in extra-ganglionic and intra-ganglionic area were negative for pan-neuronal markers HuD or Peripherin. Relatively high NIBP-like-IR was found in 35-44% of myenteric neurons and 9-10% of submucosal neurons. Approximately 98%, 87%, and 43% of these relatively high NIBP-expressing neurons were positive for choline acetyltransferase, neuronal nitric oxide synthase and Calretinin, respectively. NIBP shRNA knockdown in ENC inhibited TNFα-induced NFκB activation and neuronal differentiation, whereas NIBP overexpression promoted it.

CONCLUSIONS & INFERENCES

NIBP is extensively expressed in the ENS with relatively high level in a subpopulation of enteric neurons. Various NIBP expression levels in different neurons may represent dynamic trafficking or posttranslational modification of NIBP in some functionally active neurons and ultimately regulate ENS plasticity.

Transplantation of enteric neural stem/progenitor cells into the irradiated young mouse hippocampus

Radiotherapy is an effective treatment for brain tumors but often results in cognitive deficits in survivors. Transplantation of embryonic or brain-derived neural stem/progenitor cells (BNSPCs) ameliorated cognitive impairment after irradiation (IR) in animal models. However, such an approach in patients requires a clinically relevant source of cells. We show for the first time the utilization of enteric neural stem/progenitor cells (ENSPCs) from the postnatal intestinal wall as a source of autologous cells for brain repair after injury caused by IR. Cells were isolated from the intestinal wall and propagated in vitro for 1 week. Differentiation assays showed that ENSPCs are multipotent and generated neurons, astrocytes, and myofibroblasts. To investigate whether ENSPCs can be used in vivo, postnatal day 9 mice were subjected to a single moderate irradiation dose (6 or 8 Gy). Twelve days later, mice received an intrahippocampal injection of syngeneic ENSPCs. Four weeks after transplantation, 0.5% and 1% of grafted ENSPCs were detected in the dentate gyrus of sham and irradiated animals, respectively, and only 0.1% was detected after 16 weeks. Grafted ENSPCs remained undifferentiated but failed to restore IR-induced loss of BNSPCs and the subsequent impaired growth of the dentate gyrus. We observed microglia activation, astrogliosis, and loss of granule neurons associated with grafted ENSPC clusters. Transplantation of ENSPCs did not ameliorate IR-induced impaired learning and memory. In summary, while autologous ENSPC grafting to the brain worked technically, even in the absence of immunosuppression, the protocols need to be modified to improve survival and integration.

Neuroglial differentiation of adult enteric neuronal progenitor cells as a function of extracellular matrix composition

Enteric neuronal progenitor cells are neural crest-derived stem cells that can be isolated from fetal, post-natal and adult gut. Neural stem cell transplantation is an emerging therapeutic paradigm to replace dysfunctional or lost enteric neurons in several aganglionic disorders of the GI tract. The impetus to identify an appropriate microenvironment for enteric neuronal progenitor cells derives from the need to improve survival and phenotypic stability following implantation. Extracellular matrix composition can modulate stem cell fate and direct differentiation. Adult mammalian myenteric ganglia in vivo are surrounded by a matrix composed primarily of Collagen IV, Laminin and a Heparan sulfate proteoglycan. In these studies, adult mammalian enteric neuronal progenitor cells isolated from full thickness rabbit intestines were induced to differentiate when cultured on various combinations of neural ECM substrates. Neuronal and glial differentiation was studied as a function of ECM composition on coated glass coverslips. Poly-lysine coated coverslips (control) supported extensive glial differentiation but very minimal neuronal differentiation. Individual culture substrata (Laminin, Collagen I and Collagen IV) were conducive for both neuronal and glial differentiation. The addition of laminin or heparan sulfate to collagen substrates improved neuronal differentiation, significantly increased neurite lengths, branching and initiation of neuronal network formation. Glial differentiation was extensive on control poly lysine coated coverslips. Addition of laminin or heparan sulfate to composite collagen substrates significantly reduced glial immunofluorescence. Various neural ECM components were evaluated individually and in combination to study their effect of neuroglial differentiation of adult enteric neuronal progenitor cells. Our results indicate that specific ECM substrates that include type IV Collagen, laminin and heparan sulfate support and maintain neuronal and glial differentiation to different extents. Here, we identify a matrix composition optimized to tissue engineer transplantable innervated GI smooth muscle constructs to remedy aganglionic disorders.

Ex vivo neurogenesis within enteric ganglia occurs in a PTEN dependent manner

A population of multipotent stem cells capable of differentiating into neurons and glia has been isolated from adult intestine in humans and rodents. While these cells may provide a pool of stem cells for neurogenesis in the enteric nervous system (ENS), such a function has been difficult to demonstrate in vivo. An extensive study by Joseph et al. involving 108 rats and 51 mice submitted to various insults demonstrated neuronal uptake of thymidine analog BrdU in only 1 rat. Here we introduce a novel approach to study neurogenesis in the ENS using an ex vivo organotypic tissue culturing system. Culturing longitudinal muscle and myenteric plexus tissue, we show that the enteric nervous system has tremendous replicative capacity with the majority of neural crest cells demonstrating EdU uptake by 48 hours. EdU⁺ cells express both neuronal and glial markers. Proliferation appears dependent on the PTEN/PI3K/Akt pathway with decreased PTEN mRNA expression and increased PTEN phosphorylation (inactivation) corresponding to increased Akt activity and proliferation. Inhibition of PTEN with bpV(phen) augments proliferation while LY294002, a PI3K inhibitor, blocks it. These data suggest that the ENS is capable of neurogenesis in a PTEN dependent manner.

Regulation of progenitor cell proliferation and neuronal differentiation in enteric nervous system neurospheres

Enteric nervous system (ENS) progenitor cells isolated from mouse and human bowel can be cultured in vitro as neurospheres which are aggregates of the proliferating progenitor cells, together with neurons and glial cells derived from them. To investigate the factors regulating progenitor cell proliferation and differentiation, we first characterised cell proliferation in mouse ENS neurospheres by pulse chase experiments using thymidine analogs. We demonstrate rapid and continuous cell proliferation near the neurosphere periphery, after which postmitotic cells move away from the periphery to become distributed throughout the neurosphere. While many proliferating cells expressed glial markers, expression of the neuronal markers β-tubulin III (Tuj1) and nitric oxide synthase was detected in increasing numbers of post-mitotic cells after a delay of several days. Treatment of both mouse and human neurospheres with the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) reduced expression of the transcription factors Hes1 and Hes5, demonstrating inhibition of Notch signaling. DAPT treatment also inhibited progenitor cell proliferation and increased the numbers of differentiating neurons expressing Tuj1 and nitric oxide synthase. To confirm that the cellular effects of DAPT treatment were due to inhibition of Notch signaling, siRNA knockdown of RBPjκ, a key component of the canonical Notch signaling pathway, was demonstrated both to reduce proliferation and to increase neuronal differentiation in neurosphere cells. These observations indicate that Notch signaling promotes progenitor cell proliferation and inhibits neuronal differentiation in ENS neurospheres.