Enteric nervous system: development and developmental disturbances--part 2

Untargeted Maternal Plasma Metabolomics in Hirschsprung Disease: A Pilot Study

Background and Aims

Hirschsprung disease (HSCR) is a congenital disorder of unknown etiology affecting the enteric nervous system (ENS). Since the early gestational development of the ENS is dependent on the prenatal maternal metabolic environment, the objective of this pilot study was to explore the role of specific maternal plasma metabolites in the etiology of HSCR.

Methods

In this cross-sectional study, postnatal (as a surrogate for prenatal) plasma samples were obtained from mothers of children diagnosed with HSCR (n = 7) and age-matched mothers of normal children (n = 6). The plasma metabolome was analyzed by ultra-high-pressure liquid chromatography and mass spectrometry. Metabolites were identified by mzCloud using Compound Discoverer software. Using an untargeted metabolomics workflow, metabolites with case versus control group differences were identified.

Results

A total of 268 unique plasma metabolites were identified and annotated in maternal plasma. Of these, 57 were significantly different between case and control groups (P < 0.05, t-test). Using a false discovery rate corrected cutoff of 10% to adjust for multiple comparisons, 19 metabolites were significantly different in HSCR cases, including carnitines, medium-chain fatty acids, and glutamic acid. Pathways affected were for amino acid and lipid metabolism.

Conclusion

Disordered prenatal metabolic pathways may be involved in the etiopathogenesis of HSCR in the developing fetus. This is the first study to assess maternal plasma metabolomics in HSCR.

Interstitial cells of Cajal: clinical relevance in pediatric gastrointestinal motility disorders

Interstitial cells of Cajal (ICCs) are pacemaker cells of gastrointestinal motility that generate and transmit electrical slow waves to smooth muscle cells in the gut wall, thus inducing phasic contractions and coordinated peristalsis. Traditionally, tyrosine-protein kinase Kit (c-kit), also known as CD117 or mast/stem cell growth factor receptor, has been used as the primary marker of ICCs in pathology specimens. More recently, the Ca2+-activated chloride channel, anoctamin-1, has been introduced as a more specific marker of ICCs. Over the years, various gastrointestinal motility disorders have been described in infants and young children in which symptoms of functional bowel obstruction arise from ICC-related neuromuscular dysfunction of the colon and rectum. The current article provides a comprehensive overview of the embryonic origin, distribution, and functions of ICCs, while also illustrating the absence or deficiency of ICCs in pediatric patients with Hirschsprung disease intestinal neuronal dysplasia, isolated hypoganglionosis, internal anal sphincter achalasia, and congenital smooth muscle cell disorders such as megacystis microcolon intestinal hypoperistalsis syndrome.

Who's talking to whom: microbiome-enteric nervous system interactions in early life

The enteric nervous system (ENS) is the intrinsic nervous system of the gastrointestinal tract (GI) and regulates important GI functions, including motility, nutrient uptake, and immune response. The development of the ENS begins during early organogenesis and continues to develop once feeding begins, with ongoing plasticity into adulthood. There has been increasing recognition that the intestinal microbiota and ENS interact during critical periods, with implications for normal development and potential disease pathogenesis. In this review, we focus on insights from mouse and zebrafish model systems to compare and contrast how each model can serve in elucidating the bidirectional communication between the ENS and the microbiome. At the end of this review, we further outline implications for human disease and highlight research innovations that can lead the field forward.

A Model for Cell Proliferation in a Developing Organism

In mathematical biology, there is a great deal of interest in producing continuum models by scaling discrete agent-based models governed by local stochastic rules. We discuss a particular example of this approach: a model for the proliferation of neural crest cells that can help us understand the development of Hirschprung's disease, a potentially-fatal condition in which the enteric nervous system of a new-born child does not extend all the way through the intestine and colon. Our starting point is a discrete-state, continuous-time Markov chain model proposed by Hywood et al. (2013a) for the location of the neural crest cells that make up the enteric nervous system. Hywood et al. (2013a) scaled their model to derive an approximate second order partial differential equation describing how the limiting expected number of neural crest cells evolve in space and time. In contrast, we exploit the relationship between the above-mentioned Markov chain model and the well-known Yule-Furry process to derive the exact form of the scaled version of the process. Furthermore, we provide expressions for other features of the domain agent occupancy process, such as the variance of the marginal occupancy at a particular site, the distribution of the number of agents that are yet to reach a given site and a stochastic description of the process itself.

Apoptotic and Degenerative Changes in the Enteric Nervous System Following Exposure to Fluoride During Pre- and Post-natal Periods

Children born in fluorosis endemic areas usually suffer from gastrointestinal complications and are unable to attain normal growth as per their age group. The enteric nervous system (ENS) controls gut movement and functions. It is highly vulnerable to any ingested toxins. Based on observations, it was hypothesized that fluoride exposure during pregnancy and lactation might induce ENS developmental defects. The aim of this study is to investigate the effects of fluoride exposure during pregnancy and lactation on ENS of the first-generation rat pups. After confirmation of pregnancy, female rats were divided into 3 groups and kept on normal water (group 1), 50 ppm of fluoride (group 2), and 100 ppm of fluoride (group 3). The fluoride exposure started at the start of pregnancy and continued until lactation. On the 21st post-natal day, the pups were euthanized and the gut tissue and blood were harvested and subjected to fluoride measurement, oxidative stress estimation, histopathological and ultrastructural analysis, TUNEL, and immunofluorescence. The quantitative expressional analysis of embryonic lethal abnormal vision-like 4 (ELAVL4) (a pan-neuronal marker) and glial fibrillary acidic protein (GFAP) (a glial cell marker) genes was performed by RT-qPCR. An increase in oxidative stress, subcellular and cellular injuries, and apoptosis in enteric neuronal, glial, and epithelial cells was observed in the distal colon of the first-generation pups. Ganglionic degeneration, reduced expression of HuC/D and GFAP, altered colon muscle layer thickness, and tissue edema were observed in the fluoride-treated groups compared with the control. Fluoride exposure during prenatal and lactation period leads to subcellular and cellular injuries due to increased oxidative stress and apoptosis in the ENS. The reduction in the number of neurons and glia due to increased apoptosis may cause alterations in ENS development.

A study on genetic polymorphism of RET proto-oncogene in Hirschsprung's disease in children

BACKGROUND

Hirschsprung's disease (HD) is a genetic disorder with a complex pattern of inheritance. Some single-nucleotide polymorphisms (SNPs) are identified to be associated with the risk of Hirschsprung's Disease (HSCR).

AIMS AND OBJECTIVES

The aim of this study is to know the association between the rearranged during transfection (RET) proto-oncogene polymorphism and HD and to characterize the SNPs of RET proto-oncogene affecting HD.

MATERIALS AND METHODS

The study was conducted in the Department of Pathology in association with the Department of Pediatric Surgery. Blood samples were collected from the patients diagnosed with confirmed HD and from age- and sex-matched controls. This case-control study consisted of 53 HSCR cases and 50 controls. Genotypes of rs1800860 and rs1800861 were analysed in by polymerase chain reaction amplification and sanger sequencing. Associations with the risk of HSCR were estimated by odds ratio (OR) and their 95% confidence intervals (95% CI) using.

RESULTS

We observed that in the case of rs1800860A > G genotype AG was not associated with the increasing risk of disease (OR with 95% CI = 0.568 [0.238-1.356]) while genotype GG was associated with increasing the risk of the disease (OR with 95% CI = 2.278 [0.967-5.366]). In the case of rs1800861G > T genotype GT was associated with lowering the risk of the disease (OR with 95% CI = 0.230 [0.0981-0.539]) while genotype TT was associated with increasing the risk of the disease (OR with 95% CI = 9.647 [3.830-24.302]). The difference in the genotypic distribution of GT and TT at rs1800861G > T between Short segment disease (SSD) cases and Long Segment Disease (LSD) and total colonic aganglionosis was made by Fisher's exact test and it was statistically significant (P = 0.0476 and 0.0054).

CONCLUSION

The results of this study support the hypothesis that variations in RET pathway might play an important role in the development of HSCR.

Immunohistochemistry-based comparative study in detection of Hirschsprung's disease in infants in a Tertiary Care Center

BACKGROUND:

Hirschsprung's disease (HD) is the major cause of pediatric intestinal obstruction with a complex pattern of inheritance. The absence of ganglion cells along with an analysis of hypertrophy and hyperplasia of nerves in the nerve plexus of submucosa and muscularis mucosae is regarded as a potential hallmark for its diagnosis.

AIMS AND OBJECTIVES:

This study was undertaken to ascertain the (1) clinical profile, (2) mode of presentation, and (3) to compare the role of calretinin immunostaining with acetylcholinesterase in the diagnosis of HD.

MATERIALS AND METHODS:

This prospective and observational study was conducted in the Department of Pathology, IPGME & R from June 2014 to May 2015. One hundred and four patients clinically and radiologically diagnosed with HD underwent surgery were included in the study. The data of every patient including age, sex, and presenting symptoms were recorded. Eventually, histopathological, calretinin, and acetylcholinesterase immunohistochemical examination were done.

RESULTS:

Total numbers of cases studied were 104, which aged between 0 days and 365 days. Male preponderance (76.92%) was noted. The overall sensitivity, specificity, positive, and negative predictive value of acetylcholinesterase were 100%, 86.44%, 84.91%, and 100%, respectively. The concordance of detection of ganglion cells and nerve fibers, and thereby diagnosis of Hirschsprung's and non-HD using calretinin and the gold standard was statistically in strong agreement (κ = 0.749, 95% confidence interval: 0.635–0.863).

CONCLUSIONS:

Calretinin stands out as the single and indispensable tool that differentiates HD from other mimickers.

Addressing Interdisciplinary Difficulties in Developmental Biology/Mathematical Collaborations: A Neural Crest Example

Mathematical modeling can allow insight into the biological processes that can be difficult to access by conventional biological means alone. Such projects are becoming increasingly attractive with the appearance of faster and more powerful quantitative techniques in both biological data acquisition and data storage, manipulation, and presentation. However, as is frequent in interdisciplinary research, the main hurdles are not within the mindset and techniques of each discipline but are usually encountered in attempting to meld the different disciplines together. Based upon our experience in applying mathematical methods to investigate how neural crest cells interact to form the enteric nervous system, we present our views on how to pursue biomathematical modeling projects, what difficulties to expect, and how to overcome, or at least survive, these hurdles. The main advice being: persevere.

Advances in Enteric Neurobiology: The "Brain" in the Gut in Health and Disease

The enteric nervous system (ENS) is a large, complex division of the peripheral nervous system that regulates many digestive, immune, hormonal, and metabolic functions. Recent advances have elucidated the dynamic nature of the mature ENS, as well as the complex, bidirectional interactions among enteric neurons, glia, and the many other cell types that are important for mediating gut behaviors. Here, we provide an overview of ENS development and maintenance, and focus on the latest insights gained from the use of novel model systems and live-imaging techniques. We discuss major advances in the understanding of enteric glia, and the functional interactions among enteric neurons, glia, and enteroendocrine cells, a large class of sensory epithelial cells. We conclude by highlighting recent work on muscularis macrophages, a group of immune cells that closely interact with the ENS in the gut wall, and the importance of neurological-immune system communication in digestive health and disease.

Gene expression profiling coupled with Connectivity Map database mining reveals potential therapeutic drugs for Hirschsprung disease

BACKGROUND

Hirschsprung disease (HD) is a congenital intestinal anomaly resulting from a failure to form enteric ganglia in the lower bowel. Surgery is the main therapeutic strategy, although neural stem cell transplantation has recently shown promise. However, HD remains a challenging disorder to treat. Our aim was to identify drugs that could counteract the dysregulated pathways in HD and could thus be potential novel therapies.

METHODS

We used microarray analysis to identify genes differentially expressed in ganglionic and aganglionic bowel samples from eight children with HD. The signature of differentially expressed genes was then used as a search query to explore the Connectivity Map (cMAP), a transcriptional expression database that catalogs gene signatures elicited by chemical perturbagens.

RESULTS

We uncovered several dysregulated signaling pathways, and in particular regulation of neuron development, in HD. The cMAP search identified some compounds with the potential to counteract the effects of the dysregulated molecular signature in this disease. One of these, pepstatin A, was recently shown to rescue the migration defects observed in a mouse model of HD, providing strong support for our findings.

CONCLUSIONS

This study advances our understanding of the molecular changes in HD and identifies several potential pharmacological interventions. Further testing of the identified compounds is warranted.

GFRA1: A Novel Molecular Target for the Prevention of Osteosarcoma Chemoresistance

The glycosylphosphatidylinositol-linked GDNF (glial cell derived neurotrophic factor) receptor alpha (GFRA), a coreceptor that recognizes the GDNF family of ligands, has a crucial role in the development and maintenance of the nervous system. Of the four identified GFRA isoforms, GFRA1 specifically recognizes GDNF and is involved in the regulation of proliferation, differentiation, and migration of neuronal cells. GFRA1 has also been implicated in cancer cell progression and metastasis. Recent findings show that GFRA1 can contribute to the development of chemoresistance in osteosarcoma. GFRA1 expression was induced following treatment of osteosarcoma cells with the popular anticancer drug, cisplatin and induction of GFRA1 expression significantly suppressed apoptosis mediated by cisplatin in osteosarcoma cells. GFRA1 expression promotes autophagy by activating the SRC-AMPK signaling axis following cisplatin treatment, resulting in enhanced osteosarcoma cell survival. GFRA1-induced autophagy promoted tumor growth in mouse xenograft models, suggesting a novel function of GFRA1 in osteosarcoma chemoresistance.

Identification of two novel PCDHA9 mutations associated with Hirschsprung's disease

Hirschsprung's disease (HSCR) is a complex disorder with multiple pathogenic gene mutations. Protocadherin alpha 9 (PCDHA9) was identified as a potential candidate gene for HSCR by whole-exome sequencing in a Chinese family. Sanger sequencing in 298 HSCR cases revealed two sporadic Chinese patients with a novel missence PCDHΑ9 mutation (NM_031857; c.1280C > T[p.Ala427Val]) and one sporadic Chinese patient with another novel missence PCDHΑ9 mutation (c.1425C > G[p.Phe475Leu]).The silico predictions and 3D modeling suggest the deleterious effect of identified mutations on protein function. Immunohistochemistry analysis showed PCDHΑ9 was predominantly expressed in the myenteric plexus of human colon tissues. For mouse embryos, PCDHΑ9 was expressed in the stomach but rarely seen in the intestine during E10.5-12.5, then obviously expressed in the intestinal mucosa at E13.5 and extensively expressed in intestinal muscularis and mucosa at E14.5. Moreover, the down-regulation of PCDHΑ9 in the SH-SY5Y cell line promoted the proliferation and migration rate but inhibited the apoptotic rate. In summary, PCDHΑ9 is potentially related to HSCR and the clustered protocadherins (Pcdhs) may involve in the enteric nervous system (ENS) ontogeny.

Enhancer Variants Synergistically Drive Dysfunction of a Gene Regulatory Network In Hirschsprung Disease

Common sequence variants in cis-regulatory elements (CREs) are suspected etiological causes of complex disorders. We previously identified an intronic enhancer variant in the RET gene disrupting SOX10 binding and increasing Hirschsprung disease (HSCR) risk 4-fold. We now show that two other functionally independent CRE variants, one binding Gata2 and the other binding Rarb, also reduce Ret expression and increase risk 2- and 1.7-fold. By studying human and mouse fetal gut tissues and cell lines, we demonstrate that reduced RET expression propagates throughout its gene regulatory network, exerting effects on both its positive and negative feedback components. We also provide evidence that the presence of a combination of CRE variants synergistically reduces RET expression and its effects throughout the GRN. These studies show how the effects of functionally independent non-coding variants in a coordinated gene regulatory network amplify their individually small effects, providing a model for complex disorders.

Identification of different mechanisms leading to PAX6 down-regulation as potential events contributing to the onset of Hirschsprung disease

Hirschsprung disease (HSCR) is attributed to a failure of neural crest derived cells to migrate, proliferate, differentiate or survive in the bowel wall during embryonic Enteric Nervous System (ENS) development. This process requires a wide and complex variety of molecules and signaling pathways which are activated by transcription factors. In an effort to better understand the etiology of HSCR, we have designed a study to identify new transcription factors participating in different stages of the colonization process. A differential expression study has been performed on a set of transcription factors using Neurosphere-like bodies from both HSCR and control patients. Differential expression levels were found for CDYL, MEIS1, STAT3 and PAX6. A significantly lower expression level for PAX6 in HSCR patients, would suit with the finding of an over-representation of the larger tandem (AC)m(AG)n repeats within the PAX6 promoter in HSCR patients, with the subsequent loss of protein P300 binding. Alternatively, PAX6 is a target for DNMT3B-dependant methylation, a process already proposed as a mechanism with a role in HSCR. Such decrease in PAX6 expression may influence in the proper function of signaling pathways involved in ENS with the confluence of additional genetic factors to the manifestation of HSCR phenotype.

Expression of the Wnt Receptor Frizzled-4 in the Human Enteric Nervous System of Infants

The Wnt signalling pathway plays a crucial role in the development of the nervous system. This signalling cascade is initiated upon binding of the secreted Wnt ligand to a member of the family of frizzled receptors. In the present study, we analysed the presence of frizzled-4 in the enteric nervous system of human infants. Frizzled-4 could be identified by immunohistochemistry in a subpopulation of enteric neuronal and glial cells in the small and large intestine. Detection of frizzled-4 in the tunica muscularis by RT-PCR confirmed this receptor's expression on the mRNA level. Interestingly, we observed distinct cell populations that co-expressed frizzled-4 with the intermediate filament protein nestin and the neurotrophin receptor p75^NTR, which have been reported to be expressed in neural progenitor cells. Flow cytometry analysis revealed that 60% of p75^NTR positive cells of the tunica muscularis were positive for frizzled-4. Additionally, in pathological samples of Hirschsprung's disease, the expression of this Wnt receptor correlated with the number of myenteric ganglion cells and decreased from normoganglionic to aganglionic areas of large intestine. The expression pattern of frizzled-4 indicates that this Wnt receptor could be involved in postnatal development and/or function of the enteric nervous system.

Enteric Neural Cells From Hirschsprung Disease Patients Form Ganglia in Autologous Aneuronal Colon

BACKGROUND & AIMS

Hirschsprung disease (HSCR) is caused by failure of cells derived from the neural crest (NC) to colonize the distal bowel in early embryogenesis, resulting in absence of the enteric nervous system (ENS) and failure of intestinal transit postnatally. Treatment is by distal bowel resection, but neural cell replacement may be an alternative. We tested whether aneuronal (aganglionic) colon tissue from patients may be colonized by autologous ENS-derived cells.

METHODS

Cells were obtained and cryopreserved from 31 HSCR patients from the proximal resection margin of colon, and ENS cells were isolated using flow cytometry for the NC marker p75 (nine patients). Aneuronal colon tissue was obtained from the distal resection margin (23 patients). ENS cells were assessed for NC markers immunohistologically and by quantitative reverse-transcription polymerase chain reaction, and mitosis was detected by ethynyl-2'-deoxyuridine labeling. The ability of human HSCR postnatal ENS-derived cells to colonize the embryonic intestine was demonstrated by organ coculture with avian embryo gut, and the ability of human postnatal HSCR aneuronal colon muscle to support ENS formation was tested by organ coculture with embryonic mouse ENS cells. Finally, the ability of HSCR patient ENS cells to colonize autologous aneuronal colon muscle tissue was assessed.

RESULTS

ENS-derived p75-sorted cells from patients expressed multiple NC progenitor and differentiation markers and proliferated in culture under conditions simulating Wnt signaling. In organ culture, patient ENS cells migrated appropriately in aneural quail embryo gut, and mouse embryo ENS cells rapidly spread, differentiated, and extended axons in patient aneuronal colon muscle tissue. Postnatal ENS cells derived from HSCR patients colonized autologous aneuronal colon tissue in cocultures, proliferating and differentiating as neurons and glia.

CONCLUSIONS

NC-lineage cells can be obtained from HSCR patient colon and can form ENS-like structures in aneuronal colonic muscle from the same patient.

Knockout mouse models of Hirschsprung's disease

PURPOSE

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cell migration. Rodent animal models of aganglionosis have contributed greatly to our understanding of the genetic basis of HSCR. Several natural or target mutations in specific genes have been reported to produce developmental defects in neural crest migration, differentiation or survival. The aim of this study was to review the currently available knockout models of HSCR to better understand the molecular basis of HSCR.

METHODS

A review of the literature using the keywords "Hirschsprung's disease", "aganglionosis", "megacolon" and "knockout mice model" was performed. Resulting publications were reviewed for relevant mouse models of human aganglionosis. Reference lists were screened for additional relevant studies.

RESULTS

16 gene knockout mouse models were identified as relevant rodent models of human HSCR. Due to the deletion of a specific gene, the phenotypes of these knockout models are diverse and range from small bowel dilatation and muscular hypertrophy to total intestinal aganglionosis.

CONCLUSIONS

Mouse models of aganglionosis have been instrumental in the discovery of the causative genes of HSCR. Although important advances have been made in understanding the genetic basis of HSCR, animal models of aganglionosis in future should further help to identify the unknown susceptibility genes in HSCR.

Isolation, expansion and transplantation of postnatal murine progenitor cells of the enteric nervous system

Neural stem or progenitor cells have been proposed to restore gastrointestinal function in patients suffering from congenital or acquired defects of the enteric nervous system. Various, mainly embryonic cell sources have been identified for this purpose. However, immunological and ethical issues make a postnatal cell based therapy desirable. We therefore evaluated and quantified the potential of progenitor cells of the postnatal murine enteric nervous system to give rise to neurons and glial cells in vitro. Electrophysiological analysis and BrdU uptake studies provided direct evidence that generated neurons derive from expanded cells in vitro. Transplantation of isolated and expanded postnatal progenitor cells into the distal colon of adult mice demonstrated cell survival for 12 weeks (end of study). Implanted cells migrated within the gut wall and differentiated into neurons and glial cells, both of which were shown to derive from proliferated cells by BrdU uptake. This study indicates that progenitor cells isolated from the postnatal enteric nervous system might have the potential to serve as a source for a cell based therapy for neurogastrointestinal motility disorders. However, further studies are necessary to provide evidence that the generated cells are capable to positively influence the motility of the diseased gastrointestinal tract.

Interstitial cells of Cajal in the normal human gut and in Hirschsprung disease

Hirschsprung disease (HD) is the most prevalent congenital gastrointestinal motility disorder. The pathogenesis of HD is defined as a functional intestinal obstruction resulting from a defect in the intrinsic innervation of the distal bowel. In addition to the enteric nervous system, the interstitial cells of Cajal (ICC) play an important role in the generation of coordinated gastrointestinal peristalsis. The major function of the ICCs is the generation of slow waves that allow these cells to act as specialised pacemaker cells within various tissues. ICCs have additional functions in the gastrointestinal tract as regulators of mechanical activity and neurotransmission. Due to the central role of ICCs in gastrointestinal peristalsis, it has been suggested that defects or impairments of the ICCs may contribute to motility dysfunction in several gastrointestinal motility disorders. This review describes the distribution and functions of ICCs in the normal gut and in Hirschsprung disease.

Choices choices: regulation of precursor differentiation during enteric nervous system development

Background The enteric nervous system (ENS) is the largest subdivision of the peripheral nervous system and forms a complex circuit of neurons and glia that controls the function of the gastrointestinal (GI) tract. Within this circuit, there are multiple subtypes of neurons and glia. Appropriate differentiation of these various cell subtypes is vital for normal ENS and GI function. Studies of the pediatric disorder Hirschprung's Disease (HSCR) have provided a number of important insights into the mechanisms and molecules involved in ENS development; however, there are numerous other GI disorders that potentially may result from defects in development/differentiation of only a subset of ENS neurons or glia. Purpose Our understanding of the mechanisms and molecules involved in enteric nervous system differentiation is far from complete. Critically, it remains unclear at what point the fates of enteric neural crest cells (ENCCs) become committed to a specific subtype cell fate and how these cell fate choices are made. We will review our current understanding of ENS differentiation and highlight key questions that need to be addressed to gain a more complete understanding of this biological process.

The developmental etiology and pathogenesis of Hirschsprung disease

The enteric nervous system is the part of the autonomic nervous system that directly controls the gastrointestinal tract. Derived from a multipotent, migratory cell population called the neural crest, a complete enteric nervous system is necessary for proper gut function. Disorders that arise as a consequence of defective neural crest cell development are termed neurocristopathies. One such disorder is Hirschsprung disease (HSCR), also known as congenital megacolon or intestinal aganglionosis. HSCR occurs in 1/5000 live births and typically presents with the inability to pass meconium, along with abdominal distension and discomfort that usually requires surgical resection of the aganglionic bowel. This disorder is characterized by a congenital absence of neurons in a portion of the intestinal tract, usually the distal colon, because of a disruption of normal neural crest cell migration, proliferation, differentiation, survival, and/or apoptosis. The inheritance of HSCR disease is complex, often non-Mendelian, and characterized by variable penetrance. Extensive research has identified a number of key genes that regulate neural crest cell development in the pathogenesis of HSCR including RET, GDNF, GFRα1, NRTN, EDNRB, ET3, ZFHX1B, PHOX2b, SOX10, and SHH. However, mutations in these genes account for only ∼50% of the known cases of HSCR. Thus, other genetic mutations and combinations of genetic mutations and modifiers likely contribute to the etiology and pathogenesis of HSCR. The aims of this review are to summarize the HSCR phenotype, diagnosis, and treatment options; to discuss the major genetic causes and the mechanisms by which they disrupt normal enteric neural crest cell development; and to explore new pathways that may contribute to HSCR pathogenesis.

Histopathologic delineation of the transition zone in short-segment Hirschsprung disease

Failure to completely resect the transition zone (TZ) between aganglionic and neuroanatomically normal bowel ("TZ pull-through") is considered one reason for postoperative obstructive symptoms in Hirschsprung disease (HD). Despite years of study, the proximal boundary of the TZ remains nebulous, complicated by discordant, often subjective, histopathologic definitions. In order to objectively delineate the TZ, transverse sections at 1 cm intervals from the rectums of 9 non-HD autopsy subjects and resections from 15 infants with short-segment HD were immunostained with Hu (ganglion cell bodies) and glucose transporter 1 (Glut1) (perineurium of extrinsic nerves), and 6 putative features of TZ were examined: (1) aganglionosis of ≥1/8th circumference; (2) myenteric or submucosal hypoganglionosis; (3) hypertrophic submucosal nerves; (4) Glut1+ submucosal innervation; (5) submucosal hyperganglionosis; and (6) "ectopic" ganglia in lamina propria, muscularis propria, or serosa. In non-HD controls, Glut1+ submucosal innervation, hypertrophic nerves, partial circumferential aganglionosis, and hypoganglionosis were absent or restricted to the distal 2 cm. In contrast, all 6 neuropathologic features of TZ were identified proximal to the aganglionic segment in the majority of HD resections, but the length of the TZ ranged from 0 to 12 cm, depending on which neuropathologic feature was considered. Excluding submucosal hyperganglionosis and ectopic ganglia, the TZ was generally ≤5 cm. Many features of TZ cannot be excluded intraoperatively with a biopsy or a full-circumference frozen section. However, partial circumferential aganglionosis, severe myenteric hypoganglionosis, and hypertrophic submucosal nerves can, and probably should, be assessed in full-circumference frozen sections of the proximal resection margin, to reduce the likelihood of TZ pull-through.

Retinoic acid upregulates ret and induces chain migration and population expansion in vagal neural crest cells to colonise the embryonic gut

Vagal neural crest cells (VNCCs) arise in the hindbrain, and at (avian) embryonic day (E) 1.5 commence migration through paraxial tissues to reach the foregut as chains of cells 1–2 days later. They then colonise the rest of the gut in a rostrocaudal wave. The chains of migrating cells later resolve into the ganglia of the enteric nervous system. In organ culture, E4.5 VNCCs resident in the gut (termed enteric or ENCC) which have previously encountered vagal paraxial tissues, rapidly colonised aneural gut tissue in large numbers as chains of cells. Within the same timeframe, E1.5 VNCCs not previously exposed to paraxial tissues provided very few cells that entered the gut mesenchyme, and these never formed chains, despite their ability to migrate in paraxial tissue and in conventional cell culture. Exposing VNCCs in vitro to paraxial tissue normally encountered en route to the foregut conferred enteric migratory ability. VNCC after passage through paraxial tissue developed elements of retinoic acid signalling such as Retinoic Acid Binding Protein 1 expression. The paraxial tissue's ability to promote gut colonisation was reproduced by the addition of retinoic acid, or the synthetic retinoid Am80, to VNCCs (but not to trunk NCCs) in organ culture. The retinoic acid receptor antagonist CD 2665 strongly reduced enteric colonisation by E1.5 VNCC and E4.5 ENCCs, at a concentration suggesting RARα signalling. By FACS analysis, retinoic acid application to vagal neural tube and NCCs in vitro upregulated Ret; a Glial-derived-neurotrophic-factor receptor expressed by ENCCs which is necessary for normal enteric colonisation. This shows that early VNCC, although migratory, are incapable of migrating in appropriate chains in gut mesenchyme, but can be primed for this by retinoic acid. This is the first instance of the characteristic form of NCC migration, chain migration, being attributed to the application of a morphogen.

Development and developmental disorders of the enteric nervous system

The enteric nervous system (ENS) arises from neural crest-derived cells that migrate into and along the gut, leading to the formation of a complex network of neurons and glial cells that regulates motility, secretion and blood flow. This Review summarizes the progress made in the past 5 years in our understanding of ENS development, including the migratory pathways of neural crest-derived cells as they colonize the gut. The importance of interactions between neural crest-derived cells, between signalling pathways and between developmental processes (such as proliferation and migration) in ensuring the correct development of the ENS is also presented. The signalling pathways involved in ENS development that were determined using animal models are also described, as is the evidence for the involvement of the genes encoding these molecules in Hirschsprung disease-the best characterized paediatric enteric neuropathy. Finally, the aetiology and treatment of Hirschsprung disease in the clinic and the potential involvement of defects in ENS development in other paediatric motility disorders are outlined.

Diabetes-related alterations in the enteric nervous system and its microenvironment

Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.

Neural crest stem cells: discovery, properties and potential for therapy

Neural crest (NC) cells are a migratory cell population synonymous with vertebrate evolution. They generate a wide variety of cell and tissue types during embryonic and adult development including cartilage and bone, connective tissue, pigment and endocrine cells as well as neurons and glia amongst many others. Such incredible lineage potential combined with a limited capacity for self-renewal, which persists even into adult life, demonstrates that NC cells bear the key hallmarks of stem and progenitor cells. In this review, we describe the identification, characterization and isolation of NC stem and progenitor cells from different tissues in both embryo and adult organisms. We discuss their specific properties and their potential application in cell-based tissue and disease-specific repair.

A firm grip does not always pay off: a new Phact(r) 4 integrin signaling

β1 integrin signaling plays crucial roles in enteric nervous system development. Zhang and colleagues (pp. 69-81) discovered that phosphatase and actin regulator 4 (Phactr4) antagonizes β1 integrin signaling through protein phosphatase 1 (PP1) in focal adhesions of enteric neural crest cells (ENCCs). Loss of Phactr4-PP1 interaction leads to increased β1 integrin signaling, loss of collective and directional migration, and hindgut hypogangaliosis, indicating that the right adjustment of β1 integrin signaling is required for the normal migration and organization of ENCCs.

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.

Genetic background strongly modifies the severity of symptoms of Hirschsprung disease, but not hearing loss in rats carrying Ednrb(sl) mutations

Hirschsprung disease (HSCR) is thought to result as a consequence of multiple gene interactions that modulate the ability of enteric neural crest cells to populate the developing gut. However, it remains unknown whether the single complete deletion of important HSCR-associated genes is sufficient to result in HSCR disease. In this study, we found that the null mutation of the Ednrb gene, thought indispensable for enteric neuron development, is insufficient to result in HSCR disease when bred onto a different genetic background in rats carrying Ednrb^sl mutations. Moreover, we found that this mutation results in serious congenital sensorineural deafness, and these strains may be used as ideal models of Waardenburg Syndrome Type 4 (WS4). Furthermore, we evaluated how the same changed genetic background modifies three features of WS4 syndrome, aganglionosis, hearing loss, and pigment disorder in these congenic strains. We found that the same genetic background markedly changed the aganglionosis, but resulted in only slight changes to hearing loss and pigment disorder. This provided the important evidence, in support of previous studies, that different lineages of neural crest-derived cells migrating along with various pathways are regulated by different signal molecules. This study will help us to better understand complicated diseases such as HSCR and WS4 syndrome.

RGMa inhibits neurite outgrowth of neuronal progenitors from murine enteric nervous system via the neogenin receptor in vitro

The enteric nervous system (ENS) in vertebrate embryos is formed by neural crest-derived cells. During development, these cells undergo extensive migration from the vagal and sacral regions to colonize the entire gut, where they differentiate into neurons and glial cells. Guidance molecules like netrins, semaphorins, slits, and ephrins are known to be involved in neuronal migration and axon guidance. In the CNS, the repulsive guidance molecule (RGMa) has been implicated in neuronal differentiation, migration, and apoptosis. Recently, we described the expression of the subtypes RGMa and RGMb and their receptor neogenin during murine gut development. In the present study, we investigated the influence of RGMa on neurosphere cultures derived from fetal ENS. In functional in vitro assays, RGMa strongly inhibited neurite outgrowth of differentiating progenitors via the receptor neogenin. The repulsive effect of RGMa on processes of differentiated enteric neural progenitors could be demonstrated by collapse assay. The influence of the RGM receptor on ENS was also analyzed in neogenin knockout mice. In the adult large intestine of mutants we observed disturbed ganglia formation in the myenteric plexus. Our data indicate that RGMa may be involved in differentiation processes of enteric neurons in the murine gut.

n-3 polyunsaturated fatty acids in the maternal diet modify the postnatal development of nervous regulation of intestinal permeability in piglets

The intestinal epithelial barrier (IEB) plays a key role in the maintenance of gut homeostasis and the development of the immune system in newborns. The enteric nervous system (ENS), a key regulator of gastrointestinal functions, has been shown to be modulated by nutritional factors. However, it remains currently unknown whether maternal diet, in particular n-3 polyunsaturated fatty acids (n-3PUFAs), can impact upon the IEB in newborn piglets and whether the ENS is involved in this effect. Sows received either a control diet (lard based) or an n-3PUFA diet (linseed oil based) during gestation and lactation. Intestinal paracellular permeability was assessed in Ussing chambers on piglets at birth, 3, 7, 14, 21 and 28 postnatal days (PND). Basal jejunal permeability increased significantly and similarly in both groups until PND14 and decreased thereafter. However, at PND28, permeability was higher in n-3PUFA animals as compared to controls. In addition, a vasoactive intestinal peptide (VIP) receptor antagonist increased paracellular permeability in controls but not in n-3PUFA piglets. Conversely, atropine and hexamethonium decreased paracellular permeability in the n-3PUFA group but not in the control group. Moreover, the n-3PUFA diet increased the proportion of choline acetyltransferase (ChAT)-immunoreactive (IR) neurons and decreased the proportion of VIP-IR neurons in the submucosal plexus of piglet jejunum compared to controls. In addition, in primary culture of rat ENS, we showed that 20:5n-3 but not 18:3n-3 increased the proportion of ChAT-IR neurons and decreased the proportion of VIP-IR neurons. In conclusion, supplementation of the maternal diet with n-3PUFAs modified intestinal permeability probably via diet-induced neuroplastic changes in the ENS of newborn piglets.

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.

Prospective identification and isolation of enteric nervous system progenitors using Sox2

The capacity to identify and isolate lineage-specific progenitor cells from developing and mature tissues would enable the development of cell replacement therapies for disease treatment. The enteric nervous system (ENS) regulates important gut functions, including controlling peristaltic muscular contractions, and consists of interconnected ganglia containing neurons and glial cells. Hirschsprung's disease (HSCR), one of the most common and best understood diseases affecting the ENS, is characterized by absence of enteric ganglia from the distal gut due to defects in gut colonization by neural crest progenitor cells and is an excellent candidate for future cell replacement therapies. Our previous microarray experiments identified the neural progenitor and stem cell marker SRY-related homoebox transcription factor 2 (Sox2) as expressed in the embryonic ENS. We now show that Sox2 is expressed in the ENS from embryonic to adult stages and constitutes a novel marker of ENS progenitor cells and their glial cell derivatives. We also show that Sox2 expression overlaps significantly with SOX10, a well-established marker of ENS progenitors and enteric glial cells. We have developed a strategy to select cells expressing Sox2, by using G418 selection on cultured gut cells derived from Sox2^βgeo/+ mouse embryos, thus allowing substantial enrichment and expansion of neomycin-resistant Sox2-expressing cells. Sox2^βgeo cell cultures are enriched for ENS progenitors. Following transplantation into embryonic mouse gut, Sox2^βgeo cells migrate, differentiate, and colocalize with the endogenous ENS plexus. Our studies will facilitate development of cell replacement strategies in animal models, critical to develop human cell replacement therapies for HSCR. Stem Cells 2011;29:128–140

Building stable chains with motile agents: Insights into the morphology of enteric neural crest cell migration

A defining characteristic of the normal development of the enteric nervous system (ENS) is the existence of an enteric neural crest (ENC) cell colonization wave, where the ENC cells form stable chains often associated with axons and near the vascular network. However, within this evolving neural network, the individual ENC cell elements constantly move, change direction and appear to act independently of neighbors. Three possible hypotheses are investigated. The simplest of these postulates that the ENS follows the vascular network as a template. We present evidence which does not support this hypothesis. Two viable alternatives are either that (i) the axons muster the ENC cells, providing the pattern for the chain migration or (ii) ENC cells form chains and the axons follow these paths. These two hypotheses are explored by developing a stochastic cellular automata model, where ENC agents follow simple rules, which reflect the underlying biology of movement, proliferation and differentiation. By simulating ENC precursors and the associated neurons and axons, two models with different fundamental mechanisms are developed. From local rules, a mesoscale network pattern with lacunae emerges, which can be analyzed quantitatively. Simulation and analysis establishes the parameters that affect the morphology of the resulting network. This investigation into the axon/ENC and ENC/ENC interplay suggests possible explanations for observations in mouse and avian embryos in normal and abnormal ENS development, as well as further experimentation.

Abnormal development of the enteric nervous system in rat embryos and fetuses with congenital diaphragmatic hernia

BACKGROUND/AIM

Esophageal dilatation, gastroesophageal reflux, and intestinal obstruction have been demonstrated in CDH survivors. Abnormal esophageal and intestinal innervations were recently found in rats and babies with this disease. Our aim was to further characterize these malformations in embryos and fetal rats exposed to nitrofen.

METHODS

Pregnant rats received either 100 mg nitrofen or vehicle on E9.5. Fetuses were recovered at E15, E18, and E21. Sections of esophagus and small bowel were histochemically stained with acetylcholinesterase (AChE) and immunostained for PGP9.5. PGP9.5 gen protein were measured on E21 and PGP9.5 mRNA on E15, E18 and E21. Comparisons between groups were made with non-parametrics tests.

RESULTS

Histochemistry and immunohistochemistry showed deficient innervation in all anatomical areas studied at E15, E18, and E21, and WB confirmed this decrease in E21 fetuses. PGP9.5 messenger was decreased in nitrofen-exposed animals on E18 (esophagus) or E15 (small bowel), and increased on E21 in the esophagus and E18 in small bowel.

CONCLUSIONS

Development of the enteric nervous system of the esophagus, stomach, and small bowel is deficient in rat embryos and fetuses exposed to nitrofen. These anomalies could account in part for the long-term gastrointestinal morbidity observed in CDH survivors.

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.

Genetic background impacts developmental potential of enteric neural crest-derived progenitors in the Sox10Dom model of Hirschsprung disease

Abnormalities in the development of enteric neural crest-derived progenitors (ENPs) that generate the enteric nervous system (ENS) can lead to aganglionosis in a variable portion of the distal gastrointestinal tract. Cumulative evidence suggests that variation of aganglionosis is due to gene interactions that modulate the ability of ENPs to populate the intestine; however, the developmental processes underlying this effect are unknown. We hypothesized that differences in enteric ganglion deficits could be attributable to the effects of genetic background on early developmental processes, including migration, proliferation, or lineage divergence. Developmental processes were investigated in congenic Sox10(Dom) mice, an established Hirschsprung disease (HSCR) model, on distinct inbred backgrounds, C57BL/6J (B6) and C3HeB/FeJ (C3Fe). Immuno-staining on whole-mount fetal gut tissue and dissociated cell suspensions was used to assess migration and proliferation. Flow cytometry utilizing the cell surface markers p75 and HNK-1 was used to isolate live ENPs for analysis of developmental potential. Frequency of ENPs was reduced in Sox10(Dom) embryos relative to wild-type embryos, but was unaffected by genetic background. Both migration and developmental potential of ENPs in Sox10(Dom) embryos were altered by inbred strain background with the most highly significant differences seen for developmental potential between strains and genotypes. In vivo imaging of fetal ENPs and postnatal ganglia demonstrates that altered lineage divergence impacts ganglia in the proximal intestine. Our analysis demonstrates that genetic background alters early ENS development and suggests that abnormalities in lineage diversification can shift the proportions of ENP populations and thus may contribute to ENS deficiencies in vivo.

L1cam acts as a modifier gene during enteric nervous system development

The enteric nervous system is derived from neural crest cells that migrate from the caudal hindbrain and colonise the gut. Failure of neural crest cells to fully colonise the gut results in an "aganglionic zone" that lacks a functional enteric nervous system over a variable length of the distal bowel, a condition in human infants known as Hirschsprung's disease. The variability observed in the penetrance and severity of Hirschsprung's disease suggests a role for modifier genes. Clinical studies have identified a population of Hirschsprung's patients with mutations in L1CAM that also have a common polymorphism in RET, suggesting a possible interaction between L1CAM and RET. Therefore, we examined whether L1cam could interact with Ret, its ligand Gdnf, and a known transcriptional activator of Ret, Sox10. Using a two-locus complementation approach, we show that loss of L1cam in conjunction with a heterozygous loss of Ret or Gdnf did not result in aganglionosis. However, L1cam did interact with Sox10 to significantly increase the incidence of aganglionosis. We show that an interaction between L1cam and Sox10 significantly perturbs neural crest migration within the developing gut, and that neural crest cells undergo excessive cell death prior to gut entry. Finally, we show that Sox10 can regulate the expression of L1cam. Thus, L1cam can act as a modifier gene for the HSCR associated gene, Sox10, and is likely to play a role in the etiology of Hirschsprung's disease.

The timing and location of glial cell line-derived neurotrophic factor expression determine enteric nervous system structure and function

Ret signaling is critical for formation of the enteric nervous system (ENS) because Ret activation promotes ENS precursor survival, proliferation, and migration and provides trophic support for mature enteric neurons. Although these roles are well established, we now provide evidence that increasing levels of the Ret ligand glial cell line-derived neurotrophic factor (GDNF) in mice causes alterations in ENS structure and function that are critically dependent on the time and location of increased GDNF availability. This is demonstrated using two different strains of transgenic mice and by injecting newborn mice with GDNF. Furthermore, because different subclasses of ENS precursors withdraw from the cell cycle at different times during development, increases in GDNF at specific times alter the ratio of neuronal subclasses in the mature ENS. In addition, we confirm that esophageal neurons are GDNF responsive and demonstrate that the location of GDNF production influences neuronal process projection for NADPH diaphorase-expressing, but not acetylcholinesterase-, choline acetyltransferase-, or tryptophan hydroxylase-expressing, small bowel myenteric neurons. We further demonstrate that changes in GDNF availability influence intestinal function in vitro and in vivo. Thus, changes in GDNF expression can create a wide variety of alterations in ENS structure and function and may in part contribute to human motility disorders.

BMP2 promotes differentiation of nitrergic and catecholaminergic enteric neurons through a Smad1-dependent pathway

The bone morphogenetic protein (BMP) family is a class of transforming growth factor (TGF-beta) superfamily molecules that have been implicated in neuronal differentiation. We studied the effects of BMP2 and glial cell line-derived neurotrophic factor (GDNF) on inducing differentiation of enteric neurons and the signal transduction pathways involved. Studies were performed using a novel murine fetal enteric neuronal cell line (IM-FEN) and primary enteric neurons. Enteric neurons were cultured in the presence of vehicle, GDNF (100 ng/ml), BMP2 (10 ng/ml), or both (GDNF + BMP2), and differentiation was assessed by neurite length, markers of neuronal differentiation (neurofilament medium polypeptide and beta-III-tubulin), and neurotransmitter expression [neuropeptide Y (NPY), neuronal nitric oxide synthase (nNOS), tyrosine hydroxylase (TH), choline acetyltransferase (ChAT) and Substance P]. BMP2 increased the differentiation of enteric neurons compared with vehicle and GDNF-treated neurons (P < 0.001). BMP2 increased the expression of the mature neuronal markers (P < 0.05). BMP2 promoted differentiation of NPY-, nNOS-, and TH-expressing neurons (P < 0.001) but had no effect on the expression of cholinergic neurons (ChAT, Substance P). Neurons cultured in the presence of BMP2 have higher numbers of TH-expressing neurons after exposure to 1-methyl 4-phenylpyridinium (MPP(+)) compared with those cultured with MPP(+) alone (P < 0.01). The Smad signal transduction pathway has been implicated in TGF-beta signaling. BMP2 induced phosphorylation of Smad1, and the effects of BMP2 on differentiation of enteric neurons were significantly reduced in the presence of Smad1 siRNA, implicating the role of Smad1 in BMP2-induced differentiation. The effects of BMP2 on catecholaminergic neurons may have therapeutic implications in gastrointestinal motility disturbances.

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.

Vitamin A facilitates enteric nervous system precursor migration by reducing Pten accumulation

Hirschsprung disease is a serious disorder of enteric nervous system (ENS) development caused by the failure of ENS precursor migration into the distal bowel. We now demonstrate that retinoic acid (RA) is crucial for GDNF-induced ENS precursor migration, cell polarization and lamellipodia formation, and that vitamin A depletion causes distal bowel aganglionosis in serum retinol-binding-protein-deficient (Rbp4(-/-)) mice. Ret heterozygosity increases the incidence and severity of distal bowel aganglionosis induced by vitamin A deficiency in Rbp4(-/-) animals. Furthermore, RA reduces phosphatase and tensin homolog (Pten) accumulation in migrating cells, whereas Pten overexpression slows ENS precursor migration. Collectively, these data support the hypothesis that vitamin A deficiency is a non-genetic risk factor that increases Hirschsprung disease penetrance and expressivity, suggesting that some cases of Hirschsprung disease might be preventable by optimizing maternal nutrition.

Expansion and differentiation of neural progenitors derived from the human adult enteric nervous system

BACKGROUND & AIMS

Neural stem and progenitor cells from the enteric nervous system have been proposed for use in cell-based therapies against specific neurogastrointestinal disorders. Recently, enteric neural progenitors were generated from human neonatal and early postnatal (until 5 years after birth) gastrointestinal tract tissues. We investigated the proliferation and differentiation of enteric nervous system progenitors isolated from human adult gastrointestinal tract.

METHODS

Human enteric spheroids were generated from adult small and large intestine tissues and then expanded and differentiated, depending on the applied cell culture conditions. For implantation studies, spheres were grafted into fetal slice cultures and embryonic aganglionic hindgut explants from mice. Differentiating enteric neural progenitors were characterized by 5-bromo-2-deoxyuridine labeling, in situ hybridization, immunocytochemistry, quantitative real-time polymerase chain reaction, and electrophysiological studies.

RESULTS

The yield of human neurosphere-like bodies was increased by culture in conditional medium derived from fetal mouse enteric progenitors. We were able to generate proliferating enterospheres from adult human small or large intestine tissues; these enterospheres could be subcultured and maintained for several weeks in vitro. Spheroid-derived cells could be differentiated into a variety of neuronal subtypes and glial cells with characteristics of the enteric nervous system. Experiments involving implantation into organotypic intestinal cultures showed the differentiation capacity of neural progenitors in a 3-dimensional environment.

CONCLUSIONS

It is feasible to isolate and expand enteric progenitor cells from human adult tissue. These findings offer new strategies for enteric stem cell research and future cell-based therapies.

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.

Development of the enteric nervous system and its role in intestinal motility during fetal and early postnatal stages

Motility patterns in the mature intestine require the coordinated interaction of enteric neurons, gastrointestinal smooth muscle, and interstitial cells of Cajal. In Hirschsprung's disease, the aganglionic segment causes functional obstruction, and thus the enteric nervous system (ENS) is essential for gastrointestinal motility after birth. Here we review the development of the ENS. We then focus on motility patterns in the small intestine and colon of fetal mice and larval zebrafish, where recent studies have shown that the first intestinal motility patterns are not neurally mediated. Finally, we review the development of gastrointestinal motility in humans.

Postnatal downregulation of inhibitory neuromuscular transmission to the longitudinal muscle of the guinea pig ileum

Neuromuscular transmission is crucial for normal gut motility but little is known about its postnatal maturation. This study investigated excitatory/inhibitory neuromuscular transmission in vitro using ileal nerve-muscle preparations made from neonatal (< or =48 h postnatal) and adult ( approximately 4 months postnatal) guinea pigs. In tissues from neonates and adults, nicotine (0.3-30 micromol L(-1)) contracted longitudinal muscle preparations in a tetrodotoxin (TTX) (0.3 micromol L(-1))-sensitive manner. The muscarinic receptor antagonist, scopolamine (1 micromol L(-1)), reduced substantially nicotine-induced contractions in neonatal tissues but not adult tissues. In the presence of N(omega)-nitro-l-arginine (NLA, 100 micromol L(-1)) to block nitric oxide (NO) mediated inhibitory neuromuscular transmission, scopolamine-resistant nicotine-induced contractions were revealed in neonatal tissues. NLA enhanced the nicotine-induced contractions in neonatal but not in adult tissues. Electrical field stimulation (20 V; 0.3 ms; 5-25 Hz, scopolamine 1 micromol L(-1) present) caused NLA and TTX-sensitive longitudinal muscle relaxations. Frequency-response curves in neonatal tissues were left-shifted compared with those obtained in adult tissues. Immunohistochemical studies revealed that NO synthase (NOS)-immunoreactivity (ir) was present in nerve fibres supplying the longitudinal muscle in neonatal and adult tissues. However, quantitative studies demonstrated that fluorescence intensity of NOS-ir nerve fibres was higher in neonatal than adult tissues. Nerve fibres containing substance P were abundant in longitudinal muscle in adult but not in neonatal tissues. Inhibitory neuromuscular transmission is relatively more effective in the neonatal guinea pig small intestine. Delayed maturation of excitatory motor pathways might contribute to paediatric motility disturbances.