Hirschsprung-like disease is exacerbated by reduced de novo GMP synthesis

Virus-Triggered Autoimmunity Was Associated With Hirschsprung's Disease Through Activation of Innate Immunity

Background: Hirschsprung's disease (HSCR) is a congenital enteric nervous system (ENS) disorder. Genetics cannot explain most sporadic cases. To explore the relationship between pathogen infection, autoantibodies, innate immune, and HSCR. Methods: Pathogen microarray was conducted in the serum of the prospective neonatal abdominal distension (NAD) cohort, consisting of 56 children followed for at least 6 months until the final diagnosis of HSCR was determined or excluded. We conducted an autoantibody microarray in an HSCR cohort, which is comprised of diagnosed HSCR patients (HSCR) and healthy control subjects (HC). RNA-seq of colon tissues from aganglionic and ganglionic segments of HSCR patients was performed. Results: Experimental results show that the serum lgM and lgG of enterovirus 71 (EV71) were significantly higher in HSCR than in the gastrointestinal dysfunction (GI) group, with a prediagnose value reaching area under the curve (AUC) over 0.76. We discovered that a group of autoantibodies were significantly higher in HSCR including neuronal pentraxin 1 (NPTX1), amyloid, neuron lysate, and myelin-associated oligodendrocytic basic protein (MOBP) than that in the HC group. These four autoantibodies could distinguish HSCR from the HC group, with a combined AUC of over 0.90 using both serum IgG and IgM. Further analysis showed that wide activation of innate immune pathways, including toll-like receptor (TLR) signaling pathway, neutrophil-to-lymphocyte ratio (NLR) signaling pathway, red cell distribution width to lymphocyte ratio (RLR) signaling pathway, and cyclic adenosine monophosphate (cAMP) signaling pathway in aganglionic compared to ganglionic segments of HSCR. Conclusion: This study suggested that virus-triggered autoimmunity may contribute to HSCR through activation of innate immunity, which facilitates the diagnosis and prevention of HSCR.

Cinchophen induces RPA1 related DNA damage and apoptosis to impair ENS development of zebrafish

Nonsteroidal anti-inflammatory drugs (NSAIDs) have become contaminants widely distributed in the environment due to improper disposal and discharge. Previous study has found several components might involve in impairing enteric nervous system (ENS) development of zebrafish, including NSAIDs cinchophen. Deficient ENS development in fetal could lead to Hirschsprung disease (HSCR), a congenital neurocristopathy characterized by absence of enteric neurons in hindgut. However, the intrinsic mechanism of neurotoxicity of cinchophen is unclear. We confirmed that cinchophen could impair ENS development of zebrafish and transcriptome sequencing revealed that disfunction of Replication protein A1 (RPA1), which is involved in DNA replication and repairment, might be relevant to the neurotoxicity effects induced by cinchophen. Based on previous data of single cell RNA sequencing (scRNA-seq) of zebrafish gut cells, we observed that rpa1 mainly expressed in proliferating, differentiating ENS cells and neural crest progenitors. Interestingly, cinchophen induced apoptosis and impaired proliferation. Furthermore, cinchophen caused DNA damage and abnormal activation of ataxia telangiectasia mutated/ Rad3 related (ATM/ATR) and checkpoint kinase 2 (CHK2). Finally, molecular docking indicated cinchophen could bind and antagonize RPA1 more effectively. Our study might provide a better understanding and draw more attention to the role of environmental factors in the pathogenesis of HSCR. And the mechanism of cinchophen neurotoxicity would give theoretical guidance for clinical pharmacy.

Suppression of PGE2/EP2 signaling alleviates Hirschsprung disease by upregulating p38 mitogen-activated protein kinase activity

Hirschsprung disease (HSCR) is a congenital disorder caused by the failure of enteric neural crest cells (ENCCs) to colonize the distal bowel, resulting in absence of enteric nervous system. While a range of molecules and signaling pathways have been found to contribute to HSCR development, the risk factors and pathogenesis of this disease in many patients remain unknown. We previously demonstrated that increased activity of the prostaglandin E2 (PGE2)/PGE2 receptor subtype EP2 pathway can be a risk factor for HSCR. In this study, an Ednrb-deficient mouse model of HSCR was generated and used to investigate if PGE2/EP2 pathway could be a potential therapeutic target for HSCR. We found that downregulation of PGE2/EP2 signaling by siRNA-mediated ablation of a PGE2 synthase or pharmacologic blockage of EP2 enhanced ENCC colonization in the distal bowel of Ednrb-/- mice and alleviated their HSCR-like symptoms. Furthermore, blockage of EP2 was shown to promote ENCC migration through upregulating p38 mitogen-activated protein kinase activity, which was downregulated in the colon of Ednrb-/- mice and in the distal aganglionic bowel of HSCR patients. These data provide evidence that maternal exposure during embryonic development to an environment with dysregulated activation of the PGE2/EP2 pathway may predispose genetically susceptible offspring to HSCR, and avoidance or early disruption of maternal events (e.g. inflammation) that possibly enhance PGE2/EP2 signaling during pregnancy would reduce the occurrence and severity of this disease. KEY MESSAGES : Knockdown of PTGES alleviates HSCR severity in Ednrb-/- mice. Blockage of EP2-mediated PGE2 signaling alleviates HSCR severity in Ednrb-/- mice. Blockage of EP2-mediated PGE2 signaling promotes ENCC migration via enhancing p38 activity.

Hirschsprung-Associated Enterocolitis: Transformative Research from Bench to Bedside

Hirschsprung disease (HSCR) is a congenital disease that is characterized by the absence of intrinsic ganglion cells in the submucosal and myenteric plexuses of the distal colon and is the most common cause of congenital intestinal obstruction. Hirschsprung-associated enterocolitis (HAEC) is a life-threatening complication of HSCR, which can occur either before or after surgical resection of the aganglionic bowel. Even though HAEC is a leading cause of death in HSCR patients, its etiology and pathophysiology remain poorly understood. Various factors have been associated with HAEC, including the mucus barrier, microbiota, immune function, obstruction of the colon, and genetic variations. In this review, we examine our current mouse model of HAEC and how it informs our understanding of the disease. We also describe current emerging research that highlights the potential future of HAEC treatment.

Identification and validation of the common pathogenesis and hub biomarkers in Hirschsprung disease complicated with Crohn’s disease

Background

Although increasing evidence has supported that Hirschsprung disease (HSCR) is the risk factor for children developing Crohn’s disease (CD), the common mechanism of its co-occurrence remains unknown. The purpose of this study is to further explore the underlying mechanism and biomarkers for the co-occurrence of HSCR and CD.

Methods

The Gene Expression Omnibus (GEO) database was used to obtain gene expression profiles for CD (GSE95095) and HSCR (GSE98502). Following the identification of the shared differentially expressed genes (DEGs) of CD and HSCR, functional annotation, protein–protein interaction (PPI) network creation, and module assembly were performed to discover hub genes. RT-qPCR was performed to validate the expression of the hub genes in HSCR samples. The receiver operating characteristic (ROC) curve was utilized to assess the accuracy of the hub genes as biomarkers in predicting CD in both the training dataset and test dataset.

Results

A total of 103 common DEGs (50 downregulated genes and 53 upregulated genes) were chosen for further investigation. The importance of chemokines and cytokines in these two disorders is highlighted by functional analysis. MCODE plug identified three important modules, which functionally enriched the immune system process. Finally, nine hub genes were identified using cytoHubba, including IL1B, IL10, CXCL10, ICAM1, EGR1, FCGR3A, S100A12, S100A9, and FPR1. The nine hub genes were mainly enriched in immune- and inflammation-related pathways. External data profiles and RT-qPCR confirmed the expression of the nine hub genes in HSCR and CD. ROC analysis revealed that the nine hub genes had a strong diagnostic value.

Conclusion

Our study reveals the common pathogenesis of HSCR and CD. These hub genes and diagnostic models may provide novel insight for the diagnosis and treatment of HSCR complicated with CD.

The science of Hirschsprung disease: What we know and where we are headed

The enteric nervous system (ENS) is a rich network of neurons and glial cells that comprise the gastrointestinal tract's intrinsic nervous system and are responsible for controlling numerous complex functions, including digestion, transit, secretion, barrier function, and maintenance of a healthy microbiome. Development of a functional ENS relies on the coordinated interaction between enteric neural crest-derived cells and their environment as the neural crest-derived cells migrate rostrocaudally along the embryonic gut mesenchyme. Congenital or acquired disruption of ENS development leads to various neurointestinal diseases. Hirschsprung disease is a congenital neurocristopathy, a disease of the neural crest. It is characterized by a variable length of distal colonic aganglionosis due to a failure in enteric neural crest-derived cell proliferation, migration, differentiation, and/or survival. In this review, we will review the science of Hirschsprung disease, targeting an audience of pediatric surgeons. We will discuss the basic biology of normal ENS development, as well as what goes awry in ENS development in Hirschsprung disease. We will review animal models that have been integral to studying this disease, as well as current hot topics and future research, including genetic risk profiling, stem cell therapy, non-invasive diagnostic techniques, single-cell sequencing techniques, and genotype-phenotype correlation.

Benzophenone-3 induced abnormal development of enteric nervous system in zebrafish through MAPK/ERK signaling pathway

Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of enteric neurons, which is derived from the failure of the proliferation, differentiation or migration of the enteric neural crest cells (ENCCs). HSCR is associated with multiple risk factors, including polygenic inheritance factors and environmental factors. Genetic studies have been extensively performed, whereas studies related to environmental factors remain insufficient. Benzophenone-3 (BP-3), one important component of the ultraviolet (UV) filters, has been proved to have cytotoxicity and neurotoxicity which might be associated with HSCR. In this study, we used zebrafish as a model to investigate the relationship between BP-3 exposure and the development of the enteric nervous system (ENS) in vivo. Embryos exposed to BP-3 showed an average of 46% reduction of the number of the enteric neurons number. Besides, the ENCCs specific markers (ret and hand2) were downregulated upon BP-3 exposure. Moreover, we identified potential targets of BP-3 through Network Pharmacology Analysis and Autodock and demonstrated that the attenuation of the MAPK/ERK signaling might be the potential mechanism underlying the inhibition of the ENS development by BP-3. Importantly, MAPK/ERK signaling agonist could be used to rescue the ENS defects of zebrafish induced by BP-3. Overall, we characterized the influence of BP-3 on ENS development in vivo and explored possible molecular mechanisms.

Cell-autonomous retinoic acid receptor signaling has stage-specific effects on mouse enteric nervous system

Retinoic acid (RA) signaling is essential for enteric nervous system (ENS) development, since vitamin A deficiency or mutations in RA signaling profoundly reduce bowel colonization by ENS precursors. These RA effects could occur because of RA activity within the ENS lineage or via RA activity in other cell types. To define cell-autonomous roles for retinoid signaling within the ENS lineage at distinct developmental time points, we activated a potent floxed dominant-negative RA receptor α (RarαDN) in the ENS using diverse CRE recombinase–expressing mouse lines. This strategy enabled us to block RA signaling at premigratory, migratory, and postmigratory stages for ENS precursors. We found that cell-autonomous loss of RA receptor (RAR) signaling dramatically affected ENS development. CRE activation of RarαDN expression at premigratory or migratory stages caused severe intestinal aganglionosis, but at later stages, RarαDN induced a broad range of phenotypes including hypoganglionosis, submucosal plexus loss, and abnormal neural differentiation. RNA sequencing highlighted distinct RA-regulated gene sets at different developmental stages. These studies show complicated context-dependent RA-mediated regulation of ENS development.

Multiple 'omics'-analysis reveals the role of prostaglandin E2 in Hirschsprung's disease

The etiology and pathogenesis of Hirschsprung's disease (HSCR) remain largely unknown. We examined colon tissues from three independent populations with a combined analysis of metabolomics, transcriptomics and proteomics to understand HSCR pathogenesis, according to which mouse model was used to examine prostaglandin E2 (PGE2) induced clinical presentation of HSCR. SH-SY5Y and SK-N-BE(2) cell lines were studied for PGE2 inhibited cell migration through EP2. Our integrated multiple 'omics'-analysis suggests that the levels of PGE2, the expression of the gene encoding PGE2 receptor (EP2), and PGE2 synthesis enzyme genes (PTGS1 and PTGES) increased in HSCR colon tissues, together with a decreased synthesis of PGE2-related byproducts. In vivo, the pregnant mice treated with PGE2 gave birth to offspring with the decrease of ganglion cells in their colon and gut function. In in vitro study, when EP2 was blocked, the PGE2-inhibited cell migration was recovered. Our study identified a novel pathway highlighting the link between expression of PTGS1 and PTGES, levels of PGE2, expression of PTGER2, and neural crest cell migration in HSCR, providing a novel strategy for future diagnosis and prevention of HSCR.

Zebrafish: A Model Organism for Studying Enteric Nervous System Development and Disease

The Enteric Nervous System (ENS) is a large network of enteric neurons and glia that regulates various processes in the gastrointestinal tract including motility, local blood flow, mucosal transport and secretion. The ENS is derived from stem cells coming from the neural crest that migrate into and along the primitive gut. Defects in ENS establishment cause enteric neuropathies, including Hirschsprung disease (HSCR), which is characterized by an absence of enteric neural crest cells in the distal part of the colon. In this review, we discuss the use of zebrafish as a model organism to study the development of the ENS. The accessibility of the rapidly developing gut in zebrafish embryos and larvae, enables in vivo visualization of ENS development, peristalsis and gut transit. These properties make the zebrafish a highly suitable model to bring new insights into ENS development, as well as in HSCR pathogenesis. Zebrafish have already proven fruitful in studying ENS functionality and in the validation of novel HSCR risk genes. With the rapid advancements in gene editing techniques and their unique properties, research using zebrafish as a disease model, will further increase our understanding on the genetics underlying HSCR, as well as possible treatment options for this disease.

ChIP-Seq-Based Approach in Mouse Enteric Precursor Cells Reveals New Potential Genes with a Role in Enteric Nervous System Development and Hirschsprung Disease

Hirschsprung disease (HSCR) is a neurocristopathy characterized by intestinal aganglionosis which is attributed to a failure in neural crest cell (NCC) development during the embryonic stage. The colonization of the intestine by NCCs is a process finely controlled by a wide and complex gene regulatory system. Several genes have been associated with HSCR, but many aspects still remain poorly understood. The present study is focused on deciphering the PAX6 interaction network during enteric nervous system (ENS) formation. A combined experimental and computational approach was performed to identify PAX6 direct targets, as well as gene networks shared among such targets as potential susceptibility factors for HSCR. As a result, genes related to PAX6 either directly (RABGGTB and BRD3) or indirectly (TGFB1, HRAS, and GRB2) were identified as putative genes associated with HSCR. Interestingly, GRB2 is involved in the RET/GDNF/GFRA1 signaling pathway, one of the main pathways implicated in the disease. Our findings represent a new contribution to advance in the knowledge of the genetic basis of HSCR. The investigation of the role of these genes could help to elucidate their implication in HSCR onset.

Glial Cell-Derived Neurotrophic Factor Induces Enteric Neurogenesis and Improves Colon Structure and Function in Mouse Models of Hirschsprung Disease

BACKGROUND & AIMS

Hirschsprung disease (HSCR) is a life-threatening birth defect in which the distal colon is devoid of enteric neural ganglia. HSCR is treated by surgical removal of aganglionic bowel, but many children continue to have severe problems after surgery. We studied whether administration of glial cell derived neurotrophic factor (GDNF) induces enteric nervous system regeneration in mouse models of HSCR.

METHODS

We performed studies with four mouse models of HSCR: Holstein (Hol^Tg/Tg, a model for trisomy 21-associated HSCR), TashT (TashT^Tg/Tg, a model for male-biased HSCR), Piebald-lethal (Ednrb^s-l//s-l, a model for EDNRB mutation-associated HSCR), and Ret^9/- (with aganglionosis induced by mycophenolate). Mice were given rectal enemas containing GDNF or saline (control) from postnatal days 4 through 8. We measured survival times of mice, and colon tissues were analyzed by histology, immunofluorescence, and immunoblots. Neural ganglia regeneration and structure, bowel motility, epithelial permeability, muscle thickness, and neutrophil infiltration were studied in colon tissues and in mice. Stool samples were collected, and microbiomes were analyzed by 16S rRNA gene sequencing. Time-lapse imaging and genetic cell-lineage tracing were used to identify a source of GDNF-targeted neural progenitors. Human aganglionic colon explants from children with HSCR were cultured with GDNF and evaluated for neurogenesis.

RESULTS

GDNF significantly prolonged mean survival times of Hol^Tg/Tg mice, Ednrb^s-l//s-l mice, and male TashT^Tg/Tg mice, compared with control mice, but not Ret^9/- mice (which had mycophenolate toxicity). Mice given GDNF developed neurons and glia in distal bowel tissues that were aganglionic in control mice, had a significant increase in colon motility, and had significant decreases in epithelial permeability, muscle thickness, and neutrophil density. We observed dysbiosis in fecal samples from Hol^Tg/Tg mice compared with feces from wild-type mice; fecal microbiomes of mice given GDNF were similar to those of wild-type mice except for Bacteroides. Exogenous luminal GDNF penetrated aganglionic colon epithelium of Hol^Tg/Tg mice, inducing production of endogenous GDNF, and new enteric neurons and glia appeared to arise from Schwann cells within extrinsic nerves. GDNF application to cultured explants of human aganglionic bowel induced proliferation of Schwann cells and formation of new neurons.

CONCLUSIONS

GDNF prolonged survival, induced enteric neurogenesis, and improved colon structure and function in 3 mouse models of HSCR. Application of GDNF to cultured explants of aganglionic bowel from children with HSCR induced proliferation of Schwann cells and formation of new neurons. GDNF might be developed for treatment of HSCR.

Dlx1/2 mice have abnormal enteric nervous system function

Decades ago, investigators reported that mice lacking DLX1 and DLX2, transcription factors expressed in the enteric nervous system (ENS), die with possible bowel motility problems. These problems were never fully elucidated. We found that mice lacking DLX1 and DLX2 (Dlx1/2-/- mice) had slower small bowel transit and reduced or absent neurally mediated contraction complexes. In contrast, small bowel motility seemed normal in adult mice lacking DLX1 (Dlx1-/-). Even with detailed anatomic studies, we found no defects in ENS precursor migration, or neuronal and glial density in Dlx1/2-/- or Dlx1-/- mice. However, RNA sequencing of Dlx1/2-/- ENS revealed dysregulation of many genes, including vasoactive intestinal peptide (Vip). Using immunohistochemistry and reporter mice, we then found that Dlx1/2-/- mice have reduced VIP expression and fewer VIP-lineage neurons in their ENS. Our study reveals what we believe is a novel connection between Dlx genes and Vip and highlights the observation that dangerous bowel motility problems can occur in the absence of easily identifiable ENS structural defects. These findings may be relevant for disorders like chronic intestinal pseudo-obstruction (CIPO) syndrome.

The role of teratogens in neural crest development

The neural crest (NC), discovered by Wilhelm His 150 years ago, gives rise to a multipotent migratory embryonic cell population that generates a remarkably diverse and important array of cell types during the development of the vertebrate embryo. These cells originate in the neural plate border (NPB), which is the ectoderm between the neural plate and the epidermis. They give rise to the neurons and glia of the peripheral nervous system, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies are a class of congenital diseases resulting from the abnormal induction, specification, migration, differentiation or death of NC cells (NCCs) during embryonic development and have an important medical and societal impact. In general, congenital defects affect an appreciable percentage of newborns worldwide. Some of these defects are caused by teratogens, which are agents that negatively impact the formation of tissues and organs during development. In this review, we will discuss the teratogens linked to the development of many birth defects, with a strong focus on those that specifically affect the development of the NC, thereby producing neurocristopathies. Although increasing attention is being paid to the effect of teratogens on embryonic development in general, there is a strong need to critically evaluate the specific role of these agents in NC development. Therefore, increased understanding of the role of these factors in NC development will contribute to the planning of strategies aimed at the prevention and treatment of human neurocristopathies, whose etiology was previously not considered.

Selective serotonin reuptake inhibitors during pregnancy Do not increase the risk of Hirschsprung disease

PURPOSE

Hirschsprung disease (HSCR) is a multifactorial disease. Maternal intake of selective serotonin reuptake inhibitors (SSRI) during early pregnancy has previously been associated with increased risk for HSCR. The aim of this study was to assess the risk for HSCR in newborns after maternal intake of SSRI in a population-based Swedish cohort.

METHODS

This was a Swedish nationwide, population-based, case-control cohort study containing all children born in Sweden between 1/12006 and 31/122012. The cases were identified in the Swedish National Patient Register and the controls (five age- and sex-matched controls per case) were randomly selected among children without HSCR in the cohort. Data on maternal SSRI use during pregnancy were collected from the Swedish Prescribed Drug Register.

RESULTS

Out of 775,024 born children during the study period, 150 cases of HSCR (112 males) and 750 controls (560 males) were included. Five (3.3%) mothers of newborns with HSCR had used SSRI during pregnancy compared to 16 (2.1%) mothers of the controls (p = 0.372). The mean age was similar in mothers who had used SSRI compared to those who had not (30.9 (SD +/- 5.1) versus 30.6 (SD +/- 5.0), p = 0.81).

CONCLUSIONS

There was no increased risk of HSCR owing to maternal intake of SSRI in this cohort.

LEVEL OF EVIDENCE

Level I.

Down syndrome mouse models have an abnormal enteric nervous system

Children with trisomy 21 (Down syndrome [DS]) have a 130-fold increased incidence of Hirschsprung Disease (HSCR), a developmental defect where the enteric nervous system (ENS) is missing from distal bowel (i.e., distal bowel is aganglionic). Treatment for HSCR is surgical resection of aganglionic bowel, but many children have bowel problems after surgery. Post-surgical problems like enterocolitis and soiling are especially common in children with DS. To determine how trisomy 21 affects ENS development, we evaluated the ENS in two DS mouse models, Ts65Dn and Tc1. These mice are trisomic for many chromosome 21 homologous genes, including Dscam and Dyrk1a, which are hypothesized to contribute to HSCR risk. Ts65Dn and Tc1 mice have normal ENS precursor migration at E12.5 and almost normal myenteric plexus structure as adults. However, Ts65Dn and Tc1 mice have markedly reduced submucosal plexus neuron density throughout the bowel. Surprisingly, the submucosal neuron defect in Ts65Dn mice is not due to excess Dscam or Dyrk1a, since normalizing copy number for these genes does not rescue the defect. These findings suggest the possibility that the high frequency of bowel problems in children with DS and HSCR may occur because of additional unrecognized problems with ENS structure.

Gut microbiota-mediated Gene-Environment interaction in the TashT mouse model of Hirschsprung disease

Based on the bilateral relationship between the gut microbiota and formation/function of the enteric nervous system (ENS), we sought to determine whether antibiotics-induced dysbiosis might impact the expressivity of genetically-induced ENS abnormalities. To address this, we took advantage of the TashT mouse model of Hirschsprung disease, in which colonic aganglionosis and hypoganglionosis are both much more severe in males. These defects result into two male-biased colon motility phenotypes: either megacolon that is lethal around weaning age or chronic constipation in adults, the latter being also associated with an increased proportion of nitrergic neurons in the distal ENS. Induction of dysbiosis using a cocktail of broad-spectrum antibiotics specifically impacted the colonic ENS of TashT^Tg/Tg mice in a stage-dependent manner. It further decreased the neuronal density at post-weaning age and differentially modulated the otherwise increased proportion of nitrergic neurons, which appeared normalized around weaning age and further increased at post-weaning age. These changes delayed the development of megacolon around weaning age but led to premature onset of severe constipation later on. Finally, local inhibition of nitric oxide signaling improved motility and prevented death by megacolon. We thus conclude that exposure to antibiotics can negatively influence the expressivity of a genetically-induced enteric neuropathy.

Increased miR-214 expression suppresses cell migration and proliferation in Hirschsprung disease by interacting with PLAGL2

BACKGROUND

The miR-214 has been reported to be associated with various diseases, but its involvement in the pathophysiology of Hirschsprung disease (HSCR) is almost completely unexplored.

METHODS

In our study, we conducted a series of experiments to unravel the biological role of miR-214 in the pathophysiology of HSCR. qRT-PCR and western blotting were utilized to investigate the relative expression levels of miR-214, mRNAs, and proteins of related genes in colon tissues from 20 controls without HSCR and 24 patients with HSCR. The potential biological role of miR-214 in two cell lines (SKN-SH and SH-SY5Y) was assessed using the CCK8 assay, EdU staining, transwell assay, and flow cytometry. The dual-luciferase reporter assay was used to confirm PLAGL2 as a common target gene of miR-214.

RESULTS

All results suggested that miR-214 is upregulated in HSCR tissue samples compared with controls. Additionally, we found that miR-214 could inhibit cell proliferation and migration by directly downregulating the expression of PLAGL2, and the extent of the miR-214-mediated inhibitory effects could be rescued by a PLAGL2 overexpression plasmid.

CONCLUSION

Our results revealed that miR-214 is indeed involved in the pathophysiology of HSCR and suppresses cell proliferation and migration by directly downregulating PLAGL2 in cell models.

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.

Loss of Tbx3 in murine neural crest reduces enteric glia and causes cleft palate, but does not influence heart development or bowel transit

Transcription factors that coordinate migration, differentiation or proliferation of enteric nervous system (ENS) precursors are not well defined. To identify novel transcriptional regulators of ENS development, we performed microarray analysis at embryonic day (E) 17.5 and identified many genes that were enriched in the ENS compared to other bowel cells. We decided to investigate the T-box transcription factor Tbx3, which is prominently expressed in developing and mature ENS. Haploinsufficiency for TBX3 causes ulnar-mammary syndrome (UMS) in humans, a multi-organ system disorder. TBX3 also regulates several genes known to be important for ENS development. To test the hypothesis that Tbx3 is important for ENS development or function, we inactivated Tbx3 in all neural crest derivatives, including ENS progenitors using Wnt1-Cre and a floxed Tbx3 allele. Tbx3 fl/fl; Wnt1-Cre conditional mutant mice die shortly after birth with cleft palate and difficulty feeding. The ENS of mutants was well-organized with a normal density of enteric neurons and nerve fiber bundles, but small bowel glial cell density was reduced. Despite this, bowel motility appeared normal. Furthermore, although Tbx3 is expressed in cardiac neural crest, Tbx3 fl/fl; Wnt1-Cre mice had structurally normal hearts. Thus, loss of Tbx3 within neural crest has selective effects on Tbx3-expressing neural crest derivatives.

Muscularis macrophage development in the absence of an enteric nervous system

The nervous system of the bowel regulates the inflammatory phenotype of tissue resident muscularis macrophages (MM), and in adult mice, enteric neurons are the main local source of colony stimulating factor 1 (CSF1), a protein required for MM survival. Surprisingly, we find that during development MM colonize the bowel before enteric neurons. This calls into question the requirement for neuron-derived CSF1 for MM colonization of the bowel. To determine if intestinal innervation is required for MM development, we analyzed MM of neonatal Ret^-/- (Ret KO) mice that have no enteric nervous system in small bowel or colon. We found normal numbers of well-patterned MM in Ret KO bowel. Similarly, the abundance and distribution of MM in aganglionic human colon obtained from Hirschsprung disease patients was normal. We also identify endothelial cells and interstitial cells of Cajal as the main sources of CSF1 in the developing bowel. Additionally, MM from neonatal Ret KOs do not differ from controls in baseline activation status or cytokine-production in response to lipopolysaccharide. Unexpectedly, these data demonstrate that the enteric nervous system is dispensable for MM colonization and patterning in the bowel, and suggest that modulatory interactions between MM and the bowel nervous system are established postnatally.

Hirschsprung disease - integrating basic science and clinical medicine to improve outcomes

Hirschsprung disease is defined by the absence of enteric neurons at the end of the bowel. The enteric nervous system (ENS) is the intrinsic nervous system of the bowel and regulates most aspects of bowel function. When the ENS is missing, there are no neurally mediated propulsive motility patterns, and the bowel remains contracted, causing functional obstruction. Symptoms of Hirschsprung disease include constipation, vomiting, abdominal distension and growth failure. Untreated disease usually causes death in childhood because bloodstream bacterial infections occur in the context of bowel inflammation (enterocolitis) or bowel perforation. Current treatment is surgical resection of the bowel to remove or bypass regions where the ENS is missing, but many children have problems after surgery. Although the anatomy of Hirschsprung disease is simple, many clinical features remain enigmatic, and diagnosis and management remain challenging. For example, the age of presentation and the type of symptoms that occur vary dramatically among patients, even though every affected child has missing neurons in the distal bowel at birth. In this Review, basic science discoveries are linked to clinical manifestations of Hirschsprung disease, including partial penetrance, enterocolitis and genetics. Insights into disease mechanisms that might lead to new prevention, diagnostic and treatment strategies are described.

Gut feelings: Studying enteric nervous system development, function, and disease in the zebrafish model system

The enteric nervous system (ENS) is the largest part of the peripheral nervous system and is entirely neural crest-derived. It provides the intrinsic innervation of the gut, controlling different aspects of gut function, such as motility. In this review, we will discuss key points of Zebrafish ENS development, genes, and signaling pathways regulating ENS development, as well as contributions of the Zebrafish model system to better understand ENS disorders. During their migration, enteric progenitor cells (EPCs) display a gradient of developmental states based on their proliferative and migratory characteristics, and show spatiotemporal heterogeneity based on gene expression patterns. Many genes and signaling pathways that regulate the migration and proliferation of EPCs have been identified, but later stages of ENS development, especially steps of neuronal and glial differentiation, remain poorly understood. In recent years, Zebrafish have become increasingly important to test candidate genes for ENS disorders (e.g., from genome-wide association studies), to identify environmental influences on ENS development (e.g., through large-scale drug screens), and to investigate the role the gut microbiota play in ENS development and disease. With its unique advantages as a model organism, Zebrafish will continue to contribute to a better understanding of ENS development, function, and disease. Developmental Dynamics 247:268-278, 2018. © 2017 Wiley Periodicals, Inc.

Sporadic Hirschsprung Disease: Mutational Spectrum and Novel Candidate Genes Revealed by Next-generation Sequencing

Hirschsprung disease (HSCR) is a common cause of functional colonic obstruction in children. The currently available genetic testing is often inadequate as it mainly focuses on RET and several other genes, accounting for only 15–20% of cases. To identify novel, potentially pathogenic variants, we isolated a panel of genes from a whole-exome sequencing study and from the published mouse aganglionosis phenotypes, enteric nervous system development, and a literature review. The coding exons of 172 genes were analyzed in 83 sporadic patients using next-generation sequencing. Rare stop-gain, splice-site variants, frameshift and in-frame insertions/deletions and non-synonymous variants (conserved and predicted to be deleterious) were prioritized as the most promising variants to have an effect on HSCR and subjected to burden analysis. GeneMANIA interaction database was used to identify protein–protein interaction-based networks. In addition, 6 genes (PTPN13, PHKB, AGL, ZFHX3, LAMA1, and AP3B2) were prioritized for follow-up studies: both their time-space expression patterns in mouse and human colon showed that they are good candidates for predicting pathogenicity. The results of this study broaden the mutational spectrum of HSCR candidate genes, and they provide an insight into the relative contributions of individual genes to this highly heterogeneous disorder.

RET somatic mutations are underrecognized in Hirschsprung disease

PURPOSE

We aimed to determine the frequency of RET mosaicism in Hirschsprung disease (HSCR), test whether it has been underestimated, and to assess its contribution to HSCR risk.

METHODS

Targeted exome sequencing (n = 83) and RET single-gene screening (n = 69) were performed. Amplicon-based deep sequencing was applied on multiple tissue samples. TA cloning and sequencing were conducted for validation.

RESULTS

We identified eight de novo mutations in 152 patients (5.2%), of which six were pathogenic mosaic mutations. Two of these patients were somatic mosaics, with mutations detected in blood, colon, and saliva (mutant allele frequency: 35-44%). In addition, germ-line mosaicism was identified in four clinically unaffected subjects, each with an affected child, in multiple tissues (mutant allele frequency: 1-28%).

CONCLUSION

Somatic mutations of the RET gene are underrecognized in HSCR. Molecular investigation of the parents of patients with seemingly sporadic mutations is essential to determine recurrence risk in these families.

Potential association between ITPKC genetic variations and Hirschsprung disease

Hirschsprung disease (HSCR) is a congenital and complex disorder characterized by intestinal obstruction due to the absence of enteric neurons along variable lengths of the hindgut. Our recent genome-wide association study (GWAS) has revealed regional associations with HSCR at several loci of inositol-trisphosphate 3-kinase C (ITPKC). For fine mapping, we additionally selected and genotyped a total of 12 single nucleotide polymorphisms (SNPs) of ITPKC in 187 HSCR patients and 283 unaffected controls, and performed a further combined imputation analysis based on genotype data from this second stage of fine mapping and our previous GWAS stage, totaling 902 subjects (187 HSCR cases and 715 controls). As a result, several SNPs (minimum P = 0.004) and a haplotype (P = 0.02) were found to be significantly associated with HSCR. In further in silico analyses to ascertain the potential functions of the significant variants, the change from the common allele to the rare allele of the highly conserved nonsynonymous rs76785336 showed a difference in mRNA folding structure. In the case of intronic SNPs, rs2607420 with a high consensus value was predicted to be a new splice site. Although this study has limitations (such as lack of functional evaluations, small number of cases, and further need of replication in other cohorts), our findings suggest that genetic variants of ITPKC may have a potential association with HSCR susceptibility and/or developmental diseases related to enteric nervous system development.

A Novel Zebrafish ret Heterozygous Model of Hirschsprung Disease Identifies a Functional Role for mapk10 as a Modifier of Enteric Nervous System Phenotype Severity

Hirschsprung disease (HSCR) is characterized by absence of enteric neurons from the distal colon and severe intestinal dysmotility. To understand the pathophysiology and genetics of HSCR we developed a unique zebrafish model that allows combined genetic, developmental and in vivo physiological studies. We show that ret mutant zebrafish exhibit cellular, physiological and genetic features of HSCR, including absence of intestinal neurons, reduced peristalsis, and varying phenotype expressivity in the heterozygous state. We perform live imaging experiments using a UAS-GAL4 binary genetic system to drive fluorescent protein expression in ENS progenitors. We demonstrate that ENS progenitors migrate at reduced speed in ret heterozygous embryos, without changes in proliferation or survival, establishing this as a principal pathogenic mechanism for distal aganglionosis. We show, using live imaging of actual intestinal movements, that intestinal motility is severely compromised in ret mutants, and partially impaired in ret heterozygous larvae, and establish a clear correlation between neuron position and organised intestinal motility. We exploited the partially penetrant ret heterozygous phenotype as a sensitised background to test the influence of a candidate modifier gene. We generated mapk10 loss-of-function mutants, which show reduced numbers of enteric neurons. Significantly, we show that introduction of mapk10 mutations into ret heterozygotes enhanced the ENS deficit, supporting MAPK10 as a HSCR susceptibility locus. Our studies demonstrate that ret heterozygous zebrafish is a sensitized model, with many significant advantages over existing murine models, to explore the pathophysiology and complex genetics of HSCR.

Hirschsprung Disease (HSCR) is a common congenital intestinal motility disorder diagnosed at birth by absence of enteric neurons in the distal gut, leading to intestinal obstruction that requires life-saving surgery. HSCR exhibits complex inheritance patterns and its genetic basis is not fully understood. Although well studied by human geneticists, and modelled using mouse, significant questions remain about the cellular and genetic causes of the disease and the relationship between neuron loss and defective intestinal motility. Here we use accessible, transparent zebrafish to address these outstanding questions. We establish that ret mutant zebrafish display key features of HSCR, including absence of intestinal neurons, reduced gut motility and varying phenotype expressivity. Using live imaging, possible in zebrafish but not in mouse, we demonstrate that decreased migration speed of enteric neuron progenitors colonising the gut is the principal defect leading to neuron deficits. By direct examination of gut motility in zebrafish larvae, we establish a clear correlation between neurons and motility patterns. Finally, we show that mapk10 mutations worsen the enteric neuron deficit of ret mutants, indicating that mutations in MAPK10 may increase susceptibility to HSCR. We show many benefits of modelling human genetic diseases in zebrafish and advance our understanding of HSCR.

Gene-environment interactions and the enteric nervous system: Neural plasticity and Hirschsprung disease prevention

Intestinal function is primarily controlled by an intrinsic nervous system of the bowel called the enteric nervous system (ENS). The cells of the ENS are neural crest derivatives that migrate into and through the bowel during early stages of organogenesis before differentiating into a wide variety of neurons and glia. Although genetic factors critically underlie ENS development, it is now clear that many non-genetic factors may influence the number of enteric neurons, types of enteric neurons, and ratio of neurons to glia. These non-genetic influences include dietary nutrients and medicines that may impact ENS structure and function before or after birth. This review summarizes current data about gene-environment interactions that affect ENS development and suggests that these factors may contribute to human intestinal motility disorders like Hirschsprung disease or irritable bowel syndrome.

Genetics of enteric neuropathies

Abnormal development or disturbed functioning of the enteric nervous system (ENS), the intrinsic innervation of the gastrointestinal tract, is associated with the development of neuropathic gastrointestinal motility disorders. Here, we review the underlying molecular basis of these disorders and hypothesize that many of them have a common defective biological mechanism. Genetic burden and environmental components affecting this common mechanism are ultimately responsible for disease severity and symptom heterogeneity. We believe that they act together as the fulcrum in a seesaw balanced with harmful and protective factors, and are responsible for a continuum of symptoms ranging from neuronal hyperplasia to absence of neurons.

Suppressive action of miRNAs to ARP2/3 complex reduces cell migration and proliferation via RAC isoforms in Hirschsprung disease

Hirschsprung disease (HSCR) is a congenital disorder caused by the defective function of the embryonic enteric neural crest. The impaired migration of embryonic enteric neural crest plays an important role in the pathogenesis of this disease. Recent studies showed that the ARP2/3 complex and RAC isoforms had effects on actin cytoskeleton remodelling, which contributes to migration. Moreover, some regulatory relationships were identified between ARP2/3 complex and RAC isoforms. Although microRNAs (miRNAs) have been known to modulate target gene expression on the post-transcriptional level, little is known about the regulation among miRNAs, ARP2/3 complex and RAC isoforms. Here, we report that down-regulation of ARP2 and ARP3, two main subunits of ARP2/3 complex, suppressed migration and proliferation in 293T and SH-SY5Y cell lines via the inhibition of RAC1 and RAC2. Meanwhile, as the target genes, ARP2 and ARP3 are reduced by increased miR-24-1* and let-7a*, respectively, in 70 HSCR samples as compared with 74 normal controls. Co-immunoprecipitation showed that aberrant reduction in ARP2 and ARP3 could weaken the function of ARP2/3 complex. Our study demonstrates that the miR-24-1*/let-7a*-ARP2/3 complex-RAC isoforms pathway may represent a novel pathogenic mechanism for HSCR.

Maternal Risk Factors and Perinatal Characteristics for Hirschsprung Disease

BACKGROUND AND OBJECTIVES

Hirschsprung disease (HSCR) is a congenital defect of the enteric nervous system characterized by a lack of ganglion cells in the distal hindgut. The aim of this study was to assess the birth prevalence, perinatal characteristics, and maternal risk factors in HSCR patients in Sweden.

METHODS

This was a nationwide, population-based, case-control study of all children born in Sweden between 1982 and 2012 and registered in the Swedish Medical Birth Register. Cases were identified in the Swedish National Patient Register and data on potential maternal risk factors and patient characteristics were collected from the Swedish National Patient Register and the Swedish Medical Birth Register. Five age- and sex-matched controls were randomly selected for each case. The association between studied risk factors and HSCR was analyzed using conditional logistic regression to calculate the odds ratio (OR) and 95% confidence interval (CI).

RESULTS

The study population comprised 600 HSCR cases and 3000 controls with a male-to-female ratio of 3.7:1. The birth prevalence of HSCR was 1.91/10 000. Maternal obesity was associated with an increased risk for the child to have HSCR (OR 1.74; CI 1.25-2.44). Children with HSCR were born at an earlier gestational age (OR 1.60; CI 1.18-2.17) than control children. Associated malformations were identified in 34.5% of the cases.

CONCLUSIONS

This study showed that the Swedish birth prevalence of HSCR was 1.91/10 000. Children with HSCR disease were born at a lower gestational age than controls. Maternal obesity may increase the risk for the child to have HSCR.

Mouse models of Hirschsprung disease and other developmental disorders of the enteric nervous system: Old and new players

Hirschsprung disease (HSCR, intestinal aganglionosis) is a multigenic disorder with variable penetrance and severity that has a general population incidence of 1/5000 live births. Studies using animal models have contributed to our understanding of the developmental origins of HSCR and the genetic complexity of this disease. This review summarizes recent progress in understanding control of enteric nervous system (ENS) development through analyses in mouse models. An overview of signaling pathways that have long been known to control the migration, proliferation and differentiation of enteric neural progenitors into and along the developing gut is provided as a framework for the latest information on factors that influence enteric ganglia formation and maintenance. Newly identified genes and additional factors beyond discrete genes that contribute to ENS pathology including regulatory sequences, miRNAs and environmental factors are also introduced. Finally, because HSCR has become a paradigm for complex oligogenic diseases with non-Mendelian inheritance, the importance of gene interactions, modifier genes, and initial studies on genetic background effects are outlined.

Enteric nervous system development in avian and zebrafish models

Our current understanding of the developmental biology of the enteric nervous system (ENS) and the genesis of ENS diseases is founded almost entirely on studies using model systems. Although genetic studies in the mouse have been at the forefront of this field over the last 20 years or so, historically it was the easy accessibility of the chick embryo for experimental manipulations that allowed the first descriptions of the neural crest origins of the ENS in the 1950s. More recently, studies in the chick and other non-mammalian model systems, notably zebrafish, have continued to advance our understanding of the basic biology of ENS development, with each animal model providing unique experimental advantages. Here we review the basic biology of ENS development in chick and zebrafish, highlighting conserved and unique features, and emphasising novel contributions to our general understanding of ENS development due to technical or biological features.

Zebrafish as a model for understanding enteric nervous system interactions in the developing intestinal tract

The enteric nervous system (ENS) forms intimate connections with many other intestinal cell types, including immune cells and bacterial consortia resident in the intestinal lumen. In this review, we highlight contributions of the zebrafish model to understanding interactions among these cells. Zebrafish is a powerful model for forward genetic screens, several of which have uncovered genes previously unknown to be important for ENS development. More recently, zebrafish has emerged as a model for testing functions of genes identified in human patients or large-scale human susceptibility screens. In several cases, zebrafish studies have revealed mechanisms connecting intestinal symptoms with other, seemingly unrelated disease phenotypes. Importantly, chemical library screens in zebrafish have provided startling new insights into potential effects of common drugs on ENS development. A key feature of the zebrafish model is the ability to rear large numbers of animals germ free or in association with only specific bacterial species. Studies utilizing these approaches have demonstrated the importance of bacterial signals for normal intestinal development. These types of studies also show how luminal bacteria and the immune system can contribute to inflammatory processes that can feedback to influence ENS development. The excellent optical properties of zebrafish embryos and larvae, coupled with the ease of generating genetically marked cells of both the host and its resident bacteria, allow visualization of multiple intestinal cell types in living larvae and should promote a more in-depth understanding of intestinal cell interactions, especially interactions between other intestinal cell types and the ENS.

Exome-Wide Association Study Identified New Risk Loci for Hirschsprung's Disease

Hirschsprung disease (HSCR) is a rare congenital disease caused by impaired proliferation and migration of neural crest cells. In this study, we aimed to investigate the genetic loci involved in the pathogenesis of HSCR. The exome-wide scan was performed to screen the genetic variants with minor allele frequency (MAF) < 0.05 in exonic regions. Candidate mutation type and the wild type were overexpressed to investigate the affection on cell proliferation and migration. We found that ten variants were associated with HSCR at P < 10^-4 in the single-variant analysis while ten genes were also associated with HSCR at P < 10^-4 in the optimized sequence kernel association test (SKAT-O) test analysis. Among these SNPs, the missense variants catechol-O-methyltransferase (COMT) (rs6267) and armadillo repeat gene deleted in velocardiofacial syndrome (ARVCF) (rs80068543) indicated an ectopic expression in colon tissues of HSCR patients. The Ala72Ser variant in COMT induced proliferation suppression through NOTCH signal pathway, while the ARVCF affected cell migration via the downregulating of RHOA and ROC. In conclusion, this exome array study identified the COMT and ARVCF missense coding variants as candidate loci for HSCR. The finding implies the abnormal variant of COMT and ARVCF may account for the pathogenesis of HSCR.

The relationship between prenatal exposure to BP-3 and Hirschsprung's disease

Hirschsprung's disease (HSCR) is neonatal intestinal abnormality which derived from the faliure of enteric neural crest cells migration to hindgut during embryogenesis from 5 to 12 weeks. Currenly, the knowledge of environmental factors contributing to HSCR is still scarce. Benzophenone-3 (BP-3) is one of the most widely used UV filters, and has weak estrogen and strong anti-androgenic effects. In order to examine the effect of maternal BP-3 exposure on development of offspring and explore the potential mechanism, we conducted case and control study and in vitro study. In this work, BP-3 concertrations in maternal urine was detected by ultra-high performance liquid chromatography. Besides, we investigated the cytotoxicity and receptor tyrosine kinase (RET) expression in cells exposed to BP-3. The results showed that maternal BP-3 exposure was associated with offspring's HSCR in the population as well as inhibited migration of 293T and SH-SY5Y cells. What's more, we discovered dose-response relationship between RET expression and BP-3 exposure dose, and miR-218 and some other genes involved in SLIT2/ROBO1-miR-218-RET/PLAG1 pathway were also related to BP-3 exposure. Therefore, we deduced that BP-3 influenced cell migration via SLIT2/ROBO1-miR-218-RET/PLAG1 pathway. Our study firstly revealed the relationship between maternal BP-3 exposure and HSCR as well as its potential mechanism.

Ibuprofen slows migration and inhibits bowel colonization by enteric nervous system precursors in zebrafish, chick and mouse

Hirschsprung Disease (HSCR) is a potentially deadly birth defect characterized by the absence of the enteric nervous system (ENS) in distal bowel. Although HSCR has clear genetic causes, no HSCR-associated mutation is 100% penetrant, suggesting gene-gene and gene-environment interactions determine HSCR occurrence. To test the hypothesis that certain medicines might alter HSCR risk we treated zebrafish with medications commonly used during early human pregnancy and discovered that ibuprofen caused HSCR-like absence of enteric neurons in distal bowel. Using fetal CF-1 mouse gut slice cultures, we found that ibuprofen treated enteric neural crest-derived cells (ENCDC) had reduced migration, fewer lamellipodia and lower levels of active RAC1/CDC42. Additionally, inhibiting ROCK, a RHOA effector and known RAC1 antagonist, reversed ibuprofen effects on migrating mouse ENCDC in culture. Ibuprofen also inhibited colonization of Ret+/- mouse bowel by ENCDC in vivo and dramatically reduced bowel colonization by chick ENCDC in culture. Interestingly, ibuprofen did not affect ENCDC migration until after at least three hours of exposure. Furthermore, mice deficient in Ptgs1 (COX 1) and Ptgs2 (COX 2) had normal bowel colonization by ENCDC and normal ENCDC migration in vitro suggesting COX-independent effects. Consistent with selective and strain specific effects on ENCDC, ibuprofen did not affect migration of gut mesenchymal cells, NIH3T3, or WT C57BL/6 ENCDC, and did not affect dorsal root ganglion cell precursor migration in zebrafish. Thus, ibuprofen inhibits ENCDC migration in vitro and bowel colonization by ENCDC in vivo in zebrafish, mouse and chick, but there are cell type and strain specific responses. These data raise concern that ibuprofen may increase Hirschsprung disease risk in some genetically susceptible children.

ENS Development Research Since 1983: Great Strides but Many Remaining Challenges

The first enteric nervous system (ENS) conference, organized by Marcello Costa and John Furness, was held in Adelaide, Australia in 1983. In this article, we review what was known about the development of the ENS in 1983 and then summarize some of the major advances in the field since 1983.

Hirschsprung's disease, Down syndrome, and missing heritability: too much collagen slows migration

Hirschsprung's disease (HSCR) causes functional intestinal obstruction due to the absence of the enteric nervous system (ENS) in the distal bowel and is usually diagnosed shortly after birth or during childhood. While several genetic and nongenetic factors have been linked to HSCR, the underlying mechanisms that prevent ENS precursors from colonizing distal bowel during fetal development are not completely understood in many affected children. In this issue of the JCI, Soret and colleagues identify a new mechanism that causes HSCR-like disease in mice and involves deposition of excess collagen VI in the intestine by migrating ENS precursors as they colonize fetal bowel. Remarkably, their findings may explain some of the so-called missing heritability of HSCR and suggest a mechanism for increased HSCR incidence in children with Down syndrome (trisomy 21).

A collagen VI-dependent pathogenic mechanism for Hirschsprung's disease

Hirschsprung's disease (HSCR) is a severe congenital anomaly of the enteric nervous system (ENS) characterized by functional intestinal obstruction due to a lack of intrinsic innervation in the distal bowel. Distal innervation deficiency results from incomplete colonization of the bowel by enteric neural crest cells (eNCCs), the ENS precursors. Here, we report the generation of a mouse model for HSCR--named Holstein--that contains an untargeted transgenic insertion upstream of the collagen-6α4 (Col6a4) gene. This insertion induces eNCC-specific upregulation of Col6a4 expression that increases total collagen VI protein levels in the extracellular matrix (ECM) surrounding both the developing and the postnatal ENS. Increased collagen VI levels during development mainly result in slower migration of eNCCs. This appears to be due to the fact that collagen VI is a poor substratum for supporting eNCC migration and can even interfere with the migration-promoting effects of fibronectin. Importantly, for a majority of patients in a HSCR cohort, the myenteric ganglia from the ganglionated region are also specifically surrounded by abundant collagen VI microfibrils, an outcome accentuated by Down syndrome. Collectively, our data thus unveil a clinically relevant pathogenic mechanism for HSCR that involves cell-autonomous changes in ECM composition surrounding eNCCs. Moreover, as COL6A1 and COL6A2 are on human Chr.21q, this mechanism is highly relevant to the predisposition of patients with Down syndrome to HSCR.

Neural crest requires Impdh2 for development of the enteric nervous system, great vessels, and craniofacial skeleton

Mutations that impair the proliferation of enteric neural crest-derived cells (ENCDC) cause Hirschsprung disease, a potentially lethal birth defect where the enteric nervous system (ENS) is absent from distal bowel. Inosine 5' monophosphate dehydrogenase (IMPDH) activity is essential for de novo GMP synthesis, and chemical inhibition of IMPDH induces Hirschsprung disease-like pathology in mouse models by reducing ENCDC proliferation. Two IMPDH isoforms are ubiquitously expressed in the embryo, but only IMPDH2 is required for life. To further understand the role of IMPDH2 in ENS and neural crest development, we characterized a conditional Impdh2 mutant mouse. Deletion of Impdh2 in the early neural crest using the Wnt1-Cre transgene produced defects in multiple neural crest derivatives including highly penetrant intestinal aganglionosis, agenesis of the craniofacial skeleton, and cardiac outflow tract and great vessel malformations. Analysis using a Rosa26 reporter mouse suggested that some or all of the remaining ENS in Impdh2 conditional-knockout animals was derived from cells that escaped Wnt1-Cre mediated DNA recombination. These data suggest that IMPDH2 mediated guanine nucleotide synthesis is essential for normal development of the ENS and other neural crest derivatives.

Human and Murine Tissue-Engineered Colon Exhibit Diverse Neuronal Subtypes and Can Be Populated by Enteric Nervous System Progenitor Cells When Donor Colon Is Aganglionic

PURPOSE

Tissue-engineered colon (TEC) might potentially replace absent or injured large intestine, but the enteric nervous system (ENS), a key component, has not been investigated. In various enteric neuropathic diseases in which the TEC is derived from aganglionic donor colon, the resulting construct might also be aganglionic, limiting tissue engineering applications in conditions such as Hirschsprung disease (HD). We hypothesized that TEC might contain a diverse population of enteric neuronal subtypes, and that aganglionic TEC can be populated by neurons and glia when supplemented with ENS progenitor cells in the form of neurospheres.

MATERIALS AND METHODS

Human and murine organoid units (OU) and multicellular clusters containing epithelium and mesenchyme were isolated from both mouse and human donor tissues, including from normally innervated and aganglionic colon. The OU were seeded onto a biodegradable scaffold and implanted within a host mouse, resulting in the growth of TEC. Aganglionic murine and human OU were supplemented with cultured neurospheres to populate the absent ENS not provided by the OU to rescue the HD phenotype.

RESULTS

TEC demonstrated abundant smooth muscle and clusters of neurons and glia beneath the epithelium and deeper within the mesenchyme. Motor and afferent neuronal subtypes were identified in TEC. Aganglionic OU formed TEC with absent neural elements, but neurons and glia were abundant when aganglionic OU were supplemented with ENS progenitor cells.

CONCLUSION

Murine and human TEC contain key components of the ENS that were not previously identified, including glia, neurons, and fundamental neuronal subtypes. TEC derived from aganglionic colon can be populated with neurons and glia when supplemented with neurospheres. Combining tissue engineering and cellular replacement therapies represents a new strategy for treating enteric neuropathies, particularly HD.

Genetic variants of IL-11 associated with risk of Hirschsprung disease

BACKGROUND

Hirschsprung disease (HSCR) is a congenital and heterogeneous disorder characterized by the absence of enteric ganglia during enteric nervous system (ENS) development. Our recent genome-wide association study has identified a variant (rs6509940) of interleukin-11 (IL-11) as a potential susceptible locus for HSCR. As interleukins play important roles in the ENS, we further studied associations with HSCR of nine common single nucleotide polymorphisms (SNPs) on IL-11.

METHODS

Biopsy specimens or surgical materials from all patients that were tested for histological examination based on the absence of the enteric ganglia were collected. A total of nine SNPs on IL-11 were genotyped in 187 HSCR patients and 283 unaffected controls using TaqMan genotyping assay.

KEY RESULTS

Combined analysis revealed that several SNPs (minimum p = 1.57 × 10(-7) ) showed statistically significant associations with HSCR, even after Bonferroni correction (pcorr  = 1.73 × 10(-6) for the SNP). Moreover, the most common haplotype was strongly associated with HSCR (pcorr  = 2.20 × 10(-6) ). In further analysis among three HSCR subtypes (short segment, S-HSCR; long segment, L-HSCR; total colonic aganglionosis, TCA) based on the extent of aganglionic segment, the result showed a different association pattern depending on the subtypes (minimum pcorr  = 6.12 × 10(-5) for rs6509940 in S-HSCR; but no significant SNP in L-HSCR and TCA).

CONCLUSIONS & INFERENCES

Although further replication in a larger cohort and functional evaluations are needed, our findings suggest that genetic variations of IL-11 may be associated with the risk of HSCR and/or the mechanisms related to ENS development.

SLIT2/ROBO1-miR-218-1-RET/PLAG1: a new disease pathway involved in Hirschsprung's disease

Hirschsprung's disease (HSCR) is a rare congenital disease caused by impaired proliferation and migration of neural crest cells. We investigated changes in expression of microRNAs (miRNAs) and the genes they regulate in tissues of patients with HSCR. Quantitative real-time PCR and immunoblot analyses were used to measure levels of miRNA, mRNAs, and proteins in colon tissues from 69 patients with HSCR and 49 individuals without HSCR (controls). Direct interactions between miRNAs and specific mRNAs were indentified in vitro, while the function role of miR-218-1 was investigated by using miR-218 transgenic mice. An increased level of miR-218-1 correlated with increased levels of SLIT2 and decreased levels of RET and PLAG1 mRNA and protein. The reductions in RET and PLAG1 by miR-218-1 reduced proliferation and migration of SH-SY5Y cells. Overexpression of the secreted form of SLIT2 inhibited cell migration via binding to its receptor ROBO1. Bowel tissues from miR-218-1 transgenic mice had nerve fibre hyperplasia and reduced numbers of gangliocytes, compared with wild-type mice. Altered miR-218-1 regulation of SLIT2, RET and PLAG1 might be involved in the pathogenesis of HSCR.

Building a second brain in the bowel

The enteric nervous system (ENS) is sometimes called the "second brain" because of the diversity of neuronal cell types and complex, integrated circuits that permit the ENS to autonomously regulate many processes in the bowel. Mechanisms supporting ENS development are intricate, with numerous proteins, small molecules, and nutrients that affect ENS morphogenesis and mature function. Damage to the ENS or developmental defects cause vomiting, abdominal pain, constipation, growth failure, and early death. Here, we review molecular mechanisms and cellular processes that govern ENS development, identify areas in which more investigation is needed, and discuss the clinical implications of new basic research.