Acetylcholine-related bowel dysmotility in homozygous mutant NCX/HOX11L.1-deficient (NCX-/-) mice-evidence that acetylcholine is implicated in causing intestinal neuronal dysplasia

A novel mouse model of intestinal neuronal dysplasia: visualization of the enteric nervous system

PURPOSE

Intestinal neuronal dysplasia (IND) is a congenital anomaly affecting gastrointestinal neural innervation, but the pathogenesis remains unclear. The homozygous Ncx/Hox11L.1 knockout (Ncx-/-) mice exhibit megacolon and enteric ganglia anomalies, resembling IND phenotypes. Sox10-Venus transgenic mouse were used to visualize enteric neural crest cells in real time. This study aims to establish a novel mouse model of Sox10-Venus+/Ncx-/- mouse to study the pathogenesis of IND.

METHODS

Sox10-Venus+/Ncx-/- (Ncx-/-) (n = 8) mice and Sox10-Venus+/Ncx+/+ controls (control) (n = 8) were euthanized at 4-5 weeks old, and excised intestines were examined with fluorescence microscopy. Immunohistochemistry was performed on tissue sections with neural marker Tuj1.

RESULTS

Ncx-/- mice exhibited dilated cecum and small intestine. Body weight of Ncx-/- mice was lower with higher ratio of small intestine length relative to body weight. The neural network (Sox10-Venus) was observed along the intestine wall in Ncx-/- and control mice without staining. Ectopic and increased expression of Tuj1 was observed in both small intestine and proximal colon of Ncx-/- mice.

CONCLUSION

This study has established a reliable animal model that exhibits characteristics similar to patients with IND. This novel mouse model can allow the easy visualization of ENS in a time- and cost-effective way to study the pathogenesis of IND.

Identification of potential molecular pathogenesis mechanisms modulated by microRNAs in patients with Intestinal Neuronal Dysplasia type B

This study proposed to determine global microRNA (miRNA) expression and miRNA-regulated pathways in Intestinal Neuronal Dysplasia type B (IND-B). Fifty patients (0–15 years old) with IND-B were included in the study. Peripheral blood samples were collected from all 50 patients and from 10 healthy asymptomatic children (controls). Rectal biopsies were collected from 29/50 patients; biopsy tissues were needle microdissected to isolate the different intestinal layers, for molecular analysis. Global miRNA expression was determined using TaqMan arrays. Correlation analysis between miRNA expression in plasma and biopsy samples as well as among tissues derived from the distinct intestinal layers was performed. Computational approaches were used for miRNA target prediction/identification of miRNA-regulated genes and enriched pathways biologically relevant to IND-B pathogenesis. miRNAs were statistically significantly deregulated (FC ≥ 2 and p ≤ 0.05) in submucosal and muscular layers: over-expressed (miR-146a and miR-146b) and under-expressed (miR-99a, miR-100, miR-130a, miR-133b, miR-145, miR-365, miR-374-5p, miR-451). Notably, let-7a-5p was highly over-expressed in patient plasma compared to healthy controls (FC = 17.4). In addition, miR-451 was significantly under-expressed in both plasma and all biopsy tissues from the same patients. Enriched pathways (p < 0.01) were axon guidance, nerve growth factor signalling, NCAM signalling for neurite out-growth, neuronal system and apoptosis. miRNA expression is deregulated in the submucosa and muscular layers of the rectum and detected in plasma from patients with IND-B. Biologically enriched pathways regulated by the identified miRNAs may play a role in IND-B disease pathogenesis, due to the activity related to the neurons of the enteric nervous system.

Nitric oxide regulates homeoprotein OTX1 and OTX2 expression in the rat myenteric plexus after intestinal ischemia-reperfusion injury

Neuronal and inducible nitric oxide synthase (nNOS and iNOS) play a protective and damaging role, respectively, on the intestinal neuromuscular function after ischemia-reperfusion (I/R) injury. To uncover the molecular pathways underlying this dichotomy we investigated their possible correlation with the orthodenticle homeobox proteins OTX1 and OTX2 in the rat small intestine myenteric plexus after in vivo I/R. Homeobox genes are fundamental for the regulation of the gut wall homeostasis both during development and in pathological conditions (inflammation, cancer). I/R injury was induced by temporary clamping the superior mesenteric artery under anesthesia, followed by 24 and 48 h of reperfusion. At 48 h after I/R intestinal transit decreased and was further reduced by N^ω-propyl-l-arginine hydrochloride (NPLA), a nNOS-selective inhibitor. By contrast this parameter was restored to control values by 1400W, an iNOS-selective inhibitor. In longitudinal muscle myenteric plexus (LMMP) preparations, iNOS, OTX1, and OTX2 mRNA and protein levels increased at 24 and 48 h after I/R. At both time periods, the number of iNOS- and OTX-immunopositive myenteric neurons increased. nNOS mRNA, protein levels, and neurons were unchanged. In LMMPs, OTX1 and OTX2 mRNA and protein upregulation was reduced by 1400W and NPLA, respectively. In myenteric ganglia, OTX1 and OTX2 staining was superimposed with that of iNOS and nNOS, respectively. Thus in myenteric ganglia iNOS- and nNOS-derived NO may promote OTX1 and OTX2 upregulation, respectively. We hypothesize that the neurodamaging and neuroprotective roles of iNOS and nNOS during I/R injury in the gut may involve corresponding activation of molecular pathways downstream of OTX1 and OTX2.NEW & NOTEWORTHY Intestinal ischemia-reperfusion (I/R) injury induces relevant alterations in myenteric neurons leading to dismotility. Nitrergic neurons seem to be selectively involved. In the present study the inference that both neuronal and inducible nitric oxide synthase (nNOS and iNOS) expressing myenteric neurons may undergo important changes sustaining derangements of motor function is reinforced. In addition, we provide data to suggest that NO produced by iNOS and nNOS regulates the expression of the vital transcription factors orthodenticle homeobox protein 1 and 2 during an I/R damage.

Intestinal neuronal dysplasia type B: A still little known diagnosis for organic causes of intestinal chronic constipation

Intestinal neuronal dysplasia type B (IND-B) is a controversial entity among the gastrointestinal neuromuscular disorders. It may occur alone or associated with other neuropathies, such as Hirschsprung's disease (HD). Chronic constipation is the most common clinical manifestation of patients. IND-B primarily affects young children and mimics HD, but has its own histopathologic features characterized mainly by hyperplasia of the submucosal nerve plexus. Thus, IND-B should be included in the differential diagnoses of organic causes of constipation. In recent years, an increasing number of cases of IND-B in adults have also been described, some presenting severe constipation since childhood and others with the onset of symptoms at adulthood. Despite the intense scientific research in the last decades, there are still knowledge gaps regarding definition, pathogenesis, diagnostic criteria and therapeutic possibilities for IND-B. However, in medical practice, we continue to encounter patients with severe constipation or intestinal obstruction who undergo to diagnostic investigation for HD and their rectal biopsies present hyperganglionosis in the submucosal nerve plexus and other features, consistent with the diagnosis of IND-B. This review critically discusses aspects related to the disease definitions, pathophysiology and genetics, epidemiology distribution, clinical presentation, diagnostic criteria and therapeutic possibilities of this still little-known organic cause of intestinal chronic constipation.

Involvement of interleukin-17A-induced hypercontractility of intestinal smooth muscle cells in persistent gut motor dysfunction

BACKGROUND AND AIM

The etiology of post-inflammatory gastrointestinal (GI) motility dysfunction, after resolution of acute symptoms of inflammatory bowel diseases (IBD) and intestinal infection, is largely unknown, however, a possible involvement of T cells is suggested.

METHODS

Using the mouse model of T cell activation-induced enteritis, we investigated whether enhancement of smooth muscle cell (SMC) contraction by interleukin (IL)-17A is involved in postinflammatory GI hypermotility.

RESULTS

Activation of CD3 induces temporal enteritis with GI hypomotility in the midst of, and hypermotility after resolution of, intestinal inflammation. Prolonged upregulation of IL-17A was prominent and IL-17A injection directly enhanced GI transit and contractility of intestinal strips. Postinflammatory hypermotility was not observed in IL-17A-deficient mice. Incubation of a muscle strip and SMCs with IL-17A in vitro resulted in enhanced contractility with increased phosphorylation of Ser19 in myosin light chain 2 (p-MLC), a surrogate marker as well as a critical mechanistic factor of SMC contractility. Using primary cultured murine and human intestinal SMCs, IκBζ- and p38 mitogen-activated protein kinase (p38MAPK)-mediated downregulation of the regulator of G protein signaling 4 (RGS4), which suppresses muscarinic signaling of contraction by promoting inactivation/desensitization of Gαq/11 protein, has been suggested to be involved in IL-17A-induced hypercontractility. The opposite effect of L-1β was mediated by IκBζ and c-jun N-terminal kinase (JNK) activation.

CONCLUSIONS

We propose and discuss the possible involvement of IL-17A and its downstream signaling cascade in SMCs in diarrheal hypermotility in various GI disorders.

A new experimental approach is required in the molecular analysis of intestinal neuronal dysplasia type B patients

Intestinal neuronal dysplasia type B (INDB) is characterized by the malformation of the parasympathetic submucous plexus of the gut. It is generally accepted that INDB has a genetic basis, and several genes produce an INDB-like phenotype in mice when disrupted, such as EDNRB. However, no mutations associated with this disease have been identified in several series analysed. In the present studu, we sought to determine whether the EDNRB/EDN3 signalling pathway plays a role in the pathogenesis of INDB in humans. Denaturing high performance liquid chromatography (dHPLC) techniques were employed to screen the EDNRB and EDN3 coding regions in 23 INDB patients. In addition, association studies were performed on these genes with single nucleotide polymorphisms strategically selected and genotyped by TaqMan technology. Although several novel variants were detected in both genes, none of these variants appeared to play a functional role in protein function or expression. Our results indicate that additional screening of other candidate genes in larger patient series is required to elucidate the molecular basis of INDB. Additionally, the systematic lack of positive results in the screening of candidate genes for INDB reported in the literature, together with our results, leads us to propose that INDB may alternatively arise as a consequence of gain of function mutations in genes related to enteric nervous system development. Therefore, the use of different molecular approaches, such as screening for genetic duplication or enhancer mutations, is recommended for future studies on the genetic basis of INDB.

[Intestinal neuronal dysplasia type B: how do we understand it today?]

Intestinal neuronal dysplasia type B (IND B) is currently considered to be a subtle malformation of the submucosal plexus, leading to an increased proportion of over-sized ganglia and potentially accompanied by a mild, chronic gastrointestinal motility disturbance. The diagnosis of IND B is morphologically based and involves the demonstration of an increased proportion of giant ganglia in the submucous plexus related to the patient's age. Giant ganglia are physiologically frequent in the neonatal period. Therefore, IND B should not be diagnosed prior to 1 year of age. Morphological features of IND B may occur as an isolated finding or may be observed proximal to an aganglionic segment. IND B and constipation may resolve spontaneously up to the age of 4 years. Treatment of IND B is usually conservative, surgical resection is currently deemed necessary only in a minority of patients. The pathogenesis of IND B is still incompletely understood and the etiology unknown. Future research on the basis of standardized diagnostic conditions is expected to result in a better understanding of this disease, and to reveal the cause of aberrant ganglion development.

[Intestinal neuronal dysplasia type B: how do we understand it today?]

Intestinal neuronal dysplasia type B (IND B) is currently considered to be a subtle malformation of the submucosal plexus, leading to an increased proportion of over-sized ganglia and potentially accompanied by a mild, chronic gastrointestinal motility disturbance. The diagnosis of IND B is morphologically based and involves the demonstration of an increased proportion of giant ganglia in the submucous plexus related to the patient's age. Giant ganglia are physiologically frequent in the neonatal period. Therefore, IND B should not be diagnosed prior to 1 year of age. Morphological features of IND B may occur as an isolated finding or may be observed proximal to an aganglionic segment. IND B and constipation may resolve spontaneously up to the age of 4 years. Treatment of IND B is usually conservative, surgical resection is currently deemed necessary only in a minority of patients. The pathogenesis of IND B is still incompletely understood and the etiology unknown. Future research on the basis of standardized diagnostic conditions is expected to result in a better understanding of this disease, and to reveal the cause of aberrant ganglion development.

The mechanism of intestinal motility in homozygous mutant Ncx/Hox11L.1-deficient mice--a model for intestinal neuronal dysplasia

PURPOSE

Homozygous mutant Ncx/Hox11L.1-deficient (Ncx-/-) mice develop mega-ileo-ceco-colon with a caliber change in the proximal colon. This study investigated the mechanism of intestinal motility in these mice.

METHOD

Five-week-old male and female Ncx-/- mice with mega-ileo-ceco-colon (n = 8) were compared with age-matched male BDF1 mice used as controls (n = 8). All mice were sacrificed, and uniform-sized strips of jejunum, ileum, proximal colon, and distal colon were exposed to electrical field stimulation and pretreatment with atropine sulfate, guanethidine, or tetrodotoxin. Contractile responses were recorded and compared.

RESULTS

Longitudinal muscle from strips of jejunum and ileum from all mice (BDF1 and Ncx-/-) did not respond to electrical field stimulation, whereas ileal circular muscle contracted in BDF1 mice and contracted and relaxed in Ncx-/- mice. Pretreatment with atropine sulfate and guanethidine inhibited the responses of circular muscle of distal colon and ileum in BDF1 mice significantly (P < .05), but no effect was observed in Ncx-/- mice.

CONCLUSION

In ileum, BDF1 mice have cholinergic and adrenergic dominant contraction patterns, whereas Ncx-/- mice have relaxation-dominant patterns because of nonadrenergic, noncholinergic nerves. Based on this, there would appear to be some kind of variation in the gastrointestinal nerve supply in Ncx-/- mice.

Identification of the consensus DNA sequence for Nczf binding

The Nczf gene, which is identified as a target gene of Ncx, encodes a novel Kruppel-associated box (KRAB) zinc finger protein, which functions as a sequence-specific transcriptional repressor. We generated a fusion protein of the zinc finger domain of Nczf and glutathione S-transferase to identify Nczf-binding consensus DNA sequences with random oligonucleotides of 15 and 35 bases. The consensus binding sequence of core nucleotides contains (A/T/C)CTTT(A/G)TTNT. In a gel mobility shift assay, the probe containing these sequences bound to the fusion protein. In silico analysis, these consensus sequences were found on regulatory regions of the endothelin receptor B and the microphthalmia-associated transcription factor genes, which are involved in neural crest development. These results suggest that Nczf functions as a sequence-specific transcription repressor to regulate neural crest cell development.

Stephen L. Gans Distinguished Overseas Lecture. The neural crest in pediatric surgery

AIM

This review highlights the relevance of the neural crest (NC) as a developmental control mechanism involved in several pediatric surgical conditions and the investigative interest of following some of its known signaling pathways.

METHODS

The participation of the NC in facial clefts, ear defects, branchial fistulae and cysts, heart outflow tract and aortic arch anomalies, pigmentary disorders, abnormal enteric innervation, neural tumors, hemangiomas, and vascular anomalies is briefly reviewed. Then, the literature on clinical and experimental esophageal atresia-tracheoesophageal fistula (EA-TEF) and congenital diaphragmatic hernia (CDH) is reviewed for the presence of associated NC defects. Finally, some of the molecular signaling pathways involved in both conditions (sonic hedgehog, Hox genes, and retinoids) are summarized.

RESULTS

The association of facial, cardiovascular, thymic, parathyroid, and C-cell defects together with anomalies of extrinsic and intrinsic esophageal innervation in babies and/or animals with both EA-TEF and CDH strongly supports the hypothesis that NC is involved in the pathogenesis of these malformative clusters. On the other hand, both EA-TEF and CDH are observed in mice mutant for genes involved in the previously mentioned signaling pathways.

CONCLUSIONS

The investigation of NC-related molecular pathogenic pathways involved in malformative associations like EA-TEF and CDH that are induced by chromosomal anomalies, chemical teratogens, and engineered mutations is a promising way of clarifying why and how some pediatric surgical conditions occur. Pediatric surgeons should be actively involved in these investigations.

Intestinal neuronal dysplasia type B: one giant ganglion is not good enough

In this "Current Practice in Pediatric Pathology" article, 2 experts in the field and an associate editor of Pediatric and Developmental Pathology discuss the definition, diagnosis, clinical significance, and management of intestinal neuronal dysplasia type B. Intestinal neuronal dysplasia type B has constituted a diagnostic challenge ever since its first description more than 30 years ago. Intestinal neuronal dysplasia type B is regarded by many as a subtle malformation of the enteric nervous system that is limited to the submucosal plexus of the colon. The precise etiology remains unknown, and, to date, no specific diagnostic test exists other than morphology. Over time, with increasing experience, obligate pathological features have been adapted and refined, leading to contemporary diagnostic criteria that are enunciated in this review and placed into context with prior published data. Rigorous application of these criteria, under standardized laboratory conditions, is crucial for accurate diagnosis and future advances in this field.

The TLX2 homeobox gene is a transcriptional target of PHOX2B in neural-crest-derived cells

The TLX2 (HOX11L1, Ncx, Enx) and PHOX2B genes encode transcription factors crucial in the development of neural-crest-derived cells, leading to ANS (autonomic nervous system) specific neuronal lineages. Moreover, they share a similar expression pattern and are both involved in downstream steps of BMP (bone morphogenetic protein) signalling. In an attempt to reconstruct the gene network sustaining the correct development of the ANS, we have undertaken an in vitro experimental strategy to identify direct upstream regulators of the TLX2 gene. After characterizing a sequence displaying enhancer property in its 5' flanking region, we confirmed the functional link between the human PHOX2B and TLX2 genes. Transient transfections and electrophoretic-mobility-shift assays suggested that PHOX2B is able to bind the cell-specific element in the 5' regulatory region of the TLX2 gene, determining its transactivation in neuroblastoma cells. Such interaction was also confirmed in vivo by means of chromatin immunoprecipitation assay and, in addition, up-regulation of endogenous TLX2 mRNA level was demonstrated following PHOX2B over-expression, by quantitative real-time PCR. Finally, PHOX2B proteins carrying mutations responsible for CCHS (congenital central hypoventilation syndrome) development showed a severe impairment in activating TLX2 expression, both in vitro and in vivo. Taken together, these results support the PHOX2B-TLX2 promoter interaction, suggesting a physiological role in the transcription-factor cascade underlying the differentiation of neuronal lineages of the ANS during human embryogenesis.

Acetylcholinesterase in Hirschsprung's disease

The association between the congenital absence of colonic ganglion cells and an increased acetylcholinesterase (AChE) expression in the affected tissue is of diagnostic importance in Hirschsprung's disease (HSCR). Investigation of AChE's function in development may also help unravel some of the complex pathophysiology in HSCR. Normal nerves do not stain for AChE, but increased AChE expression is associated with the hypertrophied extrinsic nerve fibres of the aganglionic segment in HSCR. Although a high degree of histochemical diagnostic accuracy exists, results are not always uniform, and false positives and false negatives are reported. False negative results are primarily related to age, and an absence of AChE reaction does not exclude HSCR in neonates within the first 3 weeks after birth. AChE staining results may lack uniformity, resulting in a number of technical modifications that have been made to improve standardization of AChE staining. At least two distinct histological patterns are described, types A and B. The interpretation of increased AChE staining patterns in ganglionated bowel at the time of surgical pull-through remains a problem in patients with HSCR. The development of rapid staining techniques has helped to identify normal ganglionated bowel with greater certainty. The presence of fine AChE neurofibrils in the ganglionated segment has contributed to the debate surrounding intestinal neuronal dysplasia. Quantitative assay of cholinesterase activity confirms the pattern of histochemical staining. AChE is particularly increased in relation to butrylcholinesterase, with one molecular form, the G4 tetrameric form, predominating. It is likely that the raised levels of AChE in aganglionic tissue are the transcriptional consequence of the abnormalities in signalling molecules that characterize HSCR. Evidence suggests that this AChE is functioning in a nonenzymatic capacity to promote cell adhesion and differentiation and that the hypertrophied nerves and neurofibrils may be the result of this increased AChE expression.

Ca2+ clearance in smooth muscle: lessons from gene-altered mice

The regulation of intracellular [Ca(2+)](i) is important for all cells, but in particular for smooth muscle, as [Ca(2+)](i) is a key second messenger leading to contraction. Mechanisms for the cellular clearance of [Ca(2+)](i) form one side of Ca(2+) homeostasis and include: Plasma Membrane Ca(2+) ATPases (PMCA), Sarcoplasmic/Endoplasmic Reticulum Ca(2+) ATPases (SERCA), Na(+)-Ca(2+)-exchangers (NCX) when coupled to the Na(+)-K(+) ATPases (NKA) and in some cases mitochondria. The nature and relative contribution of these various components of cytosolic Ca(2+) clearance have long been an important topic for study in smooth muscle, particularly as related to regulation of contractility. These studies have largely depended on inhibition of the various components. Recently advances in gene-targeting and transgenesis have made it possible to add or delete individual components, and importantly specific isoforms from the cell. In this brief review, we will focus on new information on Ca(2+) clearance in smooth muscle gained from studies on gene-altered mice models. These provide a deeper understanding of distinct functional roles for individual isoforms and the interactions between various components.