The development of colon innervation in trisomy 16 mice and Hirschsprungs disease

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.

Postoperative Pullthrough Obstruction in Hirschsprung Disease: Etiologies and Diagnosis

Some patients continue to have obstructive symptoms and/or incontinence after pullthrough surgery for Hirschsprung disease. Incontinence can be due to injury to the anal sphincter and/or dentate line, abnormal colonic motility (nonretentive), or a chronic large stool burden (retentive). A diagnostic algorithm based on clinical and pathological evaluations can be applied to distinguish potential etiologies for obstructive symptoms, which segregate into anatomic (mechanical or histopathological) or physiologic subgroups. Valuable clinical information may be obtained by anorectal examination under anesthesia, radiographic studies, and anorectal or colonic manometry. In addition, histopathological review of a patient's original resection specimen(s) as well as postoperative biopsies of the neorectum usually are an important component of the diagnostic workup. Goals for the surgical pathologist are to exclude incomplete resection of the aganglionic segment or transition zone and to identify other neuromuscular pathology that might explain the patient's dysmotility. Diagnoses established from a combination of clinical and pathological data dramatically alter management strategies. In rare instances, reoperative pullthrough surgery is required, in which case the pathologist must be aware of histopathological features specific to redo pullthrough resection specimens.

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.

Calretinin-Immunoreactive Hypoinnervation in Down Syndrome (DS): Report of an Infant with Very Short-Segment Hirschsprung Disease and Comparison to Biopsy Findings in 20 Normal Infants and 11 Infants with DS and Chronic Constipation

In Down syndrome (DS) constipation is common, and the incidence of Hirschsprung disease (HD) is 1-2%. Rectal suction biopsies (RSBs) in DS may show discordant features; calretinin immunoreactivity (CRir) often helps resolve discrepancies. We report a case of unequivocal very short-segment HD (vsHD) in an infant with DS who had aganglionosis with abnormal acetylcholine esterase (AChE) activity in 3 RSBs. The CRir patterns were scanty positive rather than the expected absent CRir innervation in the lamina propria (LP). The resection specimen was grossly typical for short-segment HD, with a 5.5-cm, narrow but normally ganglionated segment proximal to the verified very short distal anganglionic zone. Unequivocal calretinin hypoinnervation was limited to the distal 2 cm, substantiating the warning of Kapur that small numbers of CRir nerves in the LP do not exclude a diagnosis of vsHD. We evaluated RSBs from 11 DS and 20 randomly selected normal infants <6 months of age with chronic constipation. The normal infants had abundant mucosal calretinin innervation and AChE histochemistry. We observed variable CRir hypoinnervation in RSBs in DS infants (including 6/7 with "normal" original diagnosis and 1/4 with HD). Our findings caution against overdependence on "normal" calretinin immunohistochemistry and suggest that AChE may be more reliable than CRir in the context of DS. An unknown number of patients with DS may have enteric nervous system disorders functionally similar to HD, which are possibly related to abnormal or imbalanced autonomic innervation, of which distal calretinin hypoinnervation is one manifestation, despite the presence of ganglia.

Advances in molecular genetics of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cells to fully colonize the gut during embryonic development. It is characterized by the absence of the enteric ganglia in a variable length of the intestine. Substantial progress has been made in understanding the genetic basis of HSCR with the help of advanced genetic analysis techniques and animal models. More than 11 genes have been found to be involved in the pathogenesis of HSCR. The RET gene is the most important susceptibility gene involved in HSCR with both coding and non- coding sequence mutations. Due to phenotypic diversity and genetic complexity observed in HSCR, mutational analysis has limited practical value in genetic counseling and clinical practice. In this review, we discuss the progress that has been made in understanding the molecular genetics of HSCR and summarize the currently identified genes as well as interactions between pathways and gene-modifying loci in HSCR.

Murine model of Hirschsprung-associated enterocolitis. I: phenotypic characterization with development of a histopathologic grading system

PURPOSE

The aim of the study was to characterize enterocolitis in the Ednrb-null (Ednrb-/-) mouse with aganglionosis of the colon and to develop and validate a semiquantitative histopathologic grading system to assess enterocolitis.

METHODS

We isolated colon and ileal specimens of Ednrb-/- and control mice (Ednrb+/+) and performed histochemical staining (H&E) on tissue sections. After establishing inflammation grading criteria, 2 blinded pathologists independently assessed the severity and depth of inflammation of proximal colon segments on 2 separate occasions. Interclass correlations (ICCs) and coefficient of variation (CV) were calculated to determine interrater and intrarater agreement. We then prospectively applied the enterocolitis grading system to Ednrb-/- mice that became clinically ill. A cohort of Ednrb-/- mice were observed until they developed clinical illness, at which time they were euthanized and had multiple organ homogenates cultured for bacteria, and colon and small bowel were histopathologically graded for enterocolitis. Spearman's rank correlations comparing enterocolitis scores with level of bacteremia were performed.

RESULTS

Intra- and interrater ICCs of the histologic scoring system were satisfactory (0.61 and 0.94, respectively), as were intra- and interrater CVs (18% and 9%, respectively). Of the Ednrb-/- mice, 65% developed bacteremia. Those with bacteremia had significantly higher enterocolitis scores than those without bacteremia (P < .01). Ednrb-/- mice that developed bacteremia showed a strong positive correlation between total enterocolitis scores and number of bacterial colony forming units in peritoneal lavage, liver, kidney, and aerobic spleen.

CONCLUSIONS

The Ednrb-/- mouse with aganglionosis develops enterocolitis and has features similar to Hirschsprung-associated enterocolitis in humans. Our grading system is a reliable way to assess enterocolitis. By performing microsurgical pull-through, we can now perform controlled, hypothesis-driven, mechanistic studies to evaluate etiologic factors affecting enterocolitis in the Ednrb-/- mouse.

Murine model of Hirschsprung-associated enterocolitis II: Surgical correction of aganglionosis does not eliminate enterocolitis

BACKGROUND

Hirschsprung disease (HD) results from aganglionosis of the colon, is linked to acute and chronic enterocolitis (known as Hirschsprung-associated enterocolitis) despite successful corrective surgery, and can lead to bacteremia and even death. The genetic and molecular mechanisms underlying these disorders are largely unknown.

METHODS

We developed a microsurgical corrective pull-through procedure in mice, and applied that to Ednrb(-/-) mice, which manifest aganglionic megacolon that is very similar to HD. Wild-type littermates (Ednrb(+/+)) also underwent identical surgery. At prespecified time points postoperatively, mice were sacrificed, and histopathologic analyses of intestinal inflammation were performed. Mice of both genotypes were sacrificed after the postoperative recovery period to determine if corrective surgery itself caused inflammation. Stooling patterns were assessed as well to determine if intestinal function normalized after surgery.

RESULTS

There was no difference in histopathological enterocolitis scores after recovery from surgery. Stooling patterns in Ednrb(-/-) and Ednrb(+/+) mice were similar postoperatively, suggesting normalization of intestinal function. However, with time, approximately 40% of Ednrb(-/-) mice developed clinical illness consistent with enterocolitis. No control (Ednrb(+/+)) mice developed clinical enterocolitis. Histopathological enterocolitis scores in the 40% of Ednrb(-/-) mice that developed clinical enterocolitis postoperatively were significantly worse than those of healthy postoperative Ednrb(-/-) mice. In contrast, none of the Ednrb(+/+) control mice exhibited postoperative long-term inflammation.

CONCLUSIONS

Microsurgical pull-through operation in Ednrb(-/-) mice produces a mouse model that closely resembles key features of Hirschsprung-associated enterocolitis, enabling controlled study of genetic and molecular mechanisms in Ednrb(-/-) mice and other genotypes that produce similar phenotypes.

A novel corrective pullthrough surgery in a mouse model of Hirschsprung's disease

BACKGROUND/PURPOSE

The study aimed to develop a mouse model of post-pullthrough Hirschsprung's disease that will allow investigation of mechanisms that cause postoperative complications.

METHODS

We developed a novel microsurgical pullthrough operation on Balb/C mice and evaluated its effect on growth rate and stooling pattern. Histologic assessment of the pullthrough colon was performed. The pullthrough operation was then performed on Ednrb-/- mice that have aganglionic megacolon and Ednrb+/+ littermate controls, and the outcomes compared.

RESULTS

The Balb/C pullthrough group had 97% survival at 1 week and 70% survival at 2 weeks. Body weight of the pullthrough animals declined 15% in the first week after surgery and subsequently normalized. The stooling pattern showed consistently softer stools in the pullthrough group, but no difference in frequency compared to controls. Histopathologic analyses 4 weeks postoperatively showed well-healed coloanal anastomoses. Two-week survival after pullthrough surgery in Ednrb-/- and Ednrb+/+ mice was 50.0%, and 69.2%, respectively (P = NS). Increased mortality in the Ednrb-/- mice was related to the technical challenge of performing microsurgery on smaller-sized mice with poor baseline health status.

CONCLUSIONS

Our microsurgical pullthrough operation in mice is feasible and allows systematic investigations into potential mechanisms mediating post-pullthrough complications and poor long-term results in mouse models of Hirschsprung's disease.

Interstitial cells of Cajal, enteric nerves, and glial cells in colonic diverticular disease

BACKGROUND

Colonic diverticular disease (diverticulosis) is a common disorder in Western countries. Although its pathogenesis is probably multifactorial, motor abnormalities of the large bowel are thought to play an important role. However, little is known about the basic mechanism that may underlie abnormal colon motility in diverticulosis.

AIMS

To investigate the interstitial cells of Cajal (the gut pacemaker cells), together with myenteric and submucosal ganglion and glial cells, in patients with diverticulosis.

PATIENTS

Full thickness colonic samples were obtained from 39 patients undergoing surgery for diverticulosis. Specimens from tumour free areas of the colon in 10 age matched subjects undergoing surgery for colorectal cancer served as controls.

METHODS

Interstitial cells of Cajal were assessed using anti-Kit antibodies; submucosal and myenteric plexus neurones and glial cells were assessed by means of anti-PGP 9.5 and anti-S-100 monoclonal antibodies, respectively.

RESULTS

Patients with diverticulosis had normal numbers of myenteric and submucosal plexus neurones compared with controls (p = 0.103 and p = 0.516, respectively). All subtypes of interstitial cells of Cajal were significantly (p = 0.0003) reduced compared with controls, as were glial cells (p = 0.0041).

CONCLUSIONS

Interstitial cells of Cajal and glial cells are decreased in colonic diverticular disease, whereas enteric neurones appear to be normally represented. This finding might explain some of the large bowel motor abnormalities reported to occur in this condition.

A new mechanism for diverticular diseases: aging-related vagal withdrawal

It is widely believed that diverticulosis, a common condition among the elderly, results from repeated colonic barotrauma related to low dietary fiber and low stool bulk. Recent evidence has challenged the dietary-barotrauma hypothesis. We propose an alternative hypothesis that diverticulosis may be attributable to colonic smooth muscle dysfunction that results from vagal attrition associated with aging. We previously proposed that broad aging-related attrition of autonomic nerves may unmask intrinsic sympathetic bias of end-organs, leading to the compendium of familiar conditions associated with senility. Unexplained cholinergic hypersensitivity and receptor over-expression in bowel affected by diverticulosis have recently been observed. These findings are highly suggestive of a compensatory response to loss of vagal innervation. The resulting autonomic dysregulation may induce bowel smooth muscle dysfunction, setting the stage for diverticula formation. Thus, diverticular bowel disease may be a manifestation of the aging-related systemic vagal withdrawal. The framework may extend to diverticula formation in other parts of the gastrointestinal and genitourinary tracts. For instance, aging-related vagal attrition may represent the common upstream mechanism that induces both sphincter of Oddi dysfunction and peri-ampullary duodenal diverticula, conditions that frequently occur together. Novel approaches to preventing and treating diverticular diseases by promoting vagal activity are proposed including the electrical or pharmacologic modulation of the autonomic system.

Polymerase chain reaction-single strand conformational polymorphism analysis of rearranged during transfection proto-oncogene in Chinese familial hirschsprung’s disease

AIM: To investigate the relationship between mutations of rearranged during transfection (RET) proto-oncogene and Chinese patients with Hirschsprung’s disease (HD), and to elucidate the genetic mechanism of familial HD patient at the molecular level.

METHODS: Genomic DNA was extracted from venous blood of probands and their relatives in two genealogies. Polymerase chain reaction (PCR) products, which were amplified using specific primers (RET, exons 11, 13, 15 and 17), were electrophoresed to analyze the single-strand conformational polymorphism (SSCP) patterns. The positive amplified products were sequenced. Forty-eight sporadic HD patients and 30 normal children were screened for mutations of RET proto-oncogene simultaneously.

RESULTS: Three cases with HD in one family were found to have a G heterozygous insertion at nucleotide 18974 in exon 13 of RET cDNA (18974insG), which resulted in a frameshift mutation. In another family, a heterozygosity for T to G transition at nucleotide 18888 in the same exon which resulted in a synonymous mutation of Leu at codon 745 was detected in the proband and his father. Eight RET mutations were confirmed in 48 sporadic HD patients.

CONCLUSION: Mutations of RET proto-oncogene may play an important role in the pathogenesis of Chinese patients with HD. Detection of mutated RET proto-oncogene carriers may be used for genetic counseling of potential risk for HD in the affected families.

Clinical relationship between EDN-3 gene, EDNRB gene and Hirschsprung’s disease

AIM: To investigate the mutation of EDNRB gene and EDN-3 gene in sporadic Hirschsprung’s disease (HD) in Chinese population.

METHODS: Genomic DNA was extracted from bowel tissues of 34 unrelated HD patients which were removed by surgery. Exon 3, 4, 6 of EDNRB gene and Exon 1, 2 of EDN-3 gene were amplified by polymerase chain reaction (PCR) and analyzed by single strand conformation polymorphism (SSCP).

RESULTS: EDNRB mutations were detected in 2 of the 13 short-segment HD. One mutant was in the exon 3, the other was in the exon 6. EDN-3 mutation was detected in one of the 13 short-segment HD and in the exon 2. Both EDNRB and EDN-3 mutations were detected in one short-segment HD. No mutations were detected in the ordinary or long-segment HD.

CONCLUSION: The mutations of EDNRB gene and EDN-3 gene are found in the short-segment HD of sporadic Hirschsprung’s disease in Chinese population, which suggests that the EDNRB gene and EDN-3 gene play important roles in the pathogenesis of HD.

Smooth muscle cholinergic denervation hypersensitivity in diverticular disease

BACKGROUND

Evidence from clinical and laboratory investigations into the causes of diverticular disease suggests that disturbances in cholinergic activity are important, the effector mechanisms of which have yet to be established. We aimed to investigate the role of smooth muscle and neural cholinergic activity in the pathogenesis of this disease.

METHODS

Two investigators independently did a blinded immunohistochemical image analysis of localising antibodies to choline acetyltransferase, co-localised with protein gene product (PGP)--a marker of general neural tissue-and smooth muscle muscarinic M3 receptors, on three histological sections of sigmoid colons from ten patients with diverticular disease and ten controls, after resections for rectal tumours. We also did isotonic organ bath experiments to assess muscle strip sensitivities to exogenous acetylcholine.

FINDINGS

In circular muscle, activity of choline acetyltransferase was lower in patients with diverticular disease than in controls: median percentage surface area of choline acetyltransferase over PGP was 17.5% (range 10.0-37.0) in patients with diverticular disease and 47.0% (29.0-54.0) in controls (p<0.0001). M3 receptors were upregulated in patients with diverticular disease compared with controls: the median surface area was 13.2% (6.0-23.3) in patients with diverticular disease and 2.5% (1.6-3.7) in controls (p<0.0001). The sensitivity to exogenous acetylcholine was increased in patients with diverticular disease (mean -log EC(50) 5.6 [SD 0.3]) compared with controls (4.9 [0.5]; difference 0.7 [95% CI 0.3-1.1], p=0.006). In longitudinal muscle, choline acetyltransferase activity was lower in patients with diverticular disease (median 19.5%, range 12.0-30.0) than in controls (47.0%, 35.0-60.0; p<0.0001), with upregulation of M3 receptors in diverticular disease (diverticular disease 7.8% [1.9-20.4], controls 1.7% [0.8-3.0]; p<0.0001). However, sensitivity to exogenous acetylcholine did not differ between the two groups (diverticular disease mean 5.6% [SD 0.3], controls 5.2% [0.4]; difference 0.4% [95% CI -0.02-0.7], p=0.06).

INTERPRETATION

Our results suggest that cholinergic denervation hypersensitivity can affect smooth muscle. Upregulation of smooth muscle M3 receptors might account for specific clinical, physiological, and pharmacological abnormalities associated with diverticular disease.

Mutation of RET gene in Chinese patients with Hirschsprung’s disease

AIM: To investigate the pathogenic mechanism of Hirschsprung’s disease (HD) at the molecular level and to elucidate the relationship between RET oncogene and Chinese patients with HD.

METHODS: Exon 13 of RET oncogene from 20 unrelated HD patients was analyzed with polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). The positive amplifying products were then sequenced. According to the results of SSCP and DNA sequence, SSCP was done as well for the samples from the family other members of some cases with mutated RET gene.

RESULTS: SSCP analysis indicated that mobility abnormality existed in 4 unrelated HD patients. Direct DNA sequence analysis identified a missense mutation, T to G at the nucleotide 18888 and a frameshift mutation at the nucleotide 18926 insG. In a HD family, the sicked child and his father were the same heterozygous missense mutation (T to G at nucleotide 18888).

CONCLUSION: Among Chinese HD patients, RET gene mutations may exist in considerable proportion with different patterns. These new discoveries indicate that RET mutations may play an important role in the pathogenesis of unrelated HD in the Chinese population. PCR-SSCP combined with DNA sequence can be used as a tool in the genetic diagnosis of HD.