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

Efficient enzyme-free method to assess the development and maturation of the innate and adaptive immune systems in the mouse colon

Researchers who aim to globally analyze the gastrointestinal immune system via flow cytometry have many protocol options to choose from, with specifics generally tied to gut wall layers of interest. To get a clearer idea of the approach we should use on full-thickness colon samples from mice, we first undertook a systematic comparison of three tissue dissociation techniques: two based on enzymatic cocktails and the other one based on manual crushing. Using flow cytometry panels of general markers of lymphoid and myeloid cells, we found that the presence of cell-surface markers and relative cell population frequencies were more stable with the mechanical method. Both enzymatic approaches were associated with a marked decrease of several cell-surface markers. Using mechanical dissociation, we then developed two minimally overlapping panels, consisting of a total of 26 antibodies, for serial profiling of lymphoid and myeloid lineages from the mouse colon in greater detail. Here, we highlight how we accurately delineate these populations by manual gating, as well as the reproducibility of our panels on mouse spleen and whole blood. As a proof-of-principle of the usefulness of our general approach, we also report segment- and life stage-specific patterns of immune cell profiles in the colon. Overall, our data indicate that mechanical dissociation is more suitable and efficient than enzymatic methods for recovering immune cells from all colon layers at once. Additionally, our panels will provide researchers with a relatively simple tool for detailed immune cell profiling in the murine gastrointestinal tract, regardless of life stage or experimental conditions.

Mesenchymal Stem Cells Attenuates Hirschsprung Disease-Associated Enterocolitis by Reducing M1 Macrophages Infiltration via COX-2 Dependewhant Mechanism

OBJECTIVE AND DESIGN

Hirschsprung disease-associated enterocolitis (HAEC) is a common life-threatening complication of Hirschsprung disease (HSCR). We aimed to investigate the effectiveness, long-term safety and the underlying mechanisms of Mesenchymal stem cells (MSCs) based therapy for HAEC.

MATERIAL OR SUBJECTS

Specimens from HSCR and HAEC patients were used to assess the inflammatory condition. Ednrb knock-out mice was used as HAEC model. MSCs was intraperitoneally transplanted into HAEC mice. The therapy effects, long-term outcome, safety and toxicity and the mechanism of MSCs on the treatment of HAEC were explored in vivo and in vitro.

RESULTS

Intestinal M1 macrophages infiltration and severe inflammation condition were observed in HAEC. After the injection of MSCs, HAEC mice showed significant amelioration of the inflammatory injury and inhibition of M1 macrophages infiltration. The expression levels of pro-inflammatory cytokines (TNF-α and IFN-γ) were decreased and anti-inflammatory cytokines (IL-10 and TGF-β) were increased. In addition, we found that effective MSCs homing to the inflamed colon tissue occurred without long-term toxicity response. However, COX-2 inhibitor could diminish the therapeutic effects of MSCs. Using MSCs and macrophages co-culture system, we identified that MSCs could alleviate HAEC by inhibiting M1 macrophages activation through COX-2-dependent MAPK/ERK signaling pathway.

CONCLUSIONS

MSCs ameliorate HAEC by reducing M1 macrophages polarization via COX-2 mediated MAPK/ERK signaling pathway, thus providing novel insights and potentially promising strategy for the treatment or prevention of HAEC.

Pathological and genetic characterization of foot and mouth disease viruses collected from cattle and water buffalo in Egypt

Foot-and-mouth disease (FMD), a highly contagious viral disease caused by FMD virus (FMDV) that threatens Egypt's livestock industry. FMDV causes severe economic losses in the livestock, with restriction of international trade from endemic regions. Surveillance for FMDV serotypes circulating in Egypt is urgently needed to assess the epidemiological situation in the country. FMD outbreaks reported in Egypt in between December 2016 and January-March 2017. A cross-sectional study was conducted to identify the FMDV serotypes responsible for the outbreaks and to collect information on the virus's morphopathological effects. Postmortem tissue and clinical samples (oral swabs, vesicular fluids from ruptured vesicles, and blood) were collected from recently deceased and infected animals. Pathological examination revealed classical FMD lesions as vesicular and erosive lesions on epithelial tissues with non-suppurative lymphoplasmacytic myocarditis. Phylogenetic and sequencing analyses demonstrated that FMDV serotype O, EA-3 topotype, VP1 is the prevalent serotype responsible for the pathological alterations and the high mortality in young calves, adult cattle, and water buffalo. The outcomes indicate continuous mutations in the circulating FMDV, which result in the occasional failure of vaccination. Based on these findings, extensive continuous monitoring and serotyping of the existing circulating FMDV isolates and regular vaccination with reevaluation of the currently used vaccine in Egypt are recommended to prevent the recurrence of such outbreaks.

Comparation of robotic-assisted surgery and laparoscopic‑assisted surgery in children with Hirschsprung's disease: a single-centered retrospective study

BACKGROUND

There are few studies comparing robotic-assisted surgery (RAS) and laparoscopic-assisted surgery (LAS) in Hirschsprung's disease (HSCR). This study aimed to compare intraoperative and postoperative outcomes between RAS and LAS performed during the same period.

METHODS

All consecutive 75 patients with pathologically diagnosed as HSCR who underwent Swenson pull-through surgery from April 2020 to Nov 2022, were included. Patients were divided into RAS group and LAS group and a retrospective analysis was performed based on clinical indexes and prognosis.

RESULTS

A total of 75 patients were included, among which, 31 patients received RAS and 44 received LAS. The RAS and LAS groups had similar ages, sex, weight, postoperative hospital stays, and fasting times. Compared with LAS, blood loss (p = 0.002) and the incidence of Hirschsprung-associated enterocolitis (p = 0.046) were significantly lower in the RAS group. The first onset of Hirschsprung-associated enterocolitis in patients younger than 3 months occurred significantly earlier (p = 0.043). Two patients experienced anastomotic leakage in the LAS group and one patient experienced incisional hernia in the RAS group. The cost of RAS was significantly higher than that of LAS (p < 0.0001).

CONCLUSIONS

RAS is a safe and effective alternative for HSCR children, and a delaying primary surgery until later in infancy (> 3 months) may improve outcomes.

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.

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.

Current understanding of Hirschsprung-associated enterocolitis: Pathogenesis, diagnosis and treatment

Hirschsprung-associated enterocolitis (HAEC) was described in 1886 by Harald Hirschsprung and is a potentially deadly complication of Hirschsprung Disease. HAEC is classically characterized by abdominal distension, fever, and diarrhea, although there can be a variety of other associated symptoms, including colicky abdominal pain, lethargy, and the passage of blood-stained stools. HAEC occurs both pre-operatively and post-operatively, is the presenting symptom of HSCR in up to 25% of infants and varies in overall incidence from 20 to 60%. This article reviews our current understanding of HAEC pathogenesis, diagnosis, and treatment with discussion of areas of ongoing research, controversy, and future investigation.

Antimicrobial and self-crosslinking potential of experimentally developed dioctadecyldimethyl ammonium bromide and riboflavin dentin adhesive

The aim of the study is to investigate a new formulation, based on dioctadecyldimethyl ammonium-bromide (QA) and riboflavin (RF), combining antimicrobial activities and protease inhibitory properties with collagen crosslinking without interference to bonding capabilities in a rabbit model. Quaternary ammonium riboflavin (QARF) experimental adhesives modified with dioctadecyldimethyl ammonium-bromide and riboflavin were bonded (0.5/1.0/2.0%) to rabbit dentin to investigate for pulpal-histology, interfacial-morphology, transmission electron microscopy, mechanical properties, collagen crosslinking, micro-Raman analysis, antimicrobial, and anti-protease activities. Collagen type-I molecules were generated using molecular-docking. Odontoblasts appeared with normal histology, were seen in controls with no inflammatory cells detected in 0.5% specimens at day 7 and mild inflammatory response at day 30. In QARF 2.0%, inflammatory cells were not detected at day 7 and 30 (p < .05). Dentinal tubules are seen with intact collagen surface in 1% specimens. Resin penetrated inside 1% adhesive specimens with few irregularly funnel-shaped tags. Transmission electron microscopy showed thinner collagen in all specimens except 1% QARF specimens. Biofilms were influenced by QARF adhesives. Elastic moduli were significantly higher in 1.0% and 2.0% QARF adhesive specimens with a significant increase in total crosslinks. Stable amide groups with anti-protease activity was observed in QARF groups. Charged residues were seen in the triple helix hCOL3A1, Gly489-Gly510 after stabilisation with formulation. The 1% QARF modified adhesives improved biochemical and biomechanical properties of rabbit dentin.

Circulating exosomal microRNA-18a-5p accentuates intestinal inflammation in Hirschsprung-associated enterocolitis by targeting RORA

The relevance of stem cell-derived exosomes has been implicated in necrotizing enterocolitis, while the involvement of serum-derived exosomes from children with Hirschsprung-associated enterocolitis (HAEC) in pathogenesis of HAEC remains unclear. This study set to identify the roles of exosomal microRNA (miR)-18a-5p from sera of HAEC patients in human-derived colonic epithelial NCM460 cells and in mice with HAEC. Exosomes were isolated from the sera of healthy children (Healthy-exo), patients with Hirschsprung's disease (HSCR) (HSCR-exo) or HAEC (HAEC-exo). A microarray analysis of miRNAs was implemented to assess the enrichment of miRNAs in these exosomes. HAEC-exo was significantly enriched in miR-18a-5p. HAEC-exo led to the generation of a pro-inflammatory microenvironment, inhibition of cellular DNA synthesis, and promotion of apoptosis in NCM460 cells. Mechanistically, miR-18a-5p targeted and repressed retinoid-related orphan receptor α (RORA) expression, thereby regulating the Sirtuin 1 (SIRT1)/nuclear factor-kappa B (NFκB) pathway. Overexpression of RORA ameliorated inflammatory damage in NCM460 cells caused by exosomal miR-18a-5p. HAEC-exo exacerbated inflammatory damage in HAEC mice, and this facilitation was reversed after RORA overexpression. Collectively, exosomal miR-18a-5p was a promoter of HAEC, which induces the intestine cell apoptosis and inflammatory responses through the inhibition of SIRT1/NFκB pathway by targeting RORA.

Intestinal proinflammatory macrophages induce a phenotypic switch in interstitial cells of Cajal

Interstitial cells of Cajal (ICCs) are pacemaker cells in the intestine, and their function can be compromised by loss of C-KIT expression. Macrophage activation has been identified in intestine affected by Hirschsprung disease-associated enterocolitis (HAEC). In this study, we examined proinflammatory macrophage activation and explored the mechanisms by which it downregulates C-KIT expression in ICCs in colon affected by HAEC. We found that macrophage activation and TNF-α production were dramatically increased in the proximal dilated colon of HAEC patients and 3-week-old Ednrb-/- mice. Moreover, ICCs lost their C-KIT+ phenotype in the dilated colon, resulting in damaged pacemaker function and intestinal dysmotility. However, macrophage depletion or TNF-α neutralization led to recovery of ICC phenotype and restored their pacemaker function. In isolated ICCs, TNF-α-mediated phosphorylation of p65 induced overexpression of microRNA-221 (miR-221), resulting in suppression of C-KIT expression and pacemaker currents. We also identified a TNF-α/NF-κB/miR-221 pathway that downregulated C-KIT expression in ICCs in the colon affected by HAEC. These findings suggest the important roles of proinflammatory macrophage activation in a phenotypic switch of ICCs, representing a promising therapeutic target for HAEC.

SCGN deficiency results in colitis susceptibility

Inflammatory bowel disease (IBD) affects 1.5–3.0 million people in the United States. IBD is genetically determined and many common risk alleles have been identified. Yet, a large proportion of genetic predisposition remains unexplained. In this study, we report the identification of an ultra rare missense variant (NM_006998.3:c.230G > A;p.Arg77His) in the SCGN gene causing Mendelian early-onset ulcerative colitis. SCGN encodes a calcium sensor that is exclusively expressed in neuroendocrine lineages, including enteroendocrine cells and gut neurons. SCGN interacts with the SNARE complex, which is required for vesicle fusion with the plasma membrane. We show that the SCGN mutation identified impacted the localization of the SNARE complex partner, SNAP25, leading to impaired hormone release. Finally, we show that mouse models of Scgn deficiency recapitulate impaired hormone release and susceptibility to DSS-induced colitis. Altogether, these studies demonstrate that functional deficiency in SCGN can result in intestinal inflammation and implicates the neuroendocrine cellular compartment in IBD.

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.

Gfra1 Underexpression Causes Hirschsprung's Disease and Associated Enterocolitis in Mice

BACKGROUND & AIMS

RET, the receptor for the glial cell line-derived neurotrophic factor (GDNF) family ligands, is the most frequently mutated gene in congenital aganglionic megacolon or Hirschsprung's disease (HSCR). The leading cause of mortality in HSCR is HSCR-associated enterocolitis (HAEC), which is characterized by altered mucin composition, mucin retention, bacterial adhesion to enterocytes, and epithelial damage, although the order of these events is obscure. In mice, loss of GDNF signaling leads to a severely underdeveloped enteric nervous system and neonatally fatal kidney agenesis, thereby precluding the use of these mice for modeling postnatal HSCR and HAEC. Our aim was to generate a postnatally viable mouse model for HSCR/HAEC and analyze HAEC etiology.

METHODS

GDNF family receptor alpha-1 (GFRa1) hypomorphic mice were generated by placing a selectable marker gene in the sixth intron of the Gfra1 locus using gene targeting in mouse embryonic stem cells.

RESULTS

We report that 70%-80% reduction in GDNF co-receptor GFRa1 expression levels in mice results in HSCR and HAEC, leading to death within the first 25 postnatal days. These mice mirror the disease progression and histopathologic findings in children with untreated HSCR/HAEC.

CONCLUSIONS

In GFRa1 hypomorphic mice, HAEC proceeds from goblet cell dysplasia, with abnormal mucin production and retention, to epithelial damage. Microbial enterocyte adherence and tissue invasion are late events and therefore unlikely to be the primary cause of HAEC. These results suggest that goblet cells may be a potential target for preventative treatment and that reduced expression of GFRa1 may contribute to HSCR susceptibility.

Bacterial Microbiome Dynamics in Post Pull-Through Hirschsprung-Associated Enterocolitis (HAEC): An Experimental Study Employing the Endothelin Receptor B-Null Mouse Model

PURPOSE

Hirschsprung-associated enterocolitis (HAEC) is the most frequent potentially life-threatening complication in children with Hirschsprung disease (HSCR) even after definitive corrective surgery. Mounting evidence suggests that intestinal microbiota likely contribute to the etiology of enterocolitis, so the aim of this study was to use a mouse model of post pull-through HAEC to compare the fecal bacterial communities of animals which developed HAEC to those free of enterocolitis.

METHODS

Ten Ednrb -/- and 8wild type mice underwent the microsurgical pull-through surgery, and stool was collected at the time of surgery, and then either at 2 and 4 weeks after the operation, or when the mice developed enterocolitis. The mid-colon of all animals was collected, prepared and histologically graded for enterocolitis. Fecal DNA was isolated and bacterial 16S rRNA genes analyzed using Illumina sequencing.

RESULTS

Six Ednrb-/- mice developed HAEC with a mean enterocolitis score of 5.7, while the remaining 4 mutant and 8 WT mice remained free of enterocolitis by 4 weeks. The HAEC group had lower alpha diversity by Chao1 analysis compared with WT group, while the Ednrb-/- mice demonstrated distinct bacterial communities from WT mice on beta diversity analysis. The most striking finding was increased proportion of Akkermansia and reduced Bacteroidetes compared with the NO HAEC and WT groups, suggesting Akkermansia may contribute to development of enterocolitis while Bacteroidetes may be protective. Less abundant genera that were reduced in HAEC were Dysgonomas and Clostridium XIVa which may play a protective role.

CONCLUSIONS

This is the first study to identify Akkermansia as potentially playing a role in HAEC, either as a pathobiont taxa contributing to pathogenesis of enterocolitis, or possibly a protective commensal taxa expanded in response to inflammation. These findings characterized the dynamic shifts in the gut microbial communities through the onset of post pull-through HAEC, and suggests that there may be identifiable bacterial community differences in HSCR patients that are high risk for developing HAEC.

Guidelines for the Diagnosis and Management of Hirschsprung-Associated Enterocolitis

BACKGROUND

Patients with Hirschsprung disease are at risk for Hirschsprung-associated enterocolitis (HAEC), an inflammatory disorder of the bowel that represents the leading cause of serious morbidity and death in these patients. The diagnosis of HAEC is made based on clinical signs and symptoms which are often non-specific, making it difficult to establish a definitive diagnosis in many patients. The purpose of this guideline is to present a rational, expert-based approach to the diagnosis and management of HAEC.

METHODS

The American Pediatric Surgical Association Board of Governors established a Hirschsprung Disease Interest Group. Group discussions, literature review, and expert consensus were then used to summarize the current state of knowledge regarding diagnosis, management, and prevention of Hirschsprung-associated enterocolitis (HAEC).

RESULTS

Guidelines for the diagnosis of HAEC and its clinical grade, utilizing clinical history, physical examination findings, and radiographic findings, are presented. Treatment guidelines, including patient disposition, diet, antibiotics, rectal irrigations and surgery, are presented.

CONCLUSIONS

Clear, standardized definitions of Hirschsprung-associated enterocolitis and its treatment are lacking in the literature. This guideline serves as a first step toward standardization of diagnosis and management.

LEVEL OF EVIDENCE

V.

Established and Emerging Concepts in Hirschsprung’s-Associated Enterocolitis

Hirschsprung's disease (HSCR) is a common cause of neonatal bowel obstruction and the approach to diagnosis and surgical treatment is well defined and accepted. Hirschsprung's-associated enterocolitis (HAEC) remains a frequent cause of pre-operative and post-operative morbidity and mortality, with unchanged treatment guidelines over multiple decades. Recent advances in our understanding of the genetics underlying HSCR have allowed the development of animal models, some of which recapitulate the HAEC phenotype. These animal models, along with recent translational studies, have implicated multiple facets of mucosal immunity and microbiome dysbiosis in the development of HAEC. Here, we will review the established epidemiology, modes of diagnosis and treatment of HAEC. Furthermore, we will explore emerging concepts in the pathogenesis of this disease; including animal models, alterations in mucosal immunity, dysbiosis of the intestinal microbiome, specific genetic susceptibility, and novel treatment modalities.

Impaired Cellular Immunity in the Murine Neural Crest Conditional Deletion of Endothelin Receptor-B Model of Hirschsprung's Disease

Hirschsprung’s disease (HSCR) is characterized by aganglionosis from failure of neural crest cell (NCC) migration to the distal hindgut. Up to 40% of HSCR patients suffer Hirschsprung’s-associated enterocolitis (HAEC), with an incidence that is unchanged from the pre-operative to the post-operative state. Recent reports indicate that signaling pathways involved in NCC migration may also be involved in the development of secondary lymphoid organs. We hypothesize that gastrointestinal (GI) mucosal immune defects occur in HSCR that may contribute to enterocolitis. EdnrB was deleted from the neural crest (EdnrB^NCC-/-) resulting in mutants with defective NCC migration, distal colonic aganglionosis and the development of enterocolitis. The mucosal immune apparatus of these mice was interrogated at post-natal day (P) 21–24, prior to histological signs of enterocolitis. We found that EdnrB^NCC-/- display lymphopenia of their Peyer’s Patches, the major inductive site of GI mucosal immunity. EdnrB^NCC-/- Peyer’s Patches demonstrate decreased B-lymphocytes, specifically IgM⁺IgD^hi (Mature) B-lymphocytes, which are normally activated and produce IgA following antigen presentation. EdnrB^NCC-/- animals demonstrate decreased small intestinal secretory IgA, but unchanged nasal and bronchial airway secretory IgA, indicating a gut-specific defect in IgA production or secretion. In the spleen, which is the primary source of IgA-producing Mature B-lymphocytes, EdnrB^NCC-/- animals display decreased B-lymphocytes, but an increase in Mature B-lymphocytes. EdnrB^NCC-/- spleens are also small and show altered architecture, with decreased red pulp and a paucity of B-lymphocytes in the germinal centers and marginal zone. Taken together, these findings suggest impaired GI mucosal immunity in EdnrB^NCC-/- animals, with the spleen as a potential site of the defect. These findings build upon the growing body of literature that suggests that intestinal defects in HSCR are not restricted to the aganglionic colon but extend proximally, even into the ganglionated small intestine and immune cells.

Enterocolitis causes profound lymphoid depletion in endothelin receptor B- and endothelin 3-null mouse models of Hirschsprung-associated enterocolitis

Potentially life-threatening enterocolitis is the most frequent complication in children with colonic aganglionosis (Hirschsprung disease, HSCR), and little is known about the mechanisms leading to enterocolitis. Splenic lymphopenia has been reported in the Endothelin Receptor B (Ednrb)-null mouse model of HSCR that develops enterocolitis. In this study, we sought to identify molecular mechanisms underlying this immune phenotype. We employed the Ednrb(-/-) mouse, and the knockout of its ligand, Edn3 (Edn3(-/-)). The major finding is that enterocolitis in the Ednrb(-/-) and Edn3(-/-) mice lead to thymic involution, splenic lymphopenia, and suppression of B lymphopoiesis as a consequence of colonic aganglionosis, not an intrinsic Edn3-Ednrb signaling defect directly affecting the lymphoid organs. We showed that adoptive transfer of Ednrb(-/-) marrow repopulated the RAG2-null mice marrow, thymus and spleen without development of enterocolitis. We identified the glucocorticoid corticosterone, as a potential mediator of the immune phenotype. This previously unrecognized pattern of immune abnormalities in mouse is nearly identical to lymphoid depletion in neonatal sepsis during severe physiological stress, suggesting that the mouse model used here could be also used for sepsis studies.

Enteric neuron imbalance and proximal dysmotility in ganglionated intestine of the Sox10Dom/+ Hirschsprung mouse model

BACKGROUND & AIMS

In Hirschsprung disease (HSCR), neural crest-derived progenitors (NCPs) fail to completely colonize the intestine so that the enteric nervous system (ENS) is absent from distal bowel. Despite removal of the aganglionic region, many HSCR patients suffer from residual intestinal dysmotility. To test the hypothesis that inappropriate lineage segregation of NCPs in proximal ganglionated regions of the bowel could contribute to such postoperative disease, we investigated neural crest (NC)-derived lineages and motility in ganglionated, postnatal intestine of the Sox10Dom/+ HSCR mouse model.

METHODS

Cre-mediated fate-mapping was applied to evaluate relative proportions of NC-derived cell types. Motility assays were performed to assess gastric emptying and small intestine motility while colonic inflammation was assessed by histopathology for Sox10Dom/+ mutants relative to wildtype controls.

RESULTS

Sox10Dom/+ mice showed regional alterations in neuron and glia proportions as well as Calretinin+ and nNOS+ neuronal subtypes. In the colon, imbalance of enteric NC derivatives correlated with the extent of aganglionosis. All Sox10Dom/+ mice exhibited reduced small intestinal transit at 4-weeks of age, and at 6-weeks, Sox10Dom/+ males had increased gastric emptying rates. Sox10Dom/+ mice surviving to 6-weeks of age had little or no colonic inflammation when compared to wildtype littermates, suggesting that these changes in GI motility are neurally mediated.

CONCLUSIONS

The Sox10Dom mutation disrupts the balance of NC-derived lineages and affects GI motility in the proximal, ganglionated intestine of adult animals. This is the first report identifying alterations in enteric neuronal classes in Sox10Dom/+ mutants, which suggests a previously unrecognized role for Sox10 in neuronal subtype specification.

Intestinal dysbiosis and bacterial enteroinvasion in a murine model of Hirschsprung's disease

BACKGROUND/PURPOSE

Hirschsprung's disease (HSCR), characterized by the absence of ganglia in the distal colon, results in functional obstruction. Despite surgical resection of the aganglionic segment, around 40% of patients suffer recurrent life threatening Hirschsprung's-associated enterocolitis (HAEC). The aim of this study was to investigate whether gut microbiota and intestinal immunity changes contribute to the HAEC risk in an HSCR model.

METHODS

Mice with neural crest conditional deletion of Endothelin receptor B (EdnrB) and their littermate controls were used (EdnrB-null and EdnrB-het). Bacterial DNA was prepared from cecal contents of P16-18 and P21-24 animals and pyrosequencing employed for microbiome analysis. Ileal tissue was isolated and secretory phospholipase A2 (sPLA2) expression and activity determined. Enteroinvasion of Escherichia coli into ileal explants was measured using an ex vivo organ culture system.

RESULTS

EdnrB-het and EdnrB-nulls displayed similar flora, sPLA2 expression and activity at P16-18. However, by P21-24, EdnrB-hets demonstrated increased Lactobacillus and decreased Bacteroides and Clostridium, while EdnrB-nulls exhibited reciprocal changes. EdnrB-nulls also showed reduced sPLA2 expression and luminal activity at this stage. Functionally, EdnrB-nulls were more susceptible to enteroinvasion with E. coli ex vivo and released less sPLA2 than EdnrB-hets.

CONCLUSIONS

Initially, EdnrB-het and EdnrB-nulls contain similar cecal flora but then undergo reciprocal changes. EdnrB-nulls display dysbiosis, demonstrate impaired mucosal defense, decreased luminal sPLA2 and increased enteroinvasion of E. coli just prior to robust colonic inflammation and death. These findings suggest a role for the intestinal microbiome in the development of HAEC.

Altered goblet cell differentiation and surface mucus properties in Hirschsprung disease

Hirschsprung disease-associated enterocolitis (HAEC) leads to significant mortality and morbidity, but its pathogenesis remains unknown. Changes in the colonic epithelium related to goblet cells and the luminal mucus layer have been postulated to play a key role. Here we show that the colonic epithelium of both aganglionic and ganglionic segments are altered in patients and in mice with Hirschsprung disease (HSCR). Structurally, goblet cells were altered with increased goblet cell number and reduced intracellular mucins in the distal colon of biopsies from patients with HSCR. Endothelin receptor B (Ednrb) mutant mice showed increased goblet cell number and size and increased cell proliferation compared to wild-type mice in aganglionic segments, and reduced goblet cell size and number in ganglionic segments. Functionally, compared to littermates, Ednrb^−/− mice showed increased transepithelial resistance, reduced stool water content and similar chloride secretion in the distal colon. Transcript levels of goblet cell differentiation factors SPDEF and Math1 were increased in the distal colon of Ednrb^−/− mice. Both distal colon from Ednrb mice and biopsies from HSCR patients showed reduced Muc4 expression as compared to controls, but similar expression of Muc2. Particle tracking studies showed that mucus from Ednrb^−/− mice provided a more significant barrier to diffusion of 200 nm nanoparticles as compared to wild-type mice. These results suggest that aganglionosis is associated with increased goblet cell proliferation and differentiation and subsequent altered surface mucus properties, prior to the development of inflammation in the distal colon epithelium. Restoration of normal goblet cell function and mucus layer properties in the colonic epithelium may represent a therapeutic strategy for prevention of HAEC.

Principles for valid histopathologic scoring in research

Histopathologic scoring is a tool by which semiquantitative data can be obtained from tissues. Initially, a thorough understanding of the experimental design, study objectives, and methods is required for the pathologist to appropriately examine tissues and develop lesion scoring approaches. Many principles go into the development of a scoring system such as tissue examination, lesion identification, scoring definitions, and consistency in interpretation. Masking (aka "blinding") of the pathologist to experimental groups is often necessary to constrain bias, and multiple mechanisms are available. Development of a tissue scoring system requires appreciation of the attributes and limitations of the data (eg, nominal, ordinal, interval, and ratio data) to be evaluated. Incidence, ordinal, and rank methods of tissue scoring are demonstrated along with key principles for statistical analyses and reporting. Validation of a scoring system occurs through 2 principal measures: (1) validation of repeatability and (2) validation of tissue pathobiology. Understanding key principles of tissue scoring can help in the development and/or optimization of scoring systems so as to consistently yield meaningful and valid scoring data.

Recent developments in Hirschsprung's-associated enterocolitis

Hirschsprung's-associated enterocolitis (HAEC) continues to be a significant source of morbidity for patients with Hirschsprung's disease (HD). New clinical and histologic classification systems for HAEC will improve consistency between reports and increase the ability to compare outcomes. A complete understanding of disease pathogenesis is lacking, but evidence suggests that the intestinal microbiota may play a role in the development of HD and HAEC. The benefits of adjunctive therapies, such as anal dilations and botulinum toxin to reduce the incidence of HAEC following corrective endorectal pull-through, remain controversial. Finally, new clinical data have identified an association between HAEC and inflammatory bowel disease and will likely lead to further genetic studies to elucidate the connection between these two disease processes.

Multiphoton microscopy to identify and characterize the transition zone in a mouse model of Hirschsprung disease

BACKGROUND

The distribution of ganglion cells in the transition zone of Hirschsprung Disease (HD) colons is extremely variable. Determining the resection margin based on intraoperative biopsies may be imprecise. Multiphoton microscopy (MPM) is a novel imaging technology with the ability to visualize tissues in real time. In this study, we evaluate the potential of MPM to quantify ganglion cells in a murine model of HD.

METHODS

After IACUC approval, formalin-fixed colons from 7 wild type (WT) and 6 Endothelin Receptor B gene (EdnrB) homozygous knockout (KO) mice with distal colonic aganglionosis were assessed by MPM for the presence of myenteric ganglion cells. MPM images were captured starting from the anus progressing proximally at 5mm intervals. Hematoxylin and eosin (H&E) stained biopsies of the imaged were correlated with MPM findings.

RESULTS

WT specimens showed normal myenteric plexus ganglia throughout the examined colon. In contrast, distal colons of EdnrB KO animals were devoid of ganglia up to 10mm from the anus. Ganglion cells were visible starting at 20-30 mm proximal to the anus. The density of ganglion cells seen by MPM and histology correlated well.

CONCLUSIONS

MPM can clearly identify the myenteric plexus ganglia in both WT and KO mouse colons. Comparison with the H&E-stained sections showed reproducible correlation. MPM-based real-time imaging of the myenteric plexus may become a useful intraoperative decision-making tool in the future.

Balancing on the crest - Evidence for disruption of the enteric ganglia via inappropriate lineage segregation and consequences for gastrointestinal function

Normal enteric nervous system (ENS) development relies on numerous factors, including appropriate migration, proliferation, differentiation, and maturation of neural crest (NC) derivatives. Incomplete rostral to caudal migration of enteric neural crest-derived progenitors (ENPs) down the gut is at least partially responsible for the absence of enteric ganglia that is a hallmark feature of Hirschsprung disease (HSCR). The thought that ganglia proximal to aganglionosis are normal has guided surgical procedures for HSCR patients. However, chronic gastrointestinal dysfunction suffered by a subset of patients after surgery as well as studies in HSCR mouse models suggest that aberrant NC segregation and differentiation may be occurring in ganglionated regions of the intestine. Studies in mouse models that possess enteric ganglia throughout the length of the intestine (non-HSCR) have also found that certain genetic alterations affect neural crest lineage balance and interestingly many of these mutants also have functional gastrointestinal (GI) defects. It is possible that many GI disorders can be explained in part by imbalances in NC-derived lineages. Here we review studies evaluating ENS defects in HSCR and non-HSCR mouse models, concluding with clinical implications while highlighting areas requiring further study.

Intestinal aganglionosis is associated with early and sustained disruption of the colonic microbiome

BACKGROUND

Congenital aganglionosis (Hirschsprung's disease) results in colonic dysmotility and a risk for Hirschsprung's-associated enterocolitis (HAEC), whose cause is unknown. We hypothesized that aganglionosis leads to microbiome changes that may contribute to HAEC risk.

METHODS

Colon and fecal samples were collected from endothelin receptor B-null (Ednrb(-/-) ) mice, an established model of colorectal aganglionosis, at postnatal day 7 (P7), P20, and P24. We determined microbiome composition by 16S ribosomal RNA gene pyrosequencing and fecal metabolite profile by nuclear magnetic resonance spectroscopy.

KEY RESULTS

Wild-type (WT) mice exhibited increasing species diversity with age, with mutant mice possessing even greater diversity. WT and mutant microbiomes, both fecal and colonic, significantly segregated by principal coordinates analysis based on species composition at all ages examined. Importantly, mutant mice contained more Bacteroidetes and less Firmicutes than WT, with additional genus- and species-level differences observed. Notably, mutant P7 colon was dominated by coagulase-negative Staphylococcus species, which were rare in WT. Mutant fecal metabolite profiles also differed, particularly in the abundance of formate, a short-chain fatty acid product of microbial fermentation.

CONCLUSIONS & INFERENCES

Colorectal aganglionosis is associated with early and sustained disruption of the normal colonic and fecal microbiome, supporting the enteric nervous system as a determinant of microbiome composition. Furthermore, the differences observed suggest a potential contributory role for the microbiome in the etiology of HAEC. These findings provide a basis for further studies to determine the causative role of specific bacterial communities in HAEC and the potential to restore the normal microbiome in Hirschsprung's disease.

Splenic lymphopenia in the endothelin receptor B-null mouse: implications for Hirschsprung associated enterocolitis

PURPOSE

The aim of the study was to describe and characterize a novel small spleen phenotype with splenic lymphopenia in the Ednrb-null (Ednrb-/-) mouse with aganglionosis known to also develop enterocolitis.

METHODS

We compared spleen weight as a percent of body weight from Ednrb+/+, Ednrb+/-, and Ednrb-/- mice to quantify our initial observation. Splenic microarchitecture of Ednrb+/+ and Ednrb-/- mice was assessed using both H and E staining and immunofluorescence staining for CD45R+ (B cells) and CD3+ (T cells) on tissue sections. To identify and quantify cell type, flow cytometry for CD19+ (mature B cells), CD4+ and CD8+ (T cells) was performed on the splenocytes of Ednrb+/+ and Ednrb-/- mice and compared with student's t test. A separate cohort of Ednrb+/+ and Ednrb-/- mice was killed and splenocytes were analyzed by flow cytometry, and proximal colon was histopathologically graded for enterocolitis. Spearman's rank correlations comparing total splenocyte and CD19+ cell counts with enterocolitis scores were performed.

RESULTS

We found that the mean spleen weight expressed as a percent of body weight for Ednrb+/+ and Ednrb-/- mice was 0.72 and 0.25%, respectively (P < 0.001), at 25 days of age. In addition, the Ednrb-/- spleens also had markedly abnormal splenic microarchitecture with lymphopenia, and relative reduction of B cells compared to T cells. FACS of splenocytes revealed a 5 to 20-fold reduction in total cell number, CD19+, CD4+, and CD8+ of the Ednrb-/- mice compared to the Ednrb+/+ littermates (P < 0.01). We also found a strong inverse correlation of total spleen and CD19+ cell counts with histopathological enterocolitis scores (r (s) = -0.43, P = 0.02), showing that mice with reduced cell counts also had increased severity of enterocolitis.

CONCLUSION

The small spleen immunophenotype in the Ednrb-/- mouse suggests that Ednrb-dependent signaling may be required for normal spleen development. These results raise the possibility that primary immune abnormalities may contribute at least in part to some enterocolitis. At present, our data suggest intriguing new potential explanations for HAEC in Hirschsprung patients.

Imaging the Gastrointestinal Tract of Small Animals

Animal models of human diseases are increasingly available and are invaluable for studies of organ pathophysiology. Megacolon, abnormal dilatation of the colon not caused by mechanical obstruction, involves the destruction of the autonomic nervous system innervating the colon. Animal models of megacolon include mouse models of Chagas disease and Hirschprung's disease. Small animal imaging has become an important research tool and recent advances in preclinical imaging modalities have enhanced the information content available from longitudinal studies of animal models of human diseases. While numerous applications of imaging technologies have been reported to study the brain and heart of mouse models, fewer studies of the gastrointestinal system have been undertaken due to technical limitations caused by peristaltic and respiratory motion. Various imaging modalities relevant to study of the gastrointestinal tract of intact live animals are reviewed herein.

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.