Fluorescence Visualization of the Enteric Nervous Network in a Chemically Induced Aganglionosis Model

Cutting-edge regenerative therapy for Hirschsprung disease and its allied disorders

Hirschsprung disease (HSCR) and its associated disorders (AD-HSCR) often result in severe hypoperistalsis caused by enteric neuropathy, mesenchymopathy, and myopathy. Notably, HSCR involving the small intestine, isolated hypoganglionosis, chronic idiopathic intestinal pseudo-obstruction, and megacystis-microcolon-intestinal hypoperistalsis syndrome carry a poor prognosis. Ultimately, small-bowel transplantation (SBTx) is necessary for refractory cases, but it is highly invasive and outcomes are less than optimal, despite advances in surgical techniques and management. Thus, regenerative therapy has come to light as a potential form of treatment involving regeneration of the enteric nervous system, mesenchyme, and smooth muscle in affected areas. We review the cutting-edge regenerative therapeutic approaches for managing HSCR and AD-HSCR, including the use of enteric nervous system progenitor cells, embryonic stem cells, induced pluripotent stem cells, and mesenchymal stem cells as cell sources, the recipient intestine's microenvironment, and transplantation methods. Perspectives on the future of these treatments are also discussed.

Establishment and identification of an animal model of Hirschsprung disease in suckling mice

BACKGROUND

Hirschsprung disease (HSCR) is a congenital intestinal malformation. Previous HSCR animal model needs invasive operation on adult animal. The aim of this study is to establish an early-onset animal model which is consistent with the clinical manifestation of HSCR patients.

METHODS

The neonatal mice were randomly divided into the benzalkonium chloride (BAC) group, treated with BAC via enema, and the control group, treated with saline. Weight changes, excretion time of carmine, CT scan, hematoxylin-eosin staining and immunofluorescence staining were used to evaluate the effect of the model. Differentially expressed genes (DEGs) in the HSCR mice were analyzed by using DAVID 6.8 database and compared with DEGs from HSCR patients.

RESULTS

The weight of mice was lower and the excretion time of carmine was longer in the BAC group. Moreover, distal colon stenosis and proximal colon enlargement appeared in the BAC group. Neurons in the distal colon decreased significantly after 4 weeks of BAC treatment and almost disappeared completely after 12 weeks. Transcriptome profiling of the mouse model and HSCR patients is similar in terms of altered gene expression.

CONCLUSIONS

An economical and reliable HSCR animal model which has similar clinical characteristics to HSCR patients was successfully established.

IMPACT

The animal model of Hirschsprung disease was first established in BALB/c mice. This model is an animal model of early-onset HSCR that is easy to operate and consistent with clinical manifestations. Transcriptome profiling of the mouse model and HSCR patients is similar in terms of altered gene expression.

Gut bacterial aromatic amine production: aromatic amino acid decarboxylase and its effects on peripheral serotonin production

Colonic luminal aromatic amines have been historically considered to be derived from dietary source, especially fermented foods; however, recent studies indicate that the gut microbiota serves as an alternative source of these amines. Herein, we show that five prominent genera of Firmicutes (Blautia, Clostridium, Enterococcus, Ruminococcus, and Tyzzerella) have the ability to abundantly produce aromatic amines through the action of aromatic amino acid decarboxylase (AADC). In vitro cultivation of human fecal samples revealed that a significant positive correlation between aadc copy number of Ruminococcus gnavus and phenylethylamine (PEA) production. Furthermore, using genetically engineered Enterococcus faecalis-colonized BALB/cCrSlc mouse model, we showed that the gut bacterial aadc stimulates the production of colonic serotonin, which is reportedly involved in osteoporosis and irritable bowel syndrome. Finally, we showed that human AADC inhibitors carbidopa and benserazide inhibit PEA production in En. faecalis.

Enteric neuronal cell therapy reverses architectural changes in a novel diphtheria toxin-mediated model of colonic aganglionosis

Hirschsprung disease (HSCR) is characterized by absence of the enteric nervous system (ENS) in the distal bowel. Despite removal of the aganglionic segment, gastrointestinal (GI) problems persist. Cell therapy offers potential treatment but use of genetic models is limited by their poor survival. We have developed a novel model of aganglionosis in which enteric neural crest-derived cells (ENCDCs) express diphtheria toxin (DT) receptor. Local DT injection into the colon wall results in focal, specific, and sustained ENS ablation without altering GI transit or colonic contractility, allowing improved survival over other aganglionosis models. Focal ENS ablation leads to increased smooth muscle and mucosal thickness, and localized inflammation. Transplantation of ENCDCs into this region leads to engraftment, migration, and differentiation of enteric neurons and glial cells, with restoration of normal architecture of the colonic epithelium and muscle, reduction in inflammation, and improved survival.

BMP4 knockdown of NCSCs leads to aganglionosis in the middle embryonic stage

Transplacental bone morphogenetic protein (BMP)4 RNA interference (RNAi) is a technique used to knockdown genes in embryos. BMP4 are essential for the development of nervous system in the differentiation of neural crest stem cells (NCSCs). The failure of differentiation and migration of NCSCs may lead to aganglionosis. In the present study, pregnant mice were divided into three groups: Ringer's group, pSES group and RNAi‑BMP4 group. In order to silence the BMP4 gene in the first generation (F1), 11.5 day pregnant mice were injected with the small interfering RNA BMP4 plasmid, pSES or Ringer's solution via the tail vein. Semi‑quantitative reverse transcriptase‑polymerase chain reaction (RT‑PCR)and western blotting were employed to ensure the downregulation of BMP4. Finally, X‑rays were performed following a barium enema. Aganglionosis was diagnosed by general anatomy and immunohistochemistry. Compared with the control group, transplacental RNAi was able to downregulate the BMP4‑Smad4 of 11.5 day embryos, as determined by semi‑quantitative RT‑PCR and western blotting. The megacolons of the mice were demonstrated by X‑ray and confirmed by general anatomy. Aganglionosis of colonic mucosa and submucosa were diagnosed by pathology, and immunohistochemistry. Knockdown of BMP4 in pregnant mice at the middle embryonic stage led to aganglionosis. It was therefore demonstrated that BMP‑Smad was essential to the NCSCs of middle stage embryos. BMP‑Smad served important roles in the generation of aganglionosis. This technique of knockdown BMP4 gene may be used to establish an aganglionosis mouse model.

Technical feasibility of visualizing myenteric plexus using confocal laser endomicroscopy

BACKGROUND AND AIM

In preceding studies, we identified that the myenteric plexus (MP) could be visualized with confocal laser endomicroscopy (CLE) by applying neural fluorescent probes lacking clinical safety profiling data from the submucosal side. In this study, we evaluated the technical feasibility of MP visualization using probe-based CLE (pCLE) from the serosal side with cresyl violet (CV), which has been used clinically for chromoendoscopy.

METHODS

The dye affinity of CV for MP was first explored in an in vivo transgenic mouse model using neural crest derivatives labeled with green fluorescent protein. We also tested the feasibility of CV-assisted visualization of MP in human surgical specimens, wherein the tissue dying and pCLE observation were performed from the serosal side. In the human study, rate of MP visualization by pCLE was evaluated as the primary outcome. We also evaluated the sensitivity and specificity of MP visualization by pCLE, using pathological presence/absence of MP as the gold standard.

RESULTS

We confirmed the dye affinity of CV to MP in all tested models. The MP appeared as brightly stained ladder-like structures with pCLE, and in the human study, MP was visualized in 12/14 (85.7%) samples, with 92.3% sensitivity and 100% specificity. In positive cases showing the ladder-like structure of MP by pCLE, the mean maximum and minimum widths of nerve strands were 54.3 (± 23.6) and 19.7 (± 6.0) μm, respectively. A ganglion was detected by pCLE in 10 cases (10/12, 83.3%).

CONCLUSIONS

This study demonstrated the technical feasibility of visualizing the MP in real time by CV-assisted pCLE (UMIN-CTR number, UMIN000015056).