Smooth muscle from aganglionic bowel in Hirschsprung's disease impairs neuronal development in vitro

Autologous cell transplantation for treatment of colorectal aganglionosis in mice

Neurointestinal diseases cause significant morbidity and effective treatments are lacking. This study aimes to test the feasibility of transplanting autologous enteric neural stem cells (ENSCs) to rescue the enteric nervous system (ENS) in a model of colonic aganglionosis. ENSCs are isolated from a segment of small intestine from Wnt1::Cre;R26iDTR mice in which focal colonic aganglionosis is simultaneously created by diphtheria toxin injection. Autologous ENSCs are isolated, expanded, labeled with lentiviral-GFP, and transplanted into the aganglionic segment in vivo. ENSCs differentiate into neurons and glia, cluster to form neo-ganglia, and restore colonic contractile activity as shown by electrical field stimulation and optogenetics. Using a non-lethal model of colonic aganglionosis, our results demonstrate the potential of autologous ENSC therapy to improve functional outcomes in neurointestinal disease, laying the groundwork for clinical application of this regenerative cell-based approach.

Direct modulation of TRPC ion channels by Gα proteins

GPCR-Gi protein pathways are involved in the regulation of vagus muscarinic pathway under physiological conditions and are closely associated with the regulation of internal visceral organs. The muscarinic receptor-operated cationic channel is important in GPCR-Gi protein signal transduction as it decreases heart rate and increases GI rhythm frequency. In the SA node of the heart, acetylcholine binds to the M2 receptor and the released Gβγ activates GIRK (I(K,ACh)) channel, inducing a negative chronotropic action. In gastric smooth muscle, there are two muscarinic acetylcholine receptor (mAChR) subtypes, M2 and M3. M2 receptor activates the muscarinic receptor-operated nonselective cationic current (mIcat, NSCC(ACh)) and induces positive chronotropic effect. Meanwhile, M3 receptor induces hydrolysis of PIP2 and releases DAG and IP3. This IP3 increases intracellular Ca2+ and then leads to contraction of GI smooth muscles. The activation of mIcat is inhibited by anti-Gi/o protein antibodies in GI smooth muscle, indicating the involvement of Gαi/o protein in the activation of mIcat. TRPC4 channel is a molecular candidate for mIcat and can be directly activated by constitutively active Gαi QL proteins. TRPC4 and TRPC5 belong to the same subfamily and both are activated by Gi/o proteins. Initial studies suggested that the binding sites for G protein exist at the rib helix or the CIRB domain of TRPC4/5 channels. However, recent cryo-EM structure showed that IYY58-60 amino acids at ARD of TRPC5 binds with Gi3 protein. Considering the expression of TRPC4/5 in the brain, the direct G protein activation on TRPC4/5 is important in terms of neurophysiology. TRPC4/5 channels are also suggested as a coincidence detector for Gi and Gq pathway as Gq pathway increases intracellular Ca2+ and the increased Ca2+ facilitates the activation of TRPC4/5 channels. More complicated situation would occur when GIRK, KCNQ2/3 (IM) and TRPC4/5 channels are co-activated by stimulation of muscarinic receptors at the acetylcholine-releasing nerve terminals. This review highlights the effects of GPCR-Gi protein pathway, including dopamine, μ-opioid, serotonin, glutamate, GABA, on various oragns, and it emphasizes the importance of considering TRPC4/5 channels as crucial players in the field of neuroscience.

Comparative study of Hsp27, GSK3β, Wnt1 and PRDX3 in Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system characterized by aganglionosis in distal gut. In this study, we used two-dimensional gel electrophoresis (2-DE) technology coupled with matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis to identify differentially expressed proteins in the aganglionic (stenotic) and ganglionic (normal) colon segment tissues from patients with HSCR. We identified 15 proteins with different expression levels between the stenotic and the normal colon segment tissues from patients with HSCR. Nine proteins were upregulated and six proteins downregulated in the stenotic colon segment tissues compared to the normal colon segment tissues. Based on the biological functions, we selected the Hsp27 upregulated proteins and the PRDX3 downregulated proteins to confirm their expression in 20 patients. The protein and mRNA expressions of Hsp27 were statistically higher in the stenotic colon segment tissues than in the normal colon segment tissues, whereas the protein and mRNA expressions of PRDX3 were statistically lower in the stenotic colon segment tissues than in the normal colon segment tissues. These findings of changes in mRNA and protein in tissues from patients with HSCR provide information which may be helpful in understanding the pathomechanism that is implicated in the disease.

Up-regulated FHL1 expression maybe involved in the prognosis of Hirschsprung's disease

BACKGROUND

In a subset of patients with Hirschsprung's disease (HSCR), gastrointestinal motor dysfunction persisted long after surgical correction. Gastrointestinal motility is achieved through the coordinated activity of the enteric nervous system, interstitial cells of Cajal, and smooth muscle (SMC) cells. Inhibition of four-and-a-half LIM protein-1 (Fhl1) expression by siRNA significantly decreases pulmonary artery SMCs migration and proliferation. Furthermore when up-expressing FHL1 in atrial myocytes, K (+) current density markedly increases, therefore changing myocytes' response to an electrical stimulus. However whether FHL1 in colon SMCs (the final effector organ) influences intestinal motility in HSCR patients has not been clarified.

METHODS

FHL1 mRNA and protein expressions were analyzed in 32 HSCR colons and 4 normal colons.

RESULTS

Smooth muscle layers were thicken and disorganized in HSCR. FHL1 was expressed in the ganglion cells of the myenteric plexus, submucosa, as well as in the longitudinal and circular muscle layer of the ganglionic colon. FHL1 mRNA relative expression level in aganglionic colons was 1.06 ± 0.49 (ganglionic colon relative expression level was 1) (P=0.44). FHL1 protein gray level relative to GAPDH in normal colons was 0.83 ± 0.09. FHL1 expression level in ganglionic colon (1.66 ± 0.30) or aganglionic colon (1.81 ± 0.35) was significantly higher than that in normal colons (P=0.045 and P=0.041, respectively). Meanwhile, we found FHL1 expression in aganglionic colon was slightly stronger than that in ganglionic colon (P=0.036).

CONCLUSION

These data suggested that up-regulated FHL1 in smooth muscle in HSCR might be associated with intestinal wall remodeling in HSCR and might be one of the risk factors for gastrointestinal motor dysfunction.

The developmental etiology and pathogenesis of Hirschsprung disease

The enteric nervous system is the part of the autonomic nervous system that directly controls the gastrointestinal tract. Derived from a multipotent, migratory cell population called the neural crest, a complete enteric nervous system is necessary for proper gut function. Disorders that arise as a consequence of defective neural crest cell development are termed neurocristopathies. One such disorder is Hirschsprung disease (HSCR), also known as congenital megacolon or intestinal aganglionosis. HSCR occurs in 1/5000 live births and typically presents with the inability to pass meconium, along with abdominal distension and discomfort that usually requires surgical resection of the aganglionic bowel. This disorder is characterized by a congenital absence of neurons in a portion of the intestinal tract, usually the distal colon, because of a disruption of normal neural crest cell migration, proliferation, differentiation, survival, and/or apoptosis. The inheritance of HSCR disease is complex, often non-Mendelian, and characterized by variable penetrance. Extensive research has identified a number of key genes that regulate neural crest cell development in the pathogenesis of HSCR including RET, GDNF, GFRα1, NRTN, EDNRB, ET3, ZFHX1B, PHOX2b, SOX10, and SHH. However, mutations in these genes account for only ∼50% of the known cases of HSCR. Thus, other genetic mutations and combinations of genetic mutations and modifiers likely contribute to the etiology and pathogenesis of HSCR. The aims of this review are to summarize the HSCR phenotype, diagnosis, and treatment options; to discuss the major genetic causes and the mechanisms by which they disrupt normal enteric neural crest cell development; and to explore new pathways that may contribute to HSCR pathogenesis.

Expression profiling the developing mammalian enteric nervous system identifies marker and candidate Hirschsprung disease genes

The enteric nervous system (ENS) is composed of neurons and glial cells, organized as interconnected ganglia within the gut wall, which controls peristalsis of the gut wall and secretions from its glands. The Ret receptor tyrosine kinase is expressed throughout enteric neurogenesis and is required for normal ENS development; humans with mutations in the RET locus have Hirschsprung disease (HSCR, an absence of ganglia in the colon), and mice lacking Ret have total intestinal aganglionosis. The Ret mutant mouse provides a tool for identifying genes implicated in development of the ENS. By using RNA from WT and Ret mutant (aganglionic) gut tissue and DNA microarrays, we have conducted a differential screen for ENS-expressed genes and have identified hundreds of candidate ENS-expressed genes. Forty-seven genes were selected for further analysis, representing diverse functional classes. We show that all of the analyzed genes are expressed in the ENS and that the screen was sensitive enough to identify genes marking only subpopulations of ENS cells. Our screen, therefore, was reliable and sensitive and has identified many previously undescribed genes for studying ENS development. Moreover, two of the genes identified in our screen Arhgef3 and Ctnnal1, have human homologues that map to previously identified HSCR susceptibility loci, thus representing excellent candidates for HSCR genes. This comprehensive profile of ENS gene expression refines our understanding of ENS development and serves as a resource for future developmental, biochemical, and human genetic studies.

Sequence variability of human cytomegalovirus UL146 and UL147 genes in low-passage clinical isolates

OBJECTIVES

Human cytomegalovirus (HCMV) infects a number of organs and cell types in vivo. The different symptoms and tissue tropisms of HCMV infection perhaps result from the genetic polymorphism. A new region of DNA containing at least 19 open reading frames (ORFs - denoted UL133-151) was found in the low-passage HCMV clinical strain Toledo and several other low-passage clinical isolates, but not present in the HCMV laboratory strain AD169. Two of these genes, UL146 and UL147, encode proteins with sequence characteristics of CXC (alpha) chemokines, suggesting that they might influence the behavior of neutrophils during infection. This research was to study the sequence variability of UL146 and UL147 ORFs in HCMV clinical isolates and examine the possible associations between gene variability and the outcome of HCMV infection.

METHODS

UL146 and UL147 genes from strains obtained from suspected congenitally HCMV-infected infants were PCR amplified and sequenced.

RESULTS

High variability was found in UL146 and UL147 gene among HCMV clinical strains. However, the alpha chemokine motif in UL146 and UL147 genes was conserved in almost all sequences. According to the phylogenetic analysis, all sequences of UL146 in clinical isolates could be divided into three groups. All strains from congenital megacolon infants existed in G2A only, and all from asymptomatic infants existed in G2B peculiarly.

CONCLUSIONS

Sequence variability among HCMV clinical strains may affect the ability of UL146 and UL147 to attract human neutrophils and influence viral dissemination. No obvious linkage was observed between UL146 polymorphisms and outcome of suspected congenital HCMV infection.

Altered cytoskeleton in smooth muscle of aganglionic bowel

CONTEXT

Intestinal motility is under the control of smooth muscle cells, enteric plexus, and hormonal factors. In Hirschsprung disease (HD), the aganglionic colon remains spastic or tonically enhanced and unable to relax. The smooth muscle cell's cytoskeleton consists of proteins or structures whose primary function is to link or connect protein filaments to each other or to the anchoring sites. Dystrophin is a subsarcolemmal protein with a double adhesion property, one between the membrane elements and the contractile filaments of the cytoskeleton and the other between the cytoskeletal proteins and the extracellular matrix. Desmin and vinculin are functionally related proteins that are present in the membrane-associated dense bodies in the sarcolemma of the smooth muscle cells.

OBJECTIVE

To examine the distribution of the cytoskeletal proteins in the smooth muscle of the aganglionic bowel.

DESIGN

Bowel specimens from ganglionic and aganglionic sections of the colon were collected at the time of pull-through surgery from 8 patients with HD. Colon specimens collected from 4 patients at the time of bladder augmentation acted as controls. Anti-dystrophin, anti-desmin, and anti-vinculin antibodies were used for fluorescein immunostaining using confocal laser scanning microscopy.

RESULTS

Moderate to strong dystrophin immunoreactivity was observed at the periphery of smooth muscle fibers in normal bowel and ganglionic bowel from patients with HD, whereas dystrophin immunoreactivity was either absent or weak in the smooth muscle of aganglionic colon. Moderate to strong cytoplasmic immunostaining for vinculin and desmin was seen in the smooth muscle of normal bowel and ganglionic bowel from patients with HD, whereas vinculin and desmin staining in the aganglionic colon was absent or weak.

CONCLUSION

This study demonstrates that the cytoskeletal proteins are abundant in the smooth muscle of normal bowel, but are absent or markedly reduced in the aganglionic bowel of HD. As cytoskeletal proteins are required for the coordinated contraction of muscle cells, their absence may be responsible for the motility dysfunction in the aganglionic segment.

Transgenic expression of the endothelin-B receptor prevents congenital intestinal aganglionosis in a rat model of Hirschsprung disease

The spotting lethal rat, a naturally occurring rodent model of Hirschsprung disease, carries a deletion in the endothelin-B receptor (EDNRB) gene that abrogates expression of functional EDNRB receptors. Rats homozygous for this mutation (sl) exhibit coat color spotting and congenital intestinal aganglionosis. These deficits result from failure of the neural crest-derived epidermal melanoblasts and enteric nervous system (ENS) precursors to completely colonize the skin and intestine, respectively. We demonstrate that during normal rat development, the EDNRB mRNA expression pattern is consistent with expression by ENS precursors throughout gut colonization. We used the human dopamine-beta-hydroxylase (DbetaH) promoter to direct transgenic expression of EDNRB to colonizing ENS precursors in the sl/sl rat. The DbetaH-EDNRB transgene compensates for deficient endogenous EDNRB in these rats and prevents the intestinal defect. The transgene has no effect on coat color spotting, indicating the critical time for EDNRB expression in enteric nervous system development begins after separation of the melanocyte lineage from the ENS lineage and their common precursor. The transgene dosage affects both the incidence and severity of the congenital intestinal defect, suggesting dosage-dependent events downstream of EDNRB activation in ENS development.

Identification of distinct molecular phenotypes in cultured gastrointestinal smooth muscle cells

BACKGROUND & AIMS

Cultured gastrointestinal smooth muscle cells have been shown to dedifferentiate and reinitiate their myogenic program in vitro. The aim of this study was to determine whether the cellular phenotypes observed in vitro were similar to those previously characterized in vivo.

METHODS

Differential isoactin expression was examined in primary cultures of intestinal smooth muscle cells (ISMCs) by Northern blot and immunohistochemical analysis. Cellular phenotype was determined for cultured ISMCs grown at high density, at low density, in the presence and absence of serum supplementation, and on several distinct substrates including collagen type IV, laminin, fibronectin, and plastic.

RESULTS

The unique patterns of isoactin protein and gene expression observed in cultured ISMCs indicate that distinct cellular phenotypes were present in vitro. The production and maintenance of these distinct smooth muscle cell phenotypes was dependent on cell density, serum supplementation, and substrate used.

CONCLUSIONS

Cultured ISMCs appear to recapitulate a portion of their in vivo myogenic program in vitro, providing a unique opportunity for the molecular mechanisms controlling gastrointestinal smooth muscle myogenesis and pathogenesis to begin to be identified.

Hirschsprung's disease: a search for etiology

In 1967, Okamoto et al suggested that the absence of ganglion cells in Hirschsprung's disease (HD) was attributable to failure of migration of neural crest cells. The earlier the arrest of migration, the longer the aganglionic segment. Since then, this hypothesis generally has been accepted. However, subsequent experiments using mouse models of intestinal aganglionosis indicate that nerve cells may reach the correct position but then fail to develop or survive. An alternative hypothesis has been proposed that the aganglionosis may be caused by failure of differentiation as a result of microenvironmental changes after the migration has occurred. Extracellular matrix proteins are recognized as important microenvironmental factors. It has been shown that enteric neurogenesis is dependent on extracellular matrices, which provide a migration pathway for neural crest-derived cells and promote the maturation of settled neural crest-derived cells. Altered distributions of extracellular matrices have been shown in human HD cases and murine HD models, suggesting the role of extracellular matrices in the pathogenesis of HD. Recent studies suggest that intestinal smooth muscle cells, target cells of enteric neurons, play an important role in guiding and influencing its own innervation. Normal maturation was inhibited in neurons cultured with smooth muscle cells of aganglionic colon in comparison to normal colon. Furthermore, it was demonstrated that levels of neurotrophic factors, crucial in the development and survival of enteric neurons, are decreased in circular muscle layers of aganglionic colon in comparison to normoganglionic colon. The smooth muscle cells of the aganglionic colon may represent an unfavorable microenvironment for neuronal development compared with the normally innervated region. Recently, markedly increased immunoreactivity of major histocompatibility complex (MHC) class II antigens and ICAM-1 was demonstrated in aganglionic bowel, suggesting the immunological mechanisms may be involved in the etiology of HD. Genetic factors have been implicated in the etiology of this condition because HD is known to occur in families and in association with some chromosomal abnormalities. Recent expansion of molecular genetics identified multiple susceptibility genes of HD, including the RET gene, the glial cell line-derived neurotrophic factor gene, the endothelin-B receptor gene, and endothelin-3 gene. Of these, inactivating mutations of the RET gene are the most frequent, occurring in 50% of familial and 15% to 20% of sporadic cases of HD. To date, despite extensive research, the exact etiology of this condition remains poorly understood. The present report describes the authors' current understanding of and recent progress in the etiology of HD.

Unique spindle cells in the involved ileal segment of rats with congenital aganglionosis

Protein gene product (PGP) 9.5 is a newly characterized brain-specific protein originally detected by high-resolution two-dimensional electrophoresis of soluble human brain proteins. Immunoreactivity for PGP9.5 was investigated in the small and large intestine of aganglionic mutant and control rats with light microscopy, electron microscopy, and confocal laser scanning microscopy. Immunoreactive spindle-shaped cells were seen in the inner circular muscle layer of the aganglionic ileal segment. The long axes of these spindle cells paralleled the inner circular muscle fibers. PGP9.5-positive spindle cells were positive for enteric actin, and some of them were also positive for vimentin, a relatively specific marker for the special smooth muscle (pacemaker cells). These cells may prove to be a maldeveloped microenvironment of aganglionic segment. However, it is necessary to investigate expression of PGP9.5 in embryonal tissue with an abnormal environment to test this hypothesis. This study showed PGP9.5-positive pacemaker cells in the aganglionic ileal segment in the first time.