Laser microdissection as a new tool to investigate site-specific gene expression in enteric ganglia of the human intestine.

BACKGROUND: Myenteric ganglia are key-structures for the control of intestinal motility and their mRNA expression profiles might be altered under pathological conditions. A drawback of conventional RT-PCR from full-thickness specimens is that gene expression analysis is based on heterogeneously composed tissues. To overcome this problem, laser microdissection combined with real-time RT-PCR can be used to detect and quantify low levels of gene expression in isolated enteric ganglia. METHODS: Fresh unfixed full-thickness specimens of sigmoid colon were obtained from patients (n = 8) with diseases unrelated to intestinal motility disorders. 10 microm cryo-sections were mounted on membrane-coated slides and ultra-rapidly stained with toluidine blue. Myenteric ganglia were isolated by laser microdissection and catapulting for mRNA isolation. Real-time RT-PCR was performed for selected growth factors, neurotransmitter receptors and specific cell type markers. KEY RESULTS: Collection of 0.5 mm(2) of ganglionic tissue was sufficient to obtain positive RT-PCR results. Collection of 4 mm(2) resulted in ct-values allowing a reliable quantitative comparison of gene expression levels. mRNA analysis revealed that neurotrophic growth factor, neurotrophin-3, serotonin receptor 3A, PGP 9.5 and S100 beta are specifically expressed in myenteric ganglia of the human colon. CONCLUSIONS & INFERENCES: Laser microdissection combined with real-time RT-PCR is a novel technique to reliably detect and quantify site-specific expression of low-abundance mRNAs (e.g. growth factors, neurotransmitter receptors) related to the human enteric nervous system. This technical approach expands the spectrum of available tools to characterize enteric neuropathologies underlying human gastrointestinal motility disorders at the molecular biological level.

Topographic peculiarities of the submucous plexus in the human anorectum--consequences for histopathologic evaluation of rectal biopsies.

Chronic colorectal motility disorders are commonly encountered in the pediatric population. While most cases can be managed successfully by conservative therapy, a subgroup of patients suffers from severe constipation and requires further diagnostic procedures to identify the underlying pathologies, such as aganglionosis, hypoganglionosis or intestinal neuronal dysplasia (IND). The present study provides reference data about the quantitative distribution of nerve cells and ganglia within the submucosal plexus of the human anorectum from healthy subjects. Anorectal specimens (n = 15) obtained postmortem were divided into 6 segments beginning from the dentate line (S1 = 0-2 cm, S 2 = 2-4 cm, S3 = 4-6 cm, S4 = 6-8 cm, S5 = 8-10 cm, S6 = 10-12 cm). From each segment sections (6 microm thickness) were immunostained with a pan-neuronal marker (Protein Gene Product 9.5) to visualize the enteric nervous system. A morphometric analysis was carried out for each segment recording the number of ganglia and nerve cells of the submucous plexus. Neither ganglia nor nerve cells showed a uniform distribution pattern, but decreased continuously towards the anus. However, even the lowest segments (S1, S2) contained nerve cells and were not aganglionic. In the remaining segments ganglia with 7 or more nerve cells could be detected. The findings demonstrate segment-specific quantitative differences of the anorectal submucous plexus which should be taken into consideration for the histopathologic evaluation of rectal biopsies. Moreover, the data support the concept of a physiologic hypoganglionosis of the anal canal.

Molecular genetics of colorectal motility disorders.

In the last years, several genes have been identified which are involved in the development and differentiation of the enteric nervous system (ENS). Among the congenital intestinal innervation disorders described (aganglionosis, hypoganglionosis, heterotopic ganglia, intestinal neuronal dysplasia), up to now Hirschsprung's disease (HSCR) has been linked to mutational defects in these genes. GDNF and its co-receptor RET are the genes with the most mitogene potency on precursor cells of the ENS. The endothelin system (EDNRB/EDN3) also plays a key role in the development of the ENS by preventing its premature differentiation. Our own studies could show that, whereas a homozygous mutation of EDNRB causes long-segment HSCR, a heterozygous EDNRB deficiency leads to alterations of the ENS resembling the histopathology observed in intestinal neuronal dysplasia. Modern molecular genetic technologies combined with a subtle phenotypic assessment of the ENS will allow investigators to identify other genes within the complex signalling cascade required for the formation of the ENS. The recognition that intestinal innervation disorders are, at least in part, a multigenetic disease should provide support for consequent genetic screening in these patients.

Mitochondrial myopathy (complex I deficiency) associated with chronic intestinal pseudo-obstruction.

We report a patient presenting with severe muscular impairment and chronic intestinal pseudo-obstruction (CIP) at the age of eight months. Due to the aggravated symptoms, assisted ventilation, an ileostomy and total parenteral nutrition were required. Later on, the patient developed a locked-in syndrome (Leigh's subacute necrotising encephalomyelopathy) and finally died due to recurrent pneumonia and chronic renal failure. The assessment of muscle biopsies revealed a moderate single-fibre type II atrophy, a variation of muscle fibre calibre with focal fatty degeneration and a decreased reactivity of cytochrome-c oxidase. Although ragged red fibres had not been found, mitochondrial enzyme activities were markedly decreased with the lowest residual activity detected for NADH:Q1 oxidoreductase and NADH:O2 oxidoreductase (complex I deficiency), thereby confirming the diagnosis of mitochondrial myopathy. A molecular genetic analysis could not identify known mutations of mitochondrial DNA. Gastrointestinal full-thickness biopsies revealed myenteric hypoganglionosis of the colon and stomach and hyperplasia of the submucosal plexus of the ileum. Some of the intestinal smooth muscle cells displayed bulbous protrusions filled with lateralised mitochondria. Mitochondrial myopathies are known to be associated with a variety of clinical syndromes including CIP. However, in contrast to previous reports in which CIP has been attributed to visceral intestinal myopathies, the present case is characterised by neuronal intestinal malformations. Therefore, a mitochondrial myopathy associated with CIP requires a subtle assessment of both the intestinal smooth muscle and the enteric nervous system to identify the underlying pathology.