The GDNF System Is Altered in Diverticular Disease - Implications for Pathogenesis

Genetic, epigenetic and environmental factors in diverticular disease: systematic review

BACKGROUND

Diverticulosis is a normal anatomical variant of the colon present in more than 70% of the westernized population over the age of 80. Approximately 3% will develop diverticulitis in their lifetime. Many patients present emergently, suffer high morbidity rates and require substantial healthcare resources. Diverticulosis is the most common finding at colonoscopy and has the potential for causing a significant morbidity rate and burden on healthcare. There is a need to better understand the aetiology and pathogenesis of diverticular disease. Research suggests a genetic susceptibility of 40-50% in the formation of diverticular disease. The aim of this review is to present the hypothesized functional effects of the identified gene loci and environmental factors.

METHODS

A systematic literature review was performed using PubMed, MEDLINE and Embase. Medical subject headings terms used were: 'diverticular disease, diverticulosis, diverticulitis, genomics, genetics and epigenetics'. A review of grey literature identified environmental factors.

RESULTS

Of 995 articles identified, 59 articles met the inclusion criteria. Age, obesity and smoking are strongly associated environmental risk factors. Intrinsic factors of the colonic wall are associated with the presence of diverticula. Genetic pathways of interest and environmental risk factors were identified. The COLQ, FAM155A, PHGR1, ARHGAP15, S100A10, and TNFSF15 genes are the strongest candidates for further research.

CONCLUSION

There is increasing evidence to support the role of genomics in the spectrum of diverticular disease. Genomic, epigenetic and omic research with demographic context will help improve the understanding and management of this complex disease.

150 risk variants for diverticular disease of intestine prioritize cell types and enable polygenic prediction of disease susceptibility

We conducted a genome-wide association study (GWAS) analysis of diverticular disease (DivD) of intestine within 724,372 individuals and identified 150 independent genome-wide significant DNA variants. Integration of the GWAS results with human gut single-cell RNA sequencing data implicated gut myocyte, mesothelial and stromal cells, and enteric neurons and glia in DivD development. Ninety-five genes were prioritized based on multiple lines of evidence, including SLC9A3, a drug target gene of tenapanor used for the treatment of the constipation subtype of irritable bowel syndrome. A DivD polygenic score (PGS) enables effective risk prediction (area under the curve [AUC], 0.688; 95% confidence interval [CI], 0.645-0.732) and the top 20% PGS was associated with ∼3.6-fold increased DivD risk relative to the remaining population. Our statistical and bioinformatic analyses suggest that the mechanism of DivD is through colon structure, gut motility, gastrointestinal mucus, and ionic homeostasis. Our analyses reinforce the link between gastrointestinal disorders and the enteric nervous system through genetics.

Pathophysiology of Diverticular Disease: From Diverticula Formation to Symptom Generation

Diverticular disease is a common clinical problem, particularly in industrialized countries. In most cases, colonic diverticula remain asymptomatic throughout life and sometimes are found incidentally during colonic imaging in colorectal cancer screening programs in otherwise healthy subjects. Nonetheless, roughly 25% of patients bearing colonic diverticula develop clinical manifestations. Abdominal symptoms associated with diverticula in the absence of inflammation or complications are termed symptomatic uncomplicated diverticular disease (SUDD). The pathophysiology of diverticular disease as well as the mechanisms involved in the shift from an asymptomatic condition to a symptomatic one is still poorly understood. It is accepted that both genetic factors and environment, as well as intestinal microenvironment alterations, have a role in diverticula development and in the different phenotypic expressions of diverticular disease. In the present review, we will summarize the up-to-date knowledge on the pathophysiology of diverticula and their different clinical setting, including diverticulosis and SUDD.

Evaluation of molecular and genetic predisposing parameters at diverticular disease of the colon

BACKGROUND

Diverticular disease (DD) refers to the presence of diverticula throughout the gastrointestinal (GI) tract, mainly along colon. DD might evolve into diverticulitis that is accompanied by severe clinical presentation, which includes abscess formation, perforation, stricture, obstruction and/or fistula.

AIM

The aim of the present review is to summarize the role of molecular and genetic factors in DD development, as well as their possible contribution towards new prognostic indicators, diagnostic algorithms and new therapeutic approaches.

METHODS AND RESULTS

Except from common predisposing parameters, several genetic mutations, immune factors, neurotransmitters, hormones and protein dysfunctions have been associated to the early onset of DD symptoms, pathogenesis and prognosis of the disease. Specific structural changes in the colonic wall, altered matrix composition and compromised motility have been verified as possible pathogenic factors for the development of DD. Dysregulation in peristaltic activity and reduced ability of the longitudinal muscle to relax following contraction has been also associated with DD evolution. In addition, it has been suspected that genetic defects combined with alterations in intestinal microbiota might play an important role in diverticulitis presentation.

Colonic diverticular disease

Diverticula are outpouchings of the intestinal wall and are common anatomical alterations detected in the human colon. Colonic diverticulosis (the presence of diverticula in the colon; referred to as diverticulosis) remains asymptomatic in most individuals but ~25% of individuals will develop symptomatic diverticulosis, termed colonic diverticular disease (also known as diverticular disease). Diverticular disease can range in severity from symptomatic uncomplicated diverticular disease (SUDD) to symptomatic disease with complications such as acute diverticulitis or diverticular haemorrhage. Since the early 2000s, a greater understanding of the pathophysiology of diverticulosis and diverticular disease, which encompasses genetic alterations, chronic low-grade inflammation and gut dysbiosis, has led to improvements in diagnosis and management. Diagnosis of diverticular disease relies on imaging approaches, such as ultrasonography, CT and MRI, as biomarkers alone are insufficient to establish a diagnosis despite their role in determining disease severity and progression as well as in differential diagnosis. Treatments for diverticular disease include dietary fibre, pharmacological treatments such as antibiotics (rifaximin), anti-inflammatory drugs (mesalazine) and probiotics, alone or in combination, and eventually surgery. Despite being effective in treating primary disease, their effectiveness in primary and secondary prevention of complications is still uncertain.

Impaired Expression of Neuregulin 1 and Nicotinic Acetylcholine Receptor β4 Subunit in Diverticular Disease

Neuregulin 1 (NRG1) regulates the expression of the nicotinic acetylcholine receptor (nAChR) and is suggested to promote the survival and maintenance of the enteric nervous system (ENS), since deficiency of its corresponding receptor complex ErbB2/ErbB3 leads to postnatal colonic aganglionosis. As diverticular disease (DD) is associated with intestinal hypoganglionosis, the NRG1-ErbB2/ErbB3 system and the nAChR were studied in patients with DD and controls. Samples of tunica muscularis of the sigmoid colon from patients with DD (n = 8) and controls (n = 11) were assessed for mRNA expression of NRG1, ErbB2, and ErbB3 and the nAChR subunits α3, α5, α7, β2, and β4. Site-specific gene expression levels of the NRG1-ErbB2/3 system were determined in myenteric ganglia harvested by laser microdissection (LMD). Localization studies were performed by immunohistochemistry for the NRG1-ErbB2/3 system and nAChR subunit β4. Rat enteric nerve cell cultures were stimulated with NRG1 or glial-cell line derived neurotrophic factor (GDNF) for 6 days and mRNA expression of the aforementioned nAchR was measured. NRG1, ErbB3, and nAChR subunit β4 expression was significantly down-regulated in both the tunica muscularis and myenteric ganglia of patients with DD compared to controls, whereas mRNA expression of ErbB3 and nAChR subunits β2, α3, α5, and α7 remained unaltered. NRG1, ErbB3, and nAChR subunit β4 immunoreactive signals were reduced in neuronal somata and the neuropil of myenteric ganglia from patients with DD compared to control. nAChR subunit β4 exhibited also weaker immunoreactive signals in the tunica muscularis of patients with DD. NRG1 treatment but not GDNF treatment of enteric nerve cell cultures significantly enhanced mRNA expression of nAchR β4. The down-regulation of NRG1 and ErbB3 in myenteric ganglia of patients with DD supports the hypothesis that intestinal hypoganglionosis observed in DD may be attributed to a lack of neurotrophic factors. Regulation of nAChR subunit β4 by NRG1 and decreased nAChR β4 in patients with DD provide evidence that a lack of NRG1 may affect the composition of enteric neurotransmitter receptor subunits thus contributing to the intestinal motility disorders previously reported in DD.

Persistent Increased Enteric Glial Expression of S100β is Associated With Low-grade Inflammation in Patients With Diverticular Disease

BACKGROUND

Diverticular disease (DD) is a common gastrointestinal inflammatory disorder associated with an enteric neuropathy. Although enteric glial cells (EGCs) are essential regulators of intestinal inflammation and motility functions, their contribution to the pathophysiology of DD remains unclear. Therefore, we analyzed the expression of specific EGC markers in patients with DD.

MATERIALS AND METHODS

Expression of the glial markers S100β, GFAP, Sox10, and Connexin 43 was analyzed by real-time quantitative PCR in colonic specimens of patients with DD and in that of controls. Protein expression levels of S100β, GFAP, and Connexin 43 were further analyzed using immunohistochemistry in the submucosal and myenteric plexus of patients with DD and in that of controls. Expression of the inflammatory cytokines tumor necrosis factor-α and interleukin-6 was quantified using qPCR, and infiltration of CD3+ lymphocytes was determined using immunohistochemistry.

RESULTS

Expression of S100β was increased in the submucosal and myenteric plexus of patients with DD compared with that in controls, whereas expression of other glial factors remained unchanged. This increased expression of S100β was correlated to CD3+ lymphocytic infiltrates in patients with DD, whereas no correlation was observed in controls.

CONCLUSIONS

DD is associated with limited but significant alterations of the enteric glial network. The increased expression of S100β is associated with a persistent low-grade inflammation reported in patients with DD, further emphasizing the role of EGCs in intestinal inflammation.

Epidemiology, Pathophysiology, and Treatment of Diverticulitis

Diverticulitis is a prevalent gastrointestinal disorder that is associated with significant morbidity and health care costs. Approximately 20% of patients with incident diverticulitis have at least 1 recurrence. Complications of diverticulitis, such as abdominal sepsis, are less likely to occur with subsequent events. Several risk factors, many of which are modifiable, have been identified including obesity, diet, and physical inactivity. Diet and lifestyle factors could affect risk of diverticulitis through their effects on the intestinal microbiome and inflammation. Preliminary studies have found that the composition and function of the gut microbiome differ between individuals with vs without diverticulitis. Genetic factors, as well as alterations in colonic neuromusculature, can also contribute to the development of diverticulitis. Less-aggressive and more-nuanced treatment strategies have been developed. Two multicenter, randomized trials of patients with uncomplicated diverticulitis found that antibiotics did not speed recovery or prevent subsequent complications. Elective surgical resection is no longer recommended solely based on number of recurrent events or young patient age and might not be necessary for some patients with diverticulitis complicated by abscess. Randomized trials of hemodynamically stable patients who require urgent surgery for acute, complicated diverticulitis that has not improved with antibiotics provide evidence to support primary anastomosis vs sigmoid colectomy with end colostomy. Despite these advances, more research is needed to increase our understanding of the pathogenesis of diverticulitis and to clarify treatment algorithms.

Altered enteric expression of the homeobox transcription factor Phox2b in patients with diverticular disease

Background

Diverticular disease, a major gastrointestinal disorder, is associated with modifications of the enteric nervous system, encompassing alterations of neurochemical coding and of the tyrosine receptor kinase Ret/GDNF pathway. However, molecular factors underlying these changes remain to be determined.

Objectives

We aimed to characterise the expression of Phox2b, an essential regulator of Ret and of neuronal subtype development, in the adult human enteric nervous system, and to evaluate its potential involvement in acute diverticulitis.

Methods

Site-specific gene expression of Phox2b in the adult colon was analysed by quantitative polymerase chain reaction. Colonic specimens of adult controls and patients with diverticulitis were subjected to quantitative polymerase chain reaction for Phox2b and dual-label immunochemistry for Phox2b and the neuronal markers RET and tyrosine hydroxylase or the glial marker S100β.

Results

The results indicate that Phox2b is physiologically expressed in myenteric neuronal and glial subpopulations in the adult enteric nervous system. Messenger RNA expression of Phox2b was increased in patients with diverticulitis and both neuronal, and glial protein expression of Phox2b were altered in these patients.

Conclusions

Alterations of Phox2b expression may contribute to the enteric neuropathy observed in diverticular disease. Future studies are required to characterise the functions of Phox2b in the adult enteric nervous system and to determine its potential as a therapeutic target in gastrointestinal disorders.

The Pathophysiology of Colonic Diverticulosis: Inflammation versus Constipation?

Background

Diverticulosis of the colon is the most common anatomic alteration of the human colon, but the pathophysiologic mechanisms of its occurrence are not completely understood.

Summary

Constipation has been considered the key factor for diverticulosis occurrence. However, several fine papers questioned this pathogenetic hypothesis, showing on the contrary an inverse relationship between low number of bowel movements and diverticulosis occurrence. In the last years, several papers have showed the role of low-grade inflammation in the occurrence of symptoms in people having diverticulosis, as well as its role on symptom persistence following acute diverticulitis, even if the evidence available is not so strong. Although the trigger of this low-grade inflammation is currently under debate, some preliminary evidence found colonic dysbiosis linked to symptom occurrence in those patients.

Key Messages

Constipation no longer seems the leading cause for diverticulosis occurrence, while low-grade inflammation could play a role in symptom occurrence.

No neuronal loss, but alterations of the GDNF system in asymptomatic diverticulosis

Background

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor known to promote the survival and maintenance of neurons not only in the developing but also in the adult enteric nervous system. As diverticular disease (DD) is associated with reduced myenteric neurons, alterations of the GDNF system were studied in asymptomatic diverticulosis (diverticulosis) and DD.

Methods

Morphometric analysis for quantifying myenteric ganglia and neurons were assessed in colonic full-thickness sections of patients with diverticulosis and controls. Samples of tunica muscularis (TM) and laser-microdissected myenteric ganglia from patients with diverticulosis, DD and controls were analyzed for mRNA expression levels of GDNF, GFRA1, and RET by RT-qPCR. Myenteric protein expression of both receptors was quantified by fluorescence-immunohistochemistry of patients with diverticulosis, DD, and controls.

Results

Although no myenteric morphometric alterations were found in patients with diverticulosis, GDNF, GFRA1 and RET mRNA expression was down-regulated in the TM of patients with diverticulosis as well as DD. Furthermore GFRA1 and RET myenteric plexus mRNA expression of patients with diverticulosis and DD was down-regulated, whereas GDNF remained unaltered. Myenteric immunoreactivity of the receptors GFRα1 and RET was decreased in both asymptomatic diverticulosis and DD patients.

Conclusion

Our data provide evidence for an impaired GDNF system at gene and protein level not only in DD but also during early stages of diverticula formation. Thus, the results strengthen the idea of a disturbed GDNF-responsiveness as contributive factor for a primary enteric neuropathy involved in the pathogenesis and disturbed intestinal motility observed in DD.

Myenteric plexitis: A frequent feature in patients undergoing surgery for colonic diverticular disease

BACKGROUND

Diverticular disease of the colon is frequent in clinical practice, and a large number of patients each year undergo surgical procedures worldwide for their symptoms. Thus, there is a need for better knowledge of the basic pathophysiologic mechanisms of this disease entity.

OBJECTIVES

Because patients with colonic diverticular disease have been shown to display abnormalities of the enteric nervous system, we assessed the frequency of myenteric plexitis (i.e. the infiltration of myenteric ganglions by inflammatory cells) in patients undergoing surgery for this condition.

METHODS

We analyzed archival resection samples from the proximal resection margins of 165 patients undergoing left hemicolectomy (60 emergency and 105 elective surgeries) for colonic diverticulitis, by histology and immunochemistry.

RESULTS

Overall, plexitis was present in almost 40% of patients. It was subdivided into an eosinophilic (48%) and a lymphocytic (52%) subtype. Plexitis was more frequent in younger patients; and it was more frequent in those undergoing emergency surgery (50%), compared to elective (28%) surgery (p = 0.007). All the severe cases of plexitis displayed the lymphocytic subtype.

CONCLUSIONS

In conclusion, myenteric plexitis is frequent in patients with colonic diverticular disease needing surgery, and it might be implicated in the pathogenesis of the disease.

Expression and function of Neuregulin 1 and its signaling system ERBB2/3 in the enteric nervous system

Neuregulin 1 (NRG1) is suggested to promote the survival and maintenance of the enteric nervous system (ENS). As deficiency in its corresponding receptor signaling complex ERBB2/ERBB3 leads to postnatal colonic hypo/aganglionosis we assessed the distributional and expressional pattern of the NRG1-ERBB2/ERBB3 system in the human colon and explored the neurotrophic capacity of NRG1 on cultured enteric neurons. Site-specific mRNA expression of the NRG1-ERBB2/3 system was determined in microdissected samples harvested from enteric musculature and ganglia. Localization of NRG1, ERBB2 and ERBB3 was determined by dual-label-immunohistochemistry using pan-neuronal and pan-glial markers. Morphometric analysis was performed on NRG1-stimulated rat enteric nerve cultures to evaluate neurotrophic effects. mRNA expression of the NRG1-ERBB2/3 system was determined by qPCR. Co-localization of NRG1 with neuronal or synaptic markers was analyzed in enteric nerve cultures stimulated with glial cell line-derived neurotrophic factor (GDNF). The NRG1 system was expressed in both neurons and glial cells of enteric ganglia and in nerve fibers. NRG1 significantly enhanced growth parameters in enteric nerve cell cultures and ErB3 mRNA expression was down-regulated upon NRG1 stimulation. GDNF negatively regulates ErbB2 and ErbB3 mRNA expression. The NRG1-ERBB2/3 system is physiologically present in the human ENS and NRG1 acts as a neurotrophic factor for the ENS. The down-regulation of ErbB3/ErbB2 in GDNF stimulated nerve cell cultures points to an interaction of both neurotrophic factors. Thus, the data may provide a basis to assess disturbed signaling components of the NRG1 system in enteric neuropathies.

Inverse expression of prostaglandin E2-related enzymes highlights differences between diverticulitis and inflammatory bowel disease

BACKGROUND

Prostaglandin E2 (PGE2) is the dominant prostaglandin in the colon and is associated with colonic inflammation. PGE2 levels are regulated not only by cyclooxygenases (COX-1 and COX-2) but also by 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the major PGE2-degrading enzyme. Information about the involvement of 15-PGDH in colonic inflammation is sparse.

AIM

We thus aimed to determine the gene expression and immunoreactivity (IR) of COX-1, COX-2, and 15-PGDH in colonic mucosa from patients with diverse inflammatory disorders: ulcerative colitis (UC), Crohn's disease (CD), and acute diverticular disease (DD).

METHODS

RNA from human colonic mucosa was extracted and assessed for gene expression by real-time PCR. Intact colon sections were processed for immunohistochemistry with immunostaining of the mucosal areas quantified using ImageJ.

RESULTS

In colonic mucosa of both UC and CD, COX-2 mRNA and COX-2-IR were significantly increased, whereas 15-PGDH mRNA and 15-PGDH-IR were significantly reduced. In macroscopically undamaged acute DD mucosa, the opposite findings were seen: for both gene expression and immunoreactivity, there was a significant downregulation of COX-2 and upregulation of 15-PGDH. COX-1 mRNA and COX-1-IR remained unchanged in all diseases.

CONCLUSIONS

Our study for the first time demonstrated differential expression of the PGE2-related enzymes COX-2 and 15-PGDH in colonic mucosa from UC, CD, and acute DD. The reduction of 15-PGDH in IBD provides an additional mechanism for PGE2 increase in IBD. With respect to DD, alterations of PGE2-related enzymes suggest that a low PGE2 level may precede the onset of inflammation, thus providing new insight into the pathogenesis of DD.

Morphologic Basis for Developing Diverticular Disease, Diverticulitis, and Diverticular Bleeding

Diverticula of the colon are pseudodiverticula defined by multiple outpouchings of the mucosal and submucosal layers penetrating through weak spots of the muscle coat along intramural blood vessels. A complete prolapse consists of a diverticular opening, a narrowed neck, and a thinned diverticular dome underneath the serosal covering. The susceptibility of diverticula to inflammation is explained by local ischemia, translocation of pathogens due to retained stool, stercoral trauma by fecaliths, and microperforations. Local inflammation may lead to phlegmonous diverticulitis, paracolic/mesocolic abscess, bowel perforation, peritonitis, fistula formation, and stenotic strictures. Diverticular bleeding is due to an asymmetric rupture of distended vasa recta at the diverticular dome and not primarily linked to inflammation. Structural and functional changes of the bowel wall in diverticular disease comprise: i) Altered amount, composition, and metabolism of connective tissue; ii) Enteric myopathy with muscular thickening, deranged architecture, and altered myofilament composition; iii) Enteric neuropathy with hypoganglionosis, neurotransmitter imbalance, deficiency of neurotrophic factors and nerve fiber remodeling; and iv) Disturbed intestinal motility both in vivo (increased intraluminal pressure, motility index, high-amplitude propagated contractions) and in vitro (altered spontaneous and pharmacologically triggered contractility). Besides established etiologic factors, recent studies suggest that novel pathophysiologic concepts should be considered in the pathogenesis of diverticular disease.

Changing views on diverticular disease: impact of aging, obesity, diet, and microbiota

The development of colonic diverticulosis is a common aging change in industrialized nations. While most patients have asymptomatic diverticulosis, around one in five develops symptomatic diverticular disease. This is characterized by recurrent abdominal pain and disturbed bowel habit. Some of the pain episodes are prolonged and are due to acute diverticulitis, which itself may be complicated by abscess, perforation, fistulation, or stricture formation. Risk factors favouring the development of symptomatic diverticular disease include obesity, smoking and diets low in fiber but high in red meat and animal fat. What determines the transition from asymptomatic diverticulosis to symptomatic diverticular disease is unclear but neuromuscular changes following acute diverticulitis may be responsible in some cases. The severity of symptoms generated depends on cerebral pain processing which is influenced by psychosocial factors. These are important considerations in deciding optimal patient management. Prior theories of the cause of diverticulosis suggested that constipation was an important cause, but new data challenge this and has provoked new ideas. Underlying mechanisms causing diverticulosis include weakening of the colonic wall and/or degenerative changes in the enteric nerves. Dietary induced changes in microbiota and the host inflammatory response may underlie the subsequent development of acute/chronic diverticulitis and its sequela.

SNAP-25 is abundantly expressed in enteric neuronal networks and upregulated by the neurotrophic factor GDNF

Control of intestinal motility requires an intact enteric neurotransmission. Synaptosomal-associated protein 25 (SNAP-25) is an essential component of the synaptic vesicle fusion machinery. The aim of the study was to investigate the localization and expression of SNAP-25 in the human intestine and cultured enteric neurons and to assess its regulation by the neurotrophic factor glial cell line-derived neurotrophic factor (GDNF). SNAP-25 expression and distribution were analyzed in GDNF-stimulated enteric nerve cell cultures, and synaptic vesicles were evaluated by scanning and transmission electron microscopy. Human colonic specimens were processed for site-specific SNAP-25 gene expression analysis and SNAP-25 immunohistochemistry including dual-labeling with the pan-neuronal marker PGP 9.5. Additionally, gene expression levels and distributional patterns of SNAP-25 were analyzed in colonic specimens of patients with diverticular disease (DD). GDNF-treated enteric nerve cell cultures showed abundant expression of SNAP-25 and exhibited granular staining corresponding to synaptic vesicles. SNAP-25 gene expression was detected in all colonic layers and isolated myenteric ganglia. SNAP-25 co-localized with PGP 9.5 in submucosal and myenteric ganglia and intramuscular nerve fibers. In patients with DD, both SNAP-25 mRNA expression and immunoreactive profiles were decreased compared to controls. GDNF-induced growth and differentiation of cultured enteric neurons is paralleled by increased expression of SNAP-25 and formation of synaptic vesicles reflecting enhanced synaptogenesis. The expression of SNAP-25 within the human enteric nervous system and its downregulation in DD suggest an essential role in enteric neurotransmission and render SNAP-25 as a marker for impaired synaptic plasticity in enteric neuropathies underlying intestinal motility disorders.

[Anatomy and pathogenesis of diverticular disease]

BACKGROUND

Although diverticular disease is one of the most frequent gastrointestinal disorders the pathogenesis is not yet sufficiently clarified.

OBJECTIVES

The aim is to define the anatomy and pathogenesis of diverticular disease considering the risk factors and description of structural and functional alterations of the bowel wall.

METHODS

This article gives an appraisal of the literature, presentation and evaluation of classical etiological factors, analysis and discussion of novel pathogenetic concepts.

RESULTS

Colonic diverticulosis is defined as an acquired out-pouching of multiple and initially asymptomatic pseudodiverticula through muscular gaps in the colon wall. Diverticular disease is characterized by diverticular bleeding and/or inflammatory processes (diverticulitis) with corresponding complications (e.g. abscess formation, fistula, covered and open perforation, peritonitis and stenosis). Risk factors for diverticular disease include increasing age, genetic predisposition, congenital connective tissue diseases, low fiber diet, high meat consumption and pronounced overweight. Alterations of connective tissue cause a weakening of preformed exit sites of diverticula and rigidity of the bowel wall with reduced flexibility. It is assumed that intestinal innervation disorders and structural alterations of the musculature induce abnormal contractile patterns with increased intraluminal pressure, thereby promoting the development of diverticula. Moreover, an increased release of pain-mediating neurotransmitters is considered to be responsible for persistent pain in chronic diverticular disease.

CONCLUSIONS

According to the present data the pathogenesis of diverticular disease cannot be attributed to a single factor but should be considered as a multifactorial event.

Alterations of the enteric smooth musculature in diverticular disease

BACKGROUND

The pathogenesis of diverticular disease (DD) is considered to be multifactorial and involves intestinal motor disturbances and an underlying enteric neuromuscular pathology. While an enteric neuropathy has been well documented, actual studies on concomitant alterations of the enteric musculature are limited. This study is aimed at reassessing the smooth muscle tissue by histological, ultrastructural and molecular-biological approaches.

METHODS

Full-thickness sigmoid specimens were obtained from patients with DD (n = 20) and controls (n = 19). Morphometric analysis was performed to evaluate the thickness and connective tissue index of the circular and longitudinal muscle layers as well as the myenteric plexus. Structural alterations were determined by light and transmission electron microscopy. mRNA profiles of components of the contractile smooth muscle apparatus including smooth muscle α-actin, smoothelin, histone deacetylase 8, and smooth muscle myosin heavy chain (SMMHC) were assessed by qPCR. Altered gene expression levels were confirmed at protein level by immunohistochemistry.

RESULTS

Compared to controls, patients with DD showed (1) increased thickness of the circular and longitudinal muscle layers, (2) architectural alterations of smooth muscle cells, (3) increased connective tissue index of the longitudinal muscle layer, (4) focally reduced density of myofilaments at ultrastructural level, (5) specific down-regulation of SMMHC mRNA levels, (6) decreased immunoreactivity of SMMHC, (7) oligo-neuronal hypoganglionosis.

CONCLUSIONS

DD is associated with distinct structural and functional alterations of the enteric musculature. The enteric myopathy is characterized by disturbed muscular architecture, connective tissue replacement and loss of specific myofilaments and thus may contribute to the pathogenesis and progression of DD.