The multiple faces of inflammatory enteric glial cells: is Crohn's disease a gliopathy?

Gone are the days when enteric glial cells (EGC) were considered merely satellites of enteric neurons. Like their brain counterpart astrocytes, EGC express an impressive number of receptors for neurotransmitters and intercellular messengers, thereby contributing to neuroprotection and to the regulation of neuronal activity. EGC also produce different soluble factors that regulate neighboring cells, among which are intestinal epithelial cells. A better understanding of EGC response to an inflammatory environment, often referred to as enteric glial reactivity, could help define the physiological role of EGC and the importance of this reactivity in maintaining gut functions. In chronic inflammatory disorders of the gut such as Crohn's disease (CD) and ulcerative colitis, EGC exhibit abnormal phenotypes, and their neighboring cells are dysfunctional; however, it remains unclear whether EGC are only passive bystanders or active players in the pathophysiology of both disorders. The aim of the present study is to review the physiological roles and properties of EGC, their response to inflammation, and their role in the regulation of the intestinal epithelial barrier and to discuss the emerging concept of CD as an enteric gliopathy.

Defects in 15-HETE Production and Control of Epithelial Permeability by Human Enteric Glial Cells From Patients With Crohn's Disease.

BACKGROUND & AIMS: Enteric glial cells (EGCs) produce soluble mediators that regulate homeostasis and permeability of the intestinal epithelial barrier (IEB). We investigated the profile of polyunsaturated fatty acid (PUFA) metabolites produced by EGCs from rats and from patients with Crohn's disease (CD), compared with controls, along with the ability of one of these metabolites, 15-hydroxyeicosatetraenoic acid (15-HETE), to regulate the permeability of the IEB. METHODS: We isolated EGCs from male Sprague-Dawley rats, intestinal resections of 6 patients with CD, and uninflamed healthy areas of intestinal tissue from 6 patients who underwent surgery for colorectal cancer (controls). EGC-conditioned media was analyzed by high-sensitivity liquid-chromatography tandem mass spectrometry to determine PUFA signatures. We used immunostaining to identify 15-HETE-producing enzymes in EGCs and tissues. The effects of human EGCs and 15-HETE on permeability and transepithelial electrical resistance of the IEB were measured using Caco-2 cells; effects on signal transduction proteins were measured with immunoblots. Levels of proteins were reduced in Caco-2 cells using short-hairpin RNAs or proteins were inhibited pharmacologically. Rats were given intraperitoneal injections of 15-HETE or an inhibitor of 15-lipoxygenase (the enzyme that produces 15-HETE); colons were collected and permeability was measured. RESULTS: EGCs expressed 15-lipoxygenase-2 and produced high levels of 15-HETE, which increased IEB resistance and reduced IEB permeability. 15-HETE production was reduced in EGCs from patients with CD compared with controls. EGCs from patients with CD were unable to reduce the permeability of the IEB; the addition of 15-HETE restored permeability to levels of control tissues. Inhibiting 15-HETE production in rats increased the permeability of the IEB in colon tissues. We found that 15-HETE regulates IEB permeability by inhibiting an adenosine monophosphate-activated protein kinase and increasing expression of zonula occludens-1. CONCLUSIONS: Enteric glial cells from patients with CD have reduced production of 15-HETE, which controls IEB permeability by inhibiting adenosine monophosphate-activated protein kinase and increasing expression of zonula occludens-1.

Crohn's-like acute severe colitis associated with Hermansky-Pudlak syndrome: A case report.

BACKGROUND: Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by oculocutaneous albinism, platelet storage pool deficiency and systemic complications associated with ceroid deposition in the reticuloendothelial system. HPS types 1 and 4 are associated with Crohn's disease (CD)-like gastrointestinal disorders, such as granulomatous enterocolitis or perianal disease. Cases of colitis can be particularly severe and, before the use of anti-tumor necrosis factor alpha (TNFα) therapy had become common, were reported as showing poor responsiveness to medical treatment. CASE SUMMARY: We present the case of a 51-year-old albino woman who presented with acute severe colitis that led to the diagnosis of HPS. Histologic findings of biopsy samples showed chronic inflammation with deep ulcerations, and granulomas without caseous necrosis. Molecular genetic analysis confirmed HPS type 1, with a homozygous 27 base-pair deletion in exon 20 of the HPS1 gene. Once the patient's bleeding diathesis was corrected by platelet transfusion, the granulomatous colitis responded dramatically to a medical treatment regimen that included corticosteroids, azathioprine and infliximab; this regimen is similar to that used in CD treatment. Although it remains unclear if the granulomatous enterocolitis in HPS is due to ceroid deposition or reflects the co-existence of CD and HPS, the fact that this case of HPS-related granulomatous colitis responded to the same therapeutic approach used in CD suggests that this type of colitis may result from HPS patients' genetic susceptibility to CD. CONCLUSION: We report a case of severe colitis that led to the diagnosis of HPS, which was responsive to azathioprine and infliximab.