Interleukin-13 and transforming growth factor ß synergise in the pathogenesis of human intestinal fistulae.

OBJECTIVE: Epithelial to mesenchymal transition (EMT) seems to play an important role in the pathogenesis of fistulae, a common clinical complication of Crohn's disease (CD). TGFß and interleukin-13 (IL-13) have been correlated with the onset of EMT-associated organ fibrosis and high levels of TGFß have been shown in transitional cells (TCs) lining CD fistula tracts. This study investigated whether IL-13 could be involved in the pathogenesis of CD-associated fistulae. DESIGN: Protein or mRNA levels in HT29 intestinal epithelial cells (IECs) or colonic lamina propria fibroblasts (CLPFs) were studied by western blotting or real-time PCR. CLPFs were isolated from non-inflammatory disease controls or patients with CD with or without fistulae and IL-13 levels were analysed in surgically removed fistula specimens by immunohistochemistry. RESULTS: TGFß induced IL-13 secretion in CLPFs from patients with fistulising CD. In fistula specimens high levels of IL-13 were detected in TCs covering fistula tracts. In HT29 IEC monolayers, IL-13 induced SLUG and ß6-integrin mRNA, which are associated with cell invasion. HT29 spheroids completely disintegrated when treated with TGFß for 7 days, whereas IL-13-treated spheroids did not show morphological changes. Here, TGFß induced mRNA expression of SNAIL1 and IL-13, whereas IL-13 elevated SLUG and ß6-integrin mRNA. An anti-IL-13 antibody was able to prevent IL-13-induced SLUG expression in HT29 IECs. CONCLUSIONS: TGFß induces IL-13 expression and an EMT-like phenotype of IECs, while IL-13 promotes the expression of genes associated with cell invasion. These findings suggest that TGFß and IL-13 play a synergistic role in the pathogenesis of fistulae and inhibition of IL-13 might represent a novel therapeutic approach for fistula treatment.

Knock-out of ß-glucosidase 2 has no influence on dextran sulfate sodium-induced colitis.

BACKGROUND/AIMS: The non-lysosomal glucosylceramidase, ß-glucosidase (Gba2), hydrolyzes glucosylceramide to glucose and ceramide (Cer). Cer is a potent second-messenger lipid that plays an important role in signaling cascades involved in apoptosis. The aim of this study was to investigate whether Gba2 knock-out (Gba2(-/-)) affects the extent of dextran sulfate sodium (DSS)-induced colitis in mice. METHODS: Acute colitis was induced in wild-type (WT) and Gba2(-/-) mice by administration of 2% DSS in drinking water. After 7 days, mice underwent colonoscopy and were sacrificed. RESULTS: Both DSS-treated WT (n = 10) and Gba2(-/-) (n = 12) mice showed elevated histological and endoscopic scores compared to respective H(2)O controls (n = 9 each). However, no significant differences between the DSS groups were detected. Flow cytometric analysis of propidium iodide staining, cleavage of caspases-3 and -8, indicative for apoptosis, as well as Cer levels were not altered in DSS-treated WT or Gba2(-/-) mice. Gba2(-/-) resulted in slightly decreased expression of glucocerebrosidase (Gba1) as well as in upregulation of proteins being involved in cellular regeneration, such as STAT3 (signal transducer and activator of transcription), JNK and iNOS, upon DSS treatment. CONCLUSION: We demonstrate that Gba2(-/-) does not affect the extent of DSS-induced inflammation in mice, however, it might be involved in tissue regeneration in response to toxic agents.

Protein tyrosine phosphatase nonreceptor type 2 regulates autophagosome formation in human intestinal cells.

BACKGROUND: Autophagy is a process of central importance for maintaining cell homeostasis, survival, and the regulation of inflammation. Recent studies associated variants within the gene loci, encoding protein tyrosine phosphatase nonreceptor type 2 (PTPN2), and autophagy genes, such as autophagy-related 16-like 1 (ATG16L1), with chronic inflammatory disorders, such as Crohn's disease (CD). We show that PTPN2 regulates autophagy in human intestinal epithelial cells (IEC) and primary colonic lamina propria fibroblasts (CLPF). METHODS: Protein analysis in IEC and CLPF was performed by western blotting. Autophagososme formation was assessed by LC3B immunofluorescence or immunohistochemistry. Human intestinal tissue samples were obtained from noninflammatory bowel disease (IBD) control or from CD patients and genotyped for disease-associated PTPN2 or ATG16L1 variations. RESULTS: Knockdown of PTPN2 causes impaired autophagosome formation and dysfunctional autophagy resulted in increased levels of intracellular Listeria monocytogenes (LM) and elevated IEC apoptosis in response to tumor necrosis factor (TNF) and interferon gamma (IFN-γ). Similar findings were observed in primary CLPF derived from CD patients carrying the CD-associated PTPN2 variant. Presence of the ATG16L1 variant prevented the cytokine-induced rise in PTPN2 protein, finally resulting in impaired LC3B-II levels in IEC. Actively inflamed intestinal biopsies from CD patients carrying either ATG16L1 or PTPN2 genetic variants revealed aberrant LC3B expression patterns when compared with samples from non-IBD control patients. CONCLUSIONS: Our results demonstrate that PTPN2 regulates autophagosome formation in human intestinal cells. We provide a model of how a dysfunction of the CD susceptibility genes, PTPN2 and/or ATG16L1, may contribute to the onset and perpetuation of chronic intestinal inflammation.

Crohn's disease-associated polymorphism within the PTPN2 gene affects muramyl-dipeptide-induced cytokine secretion and autophagy.

BACKGROUND: The single nucleotide polymorphism (SNP) rs2542151 within the gene locus region encoding protein tyrosine phosphatase non-receptor type 2 (PTPN2) has been associated with Crohn's disease (CD), ulcerative colitis (UC), type-I diabetes, and rheumatoid arthritis. We have previously shown that PTPN2 regulates mitogen-activated protein kinase (MAPK) signaling and cytokine secretion in human THP-1 monocytes and intestinal epithelial cells (IEC). Here, we studied whether intronic PTPN2 SNP rs1893217 regulates immune responses to the nucleotide-oligomerization domain 2 (NOD2) ligand, muramyl-dipeptide (MDP). MATERIALS AND METHODS: Genomic DNA samples from 343 CD and 663 non-IBD control patients (male and female) from a combined German, Swiss, and Polish cohort were genotyped for the presence of the PTPN2 SNPs, rs2542151, and rs1893217. PTPN2-variant rs1893217 was introduced into T(84) IEC or THP-1 cells using a lentiviral vector. RESULTS: We identified a novel association between the genetic variant, rs1893217, located in intron 7 of the PTPN2 gene and CD. Human THP-1 monocytes carrying this variant revealed increased MAPK activation as well as elevated mRNA expression of T-bet transcription factor and secretion of interferon-γ in response to the bacterial wall component, MDP. In contrast, secretion of interleukin-8 and tumor necrosis factor were reduced. In both, T(84) IEC and THP-1 monocytes, autophagosome formation was impaired. CONCLUSIONS: We identified a novel CD-associated PTPN2 variant that modulates innate immune responses to bacterial antigens. These findings not only provide key insights into the effects of a functional mutation on a clinically relevant gene, but also reveal how such a mutation could contribute to the onset of disease.