Transcriptomic analysis of the efficacy of TG2-inhibitor trials and human intestinal organoids modelling Celiac disease pathogenesis

by Keijo Viiri
 
TG2 in Celiac disease (CeD)    
Gluten-containing cereals are essential food worldwide and in up to 2% of individuals¹, the ingestion of dietary gluten results in an abnormal immune response in the small intestine and the development of Celiac disease (CeD). Predisposing genotypes human leukocyte antigen (HLA)-DQ2 and HLA-DQ8 are necessary but not sufficient for the manifestation of CeD. Diarrhea, weight loss and malnutrition are classical bowel-related symptoms and signs of CeD but also anemia, osteoporosis, and other autoimmune diseases such as type 1 diabetes are frequently manifested^2–4. The CeD autoantigen, transglutaminase 2 (TG2), is expressed in the intestine and deamidates certain neutral glutamine residues to negatively charged glutamic acid residues in the immunogenic gluten peptides^5–7. These modified gluten-peptides are more efficiently presented by HLA-DQ2 or HLA-DQ8 molecules on mucosal antigen-presenting cells and this leads to activation and expansion of gluten-specific CD4+ type 1 helper T cells and the secretion of proinflammatory cytokines^8,9. Until now a strict lifelong gluten-free diet (GFD) is the only accepted treatment option for patients with CeD. However, the life-long strict and restrictive GFD is onerous and difficult to follow and inadvertent gluten ingestion is common^10,11.     
 
Molecular histomorphometry to detect the efficacy of the TG2-inhibitor to treat CeD    
In our previous study we showed that CeD patients on a GFD, despite having normal mucosal morphology, still suffer from deficient gene expression¹². Especially genes encoding nutrient transporters are significantly less expressed compared to healthy controls, which probably contributes to reported micronutrient deficiency amongst CeD patients on a GFD. This suggests that more sensitive methods, by virtue of molecular histomorphometry, are needed to detect these stealthy molecular scars in CeD. This study also proved that additional therapy is needed, and this call was recently addressed in the clinical study where we performed molecular histomorphometric assessment of the efficacy of TG2-inhibitor, ZED1227¹³. At the transcriptome level, orally administered ZED1227 effectively prevented gluten-induced intestinal damage and inflammation, providing molecular-level evidence that TG2 inhibition is an effective strategy for treating CeD. ZED1227 treatment preserved transcriptome signatures associated with mucosal morphology, inflammation, cell differentiation and nutrient absorption to the level of the gluten-free diet group.    
 
Enteroviruses, CeD and TG2     
It has been shown that higher gluten intake increases the risk on CeD^14,15 but it is not clear why not all genetically predisposed HLA-DQ2 and/or DQ8 positive individuals develop the disease. The possible role of enterovirus infections as a trigger for breaking oral tolerance to gluten, have been set forth^16–18. The current problem is that the exact molecular pathways triggered by enteric viruses that lead to CeD are not yet understood, making it challenging to develop interventions for inclusion in CeD treatment plans. We have previously shown that TG2 expression correlates with the epithelial response to IFN-γ and TG2 is induced by IFN-γ in human organoids in vitro¹³. We hypothesise that this Interferon response and accompanying TG2 induction are also the mechanisms how virus infections can disrupt the immune tolerance to gluten in CeD. To this end we are studying the mechanisms and molecular pathways how Coxsackie B virus infection in human intestinal organoids possibly induces TG2. Human intestinal organoids are self-organizing “mini-intestines” composed of all the epithelial cell types and thus are convenient tool to study pathogenic mechanism involved in CeD.
 

 
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