Epithelial proliferation in inflammatory skin disease is regulated by tetratricopeptide repeat domain 7 (Ttc7) in fibroblasts and lymphocytes

Publication date: Available online 14 June 2018
Source:Journal of Allergy and Clinical Immunology
Author(s): Ursina Nüesch, Andrea A. Mauracher, Lennart Opitz, Benjamin Volkmer, Katarzyna Michalak-Mićka, Jivko Kamarashev, Tom Hartwig, Ernst Reichmann, Burkhard Becher, Stefano Vavassori, Jana Pachlopnik Schmid
BackgroundMutations in tetratricopeptide repeat domain 7A (TTC7A) and its mouse orthologue, Ttc7, result in a multisystemic disease, mostly affecting the epithelial barriers and immune system. Despite successful hematopoietic stem cell transplantation, ongoing progression of gastrointestinal manifestations can be life-threatening in TTC7A-deficient patients.ObjectiveWe sought to identify whether TTC7A mutations dysregulate epithelial cells only or whether a cell-intrinsic defect in lymphocytes or other cells contributes to disease manifestations.MethodsTtc7-mutated (Ttc7^fsn/fsn) mice were crossed to generate double-mutant (Rag2^−/−Ttc7^fsn/fsn) and triple-mutant (Rag2^−/−IL2rg^−/−Ttc7^fsn/fsn) mice. These models, together with bone marrow chimeras, were used to explore the role of adaptive and innate lymphocytes in the flaky skin phenotype. The effect of the Ttc7^fsn/fsn mutation on stromal cells was tested in a xenograft model in conjunction with transcriptomic analysis of Ttc7^fsn/fsn fibroblasts.ResultsWe observed that the severity of epithelial hyperproliferation was accentuated by lymphocytes, whereas the phenotype was not induced by transfer of Ttc7-mutated hematopoietic cells. Furthermore, mice completely lacking the lymphocytic compartment were not protected from epithelial hyperproliferation. Ttc7-mutated mouse fibroblasts expressed increased transcript levels of insulin-like growth factor 1 (Igf1) and the antimicrobial protein regenerating islet-derived protein 3γ (Reg3γ). In a xenograft model Ttc7-mutated fibroblasts markedly increased epithelial proliferation of keratinocytes. Thus Ttc7-mutated fibroblasts were identified as potent instigators of epithelial hyperproliferation.ConclusionOur results reveal a previously unsuspected fundamental cell-extrinsic role of Ttc7. We have identified potential candidates for molecularly targeted treatment strategies that will need to be evaluated in future preclinical studies.



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