Regulation and localization of the Telomerase- and the Shelterin-telosom-complex in sporadic Idiopathic Pulmonary Fibrosis

Abstract

Introduction: Idiopathic pulmonary fibrosis (IPF) is an adult-onset, lethal, scarring lung disease of unknown etiology. Reports linking telomerase mutations to familial IPF suggest that reduced telomerase activity and defective telomere length maintenance are key factors in disease pathogenesis. Accelerated telomere shortening is also observed in sporadic IPF in the absence of gene mutations. We therefore aimed to analyze the expression of the Telomerase- [TERT,TERC,DKC1,NOP10,NHP2] and the Shelterin-telosom-complex [TERF1/-2,POT1,TIN2,PTOP,RAP1] in lungs from patients with sporadic IPF (n=30) and organ donors (n=12). Methods: Peripheral lung tissue was analyzed by RT-PCR, immunoblotting and immunohistochemistry (IHC). Results: Gene expression analysis for TERT and the telomerase RNA-component TERC by RT-PCR indicated a significant downregulation in IPF lungs. Using immunoblotting, we observed no significant differences in expression of Telomerase-/Shelterin-components in IPF- and donor lungs. Surprisingly, we could not detect any protein expression of Telomerase- and Shelterin-components in type-II cells of IPF- and donor lungs by means of conventional IHC. Instead, we observed a strong TERT expression in a subset of Clara cells (CC10-positive) in IPF- and donor lungs, and expression of POT1 (protection of telomeres1) was exclusively localized in a subset of TERT-negative Clara cells in both categories. The other Shelterin-members revealed strong expression in myofibroblasts of fibroblast foci [RAP1] and/or in basal cells at sites of aberrant bronchiolar proliferation [PTOP,TIN2,TERF2,RAP1]. Conclusion: We carefully suggest that the robust expression of TERT/POT1 in CC10-positive cells of IPF- and donor lungs might indicate a cell population with stem cell characteristics. The upregulation of Shelterin-components in myofibroblasts and/or basal cells may explain the persistence of myofibroblasts and the exaggerated proliferation of bronchiolar basal cells in IPF.