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Cleaved cytokeratin-18 is a mechanistically informative biomarker in idiopathic pulmonary fibrosis

  • Author(s): Cha, SI
  • Ryerson, CJ
  • Lee, JS
  • Kukreja, J
  • Barry, SS
  • Jones, KD
  • Elicker, BM
  • Kim, DS
  • Papa, FR
  • Collard, HR
  • Wolters, PJ
  • et al.
Abstract

Background: Stress of the endoplasmic reticulum (ER) leading to activation of the unfolded protein response (UPR) and alveolar epithelial cell (AEC) apoptosis may play a role in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Our objectives were to determine whether circulating caspase-cleaved cytokeratin-18 (cCK-18) is a marker of AEC apoptosis in IPF, define the relationship of cCK-18 with activation of the UPR, and assess its utility as a diagnostic biomarker.Methods: IPF and normal lung tissues were stained with the antibody (M30) that specifically binds cCK-18. The relationship between markers of the UPR and cCK-18 was determined in AECs exposed in vitro to thapsigargin to induce ER stress. cCK-18 was measured in serum from subjects with IPF, hypersensitivity pneumonitis (HP), nonspecific interstitial pneumonia (NSIP), and control subjects.Results: cCK-18 immunoreactivity was present in AECs of IPF lung, but not in control subjects. Markers of the UPR (phosphorylated IRE-1α and spliced XBP-1) were more highly expressed in IPF type II AECs than in normal type II AECs. Phosphorylated IRE-1α and cCK-18 increased following thapsigargin-induced ER stress. Serum cCK-18 level distinguished IPF from diseased and control subjects. Serum cCK-18 was not associated with disease severity or outcome.Conclusions: cCK-18 may be a marker of AEC apoptosis and UPR activation in patients with IPF. Circulating levels of cCK-18 are increased in patients with IPF and cCK-18 may be a useful diagnostic biomarker. © 2012 Cha et al.; licensee BioMed Central Ltd.

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