GRP78 and CHOP modulate macrophage apoptosis and the development of bleomycin-induced pulmonary fibrosis

Abstract

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been associated with fibrotic lung disease, although exactly how they modulate this process remains unclear. Here we investigated the role of GRP78, the main UPR regulator, in an experimental model of lung injury and fibrosis. Grp78(+/-) , Chop(-/-) and wild type C57BL6/J mice were exposed to bleomycin by oropharyngeal intubation and lungs were examined at days 7 and 21. We demonstrate here that Grp78(+/-) mice were strongly protected from bleomycin-induced fibrosis, as shown by immunohistochemical analysis, collagen content and lung function measurements. In the inflammatory phase of this model, a reduced number of lung macrophages associated with an increased number of TUNEL-positive cells were observed in Grp78(+/-) mice. Dual immunohistochemical and in situ hybridization experiments showed that the macrophage population from the protected Grp78(+/-) mice was also strongly positive for cleaved caspase-3 and Chop mRNA, respectively. In contrast, the administration of bleomycin to Chop(-/-) mice resulted in increased quasi-static elastance and extracellular matrix deposition associated with an increased number of parenchymal arginase-1-positive macrophages that were negative for cleaved caspase-3. The data presented indicate that the UPR is activated in fibrotic lung tissue and strongly localized to macrophages. GRP78- and CHOP-mediated macrophage apoptosis was found to protect against bleomycin-induced fibrosis. Overall, we demonstrate here that the fibrotic response to bleomycin is dependent on GRP78-mediated events and provides evidence that macrophage polarization and apoptosis may play a role in this process. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Oxidative and endoplasmic reticulum stress in respiratory disease

“…ER stress develops in airway cells in this model and is exacerbated by viral infection, and the UPR has been associated with the differentiation status of macrophages, and intrinsic ER stress within macrophages also occurs 16, 71, 75, 83, 84, 85, 86…”

Separate roles of IL‐6 and oncostatin M in mouse macrophage polarization in vitro and in vivo

“…Polarization of macrophages toward the M1 and M2 phenotype was established by assessing nitric oxide in the cell supernatant and arginase activity in the cell lysates, respectively. Nitric oxide was quantified using the griess reagent kit (Life technologies) and arginase activity was determined as described previously …”

Resetting proteostasis with ISRIB prevents pulmonary fibrosis

“…While genes involved in the maintenance of telomere length are ubiquitously expressed, loss of function mutations in these genes targeted to alveolar type II cells induce spontaneous or more severe fibrosis in animal models (64,65). Consistent with these findings, genetic and pharmacologic strategies to inhibit ER stress have been reported to reduce bleomycin-induced fibrosis (34,36,66).…”