Increased Levels of ER Stress and Apoptosis in a Sheep Model for Pulmonary Fibrosis Are Alleviated by In Vivo Blockade of the KCa3.1 Ion Channel.

Udari E Perera,Louise Organ,Habtamu B Derseh,Andrew Stent,Sasika N V Dewage,Kenneth J Snibson,Pierachille Santus

doi:10.1155/2021/6683195

Udari E Perera, Louise Organ + Show 5 more

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https://doi.org/10.1155/2021/6683195

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Abstract

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease, characterized by progressive damage to the lung tissues. Apoptosis and endoplasmic reticulum stress (ER stress) in type II alveolar epithelial cells (AECs) and lung macrophages have been linked with the development of IPF. Therefore, apoptosis- and ER stress-targeted therapies have drawn attention as potential avenues for treatment of IPF. The calcium-activated potassium ion channel KCa3.1 has been proposed as a potential therapeutic target for fibrotic diseases including IPF. While KCa3.1 is expressed in AECs and macrophages, its influence on ER stress and apoptosis during the disease process is unclear. We utilized a novel sheep model of pulmonary fibrosis to demonstrate that apoptosis and ER stress occur in type II AECs and macrophages in sheep with bleomycin-induced lung fibrosis. Apoptosis in type II AEC and macrophages was identified using the TUNEL method of tagging fragmented nuclear DNA, while ER stress was characterized by increased expression of GRP-78 ER chaperone proteins. We demonstrated that apoptosis and ER stress in type II AECs and macrophages increased significantly 2 weeks after the final bleomycin infusion and remained high for up to 7 weeks post-bleomycin injury. Senicapoc treatment significantly reduced the rates of ER stress in type II AECs and macrophages that were resident in bleomycin-infused lung segments. There were also significant reductions in the rates of apoptosis of type II AECs and macrophages in the lung segments of senicapoc-treated sheep. In vivo blockade of the KCa3.1 ion channel alleviates the ER stress and apoptosis in type II AECs and macrophages, and this effect potentially contributes to the anti-fibrotic effects of senicapoc.

Highlights

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by progressive damage to the lung tissues, which in turn leads to the impairment of the gas exchange function of the lungs [1,2,3]
endoplasmic reticulum (ER) stress in type II alveolar epithelial cells (AECs) and lung macrophages was shown by red cytoplasmic staining, indicating elevated expression of GRP78 proteins in (Figure 1(c)). e rate of ER stress in type II AECs was significantly increased in sheep lung tissues two weeks after they were infused with bleomycin (Figure 1(d))
KCa3.1 Ion Channel Blockade Significantly Attenuates ER Stress and Apoptosis in Type II AEC and Lung Macrophages in Lung Fibrosis Induced by Bleomycin. e KCa3.1 ion channel has been shown to play a crucial role in the development of ER stress and apoptosis in type II AECs and lung macrophages [18]. erefore, we investigated whether ER stress and apoptosis in type II AECs and lung macrophages can be reduced by blocking the Ca2+-activated K+ ion channel (KCa3.1) using the KCa3.1-specific ion channel-blocking drug senicapoc

Summary

Introduction

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterized by progressive damage to the lung tissues, which in turn leads to the impairment of the gas exchange function of the lungs [1,2,3]. E ER is a special organelle normally responsible for the folding synthesized proteins and subsequent vesicular transport of proteins to the Golgi apparatus. E progression of IPF involves many disease elements including activation of transforming growth factor β (TGFβ) and other chemokines, type II alveolar epithelial cell (AECs) apoptosis, ineffective removal of apoptotic cells, and aberrant wound healing and endoplasmic reticulum (ER) stress [8, 9]. Factors such as Ca2+ depletion, redox homeostatic alteration, nutrient deprivation, and environmental insults can affect these folding processes, eventually leading to accumulation of unfolded proteins which disrupt the ER function, resulting in ER stress [10]. Caspase-12 enables specific cleavage of caspase-9, which together with downstream effects eventually leads to apoptosis [11]

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