Cigarette smoke contributes to 90% of lung cancer cases and 80% of COPD cases. These concerns loom large as lung cancer represents 13% of all cancer deaths and estimates report by 2020 COPD will be the third leading cause of death in the world. The master regulator of the ER stress response, IRE-1, in the context of cigarette smoke exposure lacks study. Interestingly, its downstream pathways are activated. In fact, the 2014 Surgeon General’s report on the health consequences of smoking highlighted the endoplasmic reticulum (ER) stress response as a potential mechanism leading to the development of lung cancer and Chronic Obstructive Pulmonary Disorder (COPD).
Following acute cigarette smoke exposure, mouse lung homogenates exhibited increased levels of XBP-1 along with downstream mediators of IRE-1 activation— GRP-78 and CHOP. Specifically observing macrophages, an important immune cell and source of acute inflammation, cigarette smoke induced activation of IRE-1/XBP-1 pathway through splicing of XBP-1 mRNA. However, upon assaying for pro-inflammatory cytokines we were unable to determine that cigarette smoke directly caused inflammation in vitro. Furthermore, cigarette smoke inhibited the activation of M2 macrophages, an anti-inflammatory and tissue healing subset seen through CCL18 inhibition.
A majority of M2 and M1 macrophage markers were decreased from IRE-1/XBP-1 inhibition. This suggests a different phenotype than classical M1 or M2 polarization being induced by cigarette smoke. In addition, it suggests the IRE-1/XBP-1 pathway having a robust role in controlling gene expression and balance of cellular proteomics. / Thesis / Master of Science (MSc) / Cigarette smoke exposure damages the lungs and over time places the user at risk for increased infections, progressive decreases in lung function and cancer.
A specific cell of the immune system and found in the lungs, macrophages or “Big Eater” cells, responds first by picking up debris and responding to harmful foreign substances by releasing proteins signaling the immune system to become activated.
Within all animal cells, an organelle called the Endoplasmic Reticulum (ER) manufactures a third of proteins produced allowing the cell to adapt to foreign substances, including cigarette smoke. Cigarette smoke could cause the ER, a plastic organelle, to change in size and function at a heightened level due to activation of a sensing protein integrated in the ER, Inositol Requiring Enzyme-1 (IRE-1).
Both activation of the ER and cigarette smoke causes macrophages to behave as “tissue-healing” or M2 subsets that release factors promoting reconstruction of the lungs; alternatively, M1 macrophages fight diseases and promote further inflammation. Using genetic analysis of macrophages exposed to cigarette smoke in culture dishes and analyzing the proteins secreted, we determined cigarette smoke inhibits M1 macrophages and the “tissue-healing” subset, while increasing adhesion molecule expression.
Overall, cigarette smoke affected the polarization of M1 and M2 phenotype, analyzed through proteins and genes expression. We observed an increase in sXBP-1, indicative of IRE-1/XBP-1 pathway activation, from cigarette smoke extract exposure in macrophages. However, the use of IRE-1 inhibitors increased ER stress markers while affecting M1 and M2 markers. This suggests ER compensation from the use of inhibiting one arm of the ER stress response.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22319 |
| Date | January 2017 |
| Creators | Mahmood, Sohail Hassan |
| Contributors | Ask, Kjetil, Medical Sciences (Molecular Virology and Immunology Program) |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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