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Regulation of proteostasis and proteasome function by cigarette smoke
Regulation of proteostasis and proteasome function by cigarette smoke
Chronic obstructive pulmonary disease (COPD) is a chronic lung disease characterized by an irreversible and progressive airflow limitation associated with an exaggerated inflammatory response of the lung. Lungs of COPD patients show an abnormal infiltration of innate and adaptive immune cells. In particular, the increased amount of CD8+ T cells has been shown to correlate with lung tissue injury and disease severity. COPD pathogenesis progresses with acute exacerbations, which refer to periods of worsening of respiratory capacities often due to pathogen infections of the lungs. Cigarette smoke is the most important risk factor for the development of COPD. Cigarette smoke causes oxidative stress in the lung leading to repetitive challenges of the cellular protein homeostasis machinery and to adaptive immune responses. Protein homeostasis includes all cellular processes of synthesis, maturation, folding and degradation that occur during the life cycle of proteins and is responsible for maintaining proteome stability. The proteasome is the major proteolytic machinery in the cell and is responsible for the degradation of short-lived, but also misfolded and/or damaged proteins, therefore protecting the cell from proteotoxic stress. The proteasome trims intracellular proteins into small peptides that are loaded into MHC class I grooves for presentation to the immune system via binding with CD8+ T cell receptors. Furthermore, the immunoproteasome is a type of proteasome induced during infections and particularly specialized in enhancing antigen presentation by producing peptides that efficiently bind MHC class I molecules. The first publication included in this thesis (Mossina et al. 2017) investigated the effects of acute cigarette smoke exposure in vitro on the proteome of alveolar lung epithelial cells. We observed an impaired proteome stability that consisted mostly of downregulation of secreted cellular proteins. In particular, we identified altered regulation of cellular proteins involved in extracellular matrix organization and wound-healing responses. This acute response of the lung epithelium to cigarette smoke could lead to a dysregulated lung epithelium secretome which may contribute to tissue destruction and remodeling as observed in COPD patients. The second publication of this thesis (Kammerl et al. 2016) studied the effects of cigarette smoke on immunoproteasome function in vitro in murine immune cells and in vivo in mice and in COPD patients. We observed reduced immunoproteasome mRNA levels in BAL cells and in isolated macrophages from COPD patients. Immunoproteasome activity was severely impaired, both in COPD lung tissue and in vitro in murine immune cells exposed to cigarette smoke extract. Most importantly, in murine immune cells, the decline in immunoproteasome activity was associated with reduced presentation of an immunoproteasome-dependent MHC class I epitope. The use of activity-based probes enabled us to monitor the ratio between single immunoproteasome active subunits and their standard proteasome counterpart. We observed that in isolated macrophages of mice that had been acutely exposed to cigarette smoke the activity shifted from immuno- to standard proteasome after 10 days of smoke exposure. Presentation of an immunoproteasome-dependent MHC class I epitope similarly followed the course of immunoproteasome activity, with a major impairment at day 10. Such dysfunction in MHC class I antigen presentation could contribute to the impaired clearance of pathogens in COPD lungs driving disease exacerbations. Taken together, our results show that cigarette smoke at non-toxic doses affects proteome stability and composition. We observed, particularly, that a dysfunctional proteome is a major response of the lung epithelium to acute cigarette smoke exposure. As an important player in proteome stability and antigen presentation, the immunoproteasome is as well affected by cigarette smoke. Reduced immunoproteasome activity and diminished presentation of an immunoproteasome-dependent MHC class I epitope establish a causal link between cigarette smoke and the altered immune system response that may also apply to COPD pathogenesis. In particular, alterations in the antigen presentation process may contribute to increase susceptibility to virus-induced exacerbations finally resulting in autoimmune responses.
Chronic obstructive pulmonary disease, Proteasome, Immunoproteasome, Cigarette smoke, MHC class I presentation, Proteostasis
Mossina, Alessandra
2020
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Mossina, Alessandra (2020): Regulation of proteostasis and proteasome function by cigarette smoke. Dissertation, LMU München: Faculty of Medicine
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Abstract

Chronic obstructive pulmonary disease (COPD) is a chronic lung disease characterized by an irreversible and progressive airflow limitation associated with an exaggerated inflammatory response of the lung. Lungs of COPD patients show an abnormal infiltration of innate and adaptive immune cells. In particular, the increased amount of CD8+ T cells has been shown to correlate with lung tissue injury and disease severity. COPD pathogenesis progresses with acute exacerbations, which refer to periods of worsening of respiratory capacities often due to pathogen infections of the lungs. Cigarette smoke is the most important risk factor for the development of COPD. Cigarette smoke causes oxidative stress in the lung leading to repetitive challenges of the cellular protein homeostasis machinery and to adaptive immune responses. Protein homeostasis includes all cellular processes of synthesis, maturation, folding and degradation that occur during the life cycle of proteins and is responsible for maintaining proteome stability. The proteasome is the major proteolytic machinery in the cell and is responsible for the degradation of short-lived, but also misfolded and/or damaged proteins, therefore protecting the cell from proteotoxic stress. The proteasome trims intracellular proteins into small peptides that are loaded into MHC class I grooves for presentation to the immune system via binding with CD8+ T cell receptors. Furthermore, the immunoproteasome is a type of proteasome induced during infections and particularly specialized in enhancing antigen presentation by producing peptides that efficiently bind MHC class I molecules. The first publication included in this thesis (Mossina et al. 2017) investigated the effects of acute cigarette smoke exposure in vitro on the proteome of alveolar lung epithelial cells. We observed an impaired proteome stability that consisted mostly of downregulation of secreted cellular proteins. In particular, we identified altered regulation of cellular proteins involved in extracellular matrix organization and wound-healing responses. This acute response of the lung epithelium to cigarette smoke could lead to a dysregulated lung epithelium secretome which may contribute to tissue destruction and remodeling as observed in COPD patients. The second publication of this thesis (Kammerl et al. 2016) studied the effects of cigarette smoke on immunoproteasome function in vitro in murine immune cells and in vivo in mice and in COPD patients. We observed reduced immunoproteasome mRNA levels in BAL cells and in isolated macrophages from COPD patients. Immunoproteasome activity was severely impaired, both in COPD lung tissue and in vitro in murine immune cells exposed to cigarette smoke extract. Most importantly, in murine immune cells, the decline in immunoproteasome activity was associated with reduced presentation of an immunoproteasome-dependent MHC class I epitope. The use of activity-based probes enabled us to monitor the ratio between single immunoproteasome active subunits and their standard proteasome counterpart. We observed that in isolated macrophages of mice that had been acutely exposed to cigarette smoke the activity shifted from immuno- to standard proteasome after 10 days of smoke exposure. Presentation of an immunoproteasome-dependent MHC class I epitope similarly followed the course of immunoproteasome activity, with a major impairment at day 10. Such dysfunction in MHC class I antigen presentation could contribute to the impaired clearance of pathogens in COPD lungs driving disease exacerbations. Taken together, our results show that cigarette smoke at non-toxic doses affects proteome stability and composition. We observed, particularly, that a dysfunctional proteome is a major response of the lung epithelium to acute cigarette smoke exposure. As an important player in proteome stability and antigen presentation, the immunoproteasome is as well affected by cigarette smoke. Reduced immunoproteasome activity and diminished presentation of an immunoproteasome-dependent MHC class I epitope establish a causal link between cigarette smoke and the altered immune system response that may also apply to COPD pathogenesis. In particular, alterations in the antigen presentation process may contribute to increase susceptibility to virus-induced exacerbations finally resulting in autoimmune responses.