Pulmonary lipid homeostasis in cigarette smoke-associated lung diseases

Authors: Jubinville, Éric
Advisor: Arsenault, BenoitMorissette, Mathieu
Abstract: Introduction. Cigarette smoking remains a major problem in our society.While a lot of cigarette smoke impacts are actually known, few data are available on initiating mechanisms involved in the pulmonary immune response to cigarette smoke. One of the most intriguing phenomena under cigarette smoke exposure conditions is the presence of enlarged alveolar macrophages. This phenotypic change is characterized by an intracellular lipid accumulation which may be a sign of inadequate lipid export by alveolar macrophages induced by cigarette smoking. Pulmonary lipid transport begins with lipid capture, lipid reorganization and lipid droplet formation followed by lipid export by alveolar macrophages. Cigarette smoke impacts on these steps are actually unknown. Hypothesis. Cigarette smoking alters pulmonary lipid transport. Objectives: Chapter 1) To investigate the effect of cigarette smoke exposure on pulmonary lipid transport in cigarette smoke-exposed mice and in healthy controls, smokers and former smokers. To investigate the impact of high-density lipoprotein (HDLs) therapeutic potential in cigarette smoke-exposed mice. Chapter 2) To investigate, in mice, the therapeutic potential of an agonist activating the nuclear receptor liver X receptor (LXR) involved in the transcription of lipid export genes. Chapter 3) To explore, in mice, if a dietary deficiency alters the pulmonary health and the pulmonary response to cigarette smoke. Methods. 1. The pulmonary transcriptome of cigarette smoke-exposed mice and healthy controls, smokers and former smokers was assessed. Cholesterol efflux capacity of serum and bronchoalveolar lavage (BAL) was measured in unexposed and cigarette smoke-exposed mice. MDCO-216, a recombinant HDL, was administered to unexposed and cigarette smoke-exposed mice and analyzed their pulmonary immune response, lung functions and body composition. 2. T0901317, an LXR agonist, was systemically given to mice under cigarette smoke exposure conditions. Pulmonary genes associated with lipid transport, lungs and alveolar macrophage immune pulmonary response to cigarette smoke and the impact of T0901317 on the pulmonary surfactant were assessed. 3. Unexposed and cigarette smoke-exposed mice were fed with methionine deficient (MD), choline deficient (CD) or methionine and choline deficient (MCD) diet. Diets impact on lung functions, pulmonary immune response to cigarette smoke and pulmonary transcriptome were characterized. Results. Chapter 1. Cigarette smoking altered the expression of pulmonary lipid transport genes in mice and in humans. Serum and BALF cholesterol efflux capacities were increased following a twohour cigarette smoke exposure. MDCO-216 dampened the pulmonary inflammatory response and reduced the size of alveolar macrophages in our acute cigarette smoke exposure model. MDCO-216 also seemed to be beneficial to lung functions and induced an increase in lean mass in cigarette smokeexposed treated mice. Chapter 2. T0901317 treatments led to an increase in the expression of pulmonary lipid transport genes. However, it also induced an exacerbated pulmonary immune response during cigarette smoking. Cigarette smoke-exposed treated-alveolar macrophages displayed an exacerbated inflammatory phenotype and showed an augmented endoplasmic reticulum stress. Furthermore, LXR activation led to pulmonary surfactant depletion under cigarette smoke exposure conditions. Chapter 3. The MCD diet altered lung function displaying a restrictive profile and almost abolished the pulmonary immune response to cigarette smoke. Lung histology showed no signs of fibrosis, a phenotype usually associated with restrictive pulmonary functions. MCD diet led to a dramatic change in the pulmonary expression of extracellular matrix genes and also reduced pulmonary surfactant levels. Nevertheless, these pulmonary phenotypes were reversible within a week when mice were refed a control diet. Interestingly, the CD diet induced an emphysema-like profile, while MD diet showed similar pulmonary functions to the MCD diet. Conclusions. The present thesis adds major data to an underestimated field of research and demonstrates the importance of pulmonary lipid transport, especially during cigarette smoking. Recombinant HDL therapy with MDCO-216 may be a new opportunity to overcome adverse effects of cigarette smoking, while activating LXR seems rather deleterious. Nutrient deficiencies, such as methionine and choline led to unprecedented impacts on the pulmonary health and on the pulmonary response to cigarette smoke. This completely new field of research, “nutri-respiratory”, requires additional studies to fully decipher the impact of unhealthy nutrition on the respiratory system.
Document Type: Thèse de doctorat
Issue Date: 2019
Open Access Date: 19 September 2019
Permalink: http://hdl.handle.net/20.500.11794/36555
Grantor: Université Laval
Collection:Thèses et mémoires

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