Smoking alters pulmonary reverse lipid transport and leads to intracellular lipid accumulation in alveolar macrophages. We investigated whether stimulating reverse lipid transport with an agonist of the liver X receptor (LXR) would help alveolar macrophages limit lipid accumulation and dampen lung inflammation in response to cigarette smoke. Mice were exposed to cigarette smoke and treated intraperitoneally with the LXR agonist T0901317. Expression of lipid capture and lipid export genes was assessed in lung tissue and alveolar macrophages. Pulmonary inflammation was assessed in the bronchoalveolar lavage (BAL). Finally, cholesterol efflux capacity and pulmonary surfactant levels were determined. In room air-exposed mice, T0901317 increased the expression of lipid export genes in macrophages and the whole lung and increased cholesterol efflux capacity without inducing inflammation or affecting the pulmonary surfactant. However, cigarette smoke-exposed mice treated with T0901317 showed a marked increase in BAL neutrophils, IL-1α, C-C motif chemokine ligand 2, and granulocyte-colony-stimulating factor levels. T0901317 treatment in cigarette smoke-exposed mice failed to increase the ability of alveolar macrophages to export cholesterol and markedly exacerbated IL-1α release. Finally, T0901317 led to pulmonary surfactant depletion only in cigarette smoke-exposed mice. This study shows that hyperactivation of LXR and the associated lipid capture/export mechanisms only have minor pulmonary effects on the normal lung. However, in the context of cigarette smoke exposure, where the pulmonary surfactant is constantly oxidized, hyperactivation of LXR has dramatic adverse effects, once again showing the central role of lipid homeostasis in the pulmonary response to cigarette smoke exposure.
Cigarette smoke exposure induces inflammation marked by rapid and sustained neutrophil infiltration, IL-1α, release and altered surfactant homeostasis. However, the extent to which neutrophils and IL-1α contribute to the maintenance of pulmonary surfactant homeostasis is not well understood. We sought to investigate whether neutrophils play a role in surfactant clearance as well as the effect of neutrophil depletion and IL-1α blockade on the response to cigarette smoke exposure. In vitro and in vivo administration of fluorescently labeled surfactant phosphatidylcholine was used to assess internalization of surfactant by lung neutrophils and macrophages during or following cigarette smoke exposure in mice. We also depleted neutrophils using anti–Ly-6G or anti–Gr-1 Abs, or we neutralized IL-1α using a blocking Ab to determine their respective roles in regulating surfactant homeostasis during cigarette smoke exposure. We observed that neutrophils actively internalize labeled surfactant both in vitro and in vivo and that IL-1α is required for smoke-induced elevation of surfactant protein (SP)–A and SP-D levels. Neutrophil depletion during cigarette smoke exposure led to a further increase in SP-A levels in the bronchoalveolar lavage and increased IL-1α, CCL2, GM-CSF, and G-CSF release. Finally, macrophage expression of Mmp12, a protease linked to emphysema, was increased in neutrophil-depleted groups and decreased following IL-1α blockade. Taken together, our results indicate that neutrophils and IL-1α signaling are actively involved in surfactant homeostasis and that the absence of neutrophils in the lungs during cigarette smoke exposure leads to an IL-1α–dependent exacerbation of the inflammatory response.
Vaping is increasingly popular among the young and adult population. Vaping liquids contained in electronic cigarettes (e‐cigarettes) are mainly composed of propylene glycol and glycerol, to which nicotine and flavors are added. Among several biological processes, glycerol is a metabolic substrate used for lipid synthesis in fed state as well as glucose synthesis in fasting state. We aimed to investigate the effects of glycerol e‐cigarette aerosol exposure on the aspects of glycerol and glucose homeostasis. Adult and young male and female mice were exposed to e‐cigarette aerosols with glycerol as vaping liquid using an established whole‐body exposure system. Mice were exposed acutely (single 2‐h exposure) or chronically (2 h/day, 5 days/week for 9 weeks). Circulating glycerol and glucose levels were assessed and glycerol as well as glucose tolerance tests were performed. The liver was also investigated to assess changes in the histology, lipid content, inflammation, and stress markers. Lung functions were also assessed as well as hepatic mRNA expression of genes controlling the circadian rhythm. Acute exposure to glycerol aerosols generated by an e‐cigarette increased circulating glycerol levels in female mice. Increased hepatic triglyceride and phosphatidylcholine concentrations were observed in female mice with no increase in circulating alanine aminotransferase or evidence of inflammation, fibrosis, or endoplasmic reticulum stress. Chronic exposure to glycerol e‐cigarette aerosols mildly impacted glucose tolerance test in young female and male mice. Fasting glycerol, glucose, and insulin remained unchanged. Increased pulmonary resistance was observed in young male mice. Taken together, this study shows that the glycerol contained in vaping liquids can affect the liver as well as the aspects of glucose and glycerol homeostasis. Additional work is required to translate these observations to humans and determine the biological and potential pathological impacts of these findings.
Background A new mutation responsible for causing severe and early pulmonary emphysema was recently discovered in a French-Canadian family. The mutation is located in the PTPN6 gene (PTPN6Ala455Thr) leading to a reduction in the activity of SHP-1, a phosphatase that regulates numerous pathways including B cell differentiation and activation. Here, we aimed to characterize B cell abnormalities in both humans and mice carrying this mutation. Methods Circulating B cell populations in humans carrying the PTPN6Ala455Thr mutation were analyzed by flow cytometry and immunoglobulin levels were measured in serum. In mice carrying the same mutation (Ptpn6Ala457Thr) aged up to 12 months, B cell populations were analyzed by flow cytometry and lung tissue histology performed. Mice were immunized with the T cell-independent antigen NP-Ficoll and plasma was collected to assess NP-specific antibodies. Results Human carriers of the PTPN6Ala455Thr mutation had reduced IgG1 and IgG4, and increased IgG3 levels as well as high circulating immature/mature B cell ratio compared to controls. Aging Ptpn6Ala457Thr mice developed spontaneous pulmonary tertiary lymphoid tissues and exhibited higher B-1 cells and lower B-2 cells proportions in the lung and spleen. Ptpn6Ala457Thr mice had lower levels of NP-specific IgG1 antibodies compared to the wild-type group, but normal IgG3 in response to NP-Ficoll immunization. Conclusion SHP-1 appears to be important to B cell development and functions, as the PTPN6Ala455Thr mutation seems to cause a form of subclinical immunodeficiency that affects B cell populations and immunoglobulin levels. The link between B cell abnormalities and development of pulmonary emphysema requires further investigation. Supported by grants from Canadian Institutes of Health and Research and Fonds de Recherche du Québec- Santé
A new mutation (PTPN6Ala455Thr) was recently discovered in a family in which many members developed a severe, early and panacinar form of pulmonary emphysema. The mutation was found to be located in the PTPN6 gene, encoding a tyrosine phosphatase known as SHP-1. SHP-1 regulates immunological signaling pathways, such as those involved in B cells maturation and activation. To characterize the impact of the ptpn6Ala457Thr mutation in a mouse model on subpopulations of B lymphocytes and on their response to immunization. Proportions of B1a et B2 cells were analyzed in the lungs and spleens of 4-month old mice carrying the ptpn6Ala457Thr mutation by flow cytometry. Serum immunoglobulin levels were assessed. Another group of mice were immunized with a T cells-independent antigen (NP-Ficoll, 50ug i.p.). Plasma was collected at different timepoints after immunization and NP-specific antibodies were measured by ELISA (IgG1, IgG3, IgM and IgA). Mice carrying the ptpn6Ala457Thr mutation mice had a higher proportion of B1a cells and a lower proportion of B2 cells in the spleen and in the lungs. Total IgG and IgM levels in the serum were higher in ptpn6Ala457Thr mice compared to wild-type animals. Following immunization with NP-Ficoll, ptpn6Ala457Thr mice displayed levels of NP-specific IgG3 and IgM similar to those observed in wild-type mice. However, ptpn6Ala457Thr mice had lower levels of NP-specific IgG1 antibodies compared to the wild-type group. SHP-1 seems to be important for B cell differentiation and functions, as the mutation led to significant changes in B cell subpopulations. It seems that SHP-1 plays an important role in the immune response to immunization. The full scope of the immunological effects of this mutation requires further study.
Rationale: Smoking status and smoking history remain poorly accounted for as variables that could affect the efficacy of new drugs being tested in chronic obstructive pulmonary disease (COPD) patients. As a proof of concept, we used a pre-clinical model of cigarette smoke (CS) exposure to compare the impact of treatment during active CS exposure or during the cessation period on the anti-inflammatory effects IL-1α signaling blockade.Methods: Mice were exposed to CS for 2 weeks, followed by a 1-week cessation, then acutely re-exposed for 2 days. Mice were treated with an anti-IL-1α antibody either during CS exposure or during cessation and inflammatory outcomes were assessed.Results: We found that mice re-exposed to CS displayed reduced neutrophil counts and cytokine levels in the bronchoalveolar lavage (BAL) compared to mice exposed only acutely. Moreover, we found that treatment with an anti-IL-1α antibody during the initial CS exposure delayed inflammatory processes and interfered with pulmonary adaptation, leading to rebound pulmonary neutrophilia, increased BAL cytokine secretion (CCL2) and upregulated Mmp12 expression. Conversely, administration of anti-IL-1α during cessation had the opposite effect, improving BAL neutrophilia, decreasing CCL2 levels and reducing Mmp12 expression.Discussion: These results suggest that pulmonary adaptation to CS exposure dampens inflammation and blocking IL-1α signaling during CS exposure delays the inflammatory response. More importantly, the same treatment administered during cessation hastens the return to pulmonary inflammatory homeostasis, strongly suggesting that smoking status and treatment timing should be considered when testing new biologics in COPD.
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