Role of liver-X-receptors in airway remodeling in mice with chronic allergic asthma

Protective effect of liver X receptor on cigarette smoke and lipopolysaccharide induced airway inflammation and emphysema in mice

OBJECTIVE

The aim of this study is to assess the impact of Liver X receptors (LXRs) on airway inflammation, airway remodeling, and lipid deposition induced by cigarette smoke and lipopolysaccharide (LPS) exposure in the lung.

METHODS

Wild mice and LXR-deficient mice were exposed to cigarette smoke and LPS to induce airway inflammation and remodeling. In addition, some wild mice received intraperitoneal treatment with the LXR agonist GW3965 before exposure to cigarette smoke and LPS. Lung tissue and bronchoalveolar lavage fluid were collected to evaluate airway inflammation, airway remodeling and lipid deposition.

RESULTS

Exposure to cigarette smoke and LPS resulted in airway inflammation, emphysema and lipid accumulation in wild mice. These mice also exhibited downregulated LXRα and ABCA1 in the lung. Treatment with GW3965 mitigated inflammation, remodeling and lipid deposition, while the deletion of LXRs exacerbated these effects. Furthermore, GW3965 treatment following exposure to cigarette smoke and LPS increased LXRα and ABCA1 expression and attenuated MyD88 expression in wild mice.

CONCLUSION

LXRs demonstrate the potential to mitigate cigarette smoke and LPS- induced airway inflammation, emphysema and lipid disposition in mice.

Plasma levels of oxysterols 7-ketocholesterol and cholestane-3β, 5α, 6β-triol in patients with allergic asthma

The prevalence of allergic asthma is increasing on a global scale, reflecting changes in air pollution, climatic changes, and other environmental stimulants. In allergic conditions, oxidative stress occurs as a result of immune system activation. Oxidation of cholesterol leads to the formation of oxysterols. The main purpose of the study was to compare plasma levels of two oxysterols, namely 7-ketocholesterol (7-KC) and cholestane-3β, 5α, 6β-triol (C-triol), and a lipid peroxidation product, malondialdehyde (MDA) in allergic asthma patients with those of healthy controls, in order to provide information about the involvement of lipid peroxidation in allergic asthma.

Oxysterols were quantified by LC-MS/MS in plasma samples of 120 asthma patients (90 females + 30 males) and 120 healthy controls (matched by age and sex). Plasma MDA level was analyzed by a spectrophotometric method.

Plasma 7-KC (39.45 ± 20.37 ng/mL) and C-triol (25.61 ± 10.13 ng/mL) levels in patients were significantly higher than in healthy subjects (17.84 ± 4.26 ng/mL and 10.00 ± 3.90 ng/mL, respectively) (P < 0.001). Plasma MDA levels were also higher in asthmatic patients (4.98 ± 1.77 nmol/mL) than in healthy controls (1.14 ± 0.31 nmol/mL) (P < 0.001). All data support that lipid peroxidation products are involved in allergic asthma.

Oxysterols were quantified for the first time in allergic asthma. Since the high plasma 7-KC and C-triol levels of allergic asthma patients correlate with high IgE levels, detection of these oxysterols by LC-MS/MS may be helpful in the clinical monitoring of allergic asthma. Current data may also lead to new approaches for the prevention, diagnosis, and treatment of the disease.

Supplemental data for this article is available online at at.

Endocytosis of LXRs: Signaling in liver and disease

Nuclear receptors are among one of the major transcriptional factors that induces gene regulation in the nucleus. Liver X receptor (LXR) is a transcription factor which regulates essential lipid homeostasis in the body including fatty acid, cholesterol and phospholipid synthesis. Liver X receptor-retinoid X receptor (LXR-RXR) heterodimer is activated by either of the ligand binding on LXR or RXR. The promoter region of the gene which is targeted by LXR is bound to the response element of LXR. The activators bind to the heterodimer once the corepressor is dissociated. The cellular process such as endocytosis aids in intracellular trafficking and endosomal formation in transportation of molecules for essential signaling within the cell. LXR isotypes play a crucial role in maintaining lipid homeostasis by regulating the level of cholesterol. In the liver, the deficiency of LXRα can alter the normal physiological conditions depicting the symptoms of various cardiovascular and liver diseases. LXR can degrade low density lipoprotein receptors (LDLR) by the signaling of LXR-IDOL through endocytic trafficking in lipoprotein uptake. Various gene expressions associated with cholesterol level and lipid synthesis are regulated by LXR transcription factor. With its known diversified ligand binding, LXR is capable of regulating expression of various specific genes responsible for the progression of autoimmune diseases. The agonists and antagonists of LXR stand to be an important factor in transcription of the ABC family, essential for high density lipoprotein (HDL) formation. Endocytosis and signaling mechanism of the LXR family is broad and complex despite their involvement in cellular growth and proliferation. Here in this chapter, we aimed to emphasize the master regulation of LXR activation, regulators, and their implications in various metabolic activities especially in lipid homeostasis. Furthermore, we also briefed the significant role of LXR endocytosis in T cell immune regulation and a variety of human diseases including cardiovascular and neuroadaptive.

Asthma and Post-Asthmatic Fibrosis: A Search for New Promising Molecular Markers of Transition from Acute Inflammation to Pulmonary Fibrosis

Asthma is a heterogeneous pulmonary disorder, the progression and chronization of which leads to airway remodeling and fibrogenesis. To understand the molecular mechanisms of pulmonary fibrosis development, key genes forming the asthma-specific regulome and involved in lung fibrosis formation were revealed using a comprehensive bioinformatics analysis. The bioinformatics data were validated using a murine model of ovalbumin (OVA)-induced asthma and post-asthmatic fibrosis. The performed analysis revealed a range of well-known pro-fibrotic markers (Cat, Ccl2, Ccl4, Ccr2, Col1a1, Cxcl12, Igf1, Muc5ac/Muc5b, Spp1, Timp1) and a set of novel genes (C3, C3ar1, Col4a1, Col4a2, Cyp2e1, Fn1, Thbs1, Tyrobp) mediating fibrotic changes in lungs already at the stage of acute/subacute asthma-driven inflammation. The validation of genes related to non-allergic bleomycin-induced pulmonary fibrosis on asthmatic/fibrotic lungs allowed us to identify new universal genes (Col4a1 and Col4a2) associated with the development of lung fibrosis regardless of its etiology. The similarities revealed in the expression profiles of nodal fibrotic genes between asthma-driven fibrosis in mice and nascent idiopathic pulmonary fibrosis in humans suggest a tight association of identified genes with the early stages of airway remodeling and can be considered as promising predictors and early markers of pulmonary fibrosis.