Examining the role of ABC lipid transporters in pulmonary lipid homeostasis and inflammation

© The Author(s). 2017 Open Access Respiratory diseases including asthma and chronic obstructive pulmonary disease (COPD) are characterised by excessive and persistent inflammation. Current treatments are often inadequate for symptom and disease control, and hence new therapies are warranted. Recent emerging research has implicated dyslipidaemia in pulmonary inflammation. Three ATP-binding cassette (ABC) transporters are found in the mammalian lung - ABCA1, ABCG1 and ABCA3 - that are involved in movement of cholesterol and phospholipids from lung cells. The aim of this review is to corroborate the current evidence for the role of ABC lipid transporters in pulmonary lipid homeostasis and inflammation. Here, we summarise results from murine knockout studies, human diseases associated with ABC transporter mutations, and in vitro studies. Disruption to ABC transporter activity results in lipid accumulation and elevated levels of inflammatory cytokines in lung tissue. Furthermore, these ABC-knockout mice exhibit signs of respiratory distress. ABC lipid transporters appear to have a crucial and protective role in the lung. However, our knowledge of the underlying molecular mechanisms for these benefits requires further attention. Understanding the relationship between cholesterol and inflammation in the lung, and the role that ABC transporters play in this may illuminate new pathways to target for the treatment of inflammatory lung diseases

Regulation of ATP binding cassette transporter A1 (ABCA1) expression: cholesterol-dependent and - independent signaling pathways with relevance to inflammatory lung disease.

The role of the ATP binding cassette transporter A1 (ABCA1) in maintaining cellular lipid homeostasis in cardiovascular disease is well established. More recently, the important beneficial role played by ABCA1 in modulating pathogenic disease mechanisms, such as inflammation, in a broad range of chronic conditions has been realised. These studies position ABCA1 as a potential therapeutic target in a diverse range of diseases where inflammation is an underlying cause. Chronic respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD) are driven by inflammation, and as such, there is now a growing recognition that we need a greater understanding of the signaling pathways responsible for regulation of ABCA1 expression in this clinical context. While the signaling pathways responsible for cholesterol-mediated ABCA1 expression have been clearly delineated through decades of studies in the atherosclerosis field, and thus far appear to be translatable to the respiratory field, less is known about the cholesterol-independent signaling pathways that can modulate ABCA1 expression in inflammatory lung disease. This review will identify the various signaling pathways and ligands that are associated with the regulation of ABCA1 expression and may be exploited in future as therapeutic targets in the setting of chronic inflammatory lung diseases

The effect of statins and the synthetic LXR agonist T0901317 on expression of ABCA1 transporter protein in human lung epithelial cell lines in vitro

© 2019 Institute of Pharmacology, Polish Academy of Sciences Background: The pathogenesis of chronic obstructive pulmonary disease (COPD) is associated with dyslipidemia, an established co-morbidity. Statins treat hypercholesterolemia, but more recently have been trailed in the setting of COPD for their potential anti-inflammatory benefits. The outcomes of prospective trials however have been inconsistent. Thus, we hypothesize that the variation in results may have been due to statin-induced downregulation of ATP-binding cassette transporter A1 (ABCA1), thereby reducing cholesterol export. This study aims to elucidate whether statin treatment in a cellular model of COPD leads to a decrease in ABCA1 protein expression. Methods: To mimic the inflammatory environment of COPD, two commonly used lung epithelial cell lines (BEAS-2B and A549) were treated with tumor necrosis factor (TNF), and co-treated with cholesterol/25-hydroxycholesterol (25-OH) to mimic dyslipidemia. ABCA1 protein was detected by Western Blotting. Results: We unexpectedly showed that statins did not affect ABCA1 expression. However, the LXR agonist T0901317 significantly increased ABCA1 expression in both cell lines, while TNF, cholesterol or 25-OH induced ABCA1 protein upregulation in BEAS-2B cells, indicating cell line differences in response. There was also evidence of synergistic impacts of combined treatments on ABCA1 upregulation in BEAS-2B cells. Conclusion: Statins did not have an impact on ABCA1 expression in lung epithelial cell lines, disproving our original hypothesis. However, we showed for the first time, the effect of the inflammatory cytokine TNF, cholesterol/25-OH, statins and the LXR agonist T0901317 on expression of ABCA1 transporter protein in human lung epithelial cell lines in vitro. We hope that these in vitro studies may prove beneficial for addressing dyslipidemia in COPD in the future

Regulation of P-Glycoprotein in the Brain

Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood–brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity

IL-17A increases TNF-α-induced COX-2 protein stability and augments PGE<inf>2</inf> secretion from airway smooth muscle cells: Impact on β<inf>2</inf>-adrenergic receptor desensitization

© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Background IL-17A plays an important role in respiratory disease and is a known regulator of pulmonary inflammation and immunity. Recent studies have linked IL-17A with exacerbation in asthma and COPD. We have shown that the enzyme cyclooxygenase-2 (COX-2) and its prostanoid products, prostaglandin E2 (PGE2) in particular, are key contributors in in vitro models of infectious exacerbation; however, the impact of IL-17A was not known. Methods and Results We address this herein and show that IL-17A induces a robust and sustained upregulation of COX-2 protein and PGE2 secretion from airway smooth muscle (ASM) cells. COX-2 can be regulated at transcriptional, post-transcriptional and/or post-translational levels. We have elucidated the underlying molecular mechanisms responsible for the sustained upregulation of TNF-α-induced COX-2 by IL-17A in ASM cells and show that is not via increased COX-2 gene expression. Instead, TNF-α-induced COX-2 upregulation is subject to regulation by the proteasome, and IL-17A acts to increase TNF-α-induced COX-2 protein stability as confirmed by cycloheximide chase experiments. In this way, IL-17A acts to amplify the COX-2-mediated effects of TNF-α and greatly enhances PGE2 secretion from ASM cells. Conclusion As PGE2 is a multifunctional prostanoid with diverse roles in respiratory disease, our studies demonstrate a novel function for IL-17A in airway inflammation by showing for the first time that IL-17A impacts on the COX-2/PGE2 pathway, molecules known to contribute to disease exacerbation

Type 2 Diabetes Is Associated with Reduced ATP-Binding Cassette Transporter A1 Gene Expression, Protein and Function

Objective Increasing plasma glucose levels are associated with increasing risk of vascular disease. We tested the hypothesis that there is a glycaemia-mediated impairment of reverse cholesterol transport (RCT). We studied the influence of plasma glucose on expression and function of a key mediator in RCT, the ATP binding cassette transporter-A1 (ABCA1) and expression of its regulators, liver X receptor-α (LXRα) and peroxisome proliferator-activated receptor–γ (PPARγ). Methods and Results Leukocyte ABCA1, LXRα and PPARγ expression was measured by polymerase chain reaction in 63 men with varying degrees of glucose homeostasis. ABCA1 protein concentrations were measured in leukocytes. In a sub-group of 25 men, ABCA1 function was quantified as apolipoprotein-A1-mediated cholesterol efflux from 2–3 week cultured skin fibroblasts. Leukocyte ABCA1 expression correlated negatively with circulating HbA1c and glucose (rho = −0.41, p<0.001; rho = −0.34, p = 0.006 respectively) and was reduced in Type 2 diabetes (T2DM) (p = 0.03). Leukocyte ABCA1 protein was lower in T2DM (p = 0.03) and positively associated with plasma HDL cholesterol (HDL-C) (rho = 0.34, p = 0.02). Apolipoprotein-A1-mediated cholesterol efflux correlated negatively with fasting glucose (rho = −0.50, p = 0.01) and positively with HDL-C (rho = 0.41, p = 0.02). It was reduced in T2DM compared with controls (p = 0.04). These relationships were independent of LXRα and PPARγ expression. Conclusions ABCA1 expression and protein concentrations in leukocytes, as well as function in cultured skin fibroblasts, are reduced in T2DM. ABCA1 protein concentration and function are associated with HDL-C levels. These findings indicate a glycaemia- related, persistent disruption of a key component of RCT

The Ubiquitin E3 Ligase Nedd4 Regulates the Expression and Amyloid-β Peptide Export Activity of P-Glycoprotein

The ATP-binding cassette transporter, P-glycoprotein (P-gp), has been demonstrated to facilitate the clearance of amyloid-beta (Aβ) peptides, exporting the neurotoxic entity out of neurons and out of the brain via the blood–brain barrier. However, its expression and function diminish with age and in Alzheimer’s disease. P-gp is known to undergo ubiquitination, a post-translational modification that results in internalisation and/or degradation of the protein. NEDD4-1 is a ubiquitin E3 ligase that has previously been shown to ubiquitinate P-gp and reduce its cell surface expression. However, whether this effect translates into altered P-gp activity remains to be determined. siRNA was used to knockdown the expression of Nedd4 in CHO-APP cells. Western blot analysis confirmed that absence of Nedd4 was associated with increased P-gp protein expression. This was accompanied by increased transport activity, as shown by export of the P-gp substrate calcein-AM, as well as enhanced secretion of Aβ peptides, as shown by ELISA. These results implicate Nedd4 in the regulation of P-gp, and highlight a potential approach for restoring or augmenting P-gp expression and function to facilitate Aβ clearance from the brain