Crosstalk between reverse cholesterol transport and innate immunity

Bile acids promote lipopolysaccharide clearance via the hepato-biliary pathway in broiler chickens

Lipopolysaccharide (LPS) acts as a trigger that disrupts metabolic functions and the immune system. While bile acids (BA) have detoxification and anti-inflammatory effects, their role in promoting LPS excretion in broiler chickens remains unclear. This study aimed to investigate the potential of exogenous BA to enhance hepatic clearance of LPS and thereby potentially alleviate LPS-induced liver injury in broiler chickens. Forty-five 21-day-old male broiler chickens were randomly assigned to three groups: the control group, which received daily intraperitoneal injections of a solvent for LPS treatment and a gavage solvent for BA treatment; the LPS group, which received daily intraperitoneal injections of 0.5 mg/kg body weight LPS and a gavage solvent for BA treatment; the LPS + BA group, which received daily intraperitoneal injections of 0.5 mg/kg body weight LPS and 60 mg/kg body weight BA by gavage. BA administered by gavage protected the broiler chickens from increases in liver and spleen indices, systemic inflammatory response, and hepatic damage induced by LPS. Hepatic clearance of LPS was enhanced, as evidenced by decreased serum LPS levels and accelerated excretion into the gallbladder. Additionally, the LPS-induced downregulation of detoxification genes, including those for the lipoprotein receptor and bile acids export pump, was reversed by BA administered by gavage. Furthermore, nuclear transcription factors such as the Farnesoid X receptor (FXR) and Liver X receptor α (LXRα) were enhanced in BA-treated broiler chickens. These findings suggest that BA administration via gavage enhances hepatic LPS clearance through the upregulation of hepatic uptake and efflux proteins, likely mediated by the activation of nuclear transcription factors FXR and LXRα.

Endogenous Antimicrobial-Immunomodulatory Molecules: Networking Biomolecules of Innate Immunity

Endogenous antimicrobial-immunomodulatory molecules (EAIMs) are essential to immune-mediated human health and evolution. Conventionally, antimicrobial peptides (AMPs) have been regarded as the dominant endogenous antimicrobial molecule; however, AMPs are not sufficient to account for the full spectrum of antimicrobial-immunomodulatory duality occurring within the human body. The threat posed by pathogenic microbes is pervasive with the capacity for widespread impact across many organ systems and multiple biochemical pathways; accordingly, the host needs the capacity to react with an equally diverse response. This can be attained by having EAIMs that traverse the full range of molecular size (small to large molecules) and structural diversity (including molecules other than peptides). This review identifies multiple molecules (peptide/protein, lipid, carbohydrate, nucleic acid, small organic molecule, and metallic cation) as EAIMs and discusses the possibility of cooperative, additive effects amongst the various EAIM classes during the host response to a microbial assault. This comprehensive consideration of the full molecular diversity of EAIMs enables the conclusion that EAIMs constitute a previously uncatalogued structurally diverse and collectively underappreciated immuno-active group of integrated molecular responders within the innate immune system's first line of defence.

Association between serum high-density lipoprotein cholesterol and lung function in adults: three cross-sectional studies from US and Korea National Health and Nutrition Examination Survey

INTRODUCTION

Cholesterol is an irreplaceable nutrient in pulmonary metabolism; however, studies on high-density lipoprotein cholesterol (HDL-C) levels have shown conflicting results regarding lung function. Therefore, we investigated the association between lung function and HDL-C levels in three cross-sectional studies conducted in the USA and South Korea.

METHODS

US National Health and Nutrition Examination Survey (NHANES) III, US NHANES 2007-2012, and Korea National Health and Nutrition Examination Survey (KNHANES) IV-VII performed spirometry and met the American Thoracic Society recommendations. Multiple linear regression models were used to determine the relationship between serum lipid levels and lung function. The models were adjusted for age, sex, household income, body mass index, smoking pack year, use of lipid-lowering medication and race. Serum HDL-C levels were classified into three groups to assess the dose-response relationship according to the guideline from the National Cholesterol Education Program-Adult Treatment Panel III.

RESULTS

The adult participants of the KNHANES (n=31 288), NHANES III (n=12 182) and NHANES 2007-2012 (n=9122) were analysed. Multivariate linear regression analysis of the serum cholesterol profiles revealed that only serum HDL-C was associated with forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1) in all three studies. A 1 SD increase in the HDL-C level increased the percent predicted FVC by 0.5%-1.5% p, and the per cent predicted FEV1 by 0.5%-1.7% p. In terms of HDL-C levels, correlations between the HDL-C groups and the per cent predicted FVC and FEV1 showed dose-response relationships. Compared with the normal group, high HDL-C levels increased FVC by 0.75%-1.79% p and FEV1 by 0.55%-1.90% p, while low levels led to 0.74%-2.19% p and 0.86%-2.68% p reductions in FVC and FEV1, respectively. Subgroup analyses revealed weaker associations in females from KNHANES and NHANES III.

CONCLUSION

In the three nationwide cross-sectional studies, high HDL-C levels were associated with improved FVC and FEV1. However, future studies are needed to confirm this correlation and elucidate the underlying mechanisms.

Mapping the cellular and molecular landscape of cardiac non-myocytes in murine diabetic cardiomyopathy

Diabetes is associated with a significantly elevated risk of heart failure. However, despite extensive efforts to characterize the phenotype of the diabetic heart, the molecular and cellular protagonists that underpin cardiac pathological remodeling in diabetes remain unclear, with a notable paucity of data regarding the impact of diabetes on non-myocytes within the heart. Here we aimed to define key differences in cardiac non-myocytes between spontaneously type-2 diabetic (db/db) and healthy control (db/h) mouse hearts. Single-cell transcriptomic analysis revealed a concerted diabetes-induced cellular response contributing to cardiac remodeling. These included cell-specific activation of gene programs relating to fibroblast hyperplasia and cell migration, and dysregulation of pathways involving vascular homeostasis and protein folding. This work offers a new perspective for understanding the cellular mediators of diabetes-induced cardiac pathology, and pathways that may be targeted to address the cardiac complications associated with diabetes.

Hypoxia-altered cholesterol homeostasis enhances the expression of interferon-stimulated genes upon SARS-CoV-2 infections in monocytes

Hypoxia contributes to numerous pathophysiological conditions including inflammation-associated diseases. We characterized the impact of hypoxia on the immunometabolic cross-talk between cholesterol and interferon (IFN) responses. Specifically, hypoxia reduced cholesterol biosynthesis flux and provoked a compensatory activation of sterol regulatory element-binding protein 2 (SREBP2) in monocytes. Concomitantly, a broad range of interferon-stimulated genes (ISGs) increased under hypoxia in the absence of an inflammatory stimulus. While changes in cholesterol biosynthesis intermediates and SREBP2 activity did not contribute to hypoxic ISG induction, intracellular cholesterol distribution appeared critical to enhance hypoxic expression of chemokine ISGs. Importantly, hypoxia further boosted chemokine ISG expression in monocytes upon infection with severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Mechanistically, hypoxia sensitized toll-like receptor 4 (TLR4) signaling to activation by SARS-CoV-2 spike protein, which emerged as a major signaling hub to enhance chemokine ISG induction following SARS-CoV-2 infection of hypoxic monocytes. These data depict a hypoxia-regulated immunometabolic mechanism with implications for the development of systemic inflammatory responses in severe cases of coronavirus disease-2019 (COVID-19).

Effect of total cholesterol and statin therapy on mortality in ARDS patients: a secondary analysis of the SAILS and HARP-2 trials

BACKGROUND

Two acute respiratory distress syndrome (ARDS) trials showed no benefit for statin therapy, though secondary analyses suggest inflammatory subphenotypes may have a differential response to simvastatin. Statin medications decrease cholesterol levels, and low cholesterol has been associated with increased mortality in critical illness. We hypothesized that patients with ARDS and sepsis with low cholesterol could be harmed by statins.

METHODS

Secondary analysis of patients with ARDS and sepsis from two multicenter trials. We measured total cholesterol from frozen plasma samples obtained at enrollment in Statins for Acutely Injured Lungs from Sepsis (SAILS) and Simvastatin in the Acute Respiratory Distress Syndrome (HARP-2) trials, which randomized subjects with ARDS to rosuvastatin versus placebo and simvastatin versus placebo, respectively, for up to 28 days. We compared the lowest cholesterol quartile (< 69 mg/dL in SAILS, < 44 mg/dL in HARP-2) versus all other quartiles for association with 60-day mortality and medication effect. Fisher's exact test, logistic regression, and Cox Proportional Hazards were used to assess mortality.

RESULTS

There were 678 subjects with cholesterol measured in SAILS and 509 subjects in HARP-2, of whom 384 had sepsis. Median cholesterol at enrollment was 97 mg/dL in both SAILS and HARP-2. Low cholesterol was associated with higher APACHE III and shock prevalence in SAILS, and higher Sequential Organ Failure Assessment score and vasopressor use in HARP-2. Importantly, the effect of statins differed in these trials. In SAILS, patients with low cholesterol who received rosuvastatin were more likely to die (odds ratio (OR) 2.23, 95% confidence interval (95% CI) 1.06-4.77, p = 0.02; interaction p = 0.02). In contrast, in HARP-2, low cholesterol patients had lower mortality if randomized to simvastatin, though this did not reach statistical significance in the smaller cohort (OR 0.44, 95% CI 0.17-1.07, p = 0.06; interaction p = 0.22).

CONCLUSIONS

Cholesterol levels are low in two cohorts with sepsis-related ARDS, and those in the lowest cholesterol quartile are sicker. Despite the very low levels of cholesterol, simvastatin therapy seems safe and may reduce mortality in this group, though rosuvastatin was associated with harm.

Immune and metabolic cross-links in the pathogenesis of comorbid non-alcoholic fatty liver disease

In recent years, there has been a steady growth of interest in non-alcoholic fatty liver disease (NAFLD), which is associated with negative epidemiological data on the prevalence of the disease and its clinical significance. NAFLD is closely related to the metabolic syndrome and these relationships are the subject of active research. A growing body of evidence shows cross-linkages between metabolic abnormalities and the innate immune system in the development and progression of NAFLD. These links are bidirectional and largely still unclear, but a better understanding of them will improve the quality of diagnosis and management of patients. In addition, lipid metabolic disorders and the innate immune system link NAFLD with other diseases, such as atherosclerosis, which is of great clinical importance.

Apolipoprotein A-1 protected hepatic ischaemia-reperfusion injury through suppressing macrophage pyroptosis via TLR4-NF-κB pathway

BACKGROUND AND AIMS

Apolipoprotein A-1 (ApoA-1), the major apolipoprotein of high-density lipoprotein, plays anti-atherogenic role in cardiovascular diseases and exerts anti-inflammation effect in various inflammatory and infectious diseases. However, the role and mechanism of ApoA-1 in hepatic ischaemia-reperfusion (I/R) injury is unknown.

METHODS

In this study, we measured ApoA-1 expression in human liver grafts after transplantation. Mice partial hepatic I/R injury model was made in ApoA-1 knockout mice, ApoA-1 mimetic peptide D-4F treatment mice and corresponding control mice to examine the effect of ApoA-1 on liver damage, inflammation response and cell death. Primary hepatocytes and macrophages were isolated for in vitro study.

RESULTS

The results showed that ApoA-1 expression was down-regulated in human liver grafts after transplantation and mice livers subjected to hepatic I/R injury. ApoA-1 deficiency aggravated liver damage and inflammation response induced by hepatic I/R injury. Interestingly, we found that ApoA-1 deficiency increased pyroptosis instead of apoptosis during acute phase of hepatic I/R injury, which mainly occurred in macrophages rather than hepatocytes. The inhibition of pyroptosis compensated for the adverse impact of ApoA-1 deficiency. Furthermore, the up-regulated pyroptosis process was testified to be mediated by ApoA-1 through TLR4-NF-κB pathway and TLR4 inhibition significantly improved hepatic I/R injury. In addition, we confirmed that D-4F ameliorated hepatic I/R injury.

CONCLUSIONS

Our study has identified the protective role of ApoA-1 in hepatic I/R injury through inhibiting pyroptosis in macrophages via TLR4-NF-κB pathway. The effect of ApoA-1 may provide a novel therapeutic approach for hepatic I/R injury.

Clinical Significance of Lipid Transport Function of ABC Transporters in the Innate Immune System

ABC transporters are a large family of proteins that transport a variety of substrates across cell plasma membranes. Because of this, they are involved in many physiological processes. It is of interest to note that many ABC transporters are involved in the transport of various lipids. In addition, this function may be related to the innate immune system. The evidence that ABC transporters are involved in the regulation of the innate immune system through the transport of various substances greatly enhances the understanding of their clinical significance. ABC transporters are involved in the cellular homeostasis of cholesterol as well as in the regulation of its content in lipid rafts. Through these mechanisms, they can regulate the function of membrane proteins, including receptors of the innate immune system. By regulating lipid transport, some members of ABC transporters are involved in phagocytosis. In addition, ABC transporters are involved in the transport of lipopolysaccharide, lipid mediators of inflammation, and perform other functions in the innate immune system.

Impact of Non-Pharmacological Interventions on the Mechanisms of Atherosclerosis

Atherosclerosis remains the leading cause of mortality and morbidity worldwide characterized by the deposition of lipids and fibrous elements in the form of atheroma plaques in vascular areas which are hemodynamically overloaded. The global burden of atherosclerotic cardiovascular disease is steadily increasing and is considered the largest known non-infectious pandemic. The management of atherosclerotic cardiovascular disease is increasing the cost of health care worldwide, which is a concern for researchers and physicians and has caused them to strive to find effective long-term strategies to improve the efficiency of treatments by managing conventional risk factors. Primary prevention of atherosclerotic cardiovascular disease is the preferred method to reduce cardiovascular risk. Fasting, a Mediterranean diet, and caloric restriction can be considered useful clinical tools. The protective impact of physical exercise over the cardiovascular system has been studied in recent years with the intention of explaining the mechanisms involved; the increase in heat shock proteins, antioxidant enzymes and regulators of cardiac myocyte proliferation concentration seem to be the molecular and biochemical shifts that are involved. Developing new therapeutic strategies such as vagus nerve stimulation, either to prevent or slow the disease’s onset and progression, will surely have a profound effect on the lives of millions of people.

High-Density Lipoproteins: A Role in Inflammation in COPD

Chronic obstructive pulmonary disease (COPD) is a widespread disease associated with high rates of disability and mortality. COPD is characterized by chronic inflammation in the bronchi as well as systemic inflammation, which contributes significantly to the clinically heterogeneous course of the disease. Lipid metabolism disorders are common in COPD, being a part of its pathogenesis. High-density lipoproteins (HDLs) are not only involved in lipid metabolism, but are also part of the organism's immune and antioxidant defense. In addition, HDL is a versatile transport system for endogenous regulatory agents and is also involved in the removal of exogenous substances such as lipopolysaccharide. These functions, as well as information about lipoprotein metabolism disorders in COPD, allow a broader assessment of their role in the pathogenesis of heterogeneous and comorbid course of the disease.

High-density lipoprotein infusion protects from acute graft-versus-host disease in experimental allogeneic hematopoietic cell transplantation

Acute graft-versus-host disease (aGVHD) is a major limitation of the therapeutic potential of allogeneic hematopoietic cell transplantation. Lipopolysaccharides (LPS) derived from intestinal gram-negative bacteria are well-known aGVHD triggers and amplifiers. Here, we explored the LPS metabolism in aGVHD mouse models using an innovative quantification method. We demonstrated that systemic LPS accumulation after transplantation was due, at least partly, to a defect in its clearance through lipoprotein-mediated transport to the liver (i.e., the so-called reverse LPS transport). After transplantation, reduced circulating HDL concentration impaired LPS neutralization and elimination through biliary flux. Accordingly, HDL-deficient (Apoa1^tm1Unc ) recipient mice developed exacerbated aGVHD. Repeated administration of HDL isolated from human plasma significantly decreased the mortality and the severity of aGVHD. While the potential role of HDL in scavenging circulating LPS was examined in this study, it appears that HDL plays a more direct immunomodulatory role by limiting or controlling aGVHD. Notably, HDL infusion mitigated liver aGVHD by diminishing immune infiltration (e.g., interferon-γ-secreting CD8⁺ T cells and non-resident macrophages), systemic and local inflammation (notably cholangitis). Hence, our results revealed the interest of HDL-based therapies in the prevention of aGVHD.

Statins significantly repress rotavirus replication through downregulation of cholesterol synthesis

Rotavirus is the most common cause of severe diarrhea among infants and young children and is responsible for more than 200,000 pediatric deaths per year. There is currently no pharmacological treatment for rotavirus infection in clinical activity. Although cholesterol synthesis has been proven to play a key role in the infections of multiple viruses, little is known about the relationship between cholesterol biosynthesis and rotavirus replication. The models of rotavirus infected two cell lines and a human small intestinal organoid were used. We investigated the effects of cholesterol biosynthesis, including inhibition, enhancement, and their combinations on rotavirus replication on these models. The knockdown of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) was built by small hairpin RNAs in Caco2 cells. In all these models, inhibition of cholesterol synthesis by statins or HMGCR knockdown had a significant inhibitory effect on rotavirus replication. The result was further confirmed by the other inhibitors: 6-fluoromevalonate, Zaragozic acid A and U18666A, in the cholesterol biosynthesis pathway. Conversely, enhancement of cholesterol production increased rotavirus replication, suggesting that cholesterol homeostasis is relevant for rotavirus replication. The effects of all these compounds toward rotavirus were further confirmed with a clinical rotavirus isolate. We concluded that rotavirus replication is dependent on cholesterol biosynthesis. To be specific, inhibition of cholesterol synthesis can downregulate rotavirus replication; on the contrary, rotavirus replication is upregulated. Statin treatment is potentially an effective novel clinical anti-rotavirus strategy.

Artificial Sweeteners: History and New Concepts on Inflammation

Since the introduction of artificial sweeteners (AS) to the North American market in the 1950s, a growing number of epidemiological and animal studies have suggested that AS may induce changes in gut bacteria and gut wall immune reactivity, which could negatively affect individuals with or susceptible to chronic inflammatory conditions such as inflammatory bowel disease (IBD), a disorder that has been growing exponentially in westernized countries. This review summarizes the history of current FDA-approved AS and their chemical composition, metabolism, and bacterial utilization, and provides a scoping overview of the disease mechanisms associated with the induction or prevention of inflammation in IBD. We provide a general outlook on areas that have been both largely and scarcely studied, emerging concepts using silica, and describe the effects of AS on acute and chronic forms of intestinal inflammation.

Bioinformatic Analysis of ABCA1 Gene Expression in Smoking and Chronic Obstructive Pulmonary Disease

Smoking is a key modifiable risk factor for developing the chronic obstructive pulmonary disease (COPD). When smoking, many processes, including the reverse transport of cholesterol mediated by the ATP binding cassette transporter A1 (ABCA1) protein are disrupted in the lungs. Changes in the cholesterol content in the lipid rafts of plasma membranes can modulate the function of transmembrane proteins localized in them. It is believed that this mechanism participates in increasing the inflammation in COPD.

METHODS

Bioinformatic analysis of datasets from Gene Expression Omnibus (GEO) was carried out. Gene expression data from datasets of alveolar macrophages and the epithelium of the respiratory tract in smokers and COPD patients compared with non-smokers were used for the analysis. To evaluate differentially expressed genes, bioinformatic analysis was performed in comparison groups using the limma package in R (v. 4.0.2), and the GEO2R and Phantasus tools (v. 1.11.0).

RESULTS

The conducted bioinformatic analysis showed changes in the expression of the ABCA1 gene associated with smoking. In the alveolar macrophages of smokers, the expression levels of ABCA1 were lower than in non-smokers. At the same time, in most of the airway epithelial datasets, gene expression did not show any difference between the groups of smokers and non-smokers. In addition, it was shown that the expression of ABCA1 in the epithelial cells of the trachea and large bronchi is higher than in small bronchi.

CONCLUSIONS

The conducted bioinformatic analysis showed that smoking can influence the expression of the ABCA1 gene, thereby modulating lipid transport processes in macrophages, which are part of the mechanisms of inflammation development.

Lipid droplets and lipid mediators in viral infection and immunity

Lipid droplets (LDs) contribute to key pathways important for the physiology and pathophysiology of cells. In a homeostatic view, LDs regulate the storage of neutral lipids, protein sequestration, removal of toxic lipids and cellular communication; however, recent advancements in the field show these organelles as essential for various cellular stress response mechanisms, including inflammation and immunity, with LDs acting as hubs that integrate metabolic and inflammatory processes. The accumulation of LDs has become a hallmark of infection, and is often thought to be virally driven; however, recent evidence is pointing to a role for the upregulation of LDs in the production of a successful immune response to viral infection. The fatty acids housed in LDs are also gaining interest due to the role that these lipid species play during viral infection, and their link to the synthesis of bioactive lipid mediators that have been found to have a very complex role in viral infection. This review explores the role of LDs and their subsequent lipid mediators during viral infections and poses a paradigm shift in thinking in the field, whereby LDs may play pivotal roles in protecting the host against viral infection.

Lipid and Lipoprotein Dysregulation in Sepsis: Clinical and Mechanistic Insights into Chronic Critical Illness

In addition to their well-characterized roles in metabolism, lipids and lipoproteins have pleiotropic effects on the innate immune system. These undergo clinically relevant alterations during sepsis and acute inflammatory responses. High-density lipoprotein (HDL) plays an important role in regulating the immune response by clearing bacterial toxins, supporting corticosteroid release, decreasing platelet aggregation, inhibiting endothelial cell apoptosis, reducing the monocyte inflammatory response, and inhibiting expression of endothelial cell adhesion molecules. It undergoes quantitative as well as qualitative changes which can be measured using the HDL inflammatory index (HII). Pro-inflammatory, or dysfunctional HDL (dysHDL) lacks the ability to perform these functions, and we have also found it to independently predict adverse outcomes and organ failure in sepsis. Another important class of lipids known as specialized pro-resolving mediators (SPMs) positively affect the escalation and resolution of inflammation in a temporal fashion. These undergo phenotypic changes in sepsis and differ significantly between survivors and non-survivors. Certain subsets of sepsis survivors go on to have perilous post-hospitalization courses where this inflammation continues in a low grade fashion. This is associated with immunosuppression in a syndrome of persistent inflammation, immunosuppression, and catabolism syndrome (PICS). The continuous release of tissue damage-related patterns and viral reactivation secondary to immunosuppression feed this chronic cycle of inflammation. Animal data indicate that dysregulation of endogenous lipids and SPMs play important roles in this process. Lipids and their associated pathways have been the target of many clinical trials in recent years which have not shown mortality benefit. These results are limited by patient heterogeneity and poor animal models. Considerations of sepsis phenotypes and novel biomarkers in future trials are important factors to be considered in future research. Further characterization of lipid dysregulation and chronic inflammation during sepsis will aid mortality risk stratification, detection of sepsis, and inform individualized pharmacologic therapies.

Immune metabolism: a bridge of dendritic cells function

An increasing number of researches have shown that cell metabolism regulates cell function. Dendritic cells (DCs), a professional antigen presenting cells, connect innate and adaptive immune responses. The preference of DCs for sugar or lipid affects its phenotypes and functions. In many diseases such as atherosclerosis (AS), diabetes mellitus and tumor, altered glucose or lipid level in microenvironment makes DCs exert ineffective or opposite immune roles, which accelerates the development of these diseases. In this article, we review the metabolism pathways of glucose and cholesterol in DCs, and the effects of metabolic changes on the phenotype and function of DCs. In addition, we discuss the effects of changes in glucose and lipid levels on DCs in the context of different diseases for better understanding the relationship between DCs and diseases. The immune metabolism of DCs may be a potential intervention link to treat metabolic-related immune diseases.

PCSK9 inhibition, LDL and lipopolysaccharides: a complex and "dangerous" relationship

Literature concerning the causative factors of atherosclerotic cardiovascular disease shows complex and sometimes contrasting evidence. Most guidelines suggest a strategy aimed at lowering circulating low density lipoproteins (LDL) and ApoB lipoprotein levels. The use of statins and of cholesteryl ester transfer protein inhibitors has led to a number of controversial outcomes, generating a certain degree of concern about the real efficacy and especially safety of these drugs. Literature data show that the use of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors results in a dramatic reduction of various markers of lipid metabolism (namely LDL); however, several critical scientific papers have questioned the value, the need and especially the safety of these innovative drugs. LDL are a protective factor against lipopolysaccharides and other microbial derivatives. Similarly, these gram-negative bacteria-derived compounds have been identified as probable culprits of cardiovascular atherogenesis; moreover, lipopolysaccharides increase hepatic synthesis of PCSK9, as defense mechanism. This enzyme modulates LDL receptors level in the liver, as well as in other organs, such as adrenal gland and reproductive organs. Hence, PCSK9 inhibition may influence glucocorticoid secretion and fertility. Lastly, the consequent reduction of circulating LDL may relevantly hindrance immune system and favor lipopolysaccharides diffusion.

PCSK9 is associated with mortality in patients with septic shock: data from the ALBIOS study

BACKGROUND

Pro-protein convertase subtilisin/kexin 9 (PCSK9) is a proenzyme primarily known to regulate low-density lipoprotein receptor re-uptake on hepatocytes. Whether PCSK9 can concurrently trigger inflammation or not remains unclear. Here, we investigated the potential association between circulating levels of PCSK9 and mortality in patients with severe sepsis or septic shock.

METHODS

Plasma PCSK9 levels at days 1, 2 and 7 were measured in 958 patients with severe sepsis or septic shock previously enrolled in the Albumin Italian Outcome Sepsis (ALBIOS) trial. Correlations between levels of PCSK9 and pentraxin 3 (PTX3), a biomarker of disease severity, were evaluated with ranked Spearman's coefficients. Cox proportional hazards models were used to assess the association of PCSK9 levels at day 1 with 28- and 90-day mortality.

RESULTS

Median plasma PCSK9 levels were 278 [182-452] ng mL^-1 on day 1. PCSK9 correlated positively with PTX3 at the three time-points, and patients with septic shock within the first quartile of PCSK9 showed higher levels of PTX3. Similar mortality rates were observed in patients with severe sepsis across PCSK9 quartiles. Patients with septic shock with lower PCSK9 levels on day 1 (within the first quartile) showed the highest 28- and 90-day mortality rate as compared to other quartiles.

CONCLUSION

In our sub-analysis of the ALBIOS trial, we found that patients with septic shock presenting with lower plasma PCSK9 levels experienced higher mortality rate. Further studies are warranted to better evaluate the pathophysiological role of PCSK9 in sepsis.

Admission Low-Density Lipoprotein Cholesterol Stratified by Circulating CD14++CD16+ Monocytes and Risk for Recurrent Cardiovascular Events Following ST Elevation Myocardial Infarction: Lipid Paradox Revised

Lower level of low-density lipoprotein cholesterol (LDL-C) is paradoxically associated with increased mortality in ST elevation myocardial infarction (STEMI) patients. The underlying mechanism remains unclear. In a cohort of 220 de novo STEMI patients receiving timely primary percutaneous coronary intervention, admission LDL-C was negatively associated with circulating CD14++CD16+ monocyte counts. Moreover, admission LDL-C < 85 mg/dL was associated with increased risk for major adverse cardiovascular events (MACE) during a median follow-up of 2.7 years. After categorizing the patients according to the cutoff values of 85 mg/dL for LDL-C and the median for CD14++CD16+ monocytes, low LDL-C-associated MACE risk was only observed in those with high CD14++CD16+ monocyte counts (low LDL-C/high CD14++CD16+ monocytes vs. low LDL-C/low CD14++CD16+ monocytes: hazard ratio 5.38, 95% confidence interval 1.52 to 19.06, P = 0.009). This work provided the proof-of-principle evidence indicating a role of CD14++CD16+ monocytes in risk stratification of STEMI patients presenting with low LDL-C level. Graphical abstract.

MicroRNA sequences modulating inflammation and lipid accumulation in macrophage “foam” cells: Implications for atherosclerosis

Accumulation of macrophage “foam” cells, laden with cholesterol and cholesteryl ester, within the intima of large arteries, is a hallmark of early “fatty streak” lesions which can progress to complex, multicellular atheromatous plaques, involving lipoproteins from the bloodstream and cells of the innate and adaptive immune response. Sterol accumulation triggers induction of genes encoding proteins mediating the atheroprotective cholesterol efflux pathway. Within the arterial intima, however, this mechanism is overwhelmed, leading to distinct changes in macrophage phenotype and inflammatory status. Over the last decade marked gains have been made in understanding of the epigenetic landscape which influence macrophage function, and in particular the importance of small non-coding micro-RNA (miRNA) sequences in this context. This review identifies some of the miRNA sequences which play a key role in regulating “foam” cell formation and atherogenesis, highlighting sequences involved in cholesterol accumulation, those influencing inflammation in sterol-loaded cells, and novel sequences and pathways which may offer new strategies to influence macrophage function within atherosclerotic lesions.

Humoral Immunity Against HDL Particle: A New Perspective in Cardiovascular Diseases?

BACKGROUND

Autoimmune diseases are closely associated with cardiovascular diseases (CVD). Over the last decades, the comprehension of atherosclerosis, the principal initiator of CVD, evolved from a lipidcentered disease to a predominant inflammatory and immune response-driven disease displaying features of autoimmunity against a broad range of auto-antigens, including lipoproteins. Among them, high density lipoproteins (HDL) are important actors of cholesterol transport and bear several anti-atherogenic properties, raising a growing interest as therapeutic targets to decrease atherosclerosis and CVD burden, with nevertheless rather disappointing results so far. Reflecting HDL composition complexity, autoimmune responses and autoantibodies against various HDL components have been reported.

RESULTS

In this review, we addressed the important complexity of humoral autoimmunity towards HDL and particularly how this autoimmune response could help improving our understanding of HDL biological implication in atherosclerosis and CVD. We also discussed several issues related to specific HDL autoantibody subclasses characteristics, including etiology, prognosis and pathological mechanisms according to Rose criteria.

CONCLUSION

Finally, we addressed the possible clinical value of using these antibodies not only as potential biomarkers of atherogenesis and CVD, but also as a factor potentially mitigating the benefit of HDL-raising therapies.

Rutaecarpine derivative R3 attenuates atherosclerosis via inhibiting NLRP3 inflammasome-related inflammation and modulating cholesterol transport

Atherosclerosis is a chronic disease characterized by lipid deposition and inflammatory response. NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome-facilitated inflammatory responses are crucial in the pathogenesis of atherosclerosis, and thus new therapeutic approaches are emerging that target NLRP3 and inflammation. Here, we explored the anti-atherosclerotic effect and mechanisms of a new rutaecarpine derivative, 5-deoxy-rutaecarpine (R3) in vitro and in vivo. R3 treatment attenuated atherosclerosis development and increased plaque stability in Apoe^-/- mice fed a high-fat diet, and decreased levels of inflammatory mediators, such as interleukin-1β, in the serum of Apoe^-/- mice and in oxidized low-density lipoprotein (ox-LDL)-stimulated murine macrophages. R3 treatment inhibited NLRP3 inflammasome activation in the livers of Apoe^-/- mice and ox-LDL-stimulated murine macrophages by inhibiting NF-κB and MAPK pathways. Additionally, R3 significantly decreased total cholesterol in the serum and livers of Apoe^-/- mice and promoted cholesterol efflux in murine macrophages through upregulating protein expression of ATP-binding cassette subfamily A member 1 and scavenger receptor class B type I/human CD36 and lysosomal integral membrane protein-II analogous-1. Our results demonstrated that R3 prevented atherosclerotic progression via attenuating NLRP3 inflammasome-related inflammation and modulating cholesterol transport.

Association of Serum PCSK9 Levels with Antibiotic Resistance and Severity of Disease in Patients with Bacterial Infections Admitted to Intensive Care Units

BACKGROUND

The results of several studies have suggested that infections and sepsis, either bacterial or viral, might be associated with elevated plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) levels. Since there are no data on PCSK9 levels and antibiotic resistance or the severity of disease in patients with bacterial infections in intensive care units, the aim of this study was to investigate whether any such associations exist.

METHODS

100 patients (46 males, mean age 67.12 ± 1.34 years) with bacterial infections who were staying in an intensive care unit (ICU) longer than 48 h but less than 7 days and who were not receiving corticosteroids were analyzed. Their serum levels of albumin, C-reactive protein, glucose, lactate, blood urea nitrogen, prothrombin (international normalized ratio), total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, PCSK9, and procalcitonin were measured. The severity of the patients' condition was assessed by using the Glasgow Coma Scale (GCS), the Sequential Organ Failure Assessment (SOFA), and the Acute Physiology and Chronic Health Evaluation II (APACHE II) scales.

RESULTS

Using a hierarchical regression modeling approach, no significant association was found between PCSK9 levels and either the severity of disease (APACHE II, SOFA, and GCS) indices or resistance to antibiotics.

CONCLUSION

The results suggest that there is no association between PCSK9 levels and resistance to antibiotics or the condition of patients hospitalized in intensive care units.

Genital Chlamydia infection in hyperlipidemic mouse models exacerbates atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis is a chronic inflammatory disease, and recent studies have shown that infection at remote sites can contribute to the progression of atherosclerosis in hyperlipidemic mouse models. In this report, we tested the hypothesis that genital Chlamydia infection could accelerate the onset and progression of atherosclerosis.

METHODS

Apolipoprotein E (Apoe^-/-) and LDL receptor knockout (Ldlr^-/-) mice on a high-fat diet were infected intra-vaginally with Chlamydia muridarum. Atherosclerotic lesions on the aortic sinuses and in the descending aorta were assessed at 8-weeks post-infection. Systemic, macrophage, and vascular site inflammatory responses were assessed and quantified.

RESULTS

Compared to the uninfected groups, infected Apoe^-/- and Ldlr^-/- mice developed significantly more atherosclerotic lesions in the aortic sinus and in the descending aorta. Increased lesions were associated with higher circulating levels of serum amyloid A-1, IL-1β, TNF-α, and increased VCAM-1 expression in the aortic sinus, suggesting an association with inflammatory responses observed during C. muridarum infection. Genital infection courses were similar in Apoe^-/-, Ldlr^-/-, and wild type mice. Further, Apoe^-/- mice developed severe uterine pathology with increased dilatations. Apoe-deficiency also augmented cytokine/chemokine response in C. muridarum infected macrophages, suggesting that the difference in macrophage response could have contributed to the genital pathology in Apoe^-/- mice.

CONCLUSIONS

Overall, these studies demonstrate that genital Chlamydia infection exacerbates atherosclerotic lesions in hyperlipidemic mouse and suggest a novel role for Apoe in full recovery of uterine anatomy after chlamydial infection.

Intestinal Epithelial Cells and the Microbiome Undergo Swift Reprogramming at the Inception of Colonic Citrobacter rodentium Infection

The mouse pathogen C. rodentium is a widely used model for colonic infection and has been a major tool in fundamental discoveries in the fields of bacterial pathogenesis and mucosal immunology. Despite extensive studies probing acute C. rodentium infection, our understanding of the early stages preceding the infection climax remains relatively undetailed. To this end, we apply a multiomics approach to resolve temporal changes to the host and microbiome during early infection. Unexpectedly, we found immediate and dramatic responses occurring on the day of colonic infection, both in the host intestinal epithelial cells and in the microbiome. Our study suggests changes in cholesterol and carbon metabolism in epithelial cells are instantly induced upon pathogen detection in the colon, corresponding with a shift to primarily facultative anaerobes constituting the microbiome. This study contributes to our knowledge of disease pathogenesis and mechanisms of barrier regulation, which is required for development of novel therapeutics targeting the intestinal epithelium.

We used the mouse attaching and effacing (A/E) pathogen Citrobacter rodentium, which models the human A/E pathogens enteropathogenic Escherichia coli and enterohemorrhagic E. coli (EPEC and EHEC), to temporally resolve intestinal epithelial cell (IEC) responses and changes to the microbiome during in vivo infection. We found the host to be unresponsive during the first 3 days postinfection (DPI), when C. rodentium resides in the caecum. In contrast, at 4 DPI, the day of colonic colonization, despite only sporadic adhesion to the apex of the crypt, we observed robust upregulation of cell cycle and DNA repair processes, which were associated with expansion of the crypt Ki67-positive replicative zone, and downregulation of multiple metabolic processes (including the tricarboxylic acid [TCA] cycle and oxidative phosphorylation). Moreover, we observed dramatic depletion of goblet and deep crypt secretory cells and an atypical regulation of cholesterol homeostasis in IECs during early infection, with simultaneous upregulation of cholesterol biogenesis (e.g., 3-hydroxy-3-methylglutaryl–coenzyme A reductase [Hmgcr]), import (e.g., low-density lipoprotein receptor [Ldlr]), and efflux (e.g., AbcA1). We also detected interleukin 22 (IL-22) responses in IECs (e.g., Reg3γ) on the day of colonic colonization, which occurred concomitantly with a bloom of commensal Enterobacteriaceae on the mucosal surface. These results unravel a new paradigm in host-pathogen-microbiome interactions, showing for the first time that sensing a small number of pathogenic bacteria triggers swift intrinsic changes to the IEC composition and function, in tandem with significant changes to the mucosa-associated microbiome, which parallel innate immune responses.

Molecular regulation of plasma lipid levels during systemic inflammation and sepsis

PURPOSE OF REVIEW

Sepsis is a common syndrome of multiorgan system dysfunction caused by a dysregulated inflammatory response to an infection and is associated with high rates of mortality. Plasma lipid and lipoprotein levels and composition change profoundly during sepsis and have emerged as both biomarkers and potential therapeutic targets for this condition. The purpose of this article is to review recent progress in the understanding of the molecular regulation of lipid metabolism during sepsis.

RECENT FINDINGS

Patients who experience greater declines in high-density lipoprotein during sepsis are at much greater risk of succumbing to organ failure and death. Although the causality of these findings remains unclear, all lipoprotein classes can sequester and prevent the excessive inflammation caused by pathogen-associated lipids during severe infections such as sepsis. This primordial innate immune function has been best characterized for high-density lipoproteins. Most importantly, results from human genetics and preclinical animal studies have suggested that several lipid treatment strategies, initially designed for atherosclerosis, may hold promise as therapies for sepsis.

SUMMARY

Lipid and lipoprotein metabolism undergoes significant changes during sepsis. An improved understanding of the molecular regulation of these changes may lead to new opportunities for the treatment of sepsis.

Impact of PCSK9 loss-of-function genotype on 1-year mortality and recurrent infection in sepsis survivors

Background

Reduced activity of proprotein convertase subtilisin/kexin type 9 (PCSK9) has been associated with decreased short-term death in patients with septic shock. Whether PCSK9 genotype influences long-term outcomes in sepsis survivors is unknown.

Methods

We evaluated the impact of PCSK9 loss-of-function (LOF) genotype on both 1-year mortality and infection-related readmission (IRR) after an index sepsis admission. The Derivation cohort included 342 patients who survived 28 days after a sepsis admission in a tertiary hospital (Vancouver/Canada, 2004–2014), while an independent Validation cohort included 1079 septic shock patients admitted at the same hospital (2000–2006). All patients were genotyped for three common missense PCSK9 LOF variants rs11591147, rs11583680, rs562556 and were classified in 3 groups: Wildtype, single PCSK9 LOF, and multiple PCSK9 LOF, according to the number of LOF alleles per patient. We also performed a meta-analysis using both cohorts to investigate the effects of PCSK9 genotype on 90-day survival.

Findings

In the Derivation cohort, patients carrying multiple PCSK9 LOF alleles showed lower risk for the composite outcome 1-year death or IRR (HR: 0.40, P = 0.006), accelerated reduction on neutrophil counts (P = 0.010), and decreased levels of PCSK9 (P = 0.037) compared with WT/single LOF groups. Our meta-analysis revealed that the presence of multiple LOF alleles was associated with lower 90-day mortality risk (OR = 0.69, P = 0.020).

Interpretation

The presence of multiple PCSK9 LOF alleles decreased the risk of 1-year death or IRR in sepsis survivors. Biological measures suggest this may be related to an enhanced resolution of the initial infection.

Funding

Canadian Institutes of Health Research (PJT-156056).

Lipid profile perturbations in the plasma and lungs of mice with LPS-induced acute lung injury revealed by UHPLC-ESI-Q Exactive HF MS analysis

An UHPLC-ESI-Q Exactive HF MS-based lipidomics method was successfully applied to profile various lipids from the plasma and lungs of mice intranasally challenged with lipopolysaccaride (LPS). Response trends of lipids to LPS were graphically represented by variable importance in projection (VIP) plot, heat map, and bar plot. As a result, 77 differential lipids in the lung and 13 differential lipids in the plasma were identified by comparison between healthy and LPS- induced mice. These results revealed the correlation between inflammation and lipids metabolism. The differentially regulated lipids could also be potentially used as biomarkers for inflammation.

A New Frontier in Immunometabolism. Cholesterol in Lung Health and Disease

The lung has a unique relationship to cholesterol that is shaped by its singular physiology. On the one hand, the lungs receive the full cardiac output and have a predominant dependence on plasma lipoprotein uptake for their cholesterol supply. On the other hand, surfactant lipids, including cholesterol, are continually susceptible to oxidation owing to direct environmental exposure and must be cleared or recycled because of the very narrow biophysical mandates placed upon surfactant lipid composition. Interestingly, increased lipid-laden macrophage "foam cells" have been noted in a wide range of human lung pathologies. This suggests that lipid dysregulation may be a unifying and perhaps contributory event in chronic lung disease pathogenesis. Recent studies have shown that perturbations in intracellular cholesterol trafficking critically modify the immune response of macrophages and other cells. This minireview discusses literature that has begun to demonstrate the importance of regulated cholesterol traffic through the lung to pulmonary immunity, inflammation, and fibrosis. This emerging recognition of coupling between immunity and lipid homeostasis in the lung presents potentially transformative concepts for understanding lung disease and may also offer novel and exciting avenues for therapeutic development.

Perturbation of Intracellular Cholesterol and Fatty Acid Homeostasis During Flavivirus Infections

Cellular lipid homeostasis is maintained through an intricately linked array of anabolic and catabolic pathways. Upon flavivirus infections, these are significantly altered: on the one hand, these viruses can co-opt lipid metabolic pathways to generate ATP to facilitate replication, or to synthesize membrane components to generate replication sites; on the other hand, more recent evidence suggests counter strategies employed by host cells, which actively modulate several of these networks in response to infection, enhancing interferon signaling by doing so, and thus creating an antiviral environment. In this review, we discuss recent data on mechanisms of alteration of lipid metabolic pathways during infection by flaviviruses, with a focus on cholesterol and fatty acid biosynthesis, which can be manipulated by the invading viruses to support replication, but can also be modulated by the host immune system itself, as a means to fight infection.

The Oxygen Paradox, the French Paradox, and age-related diseases

A paradox is a seemingly absurd or impossible concept, proposition, or theory that is often difficult to understand or explain, sometimes apparently self-contradictory, and yet ultimately correct or true. How is it possible, for example, that oxygen "a toxic environmental poison" could be also indispensable for life (Beckman and Ames Physiol Rev 78(2):547-81, 1998; Stadtman and Berlett Chem Res Toxicol 10(5):485-94, 1997)?: the so-called Oxygen Paradox (Davies and Ursini 1995; Davies Biochem Soc Symp 61:1-31, 1995). How can French people apparently disregard the rule that high dietary intakes of cholesterol and saturated fats (e.g., cheese and paté) will result in an early death from cardiovascular diseases (Renaud and de Lorgeril Lancet 339(8808):1523-6, 1992; Catalgol et al. Front Pharmacol 3:141, 2012; Eisenberg et al. Nat Med 22(12):1428-1438, 2016)?: the so-called, French Paradox. Doubtless, the truth is not a duality and epistemological bias probably generates apparently self-contradictory conclusions. Perhaps nowhere in biology are there so many apparently contradictory views, and even experimental results, affecting human physiology and pathology as in the fields of free radicals and oxidative stress, antioxidants, foods and drinks, and dietary recommendations; this is particularly true when issues such as disease-susceptibility or avoidance, "healthspan," "lifespan," and ageing are involved. Consider, for example, the apparently paradoxical observation that treatment with low doses of a substance that is toxic at high concentrations may actually induce transient adaptations that protect against a subsequent exposure to the same (or similar) toxin. This particular paradox is now mechanistically explained as "Adaptive Homeostasis" (Davies Mol Asp Med 49:1-7, 2016; Pomatto et al. 2017a; Lomeli et al. Clin Sci (Lond) 131(21):2573-2599, 2017; Pomatto and Davies 2017); the non-damaging process by which an apparent toxicant can activate biological signal transduction pathways to increase expression of protective genes, by mechanisms that are completely different from those by which the same agent induces toxicity at high concentrations. In this review, we explore the influences and effects of paradoxes such as the Oxygen Paradox and the French Paradox on the etiology, progression, and outcomes of many of the major human age-related diseases, as well as the basic biological phenomenon of ageing itself.

Proteome of human plasma very low-density lipoprotein and low-density lipoprotein exhibits a link with coagulation and lipid metabolism

Apart from transporting lipids through the body, the human plasma lipoproteins very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) are also thought to serve as a modality for intra-organismal protein transfer, shipping proteins with important roles in inflammation and thrombosis from the site of synthesis to effector locations. To better understand the role of VLDL and LDL in the transport of proteins, we applied a combination of LTQ ORBITRAP-XL (nLC-MS/MS) with both in-SDS-PAGE gel and in-solution tryptic digestion of pure and defined VLDL and LDL fractions. We identified the presence of 95 VLDL-and 51 LDL-associated proteins including all known apolipoproteins and lipid transport proteins, and intriguingly a set of coagulation proteins, complement system and anti-microbial proteins. Prothrombin, protein S, fibrinogen γ, PLTP, CETP, CD14 and LBP were present on VLDL but not on LDL. Prenylcysteine oxidase 1, dermcidin, cathelicidin antimicrobial peptide, TFPI-1 and fibrinogen α chain were associated with both VLDL and LDL. Apo A-V is only present on VLDL and not on LDL. Collectively, this study provides a wealth of knowledge on the protein constituents of the human plasma lipoprotein system and strongly supports the notion that protein shuttling through this system is involved in the regulation of biological processes. Human diseases related to proteins carried by VLDL and LDL can be divided in three major categories: 1 – dyslipidaemia, 2 – atherosclerosis and vascular disease, and 3 – coagulation disorders.

A review of molecular imaging of atherosclerosis and the potential application of dendrimer in imaging of plaque

Despite the fact that technological advancements have been made in diagnosis and treatment, cardiovascular diseases (CVDs) remain the leading cause of mortality and morbidity worldwide. Early detection of atherosclerosis (AS), especially vulnerable plaques, plays a crucial role in the prevention of acute coronary syndrome (ACS). Targeting the critical cytokines and molecules that are upregulated during the biological process of AS by in vivo molecular imaging has been widely used in plaque imaging. With their three-dimensional architecture, composition, and abundant terminal functional groups, dendrimers provide a platform for multitargeting and multimodal imaging. Thus, modified dendrimers with the key molecules upregulated in AS plaques will be an innovative attempt to achieve targeted imaging of AS plaques specifically and efficiently. This review was aimed to address some recent works on imaging of AS plaques using various types of image technology and further discuss the applications of dendrimers, an innovative yet seldom used method in imaging of AS plaques due to some limitations and challenges, and we highlight the bright future of the modified dendrimers in characterizing AS plaques.

Lipopolysaccharide enters the rat brain by a lipoprotein-mediated transport mechanism in physiological conditions

Physiologically, lipopolysaccharide (LPS) is present in the bloodstream and can be bound to several proteins for its transport (i.e.) LPS binding protein (LBP) and plasma lipoproteins). LPS receptors CD14 and TLR-4 are constitutively expressed in the Central Nervous System (CNS). To our knowledge, LPS infiltration in CNS has not been clearly demonstrated. A naturalistic experiment with healthy rats was performed to investigate whether LPS is present with its receptors in brain. Immunofluorescences showed that lipid A and core LPS were present in circumventricular organs, choroid plexus, meningeal cells, astrocytes, tanycytes and endothelial cells. Co-localization of LPS regions with CD14/TLR-4 was found. The role of lipoprotein receptors (SR-BI, ApoER2 and LDLr) in the brain as targets for a LPS transport mechanism by plasma apolipoproteins (i.e. ApoAI) was studied. Co-localization of LPS regions with these lipoproteins markers was observed. Our results suggest that LPS infiltrates in the brain in physiological conditions, possibly, through a lipoprotein transport mechanism, and it is bound to its receptors in blood-brain interfaces.

The challenges and promise of targeting the Liver X Receptors for treatment of inflammatory disease

The Liver X Receptors (LXRs) are oxysterol-activated transcription factors that upregulate a suite of genes that together promote coordinated mobilization of excess cholesterol from cells and from the body. The LXRs, like other nuclear receptors, are anti-inflammatory, inhibiting signal-dependent induction of pro-inflammatory genes by nuclear factor-κB, activating protein-1, and other transcription factors. Synthetic LXR agonists have been shown to ameliorate atherosclerosis and a wide range of inflammatory disorders in preclinical animal models. Although this has suggested potential for application to human disease, systemic LXR activation is complicated by hepatic steatosis and hypertriglyceridemia, consequences of lipogenic gene induction in the liver by LXRα. The past several years have seen the development of multiple advanced LXR therapeutics aiming to avoid hepatic lipogenesis, including LXRβ-selective agonists, tissue-selective agonists, and transrepression-selective agonists. Although several synthetic LXR agonists have made it to phase I clinical trials, none have progressed due to unforeseen adverse reactions or undisclosed reasons. Nonetheless, several sophisticated pharmacologic strategies, including structure-guided drug design, cell-specific drug targeting, as well as non-systemic drug routes have been initiated and remain to be comprehensively explored. In addition, recent studies have identified potential utility for targeting the LXRs during therapy with other agents, such as glucocorticoids and rexinoids. Despite the pitfalls encountered to date in translation of LXR agonists to human disease, it appears likely that this accelerating field will ultimately yield effective and safe applications for LXR targeting in humans.

Surfactant Lipids at the Host-Environment Interface. Metabolic Sensors, Suppressors, and Effectors of Inflammatory Lung Disease

The lipid composition of pulmonary surfactant is unlike that of any other body fluid. This extracellular lipid reservoir is also uniquely susceptible by virtue of its direct and continuous exposure to environmental oxidants, inflammatory agents, and pathogens. Historically, the greatest attention has been focused on those biophysical features of surfactant that serve to reduce surface tension at the air-liquid interface. More recently, surfactant lipids have also been recognized as bioactive molecules that maintain immune quiescence in the lung but can also be remodeled by the inhaled environment into neolipids that mediate key roles in inflammation, immunity, and fibrosis. This review focuses on the roles in inflammatory and infectious lung disease of two classes of native surfactant lipids, glycerophospholipids and sterols, and their corresponding oxidized species, oxidized glycerophospholipids and oxysterols. We highlight evidence that surfactant composition is sensitive to circulating lipoproteins and that the lipid milieu of the alveolus should thus be recognized as susceptible to diet and common systemic metabolic disorders. We also discuss intriguing evidence suggesting that oxidized surfactant lipids may represent an evolutionary link between immunity and tissue homeostasis that arose in the primordial lung. Taken together, the emerging picture is one in which the unique environmental susceptibility of the lung, together with its unique extracellular lipid requirements, may have made this organ both an evolutionary hub and an engine for lipid-immune cross-talk.

Inhibition of PCSK9 does not improve lipopolysaccharide-induced mortality in mice

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secreted protein that targets LDL receptors (LDLRs) for degradation in liver. Blocking the interaction of PCSK9 with the LDLR potently reduces plasma LDL cholesterol levels and cardiovascular events. Recently, it has been suggested that inhibition of PCSK9 might also improve outcomes in mice and humans with sepsis, possibly by increasing LDLR-mediated clearance of endotoxins. Sepsis is a complication of a severe microbial infection that has shared pathways with lipid metabolism. Here, we tested whether anti-PCSK9 antibodies prevent death from lipopolysaccharide (LPS)-induced endotoxemia. Mice were administered PCSK9 antibodies prior to, or shortly after, injecting LPS. In both scenarios, the administration of PCSK9 antibodies did not alter endotoxemia-induced mortality. Afterward, we determined whether the complete absence of PCSK9 improved endotoxemia-induced mortality in mice with the germ-line deletion of Pcsk9. Similarly, PCSK9 knockout mice were not protected from LPS-induced death. To determine whether low LDLR expression increased LPS-induced mortality, Ldlr^−/− mice and PCSK9 transgenic mice were studied after injection of LPS. Endotoxemia-induced mortality was not altered in either mouse model. In a human cohort, we observed no correlation between plasma inflammation markers with total cholesterol levels, LDL cholesterol, and PCSK9. Combined, our data demonstrate that PCSK9 inhibition provides no protection from LPS-induced mortality in mice.

ERRα negatively regulates type I interferon induction by inhibiting TBK1-IRF3 interaction

Estrogen-related receptor α (ERRα) is a member of the nuclear receptor superfamily controlling energy homeostasis; however, its precise role in regulating antiviral innate immunity remains to be clarified. Here, we showed that ERRα deficiency conferred resistance to viral infection both in vivo and in vitro. Mechanistically, ERRα inhibited the production of type-I interferon (IFN-I) and the expression of multiple interferon-stimulated genes (ISGs). Furthermore, we found that viral infection induced TBK1-dependent ERRα stabilization, which in turn associated with TBK1 and IRF3 to impede the formation of TBK1-IRF3, IRF3 phosphorylation, IRF3 dimerization, and the DNA binding affinity of IRF3. The effect of ERRα on IFN-I production was independent of its transcriptional activity and PCG-1α. Notably, ERRα chemical inhibitor XCT790 has broad antiviral potency. This work not only identifies ERRα as a critical negative regulator of antiviral signaling, but also provides a potential target for future antiviral therapy.

Roles of the Mevalonate Pathway and Cholesterol Trafficking in Pulmonary Host Defense

The mevalonic acid synthesis pathway, cholesterol, and lipoproteins play fundamental roles in lung physiology and the innate immune response. Recent literature investigating roles for cholesterol synthesis and trafficking in host defense against respiratory infection was critically reviewed. The innate immune response and the cholesterol biosynthesis/trafficking network regulate one another, with important implications for pathogen invasion and host defense in the lung. The activation of pathogen recognition receptors and downstream cellular host defense functions are critically sensitive to cellular cholesterol. Conversely, microorganisms can co-opt the sterol/lipoprotein network in order to facilitate replication and evade immunity. Emerging literature suggests the potential for harnessing these insights towards therapeutic development. Given that >50% of adults in the U.S. have serum cholesterol abnormalities and pneumonia remains a leading cause of death, the potential impact of cholesterol on pulmonary host defense is of tremendous public health significance and warrants further mechanistic and translational investigation.

Time Series miRNA-mRNA integrated analysis reveals critical miRNAs and targets in macrophage polarization

Polarization of macrophages is regulated through complex signaling networks. Correlating miRNA and mRNA expression over time after macrophage polarization has not yet been investigated. We used paired RNA-Seq and miRNA-Seq experiments to measure the mRNA and miRNA expression in bone marrow-derived macrophages over a time-series of 8 hours. Bioinformatics analysis identified 31 differentially expressed miRNAs between M1 and M2 polarized macrophages. The top 4 M1 miRNAs (miR-155-3p, miR-155-5p, miR-147-3p and miR-9-5p) and top 4 M2 miRNAs (miR-27a-5p, let-7c-1-3p, miR-23a-5p and miR-23b-5p) were validated by qPCR. Interestingly, M1 specific miRNAs could be categorized to early- and late-response groups, in which three new miRNAs miR-1931, miR-3473e and miR-5128 were validated as early-response miRNAs. M1 polarization led to the enrichment of genes involved in immune responses and signal transduction, whereas M2 polarization enriched genes involved in cell cycle and metabolic processes. C2H2 zinc-finger family members are key targets of DE miRNAs. The integrative analysis between miRNAs and mRNAs demonstrates the regulations of miRNAs on nearly four thousand differentially expressed genes and most of the biological pathways enriched in macrophage polarization. In summary, this study elucidates the expression profiles of miRNAs and their potential targetomes during macrophage polarization.

Ozone-derived Oxysterols Affect Liver X Receptor (LXR) Signaling: A POTENTIAL ROLE FOR LIPID-PROTEIN ADDUCTS

When inhaled, ozone (O₃) interacts with cholesterols of airway epithelial cell membranes or the lung-lining fluid, generating chemically reactive oxysterols. The mechanism by which O₃-derived oxysterols affect molecular function is unknown. Our data show that in vitro exposure of human bronchial epithelial cells to O₃ results in the formation of oxysterols, epoxycholesterol-α and -β and secosterol A and B (Seco A and Seco B), in cell lysates and apical washes. Similarly, bronchoalveolar lavage fluid obtained from human volunteers exposed to O₃ contained elevated levels of these oxysterol species. As expected, O₃-derived oxysterols have a pro-inflammatory effect and increase NF-κB activity. Interestingly, expression of the cholesterol efflux pump ATP-binding cassette transporter 1 (ABCA1), which is regulated by activation of the liver X receptor (LXR), was suppressed in epithelial cells exposed to O₃ Additionally, exposure of LXR knock-out mice to O₃ enhanced pro-inflammatory cytokine production in the lung, suggesting LXR inhibits O₃-induced inflammation. Using alkynyl surrogates of O₃-derived oxysterols, our data demonstrate adduction of LXR with Seco A. Similarly, supplementation of epithelial cells with alkynyl-tagged cholesterol followed by O₃ exposure causes observable lipid-LXR adduct formation. Experiments using Seco A and the LXR agonist T0901317 (T09) showed reduced expression of ABCA1 as compared with stimulation with T0901317 alone, indicating that Seco A-LXR protein adduct formation inhibits LXR activation by traditional agonists. Overall, these data demonstrate that O₃-derived oxysterols have pro-inflammatory functions and form lipid-protein adducts with LXR, thus leading to suppressed cholesterol regulatory gene expression and providing a biochemical mechanism mediating O₃-derived formation of oxidized lipids in the airways and subsequent adverse health effects.

MicroRNA regulation of macrophages in human pathologies

Macrophages play a crucial role in the innate immune system and contribute to a broad spectrum of pathologies, like in the defence against infectious agents, in inflammation resolution, and wound repair. In the past several years, microRNAs (miRNAs) have been demonstrated to play important roles in immune diseases by regulating macrophage functions. In this review, we will summarize the role of miRNAs in the differentiation of monocytes into macrophages, in the classical and alternative activation of macrophages, and in the regulation of phagocytosis and apoptosis. Notably, miRNAs preferentially target genes related to the cellular cholesterol metabolism, which is of key importance for the inflammatory activation and phagocytic activity of macrophages. miRNAs functionally link various mechanisms involved in macrophage activation and contribute to initiation and resolution of inflammation. miRNAs represent promising diagnostic and therapeutic targets in different conditions, such as infectious diseases, atherosclerosis, and cancer.

Biology of proprotein convertase subtilisin kexin 9: beyond low-density lipoprotein cholesterol lowering

Proprotein convertase subtilisin kexin 9 (PCSK9) is a key regulator of low-density lipoprotein receptor levels and LDL-cholesterol levels. Loss-of-function mutations in PCSK9 gene are associated with hypocholesterolaemia and protection against cardiovascular disease, identifying PCSK9 inhibition as a valid therapeutic approach to manage hypercholesterolaemia and related diseases. Although PCSK9 is expressed mainly in the liver, it is present also in other tissues and organs with specific functions, raising the question of whether a pharmacological inhibition of PCSK9 to treat hypercholesterolaemia and associated cardiovascular diseases might be helpful or deleterious in non-hepatic tissues. For example, PCSK9 is expressed in the vascular wall, in the kidneys, and in the brain, where it was proposed to play a role in development, neurocognitive process, and neuronal apoptosis. A link between PCSK9 and immunity was also proposed as both sepsis and viral infections are differentially affected in the presence or absence of PCSK9. Despite the increasing number of observations, the debate on the exact roles of PCSK9 in extrahepatic tissues is still ongoing, and as very effective drugs that inhibit PCSK9 have become available to the clinician, a better understanding of the biological roles of PCSK9 is warranted.

MicroRNA-33 Regulates the Innate Immune Response via ATP Binding Cassette Transporter-mediated Remodeling of Membrane Microdomains

MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression by promoting degradation and/or repressing translation of specific target mRNAs. Several miRNAs have been identified that regulate the amplitude of the innate immune response by directly targeting Toll-like receptor (TLR) pathway members and/or cytokines. miR-33a and miR-33b (the latter present in primates but absent in rodents and lower species) are located in introns of the sterol regulatory element-binding protein (SREBP)-encoding genes and control cholesterol/lipid homeostasis in concert with their host gene products. These miRNAs regulate macrophage cholesterol by targeting the lipid efflux transporters ATP binding cassette (ABC)A1 and ABCG1. We and others have previously reported that Abca1(-/-) and Abcg1(-/-) macrophages have increased TLR proinflammatory responses due to augmented lipid raft cholesterol. Given this, we hypothesized that miR-33 would augment TLR signaling in macrophages via a raft cholesterol-dependent mechanism. Herein, we report that multiple TLR ligands down-regulate miR-33 in murine macrophages. In the case of lipopolysaccharide, this is a delayed, Toll/interleukin-1 receptor (TIR) domain-containing adapter-inducing interferon-β-dependent response that also down-regulates Srebf-2, the host gene for miR-33. miR-33 augments macrophage lipid rafts and enhances proinflammatory cytokine induction and NF-κB activation by LPS. This occurs through an ABCA1- and ABCG1-dependent mechanism and is reversible by interventions upon raft cholesterol and by ABC transporter-inducing liver X receptor agonists. Taken together, these findings extend the purview of miR-33, identifying it as an indirect regulator of innate immunity that mediates bidirectional cross-talk between lipid homeostasis and inflammation.