Krüppel-Like Factor 4 Regulation of Cholesterol-25-Hydroxylase and Liver X Receptor Mitigates Atherosclerosis Susceptibility

Macrophage polarisation and inflammatory mechanisms in atherosclerosis: Implications for prevention and treatment

Atherosclerosis is a chronic inflammatory disease characterised by plaque accumulation in the arteries. Macrophages are immune cells that are crucial in the development of atherosclerosis. Macrophages can adopt different phenotypes, with the M1 phenotype promoting inflammation while the M2 phenotype counteracting it. This review focuses on the factors that drive the polarisation of M1 macrophages towards a pro-inflammatory phenotype during AS. Additionally, we explored metabolic reprogramming mechanisms and cytokines secretion by M1 macrophages. Hyperlipidaemia is widely recognised as a major risk factor for atherosclerosis. Modified lipoproteins released in the presence of hyperlipidaemia can trigger the release of cytokines and recruit circulating monocytes, which adhere to the damaged endothelium and differentiate into macrophages. Macrophages engulf lipids, leading to the formation of foam cells. As atherosclerosis progresses, foam cells become the necrotic core within the atherosclerotic plaques, destabilising them and triggering ischaemic disease. Furthermore, we discuss recent research focusing on targeting macrophages or inflammatory pathways for preventive or therapeutic purposes. These include statins, PCSK9 inhibitors, and promising nanotargeted drugs. These new developments hold the potential for the prevention and treatment of atherosclerosis and its related complications.

Molecular mechanism of renal lipid accumulation in diabetic kidney disease

Diabetic kidney disease (DKD) is a leading cause of end stage renal disease with unmet clinical demands for treatment. Lipids are essential for cell survival; however, renal cells have limited capability to metabolize overloaded lipids. Dyslipidaemia is common in DKD patients and renal ectopic lipid accumulation is associated with disease progression. Unveiling the molecular mechanism involved in renal lipid regulation is crucial for exploring potential therapeutic targets. In this review, we focused on the mechanism underlying cholesterol, oxysterol and fatty acid metabolism disorder in the context of DKD. Specific regulators of lipid accumulation in different kidney compartment and TREM2 macrophages, a lipid-related macrophages in DKD, were discussed. The role of sodium-glucose transporter 2 inhibitors in improving renal lipid accumulation was summarized.

25-hydroxycholesterol triggers antioxidant signaling in mouse atria

Oxysterol, 25-hydroxycholesterol (25HC), is a potent regulator of immune reactions, its synthesis greatly increases by macrophages during inflammation. We hypothesize that 25HC can have cardioprotective effects by limiting consequences of excessive β-adrenoceptor (βAR) stimulation, particularly reactive oxygen species (ROS) production, in mouse atria. Isoproterenol, a βAR agonist, increased extra- and intracellular levels of ROS. This enhancement of ROS production was suppressed by NADPH oxidase antagonists as well as 25HC. Inhibition of β3ARs, Gi protein and protein kinase Cε prevented the effect of 25HC on isoproterenol-dependent ROS synthesis. Furthermore, 25HC suppressed isoproterenol-induced lipid peroxidation and mitochondrial ROS generation as well as ROS-dependent component of positive inotropic response to isoproterenol. Additionally, 25HC decreased mitochondrial ROS production and lipid peroxidation induced by antimycin A, a mitochondrial poison. Thus, 25HC exerts antioxidant properties alleviating mitochondrial dysfunction-induced and βAR-dependent cardiac oxidative damage. In the latter case, 25HC can act via signaling mechanism engaging β3ARs, Gi protein and protein kinase Cε.

Cholesterol 25-Hydroxylase Protects Against Diabetic Kidney Disease by Regulating ADP Ribosylation Factor 4

Cholesterol 25-hydroxylase (CH25H), an enzyme involved in cholesterol metabolism, regulates inflammatory responses and lipid metabolism. However, its role in kidney disease is not known.  The author found that CH25H transcript is expressed mostly in glomerular and peritubular endothelial cells and that its expression increased in human and mouse diabetic kidneys.  Global deletion of Ch25h in Leprdb/db mice aggravated diabetic kidney disease (DKD), which is associated with increased endothelial cell apoptosis. Treatment of 25-hydroxycholesterol (25-HC), the product of CH25H, alleviated kidney injury in Leprdb/db mice. Mechanistically, 25-HC binds to GTP-binding protein ADP-ribosylation factor 4 (ARF4), an essential protein required for maintaining protein transport in the Golgi apparatus. Interestingly, ARF4's GTPase-activating protein ASAP1 is also predominantly expressed in endothelial cells and its expression increased in DKD. Suppression of ARF4 activity by deleting ARF4 or overexpressing ASAP1 results in endothelial cell death. These results indicate that 25-HC binds ARF4 to inhibit its interaction with ASAP1, and thereby resulting in enhanced ARF4 activity to confer renoprotection. Therefore, treatment of 25-HC improves kidney injury in DKD in part by restoring ARF4 activity to maintain endothelial cell survival. This study provides a novel mechanism and a potential new therapy for DKD.

25-Hydroxycholesterol regulates lysosome AMP kinase activation and metabolic reprogramming to educate immunosuppressive macrophages

Macrophages are critical to turn noninflamed "cold tumors" into inflamed "hot tumors". Emerging evidence indicates abnormal cholesterol metabolites in the tumor microenvironment (TME) with unclear function. Here, we uncovered the inducible expression of cholesterol-25-hydroxylase (Ch25h) by interleukin-4 (IL-4) and interleukin-13 (IL-13) via the transcription factor STAT6, causing 25-hydroxycholesterol (25HC) accumulation. scRNA-seq analysis confirmed that CH25Hhi subsets were enriched in immunosuppressive macrophage subsets and correlated to lower survival rates in pan-cancers. Targeting CH25H abrogated macrophage immunosuppressive function to enhance infiltrating T cell numbers and activation, which synergized with anti-PD-1 to improve anti-tumor efficacy. Mechanically, lysosome-accumulated 25HC competed with cholesterol for GPR155 binding to inhibit the kinase mTORC1, leading to AMPKα activation and metabolic reprogramming. AMPKα also phosphorylated STAT6 Ser564 to enhance STAT6 activation and ARG1 production. Together, we propose CH25H as an immunometabolic checkpoint, which manipulates macrophage fate to reshape CD8+ T cell surveillance and anti-tumor response.

Pathogenic mycobacterium upregulates cholesterol 25-hydroxylase to promote granuloma development via foam cell formation

Pathogenic mycobacteria orchestrate the complex cell populations known as granuloma that is the hallmark of tuberculosis. Foam cells, a lipid-rich cell-type, are considered critical for granuloma formation; however, the causative factor in foam cell formation remains unclear. Atherosclerosis is a chronic inflammatory disease characterized by the abundant accumulation of lipid-laden-macrophage-derived foam cells during which cholesterol 25-hydroxylase (CH25H) is crucial in foam cell formation. Here, we show that M. marinum (Mm), a relative of M. tuberculosis, induces foam cell formation, leading to granuloma development following CH25H upregulation. Moreover, the Mm-driven increase in CH25H expression is associated with the presence of phthiocerol dimycocerosate, a determinant for Mm virulence and integrity. CH25H-null mice showed decreased foam cell formation and attenuated pathology. Atorvastatin, a recommended first-line lipid-lowering drug, promoted the elimination of M. marinum and concomitantly reduced CH25H production. These results define a previously unknown role for CH25H in controlling macrophage-derived foam cell formation and Tuberculosis pathology.

Identification of marker genes for spinal cord injury

Introduction

Spinal cord injury (SCI) is a profoundly disabling and devastating neurological condition, significantly impacting patients' quality of life. It imposes unbearable psychological and economic pressure on both patients and their families, as well as placing a heavy burden on society.

Methods

In this study, we integrated datasets GSE5296 and GSE47681 as training groups, analyzed gene variances between sham group and SCI group mice, and conducted Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis based on the differentially expressed genes. Subsequently, we performed Weighted Gene Correlation Network Analysis (WGCNA) and Lasso regression analyses.

Results

We identified four characteristic disease genes: Icam1, Ch25h, Plaur and Tm4sf1. We examined the relationship between SCI and immune cells, and validated the expression of the identified disease-related genes in SCI rats using PCR and immunohistochemistry experiments.

Discussion

In conclusion, we have identified and verified four genes related to SCI: Icam1, Ch25h, Plaur and Tm4sf1, which could offer insights for SCI treatment.

25-Hydroxycholesterol in health and diseases

Cholesterol is an essential structural component of all membranes of mammalian cells where it plays a fundamental role not only in cellular architecture, but also, for example, in signaling pathway transduction, endocytosis process, receptor functioning and recycling, or cytoskeleton remodeling. Consequently, intracellular cholesterol concentrations are tightly regulated by complex processes, including cholesterol synthesis, uptake from circulating lipoproteins, lipid transfer to these lipoproteins, esterification, and metabolization into oxysterols that are intermediates for bile acids. Oxysterols have been considered for long time as sterol waste products, but a large body of evidence has clearly demonstrated that they play key roles in central nervous system functioning, immune cell response, cell death, or migration and are involved in age-related diseases, cancers, autoimmunity, or neurological disorders. Among all the existing oxysterols, this review summarizes basic as well as recent knowledge on 25-hydroxycholesterol which is mainly produced during inflammatory or infectious situations and that in turn contributes to immune response, central nervous system disorders, atherosclerosis, macular degeneration, or cancer development. Effects of its metabolite 7α,25-dihydroxycholesterol are also presented and discussed.

Inhibition of EphA2 protects against atherosclerosis by synergizing with statins to mitigate macrophage inflammation

Statins are highly prevalent in patients with coronary artery disease. Statins exert their anti-inflammatory effects on the vascular wall and circulating levels of pro-inflammatory cytokines. However, increasing attention revealed the exacerbation of macrophage inflammation induced by statins, and a clear mechanistic explanation of whether the detrimental effects of statins on macrophage inflammatory phenotypes outweigh the beneficial effects is has not yet been established. Here, RNA-sequencing and RT-qPCR analyses demonstrated that statins significantly upregulated EphA2, Nlrp3, IL-1β and TNF-α expression in macrophages. Mechanistically, we found that atorvastatin reduced KLF4 binding to the EphA2 promoter using KLF4-chromatin immunoprecipitation, suppressed HDAC11-mediated deacetylation and subsequently led to enhanced EphA2 transcription. The 4D-label-free proteomics analysis further confirmed the upregulated EphA2 and inflammatory signals. Furthermore, the proinflammatory effect of atorvastatin was neutralized by an addition of recombinant Fc-ephrinA1, a selective Eph receptor tyrosine kinase inhibitor (ALW-II-41-27) or EphA2-silencing adenovirus (siEphA2). In vivo, EphA2 was identified a proatherogenic factor and apoE-/- mice placed on a high-fat diet following gastric gavage with atorvastatin exhibited a consistent elevation in EphA2 expression. We further observed that the transfection with siEphA2 in atorvastatin-treated mice significantly attenuated atherosclerotic plaque formation and abrogated statin-orchestrated macrophages proinflammatory genes expression as compared to that in atorvastatin alone. Increased plaque stability index was also observed following the addition of siEphA2, as evidenced by increased collagen and smooth muscle content and diminished lipid accumulation and macrophage infiltration. The data suggest that blockage of EphA2 provides an additional therapeutic benefit for further improving the anti-atherogenic effects of statins.

Soluble CD83 modulates human-monocyte-derived macrophages toward alternative phenotype, function, and metabolism

Alterations in macrophage (Mφ) polarization, function, and metabolic signature can foster development of chronic diseases, such as autoimmunity or fibrotic tissue remodeling. Thus, identification of novel therapeutic agents that modulate human Mφ biology is crucial for treatment of such conditions. Herein, we demonstrate that the soluble CD83 (sCD83) protein induces pro-resolving features in human monocyte-derived Mφ biology. We show that sCD83 strikingly increases the expression of inhibitory molecules including ILT-2 (immunoglobulin-like transcript 2), ILT-4, ILT-5, and CD163, whereas activation markers, such as MHC-II and MSR-1, were significantly downregulated. This goes along with a decreased capacity to stimulate alloreactive T cells in mixed lymphocyte reaction (MLR) assays. Bulk RNA sequencing and pathway analyses revealed that sCD83 downregulates pathways associated with pro-inflammatory, classically activated Mφ (CAM) differentiation including HIF-1A, IL-6, and cytokine storm, whereas pathways related to alternative Mφ activation and liver X receptor were significantly induced. By using the LXR pathway antagonist GSK2033, we show that transcription of specific genes (e.g., PPARG, ABCA1, ABCG1, CD36) induced by sCD83 is dependent on LXR activation. In summary, we herein reveal for the first time mechanistic insights into the modulation of human Mφ biology by sCD83, which is a further crucial preclinical study for the establishment of sCD83 as a new therapeutical agent to treat inflammatory conditions.

Impact of Immunity on Coronary Artery Disease: An Updated Pathogenic Interplay and Potential Therapeutic Strategies

Coronary artery disease (CAD) is the leading cause of death worldwide. It is a result of the buildup of atherosclerosis within the coronary arteries. The role of the immune system in CAD is complex and multifaceted. The immune system responds to damage or injury to the arterial walls by initiating an inflammatory response. However, this inflammatory response can become chronic and lead to plaque formation. Neutrophiles, macrophages, B lymphocytes, T lymphocytes, and NKT cells play a key role in immunity response, both with proatherogenic and antiatherogenic signaling pathways. Recent findings provide new roles and activities referring to endothelial cells and vascular smooth muscle cells, which help to clarify the intricate signaling crosstalk between the involved actors. Research is ongoing to explore immunomodulatory therapies that target the immune system to reduce inflammation and its contribution to atherosclerosis. This review aims to summarize the pathogenic interplay between immunity and CAD and the potential therapeutic strategies, and explore immunomodulatory therapies that target the immune system to reduce inflammation and its contribution to atherosclerosis.

Galectin-3 as TREM2 upstream factor contributes to lung ischemia-reperfusion injury by regulating macrophage polarization

Lung ischemia-reperfusion injury (LIRI) is a complex "aseptic" inflammatory response, macrophage play a pivotal role in the pathogenesis of LIRI. Galectin-3 (Gal3), a lectin implicated inflammation, has received limited attention in LIRI. Studies have reported Gal3 as a ligand for triggering receptor expressed on myeloid cell 2 (TREM2) in macrophages in Alzheimer's disease. Hence, we established LIRI C57BL/6 mice model and hypoxia/glucose deprivation and reoxygenation (OGD/R) model to investigate the relationship among Gal3, TREM2, and macrophage polarization. Our result demonstrated inhibition of Gal3 significantly reduced M1-type macrophage polarization while markedly increased M2-type in LIRI. In addition, we observed colocalization of Gal3 and TREM2 in macrophages, inhibition of Gal3 could recover the downregulation of TREM2 induced by LIRI while promoting TREM2 expression could attenuate lung injury in LIRI. In summary, our findings suggest Gal3 as an upstream factor of TREM2, play a crucial role in LIRI by regulating macrophage polarization.

Emerging Insights into Liver X Receptor α in the Tumorigenesis and Therapeutics of Human Cancers

Liver X receptor α (LXRα), a member of the nuclear receptor superfamily, is identified as a protein activated by ligands that interacts with the promoters of specific genes. It regulates cholesterol, bile acid, and lipid metabolism in normal physiological processes, and it participates in the development of some related diseases. However, many studies have demonstrated that LXRα is also involved in regulating numerous human malignancies. Aberrant LXRα expression is emerging as a fundamental and pivotal factor in cancer cell proliferation, invasion, apoptosis, and metastasis. Herein, we outline the expression levels of LXRα between tumor tissues and normal tissues via the Oncomine and Tumor Immune Estimation Resource (TIMER) 2.0 databases; summarize emerging insights into the roles of LXRα in the development, progression, and treatment of different human cancers and their diversified mechanisms; and highlight that LXRα can be a biomarker and therapeutic target in diverse cancers.

Agmatine-IRF2BP2 interaction induces M2 phenotype of microglia by increasing IRF2-KLF4 signaling

BACKGROUND

Following central nervous system (CNS) injury, the investigation for neuroinflammation is vital because of its pleiotropic role in both acute injury and long-term recovery. Agmatine (Agm) is well known for its neuroprotective effects and anti-neuroinflammatory properties. However, Agm's mechanism for neuroprotection is still unclear. We screened target proteins that bind to Agm using a protein microarray; the results showed that Agm strongly binds to interferon regulatory factor 2 binding protein (IRF2BP2), which partakes in the inflammatory response. Based on these prior data, we attempted to elucidate the mechanism by which the combination of Agm and IRF2BP2 induces a neuroprotective phenotype of microglia.

METHODS

To confirm the relationship between Agm and IRF2BP2 in neuroinflammation, we used microglia cell-line (BV2) and treated with lipopolysaccharide from Escherichia coli 0111:B4 (LPS; 20 ng/mL, 24 h) and interleukin (IL)-4 (20 ng/mL, 24 h). Although Agm bound to IRF2BP2, it failed to enhance IRF2BP2 expression in BV2. Therefore, we shifted our focus onto interferon regulatory factor 2 (IRF2), which is a transcription factor and interacts with IRF2BP2.

RESULTS

IRF2 was highly expressed in BV2 after LPS treatment but not after IL-4 treatment. When Agm bound to IRF2BP2 following Agm treatment, the free IRF2 translocated to the nucleus of BV2. The translocated IRF2 activated the transcription of Kruppel-like factor 4 (KLF4), causing KLF4 to be induced in BV2. The expression of KLF4 increased the CD206-positive cells in BV2.

CONCLUSIONS

Taken together, unbound IRF2, resulting from the competitive binding of Agm to IRF2BP2, may provide neuroprotection against neuroinflammation via an anti-inflammatory mechanism of microglia involving the expression of KLF4.

Evolving Diagnostic and Treatment Strategies for Pediatric CNS Tumors: The Impact of Lipid Metabolism

Pediatric neurological tumors are a heterogeneous group of cancers, many of which carry a poor prognosis and lack a "standard of care" therapy. While they have similar anatomic locations, pediatric neurological tumors harbor specific molecular signatures that distinguish them from adult brain and other neurological cancers. Recent advances through the application of genetics and imaging tools have reshaped the molecular classification and treatment of pediatric neurological tumors, specifically considering the molecular alterations involved. A multidisciplinary effort is ongoing to develop new therapeutic strategies for these tumors, employing innovative and established approaches. Strikingly, there is increasing evidence that lipid metabolism is altered during the development of these types of tumors. Thus, in addition to targeted therapies focusing on classical oncogenes, new treatments are being developed based on a broad spectrum of strategies, ranging from vaccines to viral vectors, and melitherapy. This work reviews the current therapeutic landscape for pediatric brain tumors, considering new emerging treatments and ongoing clinical trials. In addition, the role of lipid metabolism in these neoplasms and its relevance for the development of novel therapies are discussed.

The role of KLF transcription factor in the regulation of cancer progression

Kruppel-like factors (KLFs) are a family of zinc finger transcription factors that have been found to play an essential role in the development of various human tissues, including epithelial, teeth, and nerves. In addition to regulating normal physiological processes, KLFs have been implicated in promoting the onset of several cancers, such as gastric cancer, lung cancer, breast cancer, liver cancer, and colon cancer. To inhibit cancer progression, various existing medicines have been used to modulate the expression of KLFs, and anti-microRNA treatments have also emerged as a potential strategy for many cancers. Investigating the possibility of targeting KLFs in cancer therapy is urgently needed, as the roles of KLFs in cancer have not received enough attention in recent years. This review summarizes the factors that regulate KLF expression and function at both the transcriptional and posttranscriptional levels, which could aid in understanding the mechanisms of KLFs in cancer progression. We hope that this review will contribute to the development of more effective anti-cancer medicines targeting KLFs in the future.

25-Hydroxycholesterol exacerbates vascular leak during acute lung injury

Cholesterol-25-hydroxylase (CH25H), the biosynthetic enzyme for 25-hydroxycholesterol (25HC), is most highly expressed in the lung, but its role in lung biology is poorly defined. Recently, we reported that Ch25h is induced in monocyte-derived macrophages recruited to the airspace during resolution of lung inflammation and that 25HC promotes liver X receptor-dependent (LXR-dependent) clearance of apoptotic neutrophils by these cells. Ch25h and 25HC are, however, also robustly induced by lung-resident cells during the early hours of lung inflammation, suggesting additional cellular sources and targets. Here, using Ch25h-/- mice and exogenous 25HC in lung injury models, we provide evidence that 25HC sustains proinflammatory cytokines in the airspace and augments lung injury, at least in part, by inducing LXR-independent endoplasmic reticulum stress and endothelial leak. Suggesting an autocrine effect in endothelium, inhaled LPS upregulates pulmonary endothelial Ch25h, and non-hematopoietic Ch25h deletion is sufficient to confer lung protection. In patients with acute respiratory distress syndrome, airspace 25HC and alveolar macrophage CH25H were associated with markers of microvascular leak, endothelial activation, endoplasmic reticulum stress, inflammation, and clinical severity. Taken together, our findings suggest that 25HC deriving from and acting on different cell types in the lung communicates distinct, temporal LXR-independent and -dependent signals to regulate inflammatory homeostasis.

Mitochondrial dysfunction caused by SIRT3 inhibition drives proinflammatory macrophage polarization in obesity

OBJECTIVE

Metabolic reprogramming is a main feature of proinflammatory macrophage polarization, a process that leads to inflammation in dysfunctional adipose tissue. Therefore, the study aim was to explore whether sirtuin 3 (SIRT3), a mitochondrial deacetylase, participates in this pathophysiological process.

METHODS

Macrophage-specific Sirt3 knockout (Sirt3-MKO) mice and wild-type littermates were treated with a high-fat diet. Body weight, glucose tolerance, and inflammation were evaluated. Bone marrow-derived macrophages and RAW264.7 cells were treated with palmitic acid to explore the mechanism of SIRT3 on inflammation.

RESULTS

The expression of SIRT3 was significantly repressed in both bone marrow-derived macrophages and adipose tissue macrophages in mice fed with a high-fat diet. Sirt3-MKO mice exhibited accelerated body weight and severe inflammation, accompanied with reduced energy expenditure and worsened glucose metabolism. In vitro experiments showed that SIRT3 inhibition or knockdown exacerbated palmitic acid-induced proinflammatory macrophage polarization, whereas SIRT3 restoration displayed opposite effects. Mechanistically, SIRT3 deficiency resulted in hyperacetylation of succinate dehydrogenase that led to succinate accumulation, which suppressed the transcription of Kruppel-like factor 4 via increasing histone methylation on its promoter, thus evoking proinflammatory macrophages.

CONCLUSIONS

This study emphasizes an important preventive role of SIRT3 in macrophage polarization and implies that SIRT3 is a promising therapeutic target for obesity.

Participation of Krüppel-like Factors in Atherogenesis

Atherosclerosis is an important problem in modern medicine, the keys to understanding many aspects of which are still not available to clinicians. Atherosclerosis develops as a result of a complex chain of events in which many cells of the vascular wall and peripheral blood flow are involved. Endothelial cells, which line the vascular wall in a monolayer, play an important role in vascular biology. A growing body of evidence strengthens the understanding of the multifaceted functions of endothelial cells, which not only organize the barrier between blood flow and tissues but also act as regulators of hemodynamics and play an important role in regulating the function of other cells in the vascular wall. Krüppel-like factors (KLFs) perform several biological functions in various cells of the vascular wall. The large family of KLFs in humans includes 18 members, among which KLF2 and KLF4 are at the crossroads between endothelial cell mechanobiology and immunometabolism, which play important roles in both the normal vascular wall and atherosclerosis.

Endothelial cell-derived oxysterol ablation attenuates experimental autoimmune encephalomyelitis

The vasculature is a key regulator of leukocyte trafficking into the central nervous system (CNS) during inflammatory diseases including multiple sclerosis (MS). However, the impact of endothelial-derived factors on CNS immune responses remains unknown. Bioactive lipids, in particular oxysterols downstream of Cholesterol-25-hydroxylase (Ch25h), promote neuroinflammation but their functions in the CNS are not well-understood. Using floxed-reporter Ch25h knock-in mice, we trace Ch25h expression to CNS endothelial cells (ECs) and myeloid cells and demonstrate that Ch25h ablation specifically from ECs attenuates experimental autoimmune encephalomyelitis (EAE). Mechanistically, inflamed Ch25h-deficient CNS ECs display altered lipid metabolism favoring polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) expansion, which suppresses encephalitogenic T lymphocyte proliferation. Additionally, endothelial Ch25h-deficiency combined with immature neutrophil mobilization into the blood circulation nearly completely protects mice from EAE. Our findings reveal a central role for CNS endothelial Ch25h in promoting neuroinflammation by inhibiting the expansion of immunosuppressive myeloid cell populations.

ACSL1, CH25H, GPCPD1, and PLA2G12A as the potential lipid-related diagnostic biomarkers of acute myocardial infarction

Lipid metabolism plays an essential role in the genesis and progress of acute myocardial infarction (AMI). Herein, we identified and verified latent lipid-related genes involved in AMI by bioinformatic analysis. Lipid-related differentially expressed genes (DEGs) involved in AMI were identified using the GSE66360 dataset from the Gene Expression Omnibus (GEO) database and R software packages. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were conducted to analyze lipid-related DEGs. Lipid-related genes were identified by two machine learning techniques: least absolute shrinkage and selection operator (LASSO) regression and support vector machine recursive feature elimination (SVM-RFE). The receiver operating characteristic (ROC) curves were used to descript diagnostic accuracy. Furthermore, blood samples were collected from AMI patients and healthy individuals, and real-time quantitative polymerase chain reaction (RT-qPCR) was used to determine the RNA levels of four lipid-related DEGs. Fifty lipid-related DEGs were identified, 28 upregulated and 22 downregulated. Several enrichment terms related to lipid metabolism were found by GO and KEGG enrichment analyses. After LASSO and SVM-RFE screening, four genes (ACSL1, CH25H, GPCPD1, and PLA2G12A) were identified as potential diagnostic biomarkers for AMI. Moreover, the RT-qPCR analysis indicated that the expression levels of four DEGs in AMI patients and healthy individuals were consistent with bioinformatics analysis results. The validation of clinical samples suggested that 4 lipid-related DEGs are expected to be diagnostic markers for AMI and provide new targets for lipid therapy of AMI.

Macrophage-Derived 25-Hydroxycholesterol Promotes Vascular Inflammation, Atherogenesis, and Lesion Remodeling

BACKGROUND

Cross-talk between sterol metabolism and inflammatory pathways has been demonstrated to significantly affect the development of atherosclerosis. Cholesterol biosynthetic intermediates and derivatives are increasingly recognized as key immune regulators of macrophages in response to innate immune activation and lipid overloading. 25-Hydroxycholesterol (25-HC) is produced as an oxidation product of cholesterol by the enzyme cholesterol 25-hydroxylase (CH25H) and belongs to a family of bioactive cholesterol derivatives produced by cells in response to fluctuating cholesterol levels and immune activation. Despite the major role of 25-HC as a mediator of innate and adaptive immune responses, its contribution during the progression of atherosclerosis remains unclear.

METHODS

The levels of 25-HC were analyzed by liquid chromatography-mass spectrometry, and the expression of CH25H in different macrophage populations of human or mouse atherosclerotic plaques, respectively. The effect of CH25H on atherosclerosis progression was analyzed by bone marrow adoptive transfer of cells from wild-type or Ch25h-/- mice to lethally irradiated Ldlr-/- mice, followed by a Western diet feeding for 12 weeks. Lipidomic, transcriptomic analysis and effects on macrophage function and signaling were analyzed in vitro from lipid-loaded macrophage isolated from Ldlr-/- or Ch25h-/-;Ldlr-/- mice. The contribution of secreted 25-HC to fibrous cap formation was analyzed using a smooth muscle cell lineage-tracing mouse model, Myh11ERT2CREmT/mG;Ldlr-/-, adoptively transferred with wild-type or Ch25h-/- mice bone marrow followed by 12 weeks of Western diet feeding.

RESULTS

We found that 25-HC accumulated in human coronary atherosclerotic lesions and that macrophage-derived 25-HC accelerated atherosclerosis progression, promoting plaque instability through autocrine and paracrine actions. 25-HC amplified the inflammatory response of lipid-loaded macrophages and inhibited the migration of smooth muscle cells within the plaque. 25-HC intensified inflammatory responses of lipid-laden macrophages by modifying the pool of accessible cholesterol in the plasma membrane, which altered Toll-like receptor 4 signaling, promoted nuclear factor-κB-mediated proinflammatory gene expression, and increased apoptosis susceptibility. These effects were independent of 25-HC-mediated modulation of liver X receptor or SREBP (sterol regulatory element-binding protein) transcriptional activity.

CONCLUSIONS

Production of 25-HC by activated macrophages amplifies their inflammatory phenotype, thus promoting atherogenesis.

Macrophage polarization states in atherosclerosis

Atherosclerosis, a chronic inflammatory condition primarily affecting large and medium arteries, is the main cause of cardiovascular diseases. Macrophages are key mediators of inflammatory responses. They are involved in all stages of atherosclerosis development and progression, from plaque formation to transition into vulnerable plaques, and are considered important therapeutic targets. Increasing evidence suggests that the modulation of macrophage polarization can effectively control the progression of atherosclerosis. Herein, we explore the role of macrophage polarization in the progression of atherosclerosis and summarize emerging therapies for the regulation of macrophage polarization. Thus, the aim is to inspire new avenues of research in disease mechanisms and clinical prevention and treatment of atherosclerosis.

Role of Oxysterols in the Activation of the NLRP3 Inflammasome as a Potential Pharmacological Approach in Alzheimer's Disease

Alzheimer's disease (AD), the most prevalent form of dementia, is a complex clinical condition with multifactorial origin posing a major burden to health care systems across the world. Even though the pathophysiological mechanisms underlying the disease are still unclear, both central and peripheral inflammation has been implicated in the process. Piling evidence shows that the nucleotide-binding domain, leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome is activated in AD. As dyslipidemia is a risk factor for dementia, and cholesterol can also activate the inflammasome, a possible link between lipid levels and the NLRP3 inflammasome has been proposed in Alzheimer's. It is also speculated that not only cholesterol but also its metabolites, the oxysterols, may be involved in AD pathology. In this context, mounting data suggest that NLRP3 inflammasome activity can be modulated by different peripheral nuclear receptors, including liver-X receptors, which present oxysterols as endogenous ligands. In light of this, the current review explores whether the activation of NLRP3 by nuclear receptors, mediated by oxysterols, may also be involved in AD and could serve as a potential pharmacological avenue in dementia.

Shear Stress and Metabolic Disorders-Two Sides of the Same Plaque

Significance: Shear stress and metabolic disorder are the two sides of the same atherosclerotic coin. Atherosclerotic lesions are prone to develop at branches and curvatures of arteries, which are exposed to oscillatory and low shear stress exerted by blood flow. Meanwhile, metabolic disorders are pivotal contributors to the formation and advancement of atherosclerotic plaques. Recent Advances: Accumulated evidence has provided insight into the impact and mechanisms of biomechanical forces and metabolic disorder on atherogenesis, in association with mechanotransduction, epigenetic regulation, and so on. Moreover, recent studies have shed light on the cross talk between the two drivers of atherosclerosis. Critical Issues: There are extensive cross talk and interactions between shear stress and metabolic disorder during the pathogenesis of atherosclerosis. The communications may amplify the proatherogenic effects through increasing oxidative stress and inflammation. Nonetheless, the precise mechanisms underlying such interactions remain to be fully elucidated as the cross talk network is considerably complex. Future Directions: A better understanding of the cross talk network may confer benefits for a more comprehensive clinical management of atherosclerosis. Critical mediators of the cross talk may serve as promising therapeutic targets for atherosclerotic vascular diseases, as they can inhibit effects from both sides of the plaque. Hence, further in-depth investigations with advanced omics approaches are required to develop novel and effective therapeutic strategies against atherosclerosis. Antioxid. Redox Signal. 37, 820-841.

JAG1-NOTCH4 mechanosensing drives atherosclerosis

Endothelial cell (EC) sensing of disturbed blood flow triggers atherosclerosis, a disease of arteries that causes heart attack and stroke, through poorly defined mechanisms. The Notch pathway plays a central role in blood vessel growth and homeostasis, but its potential role in sensing of disturbed flow has not been previously studied. Here, we show using porcine and murine arteries and cultured human coronary artery EC that disturbed flow activates the JAG1-NOTCH4 signaling pathway. Light-sheet imaging revealed enrichment of JAG1 and NOTCH4 in EC of atherosclerotic plaques, and EC-specific genetic deletion of Jag1 (Jag1ECKO) demonstrated that Jag1 promotes atherosclerosis at sites of disturbed flow. Mechanistically, single-cell RNA sequencing in Jag1ECKO mice demonstrated that Jag1 suppresses subsets of ECs that proliferate and migrate. We conclude that JAG1-NOTCH4 sensing of disturbed flow enhances atherosclerosis susceptibility by regulating EC heterogeneity and that therapeutic targeting of this pathway may treat atherosclerosis.

Therapeutic potential of traditional Chinese medicine in atherosclerosis: A review

Atherosclerosis is the onset of endothelial cell damage and is characterized by abnormal accumulation of fibrinogen and lipid in large and middle arteries. Recent researches indicate that traditional Chinese medicine including Notoginseng Radix et Rhizoma, Astragali Radix, Salviae Miltiorrhizae Radix et Rhizoma, Ginseng Radix et Rhizoma, Fructus Crataegi, Glycyrrhizae Radix et Rhizoma, Polygoni Multiflori Radix, Fructus Lycii, and Coptidis Rhizoma have therapeutic effects on atherosclerosis. Furthermore, the pharmacological roles of these kinds of traditional Chinese medicine in atherosclerosis refer to endothelial function influences, cell proliferation and migration, platelet aggregation, thrombus formation, oxidative stress, inflammation, angiogenesis, apoptosis, autophagy, lipid metabolism, and the gut microbiome. Traditional Chinese medicine may serve as potential and effective anti-atherosclerosis drugs. However, a critical study has shown that Notoginseng Radix et Rhizoma may also have toxic effects including pustules, fever, and elevate circulating neutrophil count. Further high-quality studies are still required to determine the clinical safety and efficacy of traditional Chinese medicine and its active ingredients.

Liver X Receptor: a potential target in the treatment of atherosclerosis

INTRODUCTION

Liver X receptors (LXRs) are master regulators of atherogenesis. Their anti-atherogenic potential has been attributed to their role in the inhibition of macrophage-mediated inflammation and promotion of reverse cholesterol transport. Owing to the significance of their anti-atherogenic potential, it is essential to develop and test new generation LXR agonists, both synthetic and natural, to identify potential LXR-targeted therapeutics for the future.

AREAS COVERED

This review describes the role of LXRs in atherosclerotic development, provides a summary of LXR agonists and future directions for atherosclerosis research. We searched PubMed, Scopus and Google Scholar for relevant reports, from last 10 years, using atherosclerosis, liver X receptor, and LXR agonist as keywords.

EXPERT OPINION

LXRα has gained widespread recognition as a regulator of cholesterol homeostasis and expression of inflammatory genes. Further research using models of cell type-specific knockout and specific agonist-targeted LXR isoforms is warranted. Enthusiasm for therapeutic value of LXR agonists has been tempered due to LXRα-mediated induction of hepatic lipogenesis. LXRα agonism and LXRβ targeting, gut-specific inverse LXR agonists, investigations combining LXR agonists with other lipogenesis mitigating agents, like IDOL antagonists and synthetic HDL, and targeting ABCA1, M2 macrophages and LXRα phosphorylation, remain as promising possibilities.

Histone Deacetylase9 Represents the Epigenetic Promotion of M1 Macrophage Polarization and Inflammatory Response via TLR4 Regulation

Atherosclerosis is a chronic inflammatory response mediated by various factors, where epigenetic regulation involving histone deacetylation is envisaged to modulate the expression of related proteins by regulating the binding of transcription factors to DNA, thereby influencing the development of atherosclerosis. The mechanism of atherosclerosis by histone deacetylation is partly known; hence, this project aimed at investigating the role of histone deacetylase 9 (HDAC9) in atherosclerosis. For this purpose, serum was separated from blood samples following clotting and centrifugation from atherosclerotic and healthy patients (n = 40 each), and then, various tests were performed. The results indicated that toll-like receptor 4 (TLR4) was not only positively correlated to the HDAC9 gene, but was also upregulated in atherosclerosis, where it was also significantly upregulated in the atherosclerosis cell model of oxidized low-density lipoprotein-induced macrophages. Conversely, the TLR4 was significantly downregulated in instances of loss of HDAC9 function, cementing the bridging relationship between HDAC9 and macrophage polarization, where the HDAC9 was found to upregulate M1 macrophage polarization which translated into the release of higher content of proinflammatory cytokines such as interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α), which tend to significantly decrease following the deletion of TLR4. Hence, this study reports novel relation between epigenetic control and atherosclerosis, which could partly be explained by histone deacetylation.

Endothelial shear stress signal transduction and atherogenesis: From mechanisms to therapeutics

Atherosclerotic vascular disease and its complications are among the top causes of mortality worldwide. In the vascular lumen, atherosclerotic plaques are not randomly distributed. Instead, they are preferentially localized at the curvature and bifurcations along the arterial tree, where shear stress is low or disturbed. Numerous studies demonstrate that endothelial cell phenotypic change (e.g., inflammation, oxidative stress, endoplasmic reticulum stress, apoptosis, autophagy, endothelial-mesenchymal transition, endothelial permeability, epigenetic regulation, and endothelial metabolic adaptation) induced by oscillatory shear force play a fundamental role in the initiation and progression of atherosclerosis. Mechano-sensors, adaptor proteins, kinases, and transcriptional factors work closely at different layers to transduce the shear stress force from the plasma membrane to the nucleus in endothelial cells, thereby controlling the expression of genes that determine cell fate and phenotype. An in-depth understanding of these mechano-sensitive signaling cascades shall provide new translational strategies for therapeutic intervention of atherosclerotic vascular disease. This review updates the recent advances in endothelial mechano-transduction and its role in the pathogenesis of atherosclerosis, and highlights the perspective of new anti-atherosclerosis therapies through targeting these mechano-regulated signaling molecules.

25-Hydroxycholesterol as a Signaling Molecule of the Nervous System

Cholesterol is an essential component of plasma membrane and precursor of biological active compounds, including hydroxycholesterols (HCs). HCs regulate cellular homeostasis of cholesterol; they can pass across the membrane and vascular barriers and act distantly as para- and endocrine agents. A small amount of 25-hydroxycholesterol (25-HC) is produced in the endoplasmic reticulum of most cells, where it serves as a potent regulator of the synthesis, intracellular transport, and storage of cholesterol. Production of 25-HC is strongly increased in the macrophages, dendrite cells, and microglia at the inflammatory response. The synthesis of 25-HC can be also upregulated in some neurological disorders, such as Alzheimer’s disease, amyotrophic lateral sclerosis, spastic paraplegia type 5, and X-linked adrenoleukodystrophy. However, it is unclear whether 25-HC aggravates these pathologies or has the protective properties. The molecular targets for 25-HC are transcriptional factors (LX receptors, SREBP2, ROR), G protein-coupled receptor (GPR183), ion channels (NMDA receptors, SLO1), adhesive molecules (α5β1 and ανβ3 integrins), and oxysterol-binding proteins. The diversity of 25-HC-binding proteins points to the ability of HC to affect many physiological and pathological processes. In this review, we focused on the regulation of 25-HC production and its universal role in the control of cellular cholesterol homeostasis, as well as the effects of 25-HC as a signaling molecule mediating the influence of inflammation on the processes in the neuromuscular system and brain. Based on the evidence collected, it can be suggested that 25-HC prevents accumulation of cellular cholesterol and serves as a potent modulator of neuroinflammation, synaptic transmission, and myelinization. An increased production of 25-HC in response to a various type of damage can have a protective role and reduce neuronal loss. At the same time, an excess of 25-HC may exert the neurotoxic effects.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Ch25h and 25-HC prevent liver steatosis through regulation of cholesterol metabolism and inflammation

Non-alcoholic fatty liver disease (NAFLD) is currently the most prevalent metabolic disorder all over the world, and lipid metabolic disorders and inflammation are closely associated and contribute to the pathogenesis of NAFLD. Cholesterol 25-hydroxylase (Ch25h) and its product, 25-hydroxycholesterol (25-HC), play important roles in cholesterol homeostasis and inflammation, but whether Ch25h and 25-HC are involved in NAFLD remains uncertain. In this study, we use Ch25h knockout mice, hepatic cells and liver biopsies to explore the role of Ch25h and 25-HC in lipid metabolism and accumulation in liver, determine the molecular mechanism of lipid accumulation and inflammation influenced by Ch25h and 25-HC, and assess the regulatory effects of Ch25h and 25-HC on human NAFLD. Our results indicate that mice lacking Ch25h have normal cholesterol homeostasis with normal diet, but under the condition of high fat diet (HFD), the mice show higher total cholesterol and triglyceride in serum, and prone to hepatic steatosis. Ch25h deficiency reduces the cholesterol efflux regulated by liver X receptor α (LXRα), increases the synthesis of cholesterol mediated by sterol-regulatory element binding protein 2 (SREBP-2), and increases the activation of NLRP3 inflammasome, therefore promotes hepatic steatosis. Collectively, our data suggest that Ch25h and 25-HC play important roles in lipid metabolism and inflammation, thereby exerting anti-NAFLD functions.

Effects of Oxysterols on Immune Cells and Related Diseases

Oxysterols are the products of cholesterol oxidation. They have a wide range of effects on several cells, organs, and systems in the body. Oxysterols also have an influence on the physiology of the immune system, from immune cell maturation and migration to innate and humoral immune responses. In this regard, oxysterols have been involved in several diseases that have an immune component, from autoimmune and neurodegenerative diseases to inflammatory diseases, atherosclerosis, and cancer. Here, we review data on the participation of oxysterols, mainly 25-hydroxycholesterol and 7α,25-dihydroxycholesterol, in the immune system and related diseases. The effects of these oxysterols and main oxysterol receptors, LXR and EBI2, in cells of the immune system (B cells, T cells, macrophages, dendritic cells, oligodendrocytes, and astrocytes), and in immune-related diseases, such as neurodegenerative diseases, intestinal diseases, cancer, respiratory diseases, and atherosclerosis, are discussed.

Shyy J. Hepatic Reduction in Cholesterol 25-Hydroxylase Aggravates Diet-induced Steatosis

BACKGROUND & AIMS

Cholesterol 25-hydroxylase (Ch25h), converting cholesterol to 25-hydroxycholesterol (25-HC), is critical in modulating cellular lipid metabolism and anti-inflammatory and antiviral activities. However, its role in nonalcoholic fatty liver disease remains unclear.

METHODS

Ch25h expression was detected in livers of ob/ob mice and E3 rats fed a high-fat diet (HFD). Gain- or loss-of-function of Ch25h was performed using Ch25h^+/+ (wild type [WT]) mice receiving AAV8-Ch25h or Ch25h knockout (Ch25h^-/-) mice. WT mice fed an HFD were administered with 25-HC. The Ch25h-LXRα-CYP axis was measured in primary hepatocytes isolated from WT and Ch25h^-/- mice.

RESULTS

We found that Ch25h level was decreased in livers of ob/ob mice and E3 rats fed an HFD. Ch25h^-/- mice fed an HFD showed aggravated fatty liver and decreased level of cytochrome P450 7A1 (CYP7A1), in comparison with their WT littermates. RNA-seq analysis revealed that the differentially expressed genes in livers of HFD-fed Ch25h^-/- mice were involved in pathways of positive regulation of lipid metabolic process, steroid metabolic process, cholesterol metabolic process, and bile acid biosynthetic process. As gain-of-function experiments, WT mice receiving AAV8-Ch25h or 25-HC showed alleviated NAFLD, when compared with the control group receiving AAV8-control or vehicle control. Consistently, Ch25h overexpression significantly elevated the levels of primary and secondary bile acids and CYP7A1 but decreased those of small heterodimer partner and FGFR4.

CONCLUSIONS

Elevated levels of Ch25h and its enzymatic product 25-HC alleviate HFD-induced hepatic steatosis via regulating enterohepatic circulation of bile acids. The underlying mechanism involves 25-HC activation of CYP7A1 via liver X receptor. These data suggest that targeting Ch25h or 25-HC may have therapeutic advantages against nonalcoholic fatty liver disease.

LINC01915 Facilitates the Conversion of Normal Fibroblasts into Cancer-Associated Fibroblasts Induced by Colorectal Cancer-Derived Extracellular Vesicles through the miR-92a-3p/KLF4/CH25H Axis

Increasing long non-coding RNAs are reported to regulate the cell growth, apoptosis, and metastasis of cancer-associated fibroblasts (CAFs).This study aimed to explore how LINC01915 influences the conversion of normal fibroblasts (NFs) into CAFs in colorectal cancer (CRC). LINC01915 expression was initially measured in clinical tissue samples and in NFs and CAFs. Identification of the interaction between LINC01915, miR-92a-3p, KLF4, and CH25H was done. The effects of LINC01915, miR-92a-3p, and KLF4 on the angiogenesis, extracellular vesicle (EV) uptake by NFs, and activation of stromal cells were assessed using gain- or loss-of-function approaches. Xenograft mouse models were established to validate these in vitro findings in vivo. EVs were shown to stimulate NF proliferation, migration, and angiogenesis, as well as facilitate NF conversion into CAFs. CRC tissues and CAFs showed downregulated expression of LINC01915, which was associated with poor prognosis of patients. Moreover, employed LINC01915 inhibited tumor angiogenesis, CAF activation, and the uptake of tumor-derived EVs by NFs. Mechanistically, LINC01915 could competitively bind to miR-92a-3p and caused upregulation of the miR-92a-3p target KLF4 which, in turn, promoted the transcription of CH25H, leading to the suppressed uptake of EVs by NFs. The in vivo and in vitro experimental results showed that LINC01915 inhibited the uptake of CRC-derived EVs by NFs through the miR-92a-3p/KLF4/CH25H axis, thus arresting the angiogenesis and the conversion of NFs into CAFs and in turn prevent tumor growth. These data together supported the inhibiting role of LINC01915 in the conversion of NFs into CAFs triggered by the CRC-derived EVs and the ensuing tumor growth, which may be related to its regulation on the miR-92a-3p/KLF4/CH25H axis.

Regulation of Macrophage Activation and Differentiation in Atherosclerosis

Chronic inflammation is a hallmark of atherosclerosis and macrophages play a central role in controlling inflammation at all stages of atherosclerosis. In atherosclerosis, macrophages and monocyte-derived macrophages are continuously exposed to cholesterol, oxidized lipids, cell debris, cytokines, and chemokines. Not only do these stimuli induce a specific macrophage phenotype, but they also interact extensively, leading to macrophage heterogeneity in atherosclerotic plaques. Herein, we review the diverse phenotypes of macrophages, the mechanisms underlying macrophage activation, and the contributions of macrophages to atherosclerosis in this context. We also summarize recent studies on foamy macrophages and monocyte-derived macrophages in plaque during disease progression. We provide a comprehensive overview of transcriptional, epigenetic, and metabolic reprogramming of macrophages and discuss the emerging concepts of targeting cytokines and macrophages to modulate atherosclerosis.

Macrophage metabolic regulation in atherosclerotic plaque

Metabolism plays a key role in controlling immune cell functions. In this review, we will discuss the diversity of plaque resident myeloid cells and will focus on their metabolic demands that could reflect on their particular intraplaque localization. Defining the metabolic configuration of plaque resident myeloid cells according to their topologic distribution could provide answers to key questions regarding their functions and contribution to disease development.

Myxomavirus serpin alters macrophage function and prevents diffuse alveolar hemorrhage in pristane-induced lupus

C57BL/6 mice with pristane-induced lupus develop macrophage-dependent diffuse alveolar hemorrhage (DAH), which is blocked by treatment with liver X receptor (LXR) agonists and is exacerbated by low IL-10 levels. Serp-1, a myxomavirus-encoded serpin that impairs macrophage activation and plasminogen activation, blocks DAH caused by MHV68 infection. We investigated whether Serp-1 also could block DAH in pristane-induced lupus. Pristane-induced DAH was prevented by treatment with recombinant Serp-1 and macrophages from Serp1-treated mice exhibited an anti-inflammatory M2-like phenotype. Therapy activated LXR, promoting M2 polarization and expression of Kruppel-like factor-4 (KLH4), which upregulates IL-10. In contrast, deficiency of tissue plasminogen activator or plasminogen activator inhibitor had little effect on DAH. We conclude that Serp-1 blocks pristane-induced lung hemorrhage by enhancing LXR-regulated M2 macrophage polarization and KLH4-regulated IL-10 production. In view of the similarities between DAH in pristane-treated mice and SLE patients, Serp-1 may represent a potential new therapy for this severe complication of SLE.

Role of Tim4 in the regulation of ABCA1+ adipose tissue macrophages and post-prandial cholesterol levels

Dyslipidemia is a main driver of cardiovascular diseases. The ability of macrophages to scavenge excess lipids implicate them as mediators in this process and understanding the mechanisms underlying macrophage lipid metabolism is key to the development of new treatments. Here, we investigated how adipose tissue macrophages regulate post-prandial cholesterol transport. Single-cell RNA sequencing and protected bone marrow chimeras demonstrated that ingestion of lipids led to specific transcriptional activation of a population of resident macrophages expressing Lyve1, Tim4, and ABCA1. Blocking the phosphatidylserine receptor Tim4 inhibited lysosomal activation and the release of post-prandial high density lipoprotein cholesterol following a high fat meal. Both effects were recapitulated by chloroquine, an inhibitor of lysosomal function. Moreover, clodronate-mediated cell-depletion implicated Tim4⁺ resident adipose tissue macrophages in this process. Thus, these data indicate that Tim4 is a key regulator of post-prandial cholesterol transport and adipose tissue macrophage function and may represent a novel pathway to treat dyslipidemia.

Diverse macrophage subsets are found in adipose tissue where they regulate its physiology. Here, the authors used single-cell RNA sequencing to analyse the effect of post-prandial lipids on adipose tissue macrophages and identify Tim4 as a regulator of ABCA1⁺ macrophage function and post-prandial cholesterol transport.

Untangling the Cooperative Role of Nuclear Receptors in Cardiovascular Physiology and Disease

The heart is the first organ to acquire its physiological function during development, enabling it to supply the organism with oxygen and nutrients. Given this early commitment, cardiomyocytes were traditionally considered transcriptionally stable cells fully committed to contractile function. However, growing evidence suggests that the maintenance of cardiac function in health and disease depends on transcriptional and epigenetic regulation. Several studies have revealed that the complex transcriptional alterations underlying cardiovascular disease (CVD) manifestations such as myocardial infarction and hypertrophy is mediated by cardiac retinoid X receptors (RXR) and their partners. RXRs are members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors and drive essential biological processes such as ion handling, mitochondrial biogenesis, and glucose and lipid metabolism. RXRs are thus attractive molecular targets for the development of effective pharmacological strategies for CVD treatment and prevention. In this review, we summarize current knowledge of RXR partnership biology in cardiac homeostasis and disease, providing an up-to-date view of the molecular mechanisms and cellular pathways that sustain cardiomyocyte physiology.

KLF4 Upregulation in Atherosclerotic Thoracic Aortas: Exploring the Protective Effect of Colchicine-based Regimens in a Hyperlipidemic Rabbit Model

BACKGROUND

Inflammatory dysregulation of KLF4 is related to atheromatosis. In the present study, we explored the impact of colchicine-based regimens on the development of thoracic aortic atheromatosis and KLF4 expression.

METHODS

Twenty-eight New Zealand White rabbits were divided to 4 groups. The control group (n = 6) was fed standard chow, group A (n = 6) was fed chow enriched with 1% w/w cholesterol, group B (n = 8) was fed the same cholesterol-enriched diet plus 2 mg/kg body weight/day colchicine and 250 mg/kg body weight/day fenofibrate, while group C (n = 8) was also fed the same diet plus 2 mg/kg body weight/day colchicine and 15 mg/kg body weight/day N-acetylcysteine. After 7 weeks, all animals were euthanized, and their thoracic aortas were isolated. Atherosclerotic plaque area was estimated with morphometric analysis. KLF4 expression was quantified with quantitative RT-PCR.

RESULTS

Group A developed significantly more atherosclerosis compared to group B (MD: 13.67, 95% CI: 7.49-19.84) and C (MD: 20.29, 95% CI: 14.12-26.47). Colchicine with N-acetylcysteine resulted in more pronounced reduction in the extent of atherosclerotic plaques compared to colchicine/fibrate (MD: 6.62, 95% CI: 0.90-12.34). Group A exhibited significantly greater KLF4 expression compared to group B (MD: 4.94, 95% CI: 1.11-8.77) and C (MD: 9.94, 95% CI: 6.11-13.77). Combining colchicine with N-acetylcysteine instead of fenofibrate (MD: 5.00, 95% CI: 1.45-8.54) led to a more robust reduction in KLF4 expression.

CONCLUSIONS

In the present hyperlipidemic animal model, colchicine-based regimens curtailed de novo atherogenesis and KLF4 overexpression in thoracic aortas.

Molecular mechanism of liver X receptors in cancer therapeutics

Liver X receptors (LXRs) are receptors that belong to the nuclear receptor superfamily (NRs). It was originally called the "orphan receptor" when it was firstly discovered. Then it was found to be activated by oxysterol and it was officially named LXRs. LXRs are activated by ligands and bind to the retinol X receptor to form a heterodimer and regulate metabolism. Numerous studies have shown that LXRs are involved in regulating immune function and maintaining immune tolerance. Activating LXRs can also inhibit the tumorigenesis and promote apoptosis of tumor cells, which make LXRs as potential targets in cancer treatment. This review will discuss the recent progress of LXRs from the structure and function of LXRs, the signaling pathway of LXRs, the molecular mechanism of LXRs activation in cancers, and the potential targets of LXRs in cancer therapy.

MiR-506-3p Promotes the Proliferation and Migration of Vascular Smooth Muscle Cells via Targeting KLF4

BACKGROUND

The dysregulation of proliferation and migration of vascular smooth muscle cells (VSMCs) is one of the major causes of atherosclerosis (AS). Accumulating studies confirm that Kruppel-like factor 4 (KLF4) can regulate the proliferation and differentiation of VSMCs through multiple signaling pathways. However, the mechanism of KLF4 dysregulation remains unknown.

METHODS

Apolipoprotein E-knockout (ApoE-/-) mice and human VSMCs were used to establish AS animal model and cell model, respectively. qRT-PCR was employed to determine the expressions of miR-506-3p and KLF4. Cell Counting Kit -8, Transwell, TUNEL assays, and flow cytometry were performed to measure the proliferation, migration, and apoptosis of VSMCs. The upstream miRNAs of KLF4 were predicted by microT, miRanda, miRmap, and TargetScan databases. The interaction between KLF4 and miR-506-3p was confirmed using qRT-PCR, Western blot, and luciferase reporter gene assay.

RESULTS

KLF4 expression was significantly decreased in the VSMCs of ApoE-/- mice fed with high-fat diet and in human VSMCs treated with oxidized low-density lipoprotein in time-dependent and dose-dependent manners. The transfection of miR-506-3p mimics or KLF4 shRNA promoted the proliferation and migration of VSMCs but inhibited the apoptosis while miR-506-3p inhibitors and pcDNA3.1-KLF4 exerted opposite effects. Additionally, KLF4 was confirmed as a target gene of miR-506-3p and could be negatively regulated by miR-506-3p.

CONCLUSION

MiR-506-3p can promote the proliferation and migration of VSMCs via targeting KLF4, which can probably contribute to the pathogenesis of AS.

Genetic deficiency of Phactr1 promotes atherosclerosis development via facilitating M1 macrophage polarization and foam cell formation

Genetic variants in phosphatase and actin regulator-1 (Phactr1) are reported to be associated with arteriosclerotic cardiovascular disease (ASCVD). However, the function of Phactr1 in atherosclerosis remains unclear. Patients with acute coronary syndrome (ACS) who underwent coronary angiography and optical coherence tomography (OCT) were enrolled and divided into non-ST segment elevation (NST-ACS) group and ST-ACS group. The expression of Phactr1 on monocytes was higher in NST-ACS and ST-ACS groups as compared with control group. Furthermore, NST-ACS patients who have more vulnerable features including thin-cap fibroatheroma (TCFA) and large lipid area showed higher levels of Phactr1 on monocytes than those with stable plaques. Through mouse models of atherosclerosis, Phactr1-/-Apoe-/- mice (double knockout mice, DKO) developed more severe atherosclerotic plaques, recruiting more macrophages into subendothelium and having elevated levels of proinflammatory cytokines in plaques. Similarly, Apoe knockout mice (Apoe-/-) receiving DKO bone marrow (BM) exhibited elevated plaque burden compared with Apoe-/- mice receiving Apoe-/- BM, indicating the protective effect of Phactr1 in hematopoietic cells. We found that depletion of Phactr1 in BM-derived macrophages (BMDMs) tended to differentiate into M1 phenotype, produced more proatherogenic cytokines and eventually converted into foam cells driven by oxidized low-density lipoprotein (ox-LDL). Mechanistically, Phactr1 activated CREB signaling via directly binding to CREB, up-regulating CREB phosphorylation and inducing KLF4 expression. Finally, overexpression of KLF4 partly rescued the excessive inflammation response and foam cell formation induced by deficiency of Phactr1. In conclusion, our study demonstrates that elevated Phactr1 in monocytes is a promising biomarker for vulnerable plaques, while increased Phactr1 attenuates atherosclerotic development via activation of CREB and M2 macrophage differentiation.

The ABCA1-efferocytosis axis: A new strategy to protect against atherosclerosis

Atherosclerosis, a disease process characterized by lipid accumulation and inflammation, is the main cause of coronary heart disease (CHD) and myocardial infarction (MI). Efferocytosis involves the clearance of apoptotic cells by phagocytes. Successful engulfment triggers the release of anti-inflammatory cytokines to suppress atherosclerosis. ABCA1 is a key mediator of cholesterol efflux to apoA-I for the generation of HDL-C in reverse cholesterol transport (RCT). Intriguingly, ABCA1 promotes not only cholesterol efflux but also efferocytosis. ABCA1 promotes efferocytosis by regulating the release of "find-me" ligands, including LPC, and the exposure, release, and expression of "eat-me" ligands, including PtdSer, ANXA1, ANXA5, MEGF10, and GULP1. ABCA1 has a pathway similar to TG2, which is an "eat-me" ligand. ABCA1 has the highest known homology to ABCA7, which controls efferocytosis as the engulfment and processing ligand. In addition, ABCA1 can form several regulatory feedback axes with ANXA1, MEGF10, GULP1, TNFα, and IL-6. Therefore, ABCA1 is the central factor that links cholesterol efflux and apoptotic cell clearance. Several drugs have been studied or approved for apoptotic cell clearance, such as CD47 antibody and PD1-/PD-L1 antibody. In this article, we review the role and mechanism of action of ABCA1 in efferocytosis and focus on new insights into the ABCA1-efferocytosis axis and its potential as a novel therapeutic target in atherosclerosis.

CTRP12 ameliorates atherosclerosis by promoting cholesterol efflux and inhibiting inflammatory response via the miR-155-5p/LXRα pathway

C1q tumor necrosis factor-related protein 12 (CTRP12), a conserved paralog of adiponectin, is closely associated with cardiovascular disease. However, little is known about its role in atherogenesis. The aim of this study was to examine the influence of CTRP12 on atherosclerosis and explore the underlying mechanisms. Our results showed that lentivirus-mediated CTRP12 overexpression inhibited lipid accumulation and inflammatory response in lipid-laden macrophages. Mechanistically, CTRP12 decreased miR-155-5p levels and then increased its target gene liver X receptor α (LXRα) expression, which increased ATP binding cassette transporter A1 (ABCA1)- and ABCG1-dependent cholesterol efflux and promoted macrophage polarization to the M2 phenotype. Injection of lentiviral vector expressing CTRP12 decreased atherosclerotic lesion area, elevated plasma high-density lipoprotein cholesterol levels, promoted reverse cholesterol transport (RCT), and alleviated inflammatory response in apolipoprotein E-deficient (apoE-/-) mice fed a Western diet. Similar to the findings of in vitro experiments, CTRP12 overexpression diminished miR-155-5p levels but increased LXRα, ABCA1, and ABCG1 expression in the aortas of apoE-/- mice. Taken together, these results suggest that CTRP12 protects against atherosclerosis by enhancing RCT efficiency and mitigating vascular inflammation via the miR-155-5p/LXRα pathway. Stimulating CTRP12 production could be a novel approach for reducing atherosclerosis.

Nuclear Receptors as Multiple Regulators of NLRP3 Inflammasome Function

Nuclear receptors are important bridges between lipid signaling molecules and transcription responses. Beside their role in several developmental and physiological processes, many of these receptors have been shown to regulate and determine the fate of immune cells, and the outcome of immune responses under physiological and pathological conditions. While NLRP3 inflammasome is assumed as key regulator for innate and adaptive immune responses, and has been associated with various pathological events, the precise impact of the nuclear receptors on the function of inflammasome is hardly investigated. A wide variety of factors and conditions have been identified as modulators of NLRP3 inflammasome activation, and at the same time, many of the nuclear receptors are known to regulate, and interact with these factors, including cellular metabolism and various signaling pathways. Nuclear receptors are in the focus of many researches, as these receptors are easy to manipulate by lipid soluble molecules. Importantly, nuclear receptors mediate regulatory mechanisms at multiple levels: not only at transcription level, but also in the cytosol via non-genomic effects. Their importance is also reflected by the numerous approved drugs that have been developed in the past decade to specifically target nuclear receptors subtypes. Researches aiming to delineate mechanisms that regulate NLRP3 inflammasome activation draw a wide range of attention due to their unquestionable importance in infectious and sterile inflammatory conditions. In this review, we provide an overview of current reports and knowledge about NLRP3 inflammasome regulation from the perspective of nuclear receptors, in order to bring new insight to the potentially therapeutic aspect in targeting NLRP3 inflammasome and NLRP3 inflammasome-associated diseases.

Ethanol, neurosteroids and cellular stress responses: Impact on central nervous system toxicity, inflammation and autophagy

Alcohol intake can impair brain function, in addition to other organs such as the liver and kidney. In the brain ethanol can be detrimental to memory formation, through inducing the integrated stress response/endoplasmic reticulum stress/unfolded protein response and the molecular mechanisms linking stress to other events such as NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammation and autophagy. This literature review aims to provide an overview of our current understanding of the molecular mechanisms involved in ethanol-induced damage with endoplasmic reticulum stress, integrated stress response, NLRP3 inflammation and autophagy, while discussing the impact of neurosteroids and oxysterols, including allopregnanolone, 25-hydroxycholesterol and 24S-hydroxycholesterol, on the central nervous system.