Liver X receptors in lipid signalling and membrane homeostasis

Biological Mechanisms and Related Natural Inhibitors of CD36 in Nonalcoholic Fatty Liver

Non-alcoholic fatty liver disease (NAFLD), a spectrum of liver disorders from non-alcoholic fatty liver (NAFL) to the more severe non-alcoholic steatohepatitis (NASH), is the leading etiology of chronic liver disease and its global prevalence is increasing. Hepatic steatosis, a condition marked by an abnormal buildup of triglycerides in the liver, is the precursor to NAFLD. Differentiated cluster 36 (CD36), a scavenger receptor class B protein, is a membrane receptor that recognizes multiple lipid and non-lipid ligands. It is generally agreed that CD36 contributes significantly to hepatic steatosis by taking part in fatty acid uptake as well as triglyceride storage and secretion. While there has not been any conclusive research on how CD36 inhibitors prevent NAFLD from progressing and no clinically approved CD36 inhibitors are currently available for use in NAFLD, CD36 remains a target worthy of further investigation in NAFLD. In recent years, the potential role of natural products acting through CD36 in treating non-alcoholic fatty liver disease has attracted much attention. This paper offers an overview of the pathogenesis of CD36 in NAFLD and summarizes some of the natural compounds or extracts that are currently being investigated for modulating NAFLD via CD36 or the CD36 pathway, providing an alternative approach to the development of CD36-related drugs in NAFLD.

Differential effects of bariatric surgery on plasma levels of ANGPTL3 and ANGPTL4

BACKGROUND AND AIM

Angiopoietin-like 3 (ANGPTL3) and 4 (ANGPTL4) are regulators of triglyceride storage and utilization. Bariatric surgery (BS) leads to profound changes in adipose tissue composition and energy metabolism. We evaluated the impact of BS on plasma levels of ANGPTL3 and ANGPTL4.

METHODS AND RESULTS

Twenty-seven subjects affected by morbid obesity with or without type 2 diabetes (T2D) underwent Roux-en-Y gastric bypass (RYGB) and 18 patients with advanced T2D received Biliopancreatic Diversion (BPD). Fasting ANGPTL proteins levels, insulin sensitivity (evaluated by euglycemic hyperinsulinemic clamp), total bile acids (TBA) and free fatty acids (FFA) were measured at baseline and 1 year after surgery. Both surgical procedures resulted in the loss of fat mass, improved glucose control, and a ∼2-fold increase of insulin sensitivity. ANGPTL4 levels decreased significantly with both RYGB (26.6 ± 0.6 to 24.4 ± 0.3 ng/mL, p = 0.001) and BPD (27.9 ± 1.5 to 24.0 ± 0.5 ng/mL, p = 0.003). In contrast, ANGPTL3 concentrations did not change after RYGB but rose following BPD (225 ± 20 to 300 ± 15 ng/mL, p = 0.003). By multiple regression analysis, changes after BS in ANGPTL4 were independently associated with changes in blood glucose, (p = 0.0169) whereas changes in ANGPTL3 were associated with variations in FFA (p = 0.008) and insulin sensitivity (p = 0.043).

CONCLUSION

Circulating ANGPTL4 is reduced by BS, probably due to the loss of fat mass and improved insulin sensitivity. Conversely, ANGPTL3 levels increased after BPD, but not after RYGB, presumably because of the metabolic changes induced by the malabsorptive effect of BPD.

Discovery of an insulin-induced gene binding compound that ameliorates nonalcoholic steatohepatitis by inhibiting sterol regulatory element-binding protein-mediated lipogenesis

BACKGROUND AND AIMS

NASH is associated with high levels of cholesterol and triglyceride (TG) in the liver; however, there is still no approved pharmacological therapy. Synthesis of cholesterol and TG is controlled by sterol regulatory element-binding protein (SREBP), which is found to be abnormally activated in NASH patients. We aim to discover small molecules for treating NASH by inhibiting the SREBP pathway.

APPROACH AND RESULTS

Here, we identify a potent SREBP inhibitor, 25-hydroxylanosterol (25-HL). 25-HL binds to insulin-induced gene (INSIG) proteins, stimulates the interaction between INSIG and SCAP, and retains them in the endoplasmic reticulum, thereby suppressing SREBP activation and inhibiting lipogenesis. In NASH mouse models, 25-HL lowers levels of cholesterol and TG in serum and the liver, enhances energy expenditure to prevent obesity, and improves insulin sensitivity. 25-HL dramatically ameliorates hepatic steatosis, inflammation, ballooning, and fibrosis through down-regulating the expression of lipogenic genes. Furthermore, 25-HL exhibits both prophylactic and therapeutic efficacies of alleviating NASH and atherosclerosis in amylin liver NASH model diet-treated Ldlr^-/- mice, and reduces the formation of cholesterol crystals and associated crown-like structures of Kupffer cells. Notably, 25-HL lowers lipid contents in serum and the liver to a greater extent than lovastatin or obeticholic acid. 25-HL shows a good safety and pharmacokinetics profile.

CONCLUSIONS

This study provides the proof of concept that inhibiting SREBP activation by targeting INSIG to lower lipids could be a promising strategy for treating NASH. It suggests the translational potential of 25-HL in human NASH and demonstrates the critical role of SREBP-controlled lipogenesis in the progression of NASH by pharmacological inhibition.

Coffee modulates insulin-hepatocyte nuclear factor-4α-Cyp7b1 pathway and reduces oxysterol-driven liver toxicity in a nonalcoholic fatty liver disease mouse model

Oxysterol 7α-hydroxylase (CYP7B1) controls the levels of intracellular regulatory oxysterols generated by the "acidic pathway" of cholesterol metabolism. Previously, we demonstrated that an inability to upregulate CYP7B1 in the setting of insulin resistance leads to the accumulation of cholesterol metabolites such as (25R)26-hydroxycholesterol (26HC) that initiate and promote hepatocyte injury; followed by an inflammatory response. The current study demonstrates that dietary coffee improves insulin resistance and restores Cyp7b1 levels in a well-characterized Western diet (WD)-induced nonalcoholic fatty liver disease (NAFLD) mouse model. Ingestion of a WD containing caffeinated (regular) coffee or decaffeinated coffee markedly reduced the serum ALT level and improved insulin resistance. Cyp7b1 mRNA and protein levels were preserved at normal levels in mice fed the coffee containing WD. Additionally, coffee led to upregulated steroid sulfotransferase 2b1 (Sult2b1) mRNA expression. In accordance with the response in these oxysterol metabolic genes, hepatocellular 26HC levels were maintained at physiologically low levels. Moreover, the current study provided evidence that hepatic Cyp7b1 and Sult2b1 responses to insulin signaling can be mediated through a transcriptional factor, hepatocyte nuclear factor (HNF)-4α. We conclude coffee achieves its beneficial effects through the modulation of insulin resistance. Both decaffeinated and caffeinated coffee had beneficial effects, demonstrating caffeine is not fundamental to this effect. The effects of coffee feeding on the insulin-HNF4α-Cyp7b1 signaling pathway, whose dysregulation initiates and contributes to the onset and progression of NASH as triggered by insulin resistance, offer mechanistic insight into approaches for the treatment of NAFLD.NEW & NOTEWORTHY This study demonstrated dietary coffee prevented the accumulation of hepatic oxysterols by maintaining Cyp7b1/Sult2b1 expression in a diet-induced NAFLD mice model. Lowering liver oxysterols markedly reduced inflammation in the coffee-ingested mice. Caffeine is not fundamental to this effect. In addition, this study showed Cyp7b1/Sult2b1 responses to insulin signaling can be mediated through a transcriptional factor, HNF4α. The insulin-HNF4α-Cyp7b1/Sult2b1 signaling pathway, which directly correlates to the onset of NASH triggered by insulin resistance, offers insight into approaches for NAFLD treatment.

The Citrus Flavonoid Nobiletin Downregulates Angiopoietin-like Protein 3 (ANGPTL3) Expression and Exhibits Lipid-Modulating Effects in Hepatic Cells and Adult Zebrafish Models

Nobiletin, a dietary citrus flavonoid, exerts biological activities against hyperlipidemia, obesity, and atherosclerotic cardiovascular diseases (ASCVDs). The aim of this study was to explore the lipid-lowering effects of nobiletin and the underlying molecular mechanisms in vitro in hepatic cells and in vivo in zebrafish models. Transcriptome and gene ontology (GO) analyses of differentially expressed genes (DEGs) by gene set enrichment analysis (GSEA) showed that a set of twenty-eight core enrichment DEGs associated with “GO BP regulation of lipid metabolic process” (GO: 0019216) were significantly downregulated in nobiletin-treated cells. Among these genes, angiopoietin-like 3 (ANGPTL3), an inhibitor of lipoprotein lipase (LPL) activity that regulates TG-rich lipoprotein (TGRL) metabolism in circulation, was the protein most markedly downregulated by nobiletin. Nobiletin (20 and 40 μM) significantly reduced the levels of ANGPTL3 mRNA and intracellular and secreted ANGPTL3 proteins in hepatic cell lines. Furthermore, alleviation of secreted ANGPTL3 production by nobiletin was found to reinstate LPL catalytic activity. Nobiletin significantly inhibited ANGPTL3 promoter activity and attenuated the transcription factor liver X receptor-α (LXRα)-mediated ANGPTL3 transcription. Molecular docking analysis predicted that nobiletin could bind to the ligand-binding domain of LXRα, thereby counteracting LXRα activation. In animal studies, orally administered nobiletin significantly alleviated the levels of plasma triglycerides (TGs) and cholesterol in zebrafish fed a high-fat diet. Moreover, nobiletin significantly reduced the amounts of hepatic ANGPTL3 protein in zebrafish. Our findings suggest that nobiletin may regulate the LXRα-ANGPTL3-LPL axis and exhibit lipid-modulating effects in vitro and in vivo. Thus, nobiletin is a potential ANGPTL3 inhibitor for the regulation of lipid metabolism to ameliorate dyslipidemia and ASCVDs.

Ethyl Acetate Extract of Dracocephalum heterophyllum Benth Ameliorates Nonalcoholic Steatohepatitis and Fibrosis via Regulating Bile Acid Metabolism, Oxidative Stress and Inhibiting Inflammation

Dracocephalum heterophyllum Benth is well-known for its ability to alleviate liver heat. In this study, Dracocephalum heterophyllum Benth ethyl acetate extracts were evaluated on mouse models of nonalcoholic steatohepatitis and liver fibrosis. After 6 and 8 weeks of treatment, serum parameters and gene expressions in tissue samples, as well as stained tissue sections, demonstrated that the ethyl acetate extracts were effective in treating these liver diseases. The principal bioactive constituent (rosmarinic acid) was identified and screened by high pressure liquid chromatography-1,1-diphenyl-2-picrylhydrazyl and affinity ultrafiltration-HPLC. The rosmarinic acid was separated from extracts with high purity by medium- and high-pressure liquid chromatography. Finally, the interactions between rosmarinic acid and the key targets of lipid metabolism, oxidative stress and inflammation were verified by molecular docking. Thereby, an indirect regulation of lipid and cholesterol metabolism and inhibition of liver inflammation and liver fibrosis by the studied extract has been observed. This study demonstrated that Dracocephalum heterophyllum Benth ethyl acetate extracts have the potential to treat nonalcoholic steatohepatitis and liver fibrosis, revealing their multi-target and multi-pathway therapeutic characteristics.

Lipid metabolism in pancreatic cancer: emerging roles and potential targets

Pancreatic cancer is one of the most serious health issues in developed and developing countries, with a 5-year overall survival rate currently <9%. Patients typically present with advanced disease due to vague symptoms or lack of screening for early cancer detection. Surgical resection represents the only chance for cure, but treatment options are limited for advanced diseases, such as distant metastatic or locally progressive tumors. Although adjuvant chemotherapy has improved long-term outcomes in advanced cancer patients, its response rate is low. So, exploring other new treatments is urgent. In recent years, increasing evidence has shown that lipid metabolism can support tumorigenesis and disease progression as well as treatment resistance through enhanced lipid synthesis, storage, and catabolism. Therefore, a better understanding of lipid metabolism networks may provide novel and promising strategies for early diagnosis, prognosis estimation, and targeted therapy for pancreatic cancer patients. In this review, we first enumerate and discuss current knowledge about the advances made in understanding the regulation of lipid metabolism in pancreatic cancer. In addition, we summarize preclinical studies and clinical trials with drugs targeting lipid metabolic systems in pancreatic cancer. Finally, we highlight the challenges and opportunities for targeting lipid metabolism pathways through precision therapies in pancreatic cancer.

Long noncoding RNA CHROMR regulates antiviral immunity in humans

An effective innate immune response to virus infection requires the induction of type I interferons and up-regulation of hundreds of interferon-stimulated genes (ISGs) that instruct antiviral functions and immune regulation. Deciphering the regulatory mechanisms that direct expression of the ISG network is critical for understanding the fundamental organization of the innate immune response and the development of antiviral therapies. We define a regulatory role for the primate-specific long noncoding RNA CHROMR in coordinating ISG transcription. CHROMR sequesters the interferon regulatory factor (IRF)-2/IRF2BP2 complex that restrains ISG transcription and thus is required to restrict influenza virus replication. These data identify a novel regulator of the antiviral gene program in humans and provide insights into the multilayered regulatory network that controls the innate immune response.

Long noncoding RNAs (lncRNAs) have emerged as critical regulators of gene expression, yet their contribution to immune regulation in humans remains poorly understood. Here, we report that the primate-specific lncRNA CHROMR is induced by influenza A virus and SARS-CoV-2 infection and coordinates the expression of interferon-stimulated genes (ISGs) that execute antiviral responses. CHROMR depletion in human macrophages reduces histone acetylation at regulatory regions of ISG loci and attenuates ISG expression in response to microbial stimuli. Mechanistically, we show that CHROMR sequesters the interferon regulatory factor (IRF)-2-dependent transcriptional corepressor IRF2BP2, thereby licensing IRF-dependent signaling and transcription of the ISG network. Consequently, CHROMR expression is essential to restrict viral infection of macrophages. Our findings identify CHROMR as a key arbitrator of antiviral innate immune signaling in humans.

Liver X Receptor Regulation of Glial Cell Functions in the CNS

In this review, we discuss the role of liver X receptors (LXRs) in glial cells (microglia, oligodendrocytes and astrocytes) in the central nervous system (CNS). LXRs are oxysterol-activated nuclear receptors that, in adults, regulate genes involved in cholesterol homeostasis, the modulation of inflammatory responses and glutamate homeostasis. The study of LXR knockout mice has revealed that LXRβ plays a key role in maintaining the health of dopaminergic neurons in the substantia nigra, large motor neurons in the spinal cord and retinal ganglion cells in the eye. In the peripheral nervous system (PNS), LXRβ is responsible for the health of the spiral ganglion neurons (SGNs) in the cochlea. In addition, LXRs are essential for the homeostasis of the cerebrospinal fluid (CSF), and in LXRαβ^−/− mice, the lateral ventricles are empty and lined with lipid-laden cells. As LXRαβ^−/− mice age, lipid vacuoles accumulate in astrocytes surrounding blood vessels. By seven months of age, motor coordination becomes impaired, and there is a loss of motor neurons in the spinal cord of LXRβ^−/− mice. During development, migration of neurons in the cortex and cerebellum is retarded in LXRβ^−/− mice. Since LXRs are not expressed in dopaminergic or motor neurons in adult mice, the neuroprotective effects of LXRs appear to come from LXRs in glial cells where they are expressed. However, despite the numerous neurological deficits in LXR^−/− rodents, multiple sclerosis has the clear distinction of being the only human neurodegenerative disease in which defective LXR signaling has been identified. In this review, we summarize the regulation and functions of LXRs in glial cells and analyze how targeting LXRs in glial cells might, in the future, be used to treat neurodegenerative diseases and, perhaps, disorders caused by aberrant neuronal migration during development.

Metabolism deficiency and oxidative stress induced by plastic particles in the rotifer Brachionus plicatilis: Common and distinct phenotypic and transcriptomic responses to nano- and microplastics

Growing experimental data on the adverse effects of microplastic pollution on marine biota indicate that the size of the plastic particles is a key determinant of toxicity. Here, we investigated size-dependent toxicity at different levels of biological organizations in the marine rotifer Brachionus plicatilis, from bioaccumulation as an initiating event to adverse in-vivo outcomes, with ecotoxicogenomic approach to elucidate the size-dependent toxicity of microplastics. Nanoplastics strongly retarded the reproduction and population growth of B. plicatilis, while microplastics were associated with moderate effects. This size dependency could be attributed to the selective induction of oxidative stress by nanoplastic exposure in addition to a metabolic deficiency, which was a common toxicity mechanism with both nano- and microplastic exposure as predicted by transcriptomic analysis. Our findings suggested that metabolic deficiency is a shared toxicity mechanism of nano- and microplastics, while oxidative stress might be responsible for the stronger toxicity of nanoplastics.

Antagonism of miR-148a attenuates atherosclerosis progression in APOBTGApobec-/-Ldlr+/- mice: A brief report

OBJECTIVE

miR-148a-3p (miR-148a) is a hepatic and immune-enriched microRNA (miRNA) that regulates macrophage-related lipoprotein metabolism, cholesterol homeostasis, and inflammation. The contribution of miR-148a-3p to the progression of atherosclerosis is unknown. In this study, we determined whether miR-148a silencing mitigated atherogenesis in APOBTGApobec-/-Ldlr+/- mice.

METHODS

APOBTGApobec-/-Ldlr+/- mice were fed a typical Western-style diet for 22 weeks and injected with a nontargeting locked nucleic acid (LNA; LNA control) or miR-148a LNA (LNA 148a) for the last 10 weeks. At the end of the treatment, the mice were sacrificed, and circulating lipids, hepatic gene expression, and atherosclerotic lesions were analyzed.

RESULTS

Examination of atherosclerotic lesions revealed a significant reduction in plaque size, with marked remodeling of the lesions toward a more stable phenotype. Mechanistically, miR-148a levels influenced macrophage cholesterol efflux and the inflammatory response. Suppression of miR-148a in murine primary macrophages decreased mRNA levels of proinflammatory M1-like markers (Nos2, Il6, Cox2, and Tnf) and increased the expression of anti-inflammatory genes (Arg1, Retlna, and Mrc1).

CONCLUSIONS

Therapeutic silencing of miR148a mitigated the progression of atherosclerosis and promoted plaque stability. The antiatherogenic effect of miR-148a antisense therapy is likely mediated by the anti-inflammatory effects observed in macrophages treated with miR-148 LNA and independent of significant changes in circulating low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C).

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.

Dietary Cholesterol Metabolite Regulation of Tissue Immune Cell Development and Function

Obesity is considered the primary environmental factor associated with morbidity and severity of wide-ranging inflammatory disorders. The molecular mechanism linking high-fat or cholesterol diet to imbalances in immune responses, beyond the increased production of generic inflammatory factors, is just beginning to emerge. Diet cholesterol by-products are now known to regulate function and migration of diverse immune cell subsets in tissues. The hydroxylated metabolites of cholesterol oxysterols as central regulators of immune cell positioning in lymphoid and mucocutaneous tissues is the focus of this review. Dedicated immunocyte cell surface receptors sense spatially distributed oxysterol tissue depots to tune cell metabolism and function, to achieve the "right place at the right time" axiom of efficient tissue immunity.

Inhibition of ASGR1 decreases lipid levels by promoting cholesterol excretion

High cholesterol is a major risk factor for cardiovascular disease¹. Currently, no drug lowers cholesterol through directly promoting cholesterol excretion. Human genetic studies have identified that the loss-of-function Asialoglycoprotein receptor 1 (ASGR1) variants associate with low cholesterol and a reduced risk of cardiovascular disease². ASGR1 is exclusively expressed in liver and mediates internalization and lysosomal degradation of blood asialoglycoproteins³. The mechanism by which ASGR1 affects cholesterol metabolism is unknown. Here, we find that Asgr1 deficiency decreases lipid levels in serum and liver by stabilizing LXRα. LXRα upregulates ABCA1 and ABCG5/G8, which promotes cholesterol transport to high-density lipoprotein and excretion to bile and faeces⁴, respectively. ASGR1 deficiency blocks endocytosis and lysosomal degradation of glycoproteins, reduces amino-acid levels in lysosomes, and thereby inhibits mTORC1 and activates AMPK. On one hand, AMPK increases LXRα by decreasing its ubiquitin ligases BRCA1/BARD1. On the other hand, AMPK suppresses SREBP1 that controls lipogenesis. Anti-ASGR1 neutralizing antibody lowers lipid levels by increasing cholesterol excretion, and shows synergistic beneficial effects with atorvastatin or ezetimibe, two widely used hypocholesterolaemic drugs. In summary, this study demonstrates that targeting ASGR1 upregulates LXRα, ABCA1 and ABCG5/G8, inhibits SREBP1 and lipogenesis, and therefore promotes cholesterol excretion and decreases lipid levels.

Nuclear Receptor Atlases of Choroidal Tissues Reveal Candidate Receptors Associated with Age-Related Macular Degeneration

The choroid is a vulnerable tissue site in the eye, impacted in several blinding diseases including age related macular degeneration (AMD), which is the leading cause of central vision loss in the aging population. Choroidal thinning and choriocapillary dropout are features of the early form of AMD, and endothelial dysfunction and vascular changes are primary characteristics of the neovascular clinical sub-type of AMD. Given the importance, the choroidal endothelium and outer vasculature play in supporting visual function, a better understanding of baseline choroidal signaling pathways engaged in tissue and cellular homeostasis is needed. Nuclear receptors are a large family of transcription factors responsible for maintaining various cellular processes during development, aging and disease. Herein we developed a comprehensive nuclear receptor atlas of human choroidal endothelial cells and freshly isolated choroidal tissue by examining the expression levels of all members of this transcription family using quantitative real time PCR. Given the close relationship between the choroid and retinal pigment epithelium (RPE), this data was cross-referenced with the expression profile of nuclear receptors in human RPE cells, to discover potential overlap versus cell-specific nuclear receptor expression. Finally, to identify candidate receptors that may participate in the pathobiology of AMD, we cataloged nuclear receptor expression in a murine model of wet AMD, from which we discovered a subset of nuclear receptors differentially regulated following neovascularization. Overall, these databases serve as useful resources establishing the influence of nuclear receptor signaling pathways on the outer vascular tissue of the eye, while providing a list of receptors, for more focused investigations in the future, to determine their suitability as potential therapeutic targets for diseases, in which the choroid is affected.

Tumor metabolic reprogramming in lung cancer progression

Metabolic reprogramming is an important characteristic of tumor cells. Tumor cells reprogram their metabolic pathways to meet the material, energy and redox force needs for rapid proliferation. Metabolic reprogramming changes the level or type of specific metabolites inside and outside cells, and promotes tumor growth by affecting gene expression, cell state and the tumor microenvironment. Glucose metabolism, glutamine metabolism and lipid metabolism are significant metabolic pathways in tumors. Targeting metabolic reprogramming can significantly inhibit tumor growth and induce apoptosis. Metabolic reprogramming also plays an important role in maintaining the growth advantage of tumor cells and enhancing the chemotherapy tolerance of lung cancer. This review summarizes abnormal changes in the metabolism of glucose, fat and amino acids in lung cancer, and the underlying molecular mechanism, with the aim of providing novel ideas for the prevention, early diagnosis and treatment of lung cancer.

Suppression of nitric oxide synthase aggravates non-alcoholic steatohepatitis and atherosclerosis in SHRSP5/Dmcr rat via acceleration of abnormal lipid metabolism

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is a progressive subtype of non-alcoholic fatty liver disease (NAFLD) that is closely related to cardiovascular disease (CVD). Nitric oxide (NO) plays a critical role in the control of various biological processes. Dysfunction of the NO signaling pathway is associated with various diseases such as atherosclerosis, vascular inflammatory disease, and diabetes. Recently, it has been reported that NO is related to lipid and cholesterol metabolism. Chronic NO synthase (NOS) inhibition accelerates NAFLD by increasing hepatic lipid deposition. However, the detailed relationship between NO and abnormal lipid and cholesterol metabolism in NAFLD/NASH has not been completely explained. We aimed to determine the effects of NOS inhibition by N omega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a NOS inhibitor, on NASH and CVD via lipid and cholesterol metabolism.

METHODS

Stroke-prone spontaneously hypertensive rats were fed a high-fat and high-cholesterol diet for 8 weeks and administered L-NAME for the last 2 weeks. Following blood and tissue sampling, biochemical analysis, histopathological staining, quantitative RT-PCR analysis, and western blotting were performed.

RESULTS

L-NAME markedly increased hepatic triglyceride (TG) and cholesterol levels by promoting TG synthesis and cholesterol absorption from the diet. L-NAME increased the mRNA levels of inflammatory markers and fibrotic areas in the liver. Cholesterol secretion from the liver was promoted in rats administered L-NAME, which increased serum cholesterol. L-NAME significantly increased the level of oxidative stress marker and lipid deposition in the arteries.

CONCLUSIONS

NOS inhibition simultaneously aggravates NASH and atherosclerosis via hepatic lipid and cholesterol metabolism.

Peony seed oil decreases plasma cholesterol and favorably modulates gut microbiota in hypercholesterolemic hamsters

PURPOSE

Peony (Paeonia spp.) seed oil (PSO) contains a high amount of α-linolenic acid. The effects of PSO on hypercholesterolemia and gut microbiota remains unclear. The present study was to investigate effects of PSO supplementation on cholesterol metabolism and modulation of the gut microbiota.

METHODS

Male Golden Syrian hamsters (n = 40) were randomly divided into five groups (n = 8, each) fed one of the following diets namely low-cholesterol diet (LCD); high cholesterol diet (HCD); HCD with PSO substituting 50% lard (LPSO), PSO substituting 100% lard (HPSO) and HCD with addition of 0.5% cholestyramine (PCD), respectively, for 6 weeks.

RESULTS

PSO supplementation dose-dependently reduced plasma total cholesterol (TC) by 9-14%, non-high-density lipoprotein cholesterol (non-HDL-C) by 7-18% and triacylglycerols (TG) by 14-34% (p < 0.05). In addition, feeding PSO diets reduced the formation of plaque lesions by 49-61% and hepatic lipids by 9-19% compared with feeding HCD diet (p < 0.01). PSO also altered relative genus abundance of unclassified_f__Coriobacteriaceae, unclassified_f__Erysipelotrichaceae, Peptococcus, unclassified_f__Ruminococcaceae, norank_o__Mollicutes_RF9 and Christensenellaceae_R-7_group.

CONCLUSIONS

It was concluded that PSO was effective in reducing plasma cholesterol and hepatic lipids and favorably modulating gut microbiota associated with cholesterol metabolism.

Therapeutic effects of isosteviol sodium on non-alcoholic fatty liver disease by regulating autophagy via Sirt1/AMPK pathway

Isosteviol sodium (STVNa) is a beyerane diterpene synthesized via acid hydrolysis of stevioside, which can improve glucose and lipid metabolism in animals with diabetes. However, it remains unknown whether STVNa can exhibit a therapeutic effect on nonalcoholic fatty liver disease (NAFLD) and its underlying mechanism. We hypothesize that autophagic initiation may play a key role in mediating the development of NAFLD. Herein, we assessed the effects of STVNa on NAFLD and its underlying mechanisms. The results demonstrated that STVNa treatment effectively ameliorated NAFLD in rats fed high-fat diet (HFD). Moreover, STVNa decreased the expression of inflammation-related genes and maintained a balance of pro-inflammatory cytokines in NAFLD rats. STVNa also reduced lipid accumulation in free fatty acid (FFA)-exposed LO2 cells. In addition, STVNa attenuated hepatic oxidative stress and fibrosis in NAFLD rats. Furthermore, STVNa enhanced autophagy and activated Sirtuin 1/adenosine monophosphate-activated protein kinase (Sirt1/AMPK) pathway both in vivo and in vitro, thus attenuating intracellular lipid accumulation. In summary, STVNa could improve lipid metabolism in NAFLD by initiating autophagy via Sirt1/AMPK pathway. Therefore, STVNa may be an alternative therapeutic agent for treatment of NAFLD.

Design, synthesis and structure-activity relationship of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyisoprop-2-yl)phenylsilane derivatives as liver X receptor agonists

Liver X receptor (LXR) α and LXRβ are nuclear receptors playing key roles in lipid metabolism, and LXR ligands are attractive drug candidates for metabolic disorders. Here we report the structural development of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyprop-2-yl)phenylsilane derivatives as LXR agonists bearing silyl functionalities as the hydrophobic pharmacophore, based on the structure of the known sulfonamide LXR agonist T0901317. Most of the synthesized compounds exhibit agonistic activity toward LXRs, but the LXR subtype-selectivity differs depending upon the substituents on the silicon atom. Among them, tri(n-propyl) derivative 12 shows potent LXR-agonistic activity with moderate α subtype-selectivity, while dimethylphenylsilyl derivative 19 shows modest β-selectivity. These results indicate that silanes can serve as an alternative to the sulfonamide moiety of LXR agonists, and are promising structural options for the development of novel subtype-selective LXR agonists.

Central nervous system cholesterol metabolism in health and disease

Cholesterol is a ubiquitous and essential component of cellular membranes, as it regulates membrane structure and fluidity. Furthermore, cholesterol serves as a precursor for steroid hormones, oxysterol, and bile acids, that are essential for maintaining many of the body's metabolic processes. The biosynthesis and excretion of cholesterol is tightly regulated in order to maintain homeostasis. Although virtually all cells have the capacity to make cholesterol, the liver and brain are the two main organs producing cholesterol in mammals. Once produced, cholesterol is transported in the form of lipoprotein particles to other cell types and tissues. Upon formation of the blood-brain barrier (BBB) during embryonic development, lipoproteins cannot move between the central nervous system (CNS) and the rest of the body. As such, cholesterol biosynthesis and metabolism in the CNS operate autonomously without input from the circulation system in normal physiological conditions. Nevertheless, similar regulatory mechanisms for maintaining cholesterol homeostasis are utilized in both the CNS and peripheral systems. Here, we discuss the functions and metabolism of cholesterol in the CNS. We further focus on how different CNS cell types contribute to cholesterol metabolism, and how ApoE, the major CNS apolipoprotein, is involved in normal and pathophysiological functions. Understanding these basic mechanisms will aid our ability to elucidate how CNS cholesterol dysmetabolism contributes to neurogenerative diseases.

Nuclear hormone receptors in demyelinating diseases

Demyelination results from the pathological loss of myelin and is a hallmark of many neurodegenerative diseases. Despite the prevalence of demyelinating diseases, there are no disease modifying therapies that prevent the loss of myelin or promote remyelination. This review aims to summarize studies in the field that highlight the importance of nuclear hormone receptors in the promotion and maintenance of myelination and the relevance of nuclear hormone receptors as potential therapeutic targets for demyelinating diseases. These nuclear hormone receptors include the estrogen receptor, progesterone receptor, androgen receptor, vitamin D receptor, thyroid hormone receptor, peroxisome proliferator-activated receptor, liver X receptor, and retinoid X receptor. Pre-clinical studies in well-established animal models of demyelination have shown a prominent role of these nuclear hormone receptors in myelination through their promotion of oligodendrocyte maturation and development. The activation of the nuclear hormone receptors by their ligands also promotes the synthesis of myelin proteins and lipids in mouse models of demyelination. There are limited clinical studies that focus on how the activation of these nuclear hormone receptors could alleviate demyelination in patients with diseases such as multiple sclerosis (MS). However, the completed clinical trials have reported improved clinical outcome in MS patients treated with the ligands of some of these nuclear hormone receptors. Together, the positive results from both clinical and pre-clinical studies point to nuclear hormone receptors as promising therapeutic targets to counter demyelination.

Form of dietary selenium affects mRNA encoding cholesterol biosynthesis and immune response elements in the early luteal phase bovine corpus luteum

Widespread regions of the southeast United States have soils, and hence forages, deficient in selenium (Se), necessitating Se supplementation to grazing cattle for optimal immune function, growth, and fertility. We have reported that supplementation with an isomolar 1:1 mix (MIX) of inorganic (ISe) and organic (OSe) forms of Se increases early luteal phase (LP) progesterone (P4) above that in cows on ISe alone. Increased early LP P4 advances embryonic development. Our objective was to determine the effect of form of Se on the transcriptome of the early LP corpus luteum (CL) with the goal of elucidating form of Se-regulated processes affecting luteal steroidogenesis and function. Non-lactating, 3-yr-old Angus-cross cows underwent 45-d Se-depletion, then repletion periods, and then at least 90 d of supplementation (TRT) with 35 ppm Se/d as either ISe (n = 5) or MIX (n = 5). CL were then recovered on day 7 of the estrous cycle, total RNA isolated, and the effect of TRT on the luteal transcriptome evaluated using bovine gene 1.0 ST arrays (Affymetrix, Inc., Santa Clara, CA). The abundance of transcripts in each CL was subjected to one-way ANOVA using Partek Genomic Suite software to determine TRT effects. Microarray analysis indicated a total of 887 transcripts that were differentially expressed and functionally annotated, with 423 and 464 up- and down-regulated (P < 0.05) in MIX vs. ISe CL, respectively. Bioinformatic analysis (Ingenuity Pathway Analysis) revealed the top TRT-affected canonical pathways to include seven specific to cholesterol biosynthesis and two to inflammatory responses. Results from the microarray analysis were corroborated by targeted real-time PCR. MIX CL had increased (P < 0.05) abundance of transcripts regulating cholesterol biosynthesis including DHCR7, DHCR24, and CYP51A1 (fold changes of 1.65, 1.48, and 1.40, respectively), suggesting MIX-induced increases in P4 to be due, in part, to increased availability of substrate to luteal cells. In addition, MIX CL had increased (P < 0.05) abundance of immune-response transcripts including C1QC, FAS, ILR8B, and IL1R1 (fold changes of 2.30, 1.74, 1.66, and 1.63, respectively). SREBF1 mRNA was also increased (1.32-fold, P < 0.05) in the MIX CL, which increases cholesterol synthesis and stimulates IL1B, linking effects of form of supplemental Se (TRT) on cholesterol biosynthesis and immune function in the CL.

Deregulation of Cholesterol Homeostasis by a Nuclear Hormone Receptor Crosstalk in Advanced Prostate Cancer

Metastatic castration-resistant prostate cancer (mCRPC) features high intratumoral cholesterol levels, due to aberrant regulation of cholesterol homeostasis. However, the underlying mechanisms are still poorly understood. The retinoid acid receptor-related orphan receptor gamma (RORγ), an attractive therapeutic target for cancer and autoimmune diseases, is strongly implicated in prostate cancer progression. We demonstrate in this study that in mCRPC cells and tumors, RORγ plays a crucial role in deregulation of cholesterol homeostasis. First, we found that RORγ activates the expression of key cholesterol biosynthesis proteins, including HMGCS1, HMGCR, and SQLE. Interestingly, we also found that RORγ inhibition induces cholesterol efflux gene program including ABCA1, ABCG1 and ApoA1. Our further studies revealed that liver X receptors (LXRα and LXRβ), the master regulators of cholesterol efflux pathway, mediate the function of RORγ in repression of cholesterol efflux. Finally, we demonstrated that RORγ antagonist in combination with statins has synergistic effect in killing mCRPC cells through blocking statin-induced feedback induction of cholesterol biosynthesis program and that the combination treatment also elicits stronger anti-tumor effects than either alone. Altogether, our work revealed that in mCRPC, RORγ contributes to aberrant cholesterol homeostasis by induction of cholesterol biosynthesis program and suppression of cholesterol efflux genes. Our findings support a therapeutic strategy of targeting RORγ alone or in combination with statin for effective treatment of mCRPC.

Potential Therapeutic Effect of All-Trans Retinoic Acid on Atherosclerosis

Atherosclerosis is a major risk factor for myocardial infarction and ischemic stroke, which are the leading cause of death worldwide. All-trans retinoic acid (ATRA) is a natural derivative of essential vitamin A. Numerous studies have shown that ATRA plays an important role in cell proliferation, cell apoptosis, cell differentiation, and embryonic development. All-trans retinoic acid (ATRA) is a ligand of retinoic acid receptors that regulates various biological processes by activating retinoic acid signals. In this paper, the metabolic processes of ATRA were reviewed, with emphasis on the effects of ATRA on inflammatory cells involved in the process of atherosclerosis.

The Role of Lipid Metabolism in Gastric Cancer

Gastric cancer has been one of the most common cancers worldwide with extensive metastasis and high mortality. Chemotherapy has been found as a main treatment for metastatic gastric cancer, whereas drug resistance limits the effectiveness of chemotherapy and leads to treatment failure. Chemotherapy resistance in gastric cancer has a complex and multifactorial mechanism, among which lipid metabolism plays a vital role. Increased synthesis of new lipids or uptake of exogenous lipids can facilitate the rapid growth of cancer cells and tumor formation. Lipids form the structural basis of biofilms while serving as signal molecules and energy sources. It is noteworthy that lipid metabolism is capable of inducing drug resistance in gastric cancer cells by reshaping the tumor micro-environment. In this study, new mechanisms of lipid metabolism in gastric cancer and the metabolic pathways correlated with chemotherapy resistance are reviewed. In particular, we discuss the effects of lipid metabolism on autophagy, biomarkers treatment and drug resistance in gastric cancer from the perspective of lipid metabolism. In brief, new insights can be gained into the development of promising therapies through an in-depth investigation of the mechanism of lipid metabolism reprogramming and resensitization to chemotherapy in gastric cancer cells, and scientific treatment can be provided by applying lipid-key enzyme inhibitors as cancer chemical sensitizers in clinical settings.

The Pathological Links between Adiposity and the Carpal Tunnel Syndrome

An association between obesity and carpal tunnel syndrome is found in many epidemiological studies. Therefore, there is a need to evaluate the physiopathological links that could explain the association between these two entities. Ectopic adipose tissue is responsible for metabolic syndrome and inflammation, and is a major risk factor for diabetes and cardiovascular diseases. Taking these elements into consideration, we conducted an extensive literature revision of the subject, considering as ectopic fat-related mechanisms the following: (a) the direct compression and the association with the metabolic syndrome of the fat deposition around the wrist, (b) the insulin resistance, dyslipidemia, inflammatory, and oxidative mechanisms related to the central deposition of the fat, (c) the impaired muscle contraction and metabolism related to myosteatosis. Each section presents the cellular pathways which are modified by the ectopic deposition of the adipose tissue and the impact in the pathogeny of the carpal tunnel syndrome. In conclusion, the experimental and clinical data support the epidemiological findings. Efforts to reduce the obesity epidemics will improve not only cardio-metabolic health but will reduce the burden of the disability-free life expectancy due to the carpal tunnel syndrome.

Myeloid LXR (Liver X Receptor) Deficiency Induces Inflammatory Gene Expression in Foamy Macrophages and Accelerates Atherosclerosis

BACKGROUND

Cholesterol loaded macrophage foam cells are a prominent feature of atherosclerotic plaques. Single-cell RNA sequencing has identified foam cells as TREM2 (triggering receptor expressed on myeloid cells 2) positive populations with low expression of inflammatory genes, resembling the TREM2 positive microglia of neurodegenerative diseases. Cholesterol loading of macrophages in vitro results in activation of LXR (liver X receptor) transcription factors and suppression of inflammatory genes.

METHODS

To test the hypothesis that LXRs mediate anti-inflammatory effects in Trem2 expressing atherosclerotic plaque foam cells, we performed RNA profiling on plaque cells from hypercholesterolemic mice with myeloid LXR deficiency.

RESULTS

Myeloid LXR deficiency led to a dramatic increase in atherosclerosis with increased monocyte entry, foam cell formation, and plaque inflammation. Bulk cell-RNA profiling of plaque myeloid cells showed prominent upregulation of inflammatory mediators including oxidative, chemokine, and chemotactic genes. Single-cell RNA sequencing revealed increased numbers of foamy TREM2-expressing macrophages; however, these cells had reduced expression of the Trem2 gene expression module, including phagocytic and cholesterol efflux genes, and had switched to a proinflammatory and proliferative phenotype. Expression of Trem2 was suppressed by inflammatory signals but not directly affected by LXR activation in bone marrow-derived macrophages.

CONCLUSIONS

Our current studies reveal the key role of macrophage LXRs in promoting the Trem2 gene expression program and in suppressing inflammation in foam cells of atherosclerotic plaques.

Lipid Metabolism and Cancer

Lipid metabolism is involved in the regulation of numerous cellular processes, such as cell growth, proliferation, differentiation, survival, apoptosis, inflammation, movement, membrane homeostasis, chemotherapy response, and drug resistance. Reprogramming of lipid metabolism is a typical feature of malignant tumors. In a variety of cancers, fat uptake, storage and fat production are up-regulated, which in turn promotes the rapid growth, invasion, and migration of tumors. This paper systematically summarizes the key signal transduction pathways and molecules of lipid metabolism regulating tumors, and the role of lipid metabolism in programmed cell death. In conclusion, understanding the potential molecular mechanism of lipid metabolism and the functions of different lipid molecules may facilitate elucidating the mechanisms underlying the occurrence of cancer in order to discover new potential targets for the development of effective antitumor drugs.

The genetic basis for adult onset glaucoma: Recent advances and future directions

Glaucoma, a diverse group of eye disorders that results in the degeneration of retinal ganglion cells, is the world's leading cause of irreversible blindness. Apart from age and ancestry, the major risk factor for glaucoma is increased intraocular pressure (IOP). In primary open-angle glaucoma (POAG), the anterior chamber angle is open but there is resistance to aqueous outflow. In primary angle-closure glaucoma (PACG), crowding of the anterior chamber angle due to anatomical alterations impede aqueous drainage through the angle. In exfoliation syndrome and exfoliation glaucoma, deposition of white flaky material throughout the anterior chamber directly interfere with aqueous outflow. Observational studies have established that there is a strong hereditable component for glaucoma onset and progression. Indeed, a succession of genome wide association studies (GWAS) that were centered upon single nucleotide polymorphisms (SNP) have yielded more than a hundred genetic markers associated with glaucoma risk. However, a shortcoming of GWAS studies is the difficulty in identifying the actual effector genes responsible for disease pathogenesis. Building on the foundation laid by GWAS studies, research groups have recently begun to perform whole exome-sequencing to evaluate the contribution of protein-changing, coding sequence genetic variants to glaucoma risk. The adoption of this technology in both large population-based studies as well as family studies are revealing the presence of novel, protein-changing genetic variants that could enrich our understanding of the pathogenesis of glaucoma. This review will cover recent advances in the genetics of primary open-angle glaucoma, primary angle-closure glaucoma and exfoliation glaucoma, which collectively make up the vast majority of all glaucoma cases in the world today. We will discuss how recent advances in research methodology have uncovered new risk genes, and how follow up biological investigations could be undertaken in order to define how the risk encoded by a genetic sequence variant comes into play in patients. We will also hypothesise how data arising from characterising these genetic variants could be utilized to predict glaucoma risk and the manner in which new therapeutic strategies might be informed.

2,2',4,4'-Tetrabromodiphenyl Ether (PBDE 47) Selectively Stimulates Proatherogenic PPARγ Signatures in Human THP-1 Macrophages to Contribute to Foam Cell Formation

2,2',4,4'-Tetrabromodiphenyl ether (PBDE 47) is one of the most prominent PBDE congeners detected in the human body, suggesting that the potential health risks of PBDE 47 should be thoroughly considered. However, the cardiovascular toxicity of PBDE 47 remains poorly understood. Here, toxic outcomes of PBDE 47 in human THP-1 macrophages concerning foam cell formation, which play crucial roles in the occurrence and development of atherosclerosis, were elucidated. First, our results indicated that PBDE 47 affected the PPARγ pathway most efficiently in THP-1 macrophages by transcriptomic analysis. Second, the PPARγ target genes CD36 and FABP4, responsible for lipid uptake and accumulation in macrophages, were consistently upregulated both at transcriptional and translational levels in THP-1 macrophages upon PBDE 47. Unexpectedly, PBDE 47 failed to activate the PPARγ target gene LXRα and PPARγ-LXRα-ABCA1/G1 cascade, which is activated by the PPARγ full agonist rosiglitazone and enables cholesterol efflux in macrophages. Thus, coincident with the selective upregulation of the PPARγ target genes CD36 and FABP4, PBDE 47, distinct from rosiglitazone, functionally resulted in more lipid accumulation and oxLDL uptake in THP-1 macrophages through high-content analysis (HCA). Moreover, these effects were markedly abrogated by the addition of the PPARγ antagonist T0070907. Mechanistically, the structural basis of selective activation of PPARγ by PBDE 47 was explored by molecular docking and dynamics simulation, which indicated that PBDE 47 interacted with the PPARγ ligand binding domain (PPARγ-LBD) distinctively from that of rosiglitazone. PBDE 47 was revealed to interact with helix 3 and helix 5 but not helix 12 in the PPARγ-LBD. Collectively, these results unraveled the potential cardiovascular toxicity of PBDE 47 by selective activation of PPARγ to facilitate foam cell formation for the first time.

Non-coding RNA-Associated Therapeutic Strategies in Atherosclerosis

Atherosclerosis has been the main cause of disability and mortality in the world, resulting in a heavy medical burden for all countries. It is widely known to be a kind of chronic inflammatory disease in the blood walls, of which the key pathogenesis is the accumulation of immunologic cells in the lesion, foam cells formation, and eventually plaque rupture causing ischemia of various organs. Non-coding RNAs (ncRNAs) play a vital role in regulating the physiologic and pathophysiologic processes in cells. More and more studies have revealed that ncRNAs also participated in the development of atherosclerosis and regulated cellular phenotypes such as endothelial dysfunction, leukocyte recruitment, foam cells formation, and vascular smooth muscle cells phenotype-switching and apoptosis. Given the broad functions of ncRNAs in atherogenesis, they have become potential therapeutic targets. Apart from that, ncRNAs have become powerful blueprints to design new drugs. For example, RNA interference drugs were inspired by small interfering RNAs that exist in normal cellular physiologic processes and behave as negative regulators of specific proteins. For instance, inclisiran is a kind of RNAi drug targeting PCKS9 mRNA, which can lower the level of LDL-C and treat atherosclerosis. We introduce some recent research progresses on ncRNAs related to atherosclerotic pathophysiologic process and the current clinical trials of RNA drugs pointed at atherosclerosis.

Cardiovascular Disease in South Asian Immigrants: a Review of Dysfunctional HDL as a Potential Marker

South Asians (SAs) account for a quarter of the world's population and are one of the fastest-growing immigrant groups in the United States (US). South Asian Immigrants (SAIs) are disproportionately more at risk of developing cardiovascular disease (CVD) than other ethnic/racial groups. Atherosclerosis is a chronic inflammatory disorder and is the major cause of CVD. Traditional CVD risk factors, though important, do not fully explain the elevated risk of CVD in SAIs. High-density lipoproteins (HDLs) are heterogeneous lipoproteins that modify their composition and functionality depending on physiological or pathological conditions. With its cholesterol efflux, anti-inflammatory, and antioxidant functions, HDL is traditionally considered a protective factor for CVD. However, its functions can be compromised under pathological conditions, such as chronic inflammation, making it dysfunctional (Dys-HDL). SAIs have a high prevalence of type 2 diabetes and metabolic syndrome, which may further promote Dys-HDL. This review explores the potential association between Dys-HDL and CVD in SAIs and presents current literature discussing the role of Dys-HDL in CVD.

Aldehyde dehydrogenase 2 and PARP1 interaction modulates hepatic HDL biogenesis by LXRα-mediated ABCA1 expression

HDL cholesterol (HDL-C) predicts risk of cardiovascular disease (CVD), but the factors regulating HDL are incompletely understood. Emerging data link CVD risk to decreased HDL-C in 8% of the world population and 40% of East Asians who carry an SNP of aldehyde dehydrogenase 2 (ALDH2) rs671, responsible for alcohol flushing syndrome; however, the underlying mechanisms remain unknown. We found significantly decreased HDL-C with increased hepatosteatosis in ALDH2-KO (AKO), ALDH2/LDLR-double KO (ALKO), and ALDH2 rs671-knock-in (KI) mice after consumption of a Western diet. Metabolomics identified ADP-ribose as the most significantly increased metabolites in the ALKO mouse liver. Moreover, ALDH2 interacted with poly(ADP-ribose) polymerase 1 (PARP1) and attenuated PARP1 nuclear translocation to downregulate poly(ADP-ribosyl)ation of liver X receptor α (LXRα), leading to an upregulation of ATP-binding cassette transporter A1 (ABCA1) and HDL biogenesis. Conversely, AKO or ALKO mice exhibited lower HDL-C with ABCA1 downregulation due to increased nuclear PARP1 and upregulation of LXRα poly(ADP-ribosyl)ation. Consistently, PARP1 inhibition rescued ALDH2 deficiency-induced fatty liver and elevated HDL-C in AKO mice. Interestingly, KI mouse or human liver tissues showed ABCA1 downregulation with increased nuclear PARP1 and LXRα poly(ADP-ribosyl)ation. Our study uncovered a key role of ALDH2 in HDL biogenesis through the LXRα/PARP1/ABCA1 axis, highlighting a potential therapeutic strategy in CVD.

Endocrine control of glycogen and triacylglycerol breakdown in the fly model

Over the last decade, the combination of genetics, transcriptomic and proteomic approaches yielded substantial insights into the mechanisms behind the synthesis and breakdown of energy stores in the model organisms. The fruit fly Drosophila melanogaster has been particularly useful to unravel genetic regulations of energy metabolism. Despite the considerable evolutionary distance between humans and flies, the energy storage organs, main metabolic pathways, and even their genetic regulations remained relatively conserved. Glycogen and fat are universal energy reserves used in all animal phyla and several of their endocrine regulators, such as the insulin pathway, are highly evolutionarily conserved. Nevertheless, some of the factors inducing catabolism of energy stores have diverged significantly during evolution. Moreover, even within a single insect species, D. melanogaster, there are substantial developmental and context-dependent variances in the regulation of energy stores. These differences include, among others, the endocrine pathways that govern the catabolic events or the predominant fuel which is utilized for the given process. For example, many catabolic regulators that control energy reserves in adulthood seem to be largely dispensable for energy mobilization during development. In this review, we focus on a selection of the most important catabolic regulators from the group of peptide hormones (Adipokinetic hormone, Corazonin), catecholamines (octopamine), steroid hormones (20-hydroxyecdysone), and other factors (extracellular adenosine, regulators of lipase Brummer). We discuss their roles in the mobilization of energy reserves for processes such as development through non-feeding stages, flight or starvation survival. Finally, we conclude with future perspectives on the energy balance research in the fly model.

Oxysterols Protect Epithelial Cells Against Pore-Forming Toxins

Many species of bacteria produce toxins such as cholesterol-dependent cytolysins that form pores in cell membranes. Membrane pores facilitate infection by releasing nutrients, delivering virulence factors, and causing lytic cell damage - cytolysis. Oxysterols are oxidized forms of cholesterol that regulate cellular cholesterol and alter immune responses to bacteria. Whether oxysterols also influence the protection of cells against pore-forming toxins is unresolved. Here we tested the hypothesis that oxysterols stimulate the intrinsic protection of epithelial cells against damage caused by cholesterol-dependent cytolysins. We treated epithelial cells with oxysterols and then challenged them with the cholesterol-dependent cytolysin, pyolysin. Treating HeLa cells with 27-hydroxycholesterol, 25-hydroxycholesterol, 7α-hydroxycholesterol, or 7β-hydroxycholesterol reduced pyolysin-induced leakage of lactate dehydrogenase and reduced pyolysin-induced cytolysis. Specifically, treatment with 10 ng/ml 27-hydroxycholesterol for 24 h reduced pyolysin-induced lactate dehydrogenase leakage by 88%, and reduced cytolysis from 74% to 1%. Treating HeLa cells with 27-hydroxycholesterol also reduced pyolysin-induced leakage of potassium ions, prevented mitogen-activated protein kinase cell stress responses, and limited alterations in the cytoskeleton. Furthermore, 27-hydroxycholesterol reduced pyolysin-induced damage in lung and liver epithelial cells, and protected against the cytolysins streptolysin O and Staphylococcus aureus α-hemolysin. Although oxysterols regulate cellular cholesterol by activating liver X receptors, cytoprotection did not depend on liver X receptors or changes in total cellular cholesterol. However, oxysterol cytoprotection was partially dependent on acyl-CoA:cholesterol acyltransferase (ACAT) reducing accessible cholesterol in cell membranes. Collectively, these findings imply that oxysterols stimulate the intrinsic protection of epithelial cells against pore-forming toxins and may help protect tissues against pathogenic bacteria.

Monocyte miRNAs Are Associated With Type 2 Diabetes

miRNAs are small noncoding RNAs that may contribute to common diseases through epigenetic regulation of gene expression. Little is known regarding the role of miRNAs in type 2 diabetes (T2D). We performed miRNA sequencing and transcriptomic profiling of peripheral monocytes from the longitudinal Multi-Ethnic Study of Atherosclerosis (MESA) (N = 1,154). We examined associations between miRNAs and prevalent impaired fasting glucose and T2D and evaluated the T2D-associated miRNA effect on incident T2D. Of 774 detected miRNAs, 6 (miR-22-3p, miR-33a-5p, miR-181c-5p, miR-92b-3p, miR-222-3p, and miR-944) were associated with prevalent T2D. For five of the six miRNAs (all but miR-222-3p), our findings suggest a dose-response relationship with impaired fasting glucose and T2D. Two of the six miRNAs were associated with incident T2D (miR-92b-3p: hazard ratio [HR] 1.64, P = 1.30E-03; miR-222-3p: HR 1.97, P = 9.10E-03) in the highest versus lowest tertile of expression. Most of the T2D-associated miRNAs were also associated with HDL cholesterol concentrations. The genes targeted by these miRNAs belong to key nodes of a cholesterol metabolism transcriptomic network. Higher levels of miRNA expression expected to increase intracellular cholesterol accumulation in monocytes are linked to an increase in T2D risk.

Nuclear HMGB1 protects from nonalcoholic fatty liver disease through negative regulation of liver X receptor

Dysregulations of lipid metabolism in the liver may trigger steatosis progression, leading to potentially severe clinical consequences such as nonalcoholic fatty liver diseases (NAFLDs). Molecular mechanisms underlying liver lipogenesis are very complex and fine-tuned by chromatin dynamics and multiple key transcription factors. Here, we demonstrate that the nuclear factor HMGB1 acts as a strong repressor of liver lipogenesis. Mice with liver-specific Hmgb1 deficiency display exacerbated liver steatosis, while Hmgb1-overexpressing mice exhibited a protection from fatty liver progression when subjected to nutritional stress. Global transcriptome and functional analysis revealed that the deletion of Hmgb1 gene enhances LXRα and PPARγ activity. HMGB1 repression is not mediated through nucleosome landscape reorganization but rather via a preferential DNA occupation in a region carrying genes regulated by LXRα and PPARγ. Together, these findings suggest that hepatocellular HMGB1 protects from liver steatosis development. HMGB1 may constitute a new attractive option to therapeutically target the LXRα-PPARγ axis during NAFLD.

Natural Flavonoids Derived From Fruits Are Potential Agents Against Atherosclerosis

Atherosclerosis, as a chronic inflammatory response, is one of the main causes of cardiovascular diseases. Atherosclerosis is induced by endothelial cell dysfunction, migration and proliferation of smooth muscle cells, accumulation of foam cells and inflammatory response, resulting in plaque accumulation, narrowing and hardening of the artery wall, and ultimately leading to myocardial infarction or sudden death and other serious consequences. Flavonoid is a kind of natural polyphenol compound widely existing in fruits with various structures, mainly including flavonols, flavones, flavanones, flavanols, anthocyanins, isoflavones, and chalcone, etc. Because of its potential health benefits, it is now used in supplements, cosmetics and medicines, and researchers are increasingly paying attention to its role in atherosclerosis. In this paper, we will focus on several important nodes in the development of atherosclerotic disease, including endothelial cell dysfunction, smooth muscle cell migration and proliferation, foam cell accumulation and inflammatory response. At the same time, through the classification of flavonoids from fruits, the role and potential mechanism of flavonoids in atherosclerosis were reviewed, providing a certain direction for the development of fruit flavonoids in the treatment of atherosclerosis drugs.

SGLT-2 Inhibitors in NAFLD: Expanding Their Role beyond Diabetes and Cardioprotection

Non-alcoholic fatty liver disease (NAFLD) is an ‘umbrella’ term, comprising a spectrum ranging from benign, liver steatosis to non-alcoholic steatohepatitis, liver fibrosis and eventually cirrhosis and hepatocellular carcinoma. NAFLD has evolved as a major health problem in recent years. Discovering ways to prevent or delay the progression of NAFLD has become a global focus. Lifestyle modifications remain the cornerstone of NAFLD treatment, even though various pharmaceutical interventions are currently under clinical trial. Among them, sodium-glucose co-transporter type-2 inhibitors (SGLT-2i) are emerging as promising agents. Processes regulated by SGLT-2i, such as endoplasmic reticulum (ER) and oxidative stress, low-grade inflammation, autophagy and apoptosis are all implicated in NAFLD pathogenesis. In this review, we summarize the current understanding of the NAFLD pathophysiology, and specifically focus on the potential impact of SGLT-2i in NAFLD development and progression, providing current evidence from in vitro, animal and human studies. Given this evidence, further mechanistic studies would advance our understanding of the exact mechanisms underlying the pathogenesis of NAFLD and the potential beneficial actions of SGLT-2i in the context of NAFLD treatment.

Pseudorabies Virus Inhibits Expression of Liver X Receptors to Assist Viral Infection

Pseudorabies virus (PRV) is a contagious herpesvirus that causes Aujeszky’s disease and economic losses worldwide. Liver X receptors (LXRs) belong to the nuclear receptor superfamily and are critical for the control of lipid homeostasis. However, the role of LXR in PRV infection has not been fully established. In this study, we found that PRV infection downregulated the mRNA and protein levels of LXRα and LXRβ in vitro and in vivo. Furthermore, we discovered that LXR activation suppressed PRV proliferation, while LXR inhibition promoted PRV proliferation. We demonstrated that LXR activation-mediated reduction of cellular cholesterol was critical for the dynamics of PRV entry-dependent clathrin-coated pits. Replenishment of cholesterol restored the dynamics of clathrin-coated pits and PRV entry under LXR activation conditions. Interestingly, T0901317, an LXR agonist, prevented PRV infection in mice. Our results support a model that PRV modulates LXR-regulated cholesterol metabolism to facilitate viral proliferation.

Highly Bright AIE Nanoparticles by Regulating the Substituent of Rhodanine for Precise Early Detection of Atherosclerosis and Drug Screening

Fluorescent probes capable of precise detection of atherosclerosis (AS) at an early stage and fast assessment of anti-AS drugs in animal level are particularly valuable. Herein, a highly bright aggregation-induced emission (AIE) nanoprobe is introduced by regulating the substituent of rhodanine for early detection of atherosclerotic plaque and screening of anti-AS drugs in a precise, sensitive, and rapid manner. With dicyanomethylene-substituted rhodanine as the electron-withdrawing unit, the AIE luminogen named TPE-T-RCN shows the highest molar extinction coefficient, the largest photoluminescence quantum yield, and the most redshifted absorption/emission spectra simultaneously as compared to the control compounds. The nanoprobes are obtained with an amphiphilic copolymer as the matrix encapsulating TPE-T-RCN molecules, which are further surface functionalized with anti-CD47 antibody for specifically binding to CD47 overexpressed in AS plaques. Such nanoprobes allow efficient recognition of AS plaques at different stages in apolipoprotein E-deficient (apoE^-/- ) mice, especially for the recognition of early-stage AS plaques prior to micro-computed tomography (CT) and magnetic resonance imaging (MRI). These features impel to apply the nanoprobes in monitoring the therapeutic effects of anti-AS drugs, providing a powerful tool for anti-AS drug screening. Their potential use in targeted imaging of human carotid plaque is further demonstrated.

Lipid metabolism reprogramming in renal cell carcinoma

Metabolic reprogramming is recognized as a hallmark of cancer. Lipids are the essential biomolecules required for membrane biosynthesis, energy storage, and cell signaling. Altered lipid metabolism allows tumor cells to survive in the nutrient-deprived environment. However, lipid metabolism remodeling in renal cell carcinoma (RCC) has not received the same attention as in other cancers. RCC, the most common type of kidney cancer, is associated with almost 15,000 death in the USA annually. Being refractory to conventional chemotherapy agents and limited available targeted therapy options has made the treatment of metastatic RCC very challenging. In this article, we review recent findings that support the importance of synthesis and metabolism of cholesterol, free fatty acids (FFAs), and polyunsaturated fatty acids (PUFAs) in the carcinogenesis and biology of RCC. Delineating the detailed mechanisms underlying lipid reprogramming can help to better understand the pathophysiology of RCC and to design novel therapeutic strategies targeting this malignancy.

Metabolism in tumor-associated macrophages

Macrophages functionally adapt to a diverse set of signals, a process that is critical for their role in maintaining or restoring tissue homeostasis. This process extends to cancer, where macrophages respond to a series of inflammatory and metabolic cues that direct a maladaptive healing response. Tumor-associated macrophages (TAMs) have altered glucose, amino acid, and lipid metabolic profiles, and interfering with this metabolic shift can blunt the ability of macrophages to promote tumor growth, metastasis, and the creation of an immunosuppressive microenvironment. Here we will review changes in metabolites and metabolic pathways in TAMs and link these with the phenotypic and functional properties of the cells. We will also discuss current strategies targeting TAM metabolism as a therapeutic intervention in cancer.