Liver X receptors in lipid signalling and membrane homeostasis

Comparison of the qualitative and quantitative optical coherence tomographic features between sudden acquired retinal degeneration syndrome and normal eyes in dogs

OBJECTIVE

To quantitatively and qualitatively characterize the retinal optical coherence tomographic features of sudden acquired retinal degeneration syndrome (SARDS) and SARDS suspect dogs.

ANIMALS STUDIED

Fourteen SARDS affected dogs, 11 age-, breed-, and sex-matched control dogs, and two SARDS suspect dogs.

PROCEDURES

Spectral-domain optical coherence tomography (OCT) images were used to evaluate the quantitative features, including thickness, intereye asymmetry, and longitudinal changes in retinal layer thickness and the qualitative features, including retinal architecture and vitreous haze.

RESULTS

Mean outer retinal layer thickness (ORT), outer nuclear layer thickness (ONL), and photoreceptor layer thickness (PRL) were significantly lower in the SARDS group, whereas mean inner retinal layer thickness was significantly higher in the SARDS group than in the control group. While thickness values of all retinal layers did not differ significantly between paired eyes in each group, the absolute intereye asymmetries in the ORT (p < .0001), ONL (p = .008), and PRL (p < .0001) were significantly higher in the SARDS group than in the control group. Some SARDS patients and SARDS suspects had a greater PRL than the control group, and serial OCT evaluation showed an increase in PRL in one SARDS suspect. Vitreous haze severity was greater in the SARDS group than in the control group (vitreous relative intensity, p = .030).

CONCLUSIONS

We described the OCT features of SARDS patients and suspects. In particular, PRL thickening in the SARDS suspects might indicate an early change in SARDS. Although further studies are needed, this finding might provide new insights into the pathogenesis of SARDS.

CRISPR screens for lipid regulators reveal a role for ER-bound SNX13 in lysosomal cholesterol export

We report here two genome-wide CRISPR screens performed to identify genes that, when knocked out, alter levels of lysosomal cholesterol or bis(monoacylglycero)phosphate. In addition, these screens were also performed under conditions of NPC1 inhibition to identify modifiers of NPC1 function in lysosomal cholesterol export. The screens confirm tight coregulation of cholesterol and bis(monoacylglycero)phosphate in cells and reveal an unexpected role for the ER-localized SNX13 protein as a negative regulator of lysosomal cholesterol export and contributor to ER–lysosome membrane contact sites. In the absence of NPC1 function, SNX13 knockdown redistributes lysosomal cholesterol and is accompanied by triacylglycerol-rich lipid droplet accumulation and increased lysosomal bis(monoacylglycero)phosphate. These experiments provide unexpected insight into the regulation of lysosomal lipids and modification of these processes by novel gene products.

Cholesterol metabolism: from lipidomics to immunology

Oxysterols, the oxidized forms of cholesterol or of its precursors, are formed in the first steps of cholesterol metabolism. Oxysterols have interested chemists, biologists, and physicians for many decades, but their exact biological relevance in vivo, other than as intermediates in bile acid biosynthesis, has long been debated. However, in the first quarter of this century, a role for side-chain oxysterols and their C-7 oxidized metabolites has been convincingly established in the immune system. 25-Hydroxycholesterol has been shown to be synthesized by macrophages in response to the activation of Toll-like receptors and to offer protection against microbial pathogens, whereas 7α,25-dihydroxycholesterol has been shown to act as a chemoattractant to lymphocytes expressing the G protein-coupled receptor Epstein-Barr virus-induced gene 2 and to be important in coordinating the action of B cells, T cells, and dendritic cells in secondary lymphoid tissue. There is a growing body of evidence that not only these two oxysterols but also many of their isomers are of importance to the proper function of the immune system. Here, we review recent findings related to the roles of oxysterols in immunology.

Raman spectroscopy biochemical characterisation of bladder cancer cisplatin resistance regulated by FDFT1: a review

Bladder cancer is the fourth most common malignancy in males. It can present across the whole continuum of severity, from mild through well-differentiated disease to extremely malignant tumours with poor survival rates. As with other vital organ malignancies, proper clinical management involves accurate diagnosis and staging. Chemotherapy consisting of a cisplatin-based regimen is the mainstay in the management of muscle-invasive bladder cancers. Control via cisplatin-based chemotherapy is threatened by the development of chemoresistance. Intracellular cholesterol biosynthesis in bladder cancer cells is considered a contributory factor in determining the chemotherapy response. Farnesyl-diphosphate farnesyltransferase 1 (FDFT1), one of the main regulatory components in cholesterol biosynthesis, may play a role in determining sensitivity towards chemotherapy compounds in bladder cancer. FDFT1-associated molecular identification might serve as an alternative or appendage strategy for early prediction of potentially chemoresistant muscle-invasive bladder cancer tissues. This can be accomplished using Raman spectroscopy. Developments in the instrumentation have led to it becoming one of the most convenient forms of analysis, and there is a highly realistic chance that it will become an effective tool in the pathology lab. Chemosensitive bladder cancer tissues tend to have a higher lipid content, more protein genes and more cholesterol metabolites. These are believed to be associated with resistance towards bladder cancer chemotherapy. Herein, Raman peak assignments have been tabulated as an aid to indicating metabolic changes in bladder cancer tissues that are potentially correlated with FDFT1 expression.

Homo Sapiens (Hsa)-microRNA (miR)-6727-5p Contributes to the Impact of High-Density Lipoproteins on Fibroblast Wound Healing In Vitro

Chronic, non-healing wounds are a significant cause of global morbidity and mortality, and strategies to improve delayed wound closure represent an unmet clinical need. High-density lipoproteins (HDL) can enhance wound healing, but exploitation of this finding is challenging due to the complexity and instability of these heterogeneous lipoproteins. The responsiveness of primary human neonatal keratinocytes, and neonatal and human dermal fibroblasts (HDF) to HDL was confirmed by cholesterol efflux, but promotion of ‘scrape’ wound healing occurred only in primary human neonatal (HDFn) and adult fibroblasts (HDFa). Treatment of human fibroblasts with HDL induced multiple changes in the expression of small non-coding microRNA sequences, determined by microchip array, including hsa-miR-6727-5p. Intriguingly, levels of hsa-miR-6727-5p increased in HDFn, but decreased in HDFa, after exposure to HDL. Delivery of a hsa-miR-6727-5p mimic elicited repression of different target genes in HDFn (ZNF584) and HDFa (EDEM3, KRAS), and promoted wound closure in HDFn. By contrast, a hsa-miR-6727-5p inhibitor promoted wound closure in HDFa. We conclude that HDL treatment exerts distinct effects on the expression of hsa-miR-6727-5p in neonatal and adult fibroblasts, and that this is a sequence which plays differential roles in wound healing in these cell types, but cannot replicate the myriad effects of HDL.

Cholesterol Transport Dysfunction and Its Involvement in Atherogenesis

Atherosclerosis is the cause of the development of serious cardiovascular disorders, leading to disability and death. Numerous processes are involved in the pathogenesis of atherosclerosis, including inflammation, endothelial dysfunction, oxidative stress, and lipid metabolism disorders. Reverse transport of cholesterol is a mechanism presumably underlying the atheroprotective effect of high-density lipoprotein. In this review, we examined disorders of cholesterol metabolism and their possible effect on atherogenesis. We paid special attention to the reverse transport of cholesterol. Transformed cholesterol metabolism results in dyslipidemia and early atherosclerosis. Reverse cholesterol transport is an endogenous mechanism by which cells export cholesterol and maintain homeostasis. It is known that one of the main factors leading to the formation of atherosclerotic plaques on the walls of blood vessels are multiple modifications of low-density lipoprotein, and the formation of foam cells following them.

Meta-Analysis of APP Expression Modulated by SARS-CoV-2 Infection via the ACE2 Receptor

Alzheimer's disease (AD) is characterized by the deposition of amyloid-beta (Aβ) plaques from improper amyloid-beta precursor protein (APP) cleavage. Following studies of inflammation caused by coronavirus-2019 (COVID-19) infection, this study investigated the impact of COVID-19 on APP expression. A meta-analysis was conducted utilizing QIAGEN Ingenuity Pathway Analysis (IPA) to examine the link between severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and the modulation of APP expression upon virus binding the Angiotensin-converting enzyme-2 (ACE2) receptor. A Core Analysis was run on the infection by severe acute respiratory syndrome (SARS) coronavirus node, which included molecules affected by SARS-CoV-2, revealing its upstream regulators. Intermediary molecules were found between the upstream regulators and ACE2 and between ACE2 and APP. Activation of the upstream regulators downregulated the expression of ACE2 with a Z-score of -1.719 (p-value = 0.086) and upregulated APP with a Z-score of 1.898 (p-value = 0.058), showing a less than 10% chance of the results occurring by chance and pointing to an inverse relationship between ACE2 and APP expression. The neuroinflammation signaling pathway was the fifth top canonical pathway involved in APP upregulation. The study results suggest that ACE2 could be downregulated by SARS-CoV-2, resulting in APP upregulation, and potentially exacerbating the onset and progression of AD.

Oxysterols in the Immune Response to Bacterial and Viral Infections

Oxidized cholesterols, the so-called oxysterols, are widely known to regulate cholesterol homeostasis. However, more recently oxysterols have emerged as important lipid mediators in the response to both bacterial and viral infections. This review summarizes our current knowledge of selected oxysterols and their receptors in the control of intracellular bacterial growth as well as viral entry into the host cell and viral replication. Lastly, we briefly discuss the potential of oxysterols and their receptors as drug targets for infectious and inflammatory diseases.

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.

Modeling cholesterol metabolism and atherosclerosis

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of morbidity and mortality among Western populations. Many risk factors have been identified for ASCVD; however, elevated low-density lipoprotein cholesterol (LDL-C) remains the gold standard. Cholesterol metabolism at the cellular and whole-body level is maintained by an array of interacting components. These regulatory mechanisms have complex behavior. Likewise, the mechanisms which underpin atherogenesis are nontrivial and multifaceted. To help overcome the challenge of investigating these processes mathematical modeling, which is a core constituent of the systems biology paradigm has played a pivotal role in deciphering their dynamics. In so doing models have revealed new insights about the key drivers of ASCVD. The aim of this review is fourfold; to provide an overview of cholesterol metabolism and atherosclerosis, to briefly introduce mathematical approaches used in this field, to critically discuss models of cholesterol metabolism and atherosclerosis, and to highlight areas where mathematical modeling could help to investigate in the future. This article is categorized under: Cardiovascular Diseases > Computational Models.

Insulin-Responsive Transcription Factors

The hormone insulin executes its function via binding and activating of the insulin receptor, a receptor tyrosine kinase that is mainly expressed in skeletal muscle, adipocytes, liver, pancreatic β-cells, and in some areas of the central nervous system. Stimulation of the insulin receptor activates intracellular signaling cascades involving the enzymes extracellular signal-regulated protein kinase-1/2 (ERK1/2), phosphatidylinositol 3-kinase, protein kinase B/Akt, and phospholipase Cγ as signal transducers. Insulin receptor stimulation is correlated with multiple physiological and biochemical functions, including glucose transport, glucose homeostasis, food intake, proliferation, glycolysis, and lipogenesis. This review article focuses on the activation of gene transcription as a result of insulin receptor stimulation. Signal transducers such as protein kinases or the GLUT4-induced influx of glucose connect insulin receptor stimulation with transcription. We discuss insulin-responsive transcription factors that respond to insulin receptor activation and generate a transcriptional network executing the metabolic functions of insulin. Importantly, insulin receptor stimulation induces transcription of genes encoding essential enzymes of glycolysis and lipogenesis and inhibits genes encoding essential enzymes of gluconeogenesis. Overall, the activation or inhibition of insulin-responsive transcription factors is an essential aspect of orchestrating a wide range of insulin-induced changes in the biochemistry and physiology of insulin-responsive tissues.

PPAR-gamma agonists: Potential modulators of autophagy in obesity

Autophagy pathways are involved in the pathogenesis of some obesity related health problems. As obesity is a nutrient sufficiency condition, autophagy process can be altered in obesity through AMP activated protein kinase (AMPK) inhibition. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) as the main modulator of adipogenesis process can be effective in the regulation of obesity related phenotypes. As well, it has been revealed that PPAR-gamma and its agonists can regulate autophagy in different normal or cancer cells. However, their effects on autophagy modulation in obesity have been investigated in the limited number of studies. In the current comprehensive mechanistic review, we aimed to investigate the possible mechanisms of action of PPAR-gamma on the process of autophagy in obesity through narrating the effects of PPAR-gamma on autophagy in the non-obesity conditions. Moreover, mode of action of PPAR-gamma agonists on autophagy related implications comprehensively reviewed in the various studies. Understanding the different effects of PPAR-gamma agonists on autophagy in obesity can help to develop a new approach to management of obesity.

Association between in vitro nuclear receptor-activating profiles of chemical compounds and their in vivo hepatotoxicity in rats

The liver plays critical roles to maintain homeostasis of living organisms and is also a major target organ of chemical toxicity. Meanwhile, nuclear receptors (NRs) are known to regulate major liver functions and also as a critical target for hepatotoxic compounds. In this study, we established mammalian one-hybrid assay systems for five rat-derived NRs, namely PXR, PPARα, LXRα, FXR and RXRα, and evaluated a total of 326 compounds for their NR-activating profiles. Then, we assessed the association between their NR-activating profile and hepatotoxic endpoints in repeated-dose toxicity data of male rats from Hazard Evaluation Support System. In the in vitro cell-based assays, 68, 38, 20, 17 and 17 compounds were identified as positives for PXR, PPARα, LXRα, FXR and RXRα, respectively. The association analyses demonstrated that the PXR-positive compounds showed high frequency of endpoints related to liver hypertrophy, such as centrilobular hepatocellular hypertrophy, suggesting that PXR activation is involved in chemical-induced liver hypertrophy in rats. It is intriguing to note that the PXR-positive compounds also showed statistically significant associations with both prolonged activated partial thromboplastin time and prolonged prothrombin time, suggesting a possible involvement of PXR in the regulation of blood clotting factors. Collectively, our approach may be useful for discovering new functions of NRs as well as understanding the complex mechanism for hepatotoxicity caused by chemical compounds.

SIRT6 controls hepatic lipogenesis by suppressing LXR, ChREBP, and SREBP1

Fatty liver disease is the most prevalent chronic liver disorder, which is manifested by hepatic triglyceride elevation, inflammation, and fibrosis. Sirtuin 6 (Sirt6), an NAD+-dependent deacetylase, has been implicated in hepatic glucose and lipid metabolism; however, the underlying mechanisms are incompletely understood. The aim of this study was to identify and characterize novel players and mechanisms that are responsible for the Sirt6-mediated metabolic regulation in the liver. We generated and characterized Sirt6 liver-specific knockout mice regarding its role in the development of fatty liver disease. We used cell models to validate the molecular alterations observed in the animal models. Biochemical and molecular biological approaches were used to illustrate protein-protein interactions and gene regulation. Our data show that Sirt6 liver-specific knockout mice develop more severe fatty liver disease than wild-type mice do on a Western diet. Hepatic Sirt6 deficiency leads to elevated levels and transcriptional activities of carbohydrate response element binding protein (ChREBP) and sterol regulatory element binding protein 1 (SREBP1). Mechanistically, our data reveal protein-protein interactions between Sirt6 and liver X receptor α (LXRα), ChREBP, or SREBP1c in hepatocytes. Moreover, Sirt6 suppresses transcriptional activities of LXRα, ChREBP, and SREBP1c through direct deacetylation. In conclusion, this work has identified a key mechanism that is responsible for the salutary function of Sirt6 in the inhibition of hepatic lipogenesis by suppressing LXR, ChREBP, and SREBP1.

Nuclear receptors of NR1 and NR4 subfamilies in the regulation of microglial functions and pathology

This review provides an overview of researches on the NR1 and NR4 nuclear receptors involved in the regulation of microglial functions. Nuclear receptors are attractive candidates for drug targets in the therapies of the central nervous system disorders, because the activation of these receptors is expected to regulate the functions and the phenotypes of microglia, by controlling the expression of specific gene subsets and also by regulating the cellular signaling mechanisms in a nongenomic manner. Several members of NR1 nuclear receptor subfamily have been examined for their ability to regulate microglial functions. For example, stimulation of vitamin D receptor inhibits the production of pro-inflammatory factors and increases the production of anti-inflammatory cytokines. Similar regulatory actions of nuclear receptor ligands on inflammation-related genes have also been reported for other NR1 members such as retinoic acid receptors, peroxisome proliferator-activated receptors (PPARs), and liver X receptors (LXRs). In addition, stimulation of PPARγ and LXRs may also result in increased phagocytic activities of microglia. Consistent with these actions, the agonists at nuclear receptors of NR1 subfamily are shown to produce therapeutic effects on animal models of various neurological disorders such as experimental allergic encephalomyelitis, Alzheimer's disease, Parkinson's disease, and ischemic/hemorrhagic stroke. On the other hand, increasing lines of evidence suggest that the stimulation of NR4 subfamily members of nuclear receptors such as Nur77 and Nurr1 also regulates microglial functions and alleviates neuropathological events in several disease models. Further advancement of these research fields may prove novel therapeutic opportunities.

Aberrant Cholesterol Metabolism in Ovarian Cancer: Identification of Novel Therapeutic Targets

Cholesterol is an essential substance in mammalian cells, and cholesterol metabolism plays crucial roles in multiple biological functions. Dysregulated cholesterol metabolism is a metabolic hallmark in several cancers, beyond the Warburg effect. Reprogrammed cholesterol metabolism has been reported to enhance tumorigenesis, metastasis and chemoresistance in multiple cancer types, including ovarian cancer. Ovarian cancer is one of the most aggressive malignancies worldwide. Alterations in metabolic pathways are characteristic features of ovarian cancer; however, the specific role of cholesterol metabolism remains to be established. In this report, we provide an overview of the key proteins involved in cholesterol metabolism in ovarian cancer, including the rate-limiting enzymes in cholesterol biosynthesis, and the proteins involved in cholesterol uptake, storage and trafficking. Also, we review the roles of cholesterol and its derivatives in ovarian cancer and the tumor microenvironment, and discuss promising related therapeutic targets for ovarian cancer.

Effects of allyl isothiocyanate on the expression, function, and its mechanism of ABCA1 and ABCG1 in pulmonary of COPD rats

BACKGROUND AND AIMS

Allyl isothiocyanate(AITC) has been shown to play an important role in the improved symptoms of chronic obstructive pulmonary disease(COPD) and the inhibition of inflammation, but the role in COPD lipid metabolism disorder and the molecular mechanism remains unclear. We aimed to explore whether and how AITC affects COPD by regulating lipid metabolism and inflammatory response.

METHODS

The COPD rat model was established by cigarette smoke exposure. Cigarette smoke extract stimulated 16HBE cells to induce a cell model. The effect of AITC treatment was detected by lung function test, H&E staining, Oil red O staining, immunohistochemistry, ELISA, CCK-8, HPLC, fluorescence efflux test, siRNA, RT-PCR, and Western blotting. Biological analysis was performed to analyze the results. Graphpad Prism 8.0 software was used for statistical analysis.

RESULTS

AITC can improve lung function and pathological injury in COPD rats. The levels of IL-1 β and TNF- α in the AITC treatment group were significantly lower than those in the model group(P < 0.05), and the lipid metabolism was also improved (P < 0.05). AITC reverses CSE-induced down-regulation of LXR α, ABCA1, and ABCG1 expression and function in a time-and concentration-dependent manner (P < 0.05). AITC regulates the cholesterol metabolism disorder induced by CSE in NR8383 cells and attenuates macrophage inflammation (P < 0.05). In addition, after silencing LXR α with siRNA, the effect of AITC was also inhibited.

CONCLUSION

These results suggest that AITC improves COPD by promoting RCT process and reducing inflammatory response via activating LXR pathways.

Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

Role of the cytoskeleton in steroidogenesis

Steroidogenesis in the adrenal cortex or gonads is a complicated process, modulated by various elements either at the tissue or molecular level. The substrate-cholesterol is first delivered to the outer membrane of mitochondria, undergoing a series of enzymatic reactions along with the material exchange between the mitochondria and the ER (endoplasmic reticulum) and ultimately yield various steroids: aldosterone, cortisol, testosterone and estrone. Several valves are set to adjust the amount of production to the needs. e.g. StAR(steroidogenic acute regulator) is in charge of the rate-limiting step-traffic of cholesterol from outer membrane to inner membrane of mitochondria. And the "needs" is partly reflected by trophic signals like ACTH、LH and downstream pathways-- intracellular cAMP pathway, which represents the endocrinal regulation of steroid synthesis, too. The coordinated activities of these related factors are all associated with another crucial cellular constituent-the cytoskeleton, which plays a crucial role in the cellular architecture and substrate trafficking. Though considerable studies have been performed regarding steroid synthesis, details about the upstream signaling pathways and mechanisms of the regulation by cytoskeleton network still remain unclear. The metabolism and interplays of the pivotal cellular organelles with cytoskeleton are worth exploring as well. In this review, we summarize research of different time span, describing the roles of specific cytoskeleton elements in steroidogenesis and related signaling pathways involved in the steroid synthesis. In addition, we discussed the inner cytoskeletal network involved in steroidogenic processes such as mitochondrial movement, organelle interactions and cholesterol trafficking.

Associations between maternal mono-(2-ethylhexyl) phthalate levels, nuclear receptor gene polymorphisms, and fatty acid levels in pregnant Japanese women in the Hokkaido study

We assessed how the interaction between mono-(2-ethylhexyl) phthalate (MEHP) in maternal sera and the maternal genotypes associated with nuclear receptors affect fatty acid levels in a prospective birth cohort study of pregnant Japanese individuals (n = 437) recruited in Sapporo between 2002 and 2005. We analyzed MEHP and fatty acids using gas chromatography-mass spectrometry. Thirteen single nucleotide polymorphisms of peroxisome proliferator-activated receptor (PPAR) alpha, PPAR gamma (PPARG), PPARG coactivator 1A (PPARGC1A), PPAR delta, constitutive androstane receptor, liver X receptor (LXR) alpha, and LXR beta (LXRB) were analyzed using real-time PCR. Multiple linear regression models were used to confirm the influence of log₁₀-transformed MEHP levels and maternal genotypes on log₁₀-transformed fatty acid levels. When the effects of the interaction between MEHP levels and the maternal PPARGC1A (rs8192678) genotype on oleic acid levels were evaluated, the estimated changes (95 % confidence intervals) in oleic acid levels against MEHP levels, maternal PPARGC1A (rs8192678)-GA/AA genotype, and the interaction between them showed a mean reduction of 0.200 (0.079, 0.322), mean reduction of 0.141 (0.000, 0.283), and mean increase of 0.145 (0.010, 0.281), respectively, after adjusting for the perfluorooctanesulfonate level. The effects of the interaction between MEHP levels and maternal LXRB (rs2303044) genotype on linoleic acid levels was also significant (p_int = 0.010). In conclusion, the interaction between MEHP and the maternal genotypes PPARGC1A (rs8192678) and LXRB (rs2303044) decreased fatty acid levels. Further, the interaction between MEHP and PPARGC1A (rs8192678) may have a greater effect on fatty acid levels than the interaction between PFOS and PPARGC1A.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

Stage-Dependent Impact of RIPK1 Inhibition on Atherogenesis: Dual Effects on Inflammation and Foam Cell Dynamics

Objective: Atherosclerosis is an arterial occlusive disease with hypercholesterolemia and hypertension as common risk factors. Advanced-stage stenotic plaque, which features inflammation and necrotic core formation, is the major reason for clinical intervention. Receptor interacting serine/threonine-protein kinase 1 (RIPK1) mediates inflammation and cell death and is expressed in atherosclerotic lesions. The role of RIPK1 in advanced-stage atherosclerosis is unknown.

Approach and Results: To investigate the effect of RIPK1 inhibition in advanced atherosclerotic plaque formation, we used ApoE^SA/SA mice, which exhibit hypercholesterolemia, and develop angiotensin-II mediated hypertension upon administration of doxycycline in drinking water. These mice readily develop severe atherosclerosis, including that in coronary arteries. Eight-week-old ApoE^SA/SA mice were randomized to orally receive a highly selective RIPK1 inhibitor (RIPK1i, GSK547) mixed with a western diet, or control diet. RIPK1i administration reduced atherosclerotic plaque lesion area at 2 weeks of treatment, consistent with suppressed inflammation (MCP-1, IL-1β, TNF-α) and reduced monocyte infiltration. However, administration of RIPK1i unexpectedly exacerbated atherosclerosis at 4 weeks of treatment, concomitant with increased macrophages and lipid deposition in the plaques. Incubation of isolated macrophages with oxidized LDL resulted in foam cell formation in vitro. RIPK1i treatment promoted such foam cell formation while suppressing the death of these cells. Accordingly, RIPK1i upregulated the expression of lipid metabolism-related genes (Cd36, Ppara, Lxrα, Lxrb, Srebp1c) in macrophage foam cells with ABCA1/ABCG1 unaltered. Furthermore, RIPK1i treatment inhibited ApoA1 synthesis in the liver and reduced plasma HDL levels.

Conclusion: RIPK1 modulates the development of atherosclerosis in a stage-dependent manner, implicating both pro-atherosclerotic (monocyte infiltration and inflammation) and anti-atherosclerotic effects (suppressing foam cell accumulation and promoting ApoA1 synthesis). It is critical to identify an optimal therapeutic duration for potential clinical use of RIPK1 inhibitor in atherosclerosis or other related disease indications.

First we eat, then we do everything else: The dynamic metabolic regulation of efferocytosis

Clearance of apoptotic cells, or "efferocytosis," is essential for diverse processes including embryonic development, tissue turnover, organ regeneration, and immune cell development. The human body is estimated to remove approximately 1% of its body mass via apoptotic cell clearance daily. This poses several intriguing cell metabolism problems. For instance, phagocytes such as macrophages must induce or suppress metabolic pathways to find, engulf, and digest apoptotic cells. Then, phagocytes must manage the potentially burdensome biomass of the engulfed apoptotic cell. Finally, phagocytes reside in complex tissue architectures that vary in nutrient availability, the types of dying cells or debris that require clearance, and the neighboring cells they interact with. Here, we review advances in our understanding of these three key areas of phagocyte metabolism. We end by proposing a model of efferocytosis that integrates recent findings and establishes a new paradigm for testing how efferocytosis prevents chronic inflammatory disease and autoimmunity.

Integrative lipidomic and transcriptomic study unravels the therapeutic effects of saikosaponins A and D on non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become one of the most prominent causes of chronic liver diseases and malignancies. However, few therapy has been approved. Radix Bupleuri (RB) is the most frequently used herbal medicine for the treatment of liver diseases. In the current study, we aim to systemically evaluate the therapeutic effects of saikosaponin A (SSa) and saikosaponin D (SSd), the major bioactive monomers in RB, against NAFLD and to investigate the underlying mechanisms. Our results demonstrated that both SSa and SSd improved diet-induced NAFLD. Integrative lipidomic and transcriptomic analysis revealed that SSa and SSd modulated glycerolipid metabolism by regulating related genes, like Lipe and Lipg. SSd profoundly suppressed the fatty acid biosynthesis by downregulating Fasn and Acaca expression and promoted fatty acid degradation by inducing Acox1 and Cpt1a expression. Bioinformatic analysis further predicted the implication of master transcription factors, including peroxisome proliferator-activated receptor alpha (PPARα), in the protective effects of SSa and SSd. These results were further confirmed in vitro in mouse primary hepatocytes. In summary, our study uncoded the complicated mechanisms underlying the promising anti-steatosis activities of saikosaponins (SSs), and provided critical evidence inspiring the discovery of innovative therapies based on SSa and SSd for the treatment of NAFLD and related complications.

Lipid Metabolism Disorders in the Comorbid Course of Nonalcoholic Fatty Liver Disease and Chronic Obstructive Pulmonary Disease

Non-alcoholic fatty liver disease (NAFLD) is currently among the most common liver diseases. Unfavorable data on the epidemiology of metabolic syndrome and obesity have increased the attention of clinicians and researchers to the problem of NAFLD. The research results allow us to emphasize the systemicity and multifactoriality of the pathogenesis of liver parenchyma lesion. At the same time, many aspects of its classification, etiology, and pathogenesis remain controversial. Local and systemic metabolic disorders are also a part of the pathogenesis of chronic obstructive pulmonary disease and can influence its course. The present article analyzes the metabolic pathways mediating the links of impaired lipid metabolism in NAFLD and chronic obstructive pulmonary disease (COPD). Free fatty acids, cholesterol, and ceramides are involved in key metabolic and inflammatory pathways underlying the pathogenesis of both diseases. Moreover, inflammation and lipid metabolism demonstrate close links in the comorbid course of NAFLD and COPD.

Sterols, Oxysterols, and Accessible Cholesterol: Signalling for Homeostasis, in Immunity and During Development

In this article we discuss the concept of accessible plasma membrane cholesterol and its involvement as a signalling molecule. Changes in plasma membrane accessible cholesterol, although only being minor in the context of total cholesterol plasma membrane cholesterol and total cell cholesterol, are a key regulator of overall cellular cholesterol homeostasis by the SREBP pathway. Accessible cholesterol also provides the second messenger between patched 1 and smoothened in the hedgehog signalling pathway important during development, and its depletion may provide a mechanism of resistance to microbial pathogens including SARS-CoV-2. We revise the hypothesis that oxysterols are a signalling form of cholesterol, in this instance as a rapidly acting and paracrine version of accessible cholesterol.

Ameliorative Effect of Myricetin on Nonalcoholic Fatty Liver Disease in ob/ob Mice

Obesity, insulin resistance, and oxidative stress are important risk factors for nonalcoholic fatty liver disease (NAFLD). This study aimed at determining the beneficial effects of myricetin against NAFLD in ob/ob mice. C57BL/6-Lep^ob/ob mice (n = 21) were fed an AIN-93G diet (ob/ob control group) or diet containing 0.04% (low myricetin; LMTN group) or 0.08% (high myricetin; HMTN group) myricetin, and lean heterozygous littermates (lean control group, n = 7) were fed AIN-93G diet for 10 weeks. HMTN consumption significantly lowered serum glucose levels and homeostasis model assessment for insulin resistance values in ob/ob mice. In addition to reducing serum triglyceride (TG) and cholesterol levels, HMTN significantly decreased total hepatic lipid and TG levels partly through downregulation of carbohydrate response element-binding protein and sterol regulatory element-binding protein 1c expression. The reduction in the levels of hepatic thiobarbituric acid reactive substances by HMTN likely resulted from the elevation of nuclear factor erythroid-2-related factor 2 expression. Tumor necrosis factor-α and monocyte chemoattractant protein 1 expressions were reduced by LMTN and HMTN, and HMTN also decreased interleukin-6 expression. These results suggest that myricetin has beneficial effects against NAFLD by regulating the expression of transcription factors of hepatic lipid metabolism, the antioxidant system, and pro-inflammatory cytokines.

Pharmacological Modulation of Immune Responses by Nutritional Components

The incidence of noncommunicable diseases (NCDs) has increased over the last few decades, and one of the major contributors to this is lifestyle, especially diet. High intake of saturated fatty acids and low intake of dietary fiber is linked to an increase in NCDs. Conversely, a low intake of saturated fatty acids and a high intake of dietary fiber seem to have a protective effect on general health. Several mechanisms have been identified that underlie this phenomenon. In this review, we focus on pharmacological receptors, including the aryl hydrocarbon receptor, binding partners of the retinoid X receptor, G-coupled protein receptors, and toll-like receptors, which can be activated by nutritional components and their metabolites. Depending on the nutritional component and the receptors involved, both proinflammatory and anti-inflammatory effects occur, leading to an altered immune response. These insights may provide opportunities for the prevention and treatment of NCDs and their inherent (sub)chronic inflammation. SIGNIFICANCE STATEMENT: This review summarizes the reported effects of nutritional components and their metabolites on the immune system through manipulation of specific (pharmacological) receptors, including the aryl hydrocarbon receptor, binding partners of the retinoid X receptor, G-coupled protein receptors, and toll-like receptors. Nutritional components, such as vitamins, fibers, and unsaturated fatty acids are able to resolve inflammation, whereas saturated fatty acids tend to exhibit proinflammatory effects. This may aid decision makers and scientists in developing strategies to decrease the incidence of noncommunicable diseases.

Astaxanthin from Haematococcus pluvialis alleviates obesity by modulating lipid metabolism and gut microbiota in mice fed a high-fat diet

Obesity is a global chronic disease epidemic that is attributed to the abnormal accumulation of lipids in adipose tissue. Astaxanthin (AST) from Haematococcus pluvialis, a natural carotenoid, exhibits antioxidant, anti-lipogenic, anti-diabetic and other potent effects. Herein, we evaluated the effect of AST to illuminate its efficacy and mechanisms in high-fat diet-fed mice. AST supplementation not only significantly decreased body weight and lipid droplet accumulation in the liver but also modulated liver function and serum lipid levels. Lipidomic analysis revealed that 13 lipids might be potential biomarkers responsible for the effects of AST in lipid reduction, such as total free fatty acids (FFAs), triacylglycerols (TGs) and cholesterol esters (CEs). The gut microbiota sequencing results indicated that AST alleviated HFD-induced gut microbiota dysbiosis by optimizing the ratio of Firmicutes to Bacteroides and inhibiting the abundance of obesity-related pathogenic microbiota while promoting the abundance of probiotics related to glucose and lipid metabolism. In addition, qRT-PCR demonstrated that AST could regulate the gene expressions of the AMPK/SREBP1c pathway by downregulating lipogenesis correlated-genes and upregulating the lipid oxidant related-gene. The present study revealed the new function of AST in regulating lipid metabolism, which provided a theoretical basis for the development of high-quality AST functional food and the application of diet active substances in obesity, as demonstrated in mice.

Liver X Receptor Exerts Anti-Inflammatory Effects in Colonic Epithelial Cells via ABCA1 and Its Expression Is Decreased in Human and Experimental Inflammatory Bowel Disease

BACKGROUND

Liver X receptor (LXR) exerts anti-inflammatory effects in macrophages. The aim of this study was to explore the expression and function of LXR in the colonic epithelium under inflammatory conditions.

METHODS

The expression of LXR was explored by Western blot and immunohistochemistry in colonic biopsies from patients diagnosed with inflammatory bowel disease (IBD) and control patients. In addition, LXR and its target gene expression were analyzed in the colon from interleukin (IL)-10-deficient (IL-10-/-) and wild-type mice. Caco-2 cells were pretreated with the synthetic LXR agonist GW3965 and further challenged with IL-1β, the expression of IL-8 and chemokine (C-C motif) ligand (CCL)-28 chemokines, the activation of mitogen-activated protein (MAP) kinases, and the nuclear translocation of the p65 subunit of nuclear factor kappa B was evaluated. Glibenclamide was used as an ABCA1 antagonist.

RESULTS

We found that LXR expression was downregulated in colonic samples from patients with IBD and IL-10-/- mice. The nuclear positivity of LXR inversely correlated with ulcerative colitis histologic activity. Colonic IL-1β mRNA levels negatively correlated with both LXRα and LXRβ in the colon of IL-10-/- mice, where a decreased mRNA expression of the LXR target genes ABCA1 and FAS was shown. In addition, IL-1β decreased the expression of the LXR target gene ABCA1 in cultured intestinal epithelial cells. The synthetic LXR agonist GW3965 led to a decreased nuclear positivity of the p65 subunit of nuclear factor kappa B, a phosphorylation ratio of the p44-42 MAP kinase, and the expression of CCL-28 and IL-8 in IL-1β-stimulated Caco-2 cells. The pharmacological inhibition of ABCA1 increased the phosphorylation of p44-42 after GW3965 treatment and IL-1β stimulation.

CONCLUSIONS

The LXR-ABCA1 pathway exerts anti-inflammatory effects in intestinal epithelial cells and is impaired in the colonic mucosa of patients with IBD and IL-10-/- mice.

Mechanisms of induction of tumors by cholesterol and potential therapeutic prospects

Increasing evidence suggested that cholesterol is an important integrant of cell membranes, that plays a key role in tumor progression, immune dysregulation, and pathological changes in epigenetic mechanisms. Based on these theories, there is a growing interest on targeting cholesterol in the treatment of cancer. Here, we comprehensively reviewed the major function of cholesterol on oncogenicity, the therapeutic targets of cholesterol and its metabolites in cancer, and provide detailed insight into the essential roles of cholesterol in mediating immune and epigenetic mechanisms of the tumor microenvironment. It is also worth mentioning that the gut microbiome is an indispensable component of cancer mediation because of its role in cholesterol metabolism. Finally, we summarized recent studies on the potential targets of cholesterol and their metabolism, to provide more therapeutic interventions in oncology.

Nuclear receptor LXRβ controls fitness and functionality of activated T cells

T cells increase cholesterol biosynthesis upon activation to generate substrates for cellular growth and proliferation. The ubiquitously expressed liver X receptor β (LXRβ) encoded by the Nr1h2 gene is a critical regulator of cholesterol homeostasis in mammalian cells; however, its cell-intrinsic role in T cell biology remains poorly understood. We report that ablation of LXRβ in T cells leads to spontaneous T cell activation and T lymphocytopenia. Unexpectedly, analysis of mixed bone marrow chimeric mice revealed a cell-autonomous survival defect that reduced the fitness of LXRβ-deficient effector T cells, suggesting that the heightened immune activation in mice harboring LXRβ-deficient T cells was due to impaired regulatory T (T reg) cell functionality. Indeed, we found that single-copy deletion of Nr1h2 in T reg cells disrupted activated T reg cell metabolism and fitness and resulted in early-onset fatal autoimmune disease. Our study demonstrated an indispensable requirement for T reg cell–intrinsic LXRβ function in immune homeostasis and provides a basis for immunological therapies through targeting of this receptor.

Immune-related oxysterol modulates neuromuscular transmission via non-genomic liver X receptor-dependent mechanism

Inflammatory reactions induce changes in the neuromuscular system. The mechanisms underlying this link are unclear. Besides cytokines and reactive oxygen species (ROS), production of an antiviral oxysterol 25-hydroxycholesterol (25HC) by immune cells is quickly increased in response to inflammation. Hypothetically, 25HC could contribute to regulation of neuromuscular activity as well as redox status. We found that 25HC (0.01-10 μM) can bidirectionally modulate neurotransmission in mice diaphragm, the main respiratory muscle. Low concentrations (≤0.1 μM) of 25HC reduced involvement of synaptic vesicles (SVs) into exocytosis during 20-Hz activity, whereas higher inflammatory-related concentrations (≥1 μM) had a profound potentiating effect on SV mobilization. The latter stimulatory action of 25HC was accompanied by increase in Ca²⁺ release from intracellular stores via IP₃ receptors. Both increase in SV mobilization and [Ca²⁺]_in were suppressed by a specific antagonist of liver X receptors (LXRs). These receptors formed clusters within the synaptic membranes in a lipid raft-dependent manner. Either raft disruption or intracellular Ca²⁺ chelation prevented 25HC-mediated acceleration of the exocytotic rate. The same action had inhibition of estrogen receptor α, Gi-protein, Gβγ, phospholipase C and protein kinase C. Additionally, 1 μM 25HC upregulated ROS production in a Ca²⁺-dependent way and an antioxidant partially decreased the exocytosis-promoting effect of 25HC. Thus, 25HC has prooxidant properties and it is a potent regulator of SV mobilization via activation of lipid raft-associated LXRs which can trigger signaling via estrogen receptor α - Gi-protein - Gβγ - phospholipase C - Ca²⁺ - protein kinase C pathway. 25HC-mediated increase in ROS may modulate this signaling.

Obesity and Gallstones

BACKGROUND

The prevalence of obesity has been increasing globally and represents the main risk factor for the development of gallstone disease (GD).

SUMMARY

Excess body weight represents the main cause for the development of GD; nevertheless, there have been described multiple risk factors for its development, among them modifiable risk factors as diet, lifestyle, physical inactivity, and non-modifiable risk factors as ethnicity, female sex, advanced age, parity, and genetic mutations. Body mass index, abdominal perimeter, and waist-hip index have been used to determine the degree of adiposity of a person. Hence, central abdominal fat has been mostly associated with insulin resistance with the consequent increase in the hepatic cholesterol secretion; contributing as one of the multiple mechanisms associated with the development of gallstones. This disease has a low mortality; however, it has been associated with multiple diseases such as cardiovascular diseases, carotid atherosclerosis, metabolic associated fatty liver disease, and gallbladder cancer, probably because they share many of the risk factors.

KEY MESSAGES

GD continues to be considered a disease with a high medical burden, in which it is sought to intervene in modifiable risk factors to reduce its development.

Oxysterols protect bovine endometrial cells against pore-forming toxins from pathogenic bacteria

Many species of pathogenic bacteria secrete toxins that form pores in mammalian cell membranes. These membrane pores enable the delivery of virulence factors into cells, result in the leakage of molecules that bacteria can use as nutrients, and facilitate pathogen invasion. Inflammatory responses to bacteria are regulated by the side-chain-hydroxycholesterols 27-hydroxycholesterol and 25-hydroxycholesterol, but their effect on the intrinsic protection of cells against pore-forming toxins is unclear. Here, we tested the hypothesis that 27-hydroxycholesterol and 25-hydroxycholesterol help protect cells against pore-forming toxins. We treated bovine endometrial epithelial and stromal cells with 27-hydroxycholesterol or 25-hydroxycholesterol, and then challenged the cells with pyolysin, which is a cholesterol-dependent cytolysin from Trueperella pyogenes that targets these endometrial cells. We found that treatment with 27-hydroxycholesterol or 25-hydroxycholesterol protected both epithelial and stomal cells against pore formation and the damage caused by pyolysin. The oxysterols limited pyolysin-induced leakage of potassium and lactate dehydrogenase from cells, and reduced cytoskeletal changes and cytolysis. This oxysterol cytoprotection against pyolysin was partially dependent on reducing cytolysin-accessible cholesterol in the cell membrane and on activating liver X receptors. Treatment with 27-hydroxycholesterol also protected the endometrial cells against Staphylococcus aureus α-hemolysin. Using mass spectrometry, we found 27-hydroxycholesterol and 25-hydroxycholesterol in uterine and follicular fluid. Furthermore, epithelial cells released additional 25-hydroxycholesterol in response to pyolysin. In conclusion, both 27-hydroxycholesterol and 25-hydroxycholesterol increased the intrinsic protection of bovine endometrial cells against pore-forming toxins. Our findings imply that side-chain-hydroxycholesterols may help defend the endometrium against pathogenic bacteria.

Signal Transduction and Molecular Regulation in Fatty Liver Disease

Significance: Fatty liver disease is a major liver disorder in the modern societies. Comprehensive understanding of the pathophysiology and molecular mechanisms is essential for the prevention and treatment of the disease. Recent Advances: Remarkable progress has been made in the recent years in basic and translational research in the field of fatty liver disease. Multiple signaling pathways have been implicated in the development of fatty liver disease, including AMP-activated protein kinase, mechanistic target of rapamycin kinase, endoplasmic reticulum stress, oxidative stress, inflammation, transforming growth factor β, and yes1-associated transcriptional regulator/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). In addition, critical molecular regulations at the transcriptional and epigenetic levels have been linked to the pathogenesis of fatty liver disease. Critical Issues: Some critical issues remain to be solved so that research findings can be translated into clinical applications. Robust and reliable biomarkers are needed for diagnosis of different stages of the fatty liver disease. Effective and safe molecular targets remain to be identified and validated. Prevention strategies require solid scientific evidence and population-wide feasibility. Future Directions: As more data are generated with time, integrative approaches are needed to comprehensively understand the disease pathophysiology and mechanisms at multiple levels from population, organismal system, organ/tissue, to cell. The interactions between genes and environmental factors require deeper investigation for the purposes of prevention and personalized treatment of fatty liver disease. Antioxid. Redox Signal. 35, 689-717.

A basic model for cell cholesterol homeostasis

Cells manage their cholesterol by negative feedback using a battery of sterol-responsive proteins. How these activities are coordinated so as to specify the abundance and distribution of the sterol is unclear. We present a simple mathematical model that addresses this question. It assumes that almost all of the cholesterol is associated with phospholipids in stoichiometric complexes. A small fraction of the sterol is uncomplexed and thermodynamically active. It equilibrates among the organelles, setting their sterol level according to the affinity of their phospholipids. The activity of the homeostatic proteins in the cytoplasmic membranes is then set by their fractional saturation with uncomplexed cholesterol in competition with the phospholipids. The high-affinity phospholipids in the plasma membrane (PM) are filled to near stoichiometric equivalence, giving it most of the cell sterol. Notably, the affinity of the phospholipids in the endomembranes (EMs) is lower by orders of magnitude than that of the phospholipids in the PM. Thus, the small amount of sterol in the EMs rests far below stoichiometric capacity. Simulations match a variety of experimental data. The model captures the essence of cell cholesterol homeostasis, makes coherent a diverse set of experimental findings, provides a surprising prediction and suggests new experiments.

CREBH normalizes dyslipidemia and halts atherosclerosis in diabetes by decreasing circulating remnant lipoproteins

Loss-of-function mutations in the transcription factor CREB3L3 (CREBH) associate with severe hypertriglyceridemia in humans. CREBH is believed to lower plasma triglycerides by augmenting the action of lipoprotein lipase (LPL). However, by using a mouse model of type 1 diabetes mellitus (T1DM), we found that greater liver expression of active CREBH normalized both elevated plasma triglycerides and cholesterol. Residual triglyceride-rich lipoprotein (TRL) remnants were enriched in apolipoprotein E (APOE) and impoverished in APOC3, an apolipoprotein composition indicative of increased hepatic clearance. The underlying mechanism was independent of LPL as CREBH reduced both triglycerides and cholesterol in LPL-deficient mice. Instead, APOE was critical for CREBH's ability to lower circulating remnant lipoproteins because it failed to reduce TRL cholesterol in Apoe-/- mice. Importantly, humans with CREB3L3 loss-of-function mutations exhibited increased levels of remnant lipoproteins that were deprived of APOE. Recent evidence suggests that impaired clearance of TRL remnants promotes cardiovascular disease in patients with T1DM. Consistently, we found that hepatic expression of CREBH prevented the progression of diabetes-accelerated atherosclerosis. Our results support the proposal that CREBH acts through an APOE-dependent pathway to increase hepatic clearance of remnant lipoproteins. They also implicate elevated levels of remnants in the pathogenesis of atherosclerosis in T1DM.

RORγ is a context-specific master regulator of cholesterol biosynthesis and an emerging therapeutic target in cancer and autoimmune diseases

Aberrant cholesterol metabolism and homeostasis in the form of elevated cholesterol biosynthesis and dysregulated efflux and metabolism is well recognized as a major feature of metabolic reprogramming in solid tumors. Recent studies have emphasized on major drivers and regulators such as Myc, mutant p53, SREBP2, LXRs and oncogenic signaling pathways that play crucial roles in tumor cholesterol metabolic reprogramming. Therapeutics such as statins targeting the mevalonate pathway were tried at the clinic without showing consistent benefits to cancer patients. Nuclear receptors are prominent regulators of mammalian metabolism. Their de-regulation often drives tumorigenesis. RORγ and its immune cell-specific isoform RORγt play important functions in control of mammalian metabolism, circadian rhythm and immune responses. Although RORγ, together with its closely related members RORα and RORβ were identified initially as orphan receptors, recent studies strongly support the conclusion that specific intermediates and metabolites of cholesterol pathways serve as endogenous ligands of RORγ. More recent studies also reveal a critical role of RORγ in tumorigenesis through major oncogenic pathways including acting a new master-like regulator of tumor cholesterol biosynthesis program. Importantly, an increasing number of RORγ orthosteric and allosteric ligands are being identified that display potent activities in blocking tumor growth and autoimmune disorders in preclinical models. This review summarizes the recent preclinical and clinical progress on RORγ with emphasis on its role in reprogramming tumor cholesterol metabolism and its regulation. It will also discuss RORγ functional mechanisms, context-specificity and its value as a therapeutic target for effective cancer treatment.

The Effects of Sterol-Related Signaling Pathways on Glioma

Gliomas are considered as one of the important brain tumors in adults due to their impact on life quality and cognitive functions. Current methods that are used for treating glioma are not satisfying enough. Understanding cellular and molecular events underlying its pathogenesis and progression may lead to the discovery of novel therapeutic approaches. Sterols are a subtype of steroids and are essential for the physiologic functions of eukaryotic cells. Sterols can be produced by protozoans and microheterotrophs. Moreover, they are found in some natural sources, such as plants, animals, fungi, microalgae, and yeasts. Besides the roles of sterols in physiologic processes, studies have shown that they are involved in pathologic processes, including tumorigenesis and tumor progression. As investigations have revealed, sterol-related signaling pathways are involved in glioma and targeting them may result in new therapeutic options for patients. Thus, we summarized some of the sterol-related signaling pathways in glioma and how they can be associated with other signaling pathways, including EGFR/PI3K/Akt/mTOR, P53, and retinoblastoma protein.

Liver X receptor β is required for the survival of single-positive thymocytes by regulating IL-7Rα expression

Liver X receptors (LXRs) are known as key transcription factors in lipid metabolism and have been reported to play an important role in T-cell proliferation. However, whether LXRs play a role in thymocyte development remains largely unknown. Here, we demonstrated that LXRβ deficiency caused a reduction in single-positive (SP) thymocytes, whereas the transitions from the double-negative to SP stage were normal. Meanwhile, LXRβ-null SP thymocytes exhibited increased apoptosis and impairment of the IL-7Rα-Bcl2 axis. In addition, the LXR agonist T0901317 promoted the survival of SP thymocytes with enhanced IL-7Rα expression in wild-type mice but not in LXRβ-deficient mice. Mechanistically, LXRβ positively regulated the expression of IL-7Rα via direct binding to the Il7r allele in SP thymocytes, and forced expression of IL-7Rα or Bcl2 restored the survival of LXRβ-defective SP thymocytes. Thus, our results indicate that LXRβ functions as an important transcription factor upstream of IL-7Rα to promote the survival of SP thymocytes.

Roles of nuclear receptors in hepatic stellate cells

Introduction: Hepatic stellate cells (HSCs) are essential for physiological homeostasis of the liver extracellular matrix (ECM). Excessive transdifferentiation of HSC from a quiescent to an activated phenotype contributes to disrupt this balance and can lead to liver fibrosis. Accumulating evidence has suggested that nuclear receptors (NRs) are involved in the regulation of HSC activation, proliferation, and function. Therefore, these NRs may be therapeutic targets to balance ECM homeostasis and inhibit HSC activation in liver fibrosis.Areas covered: In this review, the authors summarized the recent progress in the understanding of the regulatory role of NRs in HSCs and their potential as drug targets in liver fibrosis.Expert opinion: NRs are still potential therapy targets for inhibiting HSCs activation and liver fibrosis. However, the development of NRs agonists or antagonists to inhibit HSCs requires fully consideration of systemic effects.

Orphan Nuclear Receptor RORγ Modulates the Genome-Wide Binding of the Cholesterol Metabolic Genes during Mycotoxin-Induced Liver Injury

Maintaining lipid homeostasis is crucial to liver function, the key organ that governs the whole-body energy metabolism. In contrast, lipid dysregulation has been implicated in mycotoxin-induced liver injury, by which the pathophysiological regulation and the molecular components involved remain elusive. Here we focused on the potential roles of orphan nuclear receptor (NR) RORγ in lipid programming, and aimed to explore its action on cholesterol regulation in the liver of mycotoxin-exposed piglets. We found that liver tissues were damaged in the mycotoxin-exposed piglets compared to the healthy controls, revealed by histological analysis, elevated seral ALT, AST and ALP levels, and increased caspase 3/7 activities. Consistent with the transcriptomic finding of down-regulated cholesterol metabolism, we demonstrated that both cholesterol contents and cholesterol biosynthesis/transformation gene expressions in the mycotoxin-exposed livers were reduced, including HMGCS1, FDPS, SQLE, EBP, FDFT1 and VLDLR. Furthermore, we reported that RORγ binds to the cholesterol metabolic genes in porcine hepatocytes using a genome-wide ChIP-seq analysis, whereas mycotoxin decreased the RORγ binding occupancies genome-wide, especially at the cholesterol metabolic pathway. In addition, we revealed the enrichment of co-factors p300 and SRC, the histone marks H3K27ac and H3K4me2, together with RNA Polymerase II (Pol-II) at the locus of HMGCS1 in hepatocytes, which were reduced by mycotoxin-exposure. Our results provide a deep insight into the cholesterol metabolism regulation during mycotoxin-induced liver injury, and propose NRs as therapeutic targets for anti-mycotoxin treatments.

Enterically derived high-density lipoprotein restrains liver injury through the portal vein

The biogenesis of high-density lipoprotein (HDL) requires apoA1 and the cholesterol transporter ABCA1. Although the liver generates most of the HDL in the blood, HDL synthesis also occurs in the small intestine. Here, we show that intestine-derived HDL traverses the portal vein in the HDL3 subspecies form, in complex with lipopolysaccharide (LPS)-binding protein (LBP). HDL3, but not HDL2 or low-density lipoprotein, prevented LPS binding to and inflammatory activation of liver macrophages and instead supported extracellular inactivation of LPS. In mouse models involving surgical, dietary, or alcoholic intestinal insult, loss of intestine-derived HDL worsened liver injury, whereas outcomes were improved by therapeutics that elevated and depended upon raising intestinal HDL. Thus, protection of the liver from injury in response to gut-derived LPS is a major function of intestinally synthesized HDL.

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.

Strategies to Inhibit Hepatitis B Virus at the Transcript Level

Approximately 240 million people are chronically infected with hepatitis B virus (HBV), despite four decades of effective HBV vaccination. During chronic infection, HBV forms two distinct templates responsible for viral transcription: (1) episomal covalently closed circular (ccc)DNA and (2) host genome-integrated viral templates. Multiple ubiquitous and liver-specific transcription factors are recruited onto these templates and modulate viral gene transcription. This review details the latest developments in antivirals that inhibit HBV gene transcription or destabilize viral transcripts. Notably, nuclear receptor agonists exhibit potent inhibition of viral gene transcription from cccDNA. Small molecule inhibitors repress HBV X protein-mediated transcription from cccDNA, while small interfering RNAs and single-stranded oligonucleotides result in transcript degradation from both cccDNA and integrated templates. These antivirals mediate their effects by reducing viral transcripts abundance, some leading to a loss of surface antigen expression, and they can potentially be added to the arsenal of drugs with demonstrable anti-HBV activity. Thus, these candidates deserve special attention for future repurposing or further development as anti-HBV therapeutics.

Selective estrogen receptor modulators (SERMs) affect cholesterol homeostasis through the master regulators SREBP and LXR

Selective estrogen receptor modulators (SERMs) are nonsteroidal drugs that display an estrogen-agonist or estrogen-antagonist effect depending on the tissue targeted. SERMs have attracted great clinical interest for the treatment of several pathologies, most notably breast cancer and osteoporosis. There is strong evidence that SERMs secondarily affect cholesterol metabolism, although the mechanism has not been fully elucidated. In this study, we analysed the effect of the SERMs tamoxifen, raloxifene, and toremifene on the expression of lipid metabolism genes by microarrays and quantitative PCR in different cell types, and ascertained the main mechanisms involved. The three SERMs increased the expression of sterol regulatory element-binding protein (SREBP) target genes, especially those targeted by SREBP-2. In consonance, SERMs increased SREBP-2 processing. These effects were associated to the interference with intracellular LDL-derived cholesterol trafficking. When the cells were exposed to LDL, but not to cholesterol/methyl-cyclodextrin complexes, the SERM-induced increases in gene expression were synergistic with those induced by lovastatin. Furthermore, the SERMs reduced the stimulation of the transcriptional activity of the liver X receptor (LXR) by exogenous cholesterol. However, their impact on the expression of the LXR canonical target ABCA1 in the presence of LDL was cell-type dependent. These actions of SERMs were independent of estrogen receptors. We conclude that, by inhibiting the intracellular trafficking of LDL-derived cholesterol, SERMs promote the activation of SREBP-2 and prevent the activation of LXR, two master regulators of cellular cholesterol metabolism. This study highlights the impact of SERMs on lipid homeostasis regulation beyond their actions as estrogen receptor modulators.

Transcriptional regulation of N6-methyladenosine orchestrates sex-dimorphic metabolic traits

Males and females exhibit striking differences in the prevalence of metabolic traits including hepatic steatosis, a key driver of cardiometabolic morbidity and mortality. RNA methylation is a widespread regulatory mechanism of transcript turnover. Here, we show that presence of the RNA modification N⁶-methyladenosine (m⁶A) triages lipogenic transcripts for degradation and guards against hepatic triglyceride accumulation. In male but not female mice, this protective checkpoint stalls under lipid-rich conditions. Loss of m⁶A control in male livers increases hepatic triglyceride stores, leading to a more 'feminized' hepatic lipid composition. Crucially, liver-specific deletion of the m⁶A complex protein Mettl14 from male and female mice significantly diminishes sex-specific differences in steatosis. We further surmise that the m⁶A installing machinery is subject to transcriptional control by the sex-responsive BCL6-STAT5 axis in response to dietary conditions. These data show that m⁶A is essential for precise and synchronized control of lipogenic enzyme activity and provide insights into the molecular basis for the existence of sex-specific differences in hepatic lipid traits.