Crosstalk Between LXR and Caveolin-1 Signaling Supports Cholesterol Efflux and Anti-Inflammatory Pathways in Macrophages

Exploring the Roles of Liver X Receptors in Lipid Metabolism and Immunity in Atherosclerosis

Hypercholesterolemia causes atherosclerosis by inducing immune cell migration and chronic inflammation in arterial walls. Recent single-cell analyses reveal the presence of lipid-enriched foamy macrophages, as well as other macrophage subtypes, neutrophils, T cells, and B cells, in atherosclerotic plaques in both animal models and humans. These cells interact with each other and other cells, including non-immune cells such as endothelial cells and smooth muscle cells. They thereby regulate metabolic, inflammatory, phagocytic, and cell death processes, thus affecting the progression and stability of atherosclerotic plaques. The nuclear receptors liver X receptor (LXR)α and LXRβ are transcription factors that are activated by oxysterols and regulate lipid metabolism and immune responses. LXRs regulate cholesterol homeostasis by controlling cholesterol's transport, absorption, synthesis, and breakdown in the liver and intestine. LXRs are also highly expressed in tissue-resident and monocyte-derived macrophages and other immune cells, including both myeloid cells and lymphocytes, and they regulate both innate and adaptive immune responses. Interestingly, LXRs have immunosuppressive and immunoregulatory functions that are cell-type-dependent. In animal models of atherosclerosis, LXRs have been shown to be involved in both progression and regression phases. The pharmacological activation of LXR enhances cholesterol efflux from macrophages and promotes atherosclerosis progression. Deleting LXR in immune cells, especially myeloid cells, accelerates atherosclerosis by increasing monocyte migration, macrophage proliferation and activation, and neutrophil extracellular traps (NETs); furthermore, the deletion of hematopoietic LXRs impairs the regression of atherosclerotic plaques. Therefore, LXRs in immune cells may be a potent therapeutic target for atherosclerosis.

Targeting Caveolin-1 for enhanced rotator cuff repair: findings from single-cell RNA sequencing

Rotator cuff injury (RCI), a prevalent cause of shoulder pain and disability, often leads to significant functional impairments due to adipocyte infiltration into the damaged tissue. Caveolin-1 (Cav-1), a critical membrane protein, plays a significant role in adipocyte differentiation and lipid metabolism. This study utilized single-cell RNA sequencing (scRNA-seq) to investigate the heterogeneity of cell subpopulations in RCI tissues and assess the regulatory effects of Cav-1. The findings revealed that Cav-1 expression negatively correlates with adipogenic activity, and its modulation through exercise or targeted therapies can significantly reduce adipocyte infiltration and enhance tissue repair. Further, Cav-1 knockout and overexpression models demonstrated the protein's impact on key genes involved in adipocyte differentiation and lipid metabolism, such as Scd1, fatty acid synthase (FASN), and peroxisome proliferator-activated receptor gamma (Pparg). Animal studies corroborated these results, showing that exercise intervention increased Cav-1 expression, decreased adipocyte infiltration, and promoted structural repair. These insights suggest that targeting Cav-1 could offer a novel therapeutic strategy for improving RCI outcomes.

Molecular mechanisms in liver repair and regeneration: from physiology to therapeutics

Liver repair and regeneration are crucial physiological responses to hepatic injury and are orchestrated through intricate cellular and molecular networks. This review systematically delineates advancements in the field, emphasizing the essential roles played by diverse liver cell types. Their coordinated actions, supported by complex crosstalk within the liver microenvironment, are pivotal to enhancing regenerative outcomes. Recent molecular investigations have elucidated key signaling pathways involved in liver injury and regeneration. Viewed through the lens of metabolic reprogramming, these pathways highlight how shifts in glucose, lipid, and amino acid metabolism support the cellular functions essential for liver repair and regeneration. An analysis of regenerative variability across pathological states reveals how disease conditions influence these dynamics, guiding the development of novel therapeutic strategies and advanced techniques to enhance liver repair and regeneration. Bridging laboratory findings with practical applications, recent clinical trials highlight the potential of optimizing liver regeneration strategies. These trials offer valuable insights into the effectiveness of novel therapies and underscore significant progress in translational research. In conclusion, this review intricately links molecular insights to therapeutic frontiers, systematically charting the trajectory from fundamental physiological mechanisms to innovative clinical applications in liver repair and regeneration.

LXRα agonist differentially regulates BAFF expression and biological effects in RAW264.7 cells depending on growth status: LXRα activation and BAFF signaling in RAW264.7 cells

B- cell-activating factor (BAFF), which is essential for the survival and development of B cells, is mainly produced by myeloid cells such as macrophages. Abnormal macrophage infiltration and high BAFF expression in kidney allografts are associated with the occurrence and development of antibody-mediated rejection (ABMR). Nuclear hormone receptor Liver X receptors (LXRs), is a nonnegligible participant in regulating cholesterol metabolism and inflammatory responses. Nowadays the effects of LXRα activation on macrophages have been widely studied, however the effects of LXRα activation on BAFF expression and cell function due to the change of BAFF signaling have not yet been fully investigated. In the present study, LXRα activation alone was found to downregulate BAFF expression in quiescent RAW 264.7 cells, whereas LXRα agonist significantly upregulated BAFF expression in cells pretreated with lipopolysaccharide (LPS) for 6 h. The increased BAFF signaling promoted M1 polarization and enhanced cell viability, migration, and phagocytic ability. LXRα can directly bind to the BAFF promoter region and decrease BAFF expression in RAW264.7 cells. LXRα activation enhanced mitochondrial metabolism, which promoted BAFF expression in the LPS-activated cells. Our results indicate that subtle changes in the microenvironment would affect the biological function of macrophages, in which a variety of BAFF signaling pathways may also be involved, providing a new perspective on exploring the mechanism of allograft rejection and uncovering the potential reason for the unstable efficacy of anti-BAFF preparations in kidney transplant recipients.

Immune Implications of Cholesterol-Containing Lipid Nanoparticles

The majority of clinically approved nanoparticle-mediated therapeutics are lipid nanoparticles (LNPs), and most of these LNPs are liposomes containing cholesterol. LNP formulations significantly alter the drug pharmacokinetics (PK) due to the propensity of nanoparticles for uptake by macrophages. In addition to readily engulfing LNPs, the high expression of cholesterol hydroxylases and reactive oxygen species (ROS) in macrophages suggests that they will readily produce oxysterols from LNP-associated cholesterol. Oxysterols are a heterogeneous group of cholesterol oxidation products that have potent immune modulatory effects. Oxysterols are implicated in the pathogenesis of atherosclerosis and certain malignancies; they have also been found in commercial liposome preparations. Yet, the in vivo metabolic fate of LNP-associated cholesterol remains unclear. We review herein the mechanisms of cellular uptake, trafficking, metabolism, and immune modulation of endogenous nanometer-sized cholesterol particles (i.e., lipoproteins) that are also relevant for cholesterol-containing nanoparticles. We believe that it would be imperative to better understand the in vivo metabolic fate of LNP-associated cholesterol and the immune implications for LNP-therapeutics. We highlight critical knowledge gaps that we believe need to be addressed in order to develop safer and more efficacious lipid nanoparticle delivery systems.

The processed Euphorbia lathyris L. alleviates the inflammatory injury via regulating LXRα/ABCA1 expression and TLR4 positioning to lipid rafts

Euphorbia lathyris L. (EL) is a traditional poisonous herbal medicine used to treat dropsy, ascites, amenorrhea, anuria and constipation. Processing to reduce toxicity of EL is essential for its safe and effective application. However, there is little known regarding the molecular mechanism of reducing toxicity after EL processing. This research aimed to screen the differential markers for EL and PEL, explore the differential mechanisms of inflammatory injury induced by EL and processed EL (PEL) to expound the mechanism of alleviating toxicity after EL processing. The results showed that 15 potential biomarkers, mainly belonging to diterpenoids, were screened to distinguish EL from PEL. EL promoted the expressions of TLR4, NLRP3, NF-κB p65, IL-1β and TNF-α, increased lipid rafts abundance and promoted TLR4 positioning to lipid rafts. Meanwhile, EL decreased LXRα and ABCA1 expression, and reduced cholesterol efflux. In contrast to EL, the effects of PEL on these indicators were markedly weakened. In addition, Euphorbia factors L1, L2, and L3 affected LXRα, ABCA1, TLR4, NLRP3, NF-κB p65, TNF-α and IL-1β expression, influenced cholesterol efflux and lipid rafts abundance, and interfered with the colocalization of TLR4 and lipid rafts. The inflammatory injury caused by processed EL was significantly weaker than that caused by crude EL, and reduction of Euphorbia factors L1, L2, and L3 as well as attenuation of inflammatory injury participated in processing-based detoxification of EL. Our results provide valuable insights into the attenuated mechanism of EL processing and will guide future research on the processing mechanism of toxic traditional Chinese medicine.

Therapeutic biomaterials with liver X receptor agonists based on the horizon of material biology to regulate atherosclerotic plaque regression in situ for devices surface engineering

Percutaneous coronary interventional is the main treatment for coronary atherosclerosis. At present, most studies focus on blood components and smooth muscle cells to achieve anticoagulation or anti-proliferation effects, while the mediated effects of materials on macrophages are also the focus of attention. Macrophage foam cells loaded with elevated cholesterol is a prominent feature of atherosclerotic plaque. Activation of liver X receptor (LXR) to regulate cholesterol efflux and efferocytosis and reduce the number of macrophage foam cells in plaque is feasible for the regression of atherosclerosis. However, cholesterol efflux promotion remains confined to targeted therapies. Herein, LXR agonists (GW3965) were introduced on the surface of the material and delivered in situ to atherogenic macrophages to improve drug utilization for anti-atherogenic therapy and plaque regression. LXR agonists act as plaque inhibition mediated by multichannel regulation macrophages, including lipid metabolism (ABCA1, ABCG1 and low-density lipoprotein receptor), macrophage migration (CCR7) and efferocytosis (MerTK). Material loaded with LXR agonists significantly reduced plaque burden in atherosclerotic model rats, most importantly, it did not cause hepatotoxicity and adverse reactions such as restenosis and thrombosis after material implantation. Both in vivo and in vitro evaluations confirmed its anti-atherosclerotic capability and safety. Overall, multi-functional LXR agonist-loaded materials with pathological microenvironment regulation effect are expected to be promising candidates for anti-atherosclerosis and have potential applications in cardiovascular devices surface engineering.

ABCA1 Deletion Does Not Affect Aqueous Humor Outflow Function in Mice

Background

ATP binding cassette transporter A1 (ABCA1) is a candidate gene within a POAG susceptibility locus by GWAS analysis, and it is involved in IOP modulation via the Cav1/eNOS/NO signaling pathway. We aim to examine the phenotype of ABCA1 deletion in the ABCA1 gene knockout (Abca1-/-) mice.

Methods

The anterior segments of Abca1-/- eyes were imaged by slit-lamp microscopy and anterior segment OCT. IOPs were measured by rebound tonometry. By perfusing enucleated eyes at various pressures, the aqueous humor outflow facility was determined. The mRNA expressions of ABCA1, Cav1, and eNOS were measured by RT-qPCR. The protein expressions were analyzed by western blot and immunofluorescence staining.

Results

There was no significant difference in the anterior segment morphology of Abca1-/- mice. IOP and aqueous humor outflow facility did not change in Abca1-/- mice compared with wild-type mice. mRNA and protein expressions of ABCA1 were significantly lower in the outflow tissue of Abca1-/- eyes. The expressions of Cav1 and eNOS were both significantly upregulated in the outflow tissue of Abca1-/- eyes.

Conclusion

ABCA1 deletion does not affect IOP and aqueous humor outflow function but the Cav1/eNOS/NO pathway is changed in Abca1-/- mice. The function of ABCA1 in aqueous humor outflow still requires further research.

Endogenous LXR signaling controls pulmonary surfactant homeostasis and prevents lung inflammation

Lung type 2 pneumocytes (T2Ps) and alveolar macrophages (AMs) play crucial roles in the synthesis, recycling and catabolism of surfactant material, a lipid/protein fluid essential for respiratory function. The liver X receptors (LXR), LXRα and LXRβ, are transcription factors important for lipid metabolism and inflammation. While LXR activation exerts anti-inflammatory actions in lung injury caused by lipopolysaccharide (LPS) and other inflammatory stimuli, the full extent of the endogenous LXR transcriptional activity in pulmonary homeostasis is incompletely understood. Here, using mice lacking LXRα and LXRβ as experimental models, we describe how the loss of LXRs causes pulmonary lipidosis, pulmonary congestion, fibrosis and chronic inflammation due to defective de novo synthesis and recycling of surfactant material by T2Ps and defective phagocytosis and degradation of excess surfactant by AMs. LXR-deficient T2Ps display aberrant lamellar bodies and decreased expression of genes encoding for surfactant proteins and enzymes involved in cholesterol, fatty acids, and phospholipid metabolism. Moreover, LXR-deficient lungs accumulate foamy AMs with aberrant expression of cholesterol and phospholipid metabolism genes. Using a house dust mite aeroallergen-induced mouse model of asthma, we show that LXR-deficient mice exhibit a more pronounced airway reactivity to a methacholine challenge and greater pulmonary infiltration, indicating an altered physiology of LXR-deficient lungs. Moreover, pretreatment with LXR agonists ameliorated the airway reactivity in WT mice sensitized to house dust mite extracts, confirming that LXR plays an important role in lung physiology and suggesting that agonist pharmacology could be used to treat inflammatory lung diseases.

Reprogramming of the LXRα Transcriptome Sustains Macrophage Secondary Inflammatory Responses

Macrophages regulate essential aspects of innate immunity against pathogens. In response to microbial components, macrophages activate primary and secondary inflammatory gene programs crucial for host defense. The liver X receptors (LXRα, LXRβ) are ligand-dependent nuclear receptors that direct gene expression important for cholesterol metabolism and inflammation, but little is known about the individual roles of LXRα and LXRβ in antimicrobial responses. Here, the results demonstrate that induction of LXRα transcription by prolonged exposure to lipopolysaccharide (LPS) supports inflammatory gene expression in macrophages. LXRα transcription is induced by NF-κB and type-I interferon downstream of TLR4 activation. Moreover, LPS triggers a reprogramming of the LXRα cistrome that promotes cytokine and chemokine gene expression through direct LXRα binding to DNA consensus sequences within cis-regulatory regions including enhancers. LXRα-deficient macrophages present fewer binding of p65 NF-κB and reduced histone H3K27 acetylation at enhancers of secondary inflammatory response genes. Mice lacking LXRα in the hematopoietic compartment show impaired responses to bacterial endotoxin in peritonitis models, exhibiting reduced neutrophil infiltration and decreased expansion and inflammatory activation of recruited F4/80lo-MHC-IIhi peritoneal macrophages. Together, these results uncover a previously unrecognized function for LXRα-dependent transcriptional cis-activation of secondary inflammatory gene expression in macrophages and the host response to microbial ligands.

QiShenYiQi pill inhibits atherosclerosis by promoting TTC39B-LXR mediated reverse cholesterol transport in liver

BACKGROUND

Tetranucleotide repeat domain protein 39B (TTC39B) was found to combine with ubiquitin ligase E3, and promote the ubiquitination modification of liver X receptor (LXR), which led to the inhibition of reverse cholesterol transport and development of atherosclerosis. QiShenYiQi pill (QSYQ) is a modern Chinese patent drug for treating ischemic cardiovascular diseases, the underlying mechanism is found to promote the expression of LXR-α/ ATP-binding cassette transporter G5 (ABCG5) in the liver of atherosclerotic mice.

PURPOSE

The aim of this study is to investigate the effect of QSYQ on TTC39B-LXR mediated reverse cholesterol transport in atherosclerotic mice.

STUDY DESIGN AND METHODS

Male apolipoprotein E gene knockout mice (7 weeks old) were fed with high-fat diet and treated with low dose of QSYQ (QSYQ-l, 0.3 g/kg·d), high dose of QSYQ (QSYQ-H, 1.2 g/kg·d) and LXR-α agonist (LXR-A, GW3965 10 mg/kg·d) for 8 weeks. C57BL/6 J mice were fed with normal diet and used as negative control. Oil red O staining, HE staining, ELISA, RNA sequencing, western blot, immunohistochemistry, RT-PCR, cell culture and RNA interference were performed to analyze the effect of QSYQ on atherosclerosis.

RESULTS

HE staining showed that QSYQ reduced the atherosclerotic lesion significantly when compared to the control group. ELISA measurement showed that QSYQ decreased serum VLDL and increased serum ApoA1. Oil Red O staining showed that QSYQ reduced the lipid content of liver and protect liver function. Comparative transcriptome RNA-sequence of liver showed that DEGs after QSYQ treatment enriched in high-density lipoprotein particle, ubiquitin ligase complex, bile secretion, etc. Immunohistochemical staining and western blot proved that QSYQ increased the protein expression of hepatic SR-B1, LXR-α, LXR-β, CYP7A1 and ABCG5. Targeted inhibiting Ttc39b gene in vitro further established that QSYQ inhibited the gene expression of Ttc39b, increased the protein expression of SR-B1, LXR-α/β, CYP7A1 and ABCG5 in rat hepatocyte.

CONCLUSION

Our results demonstrated the new anti-atherosclerotic mechanism of QSYQ by targeting TTC39B-LXR mediated reverse cholesterol transport in liver. QSYQ not only promoted reverse cholesterol transport, but also improved fatty liver and protected liver function.

Immunomodulation in diabetic wounds healing: The intersection of macrophage reprogramming and immunotherapeutic hydrogels

Diabetic wound healing presents a significant clinical challenge due to the interplay of systemic metabolic disturbances and local inflammation, which hinder the healing process. Macrophages undergo a phenotypic shift from M1 to M2 during wound healing, a transition pivotal for effective tissue repair. However, in diabetic wounds, the microenvironment disrupts this phenotypic polarization, perpetuating inflammation, and impeding healing. Reprograming macrophages to restore their M2 phenotype offers a potential avenue for modulating the wound immune microenvironment and promoting healing. This review elucidates the mechanisms underlying impaired macrophage polarization toward the M2 phenotype in diabetic wounds and discusses novel strategies, including epigenetic and metabolic interventions, to promote macrophage conversion to M2. Hydrogels, with their hydrated 3D cross-linked structure, closely resemble the physiological extracellular matrix and offer advantageous properties such as biocompatibility, tunability, and versatility. These characteristics make hydrogels promising candidates for developing immunomodulatory materials aimed at addressing diabetic wounds. Understanding the role of hydrogels in immunotherapy, particularly in the context of macrophage reprograming, is essential for the development of advanced wound care solutions. This review also highlights recent advancements in immunotherapeutic hydrogels as a step toward precise and effective treatments for diabetic wounds.

Impact of Lipid Metabolism on Macrophage Polarization: Implications for Inflammation and Tumor Immunity

Macrophage polarization is influenced by lipids, which also exert significant control over macrophage functions. Lipids and their metabolites are players in intricate signaling pathways that modulate macrophages' responses to pathogens, phagocytosis, ferroptosis, and inflammation. This review focuses on lipid metabolism and macrophage functions and addresses potential molecular targets for the treatment of macrophage-related diseases. While lipogenesis is crucial for lipid accumulation and phagocytosis in M1 macrophages, M2 macrophages likely rely on fatty acid β-oxidation to utilize fatty acids as their primary energy source. Cholesterol metabolism, regulated by factors such as SREBPs, PPARs, and LXRs, is associated with the cholesterol efflux capacity and the formation of foam cells (M2-like macrophages). Foam cells, which are targets for atherosclerosis, are associated with an increase in inflammatory cytokines. Lipolysis and fatty acid uptake markers, such as CD36, also contribute to the production of cytokines. Enhancing the immune system through the inhibition of lipid-metabolism-related factors can potentially serve as a targeted approach against tumor cells. Cyclooxygenase inhibitors, which block the conversion of arachidonic acid into various inflammatory mediators, influence macrophage polarization and have generated attention in cancer research.

Amelioration of Cholesterol Rich diet-induced Impaired Cognition in AD Transgenic Mice by an LXR Agonist TO901317 Is Associated with the Activation of the LXR-β-RXR-α-ABCA1 Transmembrane Transport System and Improving the Composition of Lipid Raft

BACKGROUND

It has been reported that LXR agonist can inhibit Aβ generation and alleviate Aβ-induced various adverse reactions in vivo and in vitro experiments, but the mechanisms have not been clarified. The study aimed to observe the effect of LXR agonist TO901317 on the cognitive function of AD transgenic mice fed with cholesterol-rich diet (CRD), and to explore the possible mechanism. Methods: 32 male 6-month-old double transgenic AD mice were enrolled and randomly divided into 4 groups: control (normal diet) group, CRD treatment group, TO901317 treatment group and GSK2033 treatment group. After 3 month, Morris water maze was for the changes of spatial exploration and memory ability; ELISA was for detecting the production of Aβ42 in the brain; the concentration of total cholesterol (TC), low density lipoprotein (LDL) and high density lipoprotein (HDL) in serum were detected by cholesterol enzyme colorimetry; Finally, the expression of LXR-β, RXR-α, ABCA1, caveolin-1, BACE1 and APP at protein level in the brains was measured by Western blotting.

RESULTS

Compared with the control group, the learning, memory ability and spatial exploration ability of the mice were more significantly serious in the CRD group (P<0.05); The contents of TC and LDL in the serum and the production of Aβ42 in the brains were significantly increased (P<0.05), but HDL was remarkably decreased (P<0.05); The protein levels of LXR-β, RXR-α and ABCA1 were also significantly decreased (P<0.05); The expression of caveolin-1, APP and BACE1 were evidently increased (P<0.05). However, after treatment with TO901317, the impaired learning and memory and spatial exploration ability of the mice were significantly improved (P<0.05); The contents of TC and LDL in serum and the production of Aβ42 in the brains were significantly decreased (P<0.05), but HLD was increased (P<0.05); The protein levels of LXR-β, RXR-α, ABCA1were all significantly increased (P<0.05), while, the expression of caveolin-1, APP and BACE1 were all significantly decreased (P<0.05). All the changes were reversed by GSK2033 (P<0.05).

CONCLUSIONS

TO901317 attenuated the more serious impairment of spatial exploration, learning and memory in transgenic AD mice induced by CRD, and the mechanism may be that TO901317 could activate the LXR-β/RXR-α/ABCA1 transmembrane transport system, promote the cholesterol efflux, and decreased caveolin-1, APP and BACE1, further reduce Aβ42 in the brains.

Caveolae Mechanotransduction at the Interface between Cytoskeleton and Extracellular Matrix

The plasma membrane (PM) is subjected to multiple mechanical forces, and it must adapt and respond to them. PM invaginations named caveolae, with a specific protein and lipid composition, play a crucial role in this mechanosensing and mechanotransduction process. They respond to PM tension changes by flattening, contributing to the buffering of high-range increases in mechanical tension, while novel structures termed dolines, sharing Caveolin1 as the main component, gradually respond to low and medium forces. Caveolae are associated with different types of cytoskeletal filaments, which regulate membrane tension and also initiate multiple mechanotransduction pathways. Caveolar components sense the mechanical properties of the substrate and orchestrate responses that modify the extracellular matrix (ECM) according to these stimuli. They perform this function through both physical remodeling of ECM, where the actin cytoskeleton is a central player, and via the chemical alteration of the ECM composition by exosome deposition. Here, we review mechanotransduction regulation mediated by caveolae and caveolar components, focusing on how mechanical cues are transmitted through the cellular cytoskeleton and how caveolae respond and remodel the ECM.

Identification of Side Chain Oxidized Sterols as Novel Liver X Receptor Agonists with Therapeutic Potential in the Treatment of Cardiovascular and Neurodegenerative Diseases

The nuclear receptors-liver X receptors (LXR α and β) are potential therapeutic targets in cardiovascular and neurodegenerative diseases because of their key role in the regulation of lipid homeostasis and inflammatory processes. Specific oxy(phyto)sterols differentially modulate the transcriptional activity of LXRs providing opportunities to develop compounds with improved therapeutic characteristics. We isolated oxyphytosterols from Sargassum fusiforme and synthesized sidechain oxidized sterol derivatives. Five 24-oxidized sterols demonstrated a high potency for LXRα/β activation in luciferase reporter assays and induction of LXR-target genes APOE, ABCA1 and ABCG1 involved in cellular cholesterol turnover in cultured cells: methyl 3β-hydroxychol-5-en-24-oate (S1), methyl (3β)-3-aldehydeoxychol-5-en-24-oate (S2), 24-ketocholesterol (S6), (3β,22E)-3-hydroxycholesta-5,22-dien-24-one (N10) and fucosterol-24,28 epoxide (N12). These compounds induced SREBF1 but not SREBP1c-mediated lipogenic genes such as SCD1, ACACA and FASN in HepG2 cells or astrocytoma cells. Moreover, S2 and S6 enhanced cholesterol efflux from HepG2 cells. All five oxysterols induced production of the endogenous LXR agonists 24(S)-hydroxycholesterol by upregulating the CYP46A1, encoding the enzyme converting cholesterol into 24(S)-hydroxycholesterol; S1 and S6 may also act via the upregulation of desmosterol production. Thus, we identified five novel LXR-activating 24-oxidized sterols with a potential for therapeutic applications in neurodegenerative and cardiovascular diseases.

Metabolic regulation of immune responses to cancer

The tumor microenvironment is an ecosystem composed of multiple types of cells, such as tumor cells, immune cells, and cancer-associated fibroblasts. Cancer cells grow faster than non-cancerous cells and consume larger amounts of nutrients. The rapid growth characteristic of cancer cells fundamentally alters nutrient availability in the tumor microenvironment and results in reprogramming of immune cell metabolic pathways. Accumulating evidence suggests that cellular metabolism of nutrients, such as lipids and amino acids, beyond being essential to meet the bioenergetic and biosynthetic demands of immune cells, also regulates a broad spectrum of cellular signal transduction, and influences immune cell survival, differentiation, and anti-tumor effector function. The cancer immunometabolism research field is rapidly evolving, and exciting new discoveries are reported in high-profile journals nearly weekly. Therefore, all new findings in this field cannot be summarized within this short review. Instead, this review is intended to provide a brief introduction to this rapidly developing research field, with a focus on the metabolism of two classes of important nutrients-lipids and amino acids-in immune cells. We highlight recent research on the roles of lipids and amino acids in regulating the metabolic fitness and immunological functions of T cells, macrophages, and natural killer cells in the tumor microenvironment. Furthermore, we discuss the possibility of "editing" metabolic pathways in immune cells to act synergistically with currently available immunotherapies in enhancing anti-tumor immune responses.

Role of miR-199a-5p in the post-transcriptional regulation of ABCA1 in response to hypoxia in peritoneal macrophages

Hypoxia is a crucial factor contributing to maintenance of atherosclerotic lesions. The ability of ABCA1 to stimulate the efflux of cholesterol from cells in the periphery, particularly foam cells in atherosclerotic plaques, is an important anti-atherosclerotic mechanism. The posttranscriptional regulation by miRNAs represents a key regulatory mechanism of a number of signaling pathways involved in atherosclerosis. Previously, miR-199a-5p has been shown to be implicated in the endocytic and retrograde intracellular transport. Although the regulation of miR-199a-5p and ABCA1 by hypoxia has been already reported independently, the role of miR-199a-5p in macrophages and its possible role in atherogenic processes such us regulation of lipid homeostasis through ABCA1 has not been yet investigated. Here, we demonstrate that both ABCA1 and miR-199a-5p show an inverse regulation by hypoxia and Ac-LDL in primary macrophages. Moreover, we demonstrated that miR-199a-5p regulates ABCA1 mRNA and protein levels by directly binding to its 3'UTR. As a result, manipulation of cellular miR-199a-5p levels alters ABCA1 expression and cholesterol efflux in primary mouse macrophages. Taken together, these results indicate that the correlation between ABCA1-miR-199a-5p could be exploited to control macrophage cholesterol efflux during the onset of atherosclerosis, where cholesterol alterations and hypoxia play a pathogenic role.

Novel insights into the regulation of cellular catabolic metabolism in macrophages through nuclear receptors

Regulation of cellular catabolic metabolism in immune cells has recently become a major concept for resolution of inflammation. Nuclear receptors (NRs), including peroxisome proliferator activator receptors (PPARs), 1,25-dihydroxyvitamin D(3) receptor (VDR), liver X receptors (LXRs), glucocorticoid receptors (GRs), estrogen-related receptor α (ERRα) and Nur77, have been identified as major modulators of inflammation, affecting innate immune cells, such as macrophages. Evidence emerges on how NRs regulate cellular metabolism in macrophages during inflammatory processes and contribute to the resolution of inflammation. This could have new implications for our understanding of how NRs shape immune responses and inform anti-inflammatory drug design. This review will highlight the recent developments about NRs and their role in cellular metabolism in macrophages.

HDL maturation and remodelling

Cholesterol in the circulation is mostly transported in an esterified form as a component of lipoproteins. The majority of these cholesteryl esters are produced in nascent, discoidal high density lipoproteins (HDLs) by the enzyme, lecithin:cholesterol acyltransferase (LCAT). Discoidal HDLs are discrete populations of particles that consist of a phospholipid bilayer, the hydrophobic acyl chains of which are shielded from the aqueous environment by apolipoproteins that also confer water solubility on the particles. The progressive LCAT-mediated accumulation of cholesteryl esters in discoidal HDLs generates the spherical HDLs that predominate in normal human plasma. Spherical HDLs contain a core of water insoluble, neutral lipids (cholesteryl esters and triglycerides) that is surrounded by a surface monolayer of phospholipids with which apolipoproteins associate. Although spherical HDLs all have the same basic structure, they are extremely diverse in size, composition, and function. This review is concerned with how the biogenesis of discoidal and spherical HDLs is regulated and the mechanistic basis of their size and compositional heterogeneity. Current understanding of the impact of this heterogeneity on the therapeutic potential of HDLs of varying size and composition is also addressed in the context of several disease states.