Promoting Lipid Uptake Research Articles

Notch signaling regulates macrophage-mediated inflammation in metabolic dysfunction-associated steatotic liver disease

The liver macrophage population comprises resident Kupffer cells (KCs) and monocyte-derived macrophages with distinct pro- or anti-inflammatory properties that affect the severity and course of liver diseases. The mechanisms underlying macrophage differentiation and functions in metabolic dysfunction-associated steatotic liver disease and/or steatohepatitis (MASLD/MASH) remain mostly unknown. Using single-cell RNA sequencing (scRNA-seq) and fate mapping of hepatic macrophage subpopulations, we unraveled the temporal and spatial dynamics of distinct monocyte and monocyte-derived macrophage subsets in MASH. We revealed a crucial role for the Notch-Recombination signal binding protein for immunoglobulin kappa J region (RBPJ) signaling pathway in controlling the monocyte-to-macrophage transition, with Rbpj deficiency blunting inflammatory macrophages and monocyte-derived KC differentiation and conversely promoting the emergence of protective Ly6Clo monocytes. Mechanistically, Rbpj deficiency promoted lipid uptake driven by elevated CD36 expression in Ly6Clo monocytes, enhancing their protective interactions with endothelial cells. Our findings uncover the crucial role of Notch-RBPJ signaling in monocyte-to-macrophage transition and will aid in the design of therapeutic strategies for MASH treatment.

Loss of NAT10 alleviates maternal high-fat diet-induced hepatic steatosis in male offspring of mice.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is becoming an escalating health problem in pediatric populations. This study aimed to investigate the role of N-acetyltransferase 10 (NAT10) in maternal high-fat diet (HFD)-induced MASLD in offspring at early life. We generated male hepatocyte-specific NAT10 knockout (Nat10HKO) mice and mated them with female Nat10fl/fl mice under chow or HFD feeding. Body weight, liver histopathology, and expression of lipid metabolism-associated genes (Srebp1c, Fasn, Pparα, Cd36, Fatp2, Mttp, and Apob) were assessed in male offspring at weaning. Lipid uptake assays were performed both in vivo and in vitro. The mRNA stability assessment and RNA immunoprecipitation were performed to determine NAT10-regulated target genes. NAT10 deletion in hepatocytes of male offspring alleviated perinatal lipid accumulation induced by maternal HFD, decreasing expression levels of Srebp1c, Fasn, Cd36, Fatp2, Mttp, and Apob while enhancing Pparα expression. Furthermore, Nat10HKO male mice exhibited reduced lipid uptake. In vitro, NAT10 promoted lipid uptake by enhancing the mRNA stability of CD36 and FATP2. RNA immunoprecipitation assays exhibited direct interactions between NAT10 and CD36/FATP2 mRNA. NAT10 deletion in offspring hepatocytes ameliorates maternal HFD-induced hepatic steatosis through decreasing mRNA stability of CD36 and FATP2, highlighting NAT10 as a potential therapeutic target for pediatric MASLD.

Regulating fat globule structure of infant formula based on MFGM to promote lipid uptake by improving lipolysis

The digestive behavior and absorption properties of lipids are affected by differences in the interface structures of fat globules in human milk (HM) and infant formula. However, it is not clear how the interface changes of fat globules further regulate lipid uptake by improving lipid digestion. Based on the milk fat globule membrane (MFGM) and milk protein, two infant formula emulsions with different interface structures (F1: MFGM-stabilized emulsion, F2: whey protein and casein-stabilized emulsion) were prepared to simulate HM fat globules. The interface structure of lipid droplets, digestion behavior and absorption characteristic of lipids in infant formula emulsions were evaluated and compared with those of HM and commercial infant formula (IFM: supplied with MFGM). The results showed that MFGM-stabilized fat globules in F1 had a similar interface structure to HM. F1 could alleviate the coalescence and aggregation of lipid and protein in comparison with F2 and IFM. The order of triglyceride secretion from high to low was: HM (51.63 ± 2.0 μmol/L), F1 (45.19 ± 1.7 μmol/L), F2 (35.28 ± 1.3 μmol/L) and IFM (32.23 ± 1.3 μmol/L), indicating that HM and F1 exhibited faster lipid digestion and more chylomicron secretion. The expression of SLC27A4, FABP2, SCARB1, DGAT2, PLIN2, and MOGAT2 in HM and F1 was significantly higher than in F2 and IFM. Altogether, the simulation of HM fat globule at the interface structure based on MFGM could better promote cellular lipid uptake by influencing the digestion behavior of fat globules.

Endothelial Dickkopf-1 Promotes Smooth Muscle Cell-derived Foam Cell Formation via USP53-mediated Deubiquitination of SR-A During Atherosclerosis.

Background: Shear stress-induced Dickkopf-1 (DKK1) secretion by endothelial cells (ECs) promotes EC dysfunction and accelerates atherosclerosis (AS). However, the paracrine role of endothelial DKK1 in modulating adjacent smooth muscle cells (SMCs) in atherosclerosis remains unclear. This study investigated the role of EC-secreted DKK1 in SMC-derived foam cell formation under shear stress, in vitro and in vivo. Methods: Parallel-plate co-culture flow system was used to explore the cellular communication between ECs and SMCs under shear stress in vitro. Endothelium-specific knockout of DKK1 (DKK1ECKO/APOE-/-) and endothelium-specific overexpression of DKK1 (DKK1ECTg) mice were constructed to investigate the role of endothelial DKK1 in atherosclerosis and SMC-derived foam cell formation in vivo. RNA sequencing (RNA-seq) was used to identify the downstream targets of DKK1. Reverse transcription quantitative polymerase chain reaction (RT-qPCR), western blot, coimmunoprecipitation (Co-IP) assays and chromatin immunoprecipitation (ChIP) experiments were conducted to explore the underlying regulatory mechanisms. Results: DKK1 is transcriptionally upregulated in ECs under conditions of low shear stress, but not in co-cultured SMCs. However, DKK1 protein in co-cultured SMCs is increased via uptake of low shear stress-induced endothelial DKK1, thereby promoting lipid uptake and foam cell formation in co-cultured SMCs via the post-translational upregulation of scavenger receptor-A (SR-A) verified in parallel-plate co-culture flow system, DKK1ECKO and DKK1ECTg mice. RNA sequencing revealed that DKK1-induced SR-A upregulation in SMCs is dependent on Ubiquitin-specific Protease 53 (USP53), which bound to SR-A via its USP domain and cysteine at position 41, exerting deubiquitination to maintain the stability of the SR-A protein by removing the K48 ubiquitin chain and preventing proteasomal pathway degradation, thereby mediating the effect of DKK1 on lipid uptake in SMCs. Moreover, DKK1 regulates the transcription of USP53 by facilitating the binding of transcription factor CREB to the USP53 promoter. SMC-specific overexpression of USP53 via adeno-associated virus serotype 2 vectors in DKK1ECKO/APOE-/- mice reversed the alleviation of atherosclerotic plaque burden, SR-A expression and lipid accumulation in SMCs within plaques resulting from DKK1 deficiency. Conclusions: Our findings demonstrate that, endothelial DKK1, induced by pathological low shear stress, acts as an intercellular mediator, promoted the foam cell formation of SMCs. These results suggest that targeted intervention with endothelial DKK1 may confer beneficial effects on atherosclerosis.

Nε-(carboxymethyl)lysine promotes lipid uptake of macrophage via cluster of differentiation 36 and receptor for advanced glycation end products.

Advanced glycation end products (AGEs) are diabetic metabolic toxic products that cannot be ignored. Nε-(carboxymethyl)lysine (CML), a component of AGEs, could increase macrophage lipid uptake, promote foam cell formation, and thereby accelerate atherosclerosis. The receptor for AGEs (RAGE) and cluster of differentiation 36 (CD36) were the receptors of CML. However, it is still unknown whether RAGE and CD36 play key roles in CML-promoted lipid uptake. Our study aimed to explore the role of RAGE and CD36 in CML-induced mac-rophage lipid uptake. In this study, we examined the effect of CML on lipid uptake by Raw264.7 macrophages. After adding 10 mmol/L CML, the lipid accumulation in macro-phages was confirmed by oil red O staining. Expression changes of CD36 and RAGE were detected with immunoblotting and quantitative real-time polymerase chain reaction. The interaction between CML with CD36 and RAGE was verified by immunoprecipitation. We synthesized a novel N-succinimidyl-4-18F-fluorobenzoate-CML radioactive probe. Radioactive receptor-ligand binding assays were performed to test the binding affinity between CML with CD36 and RAGE. The effects of blocking CD36 or RAGE on CML-promoting lipid uptake were also detected. The study revealed that CML significantly promoted lipid uptake by macro-phages. Immunoprecipitation and radioactive receptor-ligand binding assays indicated that CML could specifically bind to both CD36 and RAGE. CML had a higher affinity for CD36 than RAGE. ARG82, ASN71, and THR70 were the potential interacting amino acids that CD36 binds to CML Anti-CD36 and anti-RAGE could block the uptake of CML by macrophages. The lipid uptake promotion effect of CML was significantly attenuated after blocking CD36 or RAGE. Our results suggest that the binding of CML with CD36 and RAGE promotes macrophage lipid uptake.

Abelmoschus esculentus subfractions ameliorate hepatic lipogenesis and lipid uptake via regulating dipeptidyl peptidase-4-With improving insulin resistance.

Nonalcoholic fatty liver disease (NAFLD) is recognized as the liver component of metabolic syndrome. The regulation of hepatic lipid should be emphasized to prevent accompanying illness. As AMP-activated protein kinase (AMPK) and sterol regulatory element binding protein (SREBP) regulate lipid metabolism, CD36 and fatty acid synthase (FAS) promote lipid uptake and lipogenesis respectively, while acetyl-CoA carboxylase (ACC) is an indicator of negative feedback. The increase of IRS-1 phosphorylation at the residue ser307 (p-ser307-IRS-1) and decrease of p-ser473-Akt (p-Akt) are viewed as the insulin resistance markers, and our previous reports suggested dipeptidyl peptidase-4 (DPP-4) mediates insulin resistance, the crucial factor of metabolic syndrome. Abelmoschus esculentus (AE) fruit is well-known for its antidiabetic utility. We had isolated several AE subfractions by successive steps, and found that F1 and F2 were especially valid in suppressing DPP-4 signaling. Since little is known if AE works on NAFLD, now we first attempt to investigate whether AE is useful to attenuate hepatic lipogenesis and lipid uptake in liver cells, along with improving the metabolic targets. We demonstrated that AE subfractions attenuated the hepatic lipid accumulation induced by free fatty acids. Treatment of AE alleviated FAS and returned the level of p-ser79-ACC (p-ACC). Although F1 was more effective on AMPK, F2 seemed more stable to attenuate SREBP-1. Moreover, as fatty acids stimulated the expression of CD36, F2 showed a superior effect to down-regulate the lipid uptake. Both AE subfractions reduced the generation of ROS, decreased the level of p-ser307-IRS-1, and restored the expression of p-Akt. Moreover, treatment of DPP-4 inhibitor linagliptin revealed that, AE could prevent the hepatic lipogenesis, oxidative burden, and the related insulin resistance via downregulating DPP-4. In conclusion, the present investigation revealed that AE, especially F2, is potential to be developed as adjuvant to prevent NAFLD.

Macrophage CD36 and TLR4 Cooperation Promotes Foam Cell Formation and VSMC Migration and Proliferation Under Circadian Oscillations.

Circadian rhythm disorders can accelerate atherosclerosis. This study aimed to determine the role of circadian disordered macrophages in atherosclerotic development. Mice were divided into NC group (normal circadian rhythm), L24 group (constant light), D12L12 group (weekly shift light/dark cycle), and D24 group (constant dark). Atherosclerotic progression was significantly accelerated in L24, D12L12, and D24 groups. Peritoneal macrophages from circadian disruption groups exhibited enhanced cytokine secretion and foam cell formation. Migration and proliferation of vascular smooth muscle cells (VSMCs) were increased under the conditioned medium of circadian disordered macrophages. The blockade of CD36 markedly inhibited foam cell formation. Compared with blocking CD36 or TLR4 alone, the co-inhibition of CD36 and TLR4 in macrophages further reduced cytokine secretion and more effectively inhibited VSMC migration and proliferation. In conclusion, the activation of CD36 and TLR4 in circadian disordered macrophages promotes foam cell formation and cytokine secretion and enhances VSMC migration and proliferation. Circadian rhythm disorders promote lipid uptake and cytokine secretion of macrophages by regulating CD36 and TLR4, and enhance VSMC migration and proliferation through the paracrine effect of macrophages.

MiR-146a contributes to atherosclerotic plaque stability by regulating the expression of TRAF6 and IRAK-1.

Atherosclerosis is a chronic inflammatory disease. The vulnerable plaque of atherosclerotic can lead to the development of many diseases including acute coronary syndrome and coronary heart disease. It is well known that miR-146a is the key brake miRNA of the inflammatory signal transduction pathway. However, the effect of miR-146a on the stability of atherosclerotic plaque remains to be elucidated. We constructed animal models of atherosclerosis and foam cell models, and overexpressed and knocked-down miR-146a in models. After staining with Hematoxylin-Eosin (HE), Oil Red O, immunocytochemistry (IHC) and Sirius Red, we used the proportion of (Lipids area + Macrophage area) and (SMCs area + collagen area) to evaluate atherosclerotic plaque stability. TUNEL and flow cytometry were performed to detect the apoptosis level of macrophages. Levels of inflammatory factors were detected via ELISA assay. The results showed that miR-146a, IRAK1 and TRAF6 were abnormally expressed in plaques of atherosclerotic animals. Overexpression of miR-146a contributed to the stability of plaques that inhibited plaque formation, macrophage apoptosis and levels of pro-inflammatory factors. The Dual-luciferase reporter gene assay, IF and FISH were used to verify the regulatory mechanism of miR-146a on IRAK1 and TRAF6. We found that IRAK1 and TRAF6 promoted lipid uptake, apoptosis, and release of pro-inflammatory factors of RAW264.7 macrophages, whereas miR-146a restored RAW264.7 macrophages phenotype by inhibiting IRAK1 and TRAF6 expression. We display for the first time that miR-146a inhibits the formation of foam cells, RAW264.7 macrophage apoptosis and pro-inflammatory reaction through negative regulation of IRAK1 and TRAF6 expression, thereby enhancing the stability of atherosclerotic plaques.

Adipokine Apelin/APJ Pathway Promotes Peritoneal Dissemination of Ovarian Cancer Cells by Regulating Lipid Metabolism.

Adipose tissue, which can provide adipokines and nutrients to tumors, plays a key role in promoting ovarian cancer metastatic lesions in peritoneal cavity. The adipokine apelin promotes ovarian cancer metastasis and progression through its receptor APJ, which regulates cell proliferation, energy metabolism, and angiogenesis. The objective of this study was to investigate the functional role and mechanisms of the apelin-APJ pathway in ovarian cancer metastasis, especially in context of tumor cell-adipocyte interactions. When co-cultured in the conditioned media (AdipoCM) derived from 3T3-L1 adipocytes, which express and secrete high apelin, human ovarian cancer cells with high APJ expression showed significant increases in migration and invasion in vitro. We also found that cells expressing high levels of APJ had increased cell adhesion to omentum ex vivo, and preferentially "home-in" on the omentum in vivo. These apelin-induced pro-metastatic effects were reversed by APJ antagonist F13A in a dose-dependent manner. Apelin-APJ activation increased lipid droplet accumulation in ovarian cancer cells, which was further intensified in the presence of AdipoCM and reversed by F13A or APJ knockdown. Mechanistically, this increased lipid uptake was mediated by CD36 upregulation via APJ-STAT3 activation, and the lipids were utilized in promoting fatty acid oxidation via activation of AMPK-CPT1a axis. Together, our studies demonstrate that adipocyte-derived apelin activates APJ-expressing tumor cells in a paracrine manner, promoting lipid uptake and utilization and providing energy for ovarian cancer cell survival at the metastatic sites. Hence, the apelin-APJ pathway presents a novel therapeutic target to curb ovarian cancer metastasis. IMPLICATIONS: Targeting the APJ pathway in high-grade serous ovarian carcinoma is a novel strategy to inhibit peritoneal metastasis.

Oxidized-LDL inhibits testosterone biosynthesis by affecting mitochondrial function and the p38 MAPK/COX-2 signaling pathway in Leydig cells

Abnormal lipid/lipoprotein metabolism induced by obesity may affect spermatogenesis by inhibiting testosterone synthesis in Leydig cells. It is crucial to determine which components of lipoproteins inhibit testosterone synthesis. Circulating oxidized low-density lipoprotein (oxLDL), the oxidized form of LDL, has been reported to be an independent risk factor for decreased serum testosterone levels. However, whether oxLDL has a damaging effect on Leydig cell function and the detailed mechanisms have been rarely studied. This study first showed the specific localization of oxLDL and mitochondrial structural damage in testicular Leydig cells of high-fat diet-fed mice in vivo. We also found that oxLDL reduced the mitochondrial membrane potential (MMP) by disrupting electron transport chain and inhibited testosterone synthesis-related proteins and enzymes (StAR, P450scc, and 3β‑HSD), which ultimately led to mitochondrial dysfunction and decreased testosterone synthesis in Leydig cells. Further experiments demonstrated that oxLDL promoted lipid uptake and mitochondrial dysfunction by inducing CD36 transcription. Meanwhile, oxLDL facilitated COX2 expression through the p38 MAPK signaling pathway in Leydig cells. Blockade of COX-2 attenuated the oxLDL-induced decrease in StAR and P450scc. Our clinical results clarified that the increased serum oxLDL level was associated with a decline in circulating testosterone levels. Our findings amplify the damaging effects of oxLDL and provide the first evidence that oxLDL is a novel metabolic biomarker of male-acquired hypogonadism caused by abnormal lipid metabolism.

Too Much of a Good Thing? An Evolutionary Theory to Explain the Role of Ceramides in NAFLD.

Non-alcoholic fatty liver disease (NAFLD), which ranges from the relatively benign and reversible fatty liver (NAFL) to the more advanced and deadly steatohepatitis (NASH), affects a remarkably high percentage of adults in the population. Depending upon severity, NAFLD can increase one's risk for diabetes, cardiovascular disease, and hepatocellular carcinoma. Though the dominant histological feature of all forms of the disease is the accumulation of liver triglycerides, these molecules are likely not pathogenic, but rather serve to protect the liver from the damaging consequences of overnutrition. We propose herein that the less abundant ceramides, through evolutionarily-conserved actions intended to help organisms adapt to nutrient excess, drive the cellular events that define NAFL/NASH. In early stages of the disease process, they promote lipid uptake and storage, whilst inhibiting utilization of glucose. In later stages, they stimulate hepatocyte apoptosis and fibrosis. In rodents, blocking ceramide synthesis ameliorates all stages of NAFLD. In humans, serum and liver ceramides correlate with the severity of NAFLD and its comorbidities diabetes and heart disease. These studies identify key roles for ceramides in these hepatic manifestations of the metabolic syndrome.

Fatty Acid Oxidation Controls CD8+ Tissue-Resident Memory T-cell Survival in Gastric Adenocarcinoma.

The success of checkpoint inhibitors in cancer treatment is associated with the infiltration of tissue-resident memory T (Trm) cells. In this study, we found that about 30% of tumor-infiltrating lymphocytes (TIL) in the tumor microenvironment of gastric adenocarcinoma were CD69+CD103+ Trm cells. Trm cells were low in patients with metastasis, and the presence of Trm cells was associated with better prognosis in patients with gastric adenocarcinoma. Trm cells expressed high PD-1, TIGIT, and CD39 and represented tumor-reactive TILs. Instead of utilizing glucose, Trm cells relied on fatty acid oxidation for cell survival. Deprivation of fatty acid resulted in Trm cell death. In a tumor cell-T-cell coculture system, gastric adenocarcinoma cells outcompeted Trm cells for lipid uptake and induced Trm cell death. Targeting PD-L1 decreased fatty acid binding protein (Fabp) 4 and Fabp5 expression in tumor cells of gastric adenocarcinoma. In contrast, the blockade of PD-L1 increased Fabp4/5 expression in Trm cells, promoting lipid uptake by Trm cells and resulting in better survival of Trm cells in vitro and in vivo. PD-L1 blockade unleashed Trm cells specifically in the patient-derived xenograft (PDX) mice. PDX mice that did not respond to PD-L1 blockade had less Trm cells than responders. Together, these data demonstrated that Trm cells represent a subset of TILs in the antitumor immune response and that metabolic reprogramming could be a promising way to prolong the longevity of Trm cells and enhance antitumor immunity in gastric adenocarcinoma.

Periodontal Pathogens Modulate Lipid Flux via Fatty Acid Binding Protein 4

A strong correlation between chronic periodontitis and systemic diseases (e.g., cardiovascular disease, metabolic disorders) has been suggested for several decades. However, the evidence supporting this correlation is restricted primarily to epidemiologic studies, with only a few experimental outcomes confirming such a correlation and providing information about the underlying molecular mechanisms. To reveal a correlation between periodontitis and systemic diseases as well as a relevant molecular pathway, we investigated the effects of Porphyromonas gingivalis and Fusobacterium nucleatum, which play roles in chronic periodontitis progression, on Raw264.7 and THP-1 macrophages. Infection with P. gingivalis or F. nucleatum significantly induced the expression of fatty acid binding protein 4 (FABP4), one of the most important adipokines that play a role in the progression of systemic diseases such as atherosclerosis and type 2 diabetes. Periodontal pathogen–induced FABP4 expression in macrophages promoted lipid uptake by these cells, as demonstrated by the diminished lipid accumulation in cells treated with an FABP4 inhibitor, BMS309403, or with knockdown of FABP4 expression. This periodontal pathogen–induced FABP4 expression was dependent on the JNK pathway, and JNK inhibition reduced lipid uptake by reducing FABP4 expression. Serum levels of antibodies against P. gingivalis correlated with serum FABP4 levels in humans, whereas no association occurred between F. nucleatum antibody titers and FABP4 levels. To our knowledge, this report is the first to experimentally demonstrate that periodontal pathogens stimulate lipid uptake in macrophages by modulating FABP4 expression. These findings strongly support the hypothesis that periodontitis may affect the progression of various systemic diseases.

Inflammation-induced mTORC2-Akt-mTORC1 signaling promotes macrophage foam cell formation

The transformation of macrophages into lipid-loaded foam cells is a critical and early event in the pathogenesis of atherosclerosis. Several recent reports highlighted that induction of TLR4 signaling promotes macrophage foam cell formation; however, the underlying molecular mechanisms have not been clearly elucidated. Here, we found that the TLR4 mediated inflammatory signaling communicated with mTORC2-Akt-mTORC1 metabolic cascade in macrophage and thereby promoting lipid uptake and foam cell formation. Mechanistically, LPS treatment markedly upregulates TLR4 mediated inflammatory pathway which by activating mTORC2 induces Akt phosphorylation at serine 473 and that aggravate mTORC1 dependent scavenger receptors expression and consequent lipid accumulation in THP-1 macrophages. Inhibition of mTORC2 either by silencing Rictor expression or inhibiting its association with mTOR notably prevents LPS induced Akt activation, scavenger receptors expression, and macrophage lipid accumulation. Although suppression of mTORC1 expression by genetic knockdown of Raptor did not produce any significant change in Akt S473 phosphorylation, however, incubation with Akt activator in Rictor silenced cells failed to promote scavenger receptors expression and macrophage foam cell formation. Thus, present research explored the signaling pathway involved in inflammation-induced macrophage foam cells formation and therefore, targeting this pathway might be useful for preventing macrophage foam cell formation.

RNA helicase DDX5 participates in oxLDL-induced macrophage scavenger receptor 1 expression by suppressing mRNA degradation

The DEAD box protein DDX5, an ATP-dependent RNA helicase, plays an important role in transcriptional regulation and is associated with solid tumors and leukemia. However, its role in oxLDL-induced lipid uptake in macrophages remains unclear. In this study, we detected the expression of DDX5 mRNA and protein in oxidized low-density lipoprotein (oxLDL)-treated human primary macrophages that were induced from monocytes isolated from human peripheral blood with or without several chemical inhibitors using quantitative real-time PCR (qRT-PCR) or Western blotting. We found that oxLDL induced DDX5 expression to be independent of both the MAPK and NF-κB pathways. We also found that DDX5 promoted macrophage lipid uptake by evaluating the fluorescence intensity of engulfed dil-oxLDL. Various scavenger receptors that participate in lipid uptake were detected in siR-DDX5 transfected macrophages using qRT-PCR and Western blotting. Macrophage scavenger receptor A (MSR1) was found to be involved the upregulation of DDX5-mediated lipid uptake. Through the use of a dual luciferase reporter assay system and incubation with cycloheximide (CHX) MG132 and actidione (ActD), we found that DDX5 promoted MSR1 protein expression by stabilizing MSR1 mRNA. Moreover, the mechanism involved in DDX5 regulation of MSR1 mRNA was also explored using mass spectrum analysis; Immunoprecipitations (IPs) and RNA- Immunoprecipitations (R-IPs) revealed that mettl3 was involved in DDX5-mediated MSR1 mRNA stabilization. In addition, we also demonstrated that DDX5 inhibited mettl3 to catalyze m6a methylation in MSR1 mRNA, which contributed to the maintenance of MSR1 mRNA stability. In conclusion, ox-LDL promotes DDX5 expression in macrophages, which interacts with mettl3 to stabilize MSR1 mRNA by decreasing the m6a modification of MSR1 mRNA, ultimately promoting lipid uptake in macrophages.

A Novel Role of Id1 in Regulating Oscillatory Shear Stress-Mediated Lipid Uptake in Endothelial Cells.

Inhibitor of DNA binding 1 (Id1) has been shown to be involved in adipogenesis and metabolism, which may contribute to atherosclerotic progression. However, it remains unclear how Id1 regulates endothelial cell functions and atherosclerosis in response to oscillatory shear stress. The current study aims to evaluate the effects of oscillatory shear stress on LDL uptake by endothelial cells and to delineate the roles of Id1 in this process. Using an in vivo ligation model of ApoE-/- mice and applying low and oscillatory shear stress (OSS) in vitro, we found that OSS can effectively promote lipid uptake. In vivo en face staining results showed that OSS down-regulated Id1 expression. In vitro, OSS activated Id1 transiently but eventually inhibited its expression with time. Overexpression of Id1 can abolish OSS-mediated lipid uptake in ECs. In addition, Id1 overexpression and knockdown experiments demonstrated that Id1 can regulate LDLR expression to influence lipid uptake. Immunoprecipitation and subcellular localization results further suggested that Id1 can combine with sterol regulatory element-binding protein1 (SREBP1), which may be related to the Id1-mediated LDLR down-expression. Our study shows a biomechanical role of Id1 in endothelial cells' uptake of lipid by down-regulating LDLR, which could help understand how oscillatory flow affects atherosclerotic development.

Oroxylin A suppresses the development and growth of colorectal cancer through reprogram of HIF1\u03b1-modulated fatty acid metabolism

The occurrence and progress of colon cancer are closely associated with obesity. Therefore, the lipid metabolism, especially fatty acid metabolism, is a significant section of energy homeostasis in colon cancer cells, and it affects many important cellular processes. Oroxylin A is one of the main bioactive flavonoids of Scutellariae radix, which has a strong anticancer effect but low toxicity to normal tissue. In previous studies, we have proved that oroxylin A reprogrammes metabolism of cancer cells by inhibiting glycolysis. Here, we further investigated the metabolism-modulating effects of oroxylin A on the fatty acid metabolism in colon cancer cells under hypoxia. We found that HIF1α upregulated adipophilin, fatty acid synthase and sterol regulatory element-binding protein 1, and downregulated carnitine palmitoyltransferase 1 (CPT1), resulting in the promoted lipid uptake and transport, increased de novo fatty acid synthesis and suppressed fatty acid oxidation. Oroxylin A inactivated HIF1α and reprogrammed fatty acid metabolism of HCT116 cells, decreasing intracellular fatty acid level and enhancing fatty acid oxidation. Furthermore, the rapid decrease of fatty acid level caused by oroxylin A inhibited the nuclear translocation of β-cantenin and inactivated the Wnt pathway, arousing cell cycle arrest in G2/M phase. In vivo studies demonstrated that high-fat diet increased the incidence of colon cancer and accelerated tumor development. Importantly, besides the growth inhibitory effects on colon cancer xenograft, oroxylin A prevented carcinogenesis and delayed progress of primary colon cancer as well. Our studies enriched the metabolic regulatory mechanism of oroxylin A, and suggested that oroxylin A was a potent candidate for the treatment and prevention of colorectal cancer.

Regulation of energy balance by the hypothalamic lipoprotein lipase regulator Angptl3.

Hypothalamic lipid sensing is important for the maintenance of energy balance. Angiopoietin-like protein 3 (Angptl3) critically regulates the clearance of circulating lipids by inhibiting lipoprotein lipase (LPL). The current study demonstrated that Angptl3 is highly expressed in the neurons of the mediobasal hypothalamus, an important area in brain lipid sensing. Suppression of hypothalamic Angptl3 increased food intake but reduced energy expenditure and fat oxidation, thereby promoting weight gain. Consistently, intracerebroventricular (ICV) administration of Angptl3 caused the opposite metabolic changes, supporting an important role for hypothalamic Angptl3 in the control of energy balance. Notably, ICV Angptl3 significantly stimulated hypothalamic LPL activity. Moreover, coadministration of the LPL inhibitor apolipoprotein C3 antagonized the effects of Angptl3 on energy metabolism, indicating that LPL activation is critical for the central metabolic actions of Angptl3. Increased LPL activity is expected to promote lipid uptake by hypothalamic neurons, leading to enhanced brain lipid sensing. Indeed, ICV injection of Angptl3 increased long-chain fatty acid (LCFA) and LCFA-CoA levels in the hypothalamus. Furthermore, inhibitors of hypothalamic lipid-sensing pathways prevented Angptl3-induced anorexia and weight loss. These findings identify Angptl3 as a novel regulator of the hypothalamic lipid-sensing pathway.

Hepatitis C Virus Stimulates Low-Density Lipoprotein Receptor Expression To Facilitate Viral Propagation

Lipids play a crucial role in multiple aspects of hepatitis C virus (HCV) life cycle. HCV modulates host lipid metabolism to enrich the intracellular milieu with lipids to facilitate its proliferation. However, very little is known about the influence of HCV on lipid uptake from bloodstream. Low-density lipoprotein receptor (LDLR) is involved in uptake of cholesterol rich low-density lipoprotein (LDL) particles from the bloodstream. The association of HCV particles with lipoproteins implicates their role in HCV entry; however, the precise role of LDLR in HCV entry still remains controversial. Here, we investigate the effect of HCV infection on LDLR expression and the underlying mechanism(s) involved. We demonstrate that HCV stimulates LDLR expression in both HCV-infected Huh7 cells and in liver tissue from chronic hepatitis C patients. Fluorescence activated cell sorting and immunofluorescence analysis revealed enhanced cell surface and total expression of LDLR in HCV-infected cells. Increased LDLR expression resulted in the enhanced uptake of lipoprotein particles by HCV-infected cells. Analysis of LDLR gene promoter identified a pivotal role of sterol-regulatory element binding proteins (SREBPs), in the HCV-mediated stimulation of LDLR transcription. In addition, HCV negatively modulated the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that facilitates LDLR degradation. Ectopic expression of wild-type PCSK9 or gain-of-function PCSK9 mutant negatively affected HCV replication. Overall, our results demonstrate that HCV regulates LDLR expression at transcriptional and posttranslational level via SREBPs and PCSK9 to promote lipid uptake and facilitate viral proliferation. HCV modulates host lipid metabolism to promote enrichment of lipids in intracellular environment, which are essential in multiple aspects of HCV life cycle. However, very little is known about the influence of HCV on lipid uptake from the bloodstream. LDLR is involved in uptake of cholesterol rich lipid particles from bloodstream. In this study, we investigated the effect of HCV on LDLR expression and the underlying mechanism triggered by the virus to modulate LDLR expression. Our observations suggest that HCV upregulates LDLR expression at both the protein and the transcript levels and that this upregulation likely contributes toward the uptake of serum lipids by infected hepatocytes. Abrogation of HCV-mediated upregulation of LDLR inhibits serum lipid uptake and thereby perturbs HCV replication. Overall, our findings highlight the importance of serum lipid uptake by infected hepatocytes in HCV life cycle.

Chitinase Inhibition Promotes Atherosclerosis in Hyperlipidemic Mice

Chitinase 1 (CHIT1) is secreted by activated macrophages. Chitinase activity is raised in atherosclerotic patient sera and is present in atherosclerotic plaque. However, the role of CHIT1 in atherosclerosis is unknown. Preliminary studies of atherosclerosis in cynomolgous monkeys revealed CHIT1 to be closely correlated with areas of macrophage infiltration. Thus, we investigated the effects of a chitinase inhibitor, allosamidin, on macrophage function in vitro and on atherosclerotic development in vivo. In RAW264.7 cells, allosamidin elevated monocyte chemoattractant protein 1 and tumor necrosis factor alpha expression, and increased activator protein 1 and nuclear factor-κB transcriptional activity. Although inducible nitric oxide synthase, IL-6, and IL-1β expression were increased, Arg1 expression was decreased by chitinase inhibition, suggesting that suppression of CHIT1 activity polarizes macrophages into a M1 phenotype. Allosamidin decreased scavenger receptor AI, CD36, ABCA1, and ABCG1 expression which led to suppression of cholesterol uptake and apolipoprotein AI-mediated cholesterol efflux in macrophages. These effects were confirmed with CHIT1 siRNA transfection and CHIT1 plasmid transfection experiments in primary macrophages. Apolipoprotein E-deficient hyperlipidemic mice treated for 6 weeks with constant administration of allosamidin and fed an atherogenic diet showed aggravated atherosclerotic lesion formation. These data suggest that CHIT1 exerts protective effects against atherosclerosis by suppressing inflammatory responses and polarizing macrophages toward an M2 phenotype, and promoting lipid uptake and cholesterol efflux in macrophages.