Very Low-density Lipoprotein Receptor Expression Research Articles

Very low-density lipoprotein receptor mediates triglyceride-rich lipoprotein-induced oxidative stress and insulin resistance.

Obesity is associated with excess lipid deposition in non-adipose tissues, leading to increased oxidative stress and insulin resistance. Very-low-density lipoprotein receptor (VLDLR), a member of the LDL receptor family, binds and increases the catabolism of triglyceride-rich lipoproteins. Although VLDLR is highly expressed in the heart, its role in obesity-associated oxidative stress and insulin resistance is unclear. Here, we used lean (WT), genetically obese leptin-deficient (ob/ob), and leptin-VLDLR double-null (ob/ob-VLDLR-/-) mice to determine the impact of VLDLR deficiency on obesity-induced oxidative stress and insulin resistance in the heart. While insulin sensitivity and glucose uptake were reduced in the hearts of ob/ob mice, VLDLR expression was upregulated and was associated with increased VLDL uptake and excess lipid deposition. This was accompanied by an upregulation of cardiac NADPH oxidase (Nox) expression and increased production of Nox-dependent superoxides. Silencing the VLDLR in ob/ob mice had reduced VLDL uptake and prevented excess lipid deposition in the heart, in addition to a reduction of superoxide overproduction and the normalization of insulin sensitivity and glucose uptake. In isolated cardiomyocytes, VLDLR deficiency had prevented VLDL-mediated induction of Nox activity and superoxide overproduction while improving insulin sensitivity and glucose uptake. Our findings indicate that VLDLR deficiency prevents excess lipid accumulation and moderates oxidative stress and insulin resistance in the heart of obese mice. This effect is linked to the active role of VLDLR in VLDL uptake, which triggers a cascade of events leading to increased NOX activity, overproduction superoxide and insulin resistance.

A Sexually Dimorphic Hepatic Cycle of Very Low Density Lipoprotein Uptake and Assembly

The liver shows striking sexual dimorphism, which is reflected in differences between women and men in pathologies inherently associated with hepatic function. Recent single-cell transcriptomes revealed spatiotemporal programmes of liver function on the sublobular scale. However, how sexual dimorphism affects this space-time logic remains poorly understood. To address this, we performed single-cell RNA-seq in the mouse liver, which allowed us to model how lobular position, circadian time and sex shape the transcriptome. We found that sex, space and time markedly influence xenobiotic detoxification and lipid processing, including lipoprotein metabolism. Crucially, the very low density lipoprotein receptor (VLDLR) is restricted to the pericentral zone, with significantly higher mRNA and protein levels in female mice. Using human samples, we were able to recapitulate both VLDLR's pericentral expression as well as higher mRNA and protein levels in premenopausal women compared to similarly aged men. In humans, we found that VLDLR expression depends not just on age but also body mass index. Conversely, several genes involved in VLDL assembly are periportally biased, and we corroborated periportal VLDL generation with electron microscopy, optimized for detecting low density lipid particles. Together, this suggests a hepatic cycle of periportal formation and pericentral uptake of VLDL. Crucially, these processes provide a new window into the sexual dimorphism characterizing differences in VLDL kinetics and atherosclerotic cardiovascular disease. The work was supported by a Swiss National Science Foundation grant. The authors declare no conflicting interests. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Expression level of VLDL receptor and VLDL-c levels in the malignant and benign breast tumors: The correlation with miRNA-4465 and miRNA-1297

Breast cancer as one of the most prevalent cancers has high morbidity and mortality. Very low-density lipoprotein receptor (VLDLR) is a multifunctional receptor which plays a principal role in the tumor development through affecting cell metastasis and proliferation. The VLDLR as a target for miRNA-4465 and miRNA-1297 was predicted using bioinformatics analysis. Tissue specimens of malignant (n = 50), benign (n = 35) and corresponding normal breast (n = 20) were considered to evaluate the expression of VLDLR using RT-qPCR and western blotting. The VLDL cholesterol (VLDL-C) levels were quantified using a colorimetric assay. The relative VLDLR expression was found in the malignant tumors, which was significantly lower than that in the normal tissues (P<0.05). The expression levels of VLDLR had no significant difference between malignant and benign tissues (P>0.05). Correlation analysis revealed that the VLDLR expression level had a direct correlation with miRNA-1297 (R=0.566, P<0.05), but a reverse one with miRNA-4465 (R = −0.663, P<0.0001). The VLDL-C level in the malignant and normal tissues was lower than that in the benign tumors, which was not significant (P>0.05). The expression levels of VLDLR in E+P–H- (ER+,PR−,HER2-) tumors were higher than those in other subtypes (P<0.05). Furthermore, a negative correlation was found between the VLDLR expression level and the Ki 67% score. These data revealed that the lower expression of VLDLR mediated by the high expression levels of miRNA-4465 may be involved in the development of breast cancer. These results might provide some evidence for the effect of VLDLR on the breast cancer.

Wilms tumor 1 regulates lipid accumulation in human endometrial stromal cells during decidualization

We previously reported that the transcription factor Wilms tumor 1 (WT1) regulates the expression of insulin-like growth factor-binding protein-1 (IGFBP-1) and prolactin (PRL) during decidualization of human endometrial stromal cells (ESCs). However, other roles of WT1 in decidualization remain to be fully clarified. Here, we investigated how WT1 regulates the physiological functions of human ESCs during decidualization. We incubated ESCs isolated from proliferative-phase endometrium with cAMP to induce decidualization, knocked down WT1 with siRNA, and generated three types of treatments (nontreated cells, cAMP-treated cells, and cAMP-treated + WT1-knockdown cells). To identify WT1-regulated genes, we used gene microarrays and compared the transcriptome data obtained among these three treatments. We observed that WT1 up-regulates 121 genes during decidualization, including several genes involved in lipid transport. The WT1 knockdown inhibited lipid accumulation (LA) in the cAMP-induced ESCs. To examine the mechanisms by which WT1 regulates LA, we focused on very low-density lipoprotein receptor (VLDLR), which is involved in lipoprotein uptake. We found that cAMP up-regulates VLDLR and that the WT1 knockdown inhibits it. Results of ChIP assays revealed that cAMP increases the recruitment of WT1 to the promoter region of the VLDLR gene, indicating that WT1 regulates VLDLR expression. Moreover, VLDLR knockdown inhibited cAMP-induced LA, and VLDLR overexpression reverted the suppression of LA caused by the WT1 knockdown. Taken together, our results indicate that WT1 enhances lipid storage by up-regulating VLDLR expression in human ESCs during decidualization.

A low-carbohydrate ketogenic diet induces the expression of very-low-density lipoprotein receptor in liver and affects its associated metabolic abnormalities

A low-carbohydrate ketogenic diet (LCKD) promotes the progression of hepatic steatosis in C57BL/6 wild-type mice, but improves the condition in leptin-deficient obese (ob/ob) mice. Here, we show a novel effect of LCKD associated with the conflicting effects on these mice. Gene expression microarray analyses showed that expression of the Vldlr gene, which encodes the very-low-density lipoprotein receptor (VLDLR), was induced in LCKD-fed ob/ob mice. Although the VLDLR is not normally expressed in the liver, the LCKD led to VLDLR expression in both ob/ob and wild-type mice. To clarify this effect on VLDL dynamics, we analyzed the lipid content of serum lipoproteins and found a marked decrease in VLDL-triglycerides only in LCKD-fed wild-type mice. Further analyses suggested that transport of triglycerides via VLDL from the liver to extrahepatic tissues was inhibited by LCKD-induced hepatic VLDLR expression, but rescued under conditions of leptin deficiency.

Reelin is modulated by diet-induced obesity and has direct actions on arcuate proopiomelanocortin neurons

ObjectiveReelin (RELN) is a large glycoprotein involved in synapse maturation and neuronal organization throughout development. Deficits in RELN signaling contribute to multiple psychological disorders, such as autism spectrum disorder, schizophrenia, and bipolar disorder. Nutritional stress alters RELN expression in brain regions associated with these disorders; however, the involvement of RELN in the neural circuits involved in energy metabolism is unknown. The RELN receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VLDLR) are involved in lipid metabolism and expressed in the hypothalamus. Here we explored the involvement of RELN in hypothalamic signaling and the impact of diet-induced obesity (DIO) on this system. MethodsAdult male mice were fed a chow diet or maintained on a high-fat diet (HFD) for 12–16 weeks. HFD-fed DIO mice exhibited decreased ApoER2 and VLDLR expression and increased RELN protein in the hypothalamus. Electrophysiology was used to determine the mechanism by which the central fragment of RELN (CF-RELN) acts on arcuate nucleus (ARH) satiety-promoting proopiomelanocortin (POMC) neurons and the impact of DIO on this circuitry. ResultsCF-RELN exhibited heterogeneous presynaptic actions on inhibitory inputs onto ARH-POMC-EGFP neurons and consistent postsynaptic actions. Additionally, central administration of CF-RELN caused a significant increase in ARH c-Fos expression and an acute decrease in food intake and body weight. ConclusionsWe conclude that RELN signaling is modulated by diet, that RELN is involved in synaptic signaling onto ARH-POMC neurons, and that altering central CF-RELN levels can impact food intake and body weight.

Silencing the Very Low-density Lipoprotein Receptor (VLDLR) Prevents Obesity Associated with Excess Lipid Deposition (P21-040-19)

ObjectivesObesity is associated with an insulin resistant state, characterized by abnormalities in lipid metabolism, a leading cause of morbidity and mortality in cardiovascular diseases (CVD). Very low-density lipoprotein receptor (VLDLR), a member of the LDL receptor family, binds and increases the catabolism of apolipoprotein E triglyceride-rich lipoproteins. Although VLDLR is highly expressed in the heart, its role in obesity associated lipotoxicity is not well understood. MethodsIn the current study, lean WT, VLDLR-deficient (VLDLR−/−), genetically obese leptin-deficient (Lepob/ob), and leptin–VLDLR double-null (Lepob/ob/VLDLR−/−) mice were used to determine the impact of VLDLR deficiency on obesity-induced cardiac lipotoxicity. ResultsThe results showed that insulin sensitivity and glucose uptake were reduced in the hearts of Lepob/ob mice, and at the same time, VLDLR expression was upregulated and associated with increased VLDL uptake resulting in excess lipid deposition. These changes were accompanied by upregulation of cardiac NADPH oxidase (Nox) expression and increased production of Nox-dependent superoxides. Silencing the VLDLR in Lepob/ob mice reduced VLDL uptake and prevented excess lipid deposition. Moreover, VLDLR deficiency reduced superoxide overproduction and normalized glucose uptake. In isolated cardiomyocytes, VLDLR deficiency prevented VLDL-mediated induction of NOx activity and superoxide overproduction while improving insulin sensitivity and glucose uptake. An important observation showed that Lepob/ob/VLDLR−/− mice compared to Lepob/ob mice, had significantly improved heart performance and energetic reserves. ConclusionsThese findings suggest that that when VLDLR is silenced (deficiency), lipid deposition is also reduced, preventing cardiac lipotoxicity in obesity. In addition, the effects may be linked to the role of VLDLR on VLDL uptake, which triggers a cascade of events leading to insulin resistance and superoxide overproduction. Funding SourcesInstitutional Support.Howard University, Washington DC 20059Hackensack University Medical Center, NJ 07601

Macrophage VLDLR mediates obesity-induced insulin resistance with adipose tissue inflammation

Obesity is closely associated with increased adipose tissue macrophages (ATMs), which contribute to systemic insulin resistance and altered lipid metabolism by creating a pro-inflammatory environment. Very low-density lipoprotein receptor (VLDLR) is involved in lipoprotein uptake and storage. However, whether lipid uptake via VLDLR in macrophages affects obesity-induced inflammatory responses and insulin resistance is not well understood. Here we show that elevated VLDLR expression in ATMs promotes adipose tissue inflammation and glucose intolerance in obese mice. In macrophages, VLDL treatment upregulates intracellular levels of C16:0 ceramides in a VLDLR-dependent manner, which potentiates pro-inflammatory responses and promotes M1-like macrophage polarization. Adoptive transfer of VLDLR knockout bone marrow to wild-type mice relieves adipose tissue inflammation and improves insulin resistance in diet-induced obese mice. These findings suggest that increased VLDL-VLDLR signaling in ATMs aggravates adipose tissue inflammation and insulin resistance in obesity.

Low Very low-Density Lipoprotein Cholesterol but High Very low-Density Lipoprotein Receptor mRNA Expression in Peripheral White Blood Cells: An Atherogenic Phenotype for Atherosclerosis in a Community-Based Population

Very low-density lipoprotein cholesterol (VLDL-C), via binding very low-density lipoprotein receptor (VLDLR), can induce the development of atherosclerosis. Besides monocytes, VLDLR expression is detected in various peripheral white blood cells (WBCs), yet its underlying role remains unclear. We thereby aimed to test the hypothesis that VLDLR in all types of peripheral WBCs may be involved in the association between VLDL-C and atherosclerosis. VLDLR mRNA expression in peripheral WBC and plasma VLDL-C levels were measured in 747 participants from a community-based study. Plaque prevalence and total plaque area (TPA) were used to evaluate the burden of carotid atherosclerosis. VLDL-C was positively associated with atherosclerosis risk, whereas this association was modified by VLDLR mRNA level. In participants with the lowest VLDL-C but the highest VLDLR mRNA expression, the risk for plaque prevalence unexpectedly was the highest. This association was also observed for TPA. Moreover, this association remained unchanged after adjusting for WBC or monocytes. Our findings described an atherogenic phenotype characterized by low VLDL-C but high VLDLR mRNA expression in peripheral WBCs, which suggested that VLDLR in all types of peripheral WBCs may be involved in lipid deposition, and VLDL-C and VLDLR may co-determine the development of atherosclerosis.

Decreased expression of VLDLR is inversely correlated with miR-200c in human colorectal cancer.

Colorectal cancer (CRC) is one of the most common cancers and has a high rate of morbidity and mortality worldwide. Very-low-density-lipoprotein receptor (VLDLR), a member of the low-density-lipoprotein receptor (LDLR) superfamily, is a multifunctional receptor that regulates cellular signaling by binding numerous ligands. Several studies reported the altered expression of VLDLR and suggested that VLDLR may play a critical role in tumor development by affecting cell proliferation and metastasis. However, the function of VLDLR and regulation of its expression by miRNAs have not been investigated in CRC. In the present study, we investigated the expression of VLDLR in CRC patients and found it to be significantly decreased in tumors in comparison with paired adjacent non-tumor tissues. Moreover, VLDLR over-expression inhibited the proliferation and migration of CRC cells. We also found that VLDLR expression was negatively regulated by miR-200c in CRC cells and that their expression levels were inversely correlated in CRC patients. These data suggest that VLDLR down-regulation mediated by the increased expression of miR-200c may be involved in the development of CRC.

Abstract 411: Obesity Alters the Expression of Very Low Density Lipoprotein Receptor (vldlr) Expression in Peripheral Blood Monocytes: Possible Links Between Vldlr Expression and Monocyte Phenotypes

Objective: Very low density lipoprotein receptor (VLDLR) is a member of the low-density lipoprotein receptor family that binds multiple ligands including TG-rich lipoproteins. The role of VLDLR in lipid uptake had been demonstrated in cell culture and animal models, but little is known about the effects of obesity on VLDLR expression in human. Accordingly, we examined the impact of obesity on VLDLR expression in peripheral blood monocytes and explored possible links with monocyte inflammatory markers and circulating lipids. Subjects and measurements: Blood was collected from a total of 69 subjects including 23 normal-weight (body mass index: BMI &lt; 25 kg/m 2 ) controls and 46 obese (BMI &gt; 30 kg/m 2 ) subjects. Blood lipids, glucose and hormones were measured. Monocytes were isolated from buffy coats using Ficoll density centrifugation followed by magnetic separation of CD14-positive cells with magnetic beads. Expression of VLDLR, and pro- and ant-inflammatory markers of monocytes was examined by western blotting and quantitative qPCR. The uptake of labeled VLDL (DiI-VLDL) was also assessed in monocyte cultures. Results: Insulin, and total and VLDL triglycerides were increased in plasma of obese subjects. In addition, VLDLR protein and mRNA levels were significantly (p&lt; 0.05) higher (~ 40%) in obese compared to lean subjects. Monocytes of obese subjects exhibited higher expression of IL-6 and TNF-α (+29 to 43%), but lower expression of IL-10 and CD163 (-30 to 47%). The levels of monocyte VLDLR was positively correlated with blood triglycerides and insulin, and negatively with adiponectin. The uptake of labeled VLDL, assessed by fluorescence microscope, was higher in monocytes of obese subjects. Conclusions: Our findings indicate that obesity upregulates the expression of VLDLR and pro-inflammatory markers in peripheral blood monocytes. The uptake VLDL was also increased in monocyte of obese subjects suggesting that obesity-induced VLDLR expression may explain the changes of VLDL uptake and monocyte phenotype.

The association of very low-density lipoprotein receptor (VLDLR) haplotypes with egg production indicates VLDLR is a candidate gene for modulating egg production.

The very low-density lipoprotein receptor (VLDLR) transports egg yolk precursors into oocytes. However, our knowledge of the distribution patterns of VLDLR variants among breeds and their relationship to egg production is still incomplete. In this study, eight single nucleotide polymorphisms (SNPs) that account for 87% of all VLDLR variants were genotyped in Nick Chick (NC, n=91), Lohmann Brown (LohB, n=50) and Lueyang (LY, n=381) chickens, the latter being an Chinese indigenous breed. Egg production by NC and LY chickens was recorded from 17 to 50 weeks. Only four similar haplotypes were found in NC and LohB, of which two accounted for 100% of all NC haplotypes and 92.5% of LohB haplotypes. In contrast, there was considerable haplotypic diversity in LY. Comparison of egg production in LY showed that hens with NC-like haplotypes had a significantly higher production (p < 0.05) than those without the haplotypes. However, VLDLR expression was not significantly different between the haplotypes. These findings indicate a divergence in the distribution of VLDLR haplotypes between selected and non-selected breeds and suggest that the near fixation of VLDLR variants in NC and LohB is compatible with signature of selection. These data also support VLDLR as a candidate gene for modulating egg production.

Hepatitis C virus utilizes VLDLR as a novel entry pathway

Various host factors are involved in the cellular entry of hepatitis C virus (HCV). In addition to the factors previously reported, we discovered that the very-low-density lipoprotein receptor (VLDLR) mediates HCV entry independent of CD81. Culturing Huh7.5 cells under hypoxic conditions significantly increased HCV entry as a result of the expression of VLDLR, which was not expressed under normoxic conditions in this cell line. Ectopic VLDLR expression conferred susceptibility to HCV entry of CD81-deficient Huh7.5 cells. Additionally, VLDLR-mediated HCV entry was not affected by the knockdown of cellular factors known to act as HCV receptors or HCV entry factors. Because VLDLR is expressed in primary human hepatocytes, our results suggest that VLDLR functions in vivo as an HCV receptor independent of canonical CD81-mediated HCV entry.

Liver-specific deletion of the signal transducer and activator of transcription 5 gene aggravates fatty liver in response to a high-fat diet in mice

Growth hormone (GH) signal is mediated by signal transducer and activator of transcription 5 (STAT5), which controls hepatic lipid metabolism. Nonalcoholic fatty liver disease (NAFLD) is clinically associated with a deficiency in GH. This study was performed to understand the role of local STAT5 signaling on hepatic lipid and glucose metabolism utilizing liver-specific STAT5 gene deletion (STAT5 LKO) mice under both normal diet and high-fat diet (HFD) feeding conditions. STAT5 LKO induced hepatic steatosis under HFD feeding, while this change was not observed in mice on normal diet. STAT5 LKO caused hyperglycemia, hyperinsulinemia, hyperleptinemia and elevated free fatty acid and cholesterol concentrations under HFD feeding but induced only hyperglycemia on normal diet. At the molecular level, STAT5 LKO up-regulated the expression of genes involved in lipid uptake (CD36), very low-density lipoprotein receptor (VLDLR), lipogenic stearoyl-CoA desaturase and adipogenic peroxisome proliferator-activated receptor gamma, in both diet groups. In response to HFD feeding, further increases in CD36 and VLDLR expression were found in STAT5 LKO mice. In conclusion, our study suggests that low STAT5 signaling on normal diet predisposes STAT5 LKO mice to early development of fatty liver by hyperglycemia and activation of lipid uptake and adipogenesis. A deficiency in STAT5 signaling under HFD feeding deregulates hepatic and body glucose and lipid metabolism, leading to the development of hepatic steatosis. Our study indicates that low STAT5 signaling, due to low GH secretion, may increase a chance for NAFLD development in elderly people.

Activation of PPAR-δ induces microRNA-100 and decreases the uptake of very low-density lipoprotein in endothelial cells.

Increased level of very low-density lipoprotein (VLDL) is a key feature of the metabolic syndrome and is associated with cardiovascular diseases. PPAR-δ agonists play a protective role in lipid metabolism and vascular function. In this study, we aimed to investigate the role of PPAR-δ in the uptake of VLDL in endothelial cells and its underlying mechanism(s). Uptake of VLDL in HUVECs was assessed by Dil-fluorescent labelling of VLDL. Levels of VLDL receptor mRNA and microRNA (miR-100) were detected by quantitative PCR. The target genes of miR-100 were predicted using bioinformatics analysis. 3'-Untranslated region (3'-UTR) luciferase reporter and Argonaute 1 pull-down assays were used to validate the target of miR-100. PPAR-δ agonist GW501516 decreased uptake of VLDL and expression of VLDL receptor at mRNA and protein levels. GW501516 inhibited the luciferase reporter activity of the 3'-UTR of VLDL receptor. VLDL receptor was a direct target of miR-100. miR-100 was significantly increased by GW501516 in HUVECs. Transfection of a miR-100 mimic decreased the mRNA and protein levels of VLDL receptor and uptake of VLDL. Furthermore, a miR-100 inhibitor abolished the inhibitory effect of PPAR-δ on VLDL receptor expression and VLDL uptake. In endothelial cells, activation of PPAR-δ decreased VLDL receptor expression and VLDL uptake via the induction of miR-100. These results provided a novel mechanism for the vascular protective effect of PPAR-δ agonists.

Macrophage very low density lipoprotein receptor regulates adipose tissue inflammation in obesity

Adipose tissue macrophages (ATMs) are key players to balance pro- and anti-inflammatory responses in fat tissues. In obesity, increased ATMs have been implicated in pro-inflammatory responses and lipid dysregulation. However, underlying mechanisms of lipid accumulation in ATMs of obese animals and their roles are largely unknown. In this study, we demonstrated that elevated expression of very low density lipoprotein receptor (VLDLR) could potentiate adipose tissue inflammation and insulin resistance in obesity. The level of adipose tissue VLDLR in obese animals were elevated, and its expression level was positively correlated with those of pro-inflammatory marker genes. Compared to wild-type mice, VLDLR homozygous-null mice exhibited attenuated insulin resistance and adipose tissue inflammation, concommitantly with less proinflammatory ATMs upon high-fat diet (HFD). In macrophages, the lack of VLDLR prevented lipid uptake and suppressed VLDL-dependent proinflammatory gene expression. Taken together, these data suggest that an elevated macrophage VLDLR expression in obesity would contribute to adipose tissue inflammation via lipid accumulation in ATMs. This work was supported by National Creative Research Initiative Program (2011-0018312) funded by the ministry of Education, Science, and Technology (MEST). K. C. Shin and S. S. Choe were supported by the BK21 program, Korea.

Hypoxia triggers endothelial endoplasmic reticulum stress and apoptosis via induction of VLDL receptor

Endothelial cells express very low density lipoprotein receptor (VLDLr). Beyond the function as peripheral lipoprotein receptor, other roles of VLDLr in endothelial cells have not been completely unraveled. In the present study, human umbilical vein endothelial cells were subjected to hypoxia, and VLDLr expression, endoplasmic reticulum (ER) stress, and apoptosis were assessed. Hypoxia triggered endothelial ER stress and apoptosis, and induced VLDLr expression. Silencing or stabilization of HIF-1α reduced and enhanced VLDLr expression, respectively. HIF-1α affected vldlr promoter activity by interacting with a hypoxia-responsive element (HRE). Knockdown or overexpression of VLDLr alleviated and exacerbated hypoxia-induced ER stress and apoptosis, respectively. Thus, hypoxia induces VLDLr expression through the interaction of HIF-1α with HRE at the vldlr promoter. VLDLr then mediates ER stress and apoptosis.

Nuclear factor (erythroid-derived 2)-like 2 activation-induced hepatic very-low-density lipoprotein receptor overexpression in response to oxidative stress contributes to alcoholic liver disease in mice

Chronic alcohol consumption leads to hypertriglyceridemia, which is positively associated with alcoholic liver disease (ALD). However, whether and how it contributes to the development of fatty liver and liver injury are largely unknown. In this study we demonstrate that chronic alcohol exposure differently regulates the expression of very-low-density lipoprotein receptor (VLDLR) in adipose tissue and the liver. Whereas adipose tissue VLDLR is significantly down-regulated, its hepatic expression is dramatically increased after chronic alcohol feeding. While HepG2 cells stably overexpressing VLDLR manifests increased intracellular triglyceride accumulation, VLDLR-deficient mice are protective against fatty liver and liver injury after chronic alcohol exposure. Mechanistic investigations using both in vitro and in vivo systems reveal that oxidative stress-induced nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activation plays a critical role in alcohol-induced VLDLR up-regulation in hepatocytes, but not in adipocytes. Oxidative stress enhances VLDLR gene expression and protein abundance in primary hepatocytes, concomitant with the Nrf2 activation. Conversely, Nrf2 gene silencing abrogates oxidative stress-induced VLDLR up-regulation in the liver, but not in adipose tissue. In mice, alcohol exposure induces hepatic oxidative stress and Nrf2 activation. Supplementation of N-acetylcysteine alleviates fatty liver and liver injury induced by chronic alcohol exposure, which is associated with suppressed Nrf2 activation and attenuated VLDLR increase in the liver. Furthermore, in comparison to wild-type counterparts, Nrf2-deficient mice demonstrate attenuated hepatic VLDLR expression increase in response to chronic alcohol exposure. Chronic alcohol consumption differently alters VLDLR expression in adipose tissue and the liver. Oxidative stress-induced Nrf2 activation is mechanistically involved in VLDLR overexpression in hepatocytes in response to chronic alcohol consumption. Hepatic VLDLR overexpression plays an important role in the pathogenesis of ALD.

Hypoxia-induced regulation of the very low density lipoprotein receptor

The very low density lipoprotein receptor (VLDLr) is highly upregulated during hypoxia in mouse cardiomyocytes and in human and mouse ischemic hearts causing a detrimental lipid accumulation. To know how the gene is regulated is important for future studies. In this study, we have thoroughly mapped the 5′-flanking region of the mouse VLDLr promoter and show that the hypoxia-mediated increase in VLDLr expression is dependent on Hif-1α binding to a hypoxia responsive element (HRE) located at −162 to −158bp 5′of translation start. We show that classical HRE sites and the previously described PPARγ and Sp1 binding are not involved in the hypoxia-induced regulation of the VLDLr promoter. Using a chromatin immunoprecipitation (ChIP) assay, we show that Hif-1α specifically binds and activates the mouse VLDLr promoter at the previously described non-classical HRE in HL-1 cells. We also show that the same HRE is present and active in response to hypoxia in human cardiomyocytes, however at a different location (−812bp from translation start). These results conclude that in the hypoxic hearts of mice and men, the VLDLr gene is regulated by a direct binding of Hif-1α to the VLDLr promoter.

Endoplasmic reticulum stress induces hepatic steatosis via increased expression of the hepatic very low‐density lipoprotein receptor

Recent evidence suggests that obese animals exhibit increased endoplasmic reticulum (ER) stress in the liver and adipose tissue. Although ER stress is closely associated with lipid homeostasis, it is largely unknown how ER stress contributes to hepatic steatosis. In this study, we demonstrate that the induction of ER stress stimulates hepatic steatosis through increased expression of the hepatic very low-density lipoprotein receptor (VLDLR). Among the unfolded protein response sensors, the protein kinase RNA-like ER kinase-activating transcription factor 4 signaling pathway was required for hepatic VLDLR up-regulation. In primary hepatocytes, ER stress-dependent VLDLR expression induced intracellular triglyceride accumulation in the presence of very low-density lipoprotein. Moreover, ER stress-dependent hepatic steatosis was diminished in the livers of VLDLR-deficient and apolipoprotein E-deficient mice compared with wild-type mice. In addition, the VLDLR-deficient mice exhibited decreased hepatic steatosis upon high-fat diet feeding. These data suggest that ER stress-dependent expression of hepatic VLDLR leads to hepatic steatosis by increasing lipoprotein delivery to the liver, which might be a novel mechanism explaining ER stress-induced hepatic steatosis.