Very Low Density Lipoprotein Receptor Research Articles

The VLDL receptor plays a key role in the metabolism of postprandial remnant lipoproteins

A new concept to account for the process of postprandial remnant lipoprotein metabolism is proposed based on the characteristics of lipoprotein particles and their receptors. The characteristics of remnant lipoprotein (RLP) were investigated using an immuno-separation method. The majority of the postprandial lipoproteins increased after fat intake was shown to be VLDL remnants, not chylomicron (CM) remnants, based on the significantly high ratio of apoB100/apoB48 in the RLP and the high degree of similarity in the particle size of the apoB48 and apoB100 carrying lipoproteins, which fluctuate in parallel during a 6 h period after fat intake. The VLDL receptor was discovered as a receptor for TG-rich lipoprotein metabolism and is located in peripheral tissues such as skeletal muscle, adipose tissue, etc., but not in the liver. Postprandial VLDL particles are strongly bound and internalized into cells expressing the VLDL receptor. Ligands that bind to VLDL receptor, such as LPL and Lp(a), present in RLP. The presence of various specific ligands in VLDL remnants may enhance the capacity for binding to the VLDL receptor, which play the role primarily for energy delivery to the peripheral tissues, but is also a causal factor in atherogenic diseases when excessively and/or continuously remained in plasma.

Pharmacological PPARβ/δ activation upregulates VLDLR in hepatocytes

The very low-density lipoprotein receptor (VLDLR) plays an important function in the control of serum triglycerides and in the development of non-alcoholic fatty liver disease (NAFLD). In this study, we investigated the role of peroxisome proliferator-activated receptor (PPAR)β/δ activation in hepatic VLDLR regulation. Treatment of mice fed a high-fat diet with the PPARβ/δ agonist GW501516 increased the hepatic expression of Vldlr. Similarly, exposure of human Huh-7 hepatocytes to GW501516 increased the expression of VLDLR and triglyceride accumulation, the latter being prevented by VLDLR knockdown. Finally, treatment with another PPARβ/δ agonist increased VLDLR levels in the liver of wild-type mice, but not PPARβ/δ-deficient mice, confirming the regulation of hepatic VLDLR by this nuclear receptor. Our results suggest that upregulation of hepatic VLDLR by PPARβ/δ agonists might contribute to the hypolipidemic effect of these drugs by increasing lipoprotein delivery to the liver. Overall, these findings provide new effects by which PPARβ/δ regulate VLDLR levels and may influence serum triglyceride levels and NAFLD development.

Reelin: Diverse roles in central nervous system development, health and disease.

Over the past 20 years the structure and function of Reelin, an extracellular glycoprotein with a role in cell migration and positioning during development has been elucidated. Originally discovered in mice exhibiting a peculiar gait and hypoplastic cerebellar tissue, Reelin is secreted from Cajal-Retzius neurons during embryonic life and has been shown to act as a stop signal, guiding migrating radial neurons in a gradient-dependent manner. Reelin carries out its function by binding to the receptors, very low-density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2) resulting in the phosphorylation of the intracellular protein Disabled-1 (Dab-1) which is essential for effective Reelin signaling. Abnormalities in the RELN gene can result in multiple unusual structural outcomes including disruption of cortical layers, heterotopia, polymicrogyria and lissencephaly. Recent research has suggested a potential role for Reelin in the pathogenesis of neurological diseases such as schizophrenia, autism and Alzheimer's disease. This short review will address the current understanding of the structure and function of this protein and its emerging role in the development of neurological disorders.

Pharmacological PPARβ/δ activation upregulates VLDLR in hepatocytes

The very low-density lipoprotein receptor (VLDLR) plays an important function in the control of serum triglycerides and in the development of non-alcoholic fatty liver disease (NAFLD). In this study, we investigated the role of peroxisome proliferator-activated receptor (PPAR)β/δ activation in hepatic VLDLR regulation. Treatment of mice fed a high-fat diet with the PPARβ/δ agonist GW501516 increased the hepatic expression of Vldlr. Similarly, exposure of human Huh-7 hepatocytes to GW501516 increased the expression of VLDLR and triglyceride accumulation, the latter being prevented by VLDLR knockdown. Finally, treatment with another PPARβ/δ agonist increased VLDLR levels in the liver of wild-type mice, but not PPARβ/δ-deficient mice, confirming the regulation of hepatic VLDLR by this nuclear receptor. Our results suggest that upregulation of hepatic VLDLR by PPARβ/δ agonists might contribute to the hypolipidemic effect of these drugs by increasing lipoprotein delivery to the liver. Overall, these findings provide new effects by which PPARβ/δ regulate VLDLR levels and may influence serum triglyceride levels and NAFLD development.

Differential Action of Reelin on Oligomerization of ApoER2 and VLDL Receptor in HEK293 Cells Assessed by Time-Resolved Anisotropy and Fluorescence Lifetime Imaging Microscopy.

The canonical Reelin signaling cascade regulates correct neuronal layering during embryonic brain development. Details of this pathway are still not fully understood since the participating components are highly variable and create a complex mixture of interacting molecules. Reelin is proteolytically processed resulting in five different fragments some of which carrying the binding site for two different but highly homologous receptors, apolipoprotein E receptor 2 (ApoER2) and very low density lipoprotein receptor (VLDLR). The receptors are expressed in different variants in different areas of the developing brain. Binding of Reelin and its central fragment to the receptors results in phosphorylation of the intracellular adapter disabled-1 (Dab1) in neurons. Here, we studied the changes of the arrangement of the receptors upon Reelin binding and its central fragment at the molecular level in human embryonic kidney 293 (HEK293) cells by time-resolved anisotropy and fluorescence lifetime imaging microscopy (FLIM). In the off-state of the pathway ApoER2 and VLDLR form homo or hetero-di/oligomers. Upon binding of full length Reelin ApoER2 and VLDLR homo-oligomers are rearranged to higher order receptor clusters which leads to Dab1 phosphorylation. When the central fragment of Reelin binds to the receptors the cluster size of homo-oligomers is not affected and Dab1 is not phosphorylated. Hetero-oligomerization, however, can be induced, but does not lead to Dab1 phosphorylation. Cells expressing only ApoER2 or VLDLR change their shape when stimulated with the central fragment. Cells expressing ApoER2 produce filopodia/lamellipodia and cell size increases, whereas VLDLR-expressing cells decrease in size. These findings demonstrate that the primary event in the canonical Reelin pathway is the rearrangement of preformed receptor homo-oligomers to higher order clusters. In addition the possibility of yet another signaling mechanism which is mediated by the central Reelin fragment independent of Dab1 phosphorylation became apparent.

Proteomic profile of TGF-β1 treated lung fibroblasts identifies novel markers of activated fibroblasts in the silica exposed rat lung

We performed liquid chromatography-tandem mass spectrometry (LC-MS/MS) on control and TGF-β1-exposed rat lung fibroblasts to identify proteins differentially expressed between cell populations. A total of 196 proteins were found to be differentially expressed in response to TGF-β1 treatment. Guided by these results, we next determined whether similar changes in protein expression were detectable in the rat lung after chronic exposure to silica dust. Of the five proteins selected for further analysis, we found that levels of all proteins were markedly increased in the silica-exposed rat lung, including the proteins for the very low density lipoprotein receptor (VLDLR) and the transmembrane (type I) heparin sulfate proteoglycan called syndecan 2 (SDC2). Because VLDLR and SDC2 have not, to our knowledge, been previously linked to the pathobiology of silicosis, we next examined whether knockdown of either gene altered responses to TGF-β1 in MRC-5 lung fibroblasts. Interestingly, we found knockdown of either VLDLR or SDC2 dramatically reduced collagen production to TGF-β1, suggesting that both proteins might play a novel role in myofibroblast biology and pathogenesis of silica-induced pulmonary fibrosis. In summary, our findings suggest that performing LC-MS/MS on TGF-β1 stimulated lung fibroblasts can uncover novel molecular targets of activated myofibroblasts in silica-exposed lung.

Turkish family with Dysequilibrium syndrome with a novel mutation in the VLDLR gene.

Background: A very few diseases are reported caused due to cerebellar hypoplasia and neuronal migration defects like pachygyria. Cerebellar Ataxia, mental retardation, and Dysequilibrium Syndrome 1 (DES) (OMIM # 224050) are one among such group of diseases. DES is caused due to a homozygous mutation in the VLDLR gene involved majorly in neuronal migration. Case Presentation: Two members (siblings) from a Turkish family presented with neuromotor developmental delay, moderate learning disability, delayed psychosocial development and strabismus complaints. Whole exome sequencing (WES) was performed as consanguinity existed between the parents and specific pre-diagnosis could not provide a satisfactory conclusion for the patients. WES revealed a homozygote novel mutation in the VLDLR gene. Conclusion: Evaluation of WES data resembled a process of finding a needle in a haystack; therefore, the present study recommended clinical information and anamnesis to be very important in understanding and interpreting the WES result.

DCA can improve the ACI-induced neurological impairment through negative regulation of Nrf2 signaling pathway.

To investigate the effect of tauroursodeoxycholic acid (TUDCA) on neurological impairment induced by acute cerebral infarction (ACI) and its relevant mechanism of action. A total of 60 male Sprague-Dawley (SD) rats were randomly divided into Sham group (n = 20), ACI group (n = 20), and TUDCA group (n = 20). The rat model of ACI in middle cerebral artery was established. TUDCA was intravenously injected into rats in the TUDCA group, while an equal amount of sodium bicarbonate solution was intravenously injected into the other two groups. The blood was drawn after modeling to detect the content of serum glutamate (Glu), triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C). The degree of cerebral infarction in each experimental group was observed under an optical microscope, and the infarct area was measured and compared. The content of serum tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and high-sensitivity C-reactive protein (hs-CRP) was detected via enzyme-linked immunosorbent assay (ELISA); mRNA and protein expressions of them were detected using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively, followed by statistical analysis. Moreover, the expression levels of serum malondialdehyde (MDA), oxidized-LDL (ox-LDL), superoxide dismutase (SOD), and glutathione peroxidase (GPX) were detected, followed by statistical analysis. The protein expressions of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), very low-density lipoprotein receptor (VLDLR), nuclear factor-κB (NF-κB), B-cell lymphoma 2-associated X protein (Bax), and caspase-3 were detected via Western blotting, and the gray value was determined, followed by statistical analysis. TUDCA could improve the symptoms of neurological impairment in ACI patients, decrease the National Institute of Health Stroke Scale (NIHSS) score but increase the activity of daily living (ADL) score of patients, and significantly reduce the content of serum TG, TC, and LDL-C, showing statistically significant differences (p < 0.05). TUDCA significantly decreased the serum Glu content in ACI rats, reduced the cerebral infarction area and lowered the serum TG, TC, and LDL-C content, displaying statistically significant differences (p < 0 .05). Besides, TUDCA inhibited mRNA and protein expressions of TNF-α, IL-8, and hs-CRP, and alleviated the inflammatory response. TUDCA inhibited MDA and ox-LDL expressions, but increased SOD and GPX expressions, and relieved oxidative stress injury. In addition, TUDCA could negatively regulate Nrf2 signaling pathway, and down-regulated VLDLR and NF-κB protein expressions and expressions of apoptotic proteins (Bax and caspase-3). TUDCA can alleviate the ACI-induced neurological impairment in rats through mitigating lipid peroxidation and inflammatory response and reducing apoptosis, whose relevant mechanism may be that TUDCA negatively regulates Nrf2 signaling pathway.

The Reelin Receptors Apolipoprotein E receptor 2 (ApoER2) and VLDL Receptor.

Apolipoprotein E receptor 2 (ApoER2) and VLDL receptor belong to the low density lipoprotein receptor family and bind apolipoprotein E. These receptors interact with the clathrin machinery to mediate endocytosis of macromolecules but also interact with other adapter proteins to perform as signal transduction receptors. The best characterized signaling pathway in which ApoER2 and VLDL receptor (VLDLR) are involved is the Reelin pathway. This pathway plays a pivotal role in the development of laminated structures of the brain and in synaptic plasticity of the adult brain. Since Reelin and apolipoprotein E, are ligands of ApoER2 and VLDLR, these receptors are of interest with respect to Alzheimer’s disease. We will focus this review on the complex structure of ApoER2 and VLDLR and a recently characterized ligand, namely clusterin.

Reelin Can Modulate Migration of Olfactory Ensheathing Cells and Gonadotropin Releasing Hormone Neurons via the Canonical Pathway.

One key signaling pathway known to influence neuronal migration involves the extracellular matrix protein Reelin. Typically, signaling of Reelin occurs via apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VLDLR), and the cytoplasmic adapter protein disabled 1 (Dab1). However, non-canonical Reelin signaling has been reported, though no receptors have yet been identified. Cariboni et al. (2005) indicated Dab1-independent Reelin signaling impacts gonadotropin releasing hormone-1 (GnRH) neuronal migration. GnRH cells are essential for reproduction. Prenatal migration of GnRH neurons from the nasal placode to the forebrain, juxtaposed to olfactory axons and olfactory ensheathing cells (OECs), has been well documented, and it is clear that alterations in migration of these cells can cause delayed or absent puberty. This study was initiated to delineate the non-canonical Reelin signaling pathways used by GnRH neurons. Chronic treatment of nasal explants with CR-50, an antibody known to interfere with Reelin homopolymerization and Dab1 phosphorylation, decreased the distance GnRH neurons and OECs migrated. Normal migration of these two cell types was observed when Reelin was co-applied with CR-50. Immunocytochemistry was performed to determine if OECs might transduce Reelin signals via the canonical pathway, and subsequently indirectly altering GnRH neuronal migration. We show that in mouse: (1) both OECs and GnRH cells express ApoER2, VLDLR and Dab1, and (2) GnRH neurons and OECs show a normal distribution in the brain of two mutant reeler lines. These results indicate that the canonical Reelin pathway is present in GnRH neurons and OECs, but that Reelin is not essential for development of these two systems in vivo.

Nuclear Magnetic Resonance Solution Structure of the Recombinant Fragment Containing Three Fibrin-Binding Cysteine-Rich Domains of the Very Low Density Lipoprotein Receptor.

Our previous studies revealed that interaction of fibrin with the very low density lipoprotein (VLDL) receptor plays a prominent role in transendothelial migration of leukocytes and thereby inflammation. The major goal of our subsequent studies is to establish the structural basis for this interaction. As the first step toward this goal, we localized the fibrin-binding sites within cysteine-rich (CR) domains 2-4 of the VLDL receptor. In this study, we have made a next step toward this goal by establishing the nuclear magnetic resonance solution structure of the recombinant VLDLR(2-4) fragment containing all three fibrin-binding CR domains of this receptor. The structure revealed that all three CR domains have a similar general fold. Each domain contains a calcium-binding loop, and the loop in the CR3 domain has a unique conformation relative to the other two. Domains CR2 and CR3 interact with each other, while CR4 is flexible relative to the other two domains. In addition, analysis of the electrostatic potential surface of VLDLR(2-4) revealed extended negatively charged regions in each of its CR domains. The presence of these regions suggests that they may interact with three positively charged clusters of the fibrin βN domain whose involvement in interaction with the VLDL receptor was demonstrated earlier. Altogether, these findings provide a solid background for our next step toward establishing the structural basis for fibrin-VLDL receptor interaction.

Roles of Adipose Tissue VLDL-VLDLR Axis in Energy Metabolism

Elevated plasma triglyceride-rich lipoprotein, such as very low-density lipoprotein (VLDL), is considered a risk factor for prevalence of obesity, type 2 diabetes mellitus, and atherosclerosis. VLDL receptor (VLDLR), one of the lipoprotein receptor family proteins, is involved in clearance of circulating VLDL. In obese animals, adipose tissue macrophages (ATMs) contain high level of lipid metabolites, which seems to be linked to pro-inflammatory responses. However, it has not been thoroughly understood whether lipid uptake via VLDLR in macrophages is involved in obesity-induced inflammatory responses and insulin resistance. In this study, we demonstrate that elevated VLDLR in ATMs could accelerate adipose tissue inflammation and glucose intolerance in obesity. Expression of VLDLR was increased in ATMs from obese mice. In VLDL-treated macrophages, the level of ceramides was elevated through VLDLR, which potentiates pro-inflammatory responses and augments M1-like macrophage polarization. Moreover, adoptive transfer of VLDLR knockout bone marrow to wild type mice relieved adipose tissue inflammation and improved insulin resistance in diet-induced obesity. Taken together, these findings suggest that increased VLDL-VLDLR axis in ATMs would aggravate adipose tissue inflammation and insulin resistance in obesity. Disclosure J. Kim: None. K. Shin: None. I. Hwang: None. S. Choe: None.

Prenatal Lipopolysaccharide Exposure Promotes Dyslipidemia in the Male Offspring Rats.

Inflammation is critical to the pathogenesis of cardiovascular diseases (CVDs). We have uncovered intrauterine inflammation induced by lipopolysaccharide (LPS) increases CVDs in adult offspring rats. The present study aimed to explore the role of prenatal exposure to LPS on the lipid profiles in male offspring rats and to further assess their susceptibility to high fat diet (HFD). Maternal LPS (0.79 mg/kg) exposure produced a significant increase in serum and hepatic levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol, aspartate amino transferase as well as liver morphological abnormalities in 8-week-old offspring rats. Meanwhile, disturbed gene expressions involved in hepatic lipid metabolism and related signaling pathways were found, especially the up-regulated very-low density lipoprotein receptor (VLDLR) and down-regulated transmembrane 7 superfamily member 2 (TM7SF2). Following HFD treatment, however, the lipid profile shifts and liver dysfunction were exacerbated compared to the offsprings treated with prenatal LPS exposure alone. Compared with that in control offsprings, the hepatic mitochondria (Mt) in offspring rats solely treated with HFD exhibited remarkably higher ATP level, enforced Complex IV expression and a sharp reduction of its activity, whereas the offsprings from LPS-treated dams showed the loss of ATP content, diminished membrane potential, decline in protein expression and activity of mitochondrial respiratory complex IV, increased level of MtDNA deletion as well. Furthermore, treatment with HFD deteriorated these mitochondrial disorders in the prenatally LPS-exposed offspring rats. Taken together, maternal LPS exposure reinforces dyslipidemia in response to a HFD in adult offsprings, which should be associated with mitochondrial abnormalities and disturbed gene expressions of cholesterol metabolism.

The VLDL receptor regulates membrane progesterone receptor trafficking and non-genomic signaling.

Progesterone mediates its physiological functions through activation of both transcription-coupled nuclear receptors and seven-pass-transmembrane progesterone receptors (mPRs), which transduce the rapid non-genomic actions of progesterone by coupling to various signaling modules. However, the immediate mechanisms of action downstream of mPRs remain in question. Herein, we use an untargeted quantitative proteomics approach to identify mPR interactors to better define progesterone non-genomic signaling. Surprisingly, we identify the very-low-density lipoprotein receptor (VLDLR) as an mPRβ (PAQR8) partner that is required for mPRβ plasma membrane localization. Knocking down VLDLR abolishes non-genomic progesterone signaling, which is rescued by overexpressing VLDLR. Mechanistically, we show that VLDLR is required for mPR trafficking from the endoplasmic reticulum to the Golgi. Taken together, our data define a novel function for the VLDLR as a trafficking chaperone required for the mPR subcellular localization and, as such, non-genomic progesterone-dependent signaling.This article has an associated First Person interview with the first author of the paper.

First person – Nancy Nader

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Nancy Nader is the first author on ‘The VLDL receptor regulates membrane progesterone receptor trafficking and non-genomic signaling’, published in Journal of Cell Science. Nancy is a research associate in the lab of Khaled Machaca at Weill Cornell Medical College in Qatar, Doha, Qatar, working on the characterisation of non-classical membrane progesterone receptors and the study of their pathways in different animal and tissue models.

Influence of Fatty Acid Modification on Uptake of Lovastatin-Loaded Reconstituted High Density Lipoprotein by Foam Cells.

Spherical reconstituted high density lipoprotein (rHDL) can target atherosclerotic lesions by the very low density lipoprotein (VLDL) receptor, which is seldom expressed in liver. By promoting this pathway, the targeting efficiency was hyphothesized to be improved due to avoiding undesired uptake in liver mediated by the scavenger receptor class B type I (SR-BI). In this study, how fatty acid modification in spherical rHDL influenced the VLDL receptor-mediated endocytosis pathway was investigated. Stearic acid (SA) and arachidonic acid (AA) with different saturation levels were utilized to modify the lovastatin-loaded rHDL (LS-rHDL). Phagocytosis test on foam cells with or without cholesteryl ester transfer protein (CETP) expression was conducted to observe the cellular uptake of the SA or AA modified rHDL and the non-modified one. Raman spectroscopy, guanidine hydrochloride (Gdn-HCl) denaturation experiment and in vitro evaluation of drug release were used to analyze the related mechanism. In comparison with the non-modified rHDL, AA modification could reduce the packing order of the rHDL phospholipid acyl chains, leading to the decreased apoA-I binding extent with lipid and the increased drug release, while the opposite was true for SA modification. The AA-modified rHDL exhibited a higher uptake of foam cells expressing CETP than the non-modified one, while the SA-modified one showed the lowest cellular uptake among the three rHDLs. Increased unsaturation level can facilitate lipid-interchange process where the cargo in rHDL core may transfer to VLDL more easily, and then promote the endocytosis mediated by the VLDL receptor.

In Vivo Characterization of Spontaneous Retinal Neovascularization in the Mouse Eye by Multifunctional Optical Coherence Tomography.

To investigate the early development of spontaneous retinal neovascularization in the murine retina by a multifunctional optical coherence tomography approach. To characterize involved tissue changes in vivo and describe structural and functional changes over time. A multifunctional optical coherence tomography (OCT) system providing 3-fold contrast comprising reflectivity, polarization sensitivity, and OCT angiography (OCTA) was utilized to image very-low-density lipoprotein receptor (VLDLR) knockout mice. Baseline measurements were acquired as early as postnatal day 14 and a follow-up of neovascularization development was performed until the age of 3 months. Control mice were imaged accordingly and a multiparametric image analysis was performed to characterize different stages of pathologic vascular growth. Histology was conducted at the endpoint of the experiment. An interventional pilot experiment was conducted to investigate the effect of the anti-vascular endothelial growth factor (VEGF) agent aflibercept on the development of retinal neovascularization. Onset of neovascularization was imaged at baseline, and significant changes were encountered in the retina over time, including reduced retinal thickness, increase of lesion volume, migration of pigmented structures, and presence of abnormal blood flow in the outer retina. Multifunctional image contrast was correlated to ex vivo histology. Microscopic analysis of retinal flat mounts and cross-sectional samples confirmed the changes observed in in vivo structural and functional OCT images. Administration of an anti-VEGF agent resulted in a significantly reduced lesion volume. Longitudinal, multifunctional OCT imaging of infant VLDLR-/- mouse retinas enabled a multiparametric, in vivo staging of neovascularization formation from before lesion onset until their manifestation.

White light polarization sensitive optical coherence tomography for sub-micron axial resolution and spectroscopic contrast in the murine retina.

A white light polarization sensitive optical coherence tomography system has been developed, using a supercontinuum laser as the light source. By detecting backscattered light from 400 – 700 nm, an axial resolution of 1.0 µm in air was achieved. The system consists of a free-space interferometer and two homemade spectrometers that detect orthogonal polarization states. Following system specifications, images of a healthy murine retina as acquired by this non-contact system are presented, showing high resolution reflectivity images as well as spectroscopic and polarization sensitive contrast. Additional images of the very-low-density-lipoprotein-receptor (VLDLR) knockout mouse model were acquired. The high resolution allows the detection of small lesions in the retina.

Chronic fructose intake does not induce liver steatosis and inflammation in female Sprague-Dawley rats, but causes hypertriglyceridemia related to decreased VLDL receptor expression.

Sugar-sweetened beverage intake is a risk factor for insulin resistance, dyslipidemia, fatty liver, and steatohepatitis (NASH). Sub-chronic supplementation of liquid fructose, but not glucose, in female rats increases liver and plasma triglycerides without inflammation. We hypothesized that chronic supplementation of fructose would cause NASH and liver insulin resistance. We supplemented female Sprague-Dawley rats with water or either fructose or glucose 10% w/v solutions under isocaloric conditions for 7months. At the end, plasma analytes, insulin, and adiponectin were determined, as well as liver triglyceride content and the expression of key genes controlling inflammation, fatty acid synthesis and oxidation, endoplasmic reticulum stress, and plasma VLDL clearance, by biochemical and histological methods. Although sugar-supplemented rats increased their energy intake by 50-60%, we found no manifestation of liver steatosis, fibrosis or necrosis, unchanged plasma or tissue markers of inflammation or fibrosis, and reduced liver expression of gluconeogenic enzymes, despite both sugars increased fatty acid synthesis, mTORC1, and IRE1 activity, while decreasing fatty acid oxidation and PPARα activity. Only fructose-supplemented rats were hypertriglyceridemic, showing a reduced expression of VLDL receptor and lipoprotein lipase in skeletal muscle and vWAT. Glucose-supplemented rats showed increased adiponectinemia, which would explain the different metabolic outcomes of the two sugars. Chronic liquid simple sugar supplementation, as the sole risk factor, is not enough for female rats to develop NASH and increased liver gluconeogenesis. Nevertheless, under isocaloric conditions, only fructose induced hypertriglyceridemia, thus confirming that also the type of nutrient matters in the development of metabolic diseases.

Ethyl pyruvate can alleviate alcoholic liver disease through inhibiting Nrf2 signaling pathway.

The effects of ethyl pyruvate (EP) on alcoholic liver disease and its related mechanism were investigated. Thirty male C57/BL6 mice were randomly divided to three groups: Control (n=10), alcoholic liver disease (ALD, n=10) and ethyl pyruvate group (EP, n=10). EP group was treated with gavage using EP (100 mg/kg) for 15 consecutive days. Control and ALD group were treated with the same volume of normal saline. After the last gavage, EP and ALD group were treated with the intraperitoneal injection of 50% alcoholic solution (10 ml/kg). After that, ALD and EP group received the gavage using alcohol for 4 weeks, while Control group received the same volume of normal saline, and blood and liver tissues were taken for detection. Results showed that in this experimental study that EP could effectively alleviate the alcoholic liver disease. The levels of alanine aminotransferase (AST), triglycerides (TG), free fatty acid (FFA) and FBG in EP group were significantly lower than those in ALD group, but the number of platelets was reversed, and the differences were statistically significant; the levels of anti-inflammatory factors (TGF-β/IL-10) and superoxide dismutase (SOD) in EP were significantly higher than those in ALP group, but the levels of pro-inflammatory factors (IL-6/TNF-α) and MDA were significantly lower than those in ALP group. EP upregulated CYP2E1, downregulated PPAR-α, nuclear factor 2 (Nrf2) and very-low density lipoprotein receptor (VLDLR), positively regulated the CYP2E1-PPAR-α-ROS signaling pathway and negatively regulated the ROS-Nrf2-VLDLR signaling pathway. EP can increase anti-inflammatory factors and decrease pro-inflammatory factors, enhance the activity of SOD and reduce FFA and TG. Moreover, it can upregulate the PPAR-α expression by negative regulation of CYP2E1-PPAR-α signaling pathway and downregulate the Nrf2 expression by negative regulation of Nrf2-VLDLR signaling pathway, thus alleviating the alcoholic liver disease.