Low-density Lipoprotein Receptor Knockout Research Articles

Mitochondrial DNA variants and microbiota: An experimental strategy to identify novel therapeutic potential in chronic inflammatory diseases

We previously demonstrated that mice carrying natural mtDNA variants of the FVB/NJ strain (m.7778G>T in the mt-Atp8 gene in mitochondrial complex V), namely C57BL/6J-mtFVB/NJ (B6-mtFVB), exhibited (i) partial protection from experimental skin inflammatory diseases in an anti-murine type VII collagen antibody-induced skin inflammation model and psoriasiform dermatitis model; (ii) significantly altered metabolites, including short-chain fatty acids, according to targeted metabolomics of liver, skin and lymph node samples; and (iii) a differential composition of the gut microbiota according to bacterial 16S rRNA gene sequencing of stool samples compared to wild-type C57BL/6J (B6) mice. To further dissect these disease-contributing factors, we induced an experimental antibody-induced skin inflammatory disease in gnotobiotic mice. We performed shotgun metagenomic sequencing of caecum contents and untargeted metabolomics of liver, CD4+ T cell, and caecum content samples from conventional B6-mtFVB and B6 mice. We identified D-glucosamine as a candidate mediator that ameliorated disease severity in experimental antibody-induced skin inflammation by modulating immune cell function in T cells, neutrophils and macrophages. Because mice carrying mtDNA variants of the FVB/NJ strain show differential disease susceptibility to a wide range of experimental diseases, including diet-induced atherosclerosis in low-density lipoprotein receptor knockout mice and collagen antibody-induced arthritis in DBA/1J mice, this experimental approach is valuable for identifying novel therapeutic options for skin inflammatory conditions and other chronic inflammatory diseases to which mice carrying specific mtDNA variants show differential susceptibility.

Resident Memory T Cells in the Atherosclerotic Lesion Associate With Reduced Macrophage Content and Increased Lesion Stability.

Tissue resident memory T (TRM) cells are a T-cell subset that resides at the site of prior antigen recognition to protect the body against reoccurring encounters. Besides their protective function, TRM cells have also been implicated in inflammatory disorders. TRM cells are characterized by the expression of CD69 and transcription factors Hobit (homolog of Blimp-1 [B lymphocyte-induced maturation protein 1] in T cells) and Blimp-1. As the majority of T cells in the arterial intima expresses CD69, TRM cells may contribute to the pathogenesis of atherosclerosis as well. Here, we aimed to assess the presence and potential role of TRM cells in atherosclerosis. To identify TRM cells in human atherosclerotic lesions, a single-cell RNA-sequencing data set was interrogated, and T-cell phenotypes were compared with that of integrated predefined TRM cells. The presence and phenotype of TRM in atherosclerotic lesions was corroborated using a mouse model that enabled tracking of Hobit-expressing TRM cells. To explore the function of TRM cells during atherogenesis, RAG1-/- (RAG1 deficient) LDLr-/- (low-density lipoprotein receptor knockout) mice received a bone marrow transplant from HobitKO/CREBlimp-1flox/flox mice, which exhibit abrogated TRM cell formation, whereafter the mice were fed a Western-type diet for 10 weeks. Human atherosclerotic lesions contained T cells that exhibited a TRM cell-associated gene signature. Moreover, a fraction of these T cells clustered together with predefined TRM cells upon integration. The presence of Hobit-expressing TRM cells in the atherosclerotic lesion was confirmed in mice. These lesion-derived TRM cells were characterized by the expression of CD69 and CD49α. Moreover, we demonstrated that this small T-cell subset significantly affects lesion composition, by reducing the amount of intralesional macrophages and increasing collagen content. TRM cells, characterized by the expression of CD69 and CD49α, constitute a minor population in atherosclerotic lesions and are associated with increased lesion stability in a Hobit and Blimp-1 knockout mouse model.

Recombinant human proteoglycan 4 lowers inflammation and atherosclerosis susceptibility in female low-density lipoprotein receptor knockout mice.

Recombinant human proteoglycan 4 (rhPRG4) is a macromolecular mucin-like glycoprotein that is classically studied as a lubricant within eyes and joints. Given that endogenously produced PRG4 is present within atherosclerotic lesions and genetic PRG4 deficiency increases atherosclerosis susceptibility in mice, in the current study we investigated the anti-atherogenic potential of chronic rhPRG4 treatment. Female low-density lipoprotein receptor knockout mice were fed an atherogenic Western-type diet for 6 weeks and injected three times per week intraperitoneally with 0.5mg rhPRG4 or PBS as control. Treatment with rhPRG4 was associated with a small decrease in plasma-free cholesterol levels, without a change in cholesteryl ester levels. A marked increase in the number of peritoneal foam cells was detected in response to the peritoneal rhPRG4 administration, which could be attributed to elevated peritoneal leukocyte MSR1 expression levels. However, rhPRG4-treated mice exhibited significantly smaller aortic root lesions of 278 ± 21 × 103μm2 compared with 339 ± 15 × 103μm2 in the aortic root of control mice. The overall decreased atherosclerosis susceptibility coincided with a shift in the monocyte and macrophage polarization states towards the patrolling and anti-inflammatory M2-like phenotypes, respectively. Furthermore, rhPRG4 treatment significantly reduced macrophage gene expression levels as well as plasma protein levels of the pro-inflammatory/pro-atherogenic cytokine TNF-alpha. In conclusion, we have shown that peritoneal administration and subsequent systemic exposure to rhPRG4 beneficially impacts the inflammatory state and reduces atherosclerosis susceptibility in mice. Our findings highlight that PRG4 is not only a lubricant but also acts as an anti-inflammatory agent. KEY POINTS: Endogenously produced proteoglycan 4 is found in atherosclerotic lesions and its genetic deficiency in mice is associated with enhanced atherosclerosis susceptibility. In this study we investigated the anti-atherogenic potential of chronic treatment with recombinant human PRG4 in hypercholesterolaemic female low-density lipoprotein receptor knockout mice. We show that recombinant human PRG4 stimulates macrophage foam cell formation, but also dampens the pro-inflammatory state of monocyte/macrophages, eventually leading to a significant reduction in plasma TNF-alpha levels and a lowered atherosclerosis susceptibility. Our findings highlight that peritoneal recombinant human PRG4 treatment can execute effects both locally and systemically and suggest that it will be of interest to study whether rhPRG4 treatment is also able to inhibit the progression and/or induce regression of previously established atherosclerotic lesions.

PCSK9 stimulates Syk, PKCδ, and NF-κB, leading to atherosclerosis progression independently of LDL receptor

Proprotein convertase subtilisin/kexin type-9 (PCSK9) binds to and degrades low-density lipoprotein (LDL) receptor, leading to increase of LDL cholesterol in blood. Its blockers have emerged as promising therapeutics for cardiovascular diseases. Here we show that PCSK9 itself directly induces inflammation and aggravates atherosclerosis independently of the LDL receptor. PCSK9 exacerbates atherosclerosis in LDL receptor knockout mice. Adenylyl cyclase-associated protein 1 (CAP1) is the main binding partner of PCSK9 and indispensable for the inflammatory action of PCSK9, including induction of cytokines, Toll like receptor 4, and scavenger receptors, enhancing the uptake of oxidized LDL. We find spleen tyrosine kinase (Syk) and protein kinase C delta (PKCδ) to be the key mediators of inflammation after PCSK9-CAP1 binding. In human peripheral blood mononuclear cells, serum PCSK9 levels are positively correlated with Syk, PKCδ, and p65 phosphorylation. The CAP1-fragment crystallizable region (CAP1-Fc) mitigates PCSK9-mediated inflammatory signal transduction more than the PCSK9 blocking antibody evolocumab does.

In vivo chronic exposure to inorganic mercury worsens hypercholesterolemia, oxidative stress and atherosclerosis in the LDL receptor knockout mice

Heavy metal exposure leads to multiple system dysfunctions. The mechanisms are likely multifactorial and involve inflammation and oxidative stress. The aim of this study was to evaluate markers and risk factors for atherosclerosis in the LDL receptor knockout mouse model chronically exposed to inorganic mercury (Hg) in the drinking water. Results revealed that Hg exposed mice present increased plasma levels of cholesterol, without alterations in glucose. As a major source and target of oxidants, we evaluated mitochondrial function. We found that liver mitochondria from Hg treated mice show worse respiratory control, lower oxidative phosphorylation efficiency and increased H2O2 release. In addition, Hg induced mitochondrial membrane permeability transition. Erythrocytes from Hg treated mice showed a 50% reduction in their ability to take up oxygen, lower levels of reduced glutathione (GSH) and of antioxidant enzymes (SOD, catalase and GPx). The Hg treatment disturbed immune system cells counting and function. While lymphocytes were reduced, monocytes, eosinophils and neutrophils were increased. Peritoneal macrophages from Hg treated mice showed increased phagocytic activity. Hg exposed mice tissues present metal impregnation and parenchymal architecture alterations. In agreement, increased systemic markers of liver and kidney dysfunction were observed. Plasma, liver and kidney oxidative damage indicators (MDA and carbonyl) were increased while GSH and thiol groups were diminished by Hg exposure. Importantly, atherosclerotic lesion size in the aorta root of Hg exposed mice were larger than in controls. In conclusion, in vivo chronic exposure to Hg worsens the hypercholesterolemia, impairs mitochondrial bioenergetics and redox function, alters immune cells profile and function, causes several tissues oxidative damage and accelerates atherosclerosis development.

Prior Exposure to Experimental Preeclampsia Increases Atherosclerotic Plaque Inflammation in Atherogenic Mice-Brief Report.

Women with a history of preeclampsia have evidence of premature atherosclerosis and increased risk of myocardial infarction and stroke compared with women who had a normotensive pregnancy. Whether this is due to common risk factors or a direct impact of prior preeclampsia exposure has never been tested in a mouse atherosclerosis model. Pregnant LDLR-KO (low-density lipoprotein receptor knockout; n=35) female mice were randomized in midgestation to sFlt1 (soluble fms-like tyrosine kinase 1)-expressing adenovirus or identical control adenovirus. Postpartum, mice were fed high-fat diet for 8 weeks to induce atherogenesis. Comparison between the control and preeclampsia models was made for metabolic parameters, atherosclerosis burden and composition by histology, plaque inflammation by flow cytometry, and aortic cytokines and inflammatory markers using a cytokine array. In pregnant LDLR-KO mice, sFlt1 adenovirus significantly induced serum sFlt1, blood pressure, renal endotheliosis, and decreased pup viability. After 8 weeks of postpartum high fat feeding, body weight, fasting glucose, plasma cholesterol, HDL (high-density lipoprotein), and LDL (low-density lipoprotein) were not significantly different between groups with no change in aortic root plaque size, lipid content, or necrotic core area. Flow cytometry demonstrated significantly increased CD45+ aortic arch leukocytes and CD3+T cells and aortic lysate contained more CCL (CC motif chemokine ligand) 22 and fetuin A and decreased expression of IGFBP6 (insulin-like growth factor-binding protein 6) and CCL21 in preeclampsia-exposed mice compared with controls. In atherogenic LDLR-KO mice, exposure to sFlt1-induced preeclampsia during pregnancy increases future atherosclerotic plaque inflammation, supporting the concept that preeclampsia directly exacerbates atherosclerotic inflammation independent of preexisting risk factors. This mechanism may contribute to ischemic vascular disease in women after preeclampsia pregnancy.

Atherosclerosis: an overview of mouse models and a detailed methodology to quantify lesions in the aortic root.

Cardiovascular disease, the primary cause of human mortality globally, is predominantly caused by a progressive disorder known as atherosclerosis. Atherosclerosis refers to the process of accumulation of cholesterol-enriched lipoproteins and the concomitant initiation of inflammatory processes in the arterial wall, including the recruitment of immune cells. This leads to the formation of atherosclerotic plaques, initially causing a thickening of the arterial wall and narrowing of arteries. However, as plaque formation progresses, atherosclerotic plaques may become unstable and rupture, leading to a blood clot that blocks the affected artery or travels through the blood to block blood flow elsewhere. In the early 1990s, emerging gene editing methods enabled the development of apolipoprotein E knockout (Apoe-/- ) and low-density lipoprotein receptor knockout (Ldlr-/- ) mice. These mice have been instrumental in unraveling the complex pathogenesis of atherosclerosis. Around the same time, human APOE*3-Leiden transgenic mice were generated, which were more recently cross-bred with human cholesteryl ester transfer protein (CETP) transgenic mice to generate APOE*3-Leiden.CETP mice. This model appears to closely mimic human lipoprotein metabolism and responds to classic lipid-lowering interventions due to an intact ApoE-LDLR pathway of lipoprotein remnant clearance. In this review, we describe the role of lipid metabolism and inflammation in atherosclerosis development and highlight the characteristics of the frequently used animal models to study atherosclerosis, with a focus on mouse models, discussing their advantages and limitations. Moreover, we present a detailed methodology to quantify atherosclerotic lesion area within the aortic root region of the murine heart, as well as details required for scoring atherosclerotic lesion severity based on guidelines of the American Heart Association adapted for mice.

Cav3.1 T-type calcium channel blocker NNC 55-0396 reduces atherosclerosis by increasing cholesterol efflux

Calcium channel blockers (CCBs) are commonly used as antihypertensive agents. While certain L-type CCBs exhibit antiatherogenic effects, the impact of Cav3.1 T-type CCBs on antiatherogenesis and lipid metabolism remains unexplored. NNC 55–0396 (NNC) is a highly selective blocker of T-type calcium channels (Cav3.1 channels). We investigated the effects of NNC on relevant molecules and molecular mechanisms in human THP-1 macrophages. Cholesterol efflux, an indicator of reverse cholesterol transport (RCT) efficiency, was assessed using [3H]-labeled cholesterol. In vivo, high cholesterol diet (HCD)-fed LDL receptor knockout (Ldlr-/-) mice, an atherosclerosis-prone model, underwent histochemical staining to analyze plaque burden. Treatment of THP-1 macrophages with NNC facilitated cholesterol efflux and reduced intracellular cholesterol accumulation. Pharmacological and genetic interventions demonstrated that NNC treatment or Cav3.1 knockdown significantly enhanced the protein expression of scavenger receptor B1 (SR-B1), ATP-binding cassette transporter A1 (ABCA1), ATP-binding cassette transporter G1 (ABCG1), and liver X receptor alpha (LXRα) transcription factor. Mechanistic analysis revealed that NNC activates p38 and c-Jun N-terminal kinase (JNK) phosphorylation, leading to increased expression of ABCA1, ABCG1, and LXRα-without involving the microRNA pathway. LXRα isrequired for NNC–induced ABCA1 and ABCG1 expression. Administering NNC diminished atherosclerotic lesion area and lipid deposition in HCD-fed Ldlr-/- mice. NNC's anti-atherosclerotic effects, achieved through enhanced cholesterol efflux and inhibition of lipid accumulation, suggest a promising therapeutic approach for hypertensive patients with atherosclerosis. This research highlights the potential of Cav3.1 T-type CCBs in addressing cardiovascular complications associated with hypertension.

Osteocalcin protects islet identity in low-density lipoprotein receptor knockout mice on high-fat diet.

Metabolic syndrome (MetS) is an increasing global health threat and strong risk factor for type 2 diabetes (T2D). MetS causes both hyperinsulinemia and islet size overexpansion, and pancreatic β-cell failure impacts insulin and proinsulin secretion, mitochondrial density, and cellular identity loss. The low-density lipoprotein receptor knockout (LDLr-/-) model combined with high-fat diet (HFD) has been used to study alterations in multiple organs, but little is known about the changes to β-cell identity resulting from MetS. Osteocalcin (OC), an insulin-sensitizing protein secreted by bone, shows promising impact on β-cell identity and function. LDLr-/- mice at 12 months were fed chow or HFD for 3 months ± 4.5 ng/h OC. Islets were examined by immunofluorescence for alterations in nuclear Nkx6.1 and PDX1 presence, insulin-glucagon colocalization, islet size and %β-cell and islet area by insulin and synaptophysin, and mitochondria fluorescence intensity by Tomm20. Bone mineral density (BMD) and %fat changes were examined by Piximus Dexa scanning. HFD-fed mice showed fasting hyperglycemia by 15 months, increased weight gain, %fat, and fasting serum insulin and proinsulin; concurrent OC treatment mitigated weight increase and showed lower proinsulin-to-insulin ratio, and higher BMD. HFD increased %β and %islet area, while simultaneous OC-treatment with HFD was comparable to chow-fed mice. Significant reductions in nuclear PDX1 and Nkx6.1 expression, increased insulin-glucagon colocalization, and reduction in β-cell mitochondria fluorescence intensity were noted with HFD, but largely prevented with OC administration. OC supplementation here suggests a benefit to β-cell identity in LDLr-/- mice and offers intriguing clinical implications for countering metabolic syndrome.

The Apolipoprotein E neutralizing antibody inhibits SARS-CoV-2 infection by blocking cellular entry of lipoviral particles.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causal agent for coronavirus disease 2019 (COVID-19). Although vaccines have helped to prevent uncontrolled viral spreading, our understanding of the fundamental biology of SARS-CoV-2 infection remains insufficient, which hinders effective therapeutic development. Here, we found that Apolipoprotein E (ApoE), a lipid binding protein, is hijacked by SARS-CoV-2 for infection. Preincubation of SARS-CoV-2 with a neutralizing antibody specific to ApoE led to inhibition of SARS-CoV-2 infection. The ApoE neutralizing antibody efficiently blocked SARS-CoV-2 infection of human iPSC-derived astrocytes and air-liquid interface organoid models in addition to human ACE2-expressing HEK293T cells and Calu-3 lung cells. ApoE mediates SARS-CoV-2 entry through binding to its cellular receptors such as the low density lipoprotein receptor (LDLR). LDLR knockout or ApoE mutations at the receptor binding domain or an ApoE mimetic peptide reduced SARS-CoV-2 infection. Furthermore, we detected strong membrane LDLR expression on SARS-CoV-2 Spike-positive cells in human lung tissues, whereas no or low ACE2 expression was detected. This study provides a new paradigm for SARS-CoV-2 cellular entry through binding of ApoE on the lipoviral particles to host cell receptor(s). Moreover, this study suggests that ApoE neutralizing antibodies are promising antiviral therapies for COVID-19 by blocking entry of both parental virus and variants of concern.

Generation of a familial hypercholesterolemia model in non-human primate

Familial hypercholesterolemia (FH) is an inherited autosomal dominant disorder that is associated with a high plasma level of low-density lipoprotein (LDL) cholesterol, leading to an increased risk of cardiovascular diseases. To develop basic and translational research on FH, we here generated an FH model in a non-human primate (cynomolgus monkeys) by deleting the LDL receptor (LDLR) gene using the genome editing technique. Six LDLR knockout (KO) monkeys were produced, all of which were confirmed to have mutations in the LDLR gene by sequence analysis. The levels of plasma cholesterol and triglyceride were quite high in the monkeys, and were similar to those in FH patients with homozygous mutations in the LDLR gene. In addition, periocular xanthoma was observed only 1 year after birth. Lipoprotein profile analysis showed that the plasma very low-density lipoprotein and LDL were elevated, while the plasma high density lipoprotein was decreased in LDLR KO monkeys. The LDLR KO monkeys were also strongly resistant to medications for hypercholesterolemia. Taken together, we successfully generated a non-human primate model of hypercholesterolemia in which the phenotype is similar to that of homozygous FH patients.

Microglia contribute to cognitive decline in hypercholesterolemic LDLr-/- mice.

Familial hypercholesterolemia (FH) is caused by mutations in the gene that encodes the low-density lipoprotein (LDL) receptor, which leads to an excessive increase in plasma LDL cholesterol levels. Previous studies have shown that FH is associated with gliosis, blood-brain barrier dysfunction, and memory impairment, but the mechanisms associated with these events are still not fully understood. Therefore, we aimed to investigate the role of microgliosis in the neurochemical and behavioral changes associated with FH using LDL receptor knockout (LDLr-/- ) mice. We noticed that microgliosis was more severe in the hippocampus of middle-aged LDLr-/- mice, which was accompanied by microglial morphological changes and alterations in the immunocontent of synaptic protein markers. At three months of age, the LDLr-/- mice already showed increased microgliosis and decreased immunocontent of claudin-5 in the prefrontal cortex (PFC). Subsequently, 6-month-old male C57BL/6 wild-type and LDLr-/- mice were treated once daily for 30 days with minocycline (a pharmacological inhibitor of microglial cell reactivity) or vehicle (saline). Adult LDLr-/- mice displayed significant hippocampal memory impairment, which was ameliorated by minocycline treatment. Non-treated LDLr-/- mice showed increased microglial density in all hippocampal regions analyzed, a process that was not altered by minocycline treatment. Region-specific microglial morphological analysis revealed different effects of genotype or minocycline treatment on microglial morphology, depending on the hippocampal subregion analyzed. Moreover, 6-month-old LDLr-/- mice exhibited a slight but not significant increase in IBA-1 immunoreactivity in the PFC, which was reduced by minocycline treatment without altering microglial morphology. Minocycline treatment also reduced the presence of microglia within the perivascular area in both the PFC and hippocampus of LDLr-/- mice. However, no significant effects of either genotype or minocycline treatment were observed regarding the phagocytic activity of microglia in the PFC and hippocampus. Our results demonstrate that hippocampal microgliosis, microglial morphological changes, and the presence of these glial cells in the perivascular area, but not increased microglial phagocytic activity, are associated with cognitive deficits in a mouse model of FH.

Metyrapone Treatment Protects Low-Density Lipoprotein Receptor Knockout Mice against Hypercorticosteronemia Development without Changing Atherosclerosis Susceptibility.

The steroid 11beta-hydroxylase inhibitor metyrapone is able to effectively reverse the hypercortisolemia detected in human Cushing's Syndrome patients. In this current preclinical study, we investigated whether metyrapone monotherapy can also reverse the hypercortisolemia-associated increase in atherosclerotic cardiovascular disease risk. In this instance, female low-density lipoprotein receptor knockout mice fed a cholic acid-containing high cholesterol/high fat diet to induce the development of hypercorticosteronemia and atherosclerotic lesions were treated twice daily with 100 mg/kg metyrapone for 4 weeks. Metyrapone effectively protected against hypercorticosteronemia development with endpoint plasma corticosterone levels remaining 43% lower than in controls (p < 0.01). Gene expression analysis in livers and adrenals validated that glucocorticoid receptor signaling was also reduced. Importantly, metyrapone treatment did not impact plasma cholesterol levels or alter atherosclerotic plaque areas or lesional collagen contents. However, metyrapone induced significant systemic lymphocytopenia as evident from marked decreases in splenic white pulp contents and thymus weights (-48% and -41%, respectively; p < 0.001). In conclusion, we have shown that treatment with metyrapone diminishes hypercorticosteronemia without affecting atherosclerosis susceptibility in cholic acid-containing high cholesterol/high fat diet-fed low-density lipoprotein receptor knockout mice. These preclinical findings highlight that restoring plasma glucocorticoid levels to normal is not necessarily sufficient to overcome the cardiovascular co-morbidities associated with human Cushing's disease.

GIP receptor agonism improves dyslipidemia and atherosclerosis independently of body weight loss in preclinical mouse model for cardio-metabolic disease

BackgroundAgonism at the receptor for the glucose-dependent insulinotropic polypeptide (GIPR) is a key component of the novel unimolecular GIPR:GLP-1R co-agonists, which are among the most promising drugs in clinical development for the treatment of obesity and type 2 diabetes. The therapeutic effect of chronic GIPR agonism to treat dyslipidemia and thus to reduce the cardiovascular disease risk independently of body weight loss has not been explored yet.MethodsAfter 8 weeks on western diet, LDL receptor knockout (LDLR-/-) male mice were treated with daily subcutaneous injections of long-acting acylated GIP analog (acyl-GIP; 10nmol/kg body weight) for 28 days. Body weight, food intake, whole-body composition were monitored throughout the study. Fasting blood glucose and intraperitoneal glucose tolerance test (ipGTT) were determined on day 21 of the study. Circulating lipid levels, lipoprotein profiles and atherosclerotic lesion size was assessed at the end of the study. Acyl-GIP effects on fat depots were determined by histology and transcriptomics.ResultsHerein we found that treatment with acyl-GIP reduced dyslipidemia and atherogenesis in male LDLR-/- mice. Acyl-GIP administration resulted in smaller adipocytes within the inguinal fat depot and RNAseq analysis of the latter revealed that acyl-GIP may improve dyslipidemia by directly modulating lipid metabolism in this fat depot.ConclusionsThis study identified an unanticipated efficacy of chronic GIPR agonism to improve dyslipidemia and cardiovascular disease independently of body weight loss, indicating that treatment with acyl-GIP may be a novel approach to alleviate cardiometabolic disease.

Lipodystrophic gene Agpat2 deficiency aggravates hyperlipidemia and atherosclerosis in Ldlr−/− mice

AimsDysfunction of adipose tissue increases the risk of cardiovascular disease. It was well established that obesity aggravates atherosclerosis, but the effect of adipose tissue loss on atherosclerosis has been less studied. AGPAT2 is the first causative gene of congenital generalized lipodystrophy (CGL), but the role of AGPAT2 on atherosclerosis has not been reported. Hypertriglyceridemia is one of the clinical manifestations of CGL patients, but it is usually absent in CGL mouse model on a normal diet. This study will investigate the effect of Agpat2 on hyperlipidemia and atherosclerosis. Methods and resultsIn this study, Agpat2 knockout (Agpat2−/−) mice were generated using CRISPR/Cas system, which showed severe loss of adipose tissue and fatty liver, consistent with previous reports. Agpat2−/− mice were then crossed with hypercholesterolemic and atherosclerotic prone LDL receptor knockout (Ldlr−/−) mice to obtain double knockout mouse model (Agpat2−/−Ldlr−/−). Plasma lipid profile, insulin resistance, fatty liver, and atherosclerotic lesions were observed after 12 weeks of the atherogenic high-fat diet (HFD) feeding. We found that compared with Ldlr−/− mice, Agpat2−/−Ldlr−/− mice showed significantly higher plasma total cholesterol and triglycerides after HFD feeding. Agpat2−/−Ldlr−/− mice also developed hyperglycemia and hyperinsulinemia, with increased pancreatic islet area. The liver weight of Agpat2−/−Ldlr−/− mice was about 4 times higher than that of Ldlr−/− mice. The liver lipid deposition was severe and Sirius red staining showed liver fibrosis. In addition, in Agpat2−/−Ldlr−/− mice, the area of atherosclerotic lesions in aortic arch and aortic root was significantly increased. ConclusionsOur results show that Agpat2 deficiency led to more severe hyperlipidemia, liver fibrosis and aggravation of atherosclerosis in Ldlr−/− mice. This study provided additional insights into the role of adipose tissue in hyperlipidemia and atherosclerosis.

Dihydromyricetin Alleviates Nonalcoholic Fatty Liver Disease and Its Associated Metabolic Syndrome by Inhibiting Endoplasmic Reticulum Stress in LDLR−/− Mice Fed with a High-Fat and High-Fructose Diet

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease. Previous studies have shown that dihydromyricetin (DHM) is beneficial for NAFLD. However, whether DHM alleviates NAFLD by inhibiting liver endoplasmic reticulum (ER) stress remains unknown. Thus, this study aimed to identify the potential roles and mechanisms of DHM. Twenty-four male low-density lipoprotein receptor (LDLR−/−) knockout mice aged 8 weeks were randomly divided into normal control, control, and DHM groups. Normal control mice were fed a normal diet (ND), and the last two groups of mice were fed a high-fat and high-fructose diet (HFD) for 12 weeks, treated with or without DHM. DHM alleviated diet-induced hyperlipidemia as early as 4 weeks after and until the end of HFD feeding. HFD increased insulin resistance, and the opposite was observed in the DHM group. Compared to the control group, the body weight of the mice and adipocyte size and weight of the retroperitoneal and epididymal fat were remarkably reduced in the DHM group. The expression of genes related to lipid metabolism, such as Acox1 and Cpt1α, was significantly upregulated. Moreover, Mttp was downregulated in the two fat sits in the DHM group. DHM alleviated diet-induced lipid deposition in the liver and decreased liver triglyceride and total cholesterol content. DHM improved liver function by inhibiting ER stress, alleviating atherogenesis, and promoting vascular remodeling. In conclusion, dihydromyricetin improved NAFLD and related insulin resistance, hyperlipidemia, and atherogenesis by inhibiting liver ER stress in HFD-fed LDLR−/− mice.

The effect of HLA-DRB1*04:01 on a mouse model of atherosclerosis

ObjectivesHLA-DRB1 is associated with an increased risk of cardiovascular disease in patients with rheumatoid arthritis (RA). This study aimed to determine the effect of HLA-DRB1 on atherosclerotic cardiovascular disease (ASCVD) using a novel mouse model. MethodsMice transgenic for HLA-DRB1*04:01 (DR4tg) were crossed with low density lipoprotein receptor knock-out (Ldlr−/−) mice that develop atherosclerosis when fed a high fat, high cholesterol (HFHC) diet. Male and female DR4tgLdlr−/− (n = 48), Ldlr−/− (n = 24), DR4tg (n = 24), and C57Bl/6 (B6) background (n = 24) mice were fed HFHC or regular diet (RD) for 12 weeks. Blood samples were analyzed for serum lipoproteins using a colorimetric assay. C-reactive protein (CRP) and oxidized LDL (OxLDL) were measured using ELISA. Atherosclerosis in the aortas was assessed using the lipid stain, Sudan IV. The presence of citrulline in atherosclerotic plaque was determined by immunohistochemistry. ResultsSera low-density lipoprotein cholesterol (LDL-C) levels were higher in HFHC-fed Ldlr−/− versus DR4tgLdlr−/−-; p = 0.0056, but the aortic plaque burden and degree of citrullination in the plaque were similar for these two strains. The ratio of pro-atherogenic OxLDL to LDL levels was higher in DR4tgLdlr−/− than Ldlr−/−mice; p = 0.0017. All mice had an increase in CRP when fed a HFHC diet, most pronounced for DR4tgLdlr−/−; p = 0.0009. There were no significant sex differences for DR4tgLdlr−/− mice; however, male Ldlr−/− mice had worse atherosclerosis. B6 and DR4tg mice did not have significant elevations in serum cholesterol levels and did not develop atherosclerosis. ConclusionsExpression of HLA-DRB1 resulted in an elevation of OxLDL and a reduction in the male bias for atherosclerosis, mimicking what is observed in RA.

Glial cell reactivity drives cognitive decline in LDLr‐/‐ mice: experimental evidences

AbstractBackgroundFamilial hypercholesterolemia (FH) is a clinical condition characterized by increased plasma cholesterol levels, due to a mutation in the gene encoding the low‐density lipoprotein receptor (LDLr) in cells [Brown and Goldstein, 1984]. Importantly, clinical evidence indicates that FH negatively affects cognition and favors the development of neuropathologies [Ariza et al., 2016; Zambón et al, 2010], however, the mechanisms behind this relationship are still not fully understood. In this study we aimed to investigate the role of glial cell reactivity on the cognitive deficits related to the FH, as well as the possible neuroprotective effect of a pharmacological inhibitor of microglial cell activation.MethodFirstly, male 3‐months‐old and 14‐months‐old C57BL/6 wild‐type and LDLr knockout mice (LDLr‐/‐) mice brains were prepared for the evaluation of glial cell morphology by immunofluorescence. In addition, the mice’s hippocampus was removed to measure the immune content of synaptic and tight‐junctions proteins. Moreover, male and female 6‐months‐old C57BL/6 wild‐type and LDLr‐/‐ mice were treated with minocycline (50 mg/kg) or vehicle (saline) for four weeks. Afterwards, mice were submitted to behavioral tests.ResultMiddle‐aged LDLr‐/‐ mice (14‐months‐old) exhibited increased microgliosis in hippocampus, which was correlated with morphological change of microglial cells and astrocytes in this same brain region. Also, middle‐aged LDLr‐/‐ mice presented a reduction in the immune content of synaptophysin‐1 in the hippocampus. Moreover, young adult (3‐months‐old) LDLr‐/‐ mice exhibited reduced immune content of PSD95 in the hippocampus. Finally, the administration of minocycline to 6‐months‐old LDLr‐/‐ mice ameliorated the performance of hypercholesterolemic mice in hippocampal‐dependent memory tasks, without modifying their locomotor activity and metabolic parameters.ConclusionTaken together, our results demonstrated that FH alters the glial cell reactivity, which was associated with changes in synaptic proteins in the hippocampus. In addition, the pharmacological modulation of microglial cell reactivity ameliorated the hippocampal‐dependent memory in LDLr‐/‐ mice, suggesting that increased glial cell reactivity is a key event for HF‐related cognitive deficits.

Carbon Nanodots Attenuate Lipid Peroxidation in the LDL Receptor Knockout Mouse Brain.

Abnormal cholesterol metabolism can lead to oxidative stress in the brain. Low-density lipoprotein receptor (LDLr) knockout mice are models for studying altered cholesterol metabolism and oxidative stress onset in the brain. Carbon nanodots are a new class of carbon nanomaterials that possess antioxidant properties. The goal of our study was to evaluate the effectiveness of carbon nanodots in preventing brain lipid peroxidation. LDLr knockout mice and wild-type C57BL/6J mice were treated with saline or 2.5 mg/kg bw of carbon nanodots for a 16-week period. Brains were removed and dissected into the cortex, midbrain, and striatum. We measured lipid peroxidation in the mouse brain tissues using the Thiobarbituric Acid Reactive Substances Assay and iron and copper concentrations using Graphite Furnace Atomic Absorption Spectroscopy. We focused on iron and copper due to their association with oxidative stress. Iron concentrations were significantly elevated in the midbrain and striatum of the LDLr knockout mice compared to the C57BL/6J mice, whereas lipid peroxidation was greatest in the midbrain and cortex of the LDLr knockout mice. Treatment with carbon nanodots in the LDLr knockout mice attenuated both the rise in iron and lipid peroxidation, but they had no negative effect in the C57BL/6J mice, indicating the anti-oxidative stress properties of carbon nanodots. We also assessed locomotor and anxiety-like behaviors as functional indicators of lipid peroxidation and found that treatment with carbon nanodots prevented the anxiety-like behaviors displayed by the LDLr knockout mice. Overall, our results show that carbon nanodots are safe and may be an effective nanomaterial for combating the harmful effects caused by lipid peroxidation.

Abstract 677: Short Hydrocarbon-Stapled Apolipoprotein E Mimetic Peptides Enhance Lipoprotein Uptake

ApoE facilitates the clearance of apoB-containing lipoproteins by binding to heparan sulfate proteoglycans (HSPG), low density lipoprotein receptor (LDLR) and LDLR-related protein 1 (LRP1). ApoE has a receptor binding and a lipid binding domain, which are both needed for its biological function. Several apoE-based peptides have been developed that lower plasma lipid levels in animal models and in early-stage clinical trials. However, these peptides are long (28-61 residues), costly to synthesize and are potentially immunogenic as they often contain many amino acid substitutions that vary from the native apoE sequence. We developed novel short (10-12 residues) apoE mimetic peptides based on the apoE receptor binding region (residues 141-150) containing only 2 amino acid substitutions. We used hydrocarbon stapling to stabilize the native alpha helical structure of this region and to increase the lipid binding affinity of the peptides. In addition, octanoic or myristic acid was attached to the N-terminus of the peptides to further increase lipid binding affinity. Helical conformation and lipid binding of the peptides were confirmed by circular dichroism spectroscopy and phospholipid vesicle solubilization assay. Our peptides increased the uptake of fluorescent tagged VLDL and LDL in a concentration dependent manner (0.625-20 μM peptides) in both wild-type (WT) and LDLR knockout (KO) HepG2 cells as measured by flow cytometry. In addition, an all D-amino acid version of one of the peptides had a similar effect on LDL uptake as its all L-amino acid version. Altogether, this suggests that peptide-mediated uptake is LDLR independent. Treatment of WT HepG2 cells with heparinases diminished the low-dose effect (up to 2.5 μM) of the peptides on LDL uptake, indicating that HSPGs plays a role in peptide-mediated LDL uptake. Finally, the peptides (4.6 mg/kg, IV) lowered plasma total cholesterol (37% at 3h; 29% at 6h) and triglycerides (33% at 1h) in apoE-KO mice on a standard chow diet. In summary, the novel apoE peptides are shorter than previously reported peptides, are more similar to the native sequence of apoE, and are likely resistant to proteolysis, because of hydrocarbon stapling and, therefore, could potentially be developed into an oral therapy.