Hyperlipidemia and atherosclerotic lesion development in LDL receptor-deficient mice fed defined semipurified diets with and without cholate

Emerging Insights into the Role of BDNF on Health and Disease in Periphery

Brain-derived neurotrophic factor (BDNF) is a growth factor that promotes the survival and growth of developing neurons. It also enhances circuit formation to synaptic transmission for mature neurons in the brain. However, reduced BDNF expression and single nucleotide polymorphisms (SNP) are reported to be associated with functional deficit and disease development in the brain, suggesting that BDNF is a crucial molecule for brain health. Interestingly, BDNF is also expressed in the hypothalamus in appetite and energy metabolism. Previous reports demonstrated that BDNF knockout mice exhibited overeating and obesity phenotypes remarkably. Therefore, we could raise a hypothesis that the loss of function of BDNF may be associated with metabolic syndrome and peripheral diseases. In this review, we describe our recent finding that BDNF knockout mice develop metabolic dysfunction-associated steatohepatitis and recent reports demonstrating the role of one of the BDNF receptors, TrkB-T1, in some peripheral organ functions and diseases, and would provide an insight into the role of BDNF beyond the brain.

Dietary proteins modulate high-density lipoprotein characteristics in a sex-specific way in Apoe-deficient mice

OBJECTIVES

The type and amount of dietary protein have become a topic of renewed interest, considering their involvement in several diseases. However, little attention has been devoted to the effect of avian proteins despite their wide human consumption. In a previous study, we saw that compared with soybean protein, the consumption of avian proteins, depending on sex, resulted in similar or lower atherosclerosis with a higher paraoxonase 1 activity, an antioxidant enzyme carried by high-density lipoproteins (HDL). This suggests that under these conditions, the HDL lipoproteins may undergo important changes. The aim of this research was to study the influence of soybean, chicken, and turkey proteins on the characteristics of HDL.

METHODS

Male and female Apoe-deficient mice were fed purified Western diets based on the AIN-93 diet, differing only in the protein source, for 12 wk. After this period, blood and liver samples were taken for analysis of HDL composition and hepatic expression of genes related to HDL metabolism (Abca1, Lcat, Pltp, Pon1, and Scarb1). Depending on sex, these genes define a different network of interactions. Females consuming the turkey protein-containing diet showed decreased atherosclerotic foci, which can be due to larger very-low-density lipoproteins (VLDLs) calculated by molar ratio triacylglycerols/VLDL cholesterol and higher expression of Lcat. In contrast, in males, a higher ratio of paraoxonase1 to apolipoprotein A1 decreased the oxidative status of the different lipoproteins, and augmented Abca1 expression was observed.

CONCLUSIONS

The source of protein has an effect on the development of atherosclerosis depending on sex by modifying HDL characteristics and the expression of genes involved in their properties.

Cold shock domain-containing protein E1 is a posttranscriptional regulator of the LDL receptor

The low-density lipoprotein receptor (LDLR) controls cellular delivery of cholesterol and clears LDL from the bloodstream, protecting against atherosclerotic heart disease, the leading cause of death in the United States. We therefore sought to identify regulators of the LDLR beyond the targets of current therapies and known causes of familial hypercholesterolemia. We found that cold shock domain-containing protein E1 (CSDE1) enhanced hepatic LDLR messenger RNA (mRNA) decay via its 3' untranslated region and regulated atherogenic lipoproteins in vivo. Using parallel phenotypic genome-wide CRISPR interference screens in a tissue culture model, we identified 40 specific regulators of the LDLR that were not previously identified by observational human genetic studies. Among these, we demonstrated that, in HepG2 cells, CSDE1 regulated the LDLR at least as strongly as statins and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. In addition, we showed that hepatic gene silencing of Csde1 treated diet-induced dyslipidemia in mice to a similar degree as Pcsk9 silencing. These results suggest the therapeutic potential of targeting CSDE1 to manipulate the posttranscriptional regulation of the LDLR mRNA for the prevention of cardiovascular disease. Our approach of modeling a clinically relevant phenotype in a forward genetic screen, followed by mechanistic pharmacologic dissection and in vivo validation, may serve as a generalizable template for the identification of therapeutic targets in other human disease states.

Calcium carbonate supplementation causes motor dysfunction

We previously showed that a diet containing calcium carbonate causes impairments in spatial and recognition memory in mice. In this study, we investigated the effects of calcium carbonate supplementation on motor function. Motor function was determined using different tests that have been used to analyze different aspects of Parkinsonism. A catalepsy test for akinesia; a muscular strength assessment, pole test, beam-walking test, and gait analysis for motor coordination and balance assessment; and an open-field test for locomotor activity assessment were performed. The mice were fed diets containing 0.6% or 1.0% calcium carbonate for eight weeks, after which they were evaluated for motor functions. The diets containing calcium carbonate caused significant motor dysfunction, as revealed by the different tests, although the spontaneous locomotor activity did not change. Calcium carbonate supplementation decreased the dopamine content in the basal ganglia, including the striatum and substantia nigra, and the number of tyrosine hydroxylase-positive neurons in the substantia nigra. In addition, administration of L-dopa led to at least a partial recovery of motor dysfunction, suggesting that calcium carbonate supplementation causes motor dysfunction by decreasing the dopamine content in the basal ganglia. These results suggest that mice with calcium carbonate-induced motor dysfunction may be useful as a new animal model for Parkinson’s disease and Huntington’s disease.

Laminaria japonica Polysaccharide Suppresses Atherosclerosis via Regulating Autophagy-Mediated Macrophage Polarization

The present work aimed to explore the effect and underlying mechanism of a homogeneous Laminaria japonica polysaccharide (LJP61A) on macrophage polarization in high-fat-diet-fed LDLr-/- mice and Ox-LDL-induced macrophages. Results showed that LJP61A remarkably reduced the lesion burden in atherosclerotic mice, alleviated lipid deposition in Ox-LDL-stimulated macrophages, decreased the expression of M1 macrophage markers, and increased the expression of M2 macrophage markers, thus reducing the M1/M2 macrophage phenotype ratio. Meanwhile, the autophagic flux of macrophages was enhanced by LJP61A treatment in vitro and in vivo. 3-Methyladenine is an autophagic inhibitor. As expected, this inhibitor blocked the effects of LJP61A on macrophage polarization. SIRT1 and FoxO1 are two key upstream genes that control the autophagy behavior. We also found that LJP61A significantly up-regulated the expression of SIRT1 and FoxO1. However, these effects of LJP61A were abolished by the SIRT1 siRNA and FoxO1 inhibitor AS1842856. These results suggested that LJP61A reduced atherosclerosis in HFD-induced LDLr-/- mice via regulating autophagy-mediated macrophage polarization.

Research methods for animal models of atherosclerosis (Review)

Atherosclerosis is a chronic inflammatory disease that threatens human health and lives by causing vascular stenosis and plaque rupture. Various animal models have been employed for elucidating the pathogenesis, drug development and treatment validation studies for atherosclerosis. To the best of our knowledge, the species used for atherosclerosis research include mice, rats, hamsters, rabbits, pigs, dogs, non-human primates and birds, among which the most commonly used ones are mice and rabbits. Notably, apolipoprotein E knockout (KO) or low-density lipoprotein receptor KO mice have been the most widely used animal models for atherosclerosis research since the late 20th century. Although the aforementioned animal models can form atherosclerotic lesions, they cannot completely simulate those in humans with respect to lesion location, lesion composition, lipoprotein composition and physiological structure. Hence, an appropriate animal model needs to be selected according to the research purpose. Additionally, it is necessary for atherosclerosis research to include quantitative analysis results of atherosclerotic lesion size and plaque composition. Laboratory animals can provide not only experimental tissues for in vivo studies but also cells needed for in vitro experiments. The present review first summarizes the common animal models and their practical applications, followed by focus on mouse and rabbit models and elucidating the methods to quantify atherosclerotic lesions. Finally, the methods of culturing endothelial cells, macrophages and smooth muscle cells were elucidated in detail and the experiments involved in atherosclerosis research were discussed.

Dietary Avian Proteins Are Comparable to Soybean Proteins on the Atherosclerosis Development and Fatty Liver Disease in Apoe-Deficient Mice

Background and aim: The type and amount of dietary protein has become a topic of renewed interest in light of their involvement in metabolic diseases, atherosclerosis and thrombosis. However, little attention has been devoted to the effect of avian proteins despite their wide human consumption. The aim was to investigate the influence of chicken and turkey as sources of protein compared with that of soybean on atherosclerosis and fatty liver disease. Methods and results: To this purpose, male and female Apoe-deficient were fed purified Western diets differing in their protein sources for 12 weeks. After this period, blood, liver, aortic tree and heart base samples were taken for analyses of plasma lipids and atherosclerosis. Plasma triglycerides, non-esterified fatty acids, esterified cholesterol levels and radical oxygen species in lipoproteins changed depending on the diet and sex. Females consuming the turkey protein-containing diet showed decreased atherosclerotic foci, as evidenced by the en face atherosclerosis analyses. The presence of macrophages and smooth muscle cells in plaques were not modified, and no changes were observed in hepatic lipid droplets in the studied groups either. Paraoxonase activity was higher in the group consuming turkey protein without sex differences, but only in females, it was significantly associated with aortic lesion areas. Conclusions: Compared to soybean protein, the consumption of avian proteins depending on sex resulted in similar or lower atherosclerosis development and comparable hepatic steatosis.

Role of myeloid-derived chemokine CCL5/RANTES at an early stage of atherosclerosis

One of the hallmarks of atherosclerosis is ongoing accumulation of macrophages in the artery intima beginning at disease onset. Monocyte recruitment contributes to increasing macrophage abundance at early stages of atherosclerosis. Although the chemokine CCL5 (RANTES) has been studied in atherosclerosis, its role in the recruitment of monocytes to early lesions has not been elucidated. We show that expression of Ccl5 mRNA, as well as other ligands of the CCR5 receptor (Ccl3 and Ccl4), is induced in the aortic intima of Ldlr^-/- mice 3 weeks after the initiation of cholesterol-rich diet (CRD)-induced hypercholesterolemia. En face immunostaining revealed that CCL5 protein expression is also upregulated at 3 weeks of CRD. Blockade of CCR5 significantly reduced monocyte recruitment to 3-week lesions, suggesting that chemokine signaling through CCR5 is critical. However, we observed that Ccl5-deficiency had no effect on early lesion formation and CCL5-blockade did not affect monocyte recruitment in Ldlr^-/- mice. Immunostaining of the lesions in Ldlr^-/- mice and reciprocal bone marrow transplantation (BMT) of Ccl5^+/+ and Ccl5^-/- mice revealed that CCL5 is expressed by both myeloid and endothelial cells. BMT experiments were carried out to determine if CCL5 produced by distinct cells has functions that may be concealed in Ccl5^-/-Ldlr^-/- mice. We found that hematopoietic cell-derived CCL5 regulates monocyte recruitment and the abundance of intimal macrophages in 3-week lesions of Ldlr^-/- mice but plays a minor role in 6-week lesions. Our findings suggest that there is a short window in early lesion formation during which myeloid cell-derived CCL5 has a critical role in monocyte recruitment and macrophage abundance.

Efferocytic Defects in Early Atherosclerosis Are Driven by GATA2 Overexpression in Macrophages

The loss of efferocytosis-the phagocytic clearance of apoptotic cells-is an initiating event in atherosclerotic plaque formation. While the loss of macrophage efferocytosis is a prerequisite for advanced plaque formation, the transcriptional and cellular events in the pre-lesion site that drive these defects are poorly defined. Transcriptomic analysis of macrophages recovered from early-stage human atherosclerotic lesions identified a 50-fold increase in the expression of GATA2, a transcription factor whose expression is normally restricted to the hematopoietic compartment. GATA2 overexpression in vitro recapitulated many of the functional defects reported in patient macrophages, including deficits at multiple stages in the efferocytic process. These findings included defects in the uptake of apoptotic cells, efferosome maturation, and in phagolysosome function. These efferocytic defects were a product of GATA2-driven alterations in the expression of key regulatory proteins, including Src-family kinases, Rab7 and components of both the vacuolar ATPase and NADPH oxidase complexes. In summary, these data identify a mechanism by which efferocytic capacity is lost in the early stages of plaque formation, thus setting the stage for the accumulation of uncleared apoptotic cells that comprise the bulk of atherosclerotic plaques.

Small rodent models of atherosclerosis

The ease of breeding, low cost of maintenance, and relatively short period for developing atherosclerosis make rodents ideal for atherosclerosis research. However, none of the current models accurately model human lipoprotein profile or atherosclerosis progression since each has its advantages and disadvantages. The advent of transgenic technologies much supports animal models' establishment. Notably, two classic transgenic mouse models, apoE-/- and Ldlr-/-, constitute the primary platforms for studying underlying mechanisms and development of pharmaceutical approaches. However, there exist crucial differences between mice and humans, such as the unhumanized lipoprotein profile, and the different plaque progression and characteristics. Among rodents, hamsters and guinea pigs might be the more realistic models in atherosclerosis research based on the similarities in lipoprotein metabolism to humans. Studies involving rat models, a rodent with natural resistance to atherosclerosis, have revealed evidence of atherosclerotic plaques under dietary induction and genetic manipulation by novel technologies, notably CRISPR-Cas9. Ldlr-/- hamster models were established in recent years with severe hyperlipidemia and atherosclerotic lesion formation, which could offer an alternative to classic transgenic mouse models. In this review, we provide an overview of classic and innovative small rodent models in atherosclerosis researches, including mice, rats, hamsters, and guinea pigs, focusing on their lipoprotein metabolism and histopathological changes.

Targeted Nutrient Modifications in Purified Diets Differentially Affect Nonalcoholic Fatty Liver Disease and Metabolic Disease Development in Rodent Models

Nonalcoholic fatty liver disease (NAFLD) is a complex spectrum of disorders ranging from simple benign steatosis to more aggressive forms of nonalcoholic steatohepatitis (NASH) and fibrosis. Although not every patient with NAFLD/NASH develops liver complications, if left untreated it may eventually lead to cirrhosis and hepatocellular carcinoma. Purified diets formulated with specific nutritional components can drive the entire spectrum of NAFLD in rodent models. Although they may not perfectly replicate the clinical and histological features of human NAFLD, they provide a model to gain further understanding of disease progression in humans. Owing to the growing demand of diets for NAFLD research, and for our further understanding of how manipulation of dietary components can alter disease development, we outlined several commonly used dietary approaches for rodent models, including mice, rats, and hamsters, time frames required for disease development and whether other metabolic diseases commonly associated with NAFLD in humans occur.

Ablation of miR-144 increases vimentin expression and atherosclerotic plaque formation

It has been suggested that miR-144 is pro-atherosclerotic via effects on reverse cholesterol transportation targeting the ATP binding cassette protein. This study used proteomic analysis to identify additional cardiovascular targets of miR-144, and subsequently examined the role of a newly identified regulator of atherosclerotic burden in miR-144 knockout mice receiving a high fat diet. To identify affected secretory proteins, miR-144 treated endothelial cell culture medium was subjected to proteomic analysis including two-dimensional gel separation, trypsin digestion, and nanospray liquid chromatography coupled to tandem mass spectrometry. We identified 5 gel spots representing 19 proteins that changed consistently across the biological replicates. One of these spots, was identified as vimentin. Atherosclerosis was induced in miR-144 knockout mice by high fat diet and vascular lesions were quantified by Oil Red-O staining of the serial sectioned aortic root and from en-face views of the aortic tree. Unexpectedly, high fat diet induced extensive atherosclerosis in miR-144 knockout mice and was accompanied by severe fatty liver disease compared with wild type littermates. Vimentin levels were reduced by miR-144 and increased by antagomiR-144 in cultured cardiac endothelial cells. Compared with wild type, ablation of the miR-144/451 cluster increased plasma vimentin, while vimentin levels were decreased in control mice injected with synthetic miR-144. Furthermore, increased vimentin expression was prominent in the commissural regions of the aortic root which are highly susceptible to atherosclerotic plaque formation. We conclude that miR-144 maybe a potential regulator of the development of atherosclerosis via changes in vimentin signaling.

The interaction between STAT3 and nAChRα1 interferes with nicotine-induced atherosclerosis via Akt/mTOR signaling cascade

During atherosclerosis development, nicotine and its α1 nicotinic acetylcholine receptors (nAChRα1) activate atherogenic inflammation. However, the effect of signal transducer and activator of transcription 3 (STAT3)-related inflammatory pathways in nicotine-induced atherosclerosis has been poorly studied. This study investigated the transcriptional mechanism of STAT3 in nicotine/nAChRα1-induced atherosclerosis. In vivo, ApoE-/- mice were used to establish an atherosclerotic model. Plaque area and composition were assessed by oil red O staining and immunohistochemistry. In vitro, vascular smooth muscle cells and macrophages were used to investigate cell migration, proliferation, inflammation and related signaling pathways by Transwell migration assay, EdU assay, immunofluorescence, western blotting, coimmunoprecipitation and chromatin immunoprecipitation. nAChRα1 knockdown significantly decreases the nicotine-induced upregulation of p-STAT3, p-Akt and p-mTOR in vitro, while nAChRα1 overexpression has the opposite effects. The inhibition of STAT3 attenuated nicotine-induced atherosclerosis, by reducing the proliferation and migration of vascular smooth muscle cells and inflammation in macrophages. Moreover, there is a direct interaction between STAT3 and nAChRα1 that modulates STAT3 nuclear translocation and its binding to the Akt promoter region upon nicotine exposure. Taken together, STAT3 and nAChRα1 blockade attenuates nicotine-induced atherosclerosis by reducing the migration and proliferation of vascular smooth muscle cells and inflammation in macrophages via the Akt/mTOR pathway.

Cytokine Circuits in Cardiovascular Disease

Arterial inflammation is a hallmark of atherosclerosis, and appropriate management of this inflammation represents a major unmet therapeutic need for cardiovascular disease patients. Here, we review the diverse contributions of immune cells to atherosclerosis, the mechanisms of immune cell activation in this context, and the cytokine circuits that underlie disease progression. We discuss the recent application of these insights in the form of immunotherapy to treat cardiovascular disease and highlight how studies on the cardiovascular co-morbidity that arises in autoimmunity might reveal additional roles for cytokines in atherosclerosis. Currently, data point to interleukin-1β (IL-1β), tumor necrosis factor (TNF), and IL-17 as cytokines that, at least in some settings, are effective targets to reduce cardiovascular disease progression.

Understanding the Impact of Dietary Cholesterol on Chronic Metabolic Diseases through Studies in Rodent Models

The development of certain chronic metabolic diseases has been attributed to elevated levels of dietary cholesterol. However, decades of research in animal models and humans have demonstrated a high complexity with respect to the impact of dietary cholesterol on the progression of these diseases. Thus, recent investigations in non-alcoholic fatty liver disease (NAFLD) point to dietary cholesterol as a key factor for the activation of inflammatory pathways underlying the transition from NAFLD to non-alcoholic steatohepatitis (NASH) and to hepatic carcinoma. Dietary cholesterol was initially thought to be the key factor for cardiovascular disease development, but its impact on the disease depends partly on the capacity to modulate plasmatic circulating low-density lipoprotein (LDL) cholesterol levels. These studies evidence a complex relationship between these chronic metabolic diseases and dietary cholesterol, which, in certain conditions, might promote metabolic complications. In this review, we summarize rodent studies that evaluate the impact of dietary cholesterol on these two prevalent chronic diseases and their relevance to human pathology.

Angiotensin II Infusion Does Not Cause Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Rats

The apolipoprotein E-deficient (apoE-/-) mouse model has advanced our understanding of cardiovascular disease mechanisms and experimental therapeutics. This spontaneous model recapitulates aspects of human atherosclerosis, and allows for the development of dissecting abdominal aortic aneurysms (AAAs) when combined with angiotensin II. We characterized apoE-/- rats and hypothesized that, similar to mice, they would develop dissecting AAAs. We created rats with a 16-bp deletion of the apoE gene using transcription activator-like effector nucleases. We imaged the suprarenal aorta for 28 days after implantation of miniosmotic pumps that infuse angiotensin II (AngII, 200 ng/kg/min). Blood pressure (BP), serum lipids and lipoproteins, and histology were also analyzed. These rats did not develop pathological aortic dissection, but we did observe a decrease in circumferential cyclic strain, a rise in BP, and microstructural changes in the aortic medial layer. We also measured increased serum lipids with and without administration of a high-fat diet, but did not detect atherosclerotic plaques. Chronic infusion of AngII did not lead to the formation of dissecting AAAs or atherosclerosis in the rats used in this study. While reduced amounts of atherosclerosis may explain this resistance to dissecting aneurysms, further investigation is needed to fully characterize species-specific differences.

Leukocyte RhoA exchange factor Arhgef1 mediates vascular inflammation and atherosclerosis

Abnormal activity of the renin-angiotensin-aldosterone system plays a causal role in the development of hypertension, atherosclerosis, and associated cardiovascular events such as myocardial infarction, stroke, and heart failure. As both a vasoconstrictor and a proinflammatory mediator, angiotensin II (Ang II) is considered a potential link between hypertension and atherosclerosis. However, a role for Ang II-induced inflammation in atherosclerosis has not been clearly established, and the molecular mechanisms and intracellular signaling pathways involved are not known. Here, we demonstrated that the RhoA GEF Arhgef1 is essential for Ang II-induced inflammation. Specifically, we showed that deletion of Arhgef1 in a murine model prevents Ang II-induced integrin activation in leukocytes, thereby preventing Ang II-induced recruitment of leukocytes to the endothelium. Mice lacking both LDL receptor (LDLR) and Arhgef1 were protected from high-fat diet-induced atherosclerosis. Moreover, reconstitution of Ldlr-/- mice with Arhgef1-deficient BM prevented high-fat diet-induced atherosclerosis, while reconstitution of Ldlr-/- Arhgef1-/- with WT BM exacerbated atherosclerotic lesion formation, supporting Arhgef1 activation in leukocytes as causal in the development of atherosclerosis. Thus, our data highlight the importance of Arhgef1 in cardiovascular disease and suggest targeting Arhgef1 as a potential therapeutic strategy against atherosclerosis.

Cholic Acid Enhances Visceral Adiposity, Atherosclerosis and Nonalcoholic Fatty Liver Disease in Microminipigs

Aim: We have recently established a novel swine model for studies of atherosclerosis using Microminipigs™ (µMPs) fed a high-fat/high-cholesterol diet (HcD). Using this swine model, we re-evaluated the effects of dietary cholic acid (CA) on serum lipid profile, atherosclerosis and hepatic injuries.

Methods: The µMPs were fed HcD supplemented with 0.7% CA (HcD+CA) for eight weeks, and the effect of CA on serum lipoprotein levels, expression of oxidative stress markers, adiposity and lesion formation in the aorta, liver, and other organs was investigated.

Results: The HcD+CA-fed group exhibited more visceral adiposity, progression of atherosclerosis and higher serum levels of oxidative stress markers than the HcD-fed group, even though they showed similar serum lipid levels. The liver demonstrated increased lipid accumulation, higher expression of oxidative stress markers, accelerated activation of foamy Kupffer cells and stellate cells, and increased hepatocyte apoptosis, indicating non-alcoholic fatty liver disease (NAFLD). Intriguingly, foamy macrophage mobilization was observed in various organs, including the reticuloendothelial system, pulmonary capillary vessels and skin very often in HcD+CA-fed µMPs.

Conclusion: To our knowledge, this is the first large animal model, in which visceral obesity, NAFLD and atherosclerosis are concomitantly induced by dietary manipulation. These data suggest the detrimental effects of CA, potentially through local and systemic activation of oxidative stress-induced signaling to macrophage mobilization, on the acceleration of visceral adiposity, atherosclerosis and NAFLD.

Low-sodium diet induces atherogenesis regardless of lowering blood pressure in hypertensive hyperlipidemic mice

This study investigated the influence of sodium restriction and antihypertensive drugs on atherogenesis utilizing hypertensive (H) low-density lipoprotein-receptor knockout mice treated or not with losartan (Los) or hydralazine (Hyd) and fed low-sodium (LS) or normal-sodium (NS) chow. Despite reducing the blood pressure (BP) of H-LS mice, the LS diet caused arterial lipid infiltration due to increased plasma total cholesterol (TC) and triglycerides (TG). Los and Hyd reduced the BP of H-LS mice, and Los effectively prevented arterial injury, likely by reducing plasma TG and nonesterified fatty acids. Aortic lipid infiltration was lower in Los-treated H-LS mice (H-LS+Los) than in normotensive (N)-LS and H-LS mice. Aortic angiotensin II type 1 (AT1) receptor content was greater in H-NS than H-LS mice and in H-LS+Hyd than H-LS+Los mice. Carboxymethyl-lysine (CML) and receptor for advanced glycation end products (RAGE) immunostaining was greater in H-LS than H-NS mice. CML and RAGE levels were lower in LS animals treated with antihypertensive drugs, and Hyd enhanced the AT1 receptor level. Hyd also increased the gene expression of F4/80 but not tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-10, intercellular adhesion molecule-1 or cluster of differentiation 66. The novelty of the current study is that in a murine model of simultaneous hypertension and hyperlipidemia, the pleiotropic effect of chronic, severe sodium restriction elicited aortic damage even with reduced BP. These negative effects on the arterial wall were reduced by AT1 receptor antagonism, demonstrating the influence of angiotensin II in atherogenesis induced by a severely LS diet.

Toll-like receptor 7 deficiency protects apolipoprotein E-deficient mice from diet-induced atherosclerosis

Toll-like receptor 7 (TLR7) mediates autoantigen and viral RNA-induced cytokine production. Increased TLR7 expression in human atherosclerotic lesions suggests its involvement in atherogenesis. Here we demonstrated TLR7 expression in macrophages, smooth muscle cells (SMCs), and endothelial cells from mouse atherosclerotic lesions. To test a direct participation of TLR7 in atherosclerosis, we crossbred TLR7-deficient (Tlr7 ^-/-) mice with apolipoprotein E-deficient (Apoe ^-/-) mice and produced Apoe ^-/- Tlr7 ^-/- and Apoe ^-/- Tlr7 ^+/+ littermates, followed by feeding them an atherogenic diet to produce atherosclerosis. Compared to Apoe ^-/- Tlr7 ^+/+ mice, Apoe ^-/- Tlr7 ^-/- mice showed reduced aortic arch and sinus lesion areas. Reduced atherosclerosis in Apoe ^-/- Tlr7 ^-/- mice did not affect lesion macrophage-positive area and CD4⁺ T-cell number per lesion area, but reduced lesion expression of inflammatory markers major histocompatibility complex-class II and IL6, lesion matrix-degrading proteases cathepsin S and matrix metalloproteinase-9, and systemic serum amyloid A levels. TLR7 deficiency also reduced aortic arch SMC loss and lesion intima and media cell apoptosis. However, TLR7 deficiency did not affect aortic wall elastin fragmentation and collagen contents, or plasma lipoproteins. Therefore, TLR7 contributes to atherogenesis in Apoe ^-/- mice by regulating lesion and systemic inflammation. A TLR7 antagonist may mitigate atherosclerosis.

Alleviating VLDL overproduction is an important mechanism for Laminaria japonica polysaccharide to inhibit atherosclerosis in LDLr-/- mice with diet-induced insulin resistance

SCOPE

The overproduction of very low density lipoprotein (VLDL) is an important cause for initiation and development of atherosclerosis, which is highly associated with insulin signaling. The aim of this work is to verify whether the inhibition of VLDL overproduction is an underlying mechanism for a Laminaria japonica polysaccharide (LJP61A (where LJP is L. japonica)) to resist atherosclerosis.

METHODS AND RESULTS

LJP61A (50 and 200 mg/kg/day) was orally administered to a high-fat diet (HFD)-fed LDL receptor deficient mice for 14 weeks. LJP61A significantly attenuated insulin resistance, hepatic steatosis, atherosclerosis, and dyslipidemia. Meanwhile, LJP61A ameliorated the HFD-induced impairment of hepatic insulin signaling and reduced VLDL overproduction via regulating the expression of genes involved in the assembly and secretion of VLDL. To study the possibility that the inhibition of mammalian target of rapamycin complex 1 and stimulation of Forkhead box protein O1 (Foxo1) nuclear exclusion is a result of LJP61A via regulating insulin signaling, LJP61A was administrated to HepG2 cells in the presence or absence of mTOR inhibitor and Foxo1 inhibitor. Results showed that LJP61A alleviated VLDL overproduction via regulating insulin receptor substrate mediated phosphatidylinositide 3-kinase AKT mammalian target of rapamycin complex 1 and phosphatidylinositide 3-kinase AKT-Foxo1 signaling pathways.

CONCLUSION

These results suggested that LJP61A ameliorated HFD-induced insulin resistance to attenuate VLDL overproduction possibly via regulating insulin signaling, leading to the inhibition of atherosclerosis.

Altered hepatic lipid metabolism in mice lacking both the melanocortin type 4 receptor and low density lipoprotein receptor

Obesity is often associated with dyslipidemia and hepatosteatosis. A number of animal models of non-alcoholic fatty liver disease (NAFLD) are established but they significantly differ in the molecular and biochemical changes depending on the genetic modification and diet used. Mice deficient for melanocortin type 4 receptor (Mc4r^mut) develop hyperphagia, obesity, and subsequently NAFLD already under regular chow and resemble more closely the energy supply-driven obesity found in humans. This animal model was used to assess the molecular and biochemical consequences of hyperphagia-induced obesity on hepatic lipid metabolism. We analyzed transcriptome changes in Mc4r^mut mice by RNA sequencing and used high resolution ¹H magic angle spinning NMR spectroscopy and MALDI-TOF mass spectrometry to assess changes in the lipid composition. On the transcriptomic level we found significant changes in components of the triacylglycerol metabolism, unsaturated fatty acids biosynthesis, peroxisome proliferator-activated receptor signaling pathways, and lipid transport and storage compared to the wild-type. These findings were supported by increases in triacylglycerol, monounsaturated fatty acid, and arachidonic acid levels. The transcriptome signatures significantly differ from those of other NAFLD mouse models supporting the concept of hepatic subphenotypes depending on the genetic background and diet. Comparative analyses of our data with previous studies allowed for the identification of common changes and genotype-specific components and pathways involved in obesity-associated NAFLD.

Dendritic Cell KLF2 Expression Regulates T Cell Activation and Proatherogenic Immune Responses

Dendritic cells (DCs) have been implicated as important regulators of innate and adaptive inflammation in many diseases, including atherosclerosis. However, the molecular mechanisms by which DCs mitigate or promote inflammatory pathogenesis are only partially understood. Previous studies have shown an important anti-inflammatory role for the transcription factor Krüppel-like factor 2 (KLF2) in regulating activation of various cell types that participate in atherosclerotic lesion development, including endothelial cells, macrophages, and T cells. We used a pan-DC, CD11c-specific cre-lox gene knockout mouse model to assess the role of KLF2 in DC activation, function, and control of inflammation in the context of hypercholesterolemia and atherosclerosis. We found that KLF2 deficiency enhanced surface expression of costimulatory molecules CD40 and CD86 in DCs and promoted increased T cell proliferation and apoptosis. Transplant of bone marrow from mice with KLF2-deficient DCs into Ldlr-/- mice aggravated atherosclerosis compared with control mice, most likely due to heightened vascular inflammation evidenced by increased DC presence within lesions, enhanced T cell activation and cytokine production, and increased cell death in atherosclerotic lesions. Taken together, these data indicate that KLF2 governs the degree of DC activation and hence the intensity of proatherogenic T cell responses.

Omics-based approaches to understand mechanosensitive endothelial biology and atherosclerosis

Atherosclerosis is a multifactorial disease that preferentially occurs in arterial regions exposed to d-flow can be used to indicate disturbed flow or disturbed blood flow. The mechanisms by which d-flow induces atherosclerosis involve changes in the transcriptome, methylome, proteome, and metabolome of multiple vascular cells, especially endothelial cells. Initially, we begin with the pathogenesis of atherosclerosis and the changes that occur at multiple levels owing to d-flow, especially in the endothelium. Also, there are a variety of strategies used for the global profiling of the genome, transcriptome, miRNA-ome, DNA methylome, and metabolome that are important to define the biological and pathophysiological mechanisms of endothelial dysfunction and atherosclerosis. Finally, systems biology can be used to integrate these 'omics' datasets, especially those that derive data based on a single animal model, in order to better understand the pathophysiology of atherosclerosis development in a holistic manner and how this integrative approach could be used to identify novel molecular diagnostics and therapeutic targets to prevent or treat atherosclerosis. WIREs Syst Biol Med 2016, 8:378-401. doi: 10.1002/wsbm.1344 For further resources related to this article, please visit the WIREs website.

Imaging Reveals the Connection Between Spontaneous Coronary Plaque Ruptures, Atherothrombosis, and Myocardial Infarctions in HypoE/SRBI-/- Mice

The hyperlipidemic mouse model HypoE/SRBI(-/-) has been shown to develop occlusive coronary atherosclerosis followed by myocardial infarctions and premature deaths in response to high-fat, high-cholesterol diet (HFC). However, the causal connection between myocardial infarctions and atherosclerotic plaque rupture events in the coronary arteries has not been investigated so far. The objective of this study was to assess whether diet-induced coronary plaque ruptures trigger atherothrombotic occlusions, resulting in myocardial infarctions in HFC-fed HypoE/SRBI(-/-) mice.

METHODS

HypoE/SRBI(-/-) mice were characterized with respect to the individual dynamics of myocardial infarctions and features of infarct-related coronary atherosclerosis by serial noninvasive molecular and functional imaging, histopathology, and a pharmaceutical intervention. Detailed histologic analysis of whole mouse hearts was performed when spontaneously occurring acute myocardial infarctions were diagnosed by imaging.

RESULTS

Using the imaging-triggered approach, we discovered thrombi in 32 (10.8%) of all 296 atherosclerotic coronary plaques in 14 HFC-fed HypoE/SRBI(-/-) mice. These thrombi typically were found in arteries presenting with inflammatory plaque phenotypes. Acetylsalicylic acid treatment did not attenuate the development of atherosclerotic coronary plaques but profoundly reduced the incidence of premature deaths, the number of thrombi (7 in 249 plaques), and also the degree of inflammation in the culprit lesions.

CONCLUSION

HFC-induced ruptures of coronary plaques trigger atherothrombosis, vessel occlusions, myocardial infarctions, and sudden death in these mice. Thus, the HypoE/SRBI(-/-) mouse model mimics major features of human coronary heart disease and might therefore be a valuable model for the investigation of molecular and cellular parameters driving plaque rupture-related events and the development of new interventional approaches.

Prolonged Intake of Dietary Lipids Alters Membrane Structure and T Cell Responses in LDLr-/- Mice

Although it is recognized that lipids and membrane organization in T cells affect signaling and T cell activation, to what extent dietary lipids alter T cell responsiveness in the absence of obesity and inflammation is not known. In this study, we fed low-density lipoprotein receptor knockout mice a Western high-fat diet for 1 or 9 wk and examined T cell responses in vivo along with T cell lipid composition, membrane order, and activation ex vivo. Our data showed that high levels of circulating lipids for a prolonged period elevated CD4(+) and CD8(+) T cell proliferation and resulted in an increased proportion of CD4(+) central-memory T cells within the draining lymph nodes following induction of contact hypersensitivity. In addition, the 9-wk Western high-fat diet elevated the total phospholipid content and monounsaturated fatty acid level, but decreased saturated phosphatidylcholine and sphingomyelin within the T cells. The altered lipid composition in the circulation, and of T cells, was also reflected by enhanced membrane order at the activation site of ex vivo activated T cells that corresponded to increased IL-2 mRNA levels. In conclusion, dietary lipids can modulate T cell lipid composition and responses in lipoprotein receptor knockout mice even in the absence of excess weight gain and a proinflammatory environment.

The role of endothelial mechanosensitive genes in atherosclerosis and omics approaches

Atherosclerosis is the leading cause of morbidity and mortality in the U.S., and is a multifactorial disease that preferentially occurs in regions of the arterial tree exposed to disturbed blood flow. The detailed mechanisms by which d-flow induces atherosclerosis involve changes in the expression of genes, epigenetic patterns, and metabolites of multiple vascular cells, especially endothelial cells. This review presents an overview of endothelial mechanobiology and its relation to the pathogenesis of atherosclerosis with special reference to the anatomy of the artery and the underlying fluid mechanics, followed by a discussion of a variety of experimental models to study the role of fluid mechanics and atherosclerosis. Various in vitro and in vivo models to study the role of flow in endothelial biology and pathobiology are discussed in this review. Furthermore, strategies used for the global profiling of the genome, transcriptome, miR-nome, DNA methylome, and metabolome, as they are important to define the biological and pathophysiological mechanisms of atherosclerosis. These "omics" approaches, especially those which derive data based on a single animal model, provide unprecedented opportunities to not only better understand the pathophysiology of atherosclerosis development in a holistic and integrative manner, but also to identify novel molecular and diagnostic targets.

Purification, structure features and anti-atherosclerosis activity of a Laminaria japonica polysaccharide

A homogeneous polysaccharide (LJP12) was isolated from Laminaria japonica by diethylaminoethyl-cellulose and Sephacryl S-500 chromatography, with a molecular weight of 2.31×10(6)Da. Monosaccharide analysis showed that LJP12 was mainly composed of arabinose, xylose, mannose, glucose and galactose in a molar ratio of 1:0.17:1.54:2.64:0.18. For these monosaccharides, mannose was suggested to be 1,4-linked and 1,3,6-linked while glucose was linked by 1,6-glycosidic bond. The xylose, arabinose and galactose were suggested to be the terminal residues. To study the effects of LJP12 on protecting against atherosclerosis, LJP12 was administered to LDL receptor-deficient (LDLr(-/-)) mice (50, 100 and 200mg/kg/day, n=30 for each experimental group). Results showed that LJP12 exhibited the ability to inhibit high-fat-cholesterol diet (HFD)-induced formation of atherosclerotic plaques and plasma lipid levels in a dose-dependent manner. Meanwhile, both the HFD-induced systemic inflammation and local inflammation at the site of atherosclerotic lesion were significantly attenuated by LJP12, which were accompanied by the suppression of the activation of nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinases (MAPKs) signaling pathways. Taken together, we concluded that long-term oral administration of LJP12 protects against atherosclerosis in LDLr(-/-) mice via inhibiting NF-κB/MAPKs-mediated inflammatory responses.

The Neurorepellent Slit2 Inhibits Postadhesion Stabilization of Monocytes Tethered to Vascular Endothelial Cells

The secreted neurorepellent Slit2, acting through its transmembrane receptor, Roundabout (Robo)-1, inhibits chemotaxis of varied cell types, including leukocytes, endothelial cells, and vascular smooth muscle cells, toward diverse attractants. The role of Slit2 in regulating the steps involved in recruitment of monocytes in vascular inflammation is not well understood. In this study, we showed that Slit2 inhibited adhesion of monocytic cells to activated human endothelial cells, as well as to immobilized ICAM-1 and VCAM-1. Microfluidic live cell imaging showed that Slit2 inhibited the ability of monocytes tethered to endothelial cells to stabilize their actin-associated anchors and to resist detachment in response to increasing shear forces. Transfection of constitutively active plasmids revealed that Slit2 inhibited postadhesion stabilization of monocytes on endothelial cells by preventing activation of Rac1. We further found that Slit2 inhibited chemotaxis of monocytes toward CXCL12 and CCL2. To determine whether Slit2 and Robo-1 modulate pathologic monocyte recruitment associated with vascular inflammation and cardiovascular disease, we tested PBMC from patients with coronary artery disease. PBMC from these patients had reduced surface levels of Robo-1 compared with healthy age- and sex-matched subjects, and Slit2 failed to inhibit chemotaxis of PBMC of affected patients, but not healthy control subjects, toward CCL2. Furthermore, administration of Slit2 to atherosclerosis-prone LDL receptor-deficient mice inhibited monocyte recruitment to nascent atherosclerotic lesions. These results demonstrate that Slit2 inhibits chemotaxis of monocytes, as well as their ability to stabilize adhesions and resist detachment forces. Slit2 may represent a powerful new tool to inhibit pathologic monocyte recruitment in vascular inflammation and atherosclerosis.

Differential role of an NF-κB transcriptional response element in endothelial versus intimal cell VCAM-1 expression

RATIONALE

Human and murine Vcam1 promoters contain 2 adjacent nuclear factor-κB (NF-κB)-binding elements. Both are essential for cytokine-induced transcription of transiently transfected promoter-reporter constructs. However, the relevance of these insights to regulation of the endogenous Vcam1 gene and to pathophysiological processes in vivo remained unknown.

OBJECTIVE

Determine the role of the 5' NF-κB-binding element in expression of the endogenous Vcam1 gene.

METHODS AND RESULTS

Homologous recombination in embryonic stem cells was used to inactivate the 5' NF-κB element in the Vcam1 promoter and alter 3 nucleotides in the 5' untranslated region to allow direct comparison of wild-type versus mutant allele RNA expression and chromatin configuration in heterozygous mice. Systemic treatment with inflammatory cytokines or endotoxin (lipopolysaccharide) induced lower expression of the mutant allele relative to wild-type by endothelial cells in the aorta, heart, and lungs. The mutant allele also showed lower endothelial expression in 2-week atherosclerotic lesions in Vcam1 heterozygous/low-density lipoprotein receptor-deficient mice fed a cholesterol-rich diet. In vivo chromatin immunoprecipitation assays of heart showed diminished lipopolysaccharide-induced association of RNA polymerase 2 and NF-κB p65 with the mutant promoter. In contrast, expression of mutant and wild-type alleles was comparable in intimal cells of wire-injured carotid artery and 4- to 12-week atherosclerotic lesions.

CONCLUSIONS

This study highlights differences between in vivo and in vitro promoter analyses, and reveals a differential role for a NF-κB transcriptional response element in endothelial vascular cell adhesion molecule-1 expression induced by inflammatory cytokines or a cholesterol-rich diet versus intimal cell expression in atherosclerotic lesions and injured arteries.

Animal Models in Cardiovascular Research: Hypertension and Atherosclerosis

Hypertension and atherosclerosis are among the most common causes of mortality in both developed and developing countries. Experimental animal models of hypertension and atherosclerosis have become a valuable tool for providing information on etiology, pathophysiology, and complications of the disease and on the efficacy and mechanism of action of various drugs and compounds used in treatment. An animal model has been developed to study hypertension and atherosclerosis for several reasons. Compared to human models, an animal model is easily manageable, as compounding effects of dietary and environmental factors can be controlled. Blood vessels and cardiac tissue samples can be taken for detailed experimental and biomolecular examination. Choice of animal model is often determined by the research aim, as well as financial and technical factors. A thorough understanding of the animal models used and complete analysis must be validated so that the data can be extrapolated to humans. In conclusion, animal models for hypertension and atherosclerosis are invaluable in improving our understanding of cardiovascular disease and developing new pharmacological therapies.

Hypercholesterolemia induces angiogenesis and accelerates growth of breast tumors in vivo

Obesity and metabolic syndrome are linked to an increased prevalence of breast cancer among postmenopausal women. A common feature of obesity, metabolic syndrome, and a Western diet rich in saturated fat is a high level of circulating cholesterol. Epidemiological reports investigating the relationship between high circulating cholesterol levels, cholesterol-lowering drugs, and breast cancer are conflicting. Here, we modeled this complex condition in a well-controlled, preclinical animal model using innovative isocaloric diets. Female severe combined immunodeficient mice were fed a low-fat/no-cholesterol diet and then randomized to four isocaloric diet groups: low-fat/no-cholesterol diet, with or without ezetimibe (cholesterol-lowering drug), and high-fat/high-cholesterol diet, with or without ezetimibe. Mice were implanted orthotopically with MDA-MB-231 cells. Breast tumors from animals fed the high-fat/high-cholesterol diet exhibited the fastest progression. Significant differences in serum cholesterol level between groups were achieved and maintained throughout the study; however, no differences were observed in intratumoral cholesterol levels. To determine the mechanism of cholesterol-induced tumor progression, we analyzed tumor proliferation, apoptosis, and angiogenesis and found a significantly greater percentage of proliferating cells from mice fed the high-fat/high-cholesterol diet. Tumors from hypercholesterolemic animals displayed significantly less apoptosis compared with the other groups. Tumors from high-fat/high-cholesterol mice had significantly higher microvessel density compared with tumors from the other groups. These results demonstrate that hypercholesterolemia induces angiogenesis and accelerates breast tumor growth in vivo.

Syndecan 4 is required for endothelial alignment in flow and atheroprotective signaling

Atherosclerotic plaque localization correlates with regions of disturbed flow in which endothelial cells (ECs) align poorly, whereas sustained laminar flow correlates with cell alignment in the direction of flow and resistance to atherosclerosis. We now report that in hypercholesterolemic mice, deletion of syndecan 4 (S4(-/-)) drastically increased atherosclerotic plaque burden with the appearance of plaque in normally resistant locations. Strikingly, ECs from the thoracic aortas of S4(-/-) mice were poorly aligned in the direction of the flow. Depletion of S4 in human umbilical vein endothelial cells (HUVECs) using shRNA also inhibited flow-induced alignment in vitro, which was rescued by re-expression of S4. This effect was highly specific, as flow activation of VEGF receptor 2 and NF-κB was normal. S4-depleted ECs aligned in cyclic stretch and even elongated under flow, although nondirectionally. EC alignment was previously found to have a causal role in modulating activation of inflammatory versus antiinflammatory pathways by flow. Consistent with these results, S4-depleted HUVECs in long-term laminar flow showed increased activation of proinflammatory NF-κB and decreased induction of antiinflammatory kruppel-like factor (KLF) 2 and KLF4. Thus, S4 plays a critical role in sensing flow direction to promote cell alignment and inhibit atherosclerosis.

The cytochrome P450 epoxygenase pathway regulates the hepatic inflammatory response in fatty liver disease

Fatty liver disease is an emerging public health problem without effective therapies, and chronic hepatic inflammation is a key pathologic mediator in its progression. Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid to biologically active epoxyeicosatrienoic acids (EETs), which have potent anti-inflammatory effects. Although promoting the effects of EETs elicits anti-inflammatory and protective effects in the cardiovascular system, the contribution of CYP-derived EETs to the regulation of fatty liver disease-associated inflammation and injury is unknown. Using the atherogenic diet model of non-alcoholic fatty liver disease/non-alcoholic steatohepatitis (NAFLD/NASH), our studies demonstrated that induction of fatty liver disease significantly and preferentially suppresses hepatic CYP epoxygenase expression and activity, and both hepatic and circulating levels of EETs in mice. Furthermore, mice with targeted disruption of Ephx2 (the gene encoding soluble epoxide hydrolase) exhibited restored hepatic and circulating EET levels and a significantly attenuated induction of hepatic inflammation and injury. Collectively, these data suggest that suppression of hepatic CYP-mediated EET biosynthesis is an important pathological consequence of fatty liver disease-associated inflammation, and that the CYP epoxygenase pathway is a central regulator of the hepatic inflammatory response in NAFLD/NASH. Future studies investigating the utility of therapeutic strategies that promote the effects of CYP-derived EETs in NAFLD/NASH are warranted.

Early onset intrauterine growth restriction in a mouse model of gestational hypercholesterolemia and atherosclerosis

The susceptibility to develop atherosclerosis is increased by intrauterine growth restriction and prenatal exposure to maternal hypercholesterolemia. Here, we studied whether mouse gestational hypercholesterolemia and atherosclerosis affected fetal development and growth at different stages of gestation. Female LDLR KO mice fed a proatherogenic, high cholesterol (HC) diet for 3 weeks before conception and during pregnancy exhibited a significant increase in non-HDL cholesterol and developed atherosclerosis. At embryonic days 12.5 (E12.5), E15.5, and E18.5, maternal gestational hypercholesterolemia and atherosclerosis were associated to a 22-24% reduction in male and female fetal weight without alterations in fetal number/litter or morphology nor placental weight or structure. Feeding the HC diet exclusively at the periconceptional period did not alter fetal growth, suggesting that maternal hypercholesterolemia affected fetal weight only after implantation. Vitamin E supplementation (1,000 UI of α-tocopherol/kg) of HC-fed females did not change the mean weight of E18.5 fetuses but reduced the percentage of fetuses exhibiting body weights below the 10th percentile of weight (HC: 90% vs. HC/VitE: 68%). In conclusion, our results showed that maternal gestational hypercholesterolemia and atherosclerosis in mice were associated to early onset fetal growth restriction and that dietary vitamin E supplementation had a beneficial impact on this condition.

Disruption of ldlr causes increased LDL-c and vascular lipid accumulation in a zebrafish model of hypercholesterolemia

Hyperlipidemia and arterial cholesterol accumulation are primary causes of cardiovascular events. Monogenic forms of hyperlipidemia and recent genome-wide association studies indicate that genetics plays an important role. Zebrafish are a useful model for studying the genetic susceptibility to hyperlipidemia owing to conservation of many components of lipoprotein metabolism, including those related to LDL, ease of genetic manipulation, and in vivo observation of lipid transport and vascular calcification. We sought to develop a genetic model for lipid metabolism in zebrafish, capitalizing on one well-understood player in LDL cholesterol (LDL-c) transport, the LDL receptor (ldlr), and an established in vivo model of hypercholesterolemia. We report that morpholinos targeted against the gene encoding ldlr effectively suppressed its expression in embryos during the first 8 days of development. The ldlr morphants exhibited increased LDL-c levels that were exacerbated by feeding a high cholesterol diet. Increased LDL-c was ameliorated in morphants upon treatment with atorvastatin. Furthermore, we observed significant vascular and liver lipid accumulation, vascular leakage, and plaque oxidation in ldlr-deficient embryos. Finally, upon transcript analysis of several cholesterol-regulating genes, we observed changes similar to those seen in mammalian systems, suggesting that cholesterol regulation may be conserved in zebrafish. Taken together, these observations indicate conservation of ldlr function in zebrafish and demonstrate the utility of transient gene knockdown in embryos as a genetic model for hyperlipidemia.

Pathobiology of aging mice and GEM: background strains and experimental design

The use of induced and spontaneous mutant mice and genetically engineered mice (and combinations thereof) to study cancers and other aging phenotypes to advance improved functional human life spans will involve studies of aging mice. Genetic background contributes to pathology phenotypes and to causes of death as well as to longevity. Increased recognition of expected phenotypes, experimental variables that influence phenotypes and research outcomes, and experimental design options and rationales can maximize the utility of genetically engineered mice (GEM) models to translational research on aging. This review aims to provide resources to enhance the design and practice of chronic and longevity studies involving GEM. C57BL6, 129, and FVB/N strains are emphasized because of their widespread use in the generation of knockout, transgenic, and conditional mutant GEM. Resources are included also for pathology of other inbred strain families, including A, AKR, BALB/c, C3H, C57L, C58, CBA, DBA, GR, NOD.scid, SAMP, and SJL/J, and non-inbred mice, including 4WC, AB6F1, Ames dwarf, B6, 129, B6C3F1, BALB/c,129, Het3, nude, SENCAR, and several Swiss stocks. Experimental strategies for long-term cross-sectional and longitudinal studies to assess causes of or contributors to death, disease burden, spectrum of pathology phenotypes, longevity, and functional healthy life spans (health spans) are compared and discussed.

Red yeast rice and coenzyme Q10 as safe alternatives to surmount atorvastatin-induced myopathy in hyperlipidemic rats

Statins are the first line treatment for the management of hyperlipidemia. However, the primary adverse effect limiting their use is myopathy. This study examines the efficacy and safety of red yeast rice (RYR), a source of natural statins, as compared with atorvastatin, which is the most widely used synthetic statin. Statin interference with the endogenous synthesis of coenzyme Q10 (CoQ10) prompted the hypothesis that its deficiency may be implicated in the pathogenesis of statin-associated myopathy. Hence, the effects of combination of CoQ10 with either statin have been evaluated. Rats were rendered hyperlipidemic through feeding them a high-fat diet for 90 days, during the last 30 days of the diet they were treated daily with either atorvastatin, RYR, CoQ10, or combined regimens. Lipid profile, liver function tests, and creatine kinase were monitored after 15 and 30 days of drug treatments. Heart contents of CoQ9 and CoQ10 were assessed and histopathological examination of the liver and aortic wall was performed. RYR and CoQ10 had the advantage over atorvastatin in that they lower cholesterol without elevating creatine kinase, a hallmark of myopathy. RYR maintained normal levels of heart ubiquinones, which are essential components for energy production in muscles. In conclusion, RYR and CoQ10 may offer alternatives to overcome atorvastatin-associated myopathy.

Targeted disruption of LDLR causes hypercholesterolemia and atherosclerosis in Yucatan miniature pigs

Recent progress in engineering the genomes of large animals has spurred increased interest in developing better animal models for diseases where current options are inadequate. Here, we report the creation of Yucatan miniature pigs with targeted disruptions of the low-density lipoprotein receptor (LDLR) gene in an effort to provide an improved large animal model of familial hypercholesterolemia and atherosclerosis. Yucatan miniature pigs are well established as translational research models because of similarities to humans in physiology, anatomy, genetics, and size. Using recombinant adeno-associated virus-mediated gene targeting and somatic cell nuclear transfer, male and female LDLR+/− pigs were generated. Subsequent breeding of heterozygotes produced LDLR−/− pigs. When fed a standard swine diet (low fat, no cholesterol), LDLR+/− pigs exhibited a moderate, but consistent increase in total and LDL cholesterol, while LDLR−/− pigs had considerably elevated levels. This severe hypercholesterolemia in homozygote animals resulted in atherosclerotic lesions in the coronary arteries and abdominal aorta that resemble human atherosclerosis. These phenotypes were more severe and developed over a shorter time when fed a diet containing natural sources of fat and cholesterol. LDLR-targeted Yucatan miniature pigs offer several advantages over existing large animal models including size, consistency, availability, and versatility. This new model of cardiovascular disease could be an important resource for developing and testing novel detection and treatment strategies for coronary and aortic atherosclerosis and its complications.

An accelerated mouse model for atherosclerosis and adipose tissue inflammation

Background

Obesity and particularly the metabolic syndrome, which is often associated with obesity, combine a major risk for type 2 diabetes and cardiovascular disease. Emerging evidence indicate obesity-associated subclinical inflammation primarily originating from adipose tissue as a common cause for type 2 diabetes and cardiovascular disease. However, a suitable and well-characterized mouse model to simultaneously study obesity-associated metabolic disorders and atherosclerosis is not available yet. Here we established and characterized a murine model combining diet-induced obesity and associated adipose tissue inflammation and metabolic deteriorations as well as atherosclerosis, hence reflecting the human situation of cardio-metabolic disease.

Methods

We compared a common high-fat diet with 0.15% cholesterol (HFC), and a high-fat, high-sucrose diet with 0.15% cholesterol (HFSC) fed to LDL receptor-deficient (LDLR^-/-) mice. Insulin resistance, glucose tolerance, atherosclerotic lesion formation, hepatic lipid accumulation, and inflammatory gene expression in adipose tissue and liver were assessed.

Results

After 12–16 weeks, LDLR^-/- mice fed HFSC or HFC developed significant diet-induced obesity, adipose tissue inflammation, insulin resistance, and impaired glucose tolerance compared to lean controls. Notably, HFSC-fed mice developed significantly higher adipose tissue inflammation in parallel with significantly elevated atherosclerotic lesion area compared to those on HFC. Moreover, LDLR^-/- mice on HFSC showed increased insulin resistance and impaired glucose tolerance relative to those on HFC. After prolonged feeding (20 weeks), however, no significant differences in inflammatory and metabolic parameters as well as atherosclerotic lesion formation were detectable any more between LDLR^-/- mice fed HFSC or HFC.

Conclusion

The use of high sucrose rather than more complex carbohydrates in high-fat diets significantly accelerates development of obesity-driven metabolic complications and atherosclerotic plaque formation parallel to obesity-induced adipose tissue inflammation in LDLR^-/- mice. Hence LDLR^-/- mice fed high-fat high-sucrose cholesterol-enriched diet appear to be a suitable and time-saving animal model for cardio-metabolic disease. Moreover our results support the suggested interrelation between adipose tissue inflammation and atherosclerotic plaque formation.

Long-term vitamin E supplementation reduces atherosclerosis and mortality in Ldlr-/- mice, but not when fed Western style diet

OBJECTIVES

Epidemiological and experimental evidence have indicated potential health benefits of vitamin E supplementation on coronary heart disease (CHD), but several clinical trials have reported no benefit from vitamin E supplementation on CHD. We hypothesized that supplemental intake of vitamin E from an early age may prevent or retard the development and progression of atherosclerosis and CHD mortality.

METHODS

To test this hypothesis, 300 Ldlr(-/-) mice were divided into groups receiving Western style high fat/cholesterol (HFHC), moderate fat/cholesterol (MFMC), or low fat/cholesterol (LFLC) diets all containing 50 IU of vitamin E. These dietary groups were further subdivided into four sub-groups (n = 25) receiving their respective diets with no vitamin E supplementation or additionally supplemented with vitamin E (500 IU/kg diet) starting at the early age of 5 wks, or 6 mo, or 12 mo. All mice remained on their assigned diets until age 18 mo. Body weight, health status and survival rate of mice were monitored and recorded. After 18 mo of dietary treatments, mice were sacrificed.

RESULTS

Body weight was the highest in HFHC groups and the lowest in LFLC groups. Plasma concentration of cholesterol and triglycerides was high in all dietary groups, and plasma vitamin E was high in vitamin E supplemented groups. Fifty percent of mice fed Western style HFHC diet and 53% of mice fed MFMC diet survived during the 18 mo, whereas 75% of mice fed LFLC diet survived during the 18 mo dietary treatments. At the age of 18 mo, all the Ldlr(-/-) mice, regardless of dietary treatments, had several advanced atherosclerotic lesions in both aortic root and aortic tree. Within the LFLC groups, those that received vitamin E supplements from age 5 wks up to 18 mo had a significantly higher survival rate of 88% (p = 0.04) and lower mortality (12%) compared to mice that did not receive vitamin E supplements (64%). This lower mortality rate and higher survival rate coincided with significantly (p = 0.03) fewer aortic lesions in the vitamin E supplemented LFLC group (50%) compared to LFLC mice that did not receive vitamin E supplements in their diets (65%). Subjective immunohistochemical evaluation of aortic valves showed that LFLC mice that received vitamin E supplements for 18 mo had less intima media thickness compared to LFLC mice that did not receive vitamin E supplements in their diet. The LFLC mice that were supplemented with vitamin E for 18 mo had the lowest mRNA expression of inflammatory markers such as VCAM-1, MCP-1 and CD36 in samples obtained from lesion and non-lesionareas.

CONCLUSION

In conclusion, 500 mg vitamin E/kg diet in Ldlr(-/-) mice is not effective at reducing mortality and atherosclerosis when the diet contained high or medium levels of fat and cholesterol. However, a relatively low dose and long-term vitamin E supplementation started from an early age is effective in reducing mortality and atherosclerotic lesions in genetically prone Ldlr(-/-) mice fed LFLC diet.

Rapid development of atherosclerosis in the world's smallest Microminipig fed a high-fat/high-cholesterol diet

AIM

Experimental studies of human atherogenesis require an appropriate animal model that mimics human physiology and pathology. Because swine physiology is similar to human physiology, we developed a hyperlipidemia-induced atherosclerosis model using the recently developed world's smallest Microminipig(TM).

METHODS

These animals weigh only 5kg at 3months of age, much smaller than any other miniature pig. We found that the administration of a high-fat/high-cholesterol diet containing at least 0.2% cholesterol without cholic acid for as little as eight weeks induces hypercholesterolemia and subsequent atherosclerosis in these animals.

RESULTS

The serum levels of low-density lipoprotein cholesterol(LDL-C) and the percent distribution of cholesterol in the LDL fractions were markedly increased. The hepatic expression of LDL receptor and hydroxymethylglutaryl-CoA reductase was coordinately decreased. The cholesteryl ester transfer protein activity, which plays a role in reverse cholesterol transport, was detected in the serum of the Microminipigs. Niemann-Pick C1-like 1 protein was expressed in both the liver and small intestine; however, hepatic apoB mRNA editing enzyme was not expressed. As in humans, and in contrast to that observed in mice, most of the hepatic lipase activity was localized in the liver. These results suggest that the hyperlipidemia-induced gene expression profile linked to cholesterol homeostasis and atherogenesis is similar in Microminipigs and humans.

CONCLUSION

We conclude that the characteristics of the Microminipig, including its easy handling size, make it an appropriate model for studies of atherosclerosis and related conditions.

Involvement of regucalcin in lipid metabolism and diabetes

Regucalcin (RGN/SMP30) was originally discovered in 1978 as a unique calcium-binding protein that does not contain the EF-hand motif of calcium-binding domain. The regucalcin gene (rgn) is localized on the X chromosome and is identified in over 15 species consisting the regucalcin family. Regucalcin has been shown to play a multifunctional role in cell regulation; maintaining of intracellular calcium homeostasis and suppressing of signal transduction, translational protein synthesis, nuclear deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) synthesis, proliferation, and apoptosis in many cell types. Moreover, regucalcin may play a pathophysiological role in metabolic disorder. The expression of regucalcin is stimulated through the action of insulin in liver cells in vitro and in vivo and it is decreased in the liver of rats with type I diabetes induced by streptozotocin administration in vivo. Overexpression of endogenous regucalcin stimulates glucose utilization and lipid production in liver cells with glucose supplementation in vitro. Regucalcin reveals insulin resistance in liver cells. Deficiency of regucalcin induces an impairment of glucose tolerance and lipid accumulation in the liver of mice in vivo. Overexpression of endogenous regucalcin has been shown to decrease triglyceride, total cholesterol and glycogen contents in the liver of rats, inducing hyperlipidemia. Leptin and adiponectin mRNA expressions in the liver tissues are decreased in regucalcin transgenic rats. Decrease in hepatic regucalcin is associated with the development and progression of nonalcoholic fatty liver disease and fibrosis in human patients. Regucalcin may be a key molecule in lipid metabolic disorder and diabetes.

t-10, c-12 CLA dietary supplementation inhibits atherosclerotic lesion development despite adverse cardiovascular and hepatic metabolic marker profiles

Animal and human studies have indicated that fatty acids such as the conjugated linoleic acids (CLA) found in milk could potentially alter the risk of developing metabolic disorders including diabetes and cardiovascular disease (CVD). Using susceptible rodent models (apoE^−/− and LDLr^−/− mice) we investigated the interrelationship between mouse strain, dietary conjugated linoleic acids and metabolic markers of CVD. Despite an adverse metabolic risk profile, atherosclerosis (measured directly by lesion area), was significantly reduced with t-10, c-12 CLA and mixed isomer CLA (Mix) supplementation in both apoE^−/− (p<0.05, n = 11) and LDLr^−/− mice (p<0.01, n = 10). Principal component analysis was utilized to delineate the influence of multiple plasma and tissue metabolites on the development of atherosclerosis. Group clustering by dietary supplementation was evident, with the t-10, c-12 CLA supplemented animals having distinct patterns, suggestive of hepatic insulin resistance, regardless of mouse strain. The effect of CLA supplementation on hepatic lipid and fatty acid composition was explored in the LDLr^−/− strain. Dietary supplementation with t-10, c-12 CLA significantly increased liver weight (p<0.05, n = 10), triglyceride (p<0.01, n = 10) and cholesterol ester content (p<0.01, n = 10). Furthermore, t-10, c-12 CLA also increased the ratio of 18∶1 to 18∶0 fatty acid in the liver suggesting an increase in the activity of stearoyl-CoA desaturase. Changes in plasma adiponectin and liver weight with t-10, c-12 CLA supplementation were evident within 3 weeks of initiation of the diet. These observations provide evidence that the individual CLA isomers have divergent mechanisms of action and that t-10, c-12 CLA rapidly changes plasma and liver markers of metabolic syndrome, despite evidence of reduction in atherosclerosis.

Impact of probiotic-supplemented diet on the expression level of lactate dehydrogenase in the leukocytes of rabbits

Probiotics are known as living, nonpathogenic microorganisms that colonize the intestine and provide benefit to the host. The present study aims to measure one important energy metabolism-related enzyme activity in blood of rabbits fed on probiotics of recommended concentration. In addition, it also aims for the evaluation of the expression level of lactate dehydrogenase (LDH) enzyme using reverse transcriptase-polymerase chain reaction (RT-PCR) technique. Two groups of rabbits are used: control group receiving normal standardized diet and the other probiotic-supplemented group receiving the same diet containing probiotic, namely, Mega acidophilus (200 million cfu/kg body weight/day) for 4 weeks. The obtained results revealed that the rabbits supplemented with probiotics showed a significant decrease in the levels of serum total cholesterol (TC), triacylglycerol, high-density lipoprotein cholesterol (HDL-c) and low-density lipoprotein cholesterol (LDL-c) when compared with control group. Risk factors detected by measuring TC/HDL-c and LDL-c/HDL-c ratios showed statistically significant decrease in probiotic-supplemented rabbits when compared with control group. In addition, blood glucose and total LDH activity were elevated in probiotic-supplemented rabbits when compared with control group. RT-PCR products of LDH-M gene produced two specific amplicons. One amplicon has the expected size of 243 bp from all samples of rabbits as revealed by GelPro software. The level of LDH-M expression was found to be increased in the probiotic-supplemented group. However, unexpected amplicons are produced at 586 bp in all the samples, which may be a dimeric form of the amplified region. It was concluded that this probiotic blend is beneficiary for the metabolic reactions of lipids in the body. Moreover, LDH expression level can be considered as a biomarker for the effect of probiotic and hence monitoring the metabolic changes as reflected from its administration.

Haemodynamics in the mouse aortic arch computed from MRI-derived velocities at the aortic root

Mice are widely used to investigate atherogenesis, which is known to be influenced by stresses related to blood flow. However, numerical characterization of the haemodynamic environment in the commonly studied aortic arch has hitherto been based on idealizations of inflow into the aorta. Our purpose in this work was to numerically characterize the haemodynamic environment in the mouse aortic arch using measured inflow velocities, and to relate the resulting shear stress patterns to known locations of high- and low-lesion prevalence. Blood flow velocities were measured in the aortic root of C57/BL6 mice using phase-contrast MRI. Arterial geometries were obtained by micro-CT of corrosion casts. These data were used to compute blood flow and wall shear stress (WSS) patterns in the arch. WSS profiles computed using realistic and idealized aortic root velocities differed significantly. An unexpected finding was that average WSS in the high-lesion-probability region on the inner wall was actually higher than the WSS in the low-probability region on the outer wall. Future studies of mouse aortic arch haemodynamics should avoid the use of idealized inflow velocity profiles. Lesion formation does not seem to uniquely associate with low or oscillating WSS in this segment, suggesting that other factors may also play a role in lesion localization.

Hypercholesterolemia promotes an osteoporotic phenotype

A role for hypercholesterolemia in the development of osteoporosis has been suggested in published reports. However, few studies contain direct evidence of a role for maintenance of cholesterol homeostasis in bone health. Using isocaloric high-fat/high-cholesterol and low-fat/no-cholesterol diets in a 4-month feeding study combined with micro computed tomography analysis, we demonstrated in two different mouse strains that mice with hypercholesterolemia lose cortical and trabecular bone in the femurs and vertebrae (bone mineral density was decreased on average by ≈90 mg/mL in the cortical vertebrae in one strain) and cortical bone in the calvariae (bone mineral density was decreased on average by ≈60 mg/mL in one strain). Mechanical testing of the femurs demonstrated that loss of bone in the mice with hypercholesterolemia caused changes in the mechanical properties of the bone including loss of failure load (failure load was decreased by ≈10 N in one strain) and energy to failure. Serologic and histomorphologic analyses suggested that hypercholesterolemia promotes osteoclastogenesis. These studies support a role for hypercholesterolemia in the development of osteoporosis and provide a model with which to test intervention strategies to reduce the effects of hypercholesterolemia on bone health.