Non-obese diabetic (NOD) mice exhibit an increased cellular immune response to glycated-LDL but are resistant to high fat diet induced atherosclerosis

Transcriptional analysis reveals that the intracellular lipid accumulation impairs gene expression profiles involved in insulin response-associated cardiac functionality

Cardiovascular disease (CVD) is a multisystemic and multicellular pathology that is generally associated with high levels of atherogenic lipoproteins in circulation. These lipoproteins tend to be retained and modified, for example, aggregated low-density lipoprotein (aggLDL), in the extracellular matrix of different tissues, such as the vascular wall and heart. The uptake of aggLDL generates a significant increase in cholesteryl ester (CE) in these tissues. We previously found that the accumulation of CE generates alterations in the insulin response in the heart. Although the insulin response is mainly associated with the uptake and metabolism of glucose, other studies have shown that insulin would fulfill functions in this tissue, such as regulating the calcium cycle and cardiac contractility. Here, we found that aggLDL induced-lipid accumulation altered the gene expression profile involved in processes essential for cardiac functionality, including insulin response and glucose uptake (Insr, Ins1, Pik3ip1, Slc2a4 gene expression), calcium cycle (Cacna1s and Gjc2 gene expression) and calcium-dependent cardiac contractility (Myh3), and cholesterol efflux (Abca1), in HL-1 cardiomyocytes. These observations were recapitulated using an in vivo model of hypercholesterolemic ApoE-KO mice. Altogether, these results may explain the deleterious effect of lipid accumulation in the myocardium, with important implications for lipid-overloaded associated CVD, including impaired insulin response, disrupted lipid metabolism, altered cardiac structure, and increased susceptibility to cardiovascular events.

Transcriptional analysis reveals that the intracellular lipid accumulation impairs gene expression profiles involved in insulin response-associated cardiac functionality

Cardiovascular disease (CVD) is a multisystemic and multicellular pathology that is generally associated with high levels of atherogenic lipoproteins in circulation. These lipoproteins tend to be retained and modified, for example, aggregated low-density lipoprotein (aggLDL), in the extracellular matrix of different tissues, such as the vascular wall and heart. The uptake of aggLDL generates a significant increase in cholesteryl ester (CE) in these tissues. We previously found that the accumulation of CE generates alterations in the insulin response in the heart. Although the insulin response is mainly associated with the uptake and metabolism of glucose, other studies have shown that insulin would fulfill functions in this tissue, such as regulating the calcium cycle and cardiac contractility. Here, we found that aggLDL induced-lipid accumulation altered the gene expression profile involved in processes essential for cardiac functionality, including insulin response and glucose uptake ( Insr , Ins1 , Pik3ip1 , Slc2a4 gene expression), calcium cycle ( Cacna1s and Gjc2 gene expression) and calcium-dependent cardiac contractility ( Myh3 ), and cholesterol efflux ( Abca1 ), in HL-1 cardiomyocytes. These observations were recapitulated using an in vivo model of hypercholesterolemic ApoE-KO mice. Altogether, these results may explain the deleterious effect of lipid accumulation in the myocardium, with important implications for lipid-overloaded associated CVD.

Novel Nongenetic Murine Model of Hyperglycemia and Hyperlipidemia-Associated Aggravated Atherosclerosis

Objective

Atherosclerosis, the main pathology underlying cardiovascular diseases is accelerated in diabetic patients. Genetic mouse models require breeding efforts which are time-consuming and costly. Our aim was to establish a new nongenetic model of inducible metabolic risk factors that mimics hyperlipidemia, hyperglycemia, or both and allows the detection of phenotypic differences dependent on the metabolic stressor(s).

Methods and Results

Wild-type mice were injected with gain-of-function PCSK9^D377Y (proprotein convertase subtilisin/kexin type 9) mutant adeno-associated viral particles (AAV) and streptozotocin and fed either a high-fat diet (HFD) for 12 or 20 weeks or a high-cholesterol/high-fat diet (Paigen diet, PD) for 8 weeks. To evaluate atherosclerosis, two different vascular sites (aortic sinus and the truncus of the brachiocephalic artery) were examined in the mice. Combined hyperlipidemic and hyperglycemic (HGHCi) mice fed a HFD or PD displayed characteristic features of aggravated atherosclerosis when compared to hyperlipidemia (HCi HFD or PD) mice alone. Atherosclerotic plaques of HGHCi HFD animals were larger, showed a less stable phenotype (measured by the increased necrotic core area, reduced fibrous cap thickness, and less α-SMA-positive area) and had more inflammation (increased plasma IL-1β level, aortic pro-inflammatory gene expression, and MOMA-2-positive cells in the BCA) after 20 weeks of HFD. Differences between the HGHCi and HCi HFD models were confirmed using RNA-seq analysis of aortic tissue, revealing that significantly more genes were dysregulated in mice with combined hyperlipidemia and hyperglycemia than in the hyperlipidemia-only group. The HGHCi-associated genes were related to pathways regulating inflammation (increased Cd68, iNos, and Tnfa expression) and extracellular matrix degradation (Adamts4 and Mmp14). When comparing HFD with PD, the PD aggravated atherosclerosis to a greater extent in mice and showed plaque formation after 8 weeks. Hyperlipidemic and hyperglycemic mice fed a PD (HGHCi PD) showed less collagen (Sirius red) and increased inflammation (CD68-positive cells) within aortic plaques than hyperlipidemic mice (HCi PD). HGHCi-PD mice represent a directly inducible hyperglycemic atherosclerosis model compared with HFD-fed mice, in which atherosclerosis is severe by 8 weeks.

Conclusion

We established a nongenetically inducible mouse model allowing comparative analyses of atherosclerosis in HCi and HGHCi conditions and its modification by diet, allowing analyses of multiple metabolic hits in mice.

Metformin Delays the Development of Atherosclerosis in Type 1 Diabetes Mellitus via the Methylglyoxal Pathway

INTRODUCTION

The aim of our study was to determine the effect of metformin administration on juvenile type 1 diabetes mellitus and atherosclerosis in apolipoprotein E null (ApoE^-/-) mice and to explore the mechanism involved.

METHODS

Eighteen male ApoE^-/- mice were injected with streptozotocin to induce diabetes (diabetic group) and 18 mice who received no streptozotocin injection were assigned to the control (non-diabetic) group. Six mice in each group were then orally administered metformin, simvastatin, or vehicle, respectively, following which the mice were euthanized and tissue samples collected.

RESULTS

Fasting plasma glucose, low-density lipoprotein-cholesterol, and triglyceride concentrations were significantly higher in the three diabetic groups than in the three non-diabetic groups. Plasma N^∈-(carboxymethyl)lysine and N^∈-(carboxyethyl)lysine concentrations were higher in the diabetic mice than in the non-diabetic mice, but metformin treatment reduced these concentrations more effectively than simvastatin. All three diabetic groups demonstrated obvious arterial plaques, but these were largest in the vehicle-treated diabetic group. The expression of extracellular nitric oxide synthase was highest in the simvastatin-treated non-diabetic group, and in diabetic mice it was higher in the simvastatin-treated group than in the other two groups. No significant expression of AMP-activated protein kinase (AMPK) was measured in the three diabetic groups, but a low level of AMPK expression was detected in the non-diabetic groups.

CONCLUSIONS

Metformin can limit the development of atherosclerosis secondary to diabetes in young diabetic mice. A possible mechanism is the removal of methylglyoxal, thereby reducing the formation of advanced glycation endproducts, rather than by lowering the blood glucose level.

FUNDING

This work was supported by the National Natural Science Foundation of China (81901106) and Jinan clinical medical science and technology innovation plan (201907002).

A severe atherosclerosis mouse model on the resistant NOD background

Atherosclerosis is a complex disease affecting arterial blood vessels and blood flow that could result in a variety of life-threatening consequences. Disease models with diverged genomes are necessary for understanding the genetic architecture of this complex disease. Non-obese diabetic (NOD) mice are highly polymorphic and widely used for studies of type 1 diabetes and autoimmunity. Understanding atherosclerosis development in the NOD strain is of particular interest as human atherosclerosis on the diabetic and autoimmune background has not been successfully modeled. In this study, we used CRISPR/Cas9 genome editing to genetically disrupt apolipoprotein E (ApoE) and low-density lipoprotein receptor (LDLR) expression on the pure NOD background, and compared phenotype between single-gene-deleted mice and double-knockout mutants with reference to ApoE-deficient C57BL/6 mice. We found that genetic ablation of Ldlr or Apoe in NOD mice was not sufficient to establish an atherosclerosis model, in contrast to ApoE-deficient C57BL/6 mice fed a high-fat diet (HFD) for over 12 weeks. We further obtained NOD mice deficient in both LDLR and ApoE, and assessed the severity of atherosclerosis and immune response to hyperlipidemia in comparison to ApoE-deficient C57BL/6 mice. Strikingly, the double-knockout NOD mice treated with a HFD developed severe atherosclerosis with aorta narrowed by over 60% by plaques, accompanied by destruction of pancreatic islets and an inflammatory response to hyperlipidemia. Therefore, we succeeded in obtaining a genetic model with severe atherosclerosis on the NOD background, which is highly resistant to the disease. This model is useful for the study of atherosclerosis in the setting of autoimmunity.

Hypercholesterolemia induces T cell expansion in humanized immune mice

Emerging data suggest that hypercholesterolemia has stimulatory effects on adaptive immunity and that these effects can promote atherosclerosis and perhaps other inflammatory diseases. However, research in this area has relied primarily on inbred strains of mice whose adaptive immune system can differ substantially from that of humans. Moreover, the genetically induced hypercholesterolemia in these models typically results in plasma cholesterol levels that are much higher than those in most humans. To overcome these obstacles, we studied human immune system-reconstituted mice (hu-mice) rendered hypercholesterolemic by treatment with adeno-associated virus 8-proprotein convertase subtilisin/kexin type 9 (AAV8-PCSK9) and a high-fat/high-cholesterol Western-type diet (WD). These mice had a high percentage of human T cells and moderate hypercholesterolemia. Compared with hu-mice that had lower plasma cholesterol, the PCSK9-WD mice developed a T cell-mediated inflammatory response in the lung and liver. Human CD4+ and CD8+ T cells bearing an effector memory phenotype were significantly elevated in the blood, spleen, and lungs of PCSK9-WD hu-mice, whereas splenic and circulating regulatory T cells were reduced. These data show that moderately high plasma cholesterol can disrupt human T cell homeostasis in vivo. This process may not only exacerbate atherosclerosis, but also contribute to T cell-mediated inflammatory diseases in the hypercholesterolemia setting.

Absence of clinical relationship between oxidized low density lipoproteins and diabetic peripheral neuropathy: a case control study

Background

The pathophysiology of diabetic peripheral neuropathy (DPN) is complex and uncertain. A potential comorbidity in diabetes mellitus (DM) that may contribute to greater severity of DPN is a lipid disorder, such as with elevated cholesterol, low density lipoproteins or triglycerides. Oxidized low density lipoprotein (oxLDL) is a form of cholesterol that exerts direct toxic effects and contributes to pathogenicity through ligating a receptor called lectin-like receptor (LOX-1).

Methods

We examined plasma oxLDL levels in cohorts of patients with DPN with neuropathic pain (NeP), DPN patients without NeP, DM patients without DPN, patients with idiopathic peripheral neuropathy, and control subjects without DM or neuropathy. Our outcome measure was extent of oxLDL elevation, measured as fasting with Enzyme-Linked ImmunoSorbant Assay (ELISA) studies. Severity of diabetes was assessed using hemoglobin A1C measurements. Neuropathic severity was measured with the Utah Early Neuropathy Score (UENS). We hypothesized that DPN presence would be associated with oxLDL elevations.

Results

A total of 115 subjects (47 with DPN and NeP, 23 with DPN without NeP, 12 with diabetes only, 13 with idiopathic peripheral neuropathy, and 20 control subjects without diabetes or neuropathy) were studied. Duration of diabetes and diabetic glycemic measures were similar between populations with DM. Severity of DPN was similar between cohorts with DPN and NeP and DPN without NeP. Plasma oxLDL levels were similar between all cohorts, without any elevation in the presence of DM noted in any cohort with DM.

Conclusions

oxLDL levels are not different in patients with DPN, and their lack of greater presence suggests that any pathogenic role in human DPN is likely limited.

Effect of high-fat diet on peripheral neuropathy in C57BL/6 mice

Objective. Dyslipidemia may contribute to the development of peripheral neuropathy, even in prediabetics; however, few studies have evaluated vascular dysfunction and oxidative stress in patients with peripheral neuropathy. Methods. Using high-fat diet- (HFD-) induced prediabetic C57BL/6 mice, we assessed motor and sensory nerve conduction velocity (NCV) using a BIOPAC System and thermal algesia with a Plantar Test (Hargreaves' method) Analgesia Meter. Intraepidermal nerve fiber density and mean dendrite length were tested following standard protocols. Vascular endothelial growth factor-A (VEGF-A) and 12/15-lipoxygenase (12/15-LOX) were evaluated by immunohistochemistry and Western blot, respectively. Results. HFD-fed mice showed deficits in motor and sensory NCV, thermal hyperalgesia, reduced mean dendrite length, and VEGF-A expression in the plantar skin and increased 12/15-LOX in the sciatic nerve (P < 0.05 compared with controls). Conclusion. HFD may cause large myelinated nerve and small sensory nerve fiber damage, thus leading to neuropathy. The mean dendrite length may be a more sensitive marker for early detection of peripheral neuropathy. Reduced blood supply to the nerves and increased oxidative stress may contribute to the development and severity of peripheral neuropathy.

Macrophage-mediated glucolipotoxicity via myeloid-related protein 8/toll-like receptor 4 signaling in diabetic nephropathy

Dyslipidemia is an independent risk factor for the development and progression of diabetic nephropathy (DN). In this review, we summarize mouse models with both diabetes and dyslipidemia, and their associated complications. We then discuss molecules potentially involved in deterioration of DN by dyslipidemia. We focus especially upon toll-like receptor 4 (TLR4) and one of its endogenous ligands, myeloid-related protein 8 (MRP8 or S100A8), since we have found that their mRNA levels are commonly increased in glomeruli of type 1 (streptozotocin [STZ]-induced) and type 2 (A-ZIP/F-1 lipoatrophic) diabetic mice. Gene expression of MRP8 and Tlr4 is further upregulated during worsening of STZ-induced DN by a high fat diet (HFD). Moreover, these HFD-induced changes are accompanied by enhanced gene expression of CCAAT element binding protein β and phosphorylation of c-Jun N-terminal kinase in the kidney, which have also been reported in pancreatic β cells under diabetic-hyperlipidemic conditions. Effects of a HFD upon DN are cancelled in Tlr4 knockout mice. Macrophages are the predominant source of MRP8 in glomeruli. In cultured macrophages, combinatorial treatment with high glucose and palmitate amplifies MRP8 expression in a Tlr4-dependent manner, and recombinant MRP8 protein markedly increases gene expression of the inflammatory cytokines interleukin-1β and tumor necrosis factor α. Here, we propose ‘macrophage-mediated glucolipotoxicity’ via activation of MRP8/TLR4 signaling as a novel mechanism of pathophysiology for DN.

Spontaneously diabetic Ins2(+/Akita):apoE-deficient mice exhibit exaggerated hypercholesterolemia and atherosclerosis

Type 1 diabetes (T1D) increases the risk of adverse coronary events. Among risk factors, dyslipidemia due to altered hepatic lipoprotein metabolism plays a central role in diabetic atherosclerosis. Nevertheless, the likely alterations in plasma lipid/lipoprotein profile remain unclear, especially in the context of spontaneously developed T1D and atherosclerosis. To address this question, we generated Ins2(+/Akita):apoE(-/-) mouse by cross-breeding Ins2(+/Akita) mouse (which has Ins2 gene mutation, causing pancreatic β-cell apoptosis and insulin deficiency) with apoE(-/-) mouse. Ins2(+/Akita):apoE(-/-) mice developed T1D spontaneously at 4-5 wk of age. At 25 wk of age and while on a standard chow diet, diabetic Ins2(+/Akita):apoE(-/-) mice exhibited an approximately threefold increase in atherosclerotic plaque in association with an approximatelty twofold increase in plasma non-HDL cholesterol, predominantly in the LDL fraction, compared with nondiabetic controls. To determine factors contributing to the exaggerated hypercholesterolemia, we assessed hepatic VLDL secretion and triglyceride content, expression of hepatic lipoprotein receptors, and plasma apolipoprotein composition. Diabetic Ins2(+/Akita):apoE(-/-) mice exhibited diminished VLDL secretion by ~50%, which was accompanied by blunted Akt phosphorylation in response to insulin infusion and decreased triglyceride content in the liver. Although the expression of hepatic LDL receptor was not affected, there was a significant reduction in the expression of lipolysis-stimulated lipoprotein receptor (LSR) by ~28%. Moreover, there was a marked decrease in plasma apoB-100 with a significant increase in apoB-48 and apoC-III levels. In conclusion, exaggerated hypercholesterolemia and atherosclerosis in spontaneously diabetic Ins2(+/Akita):apoE(-/-) mice may be attributable to impaired lipoprotein clearance in the setting of diminished expression of LSR and altered apolipoprotein composition of lipoproteins.

Macrovascular complications of diabetes in atherosclerosisprone mice

The well-established relationship between diabetes and cardiovascular complications, combined with the rapidly increasing prevalence of diabetes, has created a pressing need for better understanding of the mechanisms of diabetic atherosclerosis. Multiple metabolic and diabetes-specific factors have been associated with accelerated atherosclerosis, including dyslipidemia, oxidative stress, inflammation, vascular cell dysfunction and coagulopathy. This discussion highlights selected studies in which researchers have employed mouse models of diabetic atherosclerosis in an attempt to examine these mechanisms and test potential therapeutic and preventative measures.

Dyslipidemia-induced neuropathy in mice: the role of oxLDL/LOX-1

OBJECTIVE

Neuropathy is a frequent and severe complication of diabetes. Multiple metabolic defects in type 2 diabetic patients result in oxidative injury of dorsal root ganglia (DRG) neurons. Our previous work focused on hyperglycemia clearly demonstrates induction of mitochondrial oxidative stress and acute injury in DRG neurons; however, this mechanism is not the only factor that produces neuropathy in vivo. Dyslipidemia also correlates with the development of neuropathy, even in pre-diabetic patients. This study was designed to explore the contribution of dyslipidemia in neuropathy.

RESEARCH DESIGN AND METHODS

Mice (n = 10) were fed a control (10% kcal %fat) or high-fat (45% kcal %fat) diet to explore the impact of plasma lipids on the development of neuropathy. We also examined oxidized lipid-mediated injury in cultured DRG neurons from adult rat using oxidized LDLs (oxLDLs).

RESULTS

Mice on a high-fat diet have increased oxLDLs and systemic and nerve oxidative stress. They develop nerve conduction velocity (NCV) and sensory deficits prior to impaired glucose tolerance. In vitro, oxLDLs lead to severe DRG neuron oxidative stress via interaction with the receptor lectin-like oxLDL receptor (LOX)-1 and subsequent NAD(P)H oxidase activity. Oxidative stress resulting from oxLDLs and high glucose is additive.

CONCLUSIONS

Multiple metabolic defects in type 2 diabetes directly injure DRG neurons through different mechanisms that all result in oxidative stress. Dyslipidemia leads to high levels of oxLDLs that may injure DRG neurons via LOX-1 and contribute to the development of diabetic neuropathy.

Oxidant stress, immune dysregulation, and vascular function in type I diabetes

Although high glucose is an important contributor to diabetic vasculopathies, complications still occur in spite of tight glycemic control, suggesting that some critical event prior to or concurrent with hyperglycemia may contribute to early vascular changes. Utilizing previously published and new experimental evidence, this review will discuss how prior to the hyperglycemic state, an imbalance between oxidants and antioxidants may contribute to early vascular dysfunction and set in motion proinflammatory insults that are further amplified as the diabetes develops. This imbalance results from the resetting of the equilibrium between vessel superoxide/H(2)O(2) production and/or decreased antioxidant defenses. Such an imbalance may cause endothelial dysfunction, characterized by abnormal endothelium-dependent vasoreactivity, as the first sign of blood vessel damage, followed by morphological changes of the vessel wall and inflammation. As such, increased oxidant stress in preglycemic states may be a critically central initiating event that underlies the pathogenesis of life-threatening vascular diseases in autoimmune diabetes. This review focuses on the relationship between oxidative stress, immune dysregulation, and vascular injury in type 1 diabetes, and how the discovery of novel pathways of vascular disease in nonobese diabetic mice may direct future studies in patients with type 1 diabetes.

Role of diabetes in atherosclerotic pathogenesis. What have we learned from animal models?

Diabetes mellitus is associated with a greater risk of developing atherosclerosis and its complications: stroke, myocardial infarction, and peripheral vascular disease. In patients with diabetes, atherosclerosis represents a complex multifactorial disease with increased lesion progression and severity compared to the nondiabetic population. Several risk factors have been proposed to explain the increased risk of cardiovascular disease with diabetes. They include: hyperglycaemia, dyslipidemia, accelerated formation of advanced glycation end-products (AGEs), increased oxidative stress, and genetic factors. It is difficult to precisely establish the elements leading to diabetes-accelerated atherosclerosis by means of epidemiological studies because all these factors coexist in diabetic patients. Thus, diabetic animal models that reproduce exacerbation of atherosclerosis would be helpful to understand why atherosclerosis is accelerated by diabetes, and to design appropriate treatments to limit its progression. This review analyzes most of the animal models developed to reproduce diabetes-accelerated atherosclerosis, and summarizes the effects of hyperglycaemia and lipid abnormalities on atherogenesis.

Effects of diabetes and CETP expression on diet-induced atherosclerosis in LDL receptor-deficient mice

The role of CETP expression and diabetes in atherogenesis was investigated in mice with heterozygous disruption of the LDL receptor gene (LDLR1). LDLR1 mice with and without CETP expression were treated with streptozotocin (STZ) and maintained on a standard diet for one month before switching to an atherogenic diet for an additional month. STZ-sensitive mice had approximately 2.5-fold higher glycemia and 7.5- to 8.0-fold higher cholesterolemia. Factorial analysis of variance showed no significant effect of diabetes, CETP or diabetes-CETP interaction on the size of the atherosclerotic lesions. CETP expression in non-diabetic mice resulted in a 50% reduction in the area of the atherosclerotic lesions. Multiple regression analysis showed a positive and independent atherogenic effect of triglyceridemia in LDLR1 mice and of cholesterolemia in diabetic mice. Logistic analysis showed that elevated plasma cholesterol level significantly increased the risk of developing large lesion size (>75th percentile). In conclusion, CETP expression did not alter the lesion formation in response to diabetes, although it may be protective in the euglycemic state; the triglyceride level was an independent risk factor for LDL receptor-deficient mice but not for CETP-expressing mice; and elevated plasma cholesterol levels increased the risk of developing large atherosclerotic lesions, independently of CETP and diabetes.

Impact of in vivo glycation of LDL on platelet aggregation and monocyte chemotaxis in diabetic Psammomys obesus

Psammomys obesus (sand rat) is an appropriate model to highlight the development of hyperinsulinemia, insulin resistance, obesity, and diabetes. This animal species, with genetically predetermined diabetes, acquires non-insulin dependent diabetes mellitus when exposed to energy-rich diets. In the present study, we explored the possibility that glycation of LDL may occur in diabetes-prone P. obesus and affect platelet and macrophage functions. The glycation of LDL, isolated from diabetic animals, was significantly (P < 0.05) higher (40%) than that of control animals. The incubation of platelets with glycated LDL enhanced the reactivity of platelets by 32-44% depending on the aggregating agents (thrombin, collagen, ADP). Furthermore, LDL derived from diabetic rats were chemotactic for normal monocytes and stimulated the incorporation of [14C]oleate into cellular cholesteryl esters. The enhancement of platelet aggregation and cholesterol esterification in monocytes may contribute toward the accelerated development of atherosclerotic cardiovascular disease in diabetic P. obesus animals. This study also illustrates the relevance of studying atherosclerosis in the P. obesus animal model, as it shows an increased tendency to develop diet-induced diabetes, which is associated with cardiovascular disorders.