Early atherosclerosis and vascular inflammation in mice with diet-induced type 2 diabetes

A long-term high-fat diet influences brain damage and is linked to the activation of HIF-1α/AMPK/mTOR/p70S6K signalling

High-fat diets (HFDs) are related to the incidence of obesity and diabetes, but the effect of high-fat diet-induced brain damage remains to be clarified. In our study, we found that 24 weeks of a HFD effectively induced obesity and a change in fur color in mice. In addition, the mice also exhibited deficits in learning and memory. We further found that autophagic flux was impaired in mice after HFD feeding. Hypoxia-inducible factor 1α (HIF-1α) expression was significantly increased in HFD-fed mice, and HFD feeding inhibited adenosine monophosphate-activated protein kinase (AMPK) phosphorylation and induced mechanistic target of rapamycin (mTOR) phosphorylation and p70S6K expression. Treatment of HFD-induced BV2 cell model with palmitic acid (PA) was used to further verify a similar result. We concluded that improving tissue hypoxia or enhancing autophagy through the AMPK/mTOR/p70S6K pathway may be a relevant strategy for improving obesity- and ageing-related disorders.

TGF-β1 and TIMP1 double directional rAAV targeted by UTMD in atherosclerotic vulnerable plaque

In the present study, we determined whether ultrasound-targeted microbubble destruction (UTMD) combined with dual targeting of transforming growth factor (TGF)-β1 and tissue inhibitors of metalloproteinase (TIMP) 1 recombinant adeno-associated virus (rAAV) can stabilize atherosclerotic vulnerable plaques. First, we used rabbit model to detect the TGF-β1/TIMP1 virus therapy result. H&E staining was used to evaluate the tissues. The protein levels of TGF-β1 and TIMP1 were detected in rabbit models. The THP-1 cells were induced into macrophages, and transfected with TGF-β1 and TIMP1 rAAV under optimized UTMD. The expression of TGF-β1 and TIMP1 was measured by RT-PCR and western blotting. We found that the apoptotic rates were induced when compared to the control group. The rAAV virus group showed a significant decrease in the p-ERT and p-AKT expression. These data support the hypothesis that TGF-β1 and TIMP1 are crucial in the regulation of atherosclerotic plaques.

High-Fat-Diet Intake Enhances Cerebral Amyloid Angiopathy and Cognitive Impairment in a Mouse Model of Alzheimer's Disease, Independently of Metabolic Disorders

Background

The high‐fat Western diet is postulated to be associated with the onset and progression of Alzheimer's disease (AD). However, the role of high‐fat‐diet consumption in AD pathology is unknown. This study was undertaken to examine the role of high‐fat‐diet intake in AD.

Methods and Results

5XFAD mice, a useful mouse model of AD, and control wild‐type mice were fed (1) high‐fat diet or (2) control diet for 10 weeks. The effects on cerebral AD pathology, cognitive function, and metabolic parameters were compared between each group of mice. High‐fat diet significantly enhanced cerebrovascular β‐amyloid (Aβ) deposition (P<0.05) and impaired cognitive function (P<0.05) in 5XFAD mice, but not in wild‐type mice. High‐fat diet enhanced hippocampal oxidative stress (P<0.05) and NADPH oxidase subunits, gp91^phox (P<0.01) and p22^phox (P<0.01) in 5XFAD mice, but not in wild‐type mice. Furthermore, high‐fat diet reduced cerebral occludin (P<0.05) in 5XFAD mice, but not in wild‐type mice. Thus, 5XFAD mice exhibited greater susceptibility to high‐fat diet than wild‐type mice regarding cerebrovascular injury and cognitive impairment. On the other hand, 5XFAD mice fed high‐fat diet exhibited much less increase in body weight, white adipose tissue weight, and adipocyte size than their wild‐type counterparts. High‐fat diet significantly impaired glucose tolerance in wild‐type mice but not in 5XFAD mice. Thus, 5XFAD mice had much less susceptibility to high‐fat‐diet‐induced metabolic disorders than wild‐type mice.

Conclusions

High‐fat diet, independently of metabolic disorders, significantly promotes the progression of AD‐like pathology through enhancement of cerebral amyloid angiopathy and oxidative stress.

Isolevuglandin-type lipid aldehydes induce the inflammatory response of macrophages by modifying phosphatidylethanolamines and activating the receptor for advanced glycation endproducts

AIMS

Increased lipid peroxidation occurs in many conditions associated with inflammation. Because lipid peroxidation produces lipid aldehydes that can induce inflammatory responses through unknown mechanisms, elucidating these mechanisms may lead to development of better treatments for inflammatory diseases. We recently demonstrated that exposure of cultured cells to lipid aldehydes such as isolevuglandins (IsoLG) results in the modification of phosphatidylethanolamine (PE). We therefore sought to determine (i) whether PE modification by isolevuglandins (IsoLG-PE) occurred in vivo, (ii) whether IsoLG-PE stimulated the inflammatory responses of macrophages, and (iii) the identity of receptors mediating the inflammatory effects of IsoLG-PE.

RESULTS

IsoLG-PE levels were elevated in plasma of patients with familial hypercholesterolemia and in the livers of mice fed a high-fat diet to induce obesity and hepatosteatosis. IsoLG-PE potently stimulated nuclear factor kappa B (NFκB) activation and expression of inflammatory cytokines in macrophages. The effects of IsoLG-PE were blocked by the soluble form of the receptor for advanced glycation endproducts (sRAGE) and by RAGE antagonists. Furthermore, macrophages derived from the bone marrow of Ager null mice failed to express inflammatory cytokines in response to IsoLG-PE to the same extent as macrophages from wild-type mice.

INNOVATION

These studies are the first to identify IsoLG-PE as a mediator of macrophage activation and a specific receptor, RAGE, which mediates its biological effects.

CONCLUSION

PE modification by IsoLG forms RAGE ligands that activate macrophages, so that the increased IsoLG-PE generated by high circulating cholesterol levels or high-fat diet may play a role in the inflammation associated with these conditions.

ASK1 is involved in cognitive impairment caused by long-term high-fat diet feeding in mice

Although high-fat diet intake is known to cause obesity and diabetes, the effect of high-fat diet itself on cognitive function remains to be clarified. We have previously shown that apoptosis signal-regulating kinase 1 (ASK1) is responsible for cognitive impairment caused by chronic cerebral hypoperfusion. The present work, by using ASK1 deficient mice, was undertaken to explore the influence of chronic high-fat diet intake on cognitive function and the role of ASK1. Cognitive function in wild-type mice fed high-fat diet from 2 to 24 months of age was significantly impaired compared to those fed control diet, which was associated with the significant white matter lesions, reduction of hippocampal capillary density, and decrement of hippocampal neuronal cell. However, ASK1 deficiency abolished the development of cognitive impairment and cerebral injury caused by high-fat diet. Our results provided the evidence that high-fat diet itself causes cognitive impairment and ASK1 participates in such cognitive impairment.

Animal models of diabetic macrovascular complications: key players in the development of new therapeutic approaches

Diabetes mellitus is a lifelong, incapacitating metabolic disease associated with chronic macrovascular complications (coronary heart disease, stroke, and peripheral vascular disease) and microvascular disorders leading to damage of the kidneys (nephropathy) and eyes (retinopathy). Based on the current trends, the rising prevalence of diabetes worldwide will lead to increased cardiovascular morbidity and mortality. Therefore, novel means to prevent and treat these complications are needed. Under the auspices of the IMI (Innovative Medicines Initiative), the SUMMIT (SUrrogate markers for Micro- and Macrovascular hard end points for Innovative diabetes Tools) consortium is working on the development of novel animal models that better replicate vascular complications of diabetes and on the characterization of the available models. In the past years, with the high level of genomic information available and more advanced molecular tools, a very large number of models has been created. Selecting the right model for a specific study is not a trivial task and will have an impact on the study results and their interpretation. This review gathers information on the available experimental animal models of diabetic macrovascular complications and evaluates their pros and cons for research purposes as well as for drug development.

Porcine adiponectin receptor 1 transgene resists high-fat/sucrose diet-induced weight gain, hepatosteatosis and insulin resistance in mice

Adiponectin and its receptors have been demonstrated to play important roles in regulating glucose and lipid metabolism in mice. Obesity, type II diabetes and cardiovascular disease are highly correlated with down-regulated adiponectin signaling. In this study, we generated mice overexpressing the porcine Adipor1 transgene (pAdipor1) to study its beneficial effects in metabolic syndromes as expressed in diet-induced obesity, hepatosteatosis and insulin resistance. Wild-type (WT) and pAdipor1 transgenic mice were fed ad libitum with a standard chow diet (Chow) or a high-fat/sucrose diet (HFSD) for 24 weeks, beginning at 6 to 7 weeks of age. There were 12 mice per genetic/diet/sex group. When challenged with HFSD to induce obesity, the pAdipor1 transgenic mice resisted development of weight gain, hepatosteatosis and insulin resistance. These mice had lowered plasma adiponectin, triglyceride and glycerol concentrations compared to WT mice. Moreover, we found that (indicated by mRNA levels) fatty acid oxidation was enhanced in skeletal muscle and adipose tissue, and liver lipogenesis was inhibited. The pAdipor1 transgene also restored HFSD-reduced phosphoenolpyruvate carboxykinase 1 (Pck1) and glucose transporter 4 mRNA in the adipose tissues, implying that the increased Pck1 may promote glyceroneogenesis to reduce glucose intolerance and thus activate the flux of glyceride-glycerol to resist diet-induced weight gain in the adipose tissues. Taken together, we demonstrated that pAdipor1 can prevent diet-induced weight gain and insulin resistance. Our findings may provide potential therapeutic strategies for treating metabolic syndromes and obesity, such as treatment with an ADIPOR1 agonist or activation of Adipor1 downstream targets.

Effect of impaired glucose tolerance on atherosclerotic lesion formation: an evaluation in selectively bred mice with different susceptibilities to glucose intolerance

OBJECTIVE

Impaired glucose tolerance (IGT) is an independent risk factor for atherosclerotic cardiovascular disease. However, due to the lack of appropriate animal models, the underlying mechanisms for IGT-induced atherosclerosis remain to be elucidated in vivo. We recently used selective breeding to establish 2 mouse lines with distinctively different susceptibilities to diet-induced glucose intolerance, designated selectively bred diet-induced glucose intolerance-resistant (SDG-R) and SDG-prone (SDG-P), respectively. Here, we assessed atherosclerotic lesion formation in these mice.

METHODS

Female SDG-R and SDG-P mice were fed an atherogenic diet (AD; 1.25% cholesterol, 0.5% sodium cholate, and 36% energy as fat) for 20 weeks (8-28 weeks of age). Oral glucose tolerance tests were performed during the AD-feeding period. Atherosclerotic lesion formation was quantitatively analyzed in serial aortic sinus sections by oil red O staining. Plasma lipids were measured after the AD-feeding period.

RESULTS

Glucose tolerance was impaired in SDG-P mice as compared to SDG-R mice over the 20-week AD-feeding period. No significant differences were observed in any plasma lipid measurement between the 2 mouse lines. Aortic sinus atherosclerotic lesion formation in SDG-P mice was approximately 4-fold greater than that in SDG-R mice.

CONCLUSION

In 2 mouse lines with different susceptibilities to diet-induced glucose intolerance, IGT accelerated atherosclerotic lesion formation. These mice may therefore serve as useful in vivo models for investigating the causal role of IGT in the pathogenesis of atherosclerosis.

The alpha linolenic acid content of flaxseed is associated with an induction of adipose leptin expression

Dietary flaxseed has cardioprotective effects that may be achieved through its rich content of the omega-3 fatty acid, alpha linolenic acid (ALA). Because ALA can be stored in adipose tissue, it is possible that some of its beneficial actions may be due to effects it has on the adipose tissue. We investigated the effects of dietary flaxseed both with and without an atherogenic cholesterol-enriched diet to determine the effects of dietary flaxseed on the expression of the adipose cytokines leptin and adiponectin. Rabbits were fed one of four diets: a regular (RG) diet, or a regular diet with added 0.5% cholesterol (CH), or 10% ground flaxseed (FX), or both (CF) for 8 weeks. Levels of leptin and adiponectin expression were assessed by RT-PCR in visceral adipose tissue. Consumption of flaxseed significantly increased plasma and adipose levels of ALA. Leptin protein and mRNA expression were lower in CH animals and were elevated in CF animals. Changes in leptin expression were strongly and positively correlated with adipose ALA levels and inversely correlated with levels of en face atherosclerosis. Adiponectin expression was not significantly affected by any of the dietary interventions. Our data demonstrate that the type of fat in the diet as well as its caloric content can specifically influence leptin expression. The findings support the hypothesis that the beneficial cardiovascular effects associated with flaxseed consumption may be related to a change in leptin expression.

Hyperglycemic myocardial damage is mediated by proinflammatory cytokine: macrophage migration inhibitory factor

Background

Diabetes has been regarded as an inflammatory condition which is associated with left ventricular diastolic dysfunction (LVDD). The purpose of this study was to examine the expression levels of macrophage migration inhibitory factor (MIF) and G protein-coupled receptor kinase 2 (GRK2) in patients with early diabetic cardiomyopathy, and to investigate the mechanisms involved in MIF expression and GRK2 activation.

Methods

83 patients in the age range of 30-64 years with type 2 diabetes and 30 matched healthy men were recruited. Left ventricular diastolic function was evaluated by cardiac Doppler echocardiography. Plasma MIF levels were determined by ELISA. To confirm the clinical observation, we also studied MIF expression in prediabetic rats with impaired glucose tolerance (IGT) and relationship between MIF and GRK2 expression in H9C2 cardiomyoblasts exposed to high glucose.

Results

Compared with healthy subjects, patients with diabetes have significantly increased levels of plasma MIF which was further increased in diabetic patients with Left ventricular diastolic dysfunction (LVDD). The increased plasma MIF levels in diabetic patients correlated with plasma glucose, glycosylated hemoglobin and urine albumin levels. We observed a significant number of TUNEL-positive cells in the myocardium of IGT-rats but not in the control rats. Moreover, we found higher MIF expression in the heart of IGT with cardiac dysfunction compared to that of the controls. In H9C2 cardiomyoblast cells, MIF and GRK2 expression was significantly increased in a glucose concentration-dependant manner. Furthermore, GRK2 expression was abolished by siRNA knockdown of MIF and by the inhibition of CXCR4 in H9C2 cells.

Conclusions

Our findings indicate that hyperglycemia is a causal factor for increased levels of pro-inflammatory cytokine MIF which plays a role in the development of cardiomyopathy occurring in patients with type 2 diabetes. The elevated levels of MIF are associated with cardiac dysfunction in diabetic patients, and the MIF effects are mediated by GRK2.

Decreased expression of natriuretic peptides associated with lipid accumulation in cardiac ventricle of obese mice

Plasma B-type natriuretic peptide (BNP) and proBNP are established markers of cardiac dysfunction. Even though obesity increases the risk of cardiovascular disease, obese individuals have reduced plasma concentrations of natriuretic peptides. The underlying mechanism is not established. We used cultured cardiomyocytes and three different mouse models to examine the impact of obesity and cardiac lipid accumulation on cardiac natriuretic peptide expression. The cardiac ventricular expression of atrial natriuretic peptide (ANP) and BNP mRNA and ANP peptide was decreased 36-72% in obese ob/ob, db/db, and fat-fed C57BL/6 mice as compared with their respective controls. The db/db and ob/ob mice displayed impaired cardiac function, whereas the fat-fed mice had almost normal cardiac function. Moreover, the ventricular expression of hypertrophic genes (α- and β-myosin heavy chain and α-actin) and natriuretic peptide receptor genes were not consistently altered by obesity across the three mouse models. In contrast, cardiac ventricular triglycerides were similarly increased by 60-115% in all three obese mouse models and incubation with oleic acid caused triglyceride accumulation and an approximately 35% (P < 0.005) depression of ANP mRNA expression in cultured HL-1 atrial myocytes. The data suggest that obesity and altered cardiac lipid metabolism are associated with reduced production of ANP and BNP in the cardiac ventricles in the setting of normal as well as impaired cardiac function.

PP2A contributes to endothelial death in high glucose: inhibition by benfotiamine

Endothelial death is critical in diabetic vascular diseases, but regulating factors have been only partially elucidated. Phosphatases play important regulatory roles in cell metabolism, but have not previously been implicated in hyperglycemia-induced cell death. We investigated the role of the phosphatase, type 2A protein phosphatase (PP2A), in hyperglycemia-induced changes in signaling and death in bovine aortic endothelial cells (BAEC). We explored also the influence of benfotiamine on this phosphatase. Activation of PP2A was assessed in BAEC by the extent of methylation and measurement of activity, and the enzyme was inhibited using selective pharmacological (okadaic acid, sodium fostriecin) and molecular (small interfering RNA) approaches. BAECs cultured in 30 mM glucose significantly increased PP2A methylation and activity, and PP2A inhibitors blocked these abnormalities. PP2A activity was increased also in aorta and retina from diabetic rats. NF-κB activity and cell death in BAEC were significantly increased in 30 mM glucose and inhibited by PP2A inhibition. NF-κB played a role in the hyperglycemia-induced death of BAEC, since blocking its translocation with SN50 also inhibited cell death. Inhibition of PP2A blocked the hyperglycemia-induced dephosphorylation of NF-κB and Bad, thus favoring cell survival. Incubation of benfotiamine with BAEC inhibited the high glucose-induced activation of PP2A and NF-κB and cell death, as well as several other metabolic defects, which likewise were inhibited by inhibitors of PP2A. Activation of PP2A contributes to endothelial cell death in high glucose, and beneficial actions of benfotiamine are due, at least in part, to inhibition of PP2A activation.

Cardiac expression of microsomal triglyceride transfer protein is increased in obesity and serves to attenuate cardiac triglyceride accumulation

Obesity causes lipid accumulation in the heart and may lead to lipotoxic heart disease. Traditionally, the size of the cardiac triglyceride pool is thought to reflect the balance between uptake and β-oxidation of fatty acids. However, triglycerides can also be exported from cardiomyocytes via secretion of apolipoproteinB-containing (apoB) lipoproteins. Lipoprotein formation depends on expression of microsomal triglyceride transfer protein (MTP); the mouse expresses two isoforms of MTP, A and B. Since many aspects of the link between obesity-induced cardiac disease and cardiac lipid metabolism remain unknown, we investigated how cardiac lipoprotein synthesis affects cardiac expression of triglyceride metabolism-controlling genes, insulin sensitivity, and function in obese mice. Heart-specific ablation of MTP-A in mice using Cre-loxP technology impaired upregulation of MTP expression in response to increased fatty acid availability during fasting and fat feeding. This resulted in cardiac triglyceride accumulation but unaffected cardiac insulin-stimulated glucose uptake. Long-term fat-feeding of male C57Bl/6 mice increased cardiac triglycerides, induced cardiac expression of triglyceride metabolism-controlling genes and attenuated heart function. Abolishing cardiac triglyceride accumulation in fat-fed mice by overexpression of an apoB transgene in the heart prevented the induction of triglyceride metabolism-controlling genes and improved heart function. The results suggest that in obesity, the physiological increase of cardiac MTP expression serves to attenuate cardiac triglyceride accumulation albeit without major effects on cardiac insulin sensitivity. Nevertheless, the data suggest that genetically increased lipoprotein secretion prevents development of obesity-induced lipotoxic heart disease.