Role of FAT/CD36 in novel PKC isoform activation in heart of spontaneously hypertensive rats

Nutrigenetic Interaction of Spontaneously Hypertensive Rat Chromosome 20 Segment and High-Sucrose Diet Sensitizes to Metabolic Syndrome

Several corresponding regions of human and mammalian genomes have been shown to affect sensitivity to the manifestation of metabolic syndrome via nutrigenetic interactions. In this study, we assessed the effect of sucrose administration in a newly established congenic strain BN.SHR20, in which a limited segment of rat chromosome 20 from a metabolic syndrome model, spontaneously hypertensive rat (SHR), was introgressed into Brown Norway (BN) genomic background. We mapped the extent of the differential segment and compared the genomic sequences of BN vs. SHR within the segment in silico. The differential segment of SHR origin in BN.SHR20 spans about 9 Mb of the telomeric portion of the short arm of chromosome 20. We identified non-synonymous mutations e.g., in ApoM, Notch4, Slc39a7, Smim29 genes and other variations in or near genes associated with metabolic syndrome in human genome-wide association studies. Male rats of BN and BN.SHR20 strains were fed a standard diet for 18 weeks (control groups) or 16 weeks of standard diet followed by 14 days of high-sucrose diet (HSD). We assessed the morphometric and metabolic profiles of all groups. Adiposity significantly increased only in BN.SHR20 after HSD. Fasting glycemia and the glucose levels during the oral glucose tolerance test were higher in BN.SHR20 than in BN groups, while insulin levels were comparable. The fasting levels of triacylglycerols were the highest in sucrose-fed BN.SHR20, both compared to the sucrose-fed BN and the control BN.SHR20. The non-esterified fatty acids and total cholesterol concentrations were higher in BN.SHR20 compared to their respective BN groups, and the HSD elicited an increase in non-esterified fatty acids only in BN.SHR20. In a new genetically defined model, we have isolated a limited genomic region involved in nutrigenetic sensitization to sucrose-induced metabolic disturbances.

How Hypertension Affects Heart Metabolism

Hypertension is one of the most frequently observed cardiovascular diseases, which precedes heart failure in 75% of its cases. It is well-established that hypertensive patients have whole body metabolic complications such as hyperlipidemia, hyperglycemia, decreased insulin sensitivity or diabetes mellitus. Since myocardial metabolism is strictly dependent on hormonal status as well as substrate milieu, the above mentioned disturbances may affect energy generation status in the heart. Interestingly, it was found that hypertension induces a shift in substrate preference toward increased glucose utilization in cardiac muscle, prior to structural changes development. The present work reports advances in the aspect of heart metabolism under high blood pressure conditions, including human and the most common animal models of hypertension.

Fatty acid amide hydrolase inhibitor (URB597) as a regulator of myocardial lipid metabolism in spontaneously hypertensive rats

Pressure overload, which is typical of hypertension, is known to evoke alterations not only in the morphology of the heart but also in the preference of myocardial energetic substrates usage. Nowadays, the endocannabinoid system (ECS) serves as a potential therapeutic target for cardiovascular disorders and, simultaneously, affects whole body metabolism homeostasis. Therefore, an open question is whether ECS, apart from decreasing blood pressure, also affects cardiac muscle metabolism in hypertensive conditions. All experiments were conducted on a genetic model of primary hypertension i.e. spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKY) served as a normotensive control. ECS was chronically activated by 2-weeks intraperitoneal injections of fatty acid amide hydrolase (FAAH) inhibitor - URB597. Lipid analyses in the left ventricle and serum were based on ex vivo heart perfusion in Langendorff perfusion system, thin layer chromatography, and gas liquid chromatography. The total expression of selected proteins was determined using Western blot as well as immunohistochemical techniques. As expected, URB597 markedly reduced systolic as well as mean blood pressures in SHRs. Moreover, prolonged FAAH inhibition resulted in stimulation of ³H-palmitate uptake and incorporation into different lipid fractions in cardiomyocytes in the hypertensive as well as normotensive conditions. An increase in fatty acid oxidation caused by URB597 treatment was observed only in WKY rats, but not SHRs, and was accompanied by an elevation in peroxisome proliferator-activated receptor alpha (PPARα) and β-hydroxyacyl-CoA dehydrogenase (β-HAD) expressions. Chronic activation of ECS significantly upregulates palmitate uptake and its esterification but not oxidation in the SHR's myocardium.

Genomic determinants of triglyceride and cholesterol distribution into lipoprotein fractions in the rat

The plasma profile of major lipoprotein classes and its subdivision into particular fractions plays a crucial role in the pathogenesis of atherosclerosis and is a major predictor of coronary artery disease. Our aim was to identify genomic determinants of triglyceride and cholesterol distribution into lipoprotein fractions and lipoprotein particle sizes in the recombinant inbred rat set PXO, in which alleles of two rat models of the metabolic syndrome (SHR and PD inbred strains) segregate together with those from Brown Norway rat strain. Adult male rats of 15 PXO strains (n = 8–13/strain) and two progenitor strains SHR-Lx (n = 13) and BXH2/Cub (n = 18) were subjected to one-week of high-sucrose diet feeding. We performed association analyses of triglyceride (TG) and cholesterol (C) concentrations in 20 lipoprotein fractions and the size of major classes of lipoprotein particles utilizing 704 polymorphic microsatellite markers, the genome-wide significance was validated by 2,000 permutations per trait. Subsequent in silico focusing of the identified quantitative trait loci was completed using a map of over 20,000 single nucleotide polymorphisms. In most of the phenotypes we identified substantial gradient among the strains (e.g. VLDL-TG from 5.6 to 66.7 mg/dl). We have identified 14 loci (encompassing 1 to 65 genes) on rat chromosomes 3, 4, 7, 8, 11 and 12 showing suggestive or significant association to one or more of the studied traits. PXO strains carrying the SHR allele displayed significantly higher values of the linked traits except for LDL-TG and adiposity index. Cholesterol concentrations in large, medium and very small LDL particles were significantly associated to a haplotype block spanning part of a single gene, low density lipoprotein receptor-related protein 1B (Lrp1b). Using genome-wide association we have identified new genetic determinants of triglyceride and cholesterol distribution into lipoprotein fractions in the recombinant inbred panel of rat model strains.

Cleavage and reduced CD36 ectodomain density on heart and spleen macrophages in the spontaneously hypertensive rat

Metabolic disease is accompanied by a range of cellular defects ("comorbidities") whose origin is uncertain. To investigate this pathophysiological phenomenon we used the Spontaneously Hypertensive Rat (SHR), which besides an elevated arterial blood pressure also has many other comorbidities, including a defective glucose and lipid metabolism. We have shown that this model of metabolic disease has elevated plasma matrix metalloproteinase (MMP) activity, which cleaves the extracellular domain of membrane receptors. We hypothesize here that the increased MMP activity also leads to abnormal cleavage of the scavenger receptor and fatty acid transporter CD36. To test this idea, chronic pharmaceutical MMP inhibition (CGS27023A) of the SHR and its normotensive control, the Wistar Kyoto Rat (WKY), was used to determine if inhibition of MMP activity serves to maintain CD36 receptor density and function. Surface density of CD36 on macrophages from the heart, spleen, and liver was determined in WKY, SHR, CGS-treated WKY (CGS WKY), and CGS-treated SHR (CGS SHR) by immunohistochemistry with an antibody against the CD36 ectodomain. The extracellular CD36 density was lower in SHR heart and spleen macrophages compared to that in the WKY. MMP inhibition by CGS served to restore the reduced CD36 density on SHR cardiac and splanchnic macrophages to levels of the WKY. To examine CD36 function, culture assays with murine macrophages (RAW 264.7) after incubation in fresh WKY or SHR plasma were used to test for adhesion of light-weight donor red blood cell (RBC) by CD36. This form of RBC adhesion to macrophages was reduced after incubation in SHR compared WKY plasma. Analysis of the supernatant macrophage media by Western blot shows a higher level of CD36 extracellular protein fragments following exposure to SHR plasma compared to WKY. MMP inhibition in the SHR plasma compared to untreated plasma, served to increase the RBC adhesion to macrophages and decrease the number of receptor fragments in the macrophage media. In conclusion, these studies bring to light that plasma in the SHR model of metabolic disease has an unchecked MMP degrading activity which causes cleavage of a variety of membrane receptors, including CD36, which attenuates several cellular functions typical for the metabolic disease, including RBC adhesion to the scavenger receptor CD36. In addition to other cell dysfunctions chronic MMP inhibition restores CD36 in the SHR.

Transgenic rescue of defective Cd36 enhances myocardial adenylyl cyclase signaling in spontaneously hypertensive rats

Dysfunction or abnormalities in the regulation of fatty acid translocase Cd36, a multifunctional membrane protein participating in uptake of long-chain fatty acids, has been linked to the development of heart diseases both in animals and humans. We have previously shown that the Cd36 transgenic spontaneously hypertensive rat (SHR-Cd36), with a wild type Cd36, has higher susceptibility to ischemic ventricular arrhythmias when compared to spontaneously hypertensive rat (SHR) carrying a mutant Cd36 gene, which may have been related to increased β-adrenergic responsiveness of these animals (Neckar et al., 2012 Physiol. Genomics 44:173-182). The present study aimed to determine whether the insertion of the wild type Cd36 into SHR would affect the function of myocardial G protein-regulated adenylyl cyclase (AC) signaling. β-Adrenergic receptors (β-ARs) were characterized by radioligand-binding experiments and the expression of selected G protein subunits, AC, and protein kinase A (PKA) was determined by RT-PCR and Western blot analyses. There was no significant difference in the amount of trimeric G proteins, but the number of β-ARs was higher (by about 35 %) in myocardial preparations from SHR-Cd36 as compared to SHR. Besides that, transgenic rats expressed increased amount (by about 20 %) of the dominant myocardial isoforms AC5/6 and contained higher levels of both nonphosphorylated (by 11 %) and phosphorylated (by 45 %) PKA. Differently stimulated AC activity in SHR-Cd36 significantly exceeded (by about 18-30 %) the enzyme activity in SHR. Changes at the molecular level were reflected by higher contractile responses to stimulation by the adrenergic agonist dobutamine. In summary, it can be concluded that the increased susceptibility to ischemic arrhythmias of SHR-Cd36 is attributable to upregulation of some components of the β-AR signaling pathway, which leads to enhanced sensitization of AC and increased cardiac adrenergic responsiveness.

Over-nutrition and metabolic cardiomyopathy

Cardiovascular disease, which accounts for the highest morbidity and mortality in the United States, has several major risk factors, including aging and diabetes. Overweight and obesity, especially abdominal obesity, have been increasingly implicated as independent risk factors in the development of cardiovascular disease. Metabolic and/or diabetic cardiomyopathy has been especially associated with excess body weight caused by chronic over-nutrition and high-fat feeding. In the initial stages, obesity is now understood to cause significant dysregulation of cardiac fatty acid and glucose metabolism. These abnormalities are due, in part, to increased oxidative stress, which in turn can cause deleterious effects on intracellular signaling pathways that control cellular growth and proliferation. This increase in oxidative stress is coupled with reduced anti-oxidant species and dysregulation of metabolic signaling pathways. The cardiomyopathy seen with obesity is associated with increased interstitial fibrosis and diastolic dysfunction. Over time, evolving abnormalities include hypertrophy and systolic dysfunction, eventually leading to heart failure.