ABSTRACT
BACKGROUND AND PURPOSE: Recent clinical data suggest beneficial effects of ivabradine, a specific heart rate (HR)-lowering drug, in heart failure patients. However, the mechanisms responsible for these effects have not been completely clarified. Thus, we investigated functional/molecular changes in I(f), the specific target of ivabradine, in the failing atrial and ventricular myocytes where this current is up-regulated as a consequence of maladaptive remodelling. EXPERIMENTAL APPROACH: We investigated the effects of ivabradine (IVA; 10 mg·kg(-1) ·day(-1) for 90 days) on electrophysiological remodelling in left atrial (LA), left ventricular (LV) and right ventricular (RV) myocytes from post-mycardial infarcted (MI) rats, with sham-operated (sham or sham + IVA) rats as controls. I(f) current was measured by patch-clamp; hyperpolarization-activated cyclic nucleotide-gated (HCN) channel isoforms and microRNA (miRNA-1 and miR-133) expression were evaluated by reverse transcription quantitative PCR. KEY RESULTS: Maximal specific conductance of I(f) was increased in MI, versus sham, in LV (P < 0.01) and LA myocytes (P < 0.05). Ivabradine reduced HR in both MI and sham rats (P < 0.05). In MI + IVA, I(f) overexpression was attenuated and HCN4 transcription reduced by 66% and 54% in LV and RV tissue, respectively, versus MI rats (all P < 0.05). miR-1 and miR-133, which modulate post-transcriptional expression of HCN2 and HCN4 genes, were significantly increased in myocytes from MI + IVA. CONCLUSION AND IMPLICATION: The beneficial effects of ivabradine may be due to the reversal of electrophysiological cardiac remodelling in post-MI rats by reduction of functional overexpression of HCN channels. This is attributable to transcriptional and post-transcriptional mechanisms.
Subject(s)
Benzazepines/pharmacology , Myocardial Infarction/drug therapy , Myocardial Infarction/metabolism , Myocytes, Cardiac/drug effects , Myocytes, Cardiac/metabolism , Animals , Cyclic Nucleotide-Gated Cation Channels/genetics , Cyclic Nucleotide-Gated Cation Channels/metabolism , Heart Atria/drug effects , Heart Atria/metabolism , Heart Rate/drug effects , Heart Rate/genetics , Heart Ventricles/drug effects , Heart Ventricles/metabolism , Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels , Ion Channels/genetics , Ion Channels/metabolism , Ivabradine , Male , MicroRNAs/genetics , MicroRNAs/metabolism , Potassium Channels/genetics , Potassium Channels/metabolism , Rats , Rats, Wistar , Ventricular Remodeling/drug effects , Ventricular Remodeling/geneticsABSTRACT
Fibrate treatment in mice is known to modulate high density lipoprotein (HDL) metabolism by regulating apolipoprotein (apo)AI and apoAII gene expression. In addition to alterations in plasma HDL levels, fibrates induce the emergence of large, cholesteryl ester-rich HDL in treated transgenic mice expressing human apoAI (HuAITg). The mechanisms of these changes may not be restricted to the modulation of apolipoprotein gene expression, and the aim of the present study was to determine whether the expression of factors known to affect HDL metabolism (i.e. phospholipid transfer protein (PLTP), lecithin:cholesterol acyltransferase, and hepatic lipase) are modified in fenofibrate-treated mice. Significant rises in plasma PLTP activity were observed after 2 weeks of fenofibrate treatment in both wild-type and HuAITg mice. Simultaneously, hepatic PLTP mRNA levels increased in a dose-dependent fashion. In contrast to PLTP, lecithin:cholesterol acyltransferase mRNA levels in HuAITg mice were not significantly modified by fenofibrate despite a significant decrease in plasma cholesterol esterification activity. Fenofibrate did not induce any change in hepatic lipase activity. Fenofibrate significantly increased HDL size, an effect that was more pronounced in HuAITg mice than in wild-type mice. This effect in wild-type mice was completely abolished in PLTP-deficient mice. Finally, fenofibrate treatment did not influence PLTP activity or hepatic mRNA in peroxisome proliferator-activated receptor-alpha-deficient mice. It is concluded that 1) fenofibrate treatment increases plasma phospholipid transfer activity as the result of up-regulation of PLTP gene expression through a peroxisome proliferator-activated receptor-alpha-dependent mechanism, and 2) increased plasma PLTP levels account for the marked enlargement of HDL in fenofibrate-treated mice.
Subject(s)
Carrier Proteins/genetics , Fenofibrate/pharmacology , Gene Expression Regulation/drug effects , Hypolipidemic Agents/pharmacology , Lipoproteins, HDL/genetics , Membrane Proteins/genetics , Phospholipid Transfer Proteins , Animals , Apolipoprotein A-I , Apolipoproteins A/genetics , Apolipoproteins A/metabolism , Carrier Proteins/metabolism , Lipoproteins, HDL/metabolism , Membrane Proteins/metabolism , Mice , Mice, TransgenicABSTRACT
Studies performed in vivo have been controversial regarding the implication of human apolipoprotein (apo)A-II in the atherogenic process. Expression of human apoA-II in transgenic mice fed a chow diet leads to (1) a bimodal distribution of high density lipoprotein (HDL) size as in humans, (2) a reduction in total cholesterol concentration that is mainly due to a reduction in non-HDL cholesterol level, and (3) a dramatic reduction in mouse endogenous apoA-I and apoA-II. After 20 weeks on an atherogenic diet, transgenic mice had reduced total cholesterol concentrations because of a reduction in cholesterol associated with all lipoprotein classes. Endogenous apoA-I and apoA-II were also dramatically decreased in transgenic mice. The mean area of atherosclerotic lesions was drastically decreased in transgenic mice (-44%, P=0.0027) compared with control mice. The amount of aortic surface covered by lesions was positively correlated with very low density lipoprotein cholesterol (P<0.01) and intermediate density lipoprotein cholesterol levels (P<0.05). Transgenic mice were protected against the development of atherosclerosis despite a marked decrease in HDL cholesterol and apoA-I concentrations. This protection may be related to the marked reduction in circulating low density lipoprotein (very low density and intermediate density lipoprotein) levels in transgenic mice.
Subject(s)
Apolipoprotein A-II/genetics , Arteriosclerosis/genetics , Arteriosclerosis/prevention & control , Diet, Atherogenic , Animal Nutritional Physiological Phenomena , Animals , Apolipoprotein A-II/blood , Apolipoproteins/blood , Arteriosclerosis/enzymology , Arteriosclerosis/pathology , Biological Transport/genetics , Cholesterol/metabolism , Cholesterol, HDL/blood , Cholesterol, HDL/chemistry , Female , Genetic Predisposition to Disease , Humans , Lipids/blood , Lipoprotein Lipase/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Phosphatidylcholine-Sterol O-Acyltransferase/metabolism , Serum AlbuminABSTRACT
BACKGROUND: Hypoalphalipoproteinemia is the most common lipoprotein abnormality in patients with coronary artery disease, yet its causes are unknown. METHODS AND RESULTS: We show that the homozygous staggerer (sg/sg) mutant mouse, which carries a deletion within the nuclear receptor RORalpha gene, develops severe atherosclerosis when maintained on an atherogenic diet. In addition, sg/sg mice display a profound hypoalphalipoproteinemia, which is associated with decreased plasma levels of the major HDL proteins, apolipoprotein (apo) A-I and apoA-II. This decrease in HDL levels in sg/sg mice is due to lowered apoA-I gene expression in the intestine but not in the liver. ApoA-II gene expression is unaffected. CONCLUSIONS: These results suggest that the RORalpha gene contributes to the plasma HDL level and susceptibility to atherosclerosis.