Masayasu Izuhara

MicroRNA-33 regulates sterol regulatory element-binding protein 1 expression in mice

MicroRNAs (miRs) are small non-protein-coding RNAs that bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports have indicated that miR-33, which is located within the intron of sterol regulatory element-binding protein (SREBP) 2, controls cholesterol homoeostasis and may be a potential therapeutic target for the treatment of atherosclerosis. Here we show that deletion of miR-33 results in marked worsening of high-fat diet-induced obesity and liver steatosis. Using miR-33−/−Srebf1+/− mice, we demonstrate that SREBP-1 is a target of miR-33 and that the mechanisms leading to obesity and liver steatosis in miR-33−/− mice involve enhanced expression of SREBP-1. These results elucidate a novel interaction between SREBP-1 and SREBP-2 mediated by miR-33 in vivo.

MicroRNA-451 Exacerbates Lipotoxicity in Cardiac Myocytes and High-Fat Diet-Induced Cardiac Hypertrophy in Mice Through Suppression of the LKB1/AMPK Pathway

Rationale: In some patients with type 2 diabetes mellitus (DM) without hypertension, cardiac hypertrophy and attenuated cardiac function are observed, and this insult is termed diabetic cardiomyopathy. To date, microRNA (miRNAs or miR) functions in diabetic cardiomyopathy remain to be elucidated. Objective: To clarify the functions of miRNAs involved in diabetic cardiomyopathy caused by type 2 DM. Methods and Results: C57BL/6 mice were fed a high-fat diet (HFD) for 20 weeks, which induced obesity and type 2 DM. miRNA microarray analyses and real-time polymerase chain reaction revealed that miR-451 levels were significantly increased in the type 2 DM mouse hearts. Because excess supply of saturated fatty acids is a cause of diabetic cardiomyopathy, we stimulated neonatal rat cardiac myocytes with palmitic acid and confirmed that miR-451 expression was increased in a dose- and time-dependent manner. Loss of miR-451 function ameliorated palmitate-induced lipotoxicity in neonatal rat cardiac myocytes. Calcium-binding protein 39 (Cab39) is a scaffold protein of liver kinase B1 (LKB1), an upstream kinase of AMP-activated protein kinase (AMPK). Cab39 was a direct target of miR-451 in neonatal rat cardiac myocytes and Cab39 overexpression rescued the lipotoxicity. To clarify miR-451 functions in vivo, we generated cardiomyocyte-specific miR-451 knockout mice. HFD-induced cardiac hypertrophy and contractile reserves were ameliorated in cardiomyocyte-specific miR-451 knockout mice compared with control mice. Protein levels of Cab39 and phosphorylated AMPK were increased and phosphorylated mammalian target of rapamycin (mTOR) was reduced in cardiomyocyte-specific miR-451 knockout mouse hearts compared with control mouse hearts. Conclusions: Our results demonstrate that miR-451 is involved in diabetic cardiomyopathy through suppression of the LKB1/AMPK pathway.

MicroRNA-33b knock-in mice for an intron of sterol regulatory element-binding factor 1 (Srebf1) exhibit reduced HDL-C in vivo

MicroRNAs (miRs) are small non-protein-coding RNAs that bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports, including ours, indicated that miR-33a located within the intron of sterol regulatory element-binding protein (SREBP) 2 controls cholesterol homeostasis and can be a possible therapeutic target for treating atherosclerosis. Primates, but not rodents, express miR-33b from an intron of SREBF1. Therefore, humanized mice, in which a miR-33b transgene is inserted within a Srebf1 intron, are required to address its function in vivo. We successfully established miR-33b knock-in (KI) mice and found that protein levels of known miR-33a target genes, such as ABCA1, ABCG1, and SREBP-1, were reduced compared with those in wild-type mice. As a consequence, macrophages from the miR-33b KI mice had a reduced cholesterol efflux capacity via apoA-I and HDL-C. Moreover, HDL-C levels were reduced by almost 35% even in miR-33b KI hetero mice compared with the control mice. These results indicate that miR-33b may account for lower HDL-C levels in humans than those in mice and that miR-33b is possibly utilized for a feedback mechanism to regulate its host gene SREBF1. Our mice will also aid in elucidating the roles of miR-33a/b in different genetic disease models.

Long-term effects of early statin therapy for patients with acute myocardial infarction treated with stent implantation.

OBJECTIVES Statins are widely administered to patients with acute myocardial infarction (AMI), but knowledge of the effects of early statin therapy on the long-term mortality of AMI patients after stent implantation is still limited, especially for beyond low-density lipoprotein cholesterol (LDL-C) lowering effects. METHODS Our 378 consecutive AMI patients who were discharged alive from the hospital with successful stent implantation between 1997 and 2005 were included. We retrospectively evaluated the effects of statin therapy on major adverse cardiovascular events (MACE), including all-cause death, reinfarction, coronary artery bypass grafting, heart failure requiring rehospitalization, and target lesion revascularization. RESULTS Statins were given to 271 patients according to the physician to achieve a LDL-C level of less than 100mg/dL. The achieved LDL-C levels in the statin group were 100.7, 95.1, 96.7, and 102.8mg/dL at discharge, 6 months, 1 year, and 3 years, respectively, whereas those in the non-statin group were 103.2, 107.3, 102.8, and 103.0mg/dL. These levels were not significantly different between the groups during 3 years. Based on Kaplan-Meier estimates, statin therapy was associated with a reduction of long-term mortality (log-rank test P=0.007). Multivariate Cox regression analysis revealed that statin therapy (P=0.015, hazard ratio: 0.10; 95% confidence interval: 0.01-0.64) was a significant predictor of favorable prognosis. Multivariate analysis revealed that statin treatment had a beneficial effect against MACE over 3 years (P=0.008). CONCLUSIONS Early statin therapy was beneficial for long-term mortality of AMI patients treated with stenting.

High-density lipoprotein cholesterol levels and cardiovascular outcomes in Japanese patients after percutaneous coronary intervention: a report from the CREDO-Kyoto registry cohort-2.

OBJECTIVE To determine whether low HDL-C is a risk factor for adverse cardiovascular events in patients with known CAD. METHODS We evaluated 10,391 patients who underwent PCI from January 2005 to December 2007. In total, 3838 (36.9%) patients had low HDL-C (HDL-C <40 mg/dL in males and <50 mg/dL in females) and 6553 (63.1%) patients had normal HDL-C based on measurements on admission. RESULTS The unadjusted 5-year incidence of major adverse cardiac events (MACE: composite of cardiovascular death, myocardial infarction or stroke) was significantly higher in the low HDL-C group than in the normal HDL-C group (17.6% vs. 14.0%, P < 0.0001). However, after adjusting for confounders, low HDL-C was not associated with a higher risk of MACE (adjusted hazard ratio [HR] 1.07, 95% confidence interval (CI) 0.97-1.19; P = 0.19). There was no significant interaction between the effect of low HDL-C on MACE and several subgroup factors including age, sex, clinical presentation of CAD, statins use, serum low-density lipoprotein cholesterol level, and serum triglycerides level. CONCLUSION Low HDL-C, as compared with normal HDL-C, was not associated with higher 5-year risk of MACE in patients who underwent PCI.

Achievement Rates of Japan Atherosclerosis Society Guidelines 2007 LDL‐Cholesterol Goals with Rosuvastatin or Atorvastatin in Patients Who Had Not Achieved Their Goal with Atorvastatin

BACKGROUND The Japan Atherosclerosis Societys 2007 Guidelines for Prevention of Atherosclerotic Cardiovascular Diseases (JAS2007GL) advocate reducing LDL cholesterol (LDL-C) to target levels in patients with dyslipidemia, but achievement rates are frequently unsatisfactory even in the presence of lipid-lowering therapy. This multicenter, open-label, randomized, parallel-group study compared the efficacy of rosuvastatin and atorvastatin on JAS2007GL LDL-C goals in Japanese patients not achieving their target goal with atorvastatin treatment. METHODS The study involved 20 clinical institutes in Japan (Kishiwada Atherosclerosis Prevention Study [KAPS] Group). Patients with category II or III risk of coronary artery disease (CAD), or those with a history of CAD (secondary prevention), who had not achieved their JAS2007GL LDL-C goals during treatment with atorvastatin for at least 4 weeks were switched either to rosuvastatin 5 mg/day (from atorvastatin 10 mg/day) or rosuvastatin 10 mg/day (from atorvastatin 20 mg/day) (n = 75) or continued to receive atorvastatin (n = 77). The primary endpoint was achievement of LDL-C goals at 3 months. The main secondary endpoint was achievement of LDL-C goal + high-sensitivity C-reactive protein level <1.0 mg/L at 3 months. RESULTS Achievement rates for the primary endpoint were 49.3% in the rosuvastatin group and 31.7% in the atorvastatin group (P = 0.022). Achievement rates for the main secondary endpoint were 40.0% in the rosuvastatin group and 20.8% in the atorvastatin group (P = 0.010). Rosuvastatin and atorvastatin were both well tolerated in this study. CONCLUSIONS Rosuvastatin is a useful treatment option for Japanese patients who are not achieving their JAS2007GL LDL-C goal with atorvastatin.

Expression patterns of miRNA-423-5p in the serum and pericardial fluid in patients undergoing cardiac surgery

Background Recently, it has been reported that specific microRNA (miRNA) levels are elevated in serum and can be used as biomarkers in patients with cardiovascular diseases. However, miRNAs expression profiles and their sources in pericardial fluid (PF) are unclear. Methods and Results The purpose of this study was to identify the levels of miRNAs in PF in relation to those in the serum in patients undergoing cardiac surgery. Serum (S) and PF from patients undergoing coronary artery bypass graft (CABG) due to stable angina pectoris (sAP) and unstable AP (uAP) and aortic valve replacement due to aortic stenosis (AS) were analyzed for the detection of miRNAs. We named these samples S-sAP, S-uAP, S-AS, PF-sAP, PF-uAP, and PF-AS, respectively. We first measured the levels of miR-423-5p, which was recognized previously as a biomarker for heart failure. miR-423-5p levels were significantly higher in PF than serum. Although there was no difference in miR-423-5p levels among the PF-AS, PF-sAP, and PF-uAP, its levels were significantly elevated in S-uAP compared with those in S-AS and S-sAP. In order to clarify the source of miR-423-5p in PF, we measured the levels of muscle-enriched miR-133a and vascular-enriched miR-126 and miR-92a in the same samples. miR-133a levels were significantly higher in serum than in PF, and it was elevated in S-uAP compared with S-AS. miR-126 level was significantly increased in serum compared with PF, and the level of miR-92a the similar tendency. miR-423-5p is located in the first intron of NSRP1. There is another miRNA, miR-3184, encoded in the opposite direction in the same region. In vitro experiments indicated that the duplex of miR-423-5p and miR-3184-3p was more resistant to RNase than the duplex of miR-423-5p and miR-133-3p, which may help to stabilize miR-423-5p in the PF. Conclusions Our results suggested that miR-423-5p is enriched in PF, and serum miR-423-5p may be associate with uAP. Its expression pattern was different to that of muscle- and vascular-enriched miRNAs, miR-133a, miR-126, and miR-92a.

Prevention of neointimal formation using miRNA-126-containing nanoparticle-conjugated stents in a rabbit model

Background Despite recent progress with drug-eluting stents, restenosis and thrombosis after endovascular intervention are still major limitations in the treatment of cardiovascular diseases. These problems are possibly caused by inappropriate inhibition of neointimal formation and retardation of re-endothelialization on the surface of the stents. miR-126 has been shown to have the potential to enhance vascular endothelial cell proliferation. Methods and results We designed and constructed a 27-nt double strand RNA (dsRNA) conjugated to cholesterol, which has high membrane permeability, and formed mature miR-126 after transfection. For site-specific induction of miR-126, we utilized poly (DL-lactide-co-glycolide) nanoparticles (NPs). miR-126-dsRNA-containing NPs (miR-126 NPs) significantly reduced the protein expression of a previously identified miR-126 target, SPRED1, in human umbilical vascular endothelial cells (HUVECs), and miR-126 NPs enhanced the proliferation and migration of HUVECs. On the other hand, miR-126 NPs reduced the proliferation and migration of vascular smooth muscle cells, via the suppression of IRS-1. Finally, we developed a stent system that eluted miR-126. This delivery system exhibited significant inhibition of neointimal formation in a rabbit model of restenosis. Conclusions miR-126 NP-conjugated stents significantly inhibited the development of neointimal hyperplasia in rabbits. The present study may indicate the possibility of a novel therapeutic option to prevent restenosis after angioplasty.

The importance of serial cardiac troponin measurement for evaluating the response to immunosuppressive therapy for myocarditis

A 71-year-old woman was admitted to our department because of acute myocarditis. She was ameliorated with conventional heart failure treatment, however she developed left ventricular dilatation and cardiac troponin T (cTnT) was elevated again to >1.0 ng/ml 6 month after the first admission. She was re-admitted because of recurrent decompensated heart failure in spite of conventional treatment. Right ventricular endomyocardial biopsy revealed active myocarditis. Immunosuppressive therapy with prednisolone and azathioprine improved her symptoms and left ventricular function accompanied by a striking decrease of cTnT levels. The decreased cTnT level indicated an effective response to immunosuppression early after the beginning of treatment. These findings suggested that it is possible to evaluate the response to immunosuppressive therapy by serial measurement of cardiac troponin.

Genetic Ablation of MicroRNA-33 Attenuates Inflammation and Abdominal Aortic Aneurysm Formation via Several Anti-Inflammatory Pathways

Objective— Abdominal aortic aneurysm (AAA) is an increasingly prevalent and ultimately fatal disease with no effective pharmacological treatment. Because matrix degradation induced by vascular inflammation is the major pathophysiology of AAA, attenuation of this inflammation may improve its outcome. Previous studies suggested that miR-33 (microRNA-33) inhibition and genetic ablation of miR-33 increased serum high-density lipoprotein cholesterol and attenuated atherosclerosis. Approach and Results— MiR-33a-5p expression in central zone of human AAA was higher than marginal zone. MiR-33 deletion attenuated AAA formation in both mouse models of angiotensin II– and calcium chloride–induced AAA. Reduced macrophage accumulation and monocyte chemotactic protein-1 expression were observed in calcium chloride–induced AAA walls in miR-33−/− mice. In vitro experiments revealed that peritoneal macrophages from miR-33−/− mice showed reduced matrix metalloproteinase 9 expression levels via c-Jun N-terminal kinase inactivation. Primary aortic vascular smooth muscle cells from miR-33−/− mice showed reduced monocyte chemotactic protein-1 expression by p38 mitogen-activated protein kinase attenuation. Both of the inactivation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase were possibly because of the increase of ATP-binding cassette transporter A1 that is a well-known target of miR-33. Moreover, high-density lipoprotein cholesterol derived from miR-33−/− mice reduced expression of matrix metalloproteinase 9 in macrophages and monocyte chemotactic protein-1 in vascular smooth muscle cells. Bone marrow transplantation experiments indicated that miR-33–deficient bone marrow cells ameliorated AAA formation in wild-type recipients. MiR-33 deficiency in recipient mice was also shown to contribute the inhibition of AAA formation. Conclusions— These data strongly suggest that inhibition of miR-33 will be effective as a novel strategy for treating AAA.