Concomitant Mitral Regurgitation in Severe Aortic Stenosis　- Insights From the CURRENT AS Registry-2.

BACKGROUND: Data on concomitant mitral regurgitation (MR) in patients with severe aortic stenosis (AS) are scarce.Methods and Results: We investigated the risk of concomitant MR in patients with severe AS in the CURRENT AS Registry-2 according to initial treatment strategy (transcatheter aortic valve implantation [TAVI], surgical aortic valve replacement [SAVR], or conservative). Among 3,365 patients with severe AS, 384 (11.4%) had moderate/severe MR (TAVI: n=126/1,148; SAVR: n=68/591; conservative: n=190/1,626). The cumulative 3-year incidence for death or heart failure (HF) hospitalization was significantly higher in the moderate/severe than no/mild MR group in the entire population (54.6% vs. 34.3%, respectively; P<0.001) and for each treatment strategy (TAVI: 45.0% vs. 31.8% [P=0.006]; SAVR: 31.9% vs. 18.7% [P<0.001]; conservative: 67.8% vs. 41.6% [P<0.001]). The higher adjusted risk of moderate/severe MR relative to no/mild MR for death or HF hospitalization was not significant in the entire population (hazard ratio [HR] 1.15; 95% confidence interval [CI] 0.95-1.39; P=0.15); however, the risk was significant in the SAVR (HR 1.92; 95% CI 1.04-3.56; P=0.04) and conservative (HR 1.30; 95% CI 1.02-1.67; P=0.04) groups, but not in the TAVI group (HR 1.03; 95% CI 0.70-1.52; P=0.86), despite no significant interaction (Pinteraction=0.37). CONCLUSIONS: Moderate/severe MR was associated with a higher risk for death or HF hospitalization in the initial SAVR and conservative strategies, while the association was less pronounced in the initial TAVI strategy.

Statins use and recurrent venous thromboembolism in the direct oral anticoagulant era: insight from the COMMAND VTE Registry-2.

Statins were reported to have a potential effect of primary prevention of venous thromboembolism (VTE), although that of secondary prevention remains uncertain. To investigate the association between statins use and recurrent VTE in the current era. The COMMAND VTE Registry-2 is a multicenter registry enrolling 5,197 consecutive VTE patients among 31 centers in Japan between January 2015 and August 2020. We divided the entire cohort into 2 groups according to statins use at the time of discharge; the statins (N = 865) and no statins groups (N = 4332). The statins group was older (72.9 vs. 66.7 years, P < 0.001), and less often had active cancer (22.0% vs. 30.4%, P < 0.001). The cumulative incidence of discontinuation of anticoagulation was significantly lower in the statins group (60.3% vs. 52.6%, Log-rank P < 0.001). The cumulative 5-year incidence of recurrent VTE was significantly lower in the statins group (6.8% vs. 10.1%, Log-rank P = 0.01). Even after adjusting for the confounders, the lower risk of the statins group relative to the no statins group remained significant for recurrent VTE (HR 0.65, 95% CI 0.45-0.91, P = 0.01). The cumulative 5-year incidence of major bleeding was significantly lower in the statins group (12.2% vs. 14.1%, Log-rank P = 0.04), although, after adjusting for the confounders, the risk of the statins group relative to the no statins group turned to be insignificant (HR 0.77, 95% CI 0.59-1.00, P = 0.054). In this large real-world VTE registry, statins use was significantly associated with a lower risk for the recurrent VTE in the current era.

Rationale, Design, and Baseline Characteristics of the CURRENT AS Registry-2.

BACKGROUND: There is scarce data evaluating the current practice pattern and clinical outcomes for patients with severe aortic stenosis (AS), including both those who underwent surgical aortic valve replacement (SAVR) or transcatheter aortic valve implantation (TAVI) and those who were managed conservatively in the TAVI era.Methods and Results: The Contemporary outcomes after sURgery and medical tREatmeNT in patients with severe Aortic Stenosis (CURRENT AS) Registry-2 is a prospective, physician-initiated, multicenter registry enrolling consecutive patients who were diagnosed with severe AS between April 2018 and December 2020 among 21 centers in Japan. The rationale for the prospective enrollment was to standardize the assessment of symptomatic status, echocardiographic evaluation, and other recommended diagnostic examinations such as computed tomography and measurement of B-type natriuretic peptide. Moreover, the schedule of clinical and echocardiographic follow up was prospectively defined and strongly recommended for patients who were managed conservatively. The entire study population consisted of 3,394 patients (mean age: 81.6 years and women: 60%). Etiology of AS was degenerative in 90% of patients. AS-related symptoms were present in 60% of patients; these were most often heart failure symptoms. The prevalence of high- and low-gradient AS was 58% and 42%, respectively, with classical and paradoxical low-flow low-gradient AS in 4.6% and 6.7%, respectively. CONCLUSIONS: The CURRENT AS Registry-2 might be large and meticulous enough to determine the appropriate timing of intervention for patients with severe AS in contemporary clinical practice.

Novel Non-Invasive Index for Prediction of Responders in Cardiac Resynchronization Therapy Using High-Resolution Magnetocardiography.

BACKGROUND: Approximately one-third of patients with advanced heart failure (HF) do not respond to cardiac resynchronization therapy (CRT). We investigated whether the left ventricular (LV) conduction pattern on magnetocardiography (MCG) can predict CRT responders.Methods and Results:This retrospective study enrolled 56 patients with advanced HF (mean [±SD] LV ejection fraction [LVEF] 23±8%; QRS duration 145±19 ms) and MCG recorded before CRT. MCG-QRS current arrow maps were classified as multidirectional (MDC; n=28) or unidirectional (UDC; n=28) conduction based on a change of either ≥35° or <35°, respectively, in the direction of the maximal current arrow after the QRS peak. Baseline New York Heart Association functional class and LVEF were comparable between the 2 groups, but QRS duration was longer and the presence of complete left bundle branch block and LV dyssynchrony was higher in the UDC than MDC group. Six months after CRT, 30 patients were defined as responders, with significantly more in the UDC than MDC group (89% vs. 14%, respectively; P<0.001). Over a 5-year follow-up, Kaplan-Meyer analysis showed that adverse cardiac events (death or implantation of an LV assist device) were less frequently observed in the UDC than MDC group (6/28 vs. 15/28, respectively; P=0.027). Multivariate analysis revealed that UDC on MCG was the most significant predictor of CRT response (odds ratio 69.8; 95% confidence interval 13.14-669.32; P<0.001). CONCLUSIONS: Preoperative non-invasive MCG may predict the CRT response and long-term outcome after CRT.

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.

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.

In-hospital outcomes after SAVR or TAVI in patients with severe aortic stenosis.

There were no data comparing the in-hospital outcomes after transcatheter aortic valve implantation (TAVI) with those after surgical aortic valve replacement (SAVR) in Japan. Among consecutive patients with severe AS between April 2018 and December 2020 in the CURRENT AS Registry-2, we identified 1714 patients who underwent aortic valve replacement (TAVI group: 1134 patients, and SAVR group: 580 patients). Patients in the TAVI group were much older (84.4 versus 73.6 years, P < 0.001) and more often had comorbidities than those in the SAVR group. In-hospital death rate was numerically lower in the TAVI group than in the SAVR group (0.6% versus 2.2%). After excluding patients with dialysis, in-hospital death rate was very low and comparable in the TAVI and SAVR groups (0.6% versus 0.8%). The rates of major bleeding and new-onset atrial fibrillation during index hospitalization were higher after SAVR than after TAVI (72% versus 20%, and 26% versus 4.6%, respectively), while the rate of pacemaker implantation was higher after TAVI than after SAVR (8.1% versus 2.4%). Regarding the echocardiographic data at discharge, the prevalence of patient-prosthesis mismatch was lower in the TAVI group than in the SAVR group (moderate: 9.0% versus 26%, and severe: 2.6% versus 4.8%). In this real-world data in Japan, TAVI compared with SAVR was chosen in much older patients with more comorbidities with severe AS. In-hospital death rate was numerically lower in the TAVI group than in the SAVR group.

Cancer-associated venous thromboembolism in the direct oral anticoagulants era: Insight from the COMMAND VTE Registry-2.

BACKGROUND: There is a paucity of data on real-world management strategies and clinical outcomes of cancer-associated venous thromboembolism (VTE) in the direct oral anticoagulants (DOACs) era. OBJECTIVES: To investigate the status of cancer-associated VTE in the DOAC era. METHODS: This multicenter, retrospective cohort study among 31 centers in Japan between 2015 and 2020 enrolled 5197 consecutive patients with acute symptomatic VTE, who were divided into 1507 patients (29 %) with active cancer and 3690 patients (71 %) without. RESULTS: The cumulative 3-year rate of anticoagulation discontinuation was significantly higher in patients with active cancer than in those without (62.7 % vs. 59.1 %, P < 0.001). The cumulative 5-year incidence of recurrent VTE was higher in patients with active cancer than in those without (10.1 % vs. 9.1 %, P = 0.01), however, after adjusting for the confounders and competing risk of mortality, the excess risk of the active cancer group relative to the no active cancer group was no longer significant (HR: 0.95, 95 % CI: 0.73-1.24). The cumulative 5-year incidence of major bleeding was much higher in the active cancer group (20.4 % vs. 11.6 %, P < 0.001). Even after adjusting for the confounders and competing risk of mortality, the risk of the active cancer group relative to the no active cancer group remained significant (HR: 1.36, 95 % CI: 1.11-1.66). CONCLUSIONS: The current large real-world registry revealed that the risk of major bleeding was still higher in patients with active cancer than in those without, leading to the frequent anticoagulation discontinuation, which has been still a huge challenge to overcome in the DOAC era.

Edoxaban, Rivaroxaban, or Apixaban for Cancer-Associated Venous Thromboembolism in the Real World: Insights from the COMMAND VTE Registry-2.

BACKGROUND: Real-world data on clinical characteristics and outcomes related to the use of different direct oral anticoagulants (DOACs) for cancer-associated venous thromboembolism (VTE) is lacking. METHODS: The COMMAND VTE Registry-2 is a multicenter registry enrolling 5,197 consecutive patients with acute symptomatic VTE from 31 centers in Japan from January 2015 to August 2020. Our study population comprised 1,197 patients with active cancer who were divided into the edoxaban (N = 643, 54%), rivaroxaban (N = 297, 25%), and apixaban (N = 257, 22%) groups. RESULTS: The cumulative 5-year incidence of recurrent VTE (9.3, 10.2, and 8.5%, respectively, p = 0.82) and all-cause death (67.5, 66.8, and 63.8%, respectively, p = 0.22) did not differ among the groups. Despite adjusting for confounders, the risks of recurrent VTE and all-cause death did not differ significantly among the groups. The cumulative 5-year incidence of major and clinically relevant bleeding was significantly lower in the rivaroxaban group than those in the other groups (22.6, 14.0, and 22.8%, p = 0.04; and 37.6, 26.8, and 38.3%, p = 0.01, respectively). After adjusting for confounders, in the rivaroxaban group, the risk for major bleeding was numerically lower (hazard ratio [HR]: 0.65, 95% confidence interval [CI]: 0.40-1.01) and that of clinically relevant all bleeding was significantly lower (HR: 0.67, 95% CI: 0.48-0.92) than those in the edoxaban group. CONCLUSION: The risks of recurrent VTE and all-cause death did not differ significantly among the different DOACs ; however, the risk of bleeding events could differ, with a potentially lower risk of bleeding with rivaroxaban.

External validation of the PE-SARD bleeding score for early major bleeding in patients with acute pulmonary embolism: From the COMMAND VTE Registry-2.

BACKGROUND: There is no established risk score for anticoagulant-related bleeding during the acute phase in patients with pulmonary embolism (PE). The Syncope, Anemia, Renal Dysfunction (PE-SARD) bleeding score was developed to predict early major bleeding, but has not yet been fully externally validated. OBJECTIVES: To externally validate the PE-SARD bleeding score. PATIENTS/METHODS: Using the COMMAND VTE Registry-2 database, which enrolled 5197 consecutive acute symptomatic venous thromboembolism patients among 31 centers in Japan between January 2015 and August 2020, we identified acute PE patients. We divided those into 3 groups by the score: high-risk (>2.5 points), intermediate-risk (1-2.5 points), and low-risk (0 points). The discriminating and calibration performances of the score for 30-day major bleeding were assessed. Subgroup analyses based on active cancer were also performed. RESULTS: Of 2781 eligible patients, the high-risk group accounted for 557 patients (20%), intermediate-risk group for 1412 (51%), and low-risk group for 812 (29%). Major bleeding occurred in 121 patients within 30 days. The cumulative 30-day incidence of major bleeding substantially increased in the higher risk categories by the score (high-risk group: 8.2% [95%CI, 5.9%-10.5%], intermediate-risk group: 4.6% [95%CI, 3.5%-5.7%], and low-risk group: 1.8% [95%CI, 0.8%-2.7%]). The discriminating power of the score was modest with a C-statistic of 0.65 (95%CI, 0.61-0.70) with a good calibration performance with a score of <4 points except for in active cancer patients. CONCLUSIONS: The PE-SARD bleeding score had a modest discriminating performance with a limited calibration performance in acute PE patients without active cancer.

Fragility and long-term clinical outcomes in patients with venous thromboembolism receiving direct oral anticoagulants: From the COMMAND VTE REGISTRY-2.

INTRODUCTION: There is limited data on the safety of direct oral anticoagulants (DOACs) in fragile patients with venous thromboembolism (VTE). MATERIALS AND METHODS: We used the COMMAND VTE Registry-2 enrolling patients with acute symptomatic VTE. The study population consisted of 3928 patients receiving DOACs, who were divided into fragile (2136 patients) and non-fragile groups (1792 patients). Fragility was defined as patients of age ≥ 75 years, creatinine clearance level ≤ 50 ml/min, and/or body weight ≤ 50 kg. RESULTS: The fragile group significantly more often received reduced doses of DOACs compared to the non-fragile group (51 % and 19 %, P < 0.001). The cumulative 5-year incidence of major bleeding was numerically higher in the fragile group than the non-fragile group (15.0 % and 11.1 %, P = 0.052), even with no significant excess risk after adjusting for confounders (HR 1.03, 95%CI 0.81-1.31, P = 0.78). The cumulative 5-year incidence of clinically relevant bleeding was significantly higher in the fragile group than the non-fragile group (28.6 % and 19.6 %, P < 0.001), even after adjusting for confounders (HR 1.28, 95%CI 1.08-1.53, P = 0.005). There was no significant difference in cumulative 5-year incidence of recurrent VTE between the groups (9.6 % and 8.9 %, P = 0.68), which was consistent after adjusting for confounders (HR 1.13, 95%CI 0.84-1.51, P = 0.41). CONCLUSIONS: Among VTE patients receiving DOACs, fragile patients were associated with a numerically higher rate of major bleeding and a significantly increased risk of clinically relevant bleeding, but not an increased risk of recurrent VTE.

Subclass phenotypes in patients with unprovoked venous thromboembolisms using a latent class analysis.

BACKGROUND: Patients with unprovoked venous thromboembolisms (VTEs) can be sub-classified based on the different phenotypes using a latent class analysis (LCA), which might be useful for selecting individual management strategies. METHODS: In the COMMAND VTE Registry-2 database enrolling 5197 VTE patients, the current derivation cohort consisted of 1556 patients with unprovoked VTEs. We conducted clustering with an LCA, and the patients were classified into subgroups with the highest probability. We compared the clinical characteristics and outcomes among the developed subgroups. RESULTS: This LCA model proposed 3 subgroups based on 8 clinically relevant variables, and classified 592, 813, and 151 patients as Class I, II, and III, respectively. Based on the clinical features, we named Class I the younger, Class II the older with a few comorbidities, and Class III the older with many comorbidities. The cumulative 3-year anticoagulation discontinuation rate was highest in the older with many comorbidities (Class III) (39.9 %, 36.1 %, and 48.4 %, P = 0.02). There was no significant difference in the cumulative 5-year incidence of recurrent VTEs among the 3 classes (12.8 %, 11.1 %, and 4.0 % P = 0.20), whereas the cumulative 5-year incidence of major bleeding was significantly higher in the older with many comorbidities (Class III) (7.8 %, 12.7 %, and 17.8 %, P = 0.04). CONCLUSION: The current LCA revealed that patients with unprovoked VTEs could be sub-classified into further phenotypes depending on the patient characteristics. Each subclass phenotype could have different clinical outcomes risks especially a bleeding risk, which could have a potential benefit when considering the individual anticoagulation strategies. CLINICAL TRIAL REGISTRATION: URL: http://www.umin.ac.jp/ctr/index.htm COMMAND VTE Registry-2: Unique identifier, UMIN000044816 COMMAND VTE Registry: Unique identifier, UMIN000021132.

Dynamic changes of serum microRNA-122-5p through therapeutic courses indicates amelioration of acute liver injury accompanied by acute cardiac decompensation.

AIMS: Recent studies have shown that serum microRNA (miR) abundance is informative for the diagnosis or prognosis of heart failure. However, the dynamics and kinetics of miRs in acute heart failure are largely unknown. Serial measurement and analysis of serum miRs changes in individuals along their therapeutic course could reduce inter-individual variation and should detect potentially important serum miRs related to disease mechanisms. Based on this concept, we profiled serum miR signatures of blood samples that were obtained sequentially on the day of admission and on hospital Day 7. METHODS AND RESULTS: This prospective, observational study included 42 consecutive acute heart failure patients (74 ± 1 years old, 24 male). From admission to Day 7, most of the patients showed clinical improvement. In such a cohort, we detected several fluctuations of serum miRs by two distinct screening methods (quantitative PCR and high-throughput sequencing). One of these fluctuating serum miRs, miR-122-5p, decreased significantly from Day 1 to Day 7 [median arbitrary unit (1st:3rd quantile value); 4.62 [2.39:12.3] to 3.07 [1.67:5.39], P = 0.007]. This fluctuation was significantly correlated with changes in serum liver function markers (estimated coefficient and 95% confidence interval; vs change in aspartate aminotransferase 1.69, 0.890-2.484, P < 0.001 and r = 0.560, vs change in alanine aminotransferase 1.09, 0.406-1.771, P = 0.007 and r = 0.428). CONCLUSIONS: The serum miR signature of patients with acute heart failure might indicate the severity of the disease or patients' response to therapeutic intervention. Notably, serum miR-122-5p levels reflect liver damage in this condition.

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.

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.

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.