Neutrophils are recruited into the heart at an early stage following a myocardial infarction (MI). These secrete several proteases, one of them being neutrophil elastase (NE), which promotes inflammatory responses in several disease models. It has been shown that there is an increase in NE activity in patients with MI; however, the role of NE in MI remains unclear. Therefore, the present study aimed to investigate the role of NE in the pathogenesis of MI in mice. NE expression peaked on day 1 in the infarcted hearts. In addition, NE deficiency improved survival and cardiac function post-MI, limiting fibrosis in the noninfarcted myocardium. Sivelestat, an NE inhibitor, also improved survival and cardiac function post-MI. Flow cytometric analysis showed that the numbers of heart-infiltrating neutrophils and inflammatory macrophages (CD11b⁺F4/80⁺CD206^low cells) were significantly lower in NE-deficient mice than in wild-type (WT) mice. At the border zone between intact and necrotic areas, the number of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells was lower in NE-deficient mice than in WT mice. Western blot analyses revealed that the expression levels of insulin receptor substrate 1 and phosphorylation of Akt were significantly upregulated in NE-knockout mouse hearts, indicating that NE deficiency might improve cardiac survival by upregulating insulin/Akt signaling post-MI. Thus, NE may enhance myocardial injury by inducing an excessive inflammatory response and suppressing Akt signaling in cardiomyocytes. Inhibition of NE might serve as a novel therapeutic target in the treatment of MI.

Aging and obesity are the most prominent risk factors for onset of atrial fibrillation (AF). Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme that catalyzes nicotinamide adenine dinucleotide (NAD) activity. Nampt and NAD are essential for maintenance of cellular redox homeostasis and modulation of cellular metabolism, and their expression levels decrease with aging and obesity. However, a role for Nampt in AF is unknown. The present study aims to test whether there is a role of Nampt/NAD axis in the pathogenesis of obesity-induced AF. Male C57BL/6J (WT) mice and heterozygous Nampt knockout (NKO) mice were fed with a normal chow diet (ND) or a high-fat diet (HFD). Electrophysiological study showed that AF inducibility was significantly increased in WT+HFD, NKO+ND, and NKO+HFD mice compared with WT+ND mice. AF duration was significantly longer in WT+HFD and NKO+ND mice and further prolonged in NKO+HFD mice compared with WT+ND mice and the calcium handling pathway was altered on molecular level. Also, treatment with nicotinamide riboside, a NAD precursor, partially restored the HFD-induced AF perpetuation. Overall, this work demonstrates that partially deletion of Nampt facilitated HFD-induced AF through increased diastolic calcium leaks. The Nampt/NAD axis may be a potent therapeutic target for AF.

Programmed death ligand 2 (PD-L2) is the second ligand of programmed death 1 (PD-1) protein. In autoimmune myocarditis, the protective roles of PD-1 and its first ligand programmed death ligand 1 (PD-L1) have been well documented; however, the role of PD-L2 remains unknown. In this study, we report that PD-L2 deficiency exacerbates myocardial inflammation in mice with experimental autoimmune myocarditis (EAM). EAM was established in wild-type (WT) and PD-L2-deficient mice by immunization with murine cardiac myosin peptide. We found that PD-L2-deficient mice had more serious inflammatory infiltration in the heart and a significantly higher myocarditis severity score than WT mice. PD-L2-deficient dendritic cells (DCs) enhanced CD4⁺ T cell proliferation in the presence of T cell receptor and CD28 signaling. These data suggest that PD-L2 on DCs protects against autoreactive CD4⁺ T cell expansion and severe inflammation in mice with EAM.

As the number of cancer survivors increases, cardiac management in anthracycline-treated patients has become more important. We planned to conduct a prospective multicenter registry study for comprehensive echocardiographic and biomarker data collection and an evaluation of the current practice in terms of diagnosis and management of anthracycline-induced cardiotoxicity (AIC registry). To examine the feasibility of this registry study, we analyzed the 1-year follow-up data of 97 patients registered during the first year of this registry. The AIC registry was launched in July 2016. Data on echocardiographic parameters (e.g., two-and three-dimensional [(2- and 3-D) left ventricular ejection fraction (LVEF) and global longitudinal strain (GLS)) and biomarkers (e.g., troponin T and brain natriuretic peptide) were collected before anthracycline treatment, every 3 months during the first year after starting anthracycline, and every 6 months during the second year. Eighty-three patients (86%) completed a 1-year follow-up. The measurable rates of 2D LVEF, 3D LVEF, and GLS on each visit were nearly optimal (100%, 86–93%, and 84–94%, respectively). During the 1-year follow-up, 5 patients (6.0%) developed cardiotoxicity (a reduction in LVEF ≥ 10 percentage points from baseline and <55%). The AIC registry study is feasible and will be the first study to collect sizable echocardiographic and biomarker data on cardiotoxicity in Japanese patients treated with anthracycline in a real-world setting.

The authors wish to make the following corrections to this paper