Shintaro Kinugawa

Background: Skeletal muscle atrophy occurs in various situations, such as denervation, fasting and ageing. Disruption of the balance between protein synthesis and degradation plays an important role in muscle atrophy, and impaired Akt phosphorylation is considered to be crucial in this process. The attachment of an O‐linked N‐acetylglucosamine motif (O‐GlcNAcylation), which is a post‐translational modification mediated by the hexosamine biosynthetic pathway, an alternative pathway of glycolysis, is involved in the regulation of protein function. Akt O‐GlcNAcylation interacts with Akt phosphorylation, thereby regulating its function. The purpose of this study was to clarify the role of O‐GlcNAcylation in skeletal muscle atrophy and to identify a therapeutic target for its prevention. Methods: Denervation was induced by cutting the sciatic nerve on the right leg of male C57BL/6J mice. A sham operation was performed on the left leg. Three days after the operation, the mice were divided into two groups: One group was treated with the O‐GlcNAcase inhibitor thiamet G (1 mg/kg body weight/day), and the other group was treated with vehicle. Seven days after the operation, the gastrocnemius muscle was collected and analysed. The effect of adeno‐associated virus serotype 1–mediated suppression of O‐GlcNAcase on skeletal muscle atrophy was also investigated. Finally, in C2C12 myotubes with adenovirus‐mediated overexpression of wild‐type Akt and O‐GlcNAcylation‐resistant mutant Akt (T479A), the interaction between the phosphorylation and O‐GlcNAcylation of Akt was investigated. Results: The weight of denervated gastrocnemius muscle was decreased by 35.6% ( p < 0.05) compared with sham. Akt phosphorylation was decreased by 27.8% ( p < 0.05), and the expression of the muscle‐specific ubiquitin ligases muscle atrophy F‐box (atrogin‐1) and muscle RING Finger‐1 (MuRF1) was increased in denervated muscle compared with sham. Akt O‐GlcNAcylation was decreased in denervated muscle compared with sham by 45.3% ( p < 0.05), together with an 8.9‐fold increase in O‐GlcNAcase expression. Thiamet G reduced gastrocnemius muscle weight loss by 22.7% ( p < 0.05) compared with vehicle, and this was achieved through an increase in Akt phosphorylation by 63.5% ( p < 0.05) and decreases in atrogin‐1 and MuRF1 expression. The inhibition of O‐GlcNAcase by gene silencing also improved skeletal muscle atrophy. The overexpression of mutant Akt (T479A) showed less O‐GlcNAcase inhibition‐induced Akt phosphorylation than the overexpression of wild‐type Akt. Conclusions: O‐GlcNAcase inhibition improved denervation‐induced skeletal muscle atrophy in mice by increasing Akt O‐GlcNAcylation. O‐GlcNAcase may hence be a therapeutic target for preventing skeletal muscle atrophy.

Background: Skeletal muscle abnormalities, including mitochondrial dysfunction, play a crucial role in decreasing exercise capacity in patients with heart failure (HF). Although enhanced reactive oxygen species (ROS) production in skeletal muscle mitochondria has been implicated in skeletal muscle abnormalities, the underlying mechanisms have not been fully elucidated to date. Superoxide dismutase 2 (SOD2), an antioxidant enzyme present in mitochondria, is modified by acetylation, which reduces its activity. The aim of this study was to clarify whether reducing SOD2 acetylation by sirtuins 3 (SIRT3) activation improves skeletal muscle mitochondrial function and exercise capacity in HF model mice.Methods: Myocardial infarction (MI) by ligation of the coronary artery or sham surgery was performed in male C57BL/6 J mice. Two weeks after surgery, these mice were treated with either the SIRT3 activator Honokiol (5 mg/kg body weight/day, i.p.) or vehicle. After 2 weeks of treatment, exercise capacity was evaluated by the treadmill test. Gastrocnemius muscle samples collected from the mice were used to measure mitochondrial function, as well as the levels of SIRT3, acetylated SOD2, and ROS production. Finally, the effect of adeno‐associated virus serotype 9 (AAV9)‐mediated overexpression of SIRT3 in the skeletal muscle on the exercise capacity of MI mice was investigated.Results: MI mice showed decreased cardiac function and skeletal muscle weight, but Honokiol did not affect these. Exercise capacity was significantly decreased in MI mice compared with sham mice by 24.9%, and Honokiol treatment improved the exercise capacity of MI mice by 40.4% (p < 0.05). The mitochondrial oxygen consumption rate was impaired in MI mice, but was improved by Honokiol treatment. SIRT3 expression was decreased by 26.8%, and SOD2 acetylation was increased by 36.9% in the skeletal muscle of MI mice compared with sham (p < 0.05), and Honokiol treatment resulted in complete recovery of these levels (p < 0.05). Consistent with SOD2 acetylation, ROS production in the skeletal muscle was increased in MI mice and was ameliorated by Honokiol (p < 0.05). SIRT3 expression was increased in MI + AAV9‐SIRT3 mice compared with MI + AAV9‐Control mice. The overexpression of SIRT3 improved exercise capacity without altering cardiac function.Conclusions: The SIRT3 activator Honokiol improved exercise capacity in MI model mice with HF, by improving mitochondrial function in skeletal muscle through the reduction of SOD2 acetylation. SIRT3 activation may thus be a novel therapeutic target for improving exercise capacity in patients with HF.

Backgrounds: Anemia is associated with poor prognosis in heart failure patients. Erythropoiesis‐stimulating agents have been used for the treatment of renal anemia, but they increase the risk of thrombotic events. Hypoxia‐inducible factor prolyl hydroxylase inhibitors (HIF‐PHIs) have emerged as a new treatment for renal anemia. HIF‐PHIs are expected to have pleiotropic effects beyond correcting anemia. Evidence regarding the effects of HIF‐PHIs in cardiorenal anemia syndrome has not been established. Methods and Results: The present study is a single‐center, retrospective analysis of patients with heart failure and renal anemia who were treated with HIF‐PHIs or oral iron supplementation at Kyushu University Hospital ( n = 39 and n = 26). Both treatments significantly raised hemoglobin levels (HIF‐PHIs 9.1 [8.6–9.6] vs. 10.3 [9.5–11.8], p < 0.001; oral iron 10.1 [9.3–11.0] vs. 11.8 [10.6–13.2], p < 0.001). Log‐transformed BNP level (logBNP) decreased in the HIF‐PHI‐treated patients but not in those treated with oral iron despite the similar improvement in hemoglobin levels (HIF‐PHIs 2.74 [2.28–2.99] vs. 2.47 [2.16–2.66], p = 0.005; oral iron 2.38 [1.89–2.66] vs. 2.37 [1.90–2.50], p = 0.711). The levels of iron metabolism–related parameters after treatment were comparable between the two groups. Δ logBNP/ Δ Hb slope was significantly steeper in the HIF‐PHI group than the oral iron supplementation group (−0.100 vs. −0.047, p = 0.039), meaning that HIF‐PHIs further reduced BNP levels than anticipated by the increase of hemoglobin with conventional treatment. Conclusion: HIF‐PHIs reduce BNP levels more than anticipated by the elevation of hemoglobin levels compared to oral iron supplementation. HIF‐PHIs may have therapeutic benefits against heart failure beyond the correction of anemia in the heart failure patients.

OBJECTIVES: Sarcopenia and malnutrition often occur simultaneously in adults with cardiovascular diseases. Our objective was to determine the associations of preoperative sarcopenia and malnutrition with major adverse cardiac and cerebral events (MACCE) after cardiac surgery METHODS: We retrospectively analysed 154 consecutive patients who underwent elective cardiac surgery between January 2015 and June 2018 at two institutions in Japan. Sarcopenia and nutritional status were preoperatively assessed by bilateral psoas muscle volume index (PMVI) using CT scans and the prognostic nutritional index (PNI), respectively. RESULTS: The median age in the total cohort was 69 years, and 43% were women. Within 30 days after surgery, 20 patients developed in-hospital MACCE and seven patients died of any cause. Low PMVI (<72.25 cm3/m2) and low PNI (<48.15) were each independent predictors of postoperative MACCE occurrence with odds ratios (95% confidence interval) of 3.58 (1.22–10.53) and 3.73 (1.25–11.09) when adjusted for age and sex, and 3.25 (1.07–9.87) and 3.27 (1.08–9.89) when adjusted for preoperative left ventricular ejection fraction, angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker, and anticoagulant. In addition, the combination of low PMVI and low PNI conferred the highest risk of in-hospital MACCE among the four groups (i.e. the low PMVI, low PNI, low PMVI + low PNI and neither low PMVI nor low PNI groups). CONCLUSIONS: Preoperative low PMVI and low PNI were respectively associated with 30-day in-hospital MACCE occurrence after cardiac surgery. Notably, coexistence of these reductions further enhanced the risk of postoperative MACCE.

Background: The triglyceride/high-density lipoprotein cholesterol (TG/HDL-C) index, calculated as TG levels divided by HDL-C levels, is suggested as a predictor of cardiovascular disease (CVD). We investigated the association between the TG/HDL-C index and initial CVD events in high-risk patients with type 2 diabetes mellitus (T2DM). Methods: We analyzed the association between the TG/HDL-C index and CVD events in T2DM patients with retinopathy and hyperlipidemia without known CVD enrolled in the EMPATHY study, which compared intensive and standard statin therapy (targeting LDL-C levels n =2013) and low (TG/HDL-C n =2652) TG/HDL-C index groups. During a median follow-up of 36.8 months, 260 CVD events occurred. The high TG/HDL-C index group had higher CVD risk compared to the low TG/HDL-C index group (HR 1.89, 95% CI 1.45–2.47, p p for interaction=0.062). Intensive statin treatment was associated with reduced CVD risk compared to standard treatment in the high TG/HDL-C index group but not in the low group. Conclusions: A TG/HDL-C index ≥2.5 was associated with increased CVD risk in T2DM patients with retinopathy and hyperlipidemia without a history of CVD. The TG/HDL-C index may be a predictor of CVD and indicate patients who could benefit from intensive statin treatment.

Background: Electrocardiographic left ventricular hypertrophy (LVH) could predict adverse renal outcome in patients with hypertension. This study aimed to investigate the association between electrocardiographic LVH and future decline of renal function in the general population. Methods: This retrospective cohort study included individuals who received population-based health checkups from 2010 to 2019 in Japan. Electrocardiographic LVH was defined according to the Minnesota code. Renal function decline was defined as a decrease of ≥25% in the estimated glomerular filtration rate from baseline to 2 . Multivariate adjusted Cox regression analysis was employed to evaluate the association between electrocardiographic LVH at baseline and renal function decline. Results: Of the 19,825 study participants, 1,263 exhibited electrocardiographic LVH at the baseline visit. The mean follow-up period was 3.4 ± 1.9 years. The incidence rates of renal function decline were 0.30 and 0.78 per 100 person-years in the non-LVH group and LVH groups, respectively. Electrocardiographic LVH was associated with the risk for renal function decline in both unadjusted analysis (hazard ratio 2.50, 95% confidence interval 1.73–3.60, P < 0.001) and adjusted analysis (hazard ratio 1.69, 95% confidence interval 1.14–2.50, P = 0.009). This association was comparable across subgroups stratified by age, sex, body mass index, diagnosed hypertension, systolic blood pressure, hemoglobin A1c, and urinary protein. Conclusions: In the general population, electrocardiographic LVH was associated with future renal function decline. To detect high-risk individuals for renal function decline, electrocardiographic LVH may be useful in the setting of health checkups in the general population. Clinical Perspectives: What is new?: This longitudinal study using a population-based annual health checkup data revealed that electrocardiographic LVH was associated with future renal function decline in the general population. The association between electrocardiographic LVH and future renal function decline was consistent regardless of individual characteristics. What are the clinical implications?: Renal dysfunction is a risk factor for cardiovascular disease and death as well as renal failure. This study shows the prognostic value of electrocardiographic LVH to predict future renal dysfunction in the general population under annual health checkups. Individuals with electrocardiographic LVH may require careful follow-up to prevent and detect the progression of renal dysfunction even if they do not have hypertension.

We evaluated a self-care intervention with a novel mobile application (app) in chronic heart failure (HF) patients. To facilitate patient-centred care in HF management, we developed a self-care support mobile app to boost HF patients’ optimal self-care. We conducted a multicentre, randomized, controlled study evaluating the feasibility of the self-care support mobile app designed for use by HF patients. The app consists of a self-monitoring assistant, education, and automated alerts of possible worsening HF. The intervention group received a tablet personal computer (PC) with the self-care support app installed, and the control group received a HF diary. All patients performed self-monitoring at home for 2 months. Their self-care behaviours were evaluated by the European Heart Failure Self-Care Behaviour Scale. We enrolled 24 outpatients with chronic HF (ages 31–78 years; 6 women, 18 men) who had a history of HF hospitalization. During the 2 month study period, the intervention group (n = 13) showed excellent adherence to the self-monitoring of each vital sign, with a median [interquartile range (IQR)] ratio of self-monitoring adherence for blood pressure, body weight, and body temperature at 100% (92–100%) and for oxygen saturation at 100% (91–100%). At 2 months, the intervention group’s self-care behaviour score was significantly improved compared with the control group (n = 11) [median (IQR): 16 (16–22) vs. 28 (20–36), P = 0.02], but the HF Knowledge Scale, the General Self-Efficacy Scale, and the Short Form-8 Health Survey scores did not differ between the groups. The novel mobile app for HF is feasible.

Background: Mitochondrial DNA (mtDNA)-induced myocardial inflammation is intimately involved in cardiac remodeling. ZBP1 (Z-DNA binding protein 1) is a pattern recognition receptor positively regulating inflammation in response to mtDNA in inflammatory cells, fibroblasts, and endothelial cells. However, the role of ZBP1 in myocardial inflammation and cardiac remodeling remains unclear. The aim of this study was to elucidate the role of ZBP1 in mtDNA-induced inflammation in cardiomyocytes and failing hearts. Methods: mtDNA was administrated into isolated cardiomyocytes. Myocardial infarctionwas conducted in wild type and ZBP1 knockout mice. Results: We here found that, unlike in macrophages, ZBP1 knockdown unexpectedly exacerbated mtDNA-induced inflammation such as increases in IL (interleukin)-1β and IL-6, accompanied by increases in RIPK3 (receptor interacting protein kinase 3), phosphorylated NF-κB (nuclear factor-κB), and NLRP3 (nucleotide-binding domain and leucine-rich-repeat family pyrin domain containing 3) in cardiomyocytes. RIPK3 knockdown canceled further increases in phosphorylated NF-κB, NLRP3, IL-1β, and IL-6 by ZBP1 knockdown in cardiomyocytes in response to mtDNA. Furthermore, NF-κB knockdown suppressed such increases in NLRP3, IL-1β, and IL-6 by ZBP1 knockdown in response to mtDNA. CpG-oligodeoxynucleotide, a Toll-like receptor 9 stimulator, increased RIPK3, IL-1β, and IL-6 and ZBP1 knockdown exacerbated them. Dloop, a component of mtDNA, but not Tert and B2m , components of nuclear DNA, was increased in cytosolic fraction from noninfarcted region of mouse hearts after myocardial infarction compared with control hearts. Consistent with this change, ZBP1, RIPK3, phosphorylated NF-κB, NLRP3, IL-1β, and IL-6 were increased in failing hearts. ZBP1 knockout mice exacerbated left ventricular dilatation and dysfunction after myocardial infarction, accompanied by further increases in RIPK3, phosphorylated NF-κB, NLRP3, IL-1β, and IL-6. In histological analysis, ZBP1 knockout increased interstitial fibrosis and myocardial apoptosis in failing hearts. Conclusions: Our study reveals unexpected protective roles of ZBP1 against cardiac remodeling as an endogenous suppressor of mtDNA-induced myocardial inflammation.

Exercise has long been known to effectively improve and enhance skeletal muscle function and performance. The favorable effects of exercise on remote organs other than skeletal muscle are well known, but the underlying mechanism has remained elusive. Recent studies have indicated that skeletal muscle not only enables body movement, but also contributes to body homeostasis and the systemic stress response via the expression and/or secretion of cytokines (so-called myokines). Not only the induction of muscle contraction itself, but also changes in intracellular calcium concentration ([Ca²⁺]i) have been suggested to be involved in myokine production and secretion. Caffeine is widely known as a Ca²⁺ ionophore, which improves skeletal muscle function and exercise performance (i.e., an “ergogenic aid”). Interestingly, some studies reported that caffeine or an increase in [Ca²⁺]i enhances the expression and/or secretion of myokines. In this review, we discuss the association between caffeine as an ergogenic aid and myokine regulation.