Yoshihiro Masaki

Angiotensin II can directly induce mitochondrial dysfunction, decrease oxidative fibre number and induce atrophy in mouse hindlimb skeletal muscle

What is the central question of this study? Does angiotensin II directly induce skeletal muscle abnormalities? What is the main finding and its importance? Angiotensin II induces skeletal muscle abnormalities and reduced exercise capacity. Mitochondrial dysfunction and a decreased number of oxidative fibres are manifest early, while muscle atrophy is seen later. Thus, angiotensin II may play an important role in the skeletal muscle abnormalities observed in a wide variety of diseases.

Angiotensin II receptor blocker improves the lowered exercise capacity and impaired mitochondrial function of the skeletal muscle in type 2 diabetic mice.

NAD(P)H oxidase-induced oxidative stress is at least in part involved with lowered exercise capacity and impaired mitochondrial function in high-fat diet (HFD)-induced diabetic mice. NAD(P)H oxidase can be activated by activation of the renin-angiotensin system. We investigated whether ANG II receptor blocker can improve exercise capacity in diabetic mice. C57BL/6J mice were fed a normal diet (ND) or HFD, and each group of mice was divided into two groups: treatment with or without olmesartan (OLM; 3 mg·kg(-1)·day(-1) in the drinking water). The following groups of mice were studied: ND, ND+OLM, HFD, and HFD+OLM (n = 10 for each group). After 8 wk, HFD significantly increased body weight, plasma glucose, and insulin compared with ND, and OLM did not affect these parameters in either group. Exercise capacity, as determined by treadmill tests, was significantly reduced in HFD, and this reduction was ameliorated in HFD+OLM. ADP-dependent mitochondrial respiration was significantly decreased, and NAD(P)H oxidase activity and superoxide production by lucigenin chemiluminescence were significantly increased in skeletal muscle from HFD, which were attenuated by OLM. There were no such effects by OLM in ND. We concluded that OLM ameliorated the decrease in exercise capacity in diabetic mice via improvement in mitochondrial function and attenuation of oxidative stress in skeletal muscle. These data may have a clinical impact on exercise capacity in the medical treatment of diabetes mellitus.

Increased plasma soluble (pro)renin receptor levels are correlated with renal dysfunction in patients with heart failure

with renal dysfunction in patients with heart failure Arata Fukushima , Shintaro Kinugawa ⁎, Tsuneaki Homma , Yoshihiro Masaki , Takaaki Furihata , Takahiro Abe , Tadashi Suga , Shingo Takada , Tomoyasu Kadoguchi , Koichi Okita , Shouji Matsushima , Hiroyuki Tsutsui a a Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan b Department of Rehabilitation Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan c Research Fellow of the Japan Society for the Promotion of Science, Japan d Graduate School of Program in Lifelong Learning Studies, Hokusho University, Ebetsu, Japan

Activation of invariant natural killer T cells by α-galactosylceramide ameliorates myocardial ischemia/reperfusion injury in mice

Invariant natural killer T (iNKT) cells orchestrate tissue inflammation via regulating various cytokine productions. However the role of iNKT cells has not been determined in myocardial ischemia/reperfusion (I/R) injury. The purpose of this study was to examine whether the activation of iNKT cells by α-galactosylceramide (α-GC), which specifically activates iNKT cells, could affect myocardial I/R injury. I/R or sham operation was performed in male C57BL/6J mice. I/R mice received the injection of either αGC (I/R+αGC, n=48) or vehicle (I/R+vehicle, n=49) 30 min before reperfusion. After 24h, infarct size/area at risk was smaller in I/R+αGC than in I/R+vehicle (37.8 ± 2.7% vs. 47.1 ± 2.5%, P<0.05), with no significant changes in area at risk. The numbers of infiltrating myeloperoxidase- and CD3-positive cells were lower in I/R+αGC. Apoptosis evaluated by TUNEL staining and caspase-3 protein was also attenuated in I/R+αGC. Myocardial gene expression of tumor necrosis factor-α and interleukin (IL)-1β in I/R+αGC was lower to 46% and 80% of that in I/R+vehicle, respectively, whereas IL-10, IL-4, and interferon (IFN)-γ were higher in I/R+αGC than I/R+vehicle by 2.0, 4.1, and 9.6 folds, respectively. The administration of anti-IL-10 receptor antibody into I/R+αGC abolished the protective effects of αGC on I/R injury (infarct size/area at risk: 53.1 ± 5.2% vs. 37.4 ± 3.5%, P<0.05). In contrast, anti-IL-4 and anti-IFN-γ antibodies did not exert such effects. In conclusion, activated iNKT cells by αGC play a protective role against myocardial I/R injury through the enhanced expression of IL-10. Therapies designed to activate iNKT cells might be beneficial to protect the heart from I/R injury.

Decreased serum brain-derived neurotrophic factor levels are correlated with exercise intolerance in patients with heart failure

a Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan b Department of Rehabilitation Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan c Research Fellow of the Japan Society for the Promotion of Science, Japan d Translational Research and Clinical Trial Center, Hokkaido University Hospital, Sapporo, Japan e Graduate School of Program in Lifelong Learning Studies, Hokusho University, Ebetsu, Japan

Combination of exercise training and diet restriction normalizes limited exercise capacity and impaired skeletal muscle function in diet-induced diabetic mice.

Exercise training (EX) and diet restriction (DR) are essential for effective management of obesity and insulin resistance in diabetes mellitus. However, whether these interventions ameliorate the limited exercise capacity and impaired skeletal muscle function in diabetes patients remains unexplored. Therefore, we investigated the effects of EX and/or DR on exercise capacity and skeletal muscle function in diet-induced diabetic mice. Male C57BL/6J mice that were fed a high-fat diet (HFD) for 8 weeks were randomly assigned for an additional 4 weeks to 4 groups: control, EX, DR, and EX+DR. A lean group fed with a normal diet was also studied. Obesity and insulin resistance induced by a HFD were significantly but partially improved by EX or DR and completely reversed by EX+DR. Although exercise capacity decreased significantly with HFD compared with normal diet, it partially improved with EX and DR and completely reversed with EX+DR. In parallel, the impaired mitochondrial function and enhanced oxidative stress in the skeletal muscle caused by the HFD were normalized only by EX+DR. Although obesity and insulin resistance were completely reversed by DR with an insulin-sensitizing drug or a long-term intervention, the exercise capacity and skeletal muscle function could not be normalized. Therefore, improvement in impaired skeletal muscle function, rather than obesity and insulin resistance, may be an important therapeutic target for normalization of the limited exercise capacity in diabetes. In conclusion, a comprehensive lifestyle therapy of exercise and diet normalizes the limited exercise capacity and impaired muscle function in diabetes mellitus.

Dipeptidyl peptidase-4 inhibitor improved exercise capacity and mitochondrial biogenesis in mice with heart failure via activation of glucagon-like peptide-1 receptor signalling

AIMS Exercise capacity is reduced in heart failure (HF) patients, due mostly to skeletal muscle abnormalities including impaired energy metabolism, mitochondrial dysfunction, fibre type transition, and atrophy. Glucagon-like peptide-1 (GLP-1) has been shown to improve exercise capacity in HF patients. We investigated the effects of the administration of a dipeptidyl peptidase (DPP)-4 inhibitor on the exercise capacity and skeletal muscle abnormalities in an HF mouse model after myocardial infarction (MI). METHODS AND RESULTS MI was created in male C57BL/6J mice by ligating the left coronary artery, and a sham operation was performed in other mice. The mice were then divided into two groups according to the treatment with or without a DPP-4 inhibitor, MK-0626 [1 mg/kg body weight (BW)/day] provided in the diet. Four weeks later, the exercise capacity evaluated by treadmill test was revealed to be limited in the MI mice, and it was ameliorated in the MI + MK-0626 group without affecting the infarct size or cardiac function. The citrate synthase activity, mitochondrial oxidative phosphorylation capacity, supercomplex formation, and their quantity were reduced in the skeletal muscle from the MI mice, and these decreases were normalized in the MI + MK-0626 group, in association with the improvement of mitochondrial biogenesis. Immunohistochemical staining also revealed that a shift toward the fast-twitch fibre type in the MI mice was also reversed by MK-0626. Favourable effects of MK-0626 were significantly inhibited by treatment of GLP-1 antagonist, Exendin-(9-39) (150 pmol/kg BW/min, subcutaneous osmotic pumps) in MI + MK-0626 mice. Similarly, exercise capacity and mitochondrial function were significantly improved by treatment of GLP-1 agonist, Exendin-4 (1 nmol/kg/BW/h, subcutaneous osmotic pumps). CONCLUSIONS A DPP-4 inhibitor may be a novel therapeutic agent against the exercise intolerance seen in HF patients by improving the mitochondrial biogenesis in their skeletal muscle.

Pro)renin receptor in skeletal muscle is involved in the development of insulin resistance associated with postinfarct heart failure in mice

We previously reported that insulin resistance was induced by the impairment of insulin signaling in the skeletal muscle from heart failure (HF) via NAD(P)H oxidase-dependent oxidative stress. (Pro)renin receptor [(P)RR] is involved in the activation of local renin-angiotensin system and subsequent oxidative stress. We thus examined whether (P)RR inhibitor, handle region peptide (HRP), could ameliorate insulin resistance in HF after myocardial infarction (MI) by improving oxidative stress and insulin signaling in the skeletal muscle. C57BL6J mice were divided into four groups: sham operated (Sham, n = 10), Sham treated with HRP (Sham+HRP, 0.1 mg·kg(-1)·day(-1), n = 10), MI operated (MI, n = 10), and MI treated with HRP (MI+HRP, 0.1 mg/kg/day, n = 10). After 4 wk, MI mice showed left ventricular dysfunction, which was not affected by HRP. (P)RR was upregulated in the skeletal muscle after MI (149% of sham, P < 0.05). The decrease in plasma glucose after insulin load was smaller in MI than in Sham (21 ± 2 vs. 44 ± 3%, P < 0.05), and was greater in MI+HRP (38 ± 2%, P < 0.05) than in MI. Insulin-stimulated serine phosphorylation of Akt and glucose transporter 4 translocation were decreased in the skeletal muscle from MI by 48 and 49% of Sham, both of which were ameliorated in MI+HRP. Superoxide production and NAD(P)H oxidase activities were increased in MI, which was inhibited in MI+HRP. HRP ameliorated insulin resistance associated with HF by improving insulin signaling via the inhibition of NAD(P)H oxidase-induced superoxide production in the skeletal muscle. The (P)RR pathway is involved in the development of insulin resistance, at least in part, via the impairment of insulin signaling in the skeletal muscle from HF.

Pioglitazone ameliorates the lowered exercise capacity and impaired mitochondrial function of the skeletal muscle in type 2 diabetic mice

We have reported that exercise capacity is reduced in high fat diet (HFD)-induced diabetic mice, and that this reduction is associated with impaired mitochondrial function in skeletal muscle (SKM). However, it remains to be clarified whether the treatment of diabetes ameliorates the reduced exercise capacity. Therefore, we examined whether an insulin-sensitizing drug, pioglitazone, could improve exercise capacity in HFD mice. C57BL/6J mice were fed a normal diet (ND) or HFD, then treated with or without pioglitazone (3 mg/kg/day) to yield the following 4 groups: ND+vehicle, ND+pioglitazone, HFD+vehicle, and HFD+pioglitazone (n=10 each). After 8 weeks, body weight, plasma glucose, and insulin in the HFD+vehicle were significantly increased compared to the ND+vehicle group. Pioglitazone normalized the insulin levels in HFD-fed mice, but did not affect the body weight or plasma glucose. Exercise capacity determined by treadmill tests was significantly reduced in the HFD+vehicle, and this reduction was almost completely ameliorated in HFD+pioglitazone mice. ADP-dependent mitochondrial respiration, complex I and III activities, and citrate synthase activity were significantly decreased in the SKM of the HFD+vehicle animals, and these decreases were also attenuated by pioglitazone. NAD(P)H oxidase activity was significantly increased in the HFD+vehicle compared with the ND+vehicle, and this increase was ameliorated in HFD+pioglitazone mice. Pioglitazone improved the exercise capacity in diabetic mice, which was due to the improvement in mitochondrial function and attenuation of oxidative stress in the SKM. Our data suggest that pioglitazone may be useful as an agent for the treatment of diabetes mellitus.

The experimental model of transition from compensated cardiac hypertrophy to failure created by transverse aortic constriction in mice

Background Transverse aortic constriction (TAC) operation is used as an experimental model of left ventricular (LV) hypertrophy and LV failure in mice. The severity of LV remodeling or failure may depend on the degree of TAC, but is variable among operated animals. Therefore, we tried to identify the optimal diameter of TAC to create this model with ease and high reproducibility. Methods and results To produce TAC in C57BL/6J mice (7–9 weeks, body weight 19–26 g, n = 109), a 7–0 nylon suture ligature was tightly tied around the transverse aorta against needles with 3 different diameters (mm); 0.40, 0.385 and 0.375. LV wall thickness, end-diastolic dimension, fractional shortening were measured by echocardiography. At 4 weeks after TAC, no mouse with the 0.400 mm gauge progressed in LV failure. The 0.385 mm pin gauge mouse kept a more survival rate compared with the 0.375 mm (59% vs 48%), representing same efficient in LV failure. With the 0.385 mm pin gauge, hearts of mice remained LV hypertrophy at 1 week after TAC, followed by LV failure at 4 weeks. Conclusion TAC with the diameter of 0.385 mm can effectively induce the transition from LV hypertrophy to failure in mice with relatively preserved survival.