Myostatin (Mstn) is predominantly expressed in skeletal muscles and plays important roles in regulating muscle growth and development, as well as fat deposition. Mstn-knockout (Mstn(-/-)) mice exhibit increased muscle mass due to both hypertrophy and hyperplasia, and leaner body composition due to reduced fat mass. Here, we show that white adipose tissue (WAT) of Mstn(-/-) develops characteristics of brown adipose tissue (BAT) with dramatically increased expression of BAT signature genes, including Ucp1 and Pgc1α, and beige adipocyte markers Tmem26 and CD137. Strikingly, the observed browning phenotype is non-cell autonomous and is instead driven by the newly defined myokine irisin (Fndc5) secreted from Mstn(-/-) skeletal muscle. Within the muscle, Mstn(-/-) leads to increased expression of AMPK and its phosphorylation, which subsequently activates PGC1α and Fndc5. Together, our study defines a paradigm of muscle-fat crosstalk mediated by Fndc5, which is up-regulated and secreted from muscle to induce beige cell markers and the browning of WAT in Mstn(-/-) mice. These results suggest that targeting muscle Mstn and its downstream signaling represents a therapeutic approach to treat obesity and type 2 diabetes.

We measured changes in basal release of nitric oxide and its effect on polymorphonuclear leukocyte (PMN) adherence to endothelial cells (ECs) in a feline model of myocardial ischemia (90 minutes) and reperfusion. Basal release of nitric oxide from the left anterior descending coronary artery (LAD) after myocardial ischemia/reperfusion and from the control left circumflex coronary artery (LCX) was assessed by NG-nitro L-arginine methyl ester (L-NAME) -induced vasocontraction. L-NAME induced a significant EC-dependent vasocontraction in control LCX rings (0.28±0.04 g), which was fully reversed by L-arginine but not D-arginine. L-NAME-induced vasocontraction of LAD rings was not significantly changed after 90 minutes of myocardial ischemia without reperfusion. However, 10 minutes of reperfusion reduced the L-NAME-induced vasocontraction to 0.13±0.04 g (p<0.05), and this was restored by addition of 3 mM L-arginine but not D-arginine. Longer periods of reperfusion progressively decreased L-NAME-induced vasocontraction. After 270 minutes of reperfusion, L-NAME-induced vasocontraction was virtually abolished. Myocardial ischemia without reperfusion did not increase PMN adherence to ECs. However, PMN adherence to LAD ECs was significantly increased after 20 minutes of reperfusion (39±6 to 105±9 PMNs/mm2, p<0.01), and incubation of LAD segments with L-arginine significantly attenuated this increase in PMN adherence. After 270 minutes of reperfusion, PMN adherence to LAD ECs was further increased to 224+ 10 PMNs/mm2 (p<0.001). This increase in PMN adherence was almost completely blocked by MAb R15.7, a monoclonal antibody against CD18 of PMNs, and was significantly attenuated by MAb RR1/1, a monoclonal antibody against intercellular adhesion molecule-1 of ECs (p<0.01). These results indicate that decreased basal release of endothelium-derived relaxing factor after myocardial ischemia/reperfusion precedes enhanced PMN adherence to the coronary endothelium, which may lead to PMN-induced myocardial injury. (Circulation Research 1993;72:403-412 release from coronary vascular endothelium is significantly impaired in myocardial ischemia followed by reperfusion.8-10 However, basal release of NO in myocardial ischemia and reperfusion has not been studied in this setting.It is now well recognized that polymorphonuclear leukocytes (PMNs) play an important role in myocardial injury associated with ischemia and reperfusion."1 Accumulating evidence suggests that PMNs also contribute to endothelial dysfunction after reperfusion of the coronary vasculature.12 Recently, NO has been shown to be an endogenous inhibitor of leukocyte chemotaxis,"3 adherence,6 and activation.'4 Since normal endothelial cells release NO basally and this NO may prevent PMNs from adhering to endothelial cells, it is conceivable that reduced basal NO release after myocardial reperfusion may promote or allow PMN adherence to endothelial cells, leading to neutrophil-induced reperfusion injury.Therefore, the purposes of this study were 1) to determine the time cours...

The cardioprotective effects of an mAb to P-selectin designated mAb PB1.3 was examined in a feline model of myocardial ischemia (MI) and reperfusion. PB1.3 (1 mg/kg), administered after 80 min of ischemia (i.e., 10 min before reperfusion), significantly attenuated myocardial necrosis compared to a nonblocking mAb (NBP1.6) for P-selectin (15±3 vs 35±3% of area at risk, P < 0.01). Moreover, endothelial release of endothelium derived relaxing factor, as assessed by relaxation to acetylcholine, was also significantly preserved in ischemic-reperfused coronary arteries isolated from cats treated with mAb PB1.3 compared to mAb NBP1.6 (67±6 vs 11±3, P < 0.01). This endothelial preservation was directly related to reduced endothelial adherence of PMNs in ischemic-reperfused coronary arteries. Immunohistochemical localization of P-selectin was significantly upregulated in the cytoplasm of endothelial cells that lined coronary arteries and veins after 90 min of ischemia and 20 min of reperfusion. The principal site of intracytoplasmic expression was in venous vessels. mAb PB1.3 significantly decreased (P < 0.01 ) adherence of unstimulated PMNs to thrombin and histamine stimulated endothelial cells in a concentration-dependent manner in vitro. These results demonstrate that PMN adherence to endothelium by P-selectin is an important early consequence of reperfusion injury, and a specific monoclonal antibody to P-selectin exerts significant endothelial preservation and cardioprotection in myocardial ischemia and reperfusion. (J. Clin. Invest. 1993. 91:2620-2629

These results demonstrate the ability of L-arginine to reduce necrotic injury in a cat model of myocardial ischemia plus reperfusion, and this reduction in infarct size is associated with the preservation of endothelial function and attenuation of neutrophil accumulation in ischemic cardiac tissue.

Background-Diabetes increases the morbidity/mortality of ischemic heart disease, but the underlying mechanisms are incompletely understood. Deficiency of both AMP-activated protein kinase (AMPK) and adiponectin occurs in diabetes, but whether AMPK is cardioprotective or a central mediator of adiponectin cardioprotection in vivo remains unknown. Methods and Results-Male adult mice with cardiomyocyte-specific overexpression of a mutant AMPK␣ 2 subunit (AMPK-DN) or wild-type (WT) littermates were subjected to in vivo myocardial ischemia/reperfusion (MI/R) and treated with vehicle or adiponectin. In comparison to WT, AMPK-DN mice subjected to MI/R endured greater cardiac injury (larger infarct size, more apoptosis, and poorer cardiac function) likely as a result of increased oxidative stress in these animals. Treatment of AMPK-DN mice with adiponectin failed to phosphorylate cardiac acetyl-CoA carboxylase as it did in WT mouse heart. However, a significant portion of the cardioprotection of adiponectin against MI/R injury was retained in AMPK-DN mice. Furthermore, treatment of AMPK-DN mice with adiponectin reduced MI/R-induced cardiac oxidative and nitrative stress to the same degree as that seen in WT mice.