We propose that prolonged CMV causes diaphragm disuse, which, in turn, leads to activation of the ALP through oxidative stress and the induction of the FOXO1 transcription factor.

Our data suggest that mitochondrial dysfunction lies at the nexus between oxidative stress and the impaired diaphragmatic contractility that develops during MV. Energy substrate oversupply relative to demand, resulting from diaphragmatic inactivity during MV, could play an important role in this process.

Although absence of the cytoskeletal protein dystrophin leads to dilated cardiomyopathy in humans, the functional role of dystrophin in cardiac muscle remains undefined. We have addressed the hypothesis that dystrophin could help protect the heart against injury and contractile dysfunction induced by mechanical stress. In normal and dystrophin‐deficient (mdx) mice, cardiac mechanical stress was first manipulated ex vivo in a perfused working heart preparation. Despite an afterload level in the normal physiologic range, ex vivo perfused mdx hearts developed severe contractile dysfunction and nonischemic tissue damage, as is shown by excessive LDH release without a rise in coronary lactate. Injury to dystrophin‐deficient hearts was significantly correlated with cardiac work, and reducing the afterload level improved contractility and prevented injury in mdx hearts studied ex vivo. The response to mechanical stress in vivo was also assessed by using the vital dye Evans blue, which penetrates into cardiomyocytes with a disrupted sarcolemma. In the mdx group only, cardiomyocyte injury was increased markedly by acute elevations of mechanical stress induced by isoproterenol or brief aortic occlusion. Strikingly accelerated mortality and cardiac necrosis were also observed in the mdx group subjected to chronically increased cardiac mechanical stress via subtotal aortic constriction. Taken together, our results provide the first direct evidence that dystrophin serves to protect cardiomyocytes from mechanical stress and workload‐induced damage. Accordingly, reducing cardiac work in patients with dystrophin deficiency could be beneficial not only in treating established cardiomyopathy, but also in preventing the onset of cardiac disease.

Myofiber necrosis and fibrosis are hallmarks of Duchenne muscular dystrophy (DMD), leading to lethal weakness of the diaphragm. Macrophages (MPs) are required for successful muscle regeneration, but the role of inflammatory monocyte (MO)-derived MPs in either promoting or mitigating DMD is unclear. We show that DMD (mdx) mouse diaphragms exhibit greatly increased expression of CCR2 and its chemokine ligands, along with inflammatory (Ly6Chigh) MO recruitment and accumulation of CD11bhigh MO-derived MPs. Loss-of-function of CCR2 preferentially reduced this CD11bhigh MP population by impeding the release of Ly6Chigh MOs from the bone marrow but not the splenic reservoir. CCR2 deficiency also helped restore the MP polarization balance by preventing excessive skewing of MPs toward a proinflammatory phenotype. These effects were linked to amelioration of histopathological features and increased muscle strength in the diaphragm. Chronic inhibition of CCR2 signaling by mutated CCL2 secreted from implanted mesenchymal stem cells resulted in similar improvements. These data uncover a previously unrecognized role of inflammatory MOs in DMD pathogenesis and indicate that CCR2 inhibition could offer a novel strategy for DMD management.

Nitric oxide (NO), a free radical that is negatively inotropic in the heart and skeletal muscle, is produced in large amounts during sepsis by an NO synthase inducible (iNOS) by LPS and/or cytokines. The aim of this study was to examine iNOS induction in the rat diaphragm after Escherichia Coli LPS inoculation (1.6 mg/kg i.p.), and its involvement in diaphragmatic contractile dysfunction. Inducible NOS protein and activity could be detected in the diaphragm as early as 6 h after LPS inoculation. 6 and 12 h after LPS, iNOS was expressed in inflammatory cells infiltrating the perivascular spaces of the diaphragm, whereas 12 and 24 h after LPS it was expressed in skeletal muscle fibers. Inducible NOS was also expressed in the left ventricular myocardium, whereas no expression was observed in the abdominal, intercostal, and peripheral skeletal muscles. Diaphragmatic force was significantly decreased 12 and 24 h after LPS. This decrease was prevented by inhibition of iNOS induction by dexamethasone or by inhibition of iNOS activity by N G -methyl-L -arginine. We conclude that iNOS was induced in the diaphragm after E. Coli LPS inoculation in rats, being involved in the decreased muscular force. ( J. Clin. Invest. 1996. 98:1550-1559.)