Increased constitutive nitric oxide production by whole body periodic acceleration ameliorates alterations in cardiomyocytes associated with utrophin/dystrophin deficiency.

Duchenne Muscular Dystrophy (DMD) cardiomyopathy is a progressive lethal disease caused by the lack of the dystrophin protein in the heart. The most widely used animal model of DMD is the dystrophin-deficient mdx mouse; however, these mice exhibit a mild dystrophic phenotype with heart failure only late in life. In contrast, mice deficient for both dystrophin and utrophin (mdx/utrn-/-, or dKO) can be used to model severe DMD cardiomyopathy where pathophysiological indicators of heart failure are detectable by 8-10weeks of age. Nitric oxide (NO) is an important signaling molecule involved in vital functions of regulating rhythm, contractility, and microcirculation of the heart, and constitutive NO production affects the function of proteins involved in excitation-contraction coupling. In this study, we explored the efficacy of enhancing NO production as a therapeutic strategy for treating DMD cardiomyopathy using the dKO mouse model of DMD. Specifically, NO production was induced via whole body periodic acceleration (pGz), a novel non-pharmacologic intervention which enhances NO synthase (NOS) activity through sinusoidal motion of the body in a headward-footward direction, introducing pulsatile shear stress to the vascular endothelium and cardiomyocyte plasma membrane. Male dKO mice were randomized at 8weeks of age to receive daily pGz (480cpm, Gz±3.0m/s2, 1h/d) for 4weeks or no treatment, and a separate age-matched group of WT animals (pGz-treated and untreated) served as non-diseased controls. At the conclusion of the protocol, cardiomyocytes from untreated dKO animals had, respectively, 4.3-fold and 3.5-fold higher diastolic resting concentration of Ca2+ ([Ca2+]d) and Na+ ([Na+]d) compared to WT, while pGz treatment significantly reduced these levels. For dKO cardiomyocytes, pGz treatment also improved the depressed contractile function, decreased oxidative stress, blunted the elevation in calpain activity, and mitigated the abnormal increase in [Ca2+]d upon mechanical stress. These improvements culminated in a significant reduction in circulating cardiac troponin T (cTnT) and an extension of the median lifespan of dKO mice from 16 to 31weeks. Treatment with L-NAME (NOS inhibitor) significantly decreased overall lifespan and abolished the cardioprotective properties elicited by pGz. Our results provide evidence that enhancement of NO synthesis by pGz can ameliorate cellular dysfunction in dKO cardiomyocytes and may represent a novel therapeutic intervention in DMD cardiomyopathy patients.

Age-dependent changes in diastolic Ca(2+) and Na(+) concentrations in dystrophic cardiomyopathy: Role of Ca(2+) entry and IP3.

Duchenne muscular dystrophy (DMD) is a lethal X-inherited disease caused by dystrophin deficiency. Besides the relatively well characterized skeletal muscle degenerative processes, DMD is also associated with a dilated cardiomyopathy that leads to progressive heart failure at the end of the second decade. The aim of the present study was to characterize the diastolic Ca(2+) concentration ([Ca(2+)]d) and diastolic Na(+) concentration ([Na(+)]d) abnormalities in cardiomyocytes isolated from 3-, 6-, 9-, and 12-month old mdx mice using ion-selective microelectrodes. In addition, the contributions of gadolinium (Gd(3+))-sensitive Ca(2+) entry and inositol triphosphate (IP3) signaling pathways in abnormal [Ca(2+)]d and [Na(+)]d were investigated. Our results showed an age-dependent increase in both [Ca(2+)]d and [Na(+)]d in dystrophic cardiomyocytes compared to those isolated from age-matched wt mice. Gd(3+) treatment significantly reduced both [Ca(2+)]d and [Na(+)]d at all ages. In addition, blockade of the IP3-pathway with either U-73122 or xestospongin C significantly reduced ion concentrations in dystrophic cardiomyocytes. Co-treatment with U-73122 and Gd(3+) normalized both [Ca(2+)]d and [Na(+)]d at all ages in dystrophic cardiomyocytes. These data showed that loss of dystrophin in mdx cardiomyocytes produced an age-dependent intracellular Ca(2+) and Na(+) overload mediated at least in part by enhanced Ca(2+) entry through Gd(3+) sensitive transient receptor potential channels (TRPC), and by IP3 receptors.

Dysregulation of Intracellular Ca2+ in Dystrophic Cortical and Hippocampal Neurons.

Duchenne muscular dystrophy (DMD) is an inherited X-linked disorder characterized by skeletal muscle wasting, cardiomyopathy, as well as cognitive impairment. Lack of dystrophin in striated muscle produces dyshomeostasis of resting intracellular Ca2+ ([Ca2+]i), Na+ ([Na+]i), and oxidative stress. Here, we test the hypothesis that similar to striated muscle cells, an absence of dystrophin in neurons from mdx mice (a mouse model for DMD) is also associated with dysfunction of [Ca2+]i homeostasis and oxidative stress. [Ca2+]i and [Na+]i in pyramidal cortical and hippocampal neurons from 3 and 6 months mdx mice were elevated compared to WT in an age-dependent manner. Removal of extracellular Ca2+ reduced [Ca2+]i in both WT and mdx neurons, but the decrease was greater and age-dependent in the latter. GsMTx-4 (a blocker of stretch-activated cation channels) significantly decreased [Ca2+]i and [Na+]i in an age-dependent manner in all mdx neurons. Blockade of ryanodine receptors (RyR) or inositol triphosphate receptors (IP3R) reduced [Ca2+]i in mdx. Mdx neurons showed elevated and age-dependent reactive oxygen species (ROS) production and an increase in neuronal damage. In addition, mdx mice showed a spatial learning deficit compared to WT. GsMTx-4 intraperitoneal injection reduced neural [Ca2+]i and improved learning deficit in mdx mice. In summary, mdx neurons show an age-dependent dysregulation in [Ca2+]i and [Na+]i which is mediated by plasmalemmal cation influx and by intracellular Ca2+ release through the RyR and IP3R. Also, mdx neurons have elevated ROS production and more extensive cell damage. Finally, a reduction of [Ca2+]i improved cognitive function in mdx mice.

Whole Body Periodic Acceleration Improves Muscle Recovery after Eccentric Exercise.

INTRODUCTION: The aim of this study was to determine whether whole body periodic acceleration (pGz) could improve muscle recovery after unaccustomed eccentric exercise (EE). METHODS: Downhill treadmill running was used to elicit EE-induced muscle damage in mice, and pGz treatment (480 cycles per minute, 1 h·d) was applied daily for 10 d after the initial EE bout (day 0). Every 2 d during the pGz treatment course starting at day 0, we 1) assessed intracellular Ca and Na concentrations and membrane potential (as indicators of intracellular ion dysfunction) in vivo in gastrocnemius muscle from anesthetized animals and 2) quantified creatine kinase (CK), tumor necrosis factor α (TNF-α), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), and interleukin-10 (IL-10) concentrations in plasma or muscle lysates (as indicators of muscle damage and inflammation). RESULTS: EE significantly increased intracellular Ca and Na, CK, TNF-α, MCP-1, IL-6, and IL-10, all of which peaked on day 2 with the exception of IL-10 and declined slowly over 10 d of recovery. pGz treatment after the EE bout mitigated ion dyshomeostasis and expedited recuperation to control values after 6 d of treatment. pGz treatment also accelerated the normalization of CK, TNF-α, MCP-1, and IL-6 while further increasing IL-10 concentrations. The nitric oxide synthase inhibitor L-N-nitroarginine methyl ester, administered in drinking water before and maintained throughout the treatment course, was sufficient to abrogate the salutary effects of pGz after EE. CONCLUSIONS: The present study demonstrates whole body periodic acceleration as an effective therapeutic strategy to accelerate muscle recovery after EE-induced skeletal muscle injury, as indicated by a faster normalization of all the studied parameters.