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Duchenne muscular dystrophy is a genetic disorder where an X-linked mutation in the DMD gene initiates pathogenic development caused by the absence of dystrophin protein. This impacts primarily the evolution of a functional muscle tissue resulting in muscle weakness and later severe disability in young male patients leading to an early death. Patients in the final stage develop dilated cardiomyopathy leading ultimately to cardiac or respiratory failure as the cause of death. This review discusses recent advances in modeling the DMD pathology in vitro. It describes in detail the molecular abnormalities found on the cellular and organoid levels. The in vitro pathology is compared to that found in patients. Likewise, the drawbacks and limitations of current models are discussed.

Sonic hedgehog (SHH) signaling pathway is involved in embryonic tissue patterning and development. Our previous work identified, in small rodent model of ischemia reperfusion, SHH as a specific efficient tool to reduce infarct size and subsequent arrhythmias by preventing ventricular repolarization abnormalities. The goal of the present study was to provide a proof of concept of the cardioprotective effect of SHH ligand in a porcine model of acute ischemia. Methods : The antiarrhythmic effect of SHH, either by a recombinant peptide (N-SHH) or shed membrane microparticles harboring SHH ligand (MPs SHH+ ), was evaluated in a first set of pigs following a short (25 min) coronary artery occlusion (CAO) followed by 24 hours-reperfusion (CAR) (Protocol A). The infarct-limiting effect was evaluated on a second set of pigs with 40 min of coronary artery occlusion followed by 24 hours reperfusion (Protocol B). Electrocardiogram (ECG) was recorded and arrhythmia's scores were evaluated. Area at risk and myocardial infarct size were quantified. Results : In protocol A, administration of N-SHH 15 min. after the onset of coronary occlusion significantly reduced the occurrence of ventricular fibrillation compared to control group. Evaluation of arrhythmic score showed that N-SHH treatment significantly reduced the overall occurrence of arrhythmias. In protocol B, massive infarction was observed in control animals. Either N-SHH or MPs SHH+ treatment reduced significantly the infarct size with a concomitant increase of salvaged area. The reduction in infarct size was both accompanied by a significant decrease in systemic biomarkers of myocardial injury, i.e., cardiac troponin I and fatty acid-binding protein and an increase of eNOS activation. Conclusions : We show for the first time in a large mammalian model that the activation of the SHH pathway by N-SHH or MPs SHH+ offers a potent protection of the heart to ischemia-reperfusion by preventing the reperfusion arrhythmias, reducing the infarct area and the circulating levels of biomarkers for myocardial injury. These data open up potentially theranostic prospects for patients suffering from myocardial infarction to prevent the occurrence of arrhythmias and reduce myocardial tissue damage., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) are widely used to reduce plasma cholesterol concentration. However, statins are also known to induce various forms of muscular toxicity. We have previously shown that acute application of simvastatin on human skeletal muscle samples induced a cascade of cellular events originating from mitochondria and resulting in a global alteration of Ca2+ homeostasis. The present study was designed to further define the origin of the mitochondria impairment and to understand the apparent lack of deleterious effect on the heart. Using fluorescence imaging analysis and oxygraphy on human and rat skinned skeletal muscle samples, we show that the simvastatin-induced mitochondria impairment results from inhibition of the complex I of respiratory chain. Similar simvastatin-induced mitochondria impairment and alteration of Ca2+ homeostasis occur in permeabilized but not in intact ventricular rat cardiomyocytes. In intact rat skeletal muscle fibers from the flexor digitorum brevis muscle, the simvastatin-induced alteration of Ca2+ homeostasis is abolished when monocarboxylate transporter (MCT4) is inhibited. The impairment of complex I by simvastatin might be the primary step of its cellular deleterious effects leading to muscle fiber death. This mechanism is seen specifically in skeletal muscles. This specificity should be in part attributed to a preferential uptake of statins by MCT4 that is not expressed in cardiomyocytes.

The "stretch-sensitization" response is essential to the regulation of heart contractility. An increase in diastolic volume improves systolic contraction. The cellular mechanisms of this modulation, the Frank-Starling law, are still uncertain. Moreover, their alterations in heart failure remains controversial. Here, using left ventricular skinned rat myocytes, we show a nonuniform stretch-sensitization of myofilament activation across the ventricular wall. Stretch-dependent Ca2+ sensitization of myofilaments increases from sub-epicardium to sub-endocardium and is correlated with an increase in passive tension. This passive tension-dependent component of myofibrillar activation is not associated with expression of titin isoforms, changes in troponin I level, and phosphorylation status. Instead, we observe that stretch induces phosphorylation of ventricular myosin light chain 2 isoform (VLC2b) in sub-endocardium specifically. Thus, VLC2b phosphorylation could act as a stretch-dependent modulator of activation tuned within normal heart. Moreover, in postmyocardial infarcted rat, the gradient of stretch-dependent Ca2+ sensitization disappears associated with a lack of VLC2b phosphorylation in sub-endocardium. In conclusion, nonuniformity is a major characteristic of the normal adult left ventricle (LV). The heterogeneous myocardial deformation pattern might be caused not only by the morphological heterogeneity of the tissue in the LV wall, but also by the nonuniform contractile properties of the myocytes across the wall. The loss of a contractile transmural gradient after myocardial infarction should contribute to the impaired LV function.

In the heart, cardiac function is regulated by the autonomic nervous system (ANS) that extends through the myocardium and establishes junctions at the sinus node and ventricular levels. Thus, an increase or decrease in neuronal activity acutely affects myocardial function and chronically affects its structure through remodeling processes. The neuro–cardiac junction (NCJ), which is the major structure of this system, is poorly understood and only a few cell models allow us to study it. Here, we present an innovant neuro–cardiac organ-on-chip model to study this structure to better understand the mechanisms involved in the establishment of NCJ. To create such a system, we used microfluidic devices composed of two separate cell culture compartments interconnected by asymmetric microchannels. Rat PC12 cells were differentiated to recapitulate the characteristics of sympathetic neurons, and cultivated with cardiomyocytes derived from human induced pluripotent stem cells (hiPSC). We confirmed the presence of a specialized structure between the two cell types that allows neuromodulation and observed that the neuronal stimulation impacts the excitation–contraction coupling properties including the intracellular calcium handling. Finally, we also co-cultivated human neurons (hiPSC-NRs) with human cardiomyocytes (hiPSC-CMs), both obtained from the same hiPSC line. Hence, we have developed a neuro–cardiac compartmentalized in vitro model system that allows us to recapitulate the structural and functional properties of the neuro–cardiac junction and that can also be used to better understand the interaction between the heart and brain in humans, as well as to evaluate the impact of drugs on a reconstructed human neuro–cardiac system. [ABSTRACT FROM AUTHOR]

Duchenne muscular dystrophy is a genetic disorder where an X-linked mutation in the DMD gene initiates pathogenic development caused by the absence of dystrophin protein. This impacts primarily the evolution of a functional muscle tissue resulting in muscle weakness and later severe disability in young male patients leading to an early death. Patients in the final stage develop dilated cardiomyopathy leading ultimately to cardiac or respiratory failure as the cause of death. This review discusses recent advances in modeling the DMD pathology in vitro. It describes in detail the molecular abnormalities found on the cellular and organoid levels. The in vitro pathology is compared to that found in patients. Likewise, the drawbacks and limitations of current models are discussed. [ABSTRACT FROM AUTHOR]

Background: Recent data suggests the involvement of mitochondrial dynamics in cardiac ischemia/reperfusion (I/R) injuries. Whilst excessive mitochondrial fission has been described as detrimental, the role of fusion proteins in this context remains uncertain. Objectives: To investigate whether Opa1 (protein involved in mitochondrial inner-membrane fusion) deficiency affects I/R injuries. Methods and Results: We examined mice exhibiting Opa1delTTAG mutations (Opa1+/-), showing 70% Opa1 protein expression in the myocardium as compared to their wild-type (WT) littermates. Cardiac left-ventricular systolic function assessed by means of echocardiography was observed to be similar in 3-month-old WT and Opa1+/- mice. After subjection to I/R, infarct size was significantly greater in Opa1+/- than in WTs both in vivo (43.2±4.1% vs. 28.4±3.5%, respectively; p<0.01) and ex vivo (71.1±3.2% vs. 59.6±8.5%, respectively; p<0.05). No difference was observed in the expression of other main fission/fusion protein, oxidative phosphorylation, apoptotic markers, or mitochondrial permeability transition pore (mPTP) function. Analysis of calcium transients in isolated ventricular cardiomyocytes demonstrated a lower sarcoplasmic reticulum Ca2+ uptake, whereas cytosolic Ca2+ removal from the Na+/Ca2+ exchanger (NCX) was increased, whilst SERCA2a, phospholamban, and NCX protein expression levels were unaffected in Opa1+/- compared to WT mice. Simultaneous whole-cell patch-clamp recordings of mitochondrial Ca2+ movements and ventricular action potential (AP) showed impairment of dynamic mitochondrial Ca2+ uptake and a marked increase in the AP late repolarization phase in conjunction with greater occurrence of arrhythmia in Opa1+/- mice. Conclusion: Opa1 deficiency was associated with increased sensitivity to I/R, imbalance in dynamic mitochondrial Ca2+ uptake, and subsequent increase in NCX activity. [ABSTRACT FROM AUTHOR]

The defects identified in the mechanical activity of the hearts from type 1 diabetic animals include alteration of Ca2+ signaling via changes in critical processes that regulate intracellular Ca2+ concentration. These defects result partially from a dysfunction of cardiac ryanodine receptor calcium release channel (RyR2). The present study was designed to determine whether the properties of the Ca2+ sparks might provide insight into the role of RyR2 in the altered Ca2+ signaling in cardiomyocytes from diabetic animals when they were analyzed together with Ca2+ transients. Basal Ca2+ level as well as Ca2+-spark frequency of cardiomyoctes isolated from 5-week streptozotocin (STZ)-induced diabetic rats significantly increased with respect to aged-matched control rats. Ca2+ transients exhibited significantly reduced amplitude and prolonged time courses as well as depressed Ca2+ loading of sarcoplasmic reticulum in diabetic rats. Spatio-temporal properties of the Ca2+ sparks in cardiomyocytes isolated from diabetic rats were also significantly altered to being almost parallel to the changes of Ca2+ transients. In addition, RyR2 from diabetic rat hearts were hyperphosphorylated and protein levels of both RyR2 and FKBP12.6 depleted. These data show that STZ-induced diabetic rat hearts exhibit altered local Ca2+ signaling with increased basal Ca2+ level. [ABSTRACT FROM AUTHOR]

1 This study examined the effects of SR33805, a fantofarone derivative and reported strong Ca[SUP2+]-antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. 2 On intact cells loaded with the Ca[SUP2+]-fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased duration of cell shortening. Amplitude of the Ca[SUP2+] transient was also decreased. 3 These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC[SUB50]=2.4×10[SUP-8]M). 4 On skinned cardiac cells, the application of a low SR33805 concentration (10[SUP-8] M) induced a significant increase in maximal Ca[SUP2+]-activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 μm. 5 The application of a larger dose of SR33805 (10[SUP-6]-10[SUP05]M) induced a significant leftward shift of the tension (pCa relation that accounts for Ca[SUP2+]-sensitization of the myofilaments, particularly at 2.3 μm SL. 6 In conclsuion, despite its strong Ca[SUP2+]-antagonistic properties SR33805 increases cardiac cell contractile activity as a consequences of its [SUP2+]-sensitizing effects. These effects are attributable to both an increase in the maximal Ca[SUP2+]-activated force and a length-dependent Ca[SUP2+]-sensitization. [ABSTRACT FROM AUTHOR]

Abstract: Cardiac pathologies remain the main cause of mortality worldwide. Among them the most common cause is cardiac ischemia. The rapid reperfusion after coronary occlusion has considerably improved the cardiac outcome, however reperfusion per se has deleterious effect also called reperfusion injuries. Cytosolic calcium overload is now well admitted as an essential pathophysiological mechanism involved in reperfusion injuries although the source and origin of calcium remain to be determined. Recent works have pointed out the potential defect of sarcoplasmic reticulum calcium release channels (ryanodine receptor, RyR) as a primary cause of calcium overload during ischemia-reperfusion. This finding opens new pharmacological perspectives in limiting reperfusion injuries since allosteric modulators able to restore and prevents RyR dysfunction have been developed during the last decade. [Copyright &y& Elsevier]