State-of-the-Art Differentiation Protocols for Patient-Derived Cardiac Pacemaker Cells.

Human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes raise the possibility of generating pluripotent stem cells from a wide range of human diseases. In the cardiology field, hiPSCs have been used to address the mechanistic bases of primary arrhythmias and in investigations of drug safety. These studies have been focused primarily on atrial and ventricular pathologies. Consequently, many hiPSC-based cardiac differentiation protocols have been developed to differentiate between atrial- or ventricular-like cardiomyocytes. Few protocols have successfully proposed ways to obtain hiPSC-derived cardiac pacemaker cells, despite the very limited availability of human tissues from the sinoatrial node. Providing an in vitro source of pacemaker-like cells would be of paramount importance in terms of furthering our understanding of the mechanisms underlying sinoatrial node pathophysiology and testing innovative clinical strategies against sinoatrial node dysfunction (i.e., biological pacemakers and genetic- and pharmacological- based therapy). Here, we summarize and detail the currently available protocols used to obtain patient-derived pacemaker-like cells.

Ryanodine receptor dysfunction causes senescence and fibrosis in Duchenne dilated cardiomyopathy.

BACKGROUND: Duchenne muscular dystrophy (DMD) is an X-linked disorder characterized by progressive muscle weakness due to the absence of functional dystrophin. DMD patients also develop dilated cardiomyopathy (DCM). We have previously shown that DMD (mdx) mice and a canine DMD model (GRMD) exhibit abnormal intracellular calcium (Ca2+) cycling related to early-stage pathological remodelling of the ryanodine receptor intracellular calcium release channel (RyR2) on the sarcoplasmic reticulum (SR) contributing to age-dependent DCM. METHODS: Here, we used hiPSC-CMs from DMD patients selected by Speckle-tracking echocardiography and canine DMD cardiac biopsies to assess key early-stage Duchenne DCM features. RESULTS: Dystrophin deficiency was associated with RyR2 remodelling and SR Ca2+ leak (RyR2 Po of 0.03 ± 0.01 for HC vs. 0.16 ± 0.01 for DMD, P < 0.01), which led to early-stage defects including senescence. We observed higher levels of senescence markers including p15 (2.03 ± 0.75 for HC vs. 13.67 ± 5.49 for DMD, P < 0.05) and p16 (1.86 ± 0.83 for HC vs. 10.71 ± 3.00 for DMD, P < 0.01) in DMD hiPSC-CMs and in the canine DMD model. The fibrosis was increased in DMD hiPSC-CMs. We observed cardiac hypocontractility in DMD hiPSC-CMs. Stabilizing RyR2 pharmacologically by S107 prevented most of these pathological features, including the rescue of the contraction amplitude (1.65 ± 0.06 µm for DMD vs. 2.26 ± 0.08 µm for DMD + S107, P < 0.01). These data were confirmed by proteomic analyses, in particular ECM remodelling and fibrosis. CONCLUSIONS: We identified key cellular damages that are established earlier than cardiac clinical pathology in DMD patients, with major perturbation of the cardiac ECC. Our results demonstrated that cardiac fibrosis and premature senescence are induced by RyR2 mediated SR Ca2+ leak in DMD cardiomyocytes. We revealed that RyR2 is an early biomarker of DMD-associated cardiac damages in DMD patients. The progressive and later DCM onset could be linked with the RyR2-mediated increased fibrosis and premature senescence, eventually causing cell death and further cardiac fibrosis in a vicious cycle leading to further hypocontractility as a major feature of DCM. The present study provides a novel understanding of the pathophysiological mechanisms of the DMD-induced DCM. By targeting RyR2 channels, it provides a potential pharmacological treatment.

Heart graft preservation technics and limits: an update and perspectives.

Heart transplantation, the gold standard treatment for end-stage heart failure, is limited by heart graft shortage, justifying expansion of the donor pool. Currently, static cold storage (SCS) of hearts from donations after brainstem death remains the standard practice, but it is usually limited to 240 min. Prolonged cold ischemia and ischemia-reperfusion injury (IRI) have been recognized as major causes of post-transplant graft failure. Continuous ex situ perfusion is a new approach for donor organ management to expand the donor pool and/or increase the utilization rate. Continuous ex situ machine perfusion (MP) can satisfy the metabolic needs of the myocardium, minimizing irreversible ischemic cell damage and cell death. Several hypothermic or normothermic MP methods have been developed and studied, particularly in the preclinical setting, but whether MP is superior to SCS remains controversial. Other approaches seem to be interesting for extending the pool of heart graft donors, such as blocking the paths of apoptosis and necrosis, extracellular vesicle therapy, or donor heart-specific gene therapy. In this systematic review, we summarize the mechanisms involved in IRI during heart transplantation and existing targeting therapies. We also critically evaluate all available data on continuous ex situ perfusion devices for adult donor hearts, highlighting its therapeutic potential and current limitations and shortcomings.

Aberrant mitochondrial dynamics contributes to diaphragmatic weakness induced by mechanical ventilation.

In critical care patients, the ""temporary inactivity of the diaphragm caused by mechanical ventilation (MV) triggers a series of events leading to diaphragmatic dysfunction and atrophy, commonly known as ventilator-induced diaphragm dysfunction (VIDD). While mitochondrial dysfunction related to oxidative stress is recognized as a crucial factor in VIDD, the exact molecular mechanism remains poorly understood. In this study, we observe that 6 h of MV triggers aberrant mitochondrial dynamics, resulting in a reduction in mitochondrial size and interaction, associated with increased expression of dynamin-related protein 1 (DRP1). This effect can be prevented by P110, a molecule that inhibits the recruitment of DRP1 to the mitochondrial membrane. Furthermore, isolated mitochondria from the diaphragms of ventilated patients exhibited increased production of reactive oxygen species (ROS). These mitochondrial changes were associated with the rapid oxidation of type 1 ryanodine receptor (RyR1) and a decrease in the stabilizing subunit calstabin 1. Subsequently, we observed that the sarcoplasmic reticulum (SR) in the ventilated diaphragms showed increased calcium leakage and reduced contractile function. Importantly, the mitochondrial fission inhibitor P110 effectively prevented all of these alterations. Taken together, the results of our study illustrate that MV leads, in the diaphragm, to both mitochondrial fragmentation and dysfunction, linked to the up-/down-regulation of 320 proteins, as assessed through global comprehensive quantitative proteomics analysis, primarily associated with mitochondrial function. These outcomes underscore the significance of developing compounds aimed at modulating the balance between mitochondrial fission and fusion as potential interventions to mitigate VIDD in human patients.

Personalized medicine in the dish to prevent calcium leak associated with short-coupled polymorphic ventricular tachycardia in patient-derived cardiomyocytes.

BACKGROUND: Polymorphic ventricular tachycardia (PMVT) is a rare genetic disease associated with structurally normal hearts which in 8% of cases can lead to sudden cardiac death, typically exercise-induced. We previously showed a link between the RyR2-H29D mutation and a clinical phenotype of short-coupled PMVT at rest using patient-specific hiPSC-derived cardiomyocytes (hiPSC-CMs). In the present study, we evaluated the effects of clinical and experimental anti-arrhythmic drugs on the intracellular Ca2+ handling, contractile and molecular properties in PMVT hiPSC-CMs in order to model a personalized medicine approach in vitro. METHODS: Previously, a blood sample from a patient carrying the RyR2-H29D mutation was collected and reprogrammed into several clones of RyR2-H29D hiPSCs, and in addition we generated an isogenic control by reverting the RyR2-H29D mutation using CRIPSR/Cas9 technology. Here, we tested 4 drugs with anti-arrhythmic properties: propranolol, verapamil, flecainide, and the Rycal S107. We performed fluorescence confocal microscopy, video-image-based analyses and biochemical analyses to investigate the impact of these drugs on the functional and molecular features of the PMVT RyR2-H29D hiPSC-CMs. RESULTS: The voltage-dependent Ca2+ channel inhibitor verapamil did not prevent the aberrant release of sarcoplasmic reticulum (SR) Ca2+ in the RyR2-H29D hiPSC-CMs, whereas it was prevented by S107, flecainide or propranolol. Cardiac tissue comprised of RyR2-H29D hiPSC-CMs exhibited aberrant contractile properties that were largely prevented by S107, flecainide and propranolol. These 3 drugs also recovered synchronous contraction in RyR2-H29D cardiac tissue, while verapamil did not. At the biochemical level, S107 was the only drug able to restore calstabin2 binding to RyR2 as observed in the isogenic control. CONCLUSIONS: By testing 4 drugs on patient-specific PMVT hiPSC-CMs, we concluded that S107 and flecainide are the most potent molecules in terms of preventing the abnormal SR Ca2+ release and contractile properties in RyR2-H29D hiPSC-CMs, whereas the effect of propranolol is partial, and verapamil appears ineffective. In contrast with the 3 other drugs, S107 was able to prevent a major post-translational modification of RyR2-H29D mutant channels, the loss of calstabin2 binding to RyR2. Using patient-specific hiPSC and CRISPR/Cas9 technologies, we showed that S107 is the most efficient in vitro candidate for treating the short-coupled PMVT at rest.

Generation of patient-specific induced pluripotent stem cell lines with Type 2 Long QT Syndrome and the KCNH2 c.379C > T pathogenic variant.

Type 2 Long QT Syndrome (LQT2) is a rare genetic heart rhythm disorder causing life-threatening arrhythmias. We derived induced pluripotent stem cell (iPSC) lines from two patients with LQT2, aged 18 and 6, both carrying a heterozygous missense mutation on the 3rd and 11th exons of KCNH2. The iPSC lines exhibited normal genomes, expressed pluripotent markers, and differentiated into trilineage embryonic layers. These patient-specific iPSC lines provide a valuable model to study the molecular and functional impact of the hERG channel gene mutation in LQT2 and to develop personalized therapeutic approaches for this syndrome.

Three-vessel coronary infusion of cardiosphere-derived cells for the treatment of heart failure with preserved ejection fraction in a pre-clinical pig model.

Heart failure with preserved ejection fraction (HFpEF) is a major public health concern. Its outcome is poor and, as of today, barely any treatments have been able to decrease its morbidity or mortality. Cardiosphere-derived cells (CDCs) are heart cell products with anti-fibrotic, anti-inflammatory and angiogenic properties. Here, we tested the efficacy of CDCs in improving left ventricular (LV) structure and function in pigs with HFpEF. Fourteen chronically instrumented pigs received continuous angiotensin II infusion for 5 weeks. LV function was investigated through hemodynamic measurements and echocardiography at baseline, after 3 weeks of angiotensin II infusion before three-vessel intra-coronary CDC (n = 6) or placebo (n = 8) administration and 2 weeks after treatment (i.e., at completion of the protocol). As expected, arterial pressure was significantly and similarly increased in both groups. This was accompanied by LV hypertrophy that was not affected by CDCs. LV systolic function remained similarly preserved during the whole protocol in both groups. In contrast, LV diastolic function was impaired (increases in Tau, LV end-diastolic pressure as well as E/A, E/E'septal and E/E'lateral ratios) but CDC treatment significantly improved all of these parameters. The beneficial effect of CDCs on LV diastolic function was not explained by reduced LV hypertrophy or increased arteriolar density; however, interstitial fibrosis was markedly reduced. Three-vessel intra-coronary administration of CDCs improves LV diastolic function and reduces LV fibrosis in this hypertensive model of HFpEF.

Heart failure-induced cognitive dysfunction is mediated by intracellular Ca2+ leak through ryanodine receptor type 2.

Cognitive dysfunction (CD) in heart failure (HF) adversely affects treatment compliance and quality of life. Although ryanodine receptor type 2 (RyR2) has been linked to cardiac muscle dysfunction, its role in CD in HF remains unclear. Here, we show in hippocampal neurons from individuals and mice with HF that the RyR2/intracellular Ca2+ release channels were subjected to post-translational modification (PTM) and were leaky. RyR2 PTM included protein kinase A phosphorylation, oxidation, nitrosylation and depletion of the stabilizing subunit calstabin2. RyR2 PTM was caused by hyper-adrenergic signaling and activation of the transforming growth factor-beta pathway. HF mice treated with a RyR2 stabilizer drug (S107), beta blocker (propranolol) or transforming growth factor-beta inhibitor (SD-208), or genetically engineered mice resistant to RyR2 Ca2+ leak (RyR2-p.Ser2808Ala), were protected against HF-induced CD. Taken together, we propose that HF is a systemic illness driven by intracellular Ca2+ leak that includes cardiogenic dementia.

Diastolic Cardiomyopathy Secondary to Experimentally Induced Exacerbated Emphysema.

Chronic obstructive pulmonary disease (COPD) is a clinical entity of increasing significance. COPD involves abnormalities of the airways and, in emphysema, parenchymal pulmonary destruction. Cardiovascular disease has emerged as a significant comorbidity to COPD. Heart failure with preserved ejection fraction (HFpEF) appears to be particularly associated with COPD-emphysema. Traditional treatments have shown limited efficacy in improving COPD-associated HFpEF. This lack of therapeutic efficacy highlights the need to identify potential mechanisms that link COPD-emphysema to HFpEF. Therefore, we aimed to study the delayed cardiac physiological impacts in a rat model with acute exacerbated emphysema. Emphysema was induced by four weekly 4 units elastase (ELA) intratracheal pulmonary instillations and exacerbation by one final additional lipolysaccharide (LPS) instillation in male Wistar rats. At 5 weeks after the ELA and LPS exposure, in vivo and ex vivo pulmonary and cardiac measurements were performed. Experimental exacerbated emphysema resulted in decreased pulmonary function and exercise intolerance. Histological analysis revealed parenchymal pulmonary destruction without signs of inflammation or cardiac fibrosis. In vivo cardiac functional analysis revealed diastolic dysfunction and tachycardia. Ex vivo analysis revealed a cellular cardiomyopathy with decreased myofilament Ca2+ sensitivity, cross-bridge cycling kinetics, and increased adrenergic PKA (protein kinase A)-dependent phosphorylation of troponin-I. Experimental exacerbated emphysema was associated with exercise intolerance that appeared to be secondary to increased ß-adrenergic tone and subsequent cardiac myofilament dysfunction. A ß1-receptor antagonist treatment (bisoprolol) started 24 hours after ELA-LPS instillation prevented in vivo and ex vivo diastolic dysfunction. These results suggest that novel treatment strategies targeted to the cardiac myofilament may be beneficial to combat exacerbated emphysema-associated HFpEF.

Enhanced Mitochondrial Calcium Uptake Suppresses Atrial Fibrillation Associated With Metabolic Syndrome.

BACKGROUND: Patients with metabolic syndrome (MetS) have an increased risk of atrial fibrillation (AF). Impaired Ca2+ homeostasis and mitochondrial dysfunction have emerged as an arrhythmogenic substrate in both patients and animal models of MetS. Whether impaired mitochondrial Ca2+ handling underlies AF associated with MetS remains poorly explored. OBJECTIVES: The aim of this study was to determine the initial mechanisms related to AF susceptibility and mitochondrial dysfunction encountered in metabolic cardiomyopathy. METHODS: A total of 161 mice and 34 patients were studied. Mitochondrial Ca2+ and mitochondrial Ca2+ uniporter complex (MCUC) were investigated in right atrial tissue of patients with (n = 18) or without (n = 16) MetS and of C57Bl/6J mice fed with a high-fat sucrose diet (HFS) for 2 (n = 42) or 12 (n = 39) weeks. Susceptibility to AF was evaluated in isolated sinoatrial tissue and in vivo in mice. RESULTS: Increased expression of the MICUs subunits of the MCUC (1.00 ± 0.33 AU vs 1.29 ± 0.23 AU; P = 0.034) was associated with impaired mitochondrial Ca2+ uptake in patients (168.7 ± 31.3 nmol/min/mg vs 127.3 ± 18.4 nmol/min/mg; P = 0.026) and HFS mice (0.10 ± 0.04 ΔF/F0 × ms-1 vs 0.06 ± 0.03 ΔF/F0 × ms-1; P = 0.0086, and 0.15 ± 0.07 ΔF/F0 × ms-1 vs 0.046 ± 0.03 ΔF/F0 × ms-1; P = 0.0076 in 2- and 12-week HFS mice, respectively). HFS mice elicited a 70% increased susceptibility to AF. The MCUC agonist kaempferol restored MCUC activity in vitro and abolished the occurrence of AF in HFS mice. CONCLUSIONS: Impaired MCUC activity and mitochondrial Ca2+ homeostasis from the early stage of metabolic cardiomyopathy in mice lead to AF. Given that similar defects in cardiac mitochondrial Ca2+ handling are present in MetS patients, the modulation of the MCUC activity represents an attractive antiarrhythmic strategy.

Impact of Neurons on Patient-Derived Cardiomyocytes Using Organ-On-A-Chip and iPSC Biotechnologies.

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.

LIX1-mediated changes in mitochondrial metabolism control the fate of digestive mesenchyme-derived cells.

YAP1 and TAZ are transcriptional co-activator proteins that play fundamental roles in many biological processes, from cell proliferation and cell lineage fate determination to tumorigenesis. We previously demonstrated that Limb Expression 1 (LIX1) regulates YAP1 and TAZ activity and controls digestive mesenchymal progenitor proliferation. However, LIX1 mode of action remains elusive. Here, we found that endogenous LIX1 is localized in mitochondria and is anchored to the outer mitochondrial membrane through S-palmitoylation of cysteine 84, a residue conserved in all LIX1 orthologs. LIX1 downregulation altered the mitochondrial ultrastructure, resulting in a significantly decreased respiration and attenuated production of mitochondrial reactive oxygen species (mtROS). Mechanistically, LIX1 knock-down impaired the stability of the mitochondrial proteins PHB2 and OPA1 that are found in complexes with mitochondrial-specific phospholipids and are required for cristae organization. Supplementation with unsaturated fatty acids counteracted the effects of LIX1 knock-down on mitochondrial morphology and ultrastructure and restored YAP1/TAZ signaling. Collectively, our data demonstrate that LIX1 is a key regulator of cristae organization, modulating mtROS level and subsequently regulating the signaling cascades that control fate commitment of digestive mesenchyme-derived cells.

Role of oxidation of excitation-contraction coupling machinery in age-dependent loss of muscle function in Caenorhabditis elegans.

Age-dependent loss of body wall muscle function and impaired locomotion occur within 2 weeks in Caenorhabditis elegans (C. elegans); however, the underlying mechanism has not been fully elucidated. In humans, age-dependent loss of muscle function occurs at about 80 years of age and has been linked to dysfunction of ryanodine receptor (RyR)/intracellular calcium (Ca2+) release channels on the sarcoplasmic reticulum (SR). Mammalian skeletal muscle RyR1 channels undergo age-related remodeling due to oxidative overload, leading to loss of the stabilizing subunit calstabin1 (FKBP12) from the channel macromolecular complex. This destabilizes the closed state of the channel resulting in intracellular Ca2+ leak, reduced muscle function, and impaired exercise capacity. We now show that the C. elegans RyR homolog, UNC-68, exhibits a remarkable degree of evolutionary conservation with mammalian RyR channels and similar age-dependent dysfunction. Like RyR1 in mammals, UNC-68 encodes a protein that comprises a macromolecular complex which includes the calstabin1 homolog FKB-2 and is immunoreactive with antibodies raised against the RyR1 complex. Furthermore, as in aged mammals, UNC-68 is oxidized and depleted of FKB-2 in an age-dependent manner, resulting in 'leaky' channels, depleted SR Ca2+ stores, reduced body wall muscle Ca2+ transients, and age-dependent muscle weakness. FKB-2 (ok3007)-deficient worms exhibit reduced exercise capacity. Pharmacologically induced oxidization of UNC-68 and depletion of FKB-2 from the channel independently caused reduced body wall muscle Ca2+ transients. Preventing FKB-2 depletion from the UNC-68 macromolecular complex using the Rycal drug S107 improved muscle Ca2+ transients and function. Taken together, these data suggest that UNC-68 oxidation plays a role in age-dependent loss of muscle function. Remarkably, this age-dependent loss of muscle function induced by oxidative overload, which takes ~2 years in mice and ~80 years in humans, occurs in less than 2-3 weeks in C. elegans, suggesting that reduced antioxidant capacity may contribute to the differences in lifespan among species.

Generation of catecholaminergic polymorphic ventricular tachycardia patient-specific induced pluripotent stem cell line.

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a genetic disorder characterized by ventricular tachycardia, that can cause the heart to stop beating leading to death. The prevalence is 1/10.000 and in approximately 60% of cases, the syndrome can be due to a mutation of the cardiac ryanodine receptor gene (RyR2). We derived an induced pluripotent stem cell (iPSC) line from an 11-year-old patient blood-cells, carrying a heterozygous missense mutation on the 8th exon of the RyR2 N-terminal part. This reprogramed CPVT line displayed normal karyotype, expressed pluripotent markers and had a capacity to differentiate in trilineage embryonic layers.

Use of speckle tracking echocardiography to detect late anthracycline-induced cardiotoxicity in childhood cancer: A prospective controlled cross-sectional study.

BACKGROUND: This study aimed to detect late sub-clinical patterns of cardiac dysfunction using speckle tracking echocardiography (STE) in children with cancer remission more than 12 months after the end of anthracycline treatment. METHODS: This prospective controlled study enrolled 196 children, 98 of which had been treated with anthracyclines (mean age 10.8 ± 3.6 years; 51% female) and 98 were age- and gender-matched healthy subjects in a 1:1 case-control design. Conventional echocardiographic variables were collected for left ventricle (LV) and right ventricle (RV). STE analyses were performed in the LV longitudinal, radial, and circumferential displacements and in the RV free wall longitudinal displacement. The association between LV global longitudinal strain (GLS) and the main clinical and biological parameters was evaluated. RESULTS: After a mean time interval of 5.1 ± 3.2 years since the end of chemotherapy (mean cumulative anthracycline dose of 192 ± 96 mg/m2), conventional echocardiographic measures were normal. GLS was significantly decreased in the anthracycline group (-19.1% vs. -21.5%, P < 0.0001), with a higher proportion of children with abnormal values (Z-score < -2 in 18.6% vs. 1.0%, P < 0.0001). No association was found between GLS and clinical or biological parameters. Circumferential strain was significantly worse in the anthracycline group (-16.8% vs. -19.4%, P < 0.0001), and radial strain significantly better (+51.4% vs. +35.9%, P < 0.0001). RV conventional echocardiography and STE parameters were normal and not different between anthracycline and control groups. CONCLUSIONS: The existence of a modified LV strain despite normal LV function in children treated with anthracyclines represents an important perspective for cardiomyopathy surveillance in childhood cancer survivors. Clinical Trial Registration -ClinicalTrials.gov Identifier: NCT02893787.

IP3 receptor orchestrates maladaptive vascular responses in heart failure.

Patients with heart failure (HF) have augmented vascular tone, which increases cardiac workload, impairing ventricular output and promoting further myocardial dysfunction. The molecular mechanisms underlying the maladaptive vascular responses observed in HF are not fully understood. Vascular smooth muscle cells (VSMCs) control vasoconstriction via a Ca2+-dependent process, in which the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) on the sarcoplasmic reticulum (SR) plays a major role. To dissect the mechanistic contribution of intracellular Ca2+ release to the increased vascular tone observed in HF, we analyzed the remodeling of IP3R1 in aortic tissues from patients with HF and from controls. VSMC IP3R1 channels from patients with HF and HF mice were hyperphosphorylated by both serine and tyrosine kinases. VSMCs isolated from IP3R1VSMC-/- mice exhibited blunted Ca2+ responses to angiotensin II (ATII) and norepinephrine compared with control VSMCs. IP3R1VSMC-/- mice displayed significantly reduced responses to ATII, both in vivo and ex vivo. HF IP3R1VSMC-/- mice developed significantly less afterload compared with HF IP3R1fl/fl mice and exhibited significantly attenuated progression toward decompensated HF and reduced interstitial fibrosis. Ca2+-dependent phosphorylation of the MLC by MLCK activated VSMC contraction. MLC phosphorylation was markedly increased in VSMCs from patients with HF and HF mice but reduced in VSMCs from HF IP3R1VSMC-/- mice and HF WT mice treated with ML-7. Taken together, our data indicate that VSMC IP3R1 is a major effector of increased vascular tone, which contributes to increased cardiac afterload and decompensation in HF.

Early Myocardial Dysfunction and Benefits of Cardiac Treatment in Young X-Linked Duchenne Muscular Dystrophy Mice.

CONTEXT: Duchenne muscular dystrophy (DMD) is associated with a progressive alteration in cardiac function. OBJECTIVE: The aim of this study was to detect early cardiac dysfunction using the high sensitive two-dimensional speckle-tracking echocardiography (2D strain) in mdx mouse model and to investigate the potential preventive effects of the S107 ryanodine receptor (RyR2) stabilizer on early onset of DMD-related cardiomyopathy. METHODS AND RESULTS: Conventional echocardiography and global and segmental left ventricle (LV) 2D strains were assessed in male mdx mice and control C57/BL10 mice from 2 to 12 months of age. Up to 12 months of age, mdx mice showed preserved myocardial function as assessed by conventional echocardiography. However, global longitudinal, radial, and circumferential LV 2D strains significantly declined in mdx mice compared to controls from the 9 months of age. Segmental 2D strain analysis found a predominant alteration in posterior, inferior, and lateral LV segments, with a more marked impairment with aging. Then, mdx mice were treated with S107 in the drinking water at a dose of 250 mg/L using two different protocols: earlier therapy from 2 to 6 months of age and later therapy from 6 to 9 months of age. The treatment with S107 was efficient only when administered earlier in very young animals (from 2 to 6 months of age) and prevented the segmental alterations seen in non-treated mdx mice. CONCLUSIONS: This is the first animal study to evaluate the therapeutic effect of a drug targeting early onset of DMD-related cardiomyopathy, using 2D strain echocardiography. Speckle-tracking analyses revealed early alterations of LV posterior segments that could be prevented by 4 months of RyR2 stabilization.