Cardiac Fibers Research Articles

Histological and Immunohistochemical Study of the Possible Therapeutic Effect of Mesenchymal Stem Cells, Their Exosomes and Vitamin E on Experimentally Induced Cardio-Toxicity in Adult Male Albino Rats

Cardiotoxicity is an important lethal complication of several cancer therapeutic agents. Clearly, DNA damaging chemotherapy treatments may cause damage to both cancer and healthy cells to generate toxic side-effects. We aimed to demonstrate and to compare the possible therapeutic effect of bone marrow mesenchymal stem cells, their Exosomes and Vitamin E on induced cardio toxicity in adult male albino rats.This work was performed on 60 adult male albino rats subdivided into 5 groups Group I (-ve control) Group III (CP plus BM-MSCs) Group IV (CP plus Exosomes group) Group V (CP plus Vitamin E) Ten rats were used to isolate the BM-MSCs and their Exosomes. Tissue sections were prepared for light microscope examination by staining with Hematoxyline & Eosin and Masson’s Trichrome, and for immunohistochemical staining for proliferating cell nuclear antigen (PCNA).The use of bone marrow mesenchymal stem cells (BM-MSCs) after administration of Cyclophosphamide (CP) showed marked reduction in the cardiac toxic effect which appeared in improvement of CP induced pathological changes on the cardiac muscle fibers detected by light microscopic examination whilethe use of their exosomes and vit. E after administration of CP, showed moderate and mild improvement of CP induced pathological changes on the cardiac muscle fibers, respectively.Bone marrow mesenchymal stem cells, their exosomes and vit.E have beneficial effect in CP induced cardiotoxicity while statistical analysis revealed that bone marrow mesenchymal stem cells was superior to exosomes and vit. E as a potent therapeutic agent against Cyclophosphamide cardiac toxicity. We speculate that the beneficial effect cannot be explained only by antioxidant effect but also by the immunogenic and pleiotropic effects of MSCs.

Acute Myocardial Infarction Reduces Respiration in Rat Cardiac Fibers, despite Adipose Tissue Mesenchymal Stromal Cell Transplant.

Adipose-derived mesenchymal stromal cell (AD-MSC) administration improves cardiac function after acute myocardial infarction (AMI). Although the mechanisms underlying this effect remain to be elucidated, the reversal of the mitochondrial dysfunction may be associated with AMI recovery. Here, we analyzed the alterations in the respiratory capacity of cardiomyocytes in the infarcted zone (IZ) and the border zone (BZ) and evaluated if mitochondrial function improved in cardiomyocytes after AD-MSC transplantation. Female rats were subjected to AMI by permanent left anterior descending coronary (LAD) ligation and were then treated with AD-MSCs or PBS in the border zone (BZ). Cardiac fibers were analyzed 24 hours (necrotic phase) and 8 days (fibrotic phase) after AMI for mitochondrial respiration, citrate synthase (CS) activity, F0F1-ATPase activity, and transmission electron microscopy (TEM). High-resolution respirometry of permeabilized cardiac fibers showed that AMI reduced numerous mitochondrial respiration parameters in cardiac tissue, including phosphorylating and nonphosphorylating conditions, respiration coupled to ATP synthesis, and maximal respiratory capacity. CS decreased in IZ and BZ at the necrotic phase, whereas it recovered in BZ and continued to drop in IZ over time when compared to Sham. Exogenous cytochrome c doubled respiration at the necrotic phase in IZ. F0F1-ATPase activity decreased in the BZ and, to more extent, in IZ in both phases. Transmission electron microscopy showed disorganized mitochondrial cristae structure, which was more accentuated in IZ but also important in BZ. All these alterations in mitochondrial respiration were still present in the group treated with AD-MSC. In conclusion, AMI led to mitochondrial dysfunction with oxidative phosphorylation disorders, and AD-MSC improved CS temporarily but was not able to avoid alterations in mitochondria function over time.

Mechanical function of cardiac fibre bundles is partly protected by exercise in response to diet-induced obesity in rats.

Decrements in contractile function resulting from obesity are thought to be major reasons for the link between obesity and cardiovascular disease, while exercise has been shown to improve cardiac muscle contractile function. The purpose of this study was to evaluate cardiac contractile properties following obesity induction and the potential protective effect of exercise. Twelve-week-old rats (n = 30) were organized into either a chow diet or a high-fat, high-sucrose (HFHS) diet group. Following 12 weeks of obesity induction the HFHS group animals were stratified and grouped into sedentary (HFHS+Sed) and exercise (HFHS+Ex) groups for an additional 12weeks. Following 24weeks of diet intervention, with 12weeks of aerobic exercise (25m/min, 30min/day, 5days/week) for the HFHS+Ex group, skinned cardiac fibre bundle testing was used to evaluate cardiac contractile properties. Body fat and mass were significantly greater in the HFHS-fed animals compared with the chow controls (p< 0.043). Hearts from rats in the HFHS+Sed group had significantly greater mass (p< 0.03), significantly slower maximum shortening velocity (p= 0.001), and tended to have lower calcium sensitivity (p= 0.077) and a lower proportion of α-myosin heavy chain composition (p= 0.074) than the sedentary chow animals. However, 12weeks of moderate aerobic exercise partially prevented these decrements in contractile properties. Novelty Cardiac muscle from animals exposed to an obesogenic diet for 24 weeks had impaired contractile properties compared with controls. Obesity-induced impairment of contractile properties of the heart were partially prevented by a 12-week aerobic exercise regime.

TANK-binding kinase 1 alleviates myocardial ischemia/reperfusion injury through regulating apoptotic pathway

Myocardial ischemia/reperfusion (MI/R) injury, a complicated pathophysiological process, is regulated by lots of signaling pathways. Here in our present study, we identified TANK-binding kinase 1 (TBK1), an IKK-related serine/threonine kinase, as a protective regulator in MI/R injury. Our results indicated that TBK1 was decreased in MI/R injury in mice. However, after overexpressing TBK1 through an intramyocardial injection of TBK1 adenovirus, TBK1 overexpression improved cardiac function detected by echocardiography, decreased infarct size detected by Evans Blue and TTC staining, reduced cardiomyocyte apoptosis measured by TUNEL staining and alleviated disruption of mitochondria and cardiac muscle fibers detected by TEM in response to MI/R injury. Consistently, TBK1 overexpression ameliorated mitochondrial oxygen consumption rate (OCR) in neonatal rat cardiomyocytes (NRCMs) in response to hypoxia/reoxygenation (H/R) injury. Mechanistically, TBK1 overexpression upregulated Bcl-2 (an anti-apoptotic protein) but downregulated Bax (a pro-apoptotic protein) in vivo and in vitro. Collectively, our findings uncovered a pivotal function of TBK1 in MI/R injury through regulating the levels of apoptotic proteins for the first time, which might represent a promising target in treating MI/R patients in the future.

Increased cardiovascular mortality in African Americans with COVID-19

Increased cardiovascular mortality in African Americans with COVID-19

Variability in electrophysiological properties and conducting obstacles controls re-entry risk in heterogeneous ischaemic tissue.

Ischaemia, in which inadequate blood supply compromises and eventually kills regions of cardiac tissue, can cause many types of arrhythmia, some life-threatening. A significant component of this is the effects of the resulting hypoxia, and concomitant hyperklaemia and acidosis, on the electrophysiological properties of myocytes. Clinical and experimental data have also shown that regions of structural heterogeneity (fibrosis, necrosis, fibro-fatty infiltration) can act as triggers for arrhythmias under acute ischaemic conditions. Mechanistic models have successfully captured these effects in silico. However, the relative significance of these separate facets of the condition, and how sensitive arrhythmic risk is to the extents of each, is far less explored. In this work, we use partitioned Gaussian process emulation and new metrics for source-sink mismatch that rely on simulations of bifurcating cardiac fibres to interrogate a model of heterogeneous ischaemic tissue. Re-entries were most sensitive to the level of hypoxia and the fraction of non-excitable tissue. In addition, our results reveal both protective and pro-arrhythmic effects of hyperklaemia, and present the levels of hyperklaemia, hypoxia and percentage of non-excitable tissue that pose the highest arrhythmic risks. This article is part of the theme issue 'Uncertainty quantification in cardiac and cardiovascular modelling and simulation'.

Empagliflozin Protects Cardiac Mitochondrial Fatty Acid Metabolism in a Mouse Model of Diet-Induced Lipid Overload

Sodium-glucose cotransporter 2 (SGLT2) inhibitors prevent heart failure and decrease cardiovascular mortality in patients with type 2 diabetes. Heart failure is associated with detrimental changes in energy metabolism, and the preservation of cardiac mitochondrial function is crucial for the failing heart. However, to date, there are no data to support the hypothesis that treatment with a SGLT2 inhibitor might alter mitochondrial bioenergetics in diabetic failing hearts. Thus, the aim of this study was to investigate the protective effects of empagliflozin on mitochondrial fatty acid metabolism. Mitochondrial dysfunction was induced by 18weeks of high-fat diet (HFD)-induced lipid overload. Empagliflozin was administered at a dose of 10mg/kg in a chow for 18weeks. Palmitate metabolism in vivo, cardiac mitochondrial functionality and biochemical parameters were measured. In HFD-fed mice, palmitate uptake was 1.7, 2.3, and 1.9 times lower in the heart, liver, and kidneys, respectively, compared with that of the normal chow control group. Treatment with empagliflozin increased palmitate uptake and decreased the accumulation of metabolites of incomplete fatty acid oxidation in cardiac tissues, but not other tissues, compared with those of the HFD control group. Moreover, empagliflozin treatment resulted in fully restored fatty acid oxidation pathway-dependent respiration in permeabilized cardiac fibers. Treatment with empagliflozin did not affect the biochemical parameters related to hyperglycemia or hyperlipidemia. Empagliflozin treatment preserves mitochondrial fatty acid oxidation in the heart under conditions of chronic lipid overload.

Therapeutic efficacy of Schistosoma japonicum cystatin on sepsis-induced cardiomyopathy in a mouse model

BackgroundMyocardial dysfunction is one of the most common complications of multiple organ failure in septic shock and significantly increases mortality in patients with sepsis. Although many studies having confirmed that helminth-derived proteins have strong immunomodulatory functions and could treat inflammatory diseases, there is no report on the therapeutic effect of Schistosoma japonicum-produced cystatin (Sj-Cys) on sepsis-induced cardiac dysfunction.MethodsA model of sepsis-induced myocardial injury was established by cecal ligation and puncture (CLP) in mice. Upon CLP operation, each mouse was intraperitoneally treated with 10 µg of recombinant Sj-Cys (rSj-Cys). Twelve hours after CLP, the systolic and diastolic functions of the left ventricular were examined by echocardiography. The levels of myoglobin (Mb), cardiac troponin I (cTnI), N-terminal pro-Brain Natriuretic peptide (NT-proBNP) in sera, and the activity of myeloperoxidase (MPO) in cardiac tissues were examined as biomarkers for heart injury. The heart tissue was collected for checking pathological changes, macrophages and pro-inflammatory cytokine levels. To address the signaling pathway involved in the anti-inflammatory effects of rSj-Cys, myeloid differentiation factor 88 (MyD88) was determined in heart tissue of mice with sepsis and LPS-stimulated H9C2 cardiomyocytes. In addition, the therapeutic effects of rSj-Cys on LPS-induced cardiomyocyte apoptosis were also detected. The levels of M1 biomarker iNOS and M2 biomarker Arg-1 were detected in heart tissue. The pro-inflammatory cytokines TNF-α and IL-6, and regulatory cytokines IL-10 and TGF-β were measured in sera and their mRNA levels in heart tissue of rSj-Cys-treated mice.ResultsAfter rSj-Cys treatment, the sepsis-induced heart malfunction was largely improved. The inflammation and injury of heart tissue were significantly alleviated, characterized as significantly decreased infiltration of inflammatory cells in cardiac tissues and fiber swelling, reduced levels of Mb, cTnI and NT-proBNP in sera, and MPO activity in heart tissue. The therapeutic efficacy of rSj-Cys is associated with downregulated pro-inflammatory cytokines (TNF-α and IL-6) and upregulated regulatory inflammatory cytokines (IL-10 and TGF-β), possibly through inhibiting the LPS-MyD88 signal pathway.ConclusionsRSj-Cys significantly reduced sepsis-induced cardiomyopathy and could be considered as a potential therapeutic agent for the prevention and treatment of sepsis associated cardiac dysfunction.

Crossbridge Recruitment Capacity of Wild-Type and Hypertrophic Cardiomyopathy-Related Mutant Troponin-T Evaluated by X-ray Diffraction and Mechanical Study of Cardiac Skinned Fibers.

X-ray diffraction and tension measurement experiments were conducted on rat left ventricular skinned fibers with or without “troponin-T treatment,” which exchanges the endogenous troponin T/I/C complex with exogenous troponin-T. These experiments were performed to observe the structural changes in troponin-T within a fiber elicited by contractile crossbridge formation and investigate the abnormality of hypertrophic cardiomyopathy-related troponin-T mutants. The intensity of the troponin reflection at 1/38.5 nm−1 was decreased significantly by ATP addition after treatment with wild-type or mutant troponin-T, indicating that crossbridge formation affected the conformation of troponin-T. In experiments on cardiac fibers treated with the hypertrophic cardiomyopathy-related mutants E244D- and K247R-troponin-T, treatment with K247R-troponin-T did not recruit contracting actomyosin to a greater extent than wild-type-troponin-T, although a similar drop in the intensity of the troponin reflection occurred. Therefore, the conformational change in K247R-troponin-T was suggested to be unable to fully recruit actomyosin interaction, which may be the cause of cardiomyopathy.

Fine structure of the cardiac muscle cells in the orb-web spider Nephila clavata

The fine structural characteristics of cardiac muscle cells and its myofibril organization in the orb web spider N. clavata were examined by transmission electron microscopy. Although myofibril striations are not remarkable as those of skeletal muscles, muscle fibers contain multiple myofibrils, abundant mitochondria, extensive sarcoplasmic reticulum and transverse tubules (T-tubules). Myofibrils are divided into distinct sarcomeres defined by Z-lines with average length of 2.0 μm, but the distinction between the A-band and the I-bands is not clear due to uniform striations over the length of the sarcomeres. Dyadic junction which consisted of a single T-tubule paired with a terminal cisterna of the sarcoplasmic reticulum is found mainly at the A-I level of sarcomere. Each cell is arranged to form multiple connections with neighboring cells through the intercalated discs. These specialized junctions include three types of intercellular junctions: gap junctions, fascia adherens and desmosomes for heart function. Our transmission electron microscopy (TEM) observations clearly show that spider’s cardiac muscle contraction is controlled by neurogenic rather than myogenic mechanism since each cardiac muscle fiber is innervated by a branch of motor neuron through neuromuscular junctions.

Retrospective Study of Intercalated Disk Defects Associated with Dilated Cardiomyopathy, Atrial Thrombosis, and Heart Failure in BALB/c Mice Deficient in IL4 Receptor α.

An increased incidence of dilated cardiomyopathy and atrial thrombosis was noted in a breeding colony of BALB/c mice deficient in IL4 receptor α. The condition affected mice of both sexes and of various ages, and extensive testing (microbiology, serology, histopathology) failed to ascertain the cause. Transmission electron microscopy of heart samples showed structural defects in the myocardial intercalated disks, characterized by unorganized and heavily convoluted arrangement with lower density and less prominent desmosomes and adherens junctions, widening of the intercellular space, myofibrillar lysis adjacent to intercalated disks, occasional sarcomere lysis with marked myofiber degeneration, vacuolation, accumulation of cell debris, and myelin figures. The intercalated disk contains cell adhesion molecules that form cell junctions, allowing contraction coupling of cardiomyocytes and the electrical and mechanical connection between cardiac fibers. Thus, defects at this level result in poor myocardial contraction, intracardiac blood stagnation, and consequently cardiac dilation with clinical signs of heart failure. The background strain or, potentially, the Cre-loxP-mediated recombination system used to create these mice may have contributed to the elevated incidence of cardiomyopathy and atrial thrombosis in this colony. Due to the backcrossing breeding scheme used, we cannot discount the emergence and colonywide dissemination of a spontaneous mutation that affects the intercalated disk. This report underscores the importance of carefully monitoring genetically modified mice colonies for unexpected phenotypes that may result from spontaneous or unintended mutations or enhanced strain background pathology.

Impaired substrate-mediated cardiac mitochondrial complex I respiration with unaltered regulation of fatty acid metabolism and oxidative stress status in type 2 diabetic Asian Indians.

The cardiovascular complications associated with type 2 diabetes mellitus could be attributed to changes in myocardial mitochondrial metabolism. Though it is a known fact that permeabilized cardiac muscle fibers and isolated mitochondria are metabolically compromised in the Caucasian population, studies of Asian Indian myocardial mitochondrial function are lacking. Thus, the objective of the present study is to analyze if there is altered cardiac mitochondrial substrate utilization in diabetic Asian Indians. Mitochondrial substrate utilization was measured using high-resolution respirometry in isolated mitochondria prepared from right atrial appendage tissues of diabetic and nondiabetic subjects undergoing coronary artery bypass graft surgery. Western blotting and densitometric analysis were also done to compare the levels of proteins involved in fatty acid metabolism and regulation. The mitochondrial oxygen consumption rate for fatty acid substrate was shown to be decreased in diabetic subjects compared to nondiabetic subjects along with an unvaried mitochondrial DNA copy number and uniform levels of electron transport chain complex proteins and proteins involved in fatty acid metabolism and regulation. Decreased glutamate but unchanged pyruvate-mediated state 3 respiration were also observed in diabetic subjects. The current study reports deranged cardiac mitochondrial fatty acid-mediated complex I respiration in type 2 diabetic Asian Indians with comparable levels of regulators of fatty acid oxidation to that of nondiabetic myocardium. Altered glutamate-mediated mitochondrial respiration also points toward possible alterations in mitochondrial complex I activity. When compared with previous reports on other ethnic populations, the current study suggests that Asian Indian population too have altered cardiac mitochondrial substrate utilization.

Experimental Methodologies for the Visualization of Cardiac Myofiber Orientations within Perfusion‐fixed Human Hearts

Cardiac myofiber structure and organizations play critical roles in the electrical and mechanical properties of the heart. Diffusion tensor magnetic resonance imaging (DTMRI) has been a useful imaging modality to visualize the myocardial fiber orientation with emerging clinical application. DTMRI takes advantage of the limited diffusion of water along the cardiac fiber’s longitudinal axis and provides the dominant direction of diffusion [1]. Until recently, DTMRI usage was relatively limited to clinical imaging of white matter within the brain. While there are limitations for cardiac use in vivo, due to tissue displacement and non‐rigid deformation, DTMRI is becoming a powerful diagnostic tool to assess structural heart damage. The data can also be the input into numerous computational simulations of the heart’s electrical activities. The Visible Heart®; Laboratories at the University of Minnesota, in collaboration with Lifesource, an organ procurement organization, maintains a large collection of human hearts that were donated for research. These organs are received fresh and subsequently preserved with 10% buffered formalin in the approximate end‐diastolic state for future anatomical studies. For the present studies, the hearts were rinsed of formalin and completely submerged in an agarose gel in attitudinally correct positions. The hearts are next scanned in a clinical 3T MRI scanner using a diffusion tensor sequence. The raw DTMRI DICOM files are then reconstructed using Diffusion Toolkit and visualized in TrackVis software [2]. This outputs a 3‐dimensional model that allows for visualization of the relative orientations of the myocardial fibers. Whole heart tissue models can also be generated using Materialise Mimics software from these scans. MRI scans of a heart from a 50 year old male with a history of myocardial infarction can be seen in Figure 1. The DTMRI axial images (Figure 1C) provide insights relative to the orientations of the myocardial fibers; which can then be transformed into a 3D diagram (Figure 1D) of directional eigenvectors. Future work will be done to improve resolutions by extending the number of averages acquired during such scanning. Increasing resolution will allow us to assess structural heart damage stemming from myocardial injuries: e.g. from ablations or due to myocardial infarction. Additionally, we hope to combine DTMRI with cardiac tissue models to create a 3D print that highlight regional myocardial fiber orientations. The fiber orientations from the DTMRI scans can also be incorporated into computer simulations, which may help elucidate the activation pathways of the heart. In some cases today, DTMRI can be utilized clinically to improve one’s understanding of the conduction system of the heart, which has implications in lead placement for pacing and ablation procedures. Researchers and clinicians can learn critical information relative to cardiac anatomy from DTMRI.An overview of the methods used to generate a 3D reconstruction of diffusion tensor MRI data. The resulting image is further refined to remove extraneous dataFigure 1

Respiratory Dysfunction in a novel mouse model of Duchenne Muscular Dystrophy.

Duchenne muscular dystrophy (DMD) is the most common genetic disease in adolescent males. It is caused by a loss of dystrophin protein, necessary for skeletal and cardiac muscle fiber membrane integrity, linking the sarcolemma to the extracellular matrix. Without dystrophin, muscle fibers are unable to maintain structure, with each contraction and relaxation leading to progressive muscle weakness. Weakness of the diaphragm results in respiratory failure for patients in early adulthood. For over 30 years, the mdx mouse which lacks dystrophin expression has served as a relevant model for DMD. However, the genotype of the mdx mouse does not reflect that of the patient population.Recently, a new mouse model harboring a human mutation in the dystrophin gene (DMD) was introduced into the mdx mouse (hDMD/Δ52;mdx) to better recapitulate a common genotype in patients. Since respiratory pathology is a significant cause of morbidity and mortality in DMD, this study sought to characterize the respiratory pathology in a novel DMD model – the hDMD/Δ52;mdx ‐ and further investigate the mdx mouse, using C57BL/6J mice as wildtype controls. The hypothesis driving this work is that the hDMD/Δ52;mdx mouse has greater respiratory deficiency compared to the mdx mouse. Whole body plethysmography (WBP) was used to assess respiration at baseline and during a challenge with hypercapnic and hypoxic conditions (FiCO2: 0.07, FiO2: 0.10; nitrogen balance). While exposed to normoxic air (FiO2: 0.21; nitrogen balance) the hDMD/Δ52;mdx was indistinguishable from either control at each time point. However, during the respiratory challenge the hDMD/Δ52;mdx mice had reduced frequency and minute ventilation by 6 months, which continued to decline at 12 months compared to the C57B/6J mice. Post mortem immunohistochemical studies of the neuromuscular junctions within the diaphragm showed that hDMD/Δ52;mdx and mdx mice had reduced overlap between presynaptic and postsynaptic endplates. Myofiber atrophy, fibrosis, and myofiber regeneration were also observed in the diaphragms of both mouse models. In conclusion, the hDMD/Δ52;mdx exhibits moderate respiratory pathology, and serves as a relevant animal model to study the impact of novel therapies on respiratory function.Support or Funding InformationDuke Department of Pediatrics Derfner Grant; R01 HD099486‐01; 1R21NS098131‐01

Cardiac TRPV1‐Afferent Signaling Promotes Arrhythmogenic Ventricular Remodeling after Myocardial Infarction

Chronic sympathoexcitation is implicated in ventricular arrhythmogenesis (VAs) following myocardial infarction (MI), but the critical neural pathways involved are not well understood. Cardiac adrenergic function is partly regulated by sympathetic afferent reflexes, transduced by spinal afferent fibers expressing the TRPV1 channel. The role of chronic TRPV1 afferent signaling in VAs is not known. We hypothesized that persistent TRPV1 afferent neurotransmission promotes VAs after MI. Using epicardial Resiniferatoxin (RTX) to deplete cardiac TRPV1‐expressing fibers, we dissected the role of this neural circuit in VAs after chronic MI in a porcine model. We examined the underlying mechanisms using molecular approaches, immunohistochemistry, in vitro and in vivo cardiac electrophysiology, and simultaneous cardio‐neural mapping. Epicardial RTX depleted cardiac TRPV1 afferent fibers and abolished functional responses to TRPV1 agonists. Ventricular tachycardia/fibrillation (VT/VF) was readily inducible in MI subjects by programmed electrical stimulation or cesium chloride administration, however, TRPV1 afferent depletion prevented VT/VF induced by either method. Mechanistically, TRPV1 afferent depletion neither altered cardiomyocyte action potentials and calcium transients; nor the expression of ion channels and calcium handling proteins. However, it attenuated fibrosis and mitigated electrical instability in the scar‐border zone. In vivo recordings of cardiovascular‐related stellate ganglion neurons (SGNs) revealed that MI enhances SGN function and disrupts integrated neural processing. Depleting TRPV1 afferents normalized these processes. Taken together, these data indicate that after MI, TRPV1 afferent‐induced adrenergic dysfunction promotes fibrosis, adverse cardiac remodeling, and worsens border zone electrical heterogeneity, resulting in electrically unstable ventricular myocardium. We propose targeting TRPV1‐expressing afferent to reduce VT/VF following MI.Support or Funding InformationNIH/NHLBI DP2 OD024323‐01

Cardiac Neuroanatomy and Chronotropic Modulation of the Adult Giant Danio Heart

Studies in non‐mammalian models species have contributed significantly to our understanding of the biology and the nature of innervation in the heart. The giant danio (D. malabaricus) is a teleost fish species closely related to zebrafish, that is also capable of heart regeneration. We previously described the development and maturation of the giant danio (GD) heart. However, little is known about its innervation. We hypothesized that the pattern of innervation in the GD heart is anatomically and physiologically complex, and that the heart is responsive to physiological modulation similar to that seen in cyprinid fish and mammals. Using various neuronal markers and electron microcopy, we described the presence, distribution, and nature of nerves in the GD heart. Our study shows first that fine intrinsic cardiac nerve fibers are present throughout the heart chambers. Second, nerve soma and ganglia are highly concentrated at nerve plexuses located near the sinoatrial (SA) and atrioventricular (AV) junctions. However, the volume density of axonal processes_ projecting from ganglia located over the ventral aorta_ is highest over the corpus of the bulbus arteriosus. Third, using an ex vivo GD heart preparation, we found that the GD heart responded to both adrenergic and cholinergic agonists, in a manner that mirrors mammalian and teleost hearts. Taken together, our studies show that the GD heart displays complex patterns of innervation, and conserved cardiac physiological responses, and strongly suggest that the GD could be used as a viable model for investigating cardiac biology.Support or Funding Information• NIH R15 HD084262‐01, Martha C. Rieth Faculty Fellowship, Buehler Family Foundation

Cytochrome P450‐Derived Epoxy Lipids of N‐3 PUFAs Protect the Heart From Ischemia‐Reperfusion Injury by Regulating Mitochondrial Sirtuin 3

ObjectiveCytochrome P450 epoxygenases can metabolize dietary n‐3 polyunsaturated fatty acids (n‐3 PUFAs) to epoxy lipids, which have known cardioprotective effects; however, it remains unclear how this cardioprotection occurs. Our recent data demonstrate that cytochrome P450 epoxygenase‐derived metabolites of the n‐3 PUFA docosahexaenoic acid (DHA), 19,20‐epoxydocosapentaenoic acid (19,20‐EDP), exhibit protective effects toward cardiac mitochondria. Maintaining mitochondrial quality is essential to limit myocardial damage following ischemia‐reperfusion (IR) injury. The mitochondrial deacetylase sirtuin 3 (SIRT3) plays a pivotal role in the maintenance of mitochondrial function and cardiac energy metabolism. We hypothesize that the cardioprotective mechanism(s) of 19,20‐EDP against IR injury involve(s) stimulating mitochondrial SIRT3.MethodsLangendorff and isolated working heart perfusions were performed in male and female C57BL/6 mice to assess changes in cardiac function and energy metabolism in response to IR injury. Hearts were perfused with either vehicle, 19,20‐EDP (1 μM) and/or the SIRT3 inhibitor nicotinamide (30 μM) for a 20 min baseline perfusion, following which hearts were subjected to 30 min of global no flow ischemia and 40 min of reperfusion. Glucose and palmitate oxidation rates were measured to detect alterations in cardiac energy metabolism. Mitochondrial fractions were assessed for changes in SIRT3 activity and total lysine acetylation levels. Mitochondrial SIRT3 downstream targets were assessed in human ventricular tissues obtained from individuals with ischemic heart disease (IHD) included in the Human Explanted Heart Program and compared to non‐failing control hearts (NFC) collected from unused transplant donors through the Human Organ Procurement and Exchange Program at the University of Alberta. In addition, mitochondrial respiration was assessed in cardiac fibers isolated from the human tissues.ResultsHearts perfused with 19,20‐EDP demonstrated improved post‐ischemic functional recovery, glucose oxidation and cardiac efficiency compared to control groups. The cardioprotective effects were associated with enhanced mitochondrial SIRT3 activity and reduced global protein acetylation. We observed increased acetylation of the mitochondrial antioxidant superoxide dismutase 2 in tissues obtained from IHD human myocardium suggesting decreased antioxidant capacity. Treatment with 19,20‐EDP also markedly improved mitochondrial respiration in permeabilized human fibers obtained from IHD hearts. Importantly, the cardioprotective effects of 19,20‐EDP was abolished by the SIRT3 inhibitor nicotinamide.ConclusionWe demonstrate that 19,20‐EDP‐mediated cardioprotective mechanisms against IR injury involve preservation of mitochondrial SIRT3 activity, which results in improved cardiac efficiency.

Connexin-43 reduction prevents muscle defects in a mouse model of manifesting Duchenne muscular dystrophy female carriers

Duchenne muscular dystrophy (DMD) is a severe X-linked neuromuscular disorder that affects males. However, 8% of female carriers are symptomatic and underrepresented in research due to the lack of animal models. We generated a symptomatic mouse model of DMD carriers via injection of mdx (murine DMD) embryonic stem cells (ESCs) into wild-type (WT) blastocysts (mdx/WT chimera). mdx/WT chimeras developed cardiomyopathic features and dystrophic skeletal muscle phenotypes including elevated mononuclear invasion, central nucleation, fibrosis and declined forelimb grip strength. The disease was accompanied by connexin-43 (Cx43) aberrantly enhanced in both cardiac and skeletal muscles and remodeled in the heart. Genetic reduction of Cx43-copy number in mdx/WT-Cx43(+/−) chimeras protected them from both cardiac and skeletal muscle fiber damage. In dystrophic skeletal muscle, Cx43 expression was not seen in the fibers but in adjacent F4/80+ mononuclear cells. Ethidium Bromide uptake in purified F4/80+/CD11b+ mdx macrophages revealed functional activity of Cx43, which was inhibited by administration of Gap19 peptide mimetic, a Cx43 hemichannel-specific inhibitor. Thus, we suggest that Cx43 reduction in symptomatic DMD carrier mice leads to prevention of Cx43 remodeling in the heart and prevention of aberrant Cx43 hemichannel activity in the skeletal muscle macrophages neighboring Cx43 non-expressing fibers.

Suppression of HDAC by sodium acetate rectifies cardiac metabolic disturbance in streptozotocin-nicotinamide-induced diabetic rats.

Diabetes mellitus, particularly type 2 occurs at global epidemic proportions and leads to cardiovascular diseases. Molecular studies suggest the involvement of epigenetic alterations such as histone code modification in the progression of cardiometabolic disorders. However, short chain fatty acids (SCFAs) are recognized as epigenetic modulators by their histone deacetylase inhibitory property. It is therefore hypothesized that cardiac histone deacetylase activity increases in type II diabetes and SCFA, acetate, would inhibit histone deacetylase with accompanying restoration of glucose dysregulation, cardiac lipid deposition, and tissue damage in male Wistar rats. Twenty-four male rats (240–270 g) were allotted into four groups ( n = 6 per group) namely: vehicle-treated ( p.o.), sodium acetate-treated (200 mg/kg), diabetic, and diabetic+sodium acetate-treated groups. Diabetes was induced by intraperitoneal injection of streptozotocin 65 mg/kg after a dose of nicotinamide 110 mg/kg. The results showed that diabetic rats had, glucose dysregulation, elevated serum and cardiac triglyceride, malondialdehyde, alanine aminotransferase, histone deacetylase, serum aspartate transaminase, cardiac low density lipoprotein cholesterol (LDLc), glutathione/glutathione disulphide ratio (GSH/GSSG), reduced serum and cardiac high density lipoprotein cholesterol (HDLc), and serum GSH/GSSG. Histological analysis revealed disrupted cardiac fiber in diabetic rats. However, sodium acetate attenuated glucose dysregulation and improved serum and cardiac GSH/GSSG. Sodium acetate normalized cardiac triglyceride accumulation, malondialdehyde, serum aspartate transaminase levels and prevented cardiac tissue damage in diabetic rats. These effects were associated with suppressed histone deacetylase activity. Therefore, sodium acetate attenuated but failed to normalize glucoregulation. Nevertheless, it ameliorated oxidative stress- and lipid dysmetabolism-driven cardiovascular complications in diabetic rats by the suppression of histone deacetylase activity. Impact statement This study provides evidence that STZ-NA-induced diabetes mellitus is associated with cardiac triglyceride accumulation and tissue disruption with corresponding increase in cardiac HDAC activity. However, sodium acetate suppresses cardiac HDAC activity and normalizes cardiac triglyceride and tissue integrity in diabetic rats. Therefore, the study suggests that sodium acetate is beneficial for cardioprotection in diabetes mellitus.

Exercise training changes mitochondrial function and its vulnerability to reactive oxygen species exposure differently in male and female silver European eels

The effects of sex and training on mitochondrial function and its sensitivity to in vitro reactive oxygen species (ROS) exposure were investigated in male and female silver European eels. The critical swimming speed (Ucrit) was used as an index of training intensity and of overall swimming performance. After four days of training (10 h at 70% and 14 h at 50% of their Ucrit before training), Ucrit increased significantly in trained eels for both sexes. In untrained eels, basal mitochondrial respiration (V0) measured in the absence of ADP in permeabilized cardiac fibres was significantly higher and more resistant to in vitro ROS exposure in males than in females. No difference in ATP production (VATP) or hydroxyl radical release ($$ {\mathrm{V}}_{\bullet_{\mathrm{OH}}} $$) was observed between male and female eels. In trained male eels, $$ {\mathrm{V}}_{\bullet_{\mathrm{OH}}} $$ decreased in red muscle fibres concomitantly to a trend in an increased ATP production. In trained female eels, a different trend in ATP decrease was observed. Training significantly enhanced respiratory rate Vmax and resistance to in vitro ROS exposure in cardiac fibres of male silver eels but not females. In male silver eels, but not females, training could induce an improvement of energy efficiency in red muscle and a greater resistance of mitochondrial function to ROS exposure in cardiac fibres. These beneficial effects could contribute to the highly efficient swimming performance of the male eel, which could serve to compensate their smaller size, helping them to achieve their transoceanic migration and synchronized arrival with the females at their reproduction area.