Nuclear Hypertrophy Reflects Increased Biosynthetic Activities in Myocytes of Human Hypertrophic Hearts

Selective dopaminergic neurotoxicity modulated by inherent cell-type specific neurobiology

Parkinson's disease (PD) is a debilitating neurodegenerative disease affecting millions of individuals worldwide. Hallmark features of PD pathology are the formation of Lewy bodies in neuromelanin-containing dopaminergic (DAergic) neurons of the substantia nigra pars compacta (SNpc), and the subsequent irreversible death of these neurons. Although genetic risk factors have been identified, around 90 % of PD cases are sporadic and likely caused by environmental exposures and gene-environment interaction. Mechanistic studies have identified a variety of chemical PD risk factors. PD neuropathology occurs throughout the brain and peripheral nervous system, but it is the loss of DAergic neurons in the SNpc that produce many of the cardinal motor symptoms. Toxicology studies have found specifically the DAergic neuron population of the SNpc exhibit heightened sensitivity to highly variable chemical insults (both in terms of chemical structure and mechanism of neurotoxic action). Thus, it has become clear that the inherent neurobiology of nigral DAergic neurons likely underlies much of this neurotoxic response to broad insults. This review focuses on inherent neurobiology of nigral DAergic neurons and how such neurobiology impacts the primary mechanism of neurotoxicity. While interactions with a variety of other cell types are important in disease pathogenesis, understanding how inherent DAergic biology contributes to selective sensitivity and primary mechanisms of neurotoxicity is critical to advancing the field. Specifically, key biological features of DAergic neurons that increase neurotoxicant susceptibility.

Myocarditis: A multi-omics approach

Myocarditis, an inflammatory condition of weakened heart muscles often triggered by a variety of causes, that can result in heart failure and sudden death. Novel ways to enhance our understanding of myocarditis pathogenesis is available through newer modalities (omics). In this review, we examine the roles of various biomolecules and associated functional pathways across genomics, transcriptomics, proteomics, and metabolomics in the pathogenesis of myocarditis. Our analysis further explores the reproducibility and variability intrinsic to omics studies, underscoring the necessity and significance of employing a multi-omics approach to gain profound insights into myocarditis pathogenesis. This integrated strategy not only enhances our understanding of the disease, but also confirms the critical importance of a holistic multi-omics approach in disease analysis.

Single-cell transcriptomics for the assessment of cardiac disease

Cardiovascular disease is the leading cause of death globally. An advanced understanding of cardiovascular disease mechanisms is required to improve therapeutic strategies and patient risk stratification. State-of-the-art, large-scale, single-cell and single-nucleus transcriptomics facilitate the exploration of the cardiac cellular landscape at an unprecedented level, beyond its descriptive features, and can further our understanding of the mechanisms of disease and guide functional studies. In this Review, we provide an overview of the technical challenges in the experimental design of single-cell and single-nucleus transcriptomics studies, as well as a discussion of the type of inferences that can be made from the data derived from these studies. Furthermore, we describe novel findings derived from transcriptomics studies for each major cardiac cell type in both health and disease, and from development to adulthood. This Review also provides a guide to interpreting the exhaustive list of newly identified cardiac cell types and states, and highlights the consensus and discordances in annotation, indicating an urgent need for standardization. We describe advanced applications such as integration of single-cell data with spatial transcriptomics to map genes and cells on tissue and define cellular microenvironments that regulate homeostasis and disease progression. Finally, we discuss current and future translational and clinical implications of novel transcriptomics approaches, and provide an outlook of how these technologies will change the way we diagnose and treat heart disease.

A comprehensive review of computational and image analysis techniques for quantitative evaluation of striated muscle tissue architecture

Unbiased evaluation of morphology is crucial to understanding development, mechanics, and pathology of striated muscle tissues. Indeed, the ability of striated muscles to contract and the strength of their contraction is dependent on their tissue-, cellular-, and cytoskeletal-level organization. Accordingly, the study of striated muscles often requires imaging and assessing aspects of their architecture at multiple different spatial scales. While an expert may be able to qualitatively appraise tissues, it is imperative to have robust, repeatable tools to quantify striated myocyte morphology and behavior that can be used to compare across different labs and experiments. There has been a recent effort to define the criteria used by experts to evaluate striated myocyte architecture. In this review, we will describe metrics that have been developed to summarize distinct aspects of striated muscle architecture in multiple different tissues, imaged with various modalities. Additionally, we will provide an overview of metrics and image processing software that needs to be developed. Importantly to any lab working on striated muscle platforms, characterization of striated myocyte morphology using the image processing pipelines discussed in this review can be used to quantitatively evaluate striated muscle tissues and contribute to a robust understanding of the development and mechanics of striated muscles.

Pitx3 deficiency promotes age-dependent alterations in striatal medium spiny neurons

Background

The classical motor symptoms of Parkinson's disease (PD) are tightly linked to the gradual loss of dopamine within the striatum. Concomitantly, medium spiny neurons (MSNs) also experience morphological changes, such as reduced dendritic complexity and spine density, which may be potentially associated with motor dysfunction as well. Thus, MSNs may serve as the emerging targets for PD therapy besides the midbrain dopaminergic neurons.

Results

To comprehensively examine pathological alterations of MSNs longitudinally, we established a TH Cre/ Pitx3 fl/fl (Pitx3cKO ) mouse model that developed canonical PD features, including a significant loss of SNc DAergic neurons and motor deficits. During aging, the targeted neurotransmitter, MSNs morphology and DNA methylation profile were significantly altered upon Pitx3 deficiency. Specifically, dopamine, GABA and glutamate decreased in the model at the early stage. While nuclear, soma and dendritic atrophy, as well as nuclear invaginations increased in the aged MSNs of Pitx3cko mice. Furthermore, more nuclear DNA damages were characterized in MSNs during aging, and Pitx3 deficiency aggravated this phenomenon, together with alterations of DNA methylation profiling associated with lipoprotein and nucleus pathway at the late stage.

Conclusion

The early perturbations of the neurotransmitters within MSNs may potentially contribute to the alterations of metabolism, morphology and epigenetics within the striatum at the late stage, which may provide new perspectives on the diagnosis and pathogenesis of PD.

Mitochondrial-cell cycle cross-talk drives endoreplication in heart disease

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Ion Channel Impairment and Myofilament Ca2+ Sensitization: Two Parallel Mechanisms Underlying Arrhythmogenesis in Hypertrophic Cardiomyopathy

Life-threatening ventricular arrhythmias are the main clinical burden in patients with hypertrophic cardiomyopathy (HCM), and frequently occur in young patients with mild structural disease. While massive hypertrophy, fibrosis and microvascular ischemia are the main mechanisms underlying sustained reentry-based ventricular arrhythmias in advanced HCM, cardiomyocyte-based functional arrhythmogenic mechanisms are likely prevalent at earlier stages of the disease. In this review, we will describe studies conducted in human surgical samples from HCM patients, transgenic animal models and human cultured cell lines derived from induced pluripotent stem cells. Current pieces of evidence concur to attribute the increased risk of ventricular arrhythmias in early HCM to different cellular mechanisms. The increase of late sodium current and L-type calcium current is an early observation in HCM, which follows post-translation channel modifications and increases the occurrence of early and delayed afterdepolarizations. Increased myofilament Ca²⁺ sensitivity, commonly observed in HCM, may promote afterdepolarizations and reentry arrhythmias with direct mechanisms. Decrease of K⁺-currents due to transcriptional regulation occurs in the advanced disease and contributes to reducing the repolarization-reserve and increasing the early afterdepolarizations (EADs). The presented evidence supports the idea that patients with early-stage HCM should be considered and managed as subjects with an acquired channelopathy rather than with a structural cardiac disease.

Hypertrophic Cardiomyopathy in Infants from the Perspective of Cardiomyocyte Maturation

Hypertrophic cardiomyopathy (HCM) in infancy is rare and many fulminant cases are fatal. Infantile HCM shows a rapid progressive clinical course and different characteristics compared with late-onset HCM presenting during the prepubertal age. There are also spontaneously resolving phenotypes of HCM that are diagnosed in neonates being treated for bronchopulmonary dysplasia with corticosteroids or in those with other problems related to maternal endocrine diseases. The pathophysiology of infantile HCM has not been well described. Therefore, this review updates the pathophysiology of infantile HCM and includes molecular studies on maturation of cardiomyocytes from a clinician's point of view.

Hypertrophic cardiomyopathy (HCM) is characterized by ventricular wall hypertrophy with diastolic dysfunction. Pediatric HCM is distinguished from the adult in many aspects. Most children with HCM do not present clinically until the adolescent period, even when they are born with genetic mutations. Some infants with early-onset HCM present with massive progressive myocardial hypertrophy in the first few months of life, which is often fatal. The mortality of pediatric HCM peaks during the infantile and adolescent periods. These periods roughly correlate with children's growth spurt. Non-sarcomeric causes of HCM are more frequent in pediatric HCM, while sarcomeric causes are more common in adults. From the perspective of cardiac development, the fetal heart has immature cardiomyocytes, which are characterized by proliferation and exit their cell cycles with a decreased regenerative property after birth. In the perinatal period, there is a dynamic change in maturation of cardiomyocytes from immature to mature cells. Infants who are treated with steroids or born to mothers with diabetes or hyperthyroidism often show phenotypes of HCM, which gradually resolve. With remarkable advancement of molecular biology, understanding on maturation of cardiomyocytes has increased. Neonates undergo abrupt environmental changes during the transitional circulation, which is affected by oxygen, metabolic and hormonal fluctuations. Derangement in physiological transition to the normal postnatal environment may influence maturation of proliferative immature cardiomyocytes during early infancy. This article reviews updates of infantile HCM and recent molecular studies related to maturation of cardiomyocytes from the clinical point of view of identifying distinct characteristics of infantile HCM.

Myocardial Changes in Diabetic and Nondiabetic Nonhuman Primates

Diabetic human patients have increased risk of heart failure compared to healthy subjects. The underlying mechanisms for this are not fully understood, and to help develop improved treatment strategies, well-characterized animal models are essential. To investigate cardiac dysfunction in diabetes, this study evaluated myocardial changes in 10 aging rhesus monkeys with and without diabetes. Based on evaluation of plasma glycosylated hemoglobin and glucose, 7 of 10 rhesus macaques had diabetes for a minimum of 11 months, while 3 of 10 were categorized as nondiabetic. A detailed histological examination of formalin-fixed left ventricular myocardial samples was followed by a semiquantitative evaluation of myocardial fibrosis and fat infiltration; digital quantifications of myocardial collagen, lipofuscin, and nuclear area fractions; and measurements of cardiomyocyte diameter. Histological myocardial evaluation revealed the presence of lipofuscin; large nuclei; interstitial, replacement, and vascular fibrosis; adipocyte infiltration; and vacuolar degeneration with atrophy of cardiomyocytes and fibrosis. However, there were no differences between groups for semiquantitative fat infiltration, fibrosis, cardiomyocyte size, collagen, or nuclear and lipofuscin area fraction. Lipofuscin area fraction correlated with plasma insulin, triglyceride, total cholesterol, and high-density lipoprotein cholesterol concentrations. In conclusion, myocardial pathological changes were found in left ventricular myocardium in aged rhesus macaques, independent of the stage of diabetes. The duration of diabetes might have been too short to cause differences between groups.

Parkinson's disease-related Leucine-rich repeat kinase 2 modulates nuclear morphology and genomic stability in striatal projection neurons during aging

BACKGROUND

Multiple missense mutations in Leucine-rich repeat kinase 2 (LRRK2) are associated with familial forms of late onset Parkinson's disease (PD), the most common age-related movement disorder. The dysfunction of dopamine transmission contributes to PD-related motor symptoms. Interestingly, LRRK2 is more abundant in the dopaminoceptive striatal spiny projection neurons (SPNs) compared to the dopamine-producing nigrostriatal dopaminergic neurons. Aging is the most important risk factor for PD and other neurodegenerative diseases. However, whether LRRK2 modulates the aging of SPNs remains to be determined.

METHODS

We conducted RNA-sequencing (RNA-seq) analyses of striatal tissues isolated from Lrrk2 knockout (Lrrk2-/-) and control (Lrrk2+/+) mice at 2 and 12 months of age. We examined SPN nuclear DNA damage and epigenetic modifications; SPN nuclear, cell body and dendritic morphology; and the locomotion and motor skill learning of Lrrk2+/+ and Lrrk2-/- mice from 2 to 24 months of age. Considering the strength of cell cultures for future mechanistic studies, we also performed preliminary studies in primary cultured SPNs derived from the Lrrk2+/+ and Lrrk2-/- mice as well as the PD-related Lrrk2 G2019S and R1441C mutant mice.

RESULTS

Lrrk2-deficiency accelerated nuclear hypertrophy and induced dendritic atrophy, soma hypertrophy and nuclear invagination in SPNs during aging. Additionally, increased nuclear DNA damage and abnormal histone methylations were also observed in aged Lrrk2-/- striatal neurons, together with alterations of molecular pathways involved in regulating neuronal excitability, genome stability and protein homeostasis. Furthermore, both the PD-related Lrrk2 G2019S mutant and LRRK2 kinase inhibitors caused nuclear hypertrophy, while the Lrrk2 R1441C mutant and γ-Aminobutyric acid type A receptor (GABA-AR) inhibitors promoted nuclear invagination in the cultured SPNs. On the other hand, inhibition of neuron excitability prevented the formation of nuclear invagination in the cultured Lrrk2-/- and R1441C SPNs.

CONCLUSIONS

Our findings support an important physiological function of LRRK2 in maintaining nuclear structure integrity and genomic stability during the normal aging process, suggesting that PD-related LRRK2 mutations may cause the deterioration of neuronal structures through accelerating the aging process.

In situ nuclear DNA methylation in dilated cardiomyopathy: an endomyocardial biopsy study

AIMS

Although distinct DNA methylation patterns have been reported, its localization and roles remain to be defined in heart failure. We investigated the cellular and subcellular localization of DNA methylation and its pathophysiological significance in human failing hearts.

METHODS AND RESULTS

Using left ventricular (LV) endomyocardial biopsy specimens from 75 patients with dilated cardiomyopathy (DCM; age: 58 ± 14 years old, %female: 32%) and 20 patients without heart failure (controls; age: 56 ± 17 years old, %female: 45%), we performed immunohistochemistry and immunoelectron microscopy for methylated DNA, 5-methylcytosine (5-mC). We next investigated possible relations of the incidence of 5-mC-positive (%5-mC⁺ ) cardiomyocytes with clinicopathological parameters. Immunopositivity for 5-mC was detected in the cardiomyocytes and other cell types. The %5-mC⁺ cardiomyocytes was significantly greater in DCM hearts than in controls (57 ± 13% in DCM vs. 25 ± 12% in controls, P < 0.0001). The localization of 5-mC immunopositivity in cardiomyocyte nuclei coincided well with that of heterochromatin, as confirmed by immunoelectron microscopy. Substantial DNA methylation was also observed in interstitial non-cardiomyocytes, but the incidences did not differ between control and DCM hearts (39 ± 7.9% in DCM vs. 41 ± 10% in controls, P = 0.4099). In DCM patients, the %5-mC⁺ cardiomyocytes showed a significant inverse correlation with LV functional parameters such as heart rate (r = 0.2391, P = 0.0388), end-diastolic pressure (r = 0.2397, P = 0.0397), and ejection fraction (r = -0.2917, P = 0.0111) and a positive correlation with LV dilatation (volume index at diastole; r = 0.2442, P = 0.0347; and volume index at systole; r = 0.3136, P = 0.0062) and LV hypertrophy (mass index; r = 0.2287, P = 0.0484)-that is, LV remodelling parameters. No significant correlations between DNA methylation and the histological parameters of the biopsies, including cardiomyocyte hypertrophy, fibrosis, and inflammatory cell infiltration, were noted.

CONCLUSIONS

The present study revealed increased nuclear DNA methylation in cardiomyocytes, but not other cell types, from DCM hearts, with predominant localization in the heterochromatin. Its significant relations with LV functional and remodelling parameters imply a pathophysiological significance of DNA methylation in heart failure.

Metabolic Alterations in Inherited Cardiomyopathies

The normal function of the heart relies on a series of complex metabolic processes orchestrating the proper generation and use of energy. In this context, mitochondria serve a crucial role as a platform for energy transduction by supplying ATP to the varying demand of cardiomyocytes, involving an intricate network of pathways regulating the metabolic flux of substrates. The failure of these processes results in structural and functional deficiencies of the cardiac muscle, including inherited cardiomyopathies. These genetic diseases are characterized by cardiac structural and functional anomalies in the absence of abnormal conditions that can explain the observed myocardial abnormality, and are frequently associated with heart failure. Since their original description, major advances have been achieved in the genetic and phenotype knowledge, highlighting the involvement of metabolic abnormalities in their pathogenesis. This review provides a brief overview of the role of mitochondria in the energy metabolism in the heart and focuses on metabolic abnormalities, mitochondrial dysfunction, and storage diseases associated with inherited cardiomyopathies.

Hypertrophic Cardiomyopathy: A Vicious Cycle Triggered by Sarcomere Mutations and Secondary Disease Hits

Significance: Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by left ventricular hypertrophy, diastolic dysfunction, and myocardial disarray. Disease onset occurs between 20 and 50 years of age, thus affecting patients in the prime of their life. HCM is caused by mutations in sarcomere proteins, the contractile building blocks of the heart. Despite increased knowledge of causal mutations, the exact path from genetic defect leading to cardiomyopathy is complex and involves additional disease hits. Recent Advances: Laboratory-based studies indicate that HCM development not only depends on the primary sarcomere impairment caused by the mutation but also on secondary disease-related alterations in the heart. Here we propose a vicious mutation-induced disease cycle, in which a mutation-induced energy depletion alters cellular metabolism with increased mitochondrial work, which triggers secondary disease modifiers that will worsen disease and ultimately lead to end-stage HCM. Critical Issues: Evidence shows excessive cellular reactive oxygen species (ROS) in HCM patients and HCM animal models. Oxidative stress markers are increased in the heart (oxidized proteins, DNA, and lipids) and serum of HCM patients. In addition, increased mitochondrial ROS production and changes in endogenous antioxidants are reported in HCM. Mutant sarcomeric protein may drive excessive levels of cardiac ROS via changes in cardiac efficiency and metabolism, mitochondrial activation and/or dysfunction, impaired protein quality control, and microvascular dysfunction. Future Directions: Interventions restoring metabolism, mitochondrial function, and improved ROS balance may be promising therapeutic approaches. We discuss the effects of current HCM pharmacological therapies and potential future therapies to prevent and reverse HCM. Antioxid. Redox Signal. 31, 318-358.

Energetic drain driving hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common form of hereditary cardiomyopathy and is mainly caused by mutations of genes encoding cardiac sarcomeric proteins. HCM is characterized by hypertrophy of the left ventricle, frequently involving the septum, that is not explained solely by loading conditions. HCM has a heterogeneous clinical profile, but diastolic dysfunction and ventricular arrhythmias represent two dominant features of the disease. Preclinical evidence indicates that the enhanced Calcium (Ca²⁺ ) sensitivity of the myofilaments plays a key role in the pathophysiology of HCM. Notably, this is not always a direct consequence of sarcomeric mutations, but can also result from secondary mutation-driven alterations. Here, we review experimental and clinical evidence indicating that increased myofilament Ca²⁺ sensitivity lies upstream of numerous cellular derangements which potentially contribute to the progression of HCM toward heart failure and sudden cardiac death.

High salt-induced hypertrophy of human vascular smooth muscle cells associated with a decrease in glycocalyx

All health organizations agree that, presently, the average daily salt (sodium chloride) consumption per person has attained almost double the recommended amount. A chronic high salt diet contributes to the increase in blood pressure and to the development of cardiovascular disease. Although our knowledge of hypertension, in general, is abundant, little is known about salt-sensitive hypertension. Here we tested the hypothesis that acute and/or chronic high salt mimicking that present in high-salt sensitive hypertensive patients may induce hypertrophy of human vascular smooth muscle cells (hVSMCs) and their nuclei that are associated with damage to the plasma membrane glycocalyx. Using quantitative 3D confocal microscopy coupled to immunofluorescence techniques, we tested the effects of acute (2-4 days) and chronic (6-16 days) treatments of hVSMCs without (145 mM) or with high (149 mM) extracellular sodium chloride. Our results showed that acute treatment with high salt significantly decreased the relative density of membrane glycocalyx without affecting the whole cell and nuclear volumes of hVSMCs. However, chronic treatments with high salts induced significant decreases in the relative density of glycocalyx accompanied by significant increases in the whole cell and nuclear volumes as well as in the protein/DNA ratio. The high salt-induced hVSMC hypertrophy was associated with a sustained increase in intracellular sodium and calcium. Our results clearly showed that, increasing salt concentration by as little as 4 mM immediately induced damage to the cell membrane glycocalyx leading to chronic Na⁺ and Ca²⁺ overloads and hVSMC hypertrophy. The latter may reduce the lumen of arteries leading to an increase in blood pressure. Future identification of the mechanisms that are implicated in a high salt-induced remodeling of hVSMCs may permit the development of new therapeutic interventions for the treatment of high salt-sensitive hypertension and the prevention of the associated cardiovascular diseases.

Early left atrial tissue features in patients with chronic mitral regurgitation and sinus rhythm: Alterations of not remodeled left atria

OBJECTIVE

Left atrial (LA) enlargement, a compensatory mechanism in chronic mitral regurgitation (MR) increasing the risk of atrial fibrillation (AF) and predictive of cardiac events, involves structural alterations. We characterized LA features in patients in sinus rhythm with severe degree of MR, similar degrees of left ventricular remodeling but divergent LA size.

METHODS

Among a consecutive series of 163 patients in stable sinus rhythm undergoing isolated mitral valve surgery for severe non-rheumatic MR, two groups were arbitrarily selected according to their LA size (antero-posterior): NRLA group (non-remodeled LA) included 8 patients with LA≤40mm, RLA group (remodeled LA) included 8 patients with LA>55mm. LA biopsies were processed for paraffin inclusion and sectioning. Fibrosis, cardiomyocytes morphology, capillaries density, cytochrome c and F-actin expression were evaluated by microscopy.

RESULTS

Histology and immunohistochemistry demonstrated alteration of moderate entity: higher amounts of endomysial fibrosis (not of collagen type III) and of hypertrophic cardiomyocytes in RLA than in NRLA. Confocal microscopy displayed focally disorganized F-actin and no nuclear fragmentation in both groups, but more intra-cytoplasm cytochrome c in RLA vs. NRLA, possibly indicative of more successful escape to apoptosis by NRLA cardiomyocytes.

CONCLUSIONS

Our study shows the presence of early cellular and interstitial alterations in LA tissue in patients with chronic MR and sinus rhythm. These features were analogous to those of patients with AF, and suggest that macroscopic remodeling LA in the settings of MR is preceded by structural changes, paving the way to further investigation on the preventive role of early mitral valve repair.

Age-Related Features of Cardiomyocyte Ploidy in Patients with Hypertrophic Obstructive Cardiomyopathy

Endomyocardial biopsy samples of the interventricular septum from patients with hypertrophic cardiomyopathy isolated during myectomy were examined. We revealed significant variability of cardiomyocyte ploidy (from 2.9c to 13.5c) that directly correlated with myocyte size; the maximum ploidy was found in young patients. Ultrastructural signs of increased contractile and synthetic activity of cells were observed in patients with high DNA content in cardiomyocytes.

Six1 is down-regulated in end-stage human dilated cardiomyopathy independently of Ezh2

Background

Recently, it was shown that a knock‐out (KO) of the polycomb histone methyltransferase Ezh2 leads to cardiac hypertrophy in mice, which was driven by the homeodomain transcription factor Six1. Here, we analyzed the expression of Six1 and its regulating factor Ezh2 in cardiac tissue of patients with end‐stage dilative cardiomyopathy (DCM).

Methods

Tissue samples of patients with end‐stage DCM (n = 35) were compared with controls (n = 12) for the protein expression of Ezh1, Ezh2, Six1, and a marker of protein expression p70S6K.

Results

Contrary to the Ezh2‐KO mouse model, we found a down‐regulation of Six1 (26%) and an up‐regulation of Ezh2 (76%) in DCM hearts, (both P < 0.05). Expression of Ezh2 and Six1 did not correlate in human tissue (DCM: r²: 0.03, P = 0.31 and donor: r²: 0.05, P = 0.45). Expression of Six1 weakly correlated with left ventricular end‐systolic diameter and fractional shortening. In DCM, Six1 also showed a positive correlation to the expression of the ribosomal protein p70S6K (r: 0.39, P = 0.029), which is involved in protein synthesis. This correlation was not seen in donor tissue, which showed a trend for a negative correlation (r: −0.49, P = 0.08).

Conclusion

Our data indicate that the Ezh2/Six1 axis might be involved in human DCM. However, Six1 expression may be regulated by factors other than Ezh2, and more research is needed to determine the precise role of Ezh2/Six1 in human DCM.

Regulation of chromatin structure in the cardiovascular system

It has been appreciated for some time that cardiovascular disease involves large-scale transcriptional changes in various cell types. What has become increasingly clear only in the past few years, however, is the role of chromatin remodeling in cardiovascular phenotypes in normal physiology, as well as in development and disease. This review summarizes the state of the chromatin field in terms of distinct mechanisms to regulate chromatin structure in vivo, identifying when these modes of regulation have been demonstrated in cardiovascular tissues. We describe areas in which a better understanding of chromatin structure is leading to new insights into the fundamental biology of cardiovascular disease. 

Immunohistochemical expression of oncological proliferation markers in the hearts of rats during normal pregnancy

Aim: Pregnancy is characterized by left ventricular hypertrophy that is potentially accounted for by cardiomyocyte proliferation, although no such evidence is currently available. This study investigates if the left ventricular mass (LVM) increase during pregnancy implies cell hyperplasia. Materials & methods: In nonpregnant and late-pregnant rats, cardiac function and LVM were evaluated by MRI, and cardiomyocyte dimensions and proliferations were assessed quantitatively by morphometric analysis and immunohistochemistry using oncological markers (Ki67 and MCM2). Results: In late-pregnant rats, LVM and cardiomyocyte area were greater. No mitotic figures were found nor was there any significant difference between groups in Ki67 expression. MCM2 expression was related to LVM. Conclusion: During pregnancy, rat cardiomyocytes undergo hypertrophy but not hyperplasia; the expression of MCM2, related to LVM, suggests it could be a marker of protein synthesis. The application of oncological markers to physiological contexts may provide insight into their role within the cell cycle.

Proteomic and biochemical analyses reveal the activation of unfolded protein response, ERK-1/2 and ribosomal protein S6 signaling in experimental autoimmune myocarditis rat model

BACKGROUND

To investigate the molecular and cellular pathogenesis underlying myocarditis, we used an experimental autoimmune myocarditis (EAM)-induced heart failure rat model that represents T cell mediated postinflammatory heart disorders.

RESULTS

By performing unbiased 2-dimensional electrophoresis of protein extracts from control rat heart tissues and EAM rat heart tissues, followed by nano-HPLC-ESI-QIT-MS, 67 proteins were identified from 71 spots that exhibited significantly altered expression levels. The majority of up-regulated proteins were confidently associated with unfolded protein responses (UPR), while the majority of down-regulated proteins were involved with the generation of precursor metabolites and energy metabolism in mitochondria. Although there was no difference in AKT signaling between EAM rat heart tissues and control rat heart tissues, the amounts and activities of extracellular signal-regulated kinase (ERK)-1/2 and ribosomal protein S6 (rpS6) were significantly increased. By comparing our data with the previously reported myocardial proteome of the Coxsackie viruses of group B (CVB)-mediated myocarditis model, we found that UPR-related proteins were commonly up-regulated in two murine myocarditis models. Even though only two out of 29 down-regulated proteins in EAM rat heart tissues were also dysregulated in CVB-infected rat heart tissues, other proteins known to be involved with the generation of precursor metabolites and energy metabolism in mitochondria were also dysregulated in CVB-mediated myocarditis rat heart tissues, suggesting that impairment of mitochondrial functions may be a common underlying mechanism of the two murine myocarditis models.

CONCLUSIONS

UPR, ERK-1/2 and S6RP signaling were activated in both EAM- and CVB-induced myocarditis murine models. Thus, the conserved components of signaling pathways in two murine models of acute myocarditis could be targets for developing new therapeutic drugs or methods aimed at treating enigmatic myocarditis.

Smaller cardiac cell size and reduced extra-cellular collagen might be beneficial for hearts of Ames dwarf mice

PURPOSE

To test the hypothesis that cardiac morphologic differences between Ames dwarf and wild-type littermates might correlate with the increased longevity observed in the Ames dwarf mice.

METHODS

Hearts removed from young adult (5-7 mo) and old (24-28 mo) Ames dwarf and wild-type littermates underwent histological and morphometric analysis. Measurements of cell size, nuclear size, and collagen content were made using computerized color deconvolution and particle analysis methodology.

RESULTS

In the young mice at six months of age, mean cardiomyocyte area was 46% less in Ames dwarf than in wild-type mice (p<0.0001). Cardiomyocyte size increased with age by about 52% in the wild-type mice and 44% in the Ames dwarf mice (p<0.001). There was no difference in nuclear size of the cardiomyocytes between the young adult wild-type and Ames dwarf mice. There was an age-associated increase in the cardiomyocyte nuclear size by approximately 50% in both the Ames and wild-type mice (p<0.001). The older Ames dwarf mice had slightly larger cardiomyocyte nuclei compared to wild-type (2%, p<0.05). The collagen content of the hearts in young adult Ames dwarf mice was estimated to be 57% less compared to wild-type littermates (p<0.05). Although collagen content of both Ames dwarf and wild-type mouse hearts increased with age, there was no significant difference at 24 months.

CONCLUSIONS

In wild-type and Ames dwarf mice, nuclear size, cardiomyocyte size, and collagen content increased with advancing age. While cardiomyocyte size was much reduced in young and old Ames dwarf mice compared with wild-type, collagen content was reduced only in the young adult mice. Taken together, these findings suggest that Ames dwarf mice may receive some longevity benefit from the reduced cardiomyocyte cell size and a period of reduced collagen content in the heart during adulthood.

Chronic treatment with anabolic steroids induces ventricular repolarization disturbances: cellular, ionic and molecular mechanism

The illicit use of supraphysiological doses of androgenic steroids (AAS) has been suggested as a cause of arrhythmia in athletes. The objectives of the present study were to investigate the time-course and the cellular, ionic and molecular processes underlying ventricular repolarization in rats chronically treated with AAS. Male Wistar rats were treated weekly for 8 weeks with 10mg/kg of nandrolone decanoate (DECA n=21) or vehicle (control n=20). ECG was recorded weekly. Action potential (AP) and transient outward potassium current (I(to)) were recorded in rat hearts. Expression of KChIP2, Kv1.4, Kv4.2, and Kv4.3 was assessed by real-time PCR. Hematoxylin/eosin and Picrosirius red staining were used for histological analysis. QTc was greater in the DECA group. After DECA treatment the left, but not right, ventricle showed a longer AP duration than did the control. I(to) current densities were 47.5% lower in the left but not in the right ventricle after DECA. In the right ventricle the I(to) inactivation time-course was slower than in the control group. After DECA the left ventricle showed lower KChIP2 ( approximately 26%), Kv1.4 ( approximately 23%) and 4.3 ( approximately 70%) expression while the Kv 4.2 increased in 4 ( approximately 250%) and diminished in 3 ( approximately 30%) animals of this group. In the right ventricle the expression of I(to) subunits was similar between the treatment and control groups. DECA-treated hearts had 25% fewer nuclei and greater nuclei diameters in both ventricles. Our results strongly suggest that supraphysiological doses of AAS induce morphological remodeling in both ventricles. However, the electrical remodeling was mainly observed in the left ventricle.

Cardiomyocyte regeneration in pericicatricial zone of the myocardium after laser tunneling and implantation of bone marrow mononuclear cells

Using canine model of chronic postinfarction myocardial ischemia we evaluated angiogenesis and cardiomyogenesis after combined revascularization by laser tunneling of the pericicatricial zone followed by implantation of bone marrow mononuclear cells into the channels. It was shown that the numerical density of arterioles and capillaries considerably increased 1 month after revascularization. We also observed a considerable increase in the density of cardiomyocyte nuclei in the test area, a 2-fold increase in the total area of nuclei, and an increase in the mean area of cardiomyocyte nuclei. The number of PNCA-positive cardiomyocytes significantly increased after combined revascularization. Our findings suggest that combined revascularization of the pericicatricial zone of the myocardium promoted angiogenesis and stimulates regeneration of cardiomyocytes.

Suppression of right ventricular hypertrophy after extensive pulmonary resection in rats by granulocyte colony-stimulating factor

BACKGROUND

The objective of the present study was to investigate the effects of granulocyte colony-stimulating factor (G-CSF) on right ventricular hypertrophy following extensive pulmonary resection in rats.

MATERIALS AND METHODS

Adult rats were divided into four groups: (1) Group S (right thoracotomy only); (2) Group L (right three lobectomy); (3) Group LG10 (Group L+G-CSF [10microg/kg/d]); and (4) Group LG100 (Group L+G-CSF [100microg/kg/d]). At postoperative day 21, weight ratio of the right ventricular to the left ventricle plus septum (RV/LV+S, indicator of right ventricular hypertrophy) were measured, and a histopathological study was conducted to determine percentage wall thickness of peripheral pulmonary arteries and proliferating cell nuclear antigen labeling index (indicator of oxidative DNA damage) of right ventricles.

RESULTS

Mean RV/LV+S for Group S was 0.27+/-0.02, significantly smaller than that for the lobectomy groups (Group L, LG10, LG100; 0.47+/-0.05, 0.35+/-0.02, 0.38+/-0.05). G-CSF significantly suppressed right ventricular hypertrophy. Mean medial wall thickness of peripheral pulmonary arteries for Group S was 13.6% +/- 4.9%, significantly smaller than that for Group L (22.9% +/- 9.6%). Compared with Group L, G-CSF reduced medial wall thickness (LG10, 17.6% +/- 9.5%; LG100, 18.0% +/- 11.2%). Incidence of proliferating cell nuclear antigen positive nuclei for Group S was 1.07% +/- 0.49%, significantly smaller than that for Group L (13.77% +/- 5.87%). G-CSF significantly reduced the incidence of proliferating cell nuclear antigen positive nuclei (LG10, 4.04% +/- 2.14%; LG100, 3.18% +/- 1.66%).

CONCLUSIONS

G-CSF administration not only reduce medial wall thickness of peripheral pulmonary arteries but also directly protect cardiomyocytes of the right ventricle, thus suppressing right ventricular hypertrophy. These results suggest that low-dose G-CSF administration can prevent right heart failure following extensive pulmonary resection.

Spontaneous Cardiac Hypertrophy in a Crl:CD(SD) Rat

Cardiac hypertrophy was observed in a 9-week-old Crl:CD(SD) rat that died unexpectedly. The animal was allocated to the control group of a toxicity study, and no abnormalities in its general conditions, body weight or food intake were observed. Necropsy revealed an increase in heart weight. Gross examination indicated cardiac enlargement with thickening of the right and left ventricular walls. Histopathological examination revealed hypertrophy of the cardiomyocytes in the right and left ventricular walls and the interventricular septum. Electron microscopic examination indicated bizarre nuclei and accumulation of an increased number of various sizes of mitochondria in the perinuclear region of the hypertrophied myocytes. Hypertrophied myocytes connected by intensely folded intercalated disks were also observed. Based on these findings, the animal was diagnosed with cardiac hypertrophy. This is the first case report of cardiac hypertrophy in this strain.

RNA induction and inheritance of epigenetic cardiac hypertrophy in the mouse

Epigenetic regulation shapes normal and pathological mammalian development and physiology. Our previous work showed that Kit RNAs injected into fertilized mouse eggs can produce heritable epigenetic defects, or paramutations, with relevant loss-of-function pigmentation phenotypes, which affect adult phenotypes in multiple succeeding generations of mice. Here, we illustrate the relevance of paramutation to pathophysiology by injecting fertilized mouse eggs with RNAs targeting Cdk9, a key regulator of cardiac growth. Microinjecting fragments of either the coding region or the related microRNA miR-1 led to high levels of expression of homologous RNA, resulting in an epigenetic defect, cardiac hypertrophy, whose efficient hereditary transmission correlated with the presence of miR-1 in the sperm nucleus. In this case, paramutation increased rather than decreased expression of Cdk9. These results highlight the diversity of RNA-mediated epigenetic effects and may provide a paradigm for clinical cases of familial diseases whose inheritance is not fully explained in Mendelian terms.