Extensive induction of important mediators of fibrosis and dystrophic calcification in desmin-deficient cardiomyopathy

PPARδ activation improves cardiac mitochondrial homeostasis in desmin deficient mice but does not alleviate systolic dysfunction

Peroxisome proliferator-activated receptor (PPAR) δ is a major transcriptional regulator of cardiac energy metabolism with pleiotropic properties, including anti-inflammatory, anti-oxidative and cardioprotective action. In this study, we sought to investigate whether pharmacological activation of PPARδ via intraperitoneal administration of the selective ligand GW0742 could ameliorate heart failure and mitochondrial dysfunction that have been previously reported in a characterized genetic model of heart failure, the desmin null mice (Des-/-). Our studies demonstrate that treatment of Des-/- mice with the PPARδ agonist attenuated cardiac inflammation, fibrosis and cardiac remodeling. In addition, PPARδ activation alleviated oxidative stress in the failing myocardium as evidenced by decreased ROS levels. Importantly, PPARδ activation stimulated mitochondrial biogenesis, prevented mitochondrial and sarcoplasmic reticulum vacuolar degeneration and improved the mitochondrial intracellular distribution. Finally, PPARδ activation alleviated the mitochondrial respiratory dysfunction, prevented energy depletion and alleviated excessive autophagy and mitophagy in Des-/- hearts. Nevertheless, improvement of all these parameters did not suffice to overcome the significant structural deficiencies that desmin deletion incurs in cardiomyocytes and cardiac function did not improve significantly. In conclusion, pharmacological PPARδ activation in Des-/- hearts exerts protective effects during myocardial degeneration and heart failure by preserving the function and quality of the mitochondrial network. These findings implicate PPARδ agonists as a supplemental constituent of heart failure medications.

Desmin Reorganization by Stimuli Inducing Oxidative Stress and Electrophiles: Role of Its Single Cysteine Residue

The type III intermediate filament proteins vimentin and GFAP are modulated by oxidants and electrophiles, mainly through perturbation of their single cysteine residues. Desmin, the type III intermediate filament protein specific to muscle cells, is critical for muscle homeostasis, playing a key role in sarcomere organization and mitochondrial function. Here, we have studied the impact of oxidants and cysteine-reactive agents on desmin behavior. Our results show that several reactive species and drugs induce covalent modifications of desmin in vitro, of which its single cysteine residue, C333, is an important target. Moreover, stimuli eliciting oxidative stress or lipoxidation, including H2O2, 15-deoxy-prostaglandin J2, and CoCl2-elicited chemical hypoxia, provoke desmin disorganization in H9c2 rat cardiomyoblasts transfected with wild-type desmin, which is partially attenuated in cells expressing a C333S mutant. Notably, in cells lacking other cytoplasmic intermediate filaments, network formation by desmin C333S appears less efficient than that of desmin wt, especially when these proteins are expressed as fluorescent fusion constructs. Nevertheless, in these cells, the desmin C333S organization is also protected from disruption by oxidants. Taken together, our results indicate that desmin is a target for oxidative and electrophilic stress, which elicit desmin remodeling conditioned by the presence of its single cysteine residue.

Targeting the cytoskeleton and extracellular matrix in cardiovascular disease drug discovery

INTRODUCTION

Currently, cardiovascular disease (CVD) drug discovery has focused primarily on addressing the inflammation and immunopathology aspects inherent to various CVD phenotypes such as cardiac fibrosis and coronary artery disease. However, recent findings suggest new biological pathways for cytoskeletal and extracellular matrix (ECM) regulation across diverse CVDs, such as the roles of matricellular proteins (e.g. tenascin-C) in regulating the cellular microenvironment. The success of anti-inflammatory drugs like colchicine, which targets microtubule polymerization, further suggests that the cardiac cytoskeleton and ECM provide prospective therapeutic opportunities.

AREAS COVERED

Potential therapeutic targets include proteins such as gelsolin and calponin 2, which play pivotal roles in plaque development. This review focuses on the dynamic role that the cytoskeleton and ECM play in CVD pathophysiology, highlighting how novel target discovery in cytoskeletal and ECM-related genes may enable therapeutics development to alter the regulation of cellular architecture in plaque formation and rupture, cardiac contractility, and other molecular mechanisms.

EXPERT OPINION

Further research into the cardiac cytoskeleton and its associated ECM proteins is an area ripe for novel target discovery. Furthermore, the structural connection between the cytoskeleton and the ECM provides an opportunity to evaluate both entities as sources of potential therapeutic targets for CVDs.

Myospryn deficiency leads to impaired cardiac structure and function and schizophrenia-associated symptoms

The desmin-associated protein myospryn, encoded by the cardiomyopathy-associated gene 5 (CMYA5), is a TRIM-like protein associated to the BLOC-1 (Biogenesis of Lysosomes Related Organelles Complex 1) protein dysbindin. Human myospryn mutations are linked to both cardiomyopathy and schizophrenia; however, there is no evidence of a direct causative link of myospryn to these diseases. Therefore, we sought to unveil the role of myospryn in heart and brain. We have genetically inactivated the myospryn gene by homologous recombination and demonstrated that myospryn null hearts have dilated phenotype and compromised cardiac function. Ultrastructural analyses revealed that the sarcomere organization is not obviously affected; however, intercalated disk (ID) integrity is impaired, along with mislocalization of ID and sarcoplasmic reticulum (SR) protein components. Importantly, cardiac and skeletal muscles of myospryn null mice have severe mitochondrial defects with abnormal internal vacuoles and extensive cristolysis. In addition, swollen SR and T-tubules often accompany the mitochondrial defects, strongly implying a potential link of myospryn together with desmin to SR- mitochondrial physical and functional cross-talk. Furthermore, given the reported link of human myospryn mutations to schizophrenia, we performed behavioral studies, which demonstrated that myospryn-deficient male mice display disrupted startle reactivity and prepulse inhibition, asocial behavior, decreased exploratory behavior, and anhedonia. Brain neurochemical and ultrastructural analyses revealed prefrontal-striatal monoaminergic neurotransmitter defects and ultrastructural degenerative aberrations in cerebellar cytoarchitecture, respectively, in myospryn-deficient mice. In conclusion, myospryn is essential for both cardiac and brain structure and function and its deficiency leads to cardiomyopathy and schizophrenia-associated symptoms.

Intermediate filaments in cardiomyopathy

Intermediate filament (IF) proteins are critical regulators in health and disease. The discovery of hundreds of mutations in IF genes and posttranslational modifications has been linked to a plethora of human diseases, including, among others, cardiomyopathies, muscular dystrophies, progeria, blistering diseases of the epidermis, and neurodegenerative diseases. The major IF proteins that have been linked to cardiomyopathies and heart failure are the muscle-specific cytoskeletal IF protein desmin and the nuclear IF protein lamin, as a subgroup of the known desminopathies and laminopathies, respectively. The studies so far, both with healthy and diseased heart, have demonstrated the importance of these IF protein networks in intracellular and intercellular integration of structure and function, mechanotransduction and gene activation, cardiomyocyte differentiation and survival, mitochondrial homeostasis, and regulation of metabolism. The high coordination of all these processes is obviously of great importance for the maintenance of proper, life-lasting, and continuous contraction of this highly organized cardiac striated muscle and consequently a healthy heart. In this review, we will cover most known information on the role of IFs in the above processes and how their deficiency or disruption leads to cardiomyopathy and heart failure.

Type III Intermediate Filaments Desmin, Glial Fibrillary Acidic Protein (GFAP), Vimentin, and Peripherin

SummaryType III intermediate filament (IF) proteins assemble into cytoplasmic homopolymeric and heteropolymeric filaments with other type III and some type IV IFs. These highly dynamic structures form an integral component of the cytoskeleton of muscle, brain, and mesenchymal cells. Here, we review the current ideas on the role of type III IFs in health and disease. It turns out that they not only offer resilience to mechanical strains, but, most importantly, they facilitate very efficiently the integration of cell structure and function, thus providing the necessary scaffolds for optimal cellular responses upon biochemical stresses and protecting against cell death, disease, and aging.

Opposite effects of catalase and MnSOD ectopic expression on stress induced defects and mortality in the desmin deficient cardiomyopathy model

Oxidative stress has been linked strongly to cell death and cardiac remodeling processes, all hallmarks of heart failure. Mice deficient for desmin (des-/-), the major muscle specific intermediate filament protein, develop dilated cardiomyopathy and heart failure characterized by mitochondrial defects and cardiomyocyte death. The cellular and biochemical alterations in the hearts of these mice strongly suggest that oxidative stress is one of the mechanisms contributing to the pathogenesis of the phenotype. Recently, we showed that indeed the desmin deficient cardiomyocytes are under increased oxidative stress. In order to verify these findings in vivo, we generated transgenic animals overexpressing SOD2 (MnSOD) and/or catalase in the heart and crossed them with des-/- mice, thus allowing us to evaluate the contribution of oxidative injury in inherited cardiomyopathies, as well as the therapeutic potential of antioxidant strategies. Moderate MnSOD and/or catalase overexpression in des-/- hearts leads to a marked decrease in intracellular reactive oxygen species (ROS), ameliorates mitochondrial and other ultrastructural defects, minimizes myocardial degeneration and leads to a significant improvement of cardiac function. Importantly, catalase overexpression increased the 50% survival rate of des-/- mice in an obligatory exercise to 100%. In contrast, MnSOD overexpression enhanced the lethality of des-/- mice, underscoring the importance of a fine balanced cellular redox status. Overall, the present study supports the contribution of oxidative stress in the development of des-/- cardiomyopathy and points to a well-considered antioxidant treatment as therapeutic for cardiomyopathies.

Cardiomyocyte Hypertrophy in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is a hereditary disease leading to sudden cardiac death or heart failure. AC pathology is characterized by cardiomyocyte loss and replacement fibrosis. Our goal was to determine whether cardiomyocytes respond to AC progression by pathological hypertrophy. To this end, we examined tissue samples from AC patients with end-stage heart failure and tissue samples that were collected at different disease stages from desmoglein 2-mutant mice, a well characterized AC model. We find that cardiomyocyte diameters are significantly increased in right ventricles of AC patients. Increased mRNA expression of the cardiac stress marker natriuretic peptide B is also observed in the right ventricle of AC patients. Elevated myosin heavy chain 7 mRNA expression is detected in left ventricles. In desmoglein 2-mutant mice, cardiomyocyte diameters are normal during the concealed disease phase but increase significantly after acute disease onset on cardiomyocyte death and fibrotic myocardial remodeling. Hypertrophy progresses further during the chronic disease stage. In parallel, mRNA expression of myosin heavy chain 7 and natriuretic peptide B is up-regulated in both ventricles with right ventricular preference. Calcineurin/nuclear factor of activated T cells (Nfat) signaling, which is linked to pathological hypertrophy, is observed during AC progression, as evidenced by Nfatc2 and Nfatc3 mRNA in cardiomyocytes and increased mRNA of the Nfat target regulator of calcineurin 1. Taken together, we demonstrate that pathological hypertrophy occurs in AC and is secondary to cardiomyocyte loss and cardiac remodeling.

Desmin and αB-crystallin interplay in the maintenance of mitochondrial homeostasis and cardiomyocyte survival

The association of desmin with the α-crystallin Β-chain (αΒ-crystallin; encoded by CRYAB), and the fact that mutations in either one of them leads to heart failure in humans and mice, suggests a potential compensatory interplay between the two in cardioprotection. To address this hypothesis, we investigated the consequences of αΒ-crystallin overexpression in the desmin-deficient (Des^-/-) mouse model, which possesses a combination of the pathologies found in most cardiomyopathies, with mitochondrial defects as a hallmark. We demonstrated that cardiac-specific αΒ-crystallin overexpression ameliorates all these defects and improves cardiac function to almost wild-type levels. Protection by αΒ-crystallin overexpression is linked to maintenance of proper mitochondrial protein levels, inhibition of abnormal mitochondrial permeability transition pore activation and maintenance of mitochondrial membrane potential (Δψ_m). Furthermore, we found that both desmin and αΒ-crystallin are localized at sarcoplasmic reticulum (SR)-mitochondria-associated membranes (MAMs), where they interact with VDAC, Mic60 - the core component of mitochondrial contact site and cristae organizing system (MICOS) complex - and ATP synthase, suggesting that these associations could be crucial in mitoprotection at different levels.

Strategies to Study Desmin in Cardiac Muscle and Culture Systems

Intermediate filament (IF) cytoskeleton comprises the fine-tuning cellular machinery regulating critical homeostatic mechanisms. In skeletal and cardiac muscle, deficiency or disturbance of the IF network leads to severe pathology, particularly in the latter. The three-dimensional scaffold of the muscle-specific IF protein desmin interconnects key features of the cardiac muscle cells, including the Z-disks, intercalated disks, plasma membrane, nucleus, mitochondria, lysosomes, and potentially sarcoplasmic reticulum. This is crucial for the highly organized striated muscle, in which effective energy production and transmission as well as mechanochemical signaling are tightly coordinated among the organelles and the contractile apparatus. The role of desmin and desmin-associated proteins in the biogenesis, trafficking, and organelle function, as well as the development, differentiation, and survival of the cardiac muscle begins to be enlightened, but the precise mechanisms remain elusive. We propose a set of experimental tools that can be used, in vivo and in vitro, to unravel crucial new pathways by which the IF cytoskeleton facilitates proper organelle function, homeostasis, and cytoprotection and further understand how its disturbance and deficiency lead to disease.

Circulating Biomarkers of Myocardial Fibrosis: The Need for a Reappraisal

Myocardial fibrosis impairs cardiac function, in addition to facilitating arrhythmias and ischemia, and thus influences the evolution and outcome of cardiac diseases. Its assessment is therefore clinically relevant. Although tissue biopsy is the gold standard for the diagnosis of myocardial fibrosis, a number of circulating biomarkers have been proposed for the noninvasive assessment of this lesion. A review of the published clinical data available on these biomarkers shows that most of them lack proof that they actually reflect the myocardial accumulation of fibrous tissue. In this "call to action" article, we propose that this absence of proof may lead to misinterpretations when considering the incremental value provided by the biomarkers with respect to traditional diagnostic tools in the clinical handling of patients. We thus argue that strategies are needed to more strictly validate whether a given circulating biomarker actually reflects histologically proven myocardial fibrosis before it is applied clinically.

Complement system modulation as a target for treatment of arrhythmogenic cardiomyopathy

Inflammation may contribute to disease progression in arrhythmogenic cardiomyopathy (ACM). However, its role in this process is unresolved. Our goal was to delineate the pathogenic role of the complement system in a new animal model of ACM and in human disease. Using cardiac histology, echocardiography, and electrocardiography, we have demonstrated that the desmin-null mouse (Des-/-) recapitulates most of the pathognomonic features of human ACM. Massive complement activation was observed in the Des-/- myocardium in areas of necrotic cells debris and inflammatory infiltrate. Analysis of C5aR-/-Des-/- double-null animals and a pharmaceutical approach using a C5a inhibitor were used to delineate the pathogenic role of the complement system in the disease progression. Our findings indicate that inhibiting C5aR (CD88) signaling improves cardiac function, histopathology, arrhythmias, and survival after endurance. Containment of the inflammatory reaction at the initiation of cardiac tissue injury (2-3 weeks of age), with consequently reduced myocardial remodeling and the absence of a direct long-lasting detrimental effect of C5a-C5aR signaling on cardiomyocytes, could explain the beneficial action of C5aR ablation in Des-/- cardiomyopathy. We extend the relevance of these findings to human pathophysiology by showing for the first time significant complement activation in the cardiac tissues of patients with ACM, thus suggesting that complement modulation could be a new therapeutic target for ACM.

Changes in desmin expression in patients with cardiac diastolic dysfunction and preserved or reduced ejection fraction

PURPOSE

Desmin regulates function of mitochondria, T-tubular system and cytosolic Ca(2+) transients. We investigated whether desmin remodeling correlates with diastolic dysfunction and whether progressive desmin abnormalities are accompanied by increasing diastolic dysfunction stages.

PATIENTS AND METHODS

Eighty five patients with idiopathic dilated cardiomyopathy and suspected myocarditis without confirmed cardiac tissue inflammation in histopathology assays were included and divided into groups: with preserved EF and reduced EF. After echocardiographic analysis of diastolic dysfunction we identified 2 preserved EF subgroups (normal diastolic function (NDF) and impaired relaxation (IR)) and 3 reduced EF subgroups (NDF, IR, and pseudonormalization). Patients with preserved EF and NDF formed the control group. Tissue desmin staining revealed 4 types of desmin expression: I - normal, with regular pattern of cross-section, IIA - increased with regular pattern, IIB - increased, with irregular pattern and presence of aggregates, III - decreased/lack desmin.

RESULTS

Desmin I was observed only in patients with NDF n=8 (100%) in preserved EF and reduced EF, desmin IIA in NDF n=8 (33%) in preserved EF and n=5 (33%) in reduced EF and IR n=16 (66%) in preserved EF and n=10 (66%) in reduced EF. Desmin IIB and III were observed in patients with reduced EF and diastolic dysfunction: IR and pseudonormalization n=9 (39%) and n=2 (29%); n=14 (61%) and n=5 (71%), respectively. Desmin was found to be an independent predictor of diastolic function parameters β=-0.63, R(2)=0.52 for E'; β=0.54, R(2)=0.42 for E/E'.

CONCLUSIONS

Increasing desmin abnormalities were correlated with diastolic dysfunction progression. Desmin expression represents a novel factor contributing or paralleling the development of diastolic dysfunction.

Fabrication of cell-laden macroporous biodegradable hydrogels with tunable porosities and pore sizes

In this work, we investigated a cytocompatible particulate leaching method for the fabrication of cell-laden macroporous hydrogels. We used dehydrated and uncrosslinked gelatin microspheres as leachable porogens to create macroporous oligo(poly(ethylene glycol) fumarate) hydrogels. Varying gelatin content and size resulted in a wide range of porosities and pore sizes, respectively. Encapsulated mesenchymal stem cells (MSCs) exhibited high viability immediately following the fabrication process, and culture of cell-laden hydrogels revealed improved cell viability with increasing porosity. Additionally, the osteogenic potential of the encapsulated MSCs was evaluated over 16 days. Overall, this study presents a robust method for the preparation of cell-laden macroporous hydrogels with desired porosity and pore size for tissue engineering applications.

Osteopontin: At the cross-roads of myocyte survival and myocardial function

Heart failure represents a major cause of morbidity and mortality in Western society. Cardiac myocyte loss due to apoptosis plays a significant role in the progression of heart failure. The extracellular matrix (ECM) maintains the structural integrity of the heart and allows the transmission of electrical and mechanical signals during cardiac contraction and relaxation. Matricellular proteins, a class of non-structural ECM proteins, play a significant role in ECM homeostasis and intracellular signaling via their interactions with cell surface receptors, structural proteins, and/or soluble extracellular factors such as growth factors and cytokines. Osteopontin (OPN), also called cytokine Eta-1, is a member of the matricellular protein family. The normal heart expresses low levels of OPN. However, OPN expression increases markedly under a variety of pathophysiological conditions of the heart. Many human and transgenic mouse studies provide evidence that increased OPN expression, specifically in myocytes, is associated with increased myocyte apoptosis and myocardial dysfunction. This review summarizes OPN expression in the heart, and its role in myocyte apoptosis and myocardial function.

Μyospryn: a multifunctional desmin-associated protein

Desmin, the muscle-specific intermediate filament protein, forms a 3D scaffold that links the contractile apparatus to the costameres of plasma membrane, intercalated disks, the nucleus, and also other membranous organelles. The cellular scaffold formed by desmin and its binding partners might be implicated in signaling and trafficking processes, vital mechanisms for the survival of the mammalian cell. One novel desmin-associated protein is the tripartite motif-like protein myospryn. Myospryn was initially identified as an associated partner to the biogenesis of lysosome-related organelles complex 1 protein dysbindin, implicating its potential involvement in vesicle trafficking and organelle biogenesis and/or positioning. Myospryn is also an A kinase anchoring protein, raising the possibility that together with desmin and other cytoskeletal and signaling proteins, it could participate in the subcellular targeting of protein kinase A activity in striated muscle. As with desmin, different members of this scaffold might play a crucial role in the pathogenesis of muscle disease, since any disturbance in these highly coordinated signaling pathways is expected to compromise efficient maintenance of structure-function integrity of muscle and lead to different cardiac and skeletal myopathies.

Complement system activation in cardiac and skeletal muscle pathology: friend or foe?

A major goal in current cardiology practice is to determine optimal strategies for minimizing myocardial necrosis and optimizing cardiac repair following an acute myocardial infarction. Temporally regulated activation and suppression of innate immunity may be critical for achieving this goal. Extensive experimental data in various animal models have indicated that inhibiting complement activation offers protection to cardiac tissue after ischemia/reperfusion. However, the results of clinical studies using complement inhibitors (mainly at the C5 level) in patients with acute myocardial infarction have largely been disappointing. In cases in which complement activation participates in the initial events of muscle cell destruction, as in autoimmune myocarditis or autoimmune muscle disorders, inhibition of complement activation is expected to prove a successful treatment. In other pathologic conditions in which complement is recruited by degenerating or dying muscle cells, as in ischemia, the ideal approach is probably to modulate rather than abruptly blunt complement activation. Beneficial effects of complement action with regard to waste disposal, recruitment of stem cells, regeneration, angiogenesis, and better utilization of energy sources under hypoxic conditions may also prove important for successful disease treatment. Patient outcome after myocardial infarction almost certainly depend upon the combined activation of several distinct but potentially interrelated signaling pathways, suggesting that a combination of treatments targeted to different pathways should be the therapy of choice, and modulation of complement could be one of them.

Histological and ultrastructural abnormalities in murine desmoglein 2-mutant hearts

Mice carrying a deletion of the adhesive extracellular domain of the desmosomal cadherin desmoglein 2 develop an arrhythmogenic right ventricular cardiomyopathylike phenotype with ventricular dilation, fibrosis and arrhythmia. To unravel the sequence of myocardial alterations and to identify potential pathomechanisms, histological analyses were performed on mutant hearts from the juvenile to the adult state, i.e., between 2 and 13 weeks. At an age of 2 weeks 30% of mutants presented lesions,which were visible as white plaques on the heart surface or in the septum. From 4 weeks onwards, all mutants displayed a cardiac phenotype. Dying cardiomyocytes with calcification were found in lesions of all ages. But lesions of young mutant animals contained high amounts of CD45+ immune cells and little collagen fibers, whereas lesions of the older animals were collagen-rich and harbored only a small but still significantly increased number of CD45+ cells. Electron microscopy further showed that distinct desmosomes cannot be distinguished in intercalated discs of mutant hearts. Widening of the intercellular cleft and even complete dissociation of intercalated discs were often observed close to lesions. Disturbed sarcomer structure, altered Z-discs, multiple autophagic vacuoles and swollen mitochondria were other prominent pathological features. Taken together, the following scenario is suggested: mutant desmoglein 2 cannot fully support the increased mechanical requirements placed on intercalated disc adhesion during postnatal heart development, resulting in compromised adhesion and cell stress. This induces cardiomyocyte death, aseptic inflammation and fibrotic replacement. The acute stage of scar formation is followed by permanent impairment of the cardiac function.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Azelnidipine protects myocardium in hyperglycemia-induced cardiac damage

Background

Azelnidipine (AZL), a long-acting dihydropyridine-based calcium antagonist, has been recently approved and used for treating ischemic heart disease and cardiac remodeling after myocardial infarction, however, its effect on hyperglycemia-induced cardiac damage has not been studied.

Methods

This study examined the effect of AZL on circulating markers of cardiac damage, altered lipid and cytokines profile and markers of oxidative stress including homocysteine in diabetic rats.

Results

STZ induced diabetes caused a significant increase in blood glucose levels. It also resulted in an increase in the levels of homocysteine and cardiac damage markers, like Troponin-1, CK-MB, CK-NAC, uric acid, LDH and alkaline phosphatase. Moreover, there was an increase in the levels of proinflammatory cytokines like TNF-α, IFN-γ, and TGF-β and decrease in the levels of IL-4 and IL-10. Additionally, there was increase in the levels of cholesterol, triglycerides, LDL, VLDL and a decrease in HDL in these animals. There was an altered antioxidant enzyme profile which resulted in a notable increase in the levels of oxidative stress markers like lipid peroxides, nitric oxide and carbonylated proteins. Compared with the untreated diabetic rats, AZL treatment significantly reduced the levels of troponin-1 (P < 0.05), CK-MB (P < 0.05), CK-NAC (P < 0.05), uric acid (P < 0.05), LDH (P < 0.05) and alkaline phosphatase (P < 0.05). It also reduced the levels of the TNF-α (P < 0.05), IFN-γ (P < 0.05), and TGF-β (P < 0.05) and increased the levels of IL-4 (P < 0.05). A significant decrease in the serum cholesterol (P < 0.05), triglycerides (P < 0.05), LDL (P < 0.05), VLDL (P < 0.05) and a significant rise in levels of HDL (P < 0.05) was also observed. Treatment with AZL corrected the distorted antioxidant enzyme profile resulting in a significant decrease in the levels of lipid peroxides, nitric oxide and carbonylated proteins.

Conclusion

Our results indicate that AZL treatment can reduce the risk of hyperglycemia induced metabolic disorders and its role can be further extended to explore its therapeutic potential in diabetic patients with cardiac complications.

Osteopontin as a novel prognostic marker in stable ischaemic heart disease: a 3-year follow-up study

OBJECTIVES

Osteopontin (OPN) is a glycoprotein, which may play a major role in the regulation of biological phenomena. Increased levels of OPN have been linked to the presence and to the severity of atherosclerosis. This study was undertaken to assess the prognostic significance of plasma OPN levels in patients with stable ischaemic heart disease (IHD).

METHODS

In 101 patients with stable IHD and angiographically documented significant coronary artery stenosis, plasma OPN levels were measured at baseline (time of coronary arteriography). Patients were prospectively followed for a median time of 3 years (minimum 2.25, maximum 3.9 years). The primary study endpoint was the composite of cardiovascular death, non-fatal myocardial infarction, need for revascularization and hospitalization for cardiovascular reasons.

RESULTS

Baseline lnOPN levels were directly related to age (r = 0.27, P < 0.001) and inversely to left ventricular ejection fraction (r = -0.32, P < 0.01). Left ventricular ejection fraction was an independent predictor of plasma OPN levels after adjustment for age and gender (beta = -0.013, P = 0.02). Median OPN value was 55 ng mL(-1). In the univariate Cox-regression analysis, OPN levels > 55 ng mL(-1) (n = 50) were significantly related to adverse cardiac outcome (HR = 2.40, 95% CI: 1.11-5.23, P = 0.027). In multivariate model, OPN levels > 55 ng mL(-1) remained statistically significant independent predictor of adverse outcome after adjustment for age, gender, left ventricular ejection fraction and the number of diseased coronary arteries (HR = 2.88, 95% CI: 1.09-7.58, P = 0.032).

CONCLUSION

OPN may provide significant prognostic information independent of other traditional prognostic markers in patients with stable IHD.

Myocardial oxidative stress, osteogenic phenotype, and energy metabolism are differentially involved in the initiation and early progression of delta-sarcoglycan-null cardiomyopathy

Dilated cardiomyopathy (DCM) is a common cause of heart failure, and identification of early pathogenic events occurring prior to the onset of cardiac dysfunction is of mechanistic, diagnostic, and therapeutic importance. The work characterized early biochemical pathogenesis in TO2 strain hamsters lacking delta-sarcoglycan. Although the TO2 hamster heart exhibits normal function at 1 month of age (presymptomatic stage), elevated levels of myeloperoxidase, monocyte chemotactic protein-1, malondialdehyde, osteopontin, and alkaline phosphatase were evident, indicating the presence of inflammation, oxidative stress, and osteogenic phenotype. These changes were localized primarily to the myocardium. Derangement in energy metabolism was identified at the symptomatic stage (4 month), and is marked by attenuated activity and expression of pyruvate dehydrogenase E1 subunit, which catalyzes the rate-limiting step in aerobic glucose metabolism. Thus, this study illustrates differential involvement of oxidative stress, osteogenic phenotype, and glucose metabolism in the initiation and early progression of delta-sarcoglycan-null DCM.

Altered expression of calreticulin during the development of fibrosis

Tissue damage following injury leads to inflammation and fibrosis. To understand the molecular mechanisms and the proteins involved in the fibrotic process, we used the well-established unilateral ureteric obstruction rat model and we analyzed the alterations at early and late time intervals using a classical proteomic approach. Data analysis demonstrates a correlation between calreticulin up-regulation and progression of fibrosis. Calreticulin is involved in Ca++ homeostasis but has not been previously implicated in animal models of fibrosis. Proteomic analysis consistently revealed up-regulation of calreticulin in both early and late time intervals. These findings were further confirmed by biochemical and morphological approaches. Next, animal models of lung fibrosis (bleomycin-induced) and heart fibrosis (desmin-null) were examined. In the lung model, calreticulin expression was up-regulated from early time intervals, whereas in the heart model no change in the expression of calreticulin was observed. In addition, TGF-beta, a well known major contributing factor in several fibrotic processes, was found to up-regulate calreticulin in cultured human proximal tubule epithelial cells. The above observations suggest that calreticulin might be involved in fibrotic processes; however the mechanism(s) underlying its possible involvement are yet unresolved.

Cardiac dysfunction in aging conscious rats: altered cardiac cytoskeletal proteins as a potential mechanism

The objective of this study was to test the hypothesis that the mechanism mediating left ventricular (LV) dysfunction in the aging rat heart involves, in part, changes in cardiac cytoskeletal components. Our results show that there were no significant differences in heart rate, LV pressure, or LV diameter between conscious, instrumented young [5.9 +/- 0.3 mo (n = 9)] and old rats [30.6 +/- 0.1 mo (n = 10)]. However, the first derivative of LV pressure (LV dP/dt) was reduced (8,309 +/- 790 vs. 11,106 +/- 555 mmHg/s, P < 0.05) and isovolumic relaxation time (tau) was increased (8.7 +/- 0.7 vs. 6.3 +/- 0.6 ms, P < 0.05) in old vs. young rats, respectively. The differences in baseline LV function in young and old rats, which were modest, were accentuated after beta-adrenergic receptor stimulation with dobutamine (20 mug/kg), which increased LV dP/dt by 170 +/- 9% in young rats, significantly more (P < 0.05) than observed in old rats (115 +/- 5%). Volume loading in anesthetized rats demonstrated significantly impaired LV compliance in old rats, as measured by the LV end-diastolic pressure and dimension relationship. In old rat hearts, there was a significant (P < 0.05) increase in the percentage of LV collagen (2.4 +/- 0.2 vs. 1.3 +/- 0.2%), alpha-tubulin (92%), and beta-tubulin (2.3-fold), whereas intact desmin decreased by 51%. Thus the cardiomyopathy of aging in old, conscious rats may be due not only to increases in collagen but also to alterations in cytoskeletal proteins.

A missense mutation in desmin tail domain linked to human dilated cardiomyopathy promotes cleavage of the head domain and abolishes its Z-disc localization

A missense mutation (Ile 451 to Met) at the tail domain of the muscle-specific intermediate filament protein desmin has been suggested to be a genetic cause of dilated cardiomyopathy. The Ile451Met mutation is located inside a conserved motif in the desmin tail domain, believed to have a potential role in the lateral packing of type III intermediate filaments. Nevertheless, the role of the type III intermediate filament tail domain remains elusive. To further study the role of this domain in the function of cardiomyocytes and in the development of cardiomyopathy, we generated transgenic mice expressing the mutant desmin(I451M) in the cardiac tissue. Analysis of hearts from transgenic animals revealed that mutant desmin loses its Z-disc localization but it can still associate with the intercalated discs, which, however, have an altered architecture, resembling other examples of dilated cardiomyopathy. This is the first report demonstrating a critical role of the desmin head and tail domains in the formation of the IF scaffold around Z discs. It is further suggested that in cardiomyocytes, an interplay between desmin tail and head domains is taking place, which potentially protects the amino terminus of desmin from specific proteases. The fact that the association with intercalated discs seems unchanged suggests that this association must take place through the desmin tail, in contrast to the head domain that is most possibly involved in the Z-disc binding.

Fine mapping of Dyscalc1, the major genetic determinant of dystrophic cardiac calcification in mice

Calcification of severely dystrophic muscle is occasionally observed in targeted mouse models of muscular dystrophy and cardiomyopathy. Intracellular calcium deposition occurs in necrotic myocytes in the absence of plasma calcium and phosphate imbalances. In the heart, this recessive trait is referred to as dystrophic cardiac calcinosis (DCC). We identified previously Dyscalc1, a major genetic determinant of DCC, in a 15.2-Mbp region on proximal chromosome 7. We report now further steps toward the identification of the Dyscalc1 gene by reverse genetics. Transferring the Dyscalc1 locus from susceptible mouse strain C3H/He onto a resistant C57BL/6 strain background, we generated congenic inbred strains B6.C3-(D7Mit56-D7Mit230) and B6.C3-(D7Nds5-D7Mit230). Three days after myocardial freeze-thaw injury, both strains exhibited calcification of necrotic lesions, confirming the pathogenetic relevance of Dyscalc1. Analysis of two (129S1 x C57BL/6) x 129S1 backcrosses allowed mapping of Dyscalc1 more precisely to a region spanning 0.76 Mbp between genes Fgf21 (39.70 Mbp) and Myod1 (40.46 Mbp). This interval contains 31 known and putative genes in three large, ancestral haplotypes shared by susceptible strains C3H/He, 129S1, and DBA/2. Thus we were able to exclude previously proposed candidate genes Bax and Hrc. Instead, a potential candidate may be the gene encoding the ATP-binding cassette C6. Mutations in the orthologous human ABCC6 gene cause pseudoxanthoma elasticum, or Gronblad-Strandberg syndrome, an elastic tissue disorder with cardiovascular calcifications.

Muscle intermediate filaments and their links to membranes and membranous organelles

Intermediate filaments (IFs) play a key role in the integration of structure and function of striated muscle, primarily by mediating mechanochemical links between the contractile apparatus and mitochondria, myonuclei, the sarcolemma and potentially the vesicle trafficking apparatus. Linkage of all these membranous structures to the contractile apparatus, mainly through the Z-disks, supports the integration and coordination of growth and energy demands of the working myocyte, not only with force transmission, but also with de novo gene expression, energy production and efficient protein and lipid trafficking and targeting. Desmin, the most abundant and intensively studied muscle intermediate filament protein, is linked to proper costamere organization, myoblast and stem cell fusion and differentiation, nuclear shape and positioning, as well as mitochondrial shape, structure, positioning and function. Similar links have been established for lysosomes and lysosome-related organelles, consistent with the presence of widespread links between IFs and membranous structures and the regulation of their fusion, morphology and stabilization necessary for cell survival.

Delayed reduction in left ventricular function following treatment of non-Hodgkin's lymphoma with chemotherapy and rituximab, unrelated to acute infusion reaction

We report 3 cases of reduced cardiac function with complications in non-Hodgkin's lymphoma patients who were treated with rituximab. Patients experienced reduced cardiac functions after the administration of rituximab; there was no evidence of any preceding infusion reactions. Reticulin fiber was observed diffusely in cardiac muscles. Transforming growth factor-beta levels were elevated after the administration of rituximab. We believe that continuous elevation of transforming growth factor-beta may promote the growth of reticulin fiber in cardiac muscles. Reduction in cardiac functions is a severe complication that must be considered when rituximab is administered.

Calcification of myocardial necrosis is common in mice

Independent of the severity, phenotypes and clinical outcomes of myocardial infarction may vary considerably in patients, suggesting a strong genetic influence on healing and adaptive processes. Since little is known about these genetic determinants, we examined the tissue response to myocardial injury in seven inbred mouse strains, including those employed for gene targeting or transgenic overexpression. Myocardial necrosis was produced by non-ischemic, trans-diaphragmal freeze-thaw injury in strains C57BL/6, C3H/He, DBA/2, BALB/c, 129S1, FVB/n and A/J. Two days after injury, necrotic cardiomyocytes calcified in C3H/He, DBA/2, BALB/c and 129S1, a phenotype known as dystrophic cardiac calcinosis (DCC). The susceptibility to DCC of 129S1 was determined by Dyscalc1, a locus on chromosome 7, which was identified previously in C3H/He and DBA/2. DCC was also observed in C3H/He following ischemic injury by permanent coronary artery ligation, indicating that DCC was independent of the mode of injury. In contrast, strains C57BL/6, FVB and A/J were resistant to DCC, showing formation of a fibrous scar without calcification. The development of DCC was studied in detail in C3H/He and C57BL/6. In both strains, no calcium deposition and only little structural disintegration were noted in necrotic myocardium 24 h after injury upon calcium-sensitive fluorescence staining. Ultrastructural examination revealed calcified mitochondria in C3H/He that may have served later as a nidus for rapid intracellular calcification of cardiomyocytes. We concluded that the susceptibility to calcification of myocardial necrosis may be common among inbred strains and should be recognised as a strong genetic modifier of experimental myocardial injury.

Desmin filaments influence myofilament spacing and lateral compliance of slow skeletal muscle fibers

Intermediate filaments composed of desmin interlink Z-disks and sarcolemma in skeletal muscle. Depletion of desmin results in lower active stress of smooth, cardiac, and skeletal muscles. Structural functions of intermediate filaments in fast (psoas) and slow (soleus) skeletal muscle were examined using x-ray diffraction on permeabilized muscle from desmin-deficient mice (Des-/-) and controls (Des+/+). To examine lateral compliance of sarcomeres and cells, filament distances and fiber width were measured during osmotic compression with dextran. Equatorial spacing (x-ray diffraction) of contractile filaments was wider in soleus Des-/- muscle compared to Des+/+, showing that desmin is important for maintaining lattice structure. Osmotic lattice compression was similar in Des-/- and Des+/+. In width measurements of single fibers and bundles, Des-/- soleus were more compressed by dextran compared to Des+/+, showing that intermediate filaments contribute to whole-cell compliance. For psoas fibers, both filament distance and cell compliance were similar in Des-/- and Des+/+. We conclude that desmin is important for stabilizing sarcomeres and maintaining cell compliance in slow skeletal muscle. Wider filament spacing in Des-/- soleus cannot, however, explain the lower active stress, but might influence resistance to stretch, possibly minimizing stretch-induced cell injury.

A Case of Massive Dystrophic Cardiac Calcinosis With Increased Bone Resorption Markers: A Novel Pathophysiologic Link?

We report a 72-year-old man who presented to our emergency room with congestive heart failure that was resistant to initial medical therapy. He had suffered from anterior myocardial infarction 20 years prior. Echocardiography and computed tomography revealed marked cardiac calcification including myocardium, chordal structures, mitral annulus, and aortic valve. Neither chronic renal insufficiency nor hypercalcemia were present in our patient. Bone resorption markers were increased and bone mineral density was consistent with severe osteoporosis. We suggested a novel mechanism, that increased bone resorption may lead to accumulation of calcium into avascular tissues in the heart (ie, chordal structures, mitral annulus, aortic valve, and fibronecrotic myocardium) especially in the setting of high left ventricular end-diastolic pressure. Dystrophic cardiac calcinosis, an age-related cardiomyopathy, is associated with elevated bone resorption markers and it may cause alterations in cellular calcium hemostasis with initiation of deleterious events leading to aggravate dilated and restrictive cardiomyopathy and may result in intractable congestive heart failure. The implication of this case report needs to be reemphasized.

Calciphylaxis and metastatic calcification associated with nephrogenic fibrosing dermopathy

BACKGROUND

Calciphylaxis and metastatic calcification are known complications of chronic renal failure. Recently, a sclerosing condition of the skin termed nephrogenic fibrosing dermopathy (NFD) has been described in patients with renal disease, many of whom have undergone hemodialysis and/or renal transplantation. To our knowledge, the simultaneous occurrence of both conditions in the same patient, in the same lesion, has not been previously reported.

CASE REPORT

We report the clinical, microscopic, and immunohistochemical features of two patients with chronic renal failure whose lesional skin biopsies showed both subcutaneous calcification and NFD. We consider the possible mechanisms that might explain the coexistence of these two disorders.

RESULTS

Both patients presented with erythematous, indurated skin over the lower extremities. Purpuric, reticulated patches, necrosis, or ulceration were not observed. Microscopic examination showed the characteristic changes of NFD involving dermis and subcutaneous septa. In addition, biopsies of both individuals showed subcutaneous calcification, one in a diffuse distribution and the other involving the walls of subcutaneous vessels, as seen in calciphylaxis. Calcification was not suspected clinically in either case.

CONCLUSIONS

Metastatic calcification or calciphylaxis and NFD can occur simultaneously in patients with chronic renal failure and may be found together in the same lesion. Because subcutaneous calcification may not be suspected clinically in these cases, and in view of the adverse outcomes frequently associated with calciphylaxis, we recommend deep incisional biopsy of patients presenting with the clinical features of NFD. Both the fibrosis and the calcification of chronic renal failure may be related to the activity of transforming growth factor-beta/Smad signaling cascades.

A locus on chromosome 7 determines dramatic up-regulation of osteopontin in dystrophic cardiac calcification in mice

Calcification of necrotic tissue is frequently observed in chronic inflammation and atherosclerosis. A similar response of myocardium to injury, referred to as dystrophic cardiac calcinosis (DCC), occurs in certain inbred strains of mice. We now examined a putative inhibitor of calcification, osteopontin, in DCC after transdiaphragmal myocardial freeze-thaw injury. Strong osteopontin expression was found co-localizing with calcification in DCC-susceptible strain C3H/HeNCrlBr, which exhibited low osteopontin plasma concentrations otherwise. Osteopontin mRNA induction was 20-fold higher than in resistant strain C57BL/6NCrlBr, which exhibited fibrous lesions without calcification and little osteopontin expression. Sequence analysis identified several polymorphisms in calcium-binding and phosphorylation sites in osteopontin cDNA. Their potential relevance for DCC was tested in congenic mice, which shared the osteopontin locus with C57BL/6NCrlBr, but retained a chromosomal segment from C3H/HeNCrlBr on proximal chromosome 7. These mice exhibited strong osteopontin expression and DCC comparable to C3H/HeNCrlBr suggesting that a trans-activator of osteopontin transcription residing on chromosome 7 and not the osteopontin gene on chromosome 5 was responsible for the genetic differences in osteopontin expression. A known osteopontin activator encoded by a gene on chromosome 7 is the transforming growth factor-beta1, which was more induced (3.5x) in C3H/HeNCrlBr than in C57BL/6NCrlBr mice.