iTRAQ-based quantitative proteomic analysis of thoracic aortas from adult rats born to preeclamptic dams

Background

Preeclampsia and gestational hypertension can cause vascular function impairment in offspring. In our previous work, we described the protein expression profiles of umbilical artery tissues from patients with preeclampsia.

Methods

To gain insights into the mechanisms of vascular dysfunction in adult rats born to preeclamptic dams, we analyzed thoracic aorta tissues by using iTRAQ isobaric tags and 2D nano LC-MS/MS.

Results

By using the iTRAQ method, we analyzed 1825 proteins, of which 106 showed significantly different expression in the thoracic aortic. Ingenuity pathway analysis (IPA) showed that the majority of differentially expressed proteins (DEPs) were associated with cardiovascular function. Further analysis indicated that glucose-6-phosphate dehydrogenase (G6PD), which is inhibited by miR-423-5p and activated by TP53, had the strongest effect on cardiovascular function. The expression of G6PD was upregulated in thoracic aorta tissues, as confirmed by Western blotting. The expression of two other vascular function-related proteins, cysteine- and glycine-rich protein 2 (CSRP2) and tubulin alpha-4 A (TUBA4A), was upregulated, as demonstrated by mass spectrometry (MS).

Conclusions

Although the results require further functional validation, these data provide novel findings related to vascular function impairment in the adult offspring of preeclamptic mothers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-021-09327-9.

Essential roles of the dystrophin-glycoprotein complex in different cardiac pathologies

The dystrophin-glycoprotein complex (DGC), situated at the sarcolemma dynamically remodels during cardiac disease. This review examines DGC remodeling as a common denominator in diseases affecting heart function and health. Dystrophin and the DGC serve as broad cytoskeletal integrators that are critical for maintaining stability of muscle membranes. The presence of pathogenic variants in genes encoding proteins of the DGC can cause absence of the protein and/or alterations in other complex members leading to muscular dystrophies. Targeted studies have allowed the individual functions of affected proteins to be defined. The DGC has demonstrated its dynamic function, remodeling under a number of conditions that stress the heart. Beyond genetic causes, pathogenic processes also impinge on the DGC, causing alterations in the abundance of dystrophin and associated proteins during cardiac insult such as ischemia-reperfusion injury, mechanical unloading, and myocarditis. When considering new therapeutic strategies, it is important to assess DGC remodeling as a common factor in various heart diseases. The DGC connects the internal F-actin-based cytoskeleton to laminin-211 of the extracellular space, playing an important role in the transmission of mechanical force to the extracellular matrix. The essential functions of dystrophin and the DGC have been long recognized. DGC based therapeutic approaches have been primarily focused on muscular dystrophies, however it may be a beneficial target in a number of disorders that affect the heart. This review provides an account of what we now know, and discusses how this knowledge can benefit persistent health conditions in the clinic.

Transcriptional Patterning of the Ventricular Cardiac Conduction System

RATIONALE

The heartbeat is organized by the cardiac conduction system (CCS), a specialized network of cardiomyocytes. Patterning of the CCS into atrial node versus ventricular conduction system (VCS) components with distinct physiology is essential for the normal heartbeat. Distinct node versus VCS physiology has been recognized for more than a century, but the molecular basis of this regional patterning is not well understood.

OBJECTIVE

To study the genetic and genomic mechanisms underlying node versus VCS distinction and investigate rhythm consequences of failed VCS patterning.

METHODS AND RESULTS

Using mouse genetics, we found that the balance between T-box transcriptional activator, Tbx5, and T-box transcriptional repressor, Tbx3, determined the molecular and functional output of VCS myocytes. Adult VCS-specific removal of Tbx5 or overexpression of Tbx3 re-patterned the fast VCS into slow, nodal-like cells based on molecular and functional criteria. In these cases, gene expression profiling showed diminished expression of genes required for VCS-specific fast conduction but maintenance of expression of genes required for nodal slow conduction physiology. Action potentials of Tbx5-deficient VCS myocytes adopted nodal-specific characteristics, including increased action potential duration and cellular automaticity. Removal of Tbx5 in vivo precipitated inappropriate depolarizations in the atrioventricular (His)-bundle associated with lethal ventricular arrhythmias. TBX5 bound and directly activated cis-regulatory elements at fast conduction channel genes required for fast physiological characteristics of the VCS action potential, defining the identity of the adult VCS.

CONCLUSIONS

The CCS is patterned entirely as a slow, nodal ground state, with a T-box dependent, physiologically dominant, fast conduction network driven specifically in the VCS. Disruption of the fast VCS gene regulatory network allowed nodal physiology to emerge, providing a plausible molecular mechanism for some lethal ventricular arrhythmias.

Syntrophins entangled in cytoskeletal meshwork: Helping to hold it all together

Syntrophins are a family of 59 kDa peripheral membrane-associated adapter proteins, containing multiple protein-protein and protein-lipid interaction domains. The syntrophin family consists of five isoforms that exhibit specific tissue distribution, distinct sub-cellular localization and unique expression patterns implying their diverse functional roles. These syntrophin isoforms form multiple functional protein complexes and ensure proper localization of signalling proteins and their binding partners to specific membrane domains and provide appropriate spatiotemporal regulation of signalling pathways. Syntrophins consist of two PH domains, a PDZ domain and a conserved SU domain. The PH1 domain is split by the PDZ domain. The PH2 and the SU domain are involved in the interaction between syntrophin and the dystrophin-glycoprotein complex (DGC). Syntrophins recruit various signalling proteins to DGC and link extracellular matrix to internal signalling apparatus via DGC. The different domains of the syntrophin isoforms are responsible for modulation of cytoskeleton. Syntrophins associate with cytoskeletal proteins and lead to various cellular responses by modulating the cytoskeleton. Syntrophins are involved in many physiological processes which involve cytoskeletal reorganization like insulin secretion, blood pressure regulation, myogenesis, cell migration, formation and retraction of focal adhesions. Syntrophins have been implicated in various pathologies like Alzheimer's disease, muscular dystrophy, cancer. Their role in cytoskeletal organization and modulation makes them perfect candidates for further studies in various cancers and other ailments that involve cytoskeletal modulation. The role of syntrophins in cytoskeletal organization and modulation has not yet been comprehensively reviewed till now. This review focuses on syntrophins and highlights their role in cytoskeletal organization, modulation and dynamics via its involvement in different cell signalling networks.

β-Sarcoglycan Deficiency Reduces Atherosclerotic Plaque Development in ApoE-Null Mice

BACKGROUND

Smooth muscle cells are important for atherosclerotic plaque stability. Their proper ability to communicate with the extracellular matrix is crucial for maintaining the correct tissue integrity. In this study, we have investigated the role of β-sarcoglycan within the matrix-binding dystrophin-glycoprotein complex in the development of atherosclerosis.

RESULTS

Atherosclerotic plaque development was significantly reduced in ApoE-deficient mice lacking β-sarcoglycan, and their plaques contained an increase in differentiated smooth muscle cells. ApoE-deficient mice lacking β-sarcoglycan showed a reduction in ovarian adipose tissue and adipocyte size, while the total weight of the animals was not significantly different. Western blot analysis of adipose tissues showed a decreased activation of protein kinase B, while that of AMP-activated kinase was increased in mice lacking β-sarcoglycan. Analysis of plasma in β-sarcoglycan-deficient mice revealed reduced levels of leptin, adiponectin, insulin, cholesterol, and triglycerides but increased levels of IL-6, IL-17, and TNF-α.

CONCLUSIONS

Our results indicate that the dystrophin-glycoprotein complex and β-sarcoglycan can affect the atherosclerotic process. Furthermore, the results show the effects of β-sarcoglycan deficiency on adipose tissue and lipid metabolism, which may also have contributed to the atherosclerotic plaque reduction.

100-fold but not 50-fold dystrophin overexpression aggravates electrocardiographic defects in the mdx model of Duchenne muscular dystrophy

Dystrophin gene replacement holds the promise of treating Duchenne muscular dystrophy. Supraphysiological expression is a concern for all gene therapy studies. In the case of Duchenne muscular dystrophy, Chamberlain and colleagues found that 50-fold overexpression did not cause deleterious side effect in skeletal muscle. To determine whether excessive dystrophin expression in the heart is safe, we studied two lines of transgenic mdx mice that selectively expressed a therapeutic minidystrophin gene in the heart at 50-fold and 100-fold of the normal levels. In the line with 50-fold overexpression, minidystrophin showed sarcolemmal localization and electrocardiogram abnormalities were corrected. However, in the line with 100-fold overexpression, we not only detected sarcolemmal minidystrophin expression but also observed accumulation of minidystrophin vesicles in the sarcoplasm. Excessive minidystrophin expression did not correct tachycardia, a characteristic feature of Duchenne muscular dystrophy. Importantly, several electrocardiogram parameters (QT interval, QRS duration and the cardiomyopathy index) became worse than that of mdx mice. Our data suggests that the mouse heart can tolerate 50-fold minidystrophin overexpression, but 100-fold overexpression leads to cardiac toxicity.

Engineered electrical conduction tract restores conduction in complete heart block: from in vitro to in vivo proof of concept

BACKGROUND

Cardiac electrical conduction delays and blocks cause rhythm disturbances such as complete heart block, which can be fatal. Standard of care relies on electronic devices to artificially restore synchrony. We sought to create a new modality for treating these disorders by engineering electrical conduction tracts designed to propagate electrical impulses.

OBJECTIVES

This study sought to create a new approach for treating cardiac conduction disorders by using engineered electrical conduction tracts (EECTs).

METHODS

Paramagnetic beads were conjugated with an antibody to gamma-sarcoglycan, a cardiomyocyte cell surface antigen, and mixed with freshly isolated neonatal rat ventricular cardiomyocytes. A magnetic field was used to pattern a linear EECT.

RESULTS

In an in vitro model of conduction block, the EECT was patterned so that it connected 2 independently beating neonatal rat ventricular cardiomyocyte monolayers; it achieved coordinated electrical activity, with action potentials propagating from 1 region to the other via EECT. Spiking the EECT with heart-derived stromal cells yielded stable structures with highly reproducible conduction velocities. Transplantation of EECTs in vivo restored atrioventricular conduction in a rat model of complete heart block.

CONCLUSIONS

An EECT can re-establish electrical conduction in the heart. This novel approach could, in principle, be used not only to treat cardiac arrhythmias but also to repair other organs.

Cardiomyopathy of Duchenne muscular dystrophy: pathogenesis and prospect of membrane sealants as a new therapeutic approach

Duchenne muscular dystrophy (DMD) is a devastating progressive disease of striated muscle deterioration. This fatal X-linked disorder results from the loss of the protein dystrophin, which in turn causes striated muscle membrane instability. Cardiac dysfunction is a growing problem in patients with DMD, but relatively little is known about the pathophysiology of the dystrophic heart. At present, there is no effective treatment for DMD and the current clinical approaches are primarily supportive in nature. This review will discuss the pathogenesis of DMD in the heart and discuss how these pathogenic processes have led to a new class of agents directed specifically at restoring membrane integrity to dystrophic myocardium. The tri-block poloxamers, specifically poloxamer 188 (P188), are able to stabilize the membranes of dystrophic myocardium in animal models and may offer a new therapeutic approach for cardiac disease in DMD.

Heterogeneous abnormalities of in-vivo left ventricular calcium influx and function in mouse models of muscular dystrophy cardiomyopathy

BACKGROUND

Manganese-enhanced cardiovascular magnetic resonance (MECMR) can non-invasively assess myocardial calcium influx, and calcium levels are known to be elevated in muscular dystrophy cardiomyopathy based on cellular studies.

METHODS

Left ventricular functional studies and MECMR were performed in mdx mice (model of Duchenne muscular dystrophy, 24 and 40 weeks) and Sgcd -/- mice (limb girdle muscular dystrophy 2 F, 16 and 32 weeks), compared to wild type controls (C57Bl/10, WT).

RESULTS

Both models had left ventricular hypertrophy at the later age compared to WT, though the mdx mice had reduced stroke volumes and the Sgcd -/- mice increased heart rate and cardiac index. Especially at the younger ages, MECMR was significantly elevated in both models (both P < 0.05 versus WT). The L-type calcium channel inhibitor diltiazem (5 mg/kg i.p.) significantly reduced MECMR in the mdx mice (P < 0.01), though only with a higher dose (10 mg/kg i.p.) in the Sgcd -/- mice (P < 0.05). As the Sgcd -/- mice had increased heart rates, to determine the role of heart rate in MECMR we studied the hyperpolarization-activated cyclic nucleotide-gated channel inhibitor ZD 7288 which selectively reduces heart rate. This reduced heart rate and MECMR in all mouse groups. However, when looking at the time course of reduction of MECMR in the Sgcd -/- mice at up to 5 minutes of the manganese infusion when heart rates were matched to the WT mice, MECMR was still significantly elevated in the Sgcd -/- mice (P < 0.01) indicating that heart rate alone could not account for all the increased MECMR.

CONCLUSIONS

Despite both mouse models exhibiting increased in-vivo calcium influx at an early stage in the development of the cardiomyopathy before left ventricular hypertrophy, there are distinct phenotypical differences between the 2 models in terms of heart rates, hemodynamics and responses to calcium channel inhibitors.

TBX5 drives Scn5a expression to regulate cardiac conduction system function

Cardiac conduction system (CCS) disease, which results in disrupted conduction and impaired cardiac rhythm, is common with significant morbidity and mortality. Current treatment options are limited, and rational efforts to develop cell-based and regenerative therapies require knowledge of the molecular networks that establish and maintain CCS function. Recent genome-wide association studies (GWAS) have identified numerous loci associated with adult human CCS function, including TBX5 and SCN5A. We hypothesized that TBX5, a critical developmental transcription factor, regulates transcriptional networks required for mature CCS function. We found that deletion of Tbx5 from the mature murine ventricular conduction system (VCS), including the AV bundle and bundle branches, resulted in severe VCS functional consequences, including loss of fast conduction, arrhythmias, and sudden death. Ventricular contractile function and the VCS fate map remained unchanged in VCS-specific Tbx5 knockouts. However, key mediators of fast conduction, including Nav1.5, which is encoded by Scn5a, and connexin 40 (Cx40), demonstrated Tbx5-dependent expression in the VCS. We identified a TBX5-responsive enhancer downstream of Scn5a sufficient to drive VCS expression in vivo, dependent on canonical T-box binding sites. Our results establish a direct molecular link between Tbx5 and Scn5a and elucidate a hierarchy between human GWAS loci that affects function of the mature VCS, establishing a paradigm for understanding the molecular pathology of CCS disease.

[Heart involvement in sarcoglycanopathies]

Sarcoglycanopathies (SG) are autosomic recessive muscular dystrophies, secondary to mutations of the sarcoglycan complex. Clinical pictures include muscle weakness affecting mainly the proximal limb girdle musculature. We review heart involvement in this group of disease.

Cell-matrix interactions in muscle disease

The extracellular matrix (ECM) provides a solid scaffold and signals to cells through ECM receptors. The cell-matrix interactions are crucial for normal biological processes and when disrupted they may lead to pathological processes. In particular, the biological importance of ECM-cell membrane-cytoskeleton interactions in skeletal muscle is accentuated by the number of inherited muscle diseases caused by mutations in proteins conferring these interactions. In this review we introduce laminins, collagens, dystroglycan, integrins, dystrophin and sarcoglycans. Mutations in corresponding genes cause various forms of muscular dystrophy. The muscle disorders are presented as well as advances toward the development of treatment.

Increased neointimal thickening in dystrophin-deficient mdx mice

BACKGROUND

The dystrophin gene, which is mutated in Duchenne muscular dystrophy (DMD), encodes a large cytoskeletal protein present in muscle fibers. While dystrophin in skeletal muscle has been extensively studied, the function of dystrophin in vascular smooth muscle is less clear. Here, we have analyzed the role of dystrophin in injury-induced arterial neointima formation.

METHODOLOGY/PRINCIPAL FINDINGS

We detected a down-regulation of dystrophin, dystroglycan and β-sarcoglycan mRNA expression when vascular smooth muscle cells de-differentiate in vitro. To further mimic development of intimal lesions, we performed a collar-induced injury of the carotid artery in the mdx mouse, a model for DMD. As compared with control mice, mdx mice develop larger lesions with increased numbers of proliferating cells. In vitro experiments demonstrate increased migration of vascular smooth muscle cells from mdx mice whereas the rate of proliferation was similar in cells isolated from wild-type and mdx mice.

CONCLUSIONS/SIGNIFICANCE

These results show that dystrophin deficiency stimulates neointima formation and suggest that expression of dystrophin in vascular smooth muscle cells may protect the artery wall against injury-induced intimal thickening.

Drosophila models of cardiac disease

The fruit fly Drosophila melanogaster has emerged as a useful model for cardiac diseases, both developmental abnormalities and adult functional impairment. Using the tools of both classical and molecular genetics, the study of the developing fly heart has been instrumental in identifying the major signaling events of cardiac field formation, cardiomyocyte specification, and the formation of the functioning heart tube. The larval stage of fly cardiac development has become an important model system for testing isolated preparations of living hearts for the effects of biological and pharmacological compounds on cardiac activity. Meanwhile, the recent development of effective techniques to study adult cardiac performance in the fly has opened new uses for the Drosophila model system. The fly system is now being used to study long-term alterations in adult performance caused by factors such as diet, exercise, and normal aging. The fly is a unique and valuable system for the study of such complex, long-term interactions, as it is the only invertebrate genetic model system with a working heart developmentally homologous to the vertebrate heart. Thus, the fly model combines the advantages of invertebrate genetics (such as large populations, facile molecular genetic techniques, and short lifespan) with physiological measurement techniques that allow meaningful comparisons with data from vertebrate model systems. As such, the fly model is well situated to make important contributions to the understanding of complicated interactions between environmental factors and genetics in the long-term regulation of cardiac performance.

Exercise-induced left ventricular systolic dysfunction in women heterozygous for dystrophinopathy

BACKGROUND

Mutations in the X-linked gene encoding dystrophin cause skeletal and cardiac muscle diseases in men. Female "carriers" also can develop overt disease. The purpose of this study was to ascertain the prevalence of cardiac contractile abnormalities in dystrophinopathy carriers.

METHODS

Twenty-four dystrophinopathy heterozygotes and 24 normal women each underwent standard exercise stress echocardiography.

RESULTS

Heterozygotes demonstrated mildly lower left ventricular ejection fractions (LVEFs) at rest compared with controls (0.56 + or - 0.10 vs 0.62 + or - 0.07, P = .02). After exercise, the mean LVEF fell to 0.53 + or - 0.14 in heterozygotes but rose to 0.73 + or - 0.07 in controls (P < .001). Twenty-one of 24 dystrophinopathy heterozygotes demonstrated > or = 1 of the following: abnormal resting LVEF, abnormal LVEF response to exercise, or exercise-induced wall motion abnormality.

CONCLUSIONS

Women heterozygous for dystrophinopathy demonstrate significant left ventricular systolic dysfunction, which is unmasked by exercise. This finding has mechanistic implications for both inherited and acquired cardiac disease states.

Ca2+ overload and mitochondrial permeability transition pore activation in living delta-sarcoglycan-deficient cardiomyocytes

Muscular dystrophies are often associated with significant cardiac disease that can be the prominent feature associated with gene mutations in sarcoglycan. Cardiac cell death is a main feature of cardiomyopathy in sarcoglycan deficiency and may arise as a cardiomyocyte intrinsic process that remains unclear. Deficiency of delta-sarcoglycan (delta-SG) induces disruption of the dystrophin-associated glycoprotein complex, a known cause of membrane instability that may explain cardiomyocytes cytosolic Ca2+ increase. In this study we assessed the hypothesis that cytosolic Ca2+ increase triggers cardiomyocyte death through mitochondrial Ca2+ overload and dysfunction in the delta-SG-deficient CHF147 hamster. We showed that virtually all isolated CHF147 ventricular myocytes exhibited elevated cytosolic and mitochondrial Ca2+ levels by the use of the Fura-2 and Rhod-2 fluorescent probes. Observation of living cells with Mito-Tracker red lead to the conclusion that approximately 15% of isolated CHF147 cardiomyocytes had disorganized mitochondria. Transmission electron microscope imaging showed mitochondrial swelling associated with crest and membrane disruption. Analysis of the mitochondrial permeability transition pore (MPTP) activity using calcein revealed that mitochondria of CHF147 ventricular cells were twofold leakier than wild types, whereas reactive oxygen species production was unchanged. Bax, Bcl-2, and LC3 expression analysis by Western blot indicated that the intrinsic apoptosis and the cell death associated to autophagy pathways were not significantly activated in CHF147 hearts. Our results lead to conclusion that cardiomyocytes death in delta-SG-deficient animals is an intrinsic phenomenon, likely related to Ca2+-induced necrosis. In this process Ca2+ overload-induced MPTP activation and mitochondrial disorganization may have an important role.

Human umbilical cord blood mononuclear cells decrease fibrosis and increase cardiac function in cardiomyopathy

AIMS

We investigated whether human umbilical cord blood mononuclear cells (HUCBC) can limit progressive cardiomyopathy in TO2 hamsters.

MATERIALS & METHODS

A total of 22 TO2 1-month-old hamsters were treated with intramyocardial HUCBC, 4 x 10(6) in Isolyte, and 23 TO2 1-month-old hamsters were treated with intramyocardial Isolyte. A total of 16 1-month-old F1B hamsters served as controls and received intramyocardial Isolyte. Echocardiograms were performed on all hamsters prior to and monthly after treatment for 6 months. Heart tissues were then stained with hematoxylin and eosin, Masson's Trichrome and human leukocyte antibody.

RESULTS

In F1B hamsters, left ventricular fractional shortening (FS) and ejection fractions (EF) did not significantly decrease over 6 months. By contrast, in Isolyte-treated TO2 hamsters, FS decreased from 56.2 +/- 1.0% to 19.7 +/- 3.2% and EF decreased from 89.5 +/- 1.4% to 44.9 +/- 5.9% at 6 months (both p < 0.0001). The FS and EF in HUCBC-treated TO2 hamsters also progressively decreased over 6 months but the changes were more gradual, especially during the first month after HUCBC treatment when FS was 52.0 +/- 1.5% and EF was 89.5 +/- 1.4%, which was not significantly different from the FS and EF in the F1B hamsters. Moreover, in the HUCBC-treated hamsters, the FS and EF were 20-30% greater than FS and EF in Isolyte TO2 hamsters at 3 and 5 months (p < 0.01). In Isolyte-treated TO2 hamsters at 6-7 months, fibrosis involved 30.0 +/- 5.0% of left ventricle and 35.0 +/- 5.0% of septum. By contrast, in HUCBC-treated hamsters, fibrosis involved only 6.5 +/- 2.3% of the left ventricle and 6.3 +/- 1.8% of septum (p < 0.05). The average number of blood vessels per myocardial microscopic field in HUCBC-treated hearts was 53.5 +/- 0.8 versus 46.2 +/- 3.0 in Isolyte-treated TO2 hearts (p < 0.05).

CONCLUSION

HUCBC, when given as a single intramyocardial injection, can limit fibrosis and increase heart function over the short term in TO2 hamsters with cardiomyopathy.

The dystrophin complex controls bk channel localization and muscle activity in Caenorhabditis elegans

Genetic defects in the dystrophin-associated protein complex (DAPC) are responsible for a variety of pathological conditions including muscular dystrophy, cardiomyopathy, and vasospasm. Conserved DAPC components from humans to Caenorhabditis elegans suggest a similar molecular function. C. elegans DAPC mutants exhibit a unique locomotory deficit resulting from prolonged muscle excitation and contraction. Here we show that the C. elegans DAPC is essential for proper localization of SLO-1, the large conductance, voltage-, and calcium-dependent potassium (BK) channel, which conducts a major outward rectifying current in muscle under the normal physiological condition. Through analysis of mutants with the same phenotype as the DAPC mutants, we identified the novel islo-1 gene that encodes a protein with two predicted transmembrane domains. We demonstrate that ISLO-1 acts as a novel adapter molecule that links the DAPC to SLO-1 in muscle. We show that a defect in either the DAPC or ISLO-1 disrupts normal SLO-1 localization in muscle. Consistent with observations that SLO-1 requires a high calcium concentration for full activation, we find that SLO-1 is localized near L-type calcium channels in muscle, thereby providing a mechanism coupling calcium influx with the outward rectifying current. Our results indicate that the DAPC modulates muscle excitability by localizing the SLO-1 channel to calcium-rich regions of C. elegans muscle.

Dystrophin is a long rod-shaped protein that forms a complex with several membrane and cytoplasmic proteins in muscle. Genetic defects in components of this dystrophin complex are responsible for many forms of muscular dystrophy, including Duchenne muscular dystrophy. C. elegans possesses the dystrophin complex and mutations in its components cause muscular defects, indicating that the dystrophin complex has an evolutionary conserved role in muscle. Accumulating evidence in mammals indicates that dystrophic muscle exhibits an abnormal calcium homeostasis. It is not clear how defects in the dystrophin complex are linked to calcium homeostasis, however. In a C. elegans genetic study we found that a novel adaptor protein links the dystrophin complex to a calcium-sensitive potassium channel that mediates muscle inactivation. We further demonstrated that both the dystrophin complex and the adaptor protein localize the potassium channel in a close proximity to a muscle-activating calcium channel. This arrangement ensures that calcium increases accompanied by muscle activation are coupled to muscle inactivation. Defects in the dystrophin complex or the adaptor disrupt the localization of the potassium channel, thereby resulting in prolonged muscle activation and calcium ion increases. Our study provides a mechanism by which the dystrophin complex regulates cellular signaling and muscle excitability.

Dystroglycan matrix receptor function in cardiac myocytes is important for limiting activity-induced myocardial damage

RATIONALE

Genetic mutations in a number of putative glycosyltransferases lead to the loss of glycosylation of dystroglycan and loss of its laminin-binding activity in genetic forms of human muscular dystrophy. Human patients and glycosylation defective myd mice develop cardiomyopathy with loss of dystroglycan matrix receptor function in both striated and smooth muscle.

OBJECTIVE

To determine the functional role of dystroglycan in cardiac muscle and smooth muscle in the development of cardiomyopathy in muscular dystrophies.

METHODS AND RESULTS

Using cre/lox-mediated gene targeting, we show here that loss of dystroglycan function in ventricular cardiac myocytes is sufficient to induce a progressive cardiomyopathy in mice characterized by focal cardiac fibrosis, increase in cardiac mass, and dilatation ultimately leading to heart failure. In contrast, disruption of dystroglycan in smooth muscle is not sufficient to induce cardiomyopathy. The specific loss of dystroglycan function in cardiac myocytes causes the accumulation of large, clustered patches of myocytes with membrane damage, which increase in number in response to exercise-induced cardiac stress, whereas exercised mice with normal dystroglycan expression accumulate membrane damage limited to individual myocytes.

CONCLUSIONS

Our findings suggest dystroglycan function as an extracellular matrix receptor in cardiac myocytes plays a primary role in limiting myocardial damage from spreading to neighboring cardiac myocytes, and loss of dystroglycan matrix receptor function in cardiac muscle cells is likely important in the development of cardiomyopathy in glycosylation-deficient muscular dystrophies.

Sarcolemmal neuronal nitric oxide synthase defect in limb-girdle muscular dystrophy: an adverse modulating factor in the disease course?

Reduction of neuronal nitric oxide synthase (nNOS) has been associated with the pathogenesis and clinical expression of inherited myopathies. To determine whether a defect in nNOS might be an adverse modulating factor in the course of limb-girdle muscular dystrophy, we investigated cytosolic and sarcolemmal nNOS expression in muscle biopsies from 32 patients with 7 forms of limb-girdle muscular dystrophy. Primary calpainopathy, dysferlinopathy, and caveolinopathy biopsies showed normal levels of cytosolic nNOS and preserved sarcolemmal nNOS immunoreactivity. By contrast, the cytosolic nNOS levels in sarcoglycanopathy muscles were variably reduced. Sarcolemmal nNOS immunoreactivity varied from absent to reduced, depending on the integrity of the sarcoglycan complex. In muscles with loss of the entire sarcoglycan complex, sarcolemmal nNOS was absent; it otherwise depended on the specific sarcoglycan gene and type of mutation. The integrity of the entire sarcoglycan complex is, therefore, essential for the stabilization of nNOS to the sarcolemma. Absence of sarcolemmal nNOS in sarcoglycanopathy muscle was always associated with severe muscular dystrophy and sometimes with dilated cardiomyopathy, supporting the hypothesis that nNOS defect might contribute to skeletal and cardiac muscle disease progression. These results emphasize the value of nNOS immunohistochemical analysis in limb-girdle muscular dystrophy and provide additional insights for future therapeutic interventions in these disorders.

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.

Muscle diseases: the muscular dystrophies

Dystrophic muscle disease can occur at any age. Early- or childhood-onset muscular dystrophies may be associated with profound loss of muscle function, affecting ambulation, posture, and cardiac and respiratory function. Late-onset muscular dystrophies or myopathies may be mild and associated with slight weakness and an inability to increase muscle mass. The phenotype of muscular dystrophy is an endpoint that arises from a diverse set of genetic pathways. Genes associated with muscular dystrophies encode proteins of the plasma membrane and extracellular matrix, and the sarcomere and Z band, as well as nuclear membrane components. Because muscle has such distinctive structural and regenerative properties, many of the genes implicated in these disorders target pathways unique to muscle or more highly expressed in muscle. This chapter reviews the basic structural properties of muscle and genetic mechanisms that lead to myopathy and muscular dystrophies that affect all age groups.

Consequences of disrupting the dystrophin-sarcoglycan complex in cardiac and skeletal myopathy

Mutations that disrupt the dystrophin glycoprotein complex lead to plasma membrane instability of cardiomyocytes and skeletal muscle myofibers. Instability of the plasma membrane leads to degeneration largely due to activation of a necrotic process in these disorders. In response to ongoing degeneration, skeletal muscle exhibits robust regeneration while in cardiac muscle regeneration is not obvious. The dystrophin complex is concentrated along the plasma membrane in costameric structures that correspond to the Z bands of sarcomeres, thus positioning the dystrophin complex to transmit force between the sarcomere and the plasma membrane to the extracellular matrix. Although it is apparent that this position is important for perpendicular force transmission, it is clear that the dystrophin complex also fulfills signaling roles. Nitric oxide synthase and stress-induced signaling cascades are activated to participate in protection but may also contribute to pathology.

Role of the extracellular matrix and its receptors in smooth muscle cell function: implications in vascular development and disease

PURPOSE OF REVIEW

Cardiovascular disease affects millions of people worldwide, while the sarcoglycan deficient cardiomyopathies are rare disorders. One important common feature, however, is the vascular smooth muscle. Here we focus on the roles of extracellular matrix components and their receptors in the functions of vascular smooth muscle cells.

RECENT FINDINGS

Recent observations highlight the importance of integrins and the dystrophin-glycoprotein complex in development and cardiomyopathy. For example, integrin alpha4 and alpha7 subunits are important for distributing vascular smooth muscle cells during blood vessel development. Studies on delta-sarcoglycan deficient animals have revealed abnormal vascular smooth muscle proliferation and apoptosis. Furthermore, data suggest that perlecan, by affecting smooth muscle cell proliferation, participates in the atherosclerotic process. Overexpression of decorin leads to reduced progression of atherosclerosis and thrombospondin-1 has been implicated in regulation of smooth muscle cell contractility via inhibition of nitric oxide. Novel findings on versican suggest that the binding of versican to fibulin is of great importance for regulating smooth muscle cell function.

SUMMARY

By regulating migration, proliferation and apoptosis as well as extracellular matrix synthesis and assembly, proteoglycans, integrins and the dystrophin-glycoprotein complex may be of great importance both during development and in vascular disease.

Impact of delta-sarcoglycan gene polymorphism on the occurrence of coronary spastic angina in Japanese patients with hypertrophic cardiomyopathy

BACKGROUND

Patients with hypertrophic cardiomyopathy (HCM) frequently complain of angina-like symptoms in the absence of organic coronary stenoses. Coronary spasm might cause myocardial ischemia in HCM patients. Delta-sarcoglycan plays a crucial role in the pathogenesis of HCM and coronary spasm in a mouse model.

METHODS AND RESULTS

This is a retrospective, single-center study with a small sample size. Seventy patients with HCM underwent coronary angiography and received acetylcholine provocation test. Coronary risk factors and 5'-untranslated region (UTR) G to C polymorphism on delta-sarcoglycan gene (n=64) were evaluated in the HCM patients. In 31 (44.3%) of 70 HCM patients, coronary spasm was induced by the provocation. None of the coronary risk factors was significantly different between the coronary spasm group and the non-coronary spasm group. The 5'-UTR gene polymorphism was associated with the occurrence of coronary spasm with an additive effect on the coexistence (p=0.025). Multiple logistic regression analysis showed that the C allele of 5'-UTR polymorphism was a significant risk factor for coronary spasm in patients with HCM (odds ratio, 3.1; 95% confidence interval, 1.0 to 9.5; p=0.045) that was independent of traditional coronary risk factors.

CONCLUSIONS

The 5'-UTR polymorphism on delta-sarcoglycan gene was associated with coronary spasm in Japanese patients with HCM.

Mutation of delta-sarcoglycan is associated with Ca(2+) -dependent vascular remodeling in the Syrian hamster

We examined whether mutation of the delta-sarcoglycan gene, which causes dilated cardiomyopathy, also alters the vascular smooth muscle cell (VSMC) phenotype and arterial function in the Syrian hamster CHF 147. Thoracic aorta media thickness showed marked variability in diseased hamsters with zones of atrophy and hypertrophied segments. CHF-147 VSMCs displayed a proliferating/"synthetic" phenotype characterized by the absence of the smooth muscle myosin heavy chain SM2, dystrophin, and Ca(2+)-handling proteins, and the presence of cyclin D1. In freshly isolated VSMCs from CHF 147 hamsters, voltage-independent basal Ca(2+) channels showed enhanced activity similar to that in proliferating wild-type (WT) cells. The transcription factor NFAT (nuclear factor of activated T cells) was spontaneously active in freshly isolated CHF 147 VSMCs, as in proliferating VSMCs from WT hamsters. Mibefradil inhibited B-type channels, NFAT activity, and VSMC proliferation. CHF 147 hamsters had abundant apoptotic cells distributed in patches along the aorta, and clusters of inactive mitochondria were observed in 25% of isolated CHF 147 cells, whereas no such clusters were seen in WT cells. In conclusion, mutation of the delta-sarcoglycan gene increases plasma membrane permeability to Ca(2+), activates the Ca(2+)-regulated transcription factor NFAT, and leads to spontaneous mitochondrial aggregation, causing abnormal VSMC proliferation and apoptosis.

Reversal of calcium cycling defects in advanced heart failure toward molecular therapy

Heart failure is a growing major cause of human morbidity and mortality worldwide. A wave of new insights from diverse laboratories has begun to uncover new therapeutic strategies that affect the molecular pathways within cardiomyocytes that drive heart failure progression. Using an integrative approach that employs insights from genetic-based studies in mouse and humans and in vivo somatic gene transfer studies, we have uncovered a new link between stress signals mediated by mechanical stretch and defects in sarcoplasmic reticulum (SR) calcium cycling. An intrinsic mechanical stress sensing system is embedded in the Z disc of cardiomyocytes, and defects in stretch responses can lead to heart failure progression and associated increases in wall stress. Reversal of the chronic increases in wall stress by promoting SR calcium cycling can prevent and partially reverse heart failure progression in multiple genetic and acquired model systems of heart failure in both small and large animals. We propose that reversal of advanced heart failure is possible by targeting the defects in SR calcium cycling, which may be a final common pathway for the progression of many forms of heart failure.

New approaches in the therapy of cardiomyopathy in muscular dystrophy

Cardiomyopathy is a frequent occurrence in muscular dystrophy, and heart disease in muscular dystrophy can contribute to both morbidity and mortality. A number of novel therapies are being developed for muscular dystrophy, and the efficacy of these therapies for heart disease is unknown. The most common X-linked recessive disease is Duchenne muscular dystrophy (DMD), which arises from defects in the dystrophin gene. Therapy specifically aimed at DMD is reviewed in the context of its projected effect on cardiomyopathy associated with DMD. Additionally, novel therapies are being pursued to treat specifically the cardiomyopathy of DMD. There is substantial genetic heterogeneity underlying the muscular dystrophies, and not all muscular dystrophy patients develop cardiomyopathy. A subset of muscular dystrophies may place patients at significantly greater risk of developing cardiomyopathy and cardiac rhythm disturbances. These disorders are discussed, highlighting recent studies and recommendations for therapy.

Genetic modifiers of muscular dystrophy: Implications for therapy

The genetic understanding of the muscular dystrophies has advanced considerably in the last two decades. Over 25 different individual genes are now known to produce muscular dystrophy, and many different "private" mutations have been described for each individual muscular dystrophy gene. For the more common forms of muscular dystrophy, phenotypic variability can be explained by precise mutations. However, for many genetic mutations, the presence of the identical mutation is associated with marked phenotypic range that affects muscle function as well as cardiac function. The explanation for phenotype variability in the muscular dystrophies is only now being explored. The availability of genetically engineered animal models has allowed the generation of single mutations on the background of highly inbred strain. Phenotypic variation that is altered by genetic background argues for the presence of genetic modifier loci that can ameliorate or enhance aspects of the dystrophic phenotype. A number of individual genes have been implicated as modifiers of muscular dystrophy by studies in genetically engineered mouse models of muscular dystrophy. The value of these genes and products is that the pathways identified through these experiments may be exploited for therapy.

Nuclear sequestration of δ-sarcoglycan disrupts the nuclear localization of lamin A/C and emerin in cardiomyocytes

Sarcoglycan is a membrane-associated protein complex found at the plasma membrane of cardiomyocytes and skeletal myofibers. Recessive mutations of delta-sarcoglycan that eliminate expression, and therefore function, lead to cardiomyopathy and muscular dystrophy by producing instability of the plasma membrane. A dominant missense mutation in the gene encoding delta-sarcoglycan was previously shown to associate with dilated cardiomyopathy in humans. To investigate the mechanism of dominantly inherited cardiomyopathy, we generated transgenic mice that express the S151A delta-sarcoglycan mutation in the heart using the alpha-myosin heavy-chain gene promoter. Similar to the human delta-sarcoglycan gene mutation, S151A delta-sarcoglycan transgenic mice developed dilated cardiomyopathy at a young age with enhanced lethality. Instead of placement at the plasma membrane, delta-sarcoglycan was found in the nucleus of S151A delta-sarcoglycan cardiomyocytes. Retention of delta-sarcoglycan in the nucleus was accompanied by partial nuclear sequestration of beta- and gamma-sarcoglycan. Additionally, the nuclear-membrane-associated proteins, lamin A/C and emerin, were mislocalized throughout the nucleoplasm. Therefore, the S151A delta-sarcoglycan gene mutation acts in a dominant negative manner to produce trafficking defects that disrupt nuclear localization of lamin A/C and emerin, thus linking together two common mechanisms of inherited cardiomyopathy.

Skeletal myosphere-derived progenitor cell transplantation promotes neovascularization in delta-sarcoglycan knockdown cardiomyopathy

Bone marrow cells have been shown to contribute to neovascularization in ischemic hearts, whereas their impaired maturation to restore the delta-sarcoglycan (delta-SG) expression responsible for focal myocardial degeneration limits their utility to treat the pathogenesis of cardiomyopathy. Here, we report the isolation of multipotent progenitor cells from adult skeletal muscle, based on their ability to generate floating-myospheres. Myosphere-derived progenitor cells (MDPCs) are distinguishable from myogenic C2C12 cells and differentiate into vascular smooth muscle cells and mesenchymal progeny. The mutation in the delta-SG has been shown to develop vascular spasm to affect sarcolemma structure causing cardiomyopathy. We originally generated delta-SD knockdown (KD) mice and transplanted MDPCs into the hearts. MDPCs enhanced neoangiogenesis and restored delta-SG expression in impaired vasculatures through trans-differentiation, leading to improvement of cardiac function associated with paracrine effectors secretion. We propose that MDPCs may be the promising progenitor cells in skeletal muscle to treat delta-sarcoglycan complex mutant cardiomyopathy.

Challenges and opportunities in dystrophin-deficient cardiomyopathy gene therapy

The last decade has evidenced unprecedented progress in gene therapy of Duchenne and Becker muscular dystrophy (DMD and BMD) skeletal muscle disease. Cardiomyopathy is a leading cause of morbidity and mortality in both patients and carriers of DMD, BMD and X-linked dilated cardiomyopathy. However, there is little advance in heart gene therapy. The gene, the vector, vector delivery, the target tissue and animal models are five fundamental components in developing an effective gene therapy. Intensive effort has been made in optimizing gene transfer vectors and methods. Systemic and/or local delivery of recombinant adeno-associated viral vector have resulted in widespread transduction in the rodent heart. The current challenge is to define other parameters that are essential for a successful gene therapy such as the best candidate gene(s), the optimal expression level and the target tissue. This review focuses on these long-ignored aspects and points out future research directions. In particular, we need to address whether all or only some of the recently developed mini- and microgenes are protective in the heart, whether partial correction can lead to whole heart function improvement, whether over-expression is hazardous and whether correcting skeletal muscle disease can slow down or stop the progression of cardiomyopathy. Discussion is also made on whether the current mouse models can meet these research needs.

The role of free radicals in the pathophysiology of muscular dystrophy

Null mutation of any one of several members of the dystrophin protein complex can cause progressive, and possibly fatal, muscle wasting. Although these muscular dystrophies arise from mutation of a single gene that is expressed primarily in muscle, the resulting pathology is complex and multisystemic, which shows a broader disruption of homeostasis than would be predicted by deletion of a single-gene product. Before the identification of the deficient proteins that underlie muscular dystrophies, such as Duchenne muscular dystrophy (DMD), oxidative stress was proposed as a major cause of the disease. Now, current knowledge supports the likelihood that interactions between the primary genetic defect and disruptions in the normal production of free radicals contribute to the pathophysiology of muscular dystrophies. In this review, we focus on the pathophysiology that results from dystrophin deficiency in humans with DMD and the mdx mouse model of DMD. Current evidence indicates three general routes through which free radical production can be disrupted in dystrophin deficiency to contribute to the ensuing pathology. First, constitutive differences in free radical production can disrupt signaling processes in muscle and other tissues and thereby exacerbate pathology. Second, tissue responses to the presence of pathology can cause a shift in free radical production that can promote cellular injury and dysfunction. Finally, behavioral differences in the affected individual can cause further changes in the production and stoichiometry of free radicals and thereby contribute to disease. Unfortunately, the complexity of the free radical-mediated processes that are perturbed in complex pathologies such as DMD will make it difficult to develop therapeutic approaches founded on systemic administration of antioxidants. More mechanistic knowledge of the specific disruptions of free radicals that underlie major features of muscular dystrophy is needed to develop more targeted and successful therapeutic approaches.

Hypertrophic response of Duchenne and limb-girdle muscular dystrophies is associated with activation of Akt pathway

Dystrophic muscle undergoes repeated cycles of degeneration/regeneration, characterized by the presence of hypertrophic fibers. In order to elucidate the signaling pathways that govern these events, we investigated Akt activation in normal and dystrophic muscle. Akt is activated in neonatal muscle and in actively dividing myoblasts, supporting a developmental role for Akt signaling. Akt activation was detected at very early, prenecrotic stages of disease pathogenesis, and maximal activation was observed during peak stages of muscle hypertrophy. Duchenne muscular dystrophy patients exhibit a similar pattern of Akt activation. Mice with sarcoglycan-deficient muscular dystrophy possess more severe muscle pathology and display elevated Akt signaling. However, the highest levels of Akt activation were found in dystrophin-utrophin-deficient muscle with very advanced dystrophy. We propose that Akt may serve as an early biomarker of disease and that Akt activation mediates hypertrophy in muscular dystrophy. Current investigations are focused on introducing constitutively active and dominant-negative Akt into prenecrotic mdx mice to determine how early modification of Akt activity influences disease pathogenesis.

ζ-Sarcoglycan is a functional homologue of γ-sarcoglycan in the formation of the sarcoglycan complex

The sarcoglycans (SGs), transmembrane components of the dystrophin-associated glycoprotein complex, are stable and functional only when they assemble into a tetrameric complex in muscle cells. A defect in any one of the four SG members disrupts the entire SG complex (SGC) and causes limb-girdle muscular dystrophy. zeta-SG has been recently found as a transmembrane protein homologous to gamma-SG and delta-SG. To characterize zeta-SG in complex formation, we co-transfected expression vectors encoding all six SGs (alpha-, beta-, gamma-, delta-, epsilon- and zeta-SG) and dystroglycan into Chinese hamster ovary cells. Immunoprecipitation analysis showed that zeta-SG or gamma-SG formed a SGC with beta-SG and delta-SG plus alpha-SG or epsilon-SG, revealing that zeta-SG can form two types of SGCs (alpha-beta-zeta-delta or epsilon-beta-zeta-delta). This result indicates the functional resemblance of zeta-SG to gamma-SG rather than delta-SG, although phylogenetic analysis suggests that zeta-SG is evolutionally closer to delta-SG than to gamma-SG. Reverse transcription (RT)-PCR showed that the expression pattern of the transcript was almost the reciprocal of that of gamma-SG in various mouse tissues and that the zeta-SG transcript was especially abundant in the brain, suggesting that zeta-SG might play a particular role in the central nervous system.

Mechanisms of cardiac fibrosis induced by urokinase plasminogen activator

Human hearts with end-stage failure and fibrosis have macrophage accumulation and elevated plasminogen activator activity. However, the mechanisms that link macrophage accumulation and plasminogen activator activity with cardiac fibrosis are unclear. We previously reported that mice with macrophage-targeted overexpression of urokinase plasminogen activator (SR-uPA+/o mice) develop cardiac macrophage accumulation by 5 weeks of age and cardiac fibrosis by 15 weeks. We used SR-uPA+/o mice to investigate mechanisms through which macrophage-expressed uPA causes cardiac macrophage accumulation and fibrosis. We hypothesized that: 1) macrophage accumulation and cardiac fibrosis in SR-uPA+/o mice are dependent on localization of uPA by the uPA receptor (uPAR); 2) activation of plasminogen by uPA and subsequent activation of transforming growth factor-beta1 (TGF-beta1) and matrix metalloproteinase (MMP)-2 and -9 by plasmin are critical pathways through which uPA-expressing macrophages accumulate in the heart and cause fibrosis; and 3) uPA-induced cardiac fibrosis can be attenuated by treatment with verapamil. To test these hypotheses, we bred the SR-uPA+/o transgene into mice deficient in either uPAR or plasminogen and measured cardiac macrophage accumulation and fibrosis. We also measured cardiac TGF-beta1 protein (total and active), Smad2 phosphorylation, and MMP activity after the onset of macrophage accumulation but before the onset of cardiac fibrosis. Finally, we treated mice with verapamil. Our studies revealed that plasminogen is necessary for uPA-induced cardiac fibrosis and macrophage accumulation but uPAR is not. We did not detect plasmin-mediated activation of TGF-beta1, MMP-2, or MMP-9 in hearts of SR-uPA+/o mice. However, verapamil treatment significantly attenuated both cardiac fibrosis and macrophage accumulation.

Autophagic cardiomyocyte death in cardiomyopathic hamsters and its prevention by granulocyte colony-stimulating factor

In UM-X7.1 hamster model of human dilated cardiomyopathy, heart failure progressively develops and causes 50% mortality by 30 weeks of age. Through ultrastructural analysis, we found that many cardiomyocytes of this model contain typical autophagic vacuoles including degraded mitochondria, glycogen granules, and myelin-like figures. In addition, ubiquitin, cathepsin D, and Rab7 were overexpressed as determined by immunoassays. Importantly, most cardiomyocytes with leaky plasma membranes were positive for cathepsin D, suggesting a direct link between autophagic degeneration and cell death. Meanwhile, cardiomyocyte apoptosis appeared insignificant. Granulocyte colony-stimulating factor (10 microg/kg/day), injected 5 days/week from 15 to 30 weeks of age, improved survival among 30-week-old hamsters (100% versus 53% in the untreated hamsters, P < 0.0001); ventricular function and remodeling, increased cardiomyocyte size, and reduced myocardial fibrosis followed by a dramatic reduction in the autophagic findings were also seen. Granulocyte colony-stimulating factor also down-regulated tumor necrosis factor-alpha and increased activities of Akt signal transducer and activator of transcription-3, and matrix metalloproteinases. However, there was no clear evidence of transdifferentiation from bone marrow cells into cardiomyocytes. In conclusion, autophagic death is important for cardiomyocyte loss in the cardiomyopathic hamster, and the beneficial effect of granulocyte colony-stimulating factor acts mainly via an anti-autophagic mechanism rather than anti-apo-ptosis or regeneration.

Spontaneous coronary vasospasm in KATP mutant mice arises from a smooth muscle-extrinsic process

In the vasculature, ATP-sensitive potassium channels (KATP) channels regulate vascular tone. Mice with targeted gene disruptions of KATP subunits expressed in vascular smooth muscle develop spontaneous coronary vascular spasm and sudden death. From these models, it was hypothesized that the loss of KATP channel activity in arterial vascular smooth muscle was responsible for coronary artery spasm. We now tested this hypothesis using a transgenic strategy where the full-length sulfonylurea receptor containing exon 40 was expressed under the control of a smooth muscle-specific SM22alpha promoter. Two transgenic founder lines were generated and independently bred to sulfonylurea receptor 2 (SUR2) null mice to generate mice that restored expression of KATP channels in vascular smooth muscle. Transgenic expression of the sulfonylurea receptor in vascular smooth muscle cells was confirmed by detecting mRNA and protein from the transgene. Functional restoration was determined by recording pinacidil-based KATP current by whole cell voltage clamping of isolated aortic vascular smooth muscle cells isolated from the transgenic restored mice. Despite successful restoration of KATP channels in vascular smooth muscle, transgene-restored SUR2 null mice continued to display frequent episodes of spontaneous ST segment elevation, identical to the phenotype seen in SUR2 null mice. As in SUR2 null mice, ST segment elevation was frequently followed by atrioventricular heart block. ST segment elevation and coronary perfusion pressure in the restored mice did not differ significantly between transgene-negative and transgene-positive SUR2 null mice. We conclude that spontaneous coronary vasospasm and sudden death in SUR2 null mice arises from a coronary artery vascular smooth muscle-extrinsic process.

Drosophila as a model for the identification of genes causing adult human heart disease

Drosophila melanogaster genetics provides the advantage of molecularly defined P-element insertions and deletions that span the entire genome. Although Drosophila has been extensively used as a model system to study heart development, it has not been used to dissect the genetics of adult human heart disease because of an inability to phenotype the adult fly heart in vivo. Here we report the development of a strategy to measure cardiac function in awake adult Drosophila that opens the field of Drosophila genetics to the study of human dilated cardiomyopathies. Through the application of optical coherence tomography, we accurately distinguish between normal and abnormal cardiac function based on measurements of internal cardiac chamber dimensions in vivo. Normal Drosophila have a fractional shortening of 87 +/- 4%, whereas cardiomyopathic flies that contain a mutation in troponin I or tropomyosin show severe impairment of systolic function. To determine whether the fly can be used as a model system to recapitulate human dilated cardiomyopathy, we generated transgenic Drosophila with inducible cardiac expression of a mutant of human delta-sarcoglycan (deltasg(S151A)), which has previously been associated with familial dilated cardiomyopathy. Compared to transgenic flies overexpressing wild-type deltasg, or the standard laboratory strain w(1118), Drosophila expressing deltasg(S151A) developed marked impairment of systolic function and significantly enlarged cardiac chambers. These data illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and the applicability of the vast genetic resources available in Drosophila to systematically study the genetic mechanisms responsible for human cardiac disease.

Therapy insight: cardiovascular complications associated with muscular dystrophies

The muscular dystrophies are commonly associated with cardiovascular complications, including cardiomyopathy and cardiac arrhythmias. These complications are caused by intrinsic defects in cardiomyocyte and cardiac conduction system function, and by the presence of severe skeletal muscle disease, which also contributes to cardiac dysfunction. Unlike the skeletal muscle degenerative process, for which treatment options are currently limited, therapy is available for the cardiovascular complications that accompany muscular dystrophy. New therapies for skeletal muscle degeneration are moving into clinical trials and, ultimately, into clinical practice. These therapies are expected to also improve the cardiac function, longevity and wellbeing of muscular dystrophy patients.

Cardiomyopathy Associated with Microcirculation Dysfunction in Laminin α4 Chain-deficient Mice

Laminin alpha4 chain is a component of extracellular matrix (ECM) laminin-8 and -9 and serves dual roles as a structure protein and as a signaling molecule. The abundance of laminin alpha4 chain transcripts in the heart suggests an important role of this protein in cardiovascular development and function. In this study, we demonstrate that laminin alpha4 deficient mice gradually develop cardiac hypertrophy with impaired function. We show that depletion of laminin alpha4 chain did not alter the levels of dystrophin-glycoprotein complex (DGC) components or affect cell membrane integrity. No alteration in integrin beta 1D protein was observed in terms of expression level or distribution pattern, indicating that the postnatal development of cardiac hypertrophy and cardiomyopathy in these mice is unlikely associated with the stability of sarcolemmal DGC and integrin complexes. Moreover, cardiomyocytes isolated from Lama4-/- mutant hearts maintained their contractility in vitro. In contrast, elevated levels of hypoxia-inducible factor 1alpha (Hif1alpha) and vascular endothelial growth factor A (Vegfa) transcripts, along with multiple foci of cardiomyocyte degeneration and fibrosis suggested sustained cardiac ischemia. Electron microscopy confirmed malformed blood vessels and wide pericapillary ECM spaces, suggesting the presence of microcirculation abnormalities in Lama4-/- mutant hearts. We thus conclude that mutation in the laminin alpha4 chain leads to abnormal cardiovascular ECM structure that cause insufficient oxygen supply to the heart and the subsequent ischemic cardiac phenotype observed. Our study links the genetic deficiency of an ECM protein to cardiomyopathy and implies a novel pathway of idiopathic cardiomyopathy in human.

Genetic causes of human heart failure

Factors that render patients with cardiovascular disease at high risk for heart failure remain incompletely defined. Recent insights into molecular genetic causes of myocardial diseases have highlighted the importance of single-gene defects in the pathogenesis of heart failure. Through analyses of the mechanisms by which a mutation selectively perturbs one component of cardiac physiology and triggers cell and molecular responses, studies of human gene mutations provide a window into the complex processes of cardiac remodeling and heart failure. Knowledge gleaned from these studies shows promise for defining novel therapeutic targets for genetic and acquired causes of heart failure.

The interaction of coronary tone and cardiac fibrosis

Regulation of coronary vascular tone is critical for proper perfusion and function of the myocardium. Many disease processes result in compromised regulation of coronary vascular tone and impaired myocardial perfusion. A common result of coronary vascular dysfunction is the development of areas of replacement fibrosis within the myocardium and surrounding the vasculature. Both intravascular processes, such as coronary atherosclerosis and endothelial dysfunction, and extravascular processes, including compromised myocardial metabolism, hormone excesses, and altered local signaling, may result in coronary vascular dysregulation. Coronary occlusion events, in turn, lead to myocardial damage and the activation of inflammatory cells and fibroblasts. The role of fibroblasts in regulating myocardial fibrosis and the contribution of myofibroblasts, cells that have limited contractile potential while retaining many of the extracellular matrix regulating processes of the fibroblast, may also contribute to the development of myocardial disease. In this review we examine the recent literature on myocardial fibrosis and myofibroblast activity, highlighting the effects of several classes of cardiovascular agents on the remodeling process.