Atrial structural remodeling in patients with atrial chronic fibrillations and in animal models

Arrhythmia's atrium fibrillation (AF) is the most often met in clinical setting and it is associated with an increased in mortality risk. For profound the structural changes in chronic AF, we are studied the morphological changes of atrium biopsies to be effected at 175 patients. With sustained AF malformative and valvular acquired cardiac diseases operated under extracorporeal circulation. Similar studies we are effected to 11 dogs with partial coronary obstructions to a made periodical EKG investigations. The morphological changes mainly concern accommodation (dedifferentiation) of cardiomyocytes (particularly at experimental model) and mal-accommodation (degeneration of cells with fibrosis replacement features) particularly in acquired valvular diseases. These changes were often interfered. Over study, maintain the hypothesis that the structural changes to be an accommodation more than degenerative response to AF.

Oxidation enhances myofibrillar protein degradation via calpain and caspase-3

Oxidative stress has been linked to accelerated rates of proteolysis and muscle fiber atrophy during periods of prolonged skeletal muscle inactivity. However, the mechanism(s) that links oxidative stress to muscle protein degradation remains unclear. A potential connection between oxidants and accelerated proteolysis in muscle fibers is that oxidative modification of myofibrillar proteins may enhance their susceptibility to proteolytic processing. In this regard, it is established that protein oxidation promotes protein recognition and degradation by the 20S proteasome. However, it is unknown whether oxidation of myofibrillar proteins increases their recognition and degradation by calpains and/or caspase-3. Therefore, we tested the hypothesis that oxidative modification of myofibrillar proteins increases their susceptibility to degradation by both calpains and caspase-3. To test this postulate, myofibrillar proteins were isolated from rat skeletal muscle and exposed to in vitro oxidation to produce varying levels of protein modification. Modified proteins were then independently incubated with active calpain I, calpain II, or caspase-3 and the rates of protein degradation were assessed via peptide mapping. Our results reveal that increased protein oxidation results in a stepwise escalation in the degradation of myofibrillar proteins by calpain I, calpain II, and caspase-3. These findings provide a mechanistic link connecting oxidative stress with accelerated myofibrillar proteolysis during disuse muscle atrophy.

Metformin selectively attenuates mitochondrial H2O2 emission without affecting respiratory capacity in skeletal muscle of obese rats

Metformin is a widely prescribed drug for treatment of type 2 diabetes, although no cellular mechanism of action has been established. To determine whether in vivo metformin treatment alters mitochondrial function in skeletal muscle, respiratory O(2) flux and H(2)O(2) emission were measured in saponin-permeabilized myofibers from lean and obese (fa/fa) Zucker rats treated for 4 weeks with metformin. Succinate- and palmitoylcarnitine-supported respiration generated greater than twofold higher rates of H(2)O(2) emission in myofibers from untreated obese versus lean rats, indicative of an obesity-associated increased mitochondrial oxidant emitting potential. In conjunction with improved glycemic control, metformin treatment reduced H(2)O(2) emission in muscle from obese rats to rates near or below those observed in lean rats during both succinate- and palmitoylcarnitine-supported respiration. Surprisingly, metformin treatment did not affect basal or maximal rates of O(2) consumption in muscle from obese or lean rats. Ex vivo dose-response experiments revealed that metformin inhibits complex I-linked H(2)O(2) emission at a concentration approximately 2 orders of magnitude lower than that required to inhibit respiratory O(2) flux. These findings suggest that therapeutic concentrations of metformin normalize mitochondrial H(2)O(2) emission by blocking reverse electron flow without affecting forward electron flow or respiratory O(2) flux in skeletal muscle.

Usefulness of the ultrastructural and immunohistochemical analysis of cardiac biopsy in affected heart

In the last few years endomyocardial biopsy becomes a useful diagnostic tool for the investigation of idiopathic dilated cardiomyopathy. The aim of our current study was to try to identify ultrastructural and immunohistochemical specificity of truncated cardiac proteins in affected heart. The focal loss of plasma membrane continuity together with the lack of dystrophin activity in affected myocytes facilitated to find mutation in dystrophin gene. The accumulation of granulofilamentous desmin-positive material in cytoplasm of myocytes was the main indicator of presented mutation in the desmin gene. Nuclear structure remodeling, concomitantly with loss of lamin A/C activity, contributed to identify mutation in lamin A/C gene. Analysis of hypertrophic heart with disarray of sarcomeres and lack of I-Z-I bands suggested embryonic faiulure in titin activity. All this findings indicate that endomyocardial biopsy reperesent a useful method for a correct diagnosis of heart dysfunction.

The absence of pathological myofibre disarray in the diabetic heart: is it a paradox?

Myofibre disarray in progressive hypertrophic cardiomyopathy (HCM) is a well established pathological cardiac tissue change and thereby represents a biomarker for that condition. On the other hand, in diabetic cardiomyopathy, myofibre disarray historically has been reported not to occur. This is surprising given that many of the pathological, remodelling and mechanical changes that present in the diabetic ventricle are also present in HCM, for example, myocardial stiffness, myocardial hypertrophy, apoptosis, cell slippage, extensive collagen expression and fibrosis. The question therefore begs is the absence of myocyte disarray in the diabetic heart a paradox or simply an oversight?

Diffusion spectrum MRI tractography reveals the presence of a complex network of residual myofibers in infarcted myocardium

BACKGROUND

Changes in myocardial microstructure are important components of the tissue response to infarction but are difficult to resolve with current imaging techniques. A novel technique, diffusion spectrum MRI tractography (DSI tractography), was thus used to image myofiber architecture in normal and infarcted myocardium. Unlike diffusion tensor imaging, DSI tractography resolves multiple myofiber populations per voxel, thus generating accurate 3D tractograms, which we present in the myocardium for the first time.

METHODS AND RESULTS

DSI tractography was performed at 4.7 T in excised rat hearts 3 weeks after left coronary artery ligation (n=4) and in 4 age-matched controls. Fiber architecture in the control hearts varied smoothly from endocardium to epicardium, producing a symmetrical array of crossing helical structures in which orthogonal myofibers were separated by fibers with intermediate helix angles. Fiber architecture in the infarcted hearts was severely perturbed. The infarct boundary in all cases was highly irregular and punctuated repeatedly by residual myofibers extending from within the infarct to the border zones. In all infarcts, longitudinal myofibers extending toward the basal-anterior wall and transversely oriented myofibers extending toward the septum lay in direct contact with each other, forming nodes of orthogonal myofiber intersection or contact.

CONCLUSIONS

DSI tractography resolves 3D myofiber architecture and reveals a complex network of orthogonal myofibers within infarcted myocardium. Meshlike networks of orthogonal myofibers in infarcted myocardium may resist mechanical remodeling but also probably increase the risk for lethal reentrant arrhythmias. DSI tractography thus provides a new and important readout of tissue injury after myocardial infarction.

Myofibrillar myopathy with limb-girdle phenotype in a Thai patient

Myofibrillar myopathy (MFM) encompasses a genetically and clinically heterogeneous group of inherited or sporadic skeletal muscle disorders characterized pathologically by the presence of myofibrillar dissolution associated with accumulation of myofibrillar degradation products and ectopic expression of multiple proteins especially Z-disk related proteins. Patients with MFM initially present with muscle weakness and commonly developed cardiomypathy in the advanced stage. To date, mutations of genes encoding Z-disk proteins or proteins maintaining myofibrillar integrity including ZASP, MYOT, DES, FLNC and CRYAB underlie MFM. The authors herein report a 29-year-old Thai woman with a clinical diagnosis of autosomal dominant limb-girdle muscular dystrophy (LGMD1) who has one affected grandmother. The patient was subsequently found to have MFM based on her myopathological findings. Analyses of all MFM-genes known to date revealed no mutations. The current case emphasizes the importance of muscle biopsy in LGMD1 patients and a wide range of phenotypic variations among patients with MFM. The causative genes underlying the majority of MFM remain uncovered. Close monitoring of the cardiac function is crucial to prevent mortality among these patients.

Maintenance of muscle mass, fiber size, and contractile function in mice lacking the Z-disc protein myotilin

BACKGROUND

Myofibrillar myopathies constitute a rare group of congenital neuromuscular disorders, frequently associated with mutations in Z-disc proteins such as myotilin. Myotilin location and interactions with other Z-disc proteins are clearly defined, but its role in the regulation of muscle structure and function remains unknown. The present study aims at investigating this specific role of myotilin.

METHODS

Skeletal and cardiac muscles were collected from adult mice with a targeted deletion of myotilin (myo(-/-)) and wild-type animals (myo(+/+)).

RESULTS AND CONCLUSION

Similar skeletal and cardiac muscle weights were observed in myo(-/-) and myo(+/+) mice. At the muscle cell level, the size and force production of single membrane permeabilized fibers were identical between myo(-/-) and myo(+/+) rodents. Thus, myotilin does not have a significant influence on muscle mass, muscle fiber size, or regulation of muscle contraction. Alternatively, compensatory over-expressions of other elements including proteins from the same subfamily, or Z-disc proteins such as telethonin, or intermediate filaments may compensate for the lack of myotilin.

Distinct muscle imaging patterns in myofibrillar myopathies

OBJECTIVE

To compare muscle imaging findings in different subtypes of myofibrillar myopathies (MFM) in order to identify characteristic patterns of muscle alterations that may be helpful to separate these genetic heterogeneous muscular disorders.

METHODS

Muscle imaging and clinical findings of 46 patients with MFM were evaluated (19 desminopathy, 12 myotilinopathy, 11 filaminopathy, 1 alphaB-crystallinopathy, and 3 ZASPopathy). The data were collected retrospectively in 43 patients and prospectively in 3 patients.

RESULTS

In patients with desminopathy, the semitendinosus was at least equally affected as the biceps femoris, and the peroneal muscles were never less involved than the tibialis anterior (sensitivity of these imaging criteria to detect desminopathy in our cohort 100%, specificity 95%). In most of the patients with myotilinopathy, the adductor magnus showed more alterations than the gracilis muscle, and the sartorius was at least equally affected as the semitendinosus (sensitivity 90%, specificity 93%). In filaminopathy, the biceps femoris and semitendinosus were at least equally affected as the sartorius muscle, and the medial gastrocnemius was more affected than the lateral gastrocnemius. The semimembranosus mostly showed more alterations than the adductor magnus (sensitivity 88%, specificity 96%). Early adult onset and cardiac involvement was most often associated with desminopathy. In patients with filaminopathy, muscle weakness typically beginning in the 5th decade of life was mostly pronounced proximally, while late adult onset (>50 years) with distal weakness was more often present in myotilinopathy.

CONCLUSIONS

Muscle imaging in combination with clinical data may be helpful for separation of distinct myofibrillar myopathy subtypes and in scheduling of genetic analysis.

Inactivation of zebrafish mrf4 leads to myofibril misalignment and motor axon growth disorganization

Mrf4 is a basic helix-loop-helix (bHLH) transcription factor associated with myogenesis. Two mrf4 transcripts, mrf4_tv1 and mrf4_tv2, were identified in zebrafish generated by alternative splicing. To study their biological functions, we separately injected the Mrf4-morpholinos, including MO1 (mrf4_tv1:mrf4_tv2 knockdown), MO2+MO3 (mrf4_tv1:mrf4_tv2 knockdown), MO3 (mrf4_tv1 knockdown), and MO4 (mrf4_tv2 knockdown), into zebrafish embryos to observe mrf4 gene knockdown phenotypes. No phenotypic abnormalities were observed following injection with 0.5 ng of MO1 but those injected with 4.5, 9, or 13.5 ng displayed curved-body phenotypes, such as indistinct somite boundaries, and a lack of uniformly sized cell blocks. Similar results were also observed in the (MO2+MO3)-, MO3-, and MO4-injected groups. To further investigate the molecular mechanisms that lead to curved-body phenotypes, we stained embryos with alpha-bungrotoxin and specific monoclonal antibodies F59, Znp1, and Zn5 to detect morphological changes in acetyl-choline receptor (AChR) clusters, muscle fibers, common path of the primary neurons, and secondary neurons axonal projections, respectively. Our results show that the muscle fibers of mrf4_(tv1:tv2)-morphant aligned disorderly and lost their integrity and attachment, while the defects became milder in either mrf4_tv1-morphant or mrf4_tv2-morphant. On the other hand, reduced axonal projections and AChR clusters were found in both mrf4_tv2-morphant and mrf4_(tv1:tv2)-morphant but distributed normally in the mrf4_tv1-morphant. We conclude that Mrf4_tv2 is involved in alignment of muscle fibers, and Mrf4_tv1 might have cooperative function with Mrf4_tv2 in muscle fiber alignment, without affecting the muscle-nerve connection.

Alcohol and dilated cardiomyopathy

Alcohol has been considered a cardiotoxin for over a century, but the pathogenesis and natural history of alcohol-related heart disease remains obscure. The diagnosis still rests on the coincidence of alcoholism and a dilated hypocontractile heart in the absence of any other cause of dilated cardiomyopathy. Advances have been made in our understanding of the effects of acute and chronic alcohol administration both at a haemodynamic and cellular level, and recent studies have indicated that preclinical changes in LV dimensions and function are common in alcoholics. It is not known whether clinical cardiomyopathy, which develops in only 1-2% of heavy drinkers, occurs because of genetic predisposition, or the presence of synergistic cardiovascular risk factors. Abstinence remains the mainstay of treatment, but the prognosis is poor after development of frank heart failure.

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

A number of studies have been conducted recently on the model organism Drosophila to determine the function of genes involved in human disease, including those implicated in neurological disorders, cancer and metabolic and cardiovascular diseases. The simple structure and physiology of the Drosophila heart tube together with the available genetics provide a suitable in vivo assay system for studying cardiac gene functions. In our study, we focus on analysis of the role of dystrophin (Dys) in heart physiology. As in humans, the Drosophila dys gene encodes multiple isoforms, of which the large isoforms (DLPs) and a truncated form (Dp117) are expressed in the adult heart. Here, we show that the loss of dys function in the heart leads to an age-dependent disruption of the myofibrillar organization within the myocardium as well as to alterations in cardiac performance. dys RNAi-mediated knockdown in the mesoderm also shortens lifespan. Knockdown of all or deletion of the large isoforms increases the heart rate by shortening the diastolic intervals (relaxation phase) of the cardiac cycle. Morphologically, loss of the large DLPs isoforms causes a widening of the cardiac tube and a lower fractional shortening, a phenotype reminiscent of dilated cardiomyopathy. The dilated dys mutant phenotype was reversed by expressing a truncated mammalian form of dys (Dp116). Our results illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and other muscular-dystrophy-associated phenotypes.

Kidney fibrosis in hypertensive rats: role of oxidative stress

Fibrosis of the glomerulus and the tubulointerstitium occurs in patients with hypertension. Studies have shown that renal oxidative stress appears in hypertensive kidney disease. The potential role of oxidative stress in renal fibrogenesis remains to be elucidated. Herein, we tested the hypothesis that oxidative stress contributes to the development of renal fibrosis during hypertension.Sprague-Dawley rats received angiotensin II (AngII; 9 microg/h s.c.) for 4 weeks with/without co-treatment of antioxidants, apocynin and tempol (120 mg/kg/day each, p.o.). Untreated rats served as controls. Appearance of renal oxidative stress and its effect on the expression of transforming growth factor (TGF)-beta(1), population of myofibroblasts, collagen synthesis/degradation and fibrosis in kidneys were examined. Chronic AngII infusion elevated systemic blood pressure (228 +/- 6 mm Hg), which was accompanied with extensive renal fibrosis and oxidative stress represented as upregulated NADPH oxidase and suppressed superoxide dismutase (SOD). Co-treatment with antioxidants led to: (1) markedly decreased renal NADPH oxidase; (2) significantly attenuated gene expression of TGF-beta(1), type I collagen, and tissue inhibitors of matrix metalloproteinase (TIMP)-I/-II in the kidney; (3) largely reduced population of myofibroblasts in both the cortex and medulla; (4) significantly reduced renal collagen volume, and (5) partially suppressed blood pressure (190 +/- 8 mm Hg). Thus, prolonged AngII administration promotes renal oxidative stress, which is associated with hypertensive renal disease. AngII induces renal oxidative stress by increasing NADPH oxidase and reducing SOD in the kidney, which, in turn, upregulates collagen synthesis, while suppressing collagen degradation, thereby promoting the development of fibrosis in kidneys of hypertensive rats.

Post-ischaemic myocardial dysfunction (stunning) results from myofibrillar oedema

OBJECTIVE

To test the hypothesis that myocardial stunning is due to myofibrillar oedema.

METHODS

Experiments were performed in anaesthetised closed-chest pigs. In 15 pigs (group 1), myocardial stunning was produced by repetitive ischaemia and reperfusion; 5 pigs each were studied at 2 hours, 2 days, and 5 days later. Circumferential left ventricular (LV) mid-wall myocardial strain (E(cc)) was estimated in vivo using tagged magnetic resonance imaging. Myocardial water content (MWC) was measured post mortem, from which interfilament lattice distance (d) was calculated. In 6 pigs (group 2), myocardial dysfunction was produced by intracoronary administration of a mast cell degranulator. Animals were euthanised immediately upon induction of regional LV dysfunction to avoid development of inflammation. In 4 pigs (group 3), transmission electron microscopy (EM) was performed to quantify d in stunned versus normal myocardium.

RESULTS

In group 1 pigs, MWC was raised in the stunned compared with normal myocardium (p<0.02) and decreased over time. An inverse relation was found between E(cc) and MWC in the stunned myocardium (r = -0.81) and between E(cc) and d (r = -0.90). A similar relation was noted between wall thickening and increase in MWC in group 2 (r = -0.84) pigs. In group 3 pigs, d on EM was significantly lower (40 (3) nmol/l) in normal myocardium than in stunned myocardium (46.4 (4) nmol/l), p<0.001.

CONCLUSIONS

Ischaemia-reperfusion results in myocardial oedema, with consequent myocyte swelling and myofibrillar oedema. The latter leads to an increase in d, causing myosin heads to either fail to latch, or to latch improperly, onto the actin filament with poor force generation, leading to myocardial dysfunction. As the myocardial oedema abates, myocyte function improves.

Myxobolus sp. can cause in vivo myoliquefaction in the host Paralichthys orbignyanus (Osteichthyes, Paralichthydae)

We found intense myoliquefaction in vivo among specimens of wild and farmed South American flatfish Paralichthys orbignyanus Valenciennes, 1839. The soft flesh condition was attributed to Myxobolus sp. since the fish were not infected by myxosporeans which are usually associated with this condition (Kudoa spp.), and other causes (bacteria, fungi) were not found. The histopathology of the infection is described.

Oxidative stress in desminopathies and myotilinopathies: a link between oxidative damage and abnormal protein aggregation

Myotilinopathies and desminopathies are subgroups of myofibrillar myopathies (MFM) caused by mutations in myotilin and desmin genes, respectively. They are characterized by the presence of protein aggregates in muscle cells. As oxidation of proteins facilitates their aggregation and makes them more resistant to proteolysis, the present study was geared to analyze oxidative stress in MFM. For this purpose, markers of glycoxidation, lipoxidation and nitration were examined with gel electrophoresis and Western blotting, single immunohistochemistry, and double- and triple-labeling immunofluorescence and confocal microscopy in muscle biopsies from patients suffering from myotilinopathy and desminopathy. Increased levels of glycation-end products (AGEs), N-carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL), malondialdehyde-lysine (MDAL), 4-hydroxynonenal (HNE) and nitrotyrosine (N-tyr) were found in MFM. Furthermore, aberrant expression of AGE, CML, CEL, MDAL and HNE, as well as of neuronal, inducible and endothelial nitric oxide synthases (nNOS, iNOS, eNOS), and superoxide dismutase 2 (SOD2), was found in muscle fibers containing protein aggregates in myotilinopathies and desminopathies. AGE, ubiquitin and p62 co-localized in several muscle fibers in MFM. As oxidized proteins are vulnerable to misfolding and are resistant to degradation by the UPS, the present observations support a link between oxidative stress, protein aggregation and abnormal protein deposition in MFMs.

Essential role for Dicer during skeletal muscle development

microRNAs (miRNAs) regulate gene expression post-transcriptionally by targeting mRNAs for degradation or by inhibiting translation. Dicer is an RNase III endonuclease which processes miRNA precursors into functional 21-23 nucleotide RNAs that are subsequently incorporated into the RNA-induced silencing complex. miRNA-mediated gene regulation is important for organogenesis of a variety of tissues including limb, lung and skin. To gain insight into the roles of Dicer and miRNAs in mammalian skeletal muscle development, we eliminated Dicer activity specifically in the myogenic compartment during embryogenesis. Dicer activity is essential for normal muscle development during embryogenesis and Dicer muscle mutants have reduced muscle miRNAs, die perinatally and display decreased skeletal muscle mass accompanied by abnormal myofiber morphology. Dicer mutant muscles also show increased apoptosis and Cre-mediated loss of Dicer in Myod-converted myoblasts results in enhanced cell death. These observations demonstrate key roles for Dicer in skeletal muscle and implicate miRNAs as critical components required for embryonic myogenesis.

Ullrich myopathy phenotype with secondary ColVI defect identified by confocal imaging and electron microscopy analysis

Ullrich congenital muscular dystrophy (UCMD) is clinically characterized by muscle weakness, proximal contractures and distal hyperlaxity and morphologically branded by absence or reduction of collagen VI (ColVI), in muscle and in cultured fibroblasts. The ColVI defect is generally related to COL6 genes mutations, however UCDM patients without COL6 mutations have been recently reported, suggesting genetic heterogeneity. We report comparative morphological findings between a UCMD patient harboring a homozygous COL6A2 mutation and a patient with a typical UCMD phenotype in which mutations in COL6 genes were excluded. The patient with no mutations in COL6 genes exhibited a partial ColVI defect, which was only detected close to the basal membrane of myofibers. We describe how confocal microscopy and rotary-shadowing electron microscopy may be useful to identify a secondary ColVI defect.

Myofibre damage in human skeletal muscle: effects of electrical stimulation versus voluntary contraction

Disruption to proteins within the myofibre after a single bout of unaccustomed eccentric exercise is hypothesized to induce delayed onset of muscle soreness and to be associated with an activation of satellite cells. This has been shown in animal models using electrical stimulation but not in humans using voluntary exercise. Untrained males (n=8, range 22-27 years) performed 210 maximal eccentric contractions with each leg on an isokinetic dynamometer, voluntarily (VOL) with one leg and electrically induced (ES) with the other leg. Assessments from the skeletal muscle were obtained prior to exercise and at 5, 24, 96 and 192 h postexercise. Muscle tenderness rose in VOL and ES after 24 h, and did not differ between groups. Maximal isometric contraction strength, rate of force development and impulse declined in the VOL leg from 4 h after exercise, but not in ES (except at 24 h). In contrast, a significant disruption of cytoskeletal proteins (desmin) and a rise of myogenic growth factors (myogenin) occurred only in ES. Intracellular disruption and destroyed Z-lines were markedly more pronounced in ES (40%) compared with VOL (10%). Likewise, the increase in satellite cell markers [neural cell adhesion molecule (N-CAM) and paired-box transcription factor (Pax-7)] was more pronounced in ES versus VOL. Finally, staining of the intramuscular connective tissue (tenascin C) was increased equally in ES and VOL after exercise. The present study demonstrates that in human muscle, the delayed onset of muscle soreness was not significantly different between the two treatments despite marked differences in intramuscular histological markers, in particular myofibre proteins and satellite cell markers. An increase in tenascin C expression in the midbelly of the skeletal muscle in both legs provides further evidence of a potential role for the extracellular matrix in the phenomenon of delayed onset of muscle soreness.

Conditional deletion of focal adhesion kinase leads to defects in ventricular septation and outflow tract alignment

To examine a role for focal adhesion kinase (FAK) in cardiac morphogenesis, we generated a line of mice with a conditional deletion of FAK in nkx2-5-expressing cells (herein termed FAKnk mice). FAKnk mice died shortly after birth, likely resulting from a profound subaortic ventricular septal defect and associated malalignment of the outflow tract. Additional less penetrant phenotypes included persistent truncus arteriosus and thickened valve leaflets. Thus, conditional inactivation of FAK in nkx2-5-expressing cells leads to the most common congenital heart defect that is also a subset of abnormalities associated with tetralogy of Fallot and the DiGeorge syndrome. No significant differences in proliferation or apoptosis between control and FAKnk hearts were observed. However, decreased myocardialization was observed for the conal ridges of the proximal outflow tract in FAKnk hearts. Interestingly, chemotaxis was significantly attenuated in isolated FAK-null cardiomyocytes in comparison to genetic controls, and these effects were concomitant with reduced tyrosine phosphorylation of Crk-associated substrate (CAS). Thus, it is possible that ventricular septation and appropriate outflow tract alignment is dependent, at least in part, upon FAK-dependent CAS activation and subsequent induction of polarized myocyte movement into the conal ridges. Future studies will be necessary to determine the precise contributions of the additional nkx2-5-derived lineages to the phenotypes observed.

The pathomechanism of filaminopathy: altered biochemical properties explain the cellular phenotype of a protein aggregation myopathy

Myofibrillar myopathy (MFM) is a pathologically defined group of hereditary human muscle diseases, characterized by focal myofibrillar destruction and cytoplasmic aggregates that contain several Z-disc-related proteins. The previously reported MFM-associated mutation (8130G --> A; W2710X) in the filamin C gene (FLNC) leads to a partial disturbance of the secondary structure of the dimerization domain of filamin C, resulting in massive protein aggregation in skeletal muscle fibers of the patients. Here, we provide a thorough characterization of the biochemical, biophysical and cellular properties of the mutated filamin C polypeptide. Our experiments revealed that the mutant dimerization domain is less stable and more susceptible to proteolysis. As a consequence, it does not dimerize properly and forms aggregates in vitro. Furthermore, the expression of mutant filamin in cultured cells results in the formation of protein aggregates. The mutant filamin does not associate with wild type filamin. These findings are of great importance to explain the pathomechanism of this disease.

Phenotypic patterns of desminopathy associated with three novel mutations in the desmin gene

Desminopathy represents a subgroup of myofibrillar myopathies caused by mutations in the desmin gene. Three novel disease-associated mutations in the desmin gene were identified in unrelated Spanish families affected by cardioskeletal myopathy. A selective pattern of muscle involvement, which differed from that observed in myofibrillar myopathy resulting from mutations in the myotilin gene, was observed in each of the three families with novel mutations and each of three desminopathy patients with known desmin mutations. Prominent joint retractions at the ankles and characteristic nasal speech were observed early in the course of illness. These findings suggest that muscle imaging in combination with routine clinical and pathological examination may be helpful in distinguishing desminopathy from other forms of myofibrillar myopathy and ordering appropriate molecular investigations.

Cardiomyocyte-restricted over-expression of C-type natriuretic peptide prevents cardiac hypertrophy induced by myocardial infarction in mice

OBJECTIVE

Infused C-type natriuretic peptide (CNP) was recently found to play a cardioprotective role in preventing myocardial ischaemia/reperfusion (I/R) injury and improving cardiac remodelling after myocardial infarction (MI) in rats. Our study aimed to investigate the effect of cardiomyocyte-specific CNP over-expression on I/R injury and MI in transgenic mice.

METHODS AND RESULTS

We generated transgenic (TG) mice over-expressing CNP in cardiomyocytes. Elevated CNP expression on RNA and protein levels was demonstrated by RNase-protection assay and radioimmunoassay. Male TG mice and age-matched wild-type (WT) littermates were subjected to 1-hour global myocardial ischaemia and 23 h of reperfusion or permanent ligation of the coronary artery for 3 weeks. Infarct size did not differ between the WT and TG groups in mice subjected to I/R. In mice that underwent permanent ligation of coronary arteries, both left and right ventricular hypertrophy were prevented by CNP over-expression 3 weeks post-MI. Histological analysis revealed less necrosis, muscular degeneration and inflammation in infarcted TG mice. Impairment of cardiac function was less pronounced in transgenic animals than in the wild-type controls.

CONCLUSIONS

Over-expression of CNP in cardiomyocytes does not affect I/R-induced infarct size but prevents cardiac hypertrophy induced by MI. Therefore, CNP may represent a potent therapeutic target for the treatment of patients with cardiac hypertrophy induced by myocardial infarction or other aetiology.