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.

Effects of Thalidomide on Isoprenaline-Induced Acute Myocardial Injury: A Haemodynamic, Histopathological and Ultrastructural Study

In the present study, we investigated the cardioprotective effects of thalidomide in a rat model of acute myocardial injury, induced by subcutaneous injection of isoprenaline hemisulphate (85 mg/kg per day for 2 days). Thalidomide (75/150/300 mg/kg) or vehicle (dimethylsulphoxide) or saline (0.9% NaCl) was administered orally for 14 days and isoprenaline injection on the 12th and 13th days. Cardiovascular responses (arterial and left ventricular haemodynamic parameters and heart rate) were obtained in anaesthetized rats on the 14th day. Histopathological and electronmicroscopical analysis of myocardial injury was done. The results showed that thalidomide 300 mg/kg per day orally caused significant improvement in isoprenaline-induced reduction of cardiac function with increases in maximum rate of pressure development (+LVdP/dt, P < 0.001) and maximum rate of pressure decline (-LVdP/dt, P < 0.001) and decreases in left ventricular end-diastolic pressure (P < 0.01), systolic arterial pressure (P < 0.001), diastolic arterial pressure (P < 0.001), mean arterial pressure (P < 0.001) and heart rate (P < 0.001). The myocardial injury caused by isoprenaline was significantly reduced by thalidomide treatment as judged by the reduction of myocardial necrosis, ultrastructural changes such as mitochondria and myofibril damage, 300 mg/kg being the most effective dose. In conclusion, oral administration of thalidomide is able to ameliorate isoprenaline-induced myocardial injury and impaired myocardial function in spite of decreases in systolic arterial pressure, diastolic arterial pressure and mean arterial pressure, which may be due to its depressant effect on the sino-atrial node and sedative action.

Tropomodulin expression in developing hearts of normal and cardiac mutant Mexican axolotl

In the axolotl, Ambystoma mexicanum, a simple, recessive cardiac-lethal mutation in gene "c" results in the hearts of c/c homozygous animals being deficient in sarcomeric tropomyosin (TM) and failing to form mature myofibrils. Subsequently, the mutant hearts do not beat. A three-step model of myofibril assembly recently developed in cell culture prompted a reassessment of the myofibril assembly process in mutant hearts using a relatively new late marker for thin filament assembly, tropomodulin (Tmod). This is, to the best of our knowledge, the first report of tropomodulin in an amphibian system. Tropomodulin antibodies were immunolocalized to the ends of the thin filaments. Tropomodulin was also found in discrete punctate spots in normal and mutant hearts, often in linear arrays suggestive of early myofibril formation. The tropomodulin spots assessed in stage 41/42 mutant hearts co-localized with antibodies to other myofibrillar proteins indicative of nascent myofibril formation. This suggests a failure of elongation/maturation of nascent myofibrils, which could be a consequence of decreased TM levels or increased Tmod/ TM ratio. Unlike tropomyosin, there is no apparent decrease in the level of Tmod expression in mutant hearts.

Nemaline myopathy with minicores caused by mutation of the CFL2 gene encoding the skeletal muscle actin-binding protein, cofilin-2

Nemaline myopathy (NM) is a congenital myopathy characterized by muscle weakness and nemaline bodies in affected myofibers. Five NM genes, all encoding components of the sarcomeric thin filament, are known. We report identification of a sixth gene, CFL2, encoding the actin-binding protein muscle cofilin-2, which is mutated in two siblings with congenital myopathy. The proband's muscle contained characteristic nemaline bodies, as well as occasional fibers with minicores, concentric laminated bodies, and areas of F-actin accumulation. Her affected sister's muscle was reported to exhibit nonspecific myopathic changes. Cofilin-2 levels were significantly lower in the proband's muscle, and the mutant protein was less soluble when expressed in Escherichia coli, suggesting that deficiency of cofilin-2 may result in reduced depolymerization of actin filaments, causing their accumulation in nemaline bodies, minicores, and, possibly, concentric laminated bodies.

Myostatin gene deletion prevents glucocorticoid-induced muscle atrophy

Glucocorticoids mediate muscle atrophy in many catabolic states. Myostatin expression, a negative regulator of muscle growth, is increased by glucocorticoids and myostatin overexpression is associated with lower muscle mass. This suggests that myostatin is required for the catabolic effects of glucocorticoids. We therefore investigated whether myostatin gene disruption could prevent muscle atrophy caused by glucocorticoids. Male myostatin knockout (KO) and wild-type mice were subjected to dexamethasone treatment (1 mg/kg.d for 10 d or 5 mg/kg.d for 4 d). In wild-type mice, daily administration of low-dose dexamethasone for 10 d resulted in muscle atrophy (tibialis anterior: -15%; gastrocnemius: -13%; P < 0.01) due to 15% decrease in the muscle fiber cross-sectional area (1621 +/- 31 vs. 1918 +/- 64 microm(2), P < 0.01). In KO mice, there was no reduction of muscle mass nor fiber cross-sectional area after dexamethasone treatment. Muscle atrophy after 4 d of high-dose dexamethasone was associated with increased mRNA of enzymes involved in proteolytic pathways (atrogin-1, muscle ring finger 1, and cathepsin L) and increased chymotrypsin-like proteasomal activity. In contrast, the mRNA of these enzymes and the proteasomal activity were not significantly affected by dexamethasone in KO mice. Muscle IGF-I mRNA was paradoxically decreased in KO mice (-35%, P < 0.05); this was associated with a potentially compensatory increase of IGF-II expression in both saline and dexamethasone-treated KO mice (2-fold, P < 0.01). In conclusion, our results show that myostatin deletion prevents muscle atrophy in glucocorticoid-treated mice, by blunting the glucocorticoid-induced enhanced proteolysis, and suggest an important role of myostatin in muscle atrophy caused by glucocorticoids.

Role of subcellular remodeling in cardiac dysfunction due to congestive heart failure

Although alterations in the size and shape of the heart (cardiac remodeling) are considered in explaining cardiac dysfunction during the development of congestive heart failure (CHF), there are several conditions including initial stages of cardiac hypertrophy, where cardiac remodeling has also been found to be associated with either an increased or no change in heart function. Extensive studies have indicated that cardiac dysfunction is related to defects in one or more subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma, depending upon the stage of CHF. Such subcellular abnormalities in the failing hearts have been shown to occur at both genetic and protein levels. Blockade of the renin-angiotensin system has been reported to partially attenuate changes in subcellular protein, gene expression, functional activities and cardiac performance in CHF. These observations provide support for the role of subcellular remodeling (alterations in molecular and biochemical composition of subcellular organelles) in cardiac dysfunction in the failing heart. On the basis of existing knowledge, it appears that subcellular remodeling during the process of cardiac remodeling plays a major role in the development of cardiac dysfunction in CHF.

Participation of stem cells from human cord blood in skeletal muscle regeneration of SCID mice

OBJECTIVE

In this report, we demonstrate the participation of human cord blood (HUCB) stem cells in the skeletal muscle regeneration of SCID (severe combined immunodeficient) mice.

MATERIALS AND METHODS

The HUCB cells were labeled with the PKH26 fluorescent marker or recognized by an anti-HLA-ABC or anti-beta-2-microglobulin antibody. The HUCB cells were implanted directly into the damaged mouse muscle. The regeneration process and the implanted HUCB cells were traced each day after the damage, throughout a period of 7 days, and additionally at day 30 with the use of flow cytometry and confocal microscopy.

RESULTS

The PKH26-labeled cells isolated from the regenerating muscle were positive for the anti-HLA-ABC antibody. The percentage of the PKH26(+) and HLA-ABC(+) cells decreased from day 1 to day 5. In the regenerating muscle, the percentage of the HLA-ABC(+) cells increased, as measured on days 7 and 30. Moreover, myofibers containing fragments of the PKH26-labeled sarcolemma were noticed. Labeling with the anti-human beta(2)-microglobulin antibody showed the presence of positive cells and myofibers at day 7 of the regeneration, suggesting fusion of human and mouse cells.

CONCLUSIONS

We suggest that the HUCB cells implanted into the damaged muscle are present there for at least 30 days and that they participate in the muscle regeneration. Moreover, our study shows that the implanted HUCB cells form human muscle precursor cells residing in the repaired mouse muscle. We suggest that the HUCB cell circulation after transplantation depends on SDF-1 (stromal-derived factor-1) expression in regenerating muscle.

Myofibrillar myopathy with congenital cataract and skeletal anomalies without mutations in the desmin, alphaB-crystallin, myotilin, LMNA or SEPN1 genes

Myofibrillar myopathies are genetically heterogeneous. We present a sporadic case of an 8-year-old boy with unusual combination of congenital skeletal muscle myopathy, cataract and poly/syndactyly. Muscle pathology revealed a mild myopathic picture with hyaline plaques, showing dark green staining in modified trichrome reaction, and strong immunoreactivity for alphaB-crystallin, desmin and dystrophin. Analysis of the coding sequences of the desmin, alphaB-crystallin, SEPN1, lamin A/C genes and of exon 2 of the myotilin gene showed no abnormalities in the patient. Presented case expands the wide clinical spectrum of myofibrillar myopathies, reinforcing the need for further exploration of genetic causes for this group of disorders.

Myofibrillar remodeling in cardiac hypertrophy, heart failure and cardiomyopathies

BACKGROUND

A wide variety of pathological conditions have been shown to result in cardiac remodelling and myocardial dysfunction. However, the mechanisms of transition from adaptive to maladaptive alterations, as well as those for changes in cardiac performance leading to heart failure, are poorly understood.

OBSERVATIONS

Extensive studies have revealed a broad spectrum of progressive changes in subcellular structures and function, as well as in signal transduction and metabolism in the heart, among different cardiovascular disorders. The present review is focused on identifying the alterations in molecular and biochemical structure of myofibrils (myofibrillar remodelling) in hypertrophied and failing myocardium in different types of heart diseases. Numerous changes at the level of gene expression for both contractile and regulatory proteins have already been reported in failing hearts and heart diseases; these changes are potential precursors for heart failure such as cardiac hypertrophy and cardiomyopathies. Myofibrillar remodelling, as a consequence of proteolysis, oxidation, and phosphorylation of some functional groups in both contractile and regulatory proteins in hearts failing due to different etiologies, has also been described.

CONCLUSIONS

Although myofibrillar remodelling appears to be associated with cardiac dysfunction, alterations in both contractile and regulatory proteins are dependent on the type and stage of heart disease.

Cell stress response in skeletal muscle myofibers

Cells respond to conditions that impair homeostasis through ex novo synthesis of stress proteins, which differ in subcellular localization and biological function and whose differential expression depends on the type of the stressing stimulus and on the involvement of the specific stress-response signaling cascade. The biological significance of such an event is the increased resistance against further perturbations of cell homeostasis, and thus, enhanced survival. We will review briefly the available evidence concerning stress response of skeletal muscle cells, including recent results indicating the involvement of endoplasmic reticulum stress response and proteins in skeletal muscle cell differentiation and in progression of muscle diseases.

Skeletal muscle repair in a mouse model of nemaline myopathy

Nemaline myopathy (NM), the most common non-dystrophic congenital myopathy, is a variably severe neuromuscular disorder for which no effective treatment is available. Although a number of genes have been identified in which mutations can cause NM, the pathogenetic mechanisms leading to the phenotypes are poorly understood. To address this question, we examined gene expression patterns in an NM mouse model carrying the human Met9Arg mutation of alpha-tropomyosin slow (Tpm3). We assessed five different skeletal muscles from affected mice, which are representative of muscles with differing fiber-type compositions, different physiological specializations and variable degrees of pathology. Although these same muscles in non-affected mice showed marked variation in patterns of gene expression, with diaphragm being the most dissimilar, the presence of the mutant protein in nemaline muscles resulted in a more similar pattern of gene expression among the muscles. This result suggests a common process or mechanism operating in nemaline muscles independent of the variable degrees of pathology. Transcriptional and protein expression data indicate the presence of a repair process and possibly delayed maturation in nemaline muscles. Markers indicative of satellite cell number, activated satellite cells and immature fibers including M-Cadherin, MyoD, desmin, Pax7 and Myf6 were elevated by western-blot analysis or immunohistochemistry. Evidence suggesting elevated focal repair was observed in nemaline muscle in electron micrographs. This analysis reveals that NM is characterized by a novel repair feature operating in multiple different muscles.

Transgenic mice expressing the myotilin T57I mutation unite the pathology associated with LGMD1A and MFM

Myotilin is a muscle-specific Z-disc protein with putative roles in myofibril assembly and structural upkeep of the sarcomere. Several myotilin point mutations have been described in patients with limb-girdle muscular dystrophy type 1A (LGMD1A), myofibrillar myopathy (MFM), spheroid body myopathy (SBM), three similar adult-onset, progressive and autosomal dominant muscular dystrophies. To further investigate myotilin's role in the pathogenesis of these muscle diseases, we have characterized three independent lines of transgenic mice expressing mutant (T57I) myotilin under the control of the human skeletal actin promoter. Similar to LGMD1A and MFM patients, these mice develop progressive myofibrillar pathology that includes Z-disc streaming, excess myofibrillar vacuolization and plaque-like myofibrillar aggregation. These aggregates become progressively larger and more numerous with age. We show that the mutant myotilin protein properly localizes to the Z-disc and also heavily populates the aggregates, along with several other Z-disc associated proteins. Whole muscle physiological analysis reveals that the extensor digitorum longus muscle of transgenic mice exhibits significantly reduced maximum specific isometric force compared with littermate controls. Intriguingly, the soleus and diaphragm muscles are spared of any abnormal myopathology and show no reductions in maximum specific force. These data provide evidence that myotilin mutations promote aggregate-dependent contractile dysfunction. In sum, we have established a promising patho-physiological mouse model that unifies the phenotypes of LGMD1A, MFM and SBM.

Subcellular remodeling as a viable target for the treatment of congestive heart failure

It is now well known that congestive heart failure (CHF) is invariably associated with cardiac hypertrophy, and changes in the shape and size of cardiomyocytes (cardiac remodeling) are considered to explain cardiac dysfunction in CHF. However, the mechanisms responsible for the transition of cardiac hypertrophy to heart failure are poorly understood. Several lines of evidence both from various experimental models of CHF and from patients with different types of CHF have indicated that the functions of different subcellular organelles such as extracellular matrix, sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, and nucleus are defective. Subcellular abnormalities for protein contents, gene expression, and enzyme activities in the failing heart become evident as a consequence of prolonged hormonal imbalance, metabolic derangements, and cation maldistribution. In particular, the occurrence of oxidative stress, development of intracellular Ca2+ overload, activation of proteases and phospholipases, and alterations in cardiac gene expression result in changes in the biochemical composition, molecular structure, and function of different subcellular organelles (subcellular remodeling). Not only does subcellular remodeling appear to be intimately involved in the transition of cardiac hypertrophy to heart failure, the mismatching of the function of different subcellular organelles leads to the development of cardiac dysfunction. Although blockade of the renin-angiotensin system, sympathetic nervous system, and various other hormonal actions have been reported to produce beneficial effects on cardiac remodeling and heart dysfunction in CHF, the actions of various cardiac drugs on subcellular remodeling have not been examined extensively. Some recent studies have indicated that both the angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists attenuate changes in sarcolemma, sarcoplasmic reticulum, and myofibril enzyme activities, protein contents, and gene expression, and partly improve cardiac function in the failing hearts. It is suggested that subcellular remodeling is an excellent target for the development of improved drug therapy for CHF. Furthermore, extensive studies should investigate the effects of different agents individually or in combination on reverse subcellular remodeling, cardiac remodeling, and cardiac dysfunction in various experimental models of CHF.

Parasternal intercostal muscle remodeling in severe chronic obstructive pulmonary disease

Studies in experimental animals indicate that chronic increases in neural drive to limb muscles elicit a fast-to-slow transformation of fiber-type proportions and myofibrillar proteins. Since neural drive to the parasternal intercostal muscles (parasternals) is chronically increased in patients with severe chronic obstructive pulmonary diseases (COPDs), we carried out the present study to test the hypothesis that the parasternals of COPD patients exhibit an increase in the proportions of both slow fibers and slow myosin heavy chains (MHCs). Accordingly, we obtained full thickness parasternal muscle biopsies from the third interspace of seven COPD patients (mean +/- SE age: 59 +/- 4 yr) and seven age-matched controls (AMCs). Fiber typing was done by immunohistochemistry, and MHC proportions were determined by SDS-PAGE followed by densitometry. COPD patients exhibited higher proportions of slow fibers than AMCs (73 +/- 4 vs. 51 +/- 3%; P < 0.01). Additionally, COPD patients exhibited higher proportions of slow MHC than AMCs (56 +/- 4 vs. 46 +/- 4%, P < 0.04). We conclude that the parasternal muscles of patients with severe COPD exhibit a fast-to-slow transformation in both fiber-type and MHC proportions. Previous workers have demonstrated that remodeling of the external intercostals, another rib cage inspiratory muscle, elicited by severe COPD is characterized by a slow-to-fast transformation in both fiber types and MHC isoform proportions. The physiological significance of this difference in remodeling between these two inspiratory rib cage muscles remains to be elucidated.

Myofibroblast transdifferentiation of mesothelial cells is mediated by RAGE and contributes to peritoneal fibrosis in uraemia

BACKGROUND

Uraemia is associated with fibrosis of the peritoneal membrane, even prior to the start of peritoneal dialysis. Increased carbonyl stress and the resultant formation of advanced glycation end-products (AGEs) are potentially involved. The interaction of AGEs with their cell surface receptor for AGE (RAGE) induces sustained cellular activation, including the production of the fibrogenic growth factor-beta (TGF-beta). TGF-beta is pivotal in the process of epithelial-to-mesenchymal transition with the acquisition of myofibroblast characteristics. We investigated whether antagonism of RAGE prevents uraemia-induced peritoneal fibrosis. In addition, we examined whether myofibroblast transdifferentiation of mesothelial cells contributes to peritoneal fibrosis in uraemia.

METHODS

Uraemia was induced in rats by subtotal nephrectomy. Uraemic and age-matched sham-operated rats were treated for 6 weeks with neutralizing monoclonal anti-RAGE antibodies or placebo. Expression of AGE, RAGE, cytokeratin and alpha-smooth muscle actin was evaluated using immunohistochemistry. TGF-beta expression was examined with immunostaining and western blotting, and Snail expression with western blotting. Fibrosis was quantified with a picro-sirius red staining and measurement of the hydroxyproline content of the tissue.

RESULTS

Uraemia resulted in the accumulation of AGE, up-regulation of RAGE and TGF-beta and the development of interstitial fibrosis and vascular sclerosis in the peritoneal membrane. Prominent myofibroblast transdifferentiation of mesothelial cells was identified by colocalization of cytokeratin and alpha-smooth muscle actin in submesothelial and interstitial fibrotic tissue. The antagonism of RAGE prevented the up-regulation of TGF-beta, epithelial-to-mesenchymal transition of mesothelial cells and fibrosis in uraemia.

CONCLUSION

The ligand engagement of RAGE and the subsequent up-regulation of TGF-beta induces peritoneal fibrosis in chronic uraemia. The process may be mediated by the conversion of mesothelial cells into myofibroblasts.

Novel slow-skeletal myosin (MYH7) mutation in the original myosin storage myopathy kindred

Myosin storage myopathy (OMIM 608358), a congenital myopathy characterised by subsarcolemmal, hyaline-like accumulations of myosin in Type I muscle fibres, was first described by Cancilla and Colleagues in 1971 [Neurology 1971;21:579-585] in two siblings as 'familial myopathy with probable lysis of myofibrils in type I muscle fibres'. Two mutations in the slow skeletal myosin heavy chain gene (MYH7) have recently been associated with the disease in other families. We have identified a novel heterozygous Leu1793Pro mutation in MYH7 in DNA from paraffin sections of one of the original siblings. This historical molecular analysis confirms the original cases had myosin storage myopathy.

Altered energy transfer from mitochondria to sarcoplasmic reticulum after cytoarchitectural perturbations in mice hearts

Sarcoplasmic reticulum (SR) calcium pump function requires a high local ATP/ADP ratio, which can be maintained by direct nucleotide channelling from mitochondria, and by SR-bound creatine kinase (CK)-catalysed phosphate-transfer from phosphocreatine. We hypothesized that SR calcium uptake supported by mitochondrial direct nucleotide channelling, but not bound CK, depends on the juxtaposition of these organelles. To test this, we studied a well-described model of cytoarchitectural disorganization, the muscle LIM protein (MLP)-null mouse heart. Subcellular organization was characterized using electron microscopy, and mitochondrial, SR and myofibrillar function were assessed in saponin-permeabilized fibres by measuring respiration rates and caffeine-induced tension transients. MLP-null hearts had fewer, less-tightly packed intermyofibrillar mitochondria, and more subsarcolemmal mitochondria. The apparent mitochondrial Km for ADP was significantly lower in the MLP-null heart than in control (175 +/- 15 and 270 +/- 33 microM, respectively), indicating greater ADP accessibility, although maximal respiration rate, mitochondrial content and total CK activity were unaltered. Active tension in the myofibres of MLP-null mice was 54% lower than in controls (39 +/- 3 and 18 +/- 1 mN mm(-2), respectively), consistent with cytoarchitectural disorganization. SR calcium loading in the myofibres of MLP-null mice was similar to that in control myofibres when energy support was provided via Bound CK, but approximately 36% lower than controls when energy support was provided by mitochondrial (P < 0.05). Mitochondrial support for SR calcium uptake was also specifically decreased in the desmin-null heart, which is another model of cytoarchitectural perturbation. Thus, despite normal oxidative capacity, direct nucleotide channelling to the SR was impaired in MLP deficiency, concomitant with looser mitochondrial packing and increased nucleotide accessibility to this organelle. Changes in cytoarchitecture may therefore impair subcellular energy transfer and contribute to energetic and contractile dysfunction.

Impaired subendocardial contractile myofiber function in asymptomatic aged humans, as detected using MRI

With aging, structural and functional changes occur in the myocardium without obvious impairment of systolic left ventricular (LV) function. Transmural differences in myocardial vulnerability for these changes may result in increase of transmural inhomogeneity in contractile myofiber function. Subendocardial fibrosis and impairment of subendocardial perfusion due to hypertension might change the transmural distribution of contractile myofiber function. The ratio of LV torsion to endocardial circumferential shortening (torsion-to-shortening ratio; TSR) during systole reflects the transmural distribution of contractile myofiber function. We investigated whether the transmural distribution of systolic contractile myofiber function changes with age. Magnetic resonance tissue tagging was performed to derive LV torsion and endocardial circumferential shortening. TSR was quantified in asymptomatic young [age 23.2 (SD 2.6) yr, n = 15] and aged volunteers [age 68.8 (SD 4.4) yr, n = 16]. TSR and its standard deviation were significantly elevated in the aged group [0.47 (SD 0.12) aged vs. 0.34 (SD 0.05) young; P = 0.0004]. In the aged group, blood pressure and the ratio of LV wall mass to end-diastolic volume were mildly elevated but could not be correlated to the increase in TSR. There were no significant differences in other indexes of systolic LV function such as end-systolic volume and ejection fraction. The elevated systolic TSR in the asymptomatic aged subjects suggests that aging is associated with local loss of contractile myofiber function in the subendocardium relative to the subepicardium potentially caused by subclinical pathological incidents.

High glucose alters cardiomyocyte contacts and inhibits myofibrillar formation

CONTEXT

The frequency of diabetes-related heart failure along with the prevalence of diabetes is increasing. Diabetic cardiomyopathy is considered to be a distinct disease in the absence of discernible coronary artery and other defined heart disease. Previously we have shown that glucose and palmitic acid induce degeneration of myofibrils and modulate apoptosis in cultivated cardiomyocytes.

OBJECTIVE

Here we studied the mechanisms of diabetic cardiomyopathy in more detail.

RESULTS

Streptozotocin-induced diabetes led to a significant increase in cardiac cell apoptosis. Furthermore, cardiomyocyte contacts were reduced. In vitro, prolonged exposure of cultured adult cardiomyocytes to high glucose concentrations drastically reduced myofibrillar formation. In particular, sarcomeric myosin heavy chains and cardiac alpha-actin were reduced, whereas the nonsarcomeric smooth muscle alpha-actin remained unaffected. The deleterious effects of glucose on myofibril formation were prevented by antioxidative regimens.

CONCLUSIONS

Thus, a diabetic milieu leads to multiple structural alterations of the heart including apoptosis, loss of intercellular contacts, and malformation of contractile structures.

Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults

Resistance training (RT) has shown the most promise in reducing/reversing effects of sarcopenia, although the optimum regime specific for older adults remains unclear. We hypothesized myofiber hypertrophy resulting from frequent (3 days/wk, 16 wk) RT would be impaired in older (O; 60-75 yr; 12 women, 13 men), sarcopenic adults compared with young (Y; 20-35 yr; 11 women, 13 men) due to slowed repair/regeneration processes. Myofiber-type distribution and cross-sectional area (CSA) were determined at 0 and 16 wk. Transcript and protein levels of myogenic regulatory factors (MRFs) were assessed as markers of regeneration at 0 and 24 h postexercise, and after 16 wk. Only Y increased type I CSA 18% (P < 0.001). O showed smaller type IIa (-16%) and type IIx (-24%) myofibers before training (P < 0.05), with differences most notable in women. Both age groups increased type IIa (O, 16%; Y, 25%) and mean type II (O, 23%; Y, 32%) size (P < 0.05). Growth was generally most favorable in young men. Percent change scores on fiber size revealed an age x gender interaction for type I fibers (P < 0.05) as growth among Y (25%) exceeded that of O (4%) men. Myogenin and myogenic differentiation factor D (MyoD) mRNAs increased (P < 0.05) in Y and O, whereas myogenic factor (myf)-5 mRNA increased in Y only (P < 0.05). Myf-6 protein increased (P < 0.05) in both Y and O. The results generally support our hypothesis as 3 days/wk training led to more robust hypertrophy in Y vs. O, particularly among men. However, this differential hypertrophy adaptation was not explained by age variation in MRF expression.

Effect of early low-intensity exercise on rat hind-limb muscles following acute ischemic stroke

This study examined the effects of daily low-intensity exercise following acute stroke on mass, Type I and II fiber cross-sectional area, and myofibrillar protein content of hind-limb muscles in a rat model. Adult male Sprague-Dawley rats were randomly assigned to 1 of 4 groups (n = 7-9 per group): stroke (occlusion of the right middle cerebral artery [RMCA]), control (sham RMCA procedure), exercise, and stroke-exercise. Beginning 48 hours post-stroke induction/sham operation, rats in the exercise group had 6 sessions of exercise in which they ran on a treadmill at grade 10 for 20 min/day at 10 m/min. At 8 days poststroke, all rats were anesthetized and soleus, plantaris, and gastrocnemius muscles were dissected from both the affected and unaffected sides. After 6 sessions of exercise following acute ischemic stroke, the stroke-exercise group showed the following significant (p < .05) increases compared to the stroke-only group: body weight and dietary intake, muscle weight of affected soleus and both affected and unaffected gastrocnemius muscle, Type I fiber cross-sectional area of affected soleus and both affected and unaffected gastrocnemius muscle, Type II fiber cross-sectional area of the unaffected soleus, both affected and unaffected plantaris and gastrocnemius muscle, Type II fiber distribution of affected gastrocnemius muscle, and myofibrillar protein content of both affected and unaffected soleus muscle. Daily low-intensity exercise following acute stroke attenuates hind-limb muscle atrophy in both affected and unaffected sides. The effects of exercise are more pronounced in the soleus and gastrocnemius as compared to the plantaris muscle.

Lysosomal dysfunction, cellular pathology and clinical symptoms: basic principles

Between 40 and 50 lysosomal storage disorders are known at present. Fine details of the pathogenic process involved are in general not known. This overview highlights the basic principles of lysosomal pathogenesis and the clinical consequences of defective genes involved in lysosomal functions. The subject is discussed in the context of the possibility of prevention and reversal of cellular and organ damage by enzyme replacement therapy. Also presented is a mechanical model for the muscle pathology observed in Pompe disease. Direct mechanical effects of the non-contractile inclusions - glycogen-loaded lysosomes - seem to be a key factor in the loss of force during both early and late stages of the disease.

CONCLUSION

Each lysosomal storage disorder and each patient with a given lysosomal disorder has unique molecular, pathological and clinical features. But, the order of pathological events is largely the same. Mutations in a gene cause lysosomal dysfunction which, in turn, results in cellular pathology affecting organ structure and function. Clinical symptoms are the ultimate manifestation. The reversibility of symptoms with enzyme replacement therapy will vary according to the disease, as well as the nature and stage of organ pathology.

Submolecular mechanisms underlying in vitro and in vivo effect of cardiac glycosides on contractile activity of myocardial myofibrils during heart failure

The development of severe heart failure associated with toxicoallergic myocarditis is accompanied by profound structural and conformational changes in the outer domain of actin (major protein in a thin filament of cardiomyocyte sarcomere). These changes were revealed in subdomains 1 (Cys374 and Cys10) and 2 (Lys61 and Tyr69). Structural and conformational changes in the monomer and protomer of the actin thread during heart failure were energetically forbidden. Variations in the distance between amino acid residues exceeded 0.26 nm. They were partly or completely reversible in vivo under the influence of cardiotropic drug refracterin with high antihypoxic activity, as well as in vitro after treatment with digitalis preparations optimizing the concentration of ATP.