Molecular mechanics of cardiac myosin-binding protein C in native thick filaments.

The heart's pumping capacity results from highly regulated interactions of actomyosin molecular motors. Mutations in the gene for a potential regulator of these motors, cardiac myosin-binding protein C (cMyBP-C), cause hypertrophic cardiomyopathy. However, cMyBP-C's ability to modulate cardiac contractility is not well understood. Using single-particle fluorescence imaging techniques, transgenic protein expression, proteomics, and modeling, we found that cMyBP-C slowed actomyosin motion generation in native cardiac thick filaments. This mechanical effect was localized to where cMyBP-C resides within the thick filament (i.e., the C-zones) and was modulated by phosphorylation and site-specific proteolytic degradation. These results provide molecular insight into why cMyBP-C should be considered a member of a tripartite complex with actin and myosin that allows fine tuning of cardiac muscle contraction.

Hepatitis C virus infection management in 2012.

Hepatitis C virus (HCV) is the most common infectious cause of chronic liver disease in Europe. With the introduction of interferon based therapy in combination with ribavirin treatment of chronic HCV has become feasible. This therapy has become the standard of care for patients with HCV and depending on the HCV genotype treatment is successful in 40-70% of patients. In the recent years a new class of drugs have emerged that changed the landscape of HCV treatment. These direct antiviral agents inhibit the NS3/N4A serine protease of HCV. Prototypes are telaprevir and boceprevir and they specifically exert antiviral activity against genotype 1 HCV. A series of landmark trials has paved the way for introduction of these agents, and they have documented a great improvement in the care of genotype 1 HCV patients. Telaprevir and boceprevir are given in combination with pegylated interferon and ribavirin and are useful for treatment naive as well as treatment experienced patients. The clinician should be aware of these developments as they have implications for side effect management, and drug-drug interactions. Finally, strategic use of these agents comes with stopping rules and require close monitoring of the HCV viral load.

Hepatic and renal manifestations in autosomal dominant polycystic kidney disease: a dichotomy of two ends of a spectrum.

Autosomal dominant polycystic kidney disease (ADPKD) is a multisystem disorder. It is the most common genetic cause of end-stage renal disease. One frequent extra-renal manifestation is hepatic cyst formation. The majority of ADPKD patients develop complications as a result of renal cyst formation; however, a small proportion develop extensive hepatic disease with minor renal features. Both phenotypes seem to represent the spectrum of ADPKD. This review discusses the current understanding of the pathogenesis of the disease, its manifestations and the mechanisms of cyst formation. Furthermore, it focuses on monitoring the disease and the treatment options currently available.

Benign myoepithelioma of the lung: a case report and review of the literature.

This report describes a benign myoepithelioma of the lung that occurred in a 60-year-old woman. The patient had experienced hoarseness for 6 weeks, and a computed tomographic scan showed a nodule of approximately 2 cm in diameter at the peripheral portion of her right upper lung. Positron emission tomography showed no uptake of F-18 fluorodeoxyglucose in the nodule. Wedge biopsy of the lesion showed benign spindle cells arranged in a whorled pattern. The cells were positive for both cytokeratin and smooth muscle actin, which corresponded to the presence of tonofilaments and myofilaments that were identified ultrastructurally. The features of the present case of benign myoepithelioma that differ from features of previously reported benign and malignant cases of myoepithelioma in the lung are discussed in the report.

Examining the in vivo role of the amino terminus of the essential myosin light chain.

The functional significance of the actin binding region at the amino terminus of the cardiac essential myosin light chain (ELC) remains obscure. Previous experiments carried out in vitro indicated that modulation of residues 5-14 could induce an inotropic effect, increasing maximal ATPase activity at submaximal Ca(2+) concentrations (Rarick, H. M., Opgenorth, T. J., von Geldern, T. W., Wu-Wong, J. R., and Solaro, R. J. (1996) J. Biol. Chem. 271, 27039-27043). Using transgenesis, we effected a cardiac-specific replacement of ELC with a protein containing a 10-amino acid deletion at positions 5-14. Both the ventricular (ELC1vDelta5-14) and atrial (ELC1aDelta5-14) isoforms lacking this peptide were stably incorporated into the sarcomere at high efficiencies. Surprisingly when the kinetics of skinned fibers isolated from the ELC1vDelta5-14 or ELC1aDelta5-14 mice were examined, no alterations in either unloaded shortening or maximum shortening velocities were apparent. Myofibrillar Mg(2+)-ATPase activity was also unchanged in these preparations. No significant changes in the fiber kinetics in the cognate compartments were observed when either deletion-containing protein replaced endogenous ELC1v or ELC1a. The data indicate that the previously postulated importance of this region in mediating critical protein interactions between the cardiac ELCs and the carboxyl-terminal residues of actin in vivo should be reassessed.

Mouse model of desmin-related cardiomyopathy.

BACKGROUND: The consequence of upregulation of desmin in the heart is unknown. Mutations in desmin have been linked to desmin-related myopathy (DRM), which is characterized by abnormal intrasarcoplasmic accumulation of desmin, but direct causative evidence that a desmin mutation leads to aberrant intrasarcoplasmic desmin accumulation, aggregation, and cardiomyopathy is lacking. METHODS AND RESULTS: Multiple transgenic mouse lines that expressed either murine wild-type desmin or a 7-amino acid deletion (R173 through E179) desmin (D7-des) mutation linked to DRM were made. The distribution of desmin protein was unchanged, and no overt phenotype was detected in the wild-type desmin transgenic mice. In contrast, the D7-des mouse heart showed aberrant intrasarcoplasmic and electron-dense granular filamentous aggregates that were desmin-positive and characteristic of human DRM. The desmin filament network was significantly disrupted, and myofibril alignment was visibly compromised. Although systolic function at the whole-organ level was substantially conserved in the young adult animals, the ability of the heart to respond to beta-agonist stimulation, as measured in the intact animal, was significantly blunted. CONCLUSIONS: Upregulation of desmin protein at moderate levels is not detrimental. However, the D7-des mutation is dominant negative, and expression of the mutant protein leads to the appearance of aggregates that are characteristic of and diagnostic for human desmin-related cardiomyopathy.

Exercise treatment for sacroiliac pain.

The reciprocal relationship of the latissimus dorsi on one side and the gluteus maximus on the other side has been demonstrated anatomically. To demonstrate this relationship by muscle action, electromyographic studies were performed in 15 healthy individuals. This formed the baseline for evaluation of 5 symptomatic patients with sacroiliac dysfunction. Abnormal hyperactivity of the gluteus muscle on the involved side and increased activity of the latissimus on the contralateral side was contrasted with the normal function of the healthy individuals. All patients in the rotary strengthening exercise program improved in strength and return of myoelectric activity to more normal patterns.

Myosin light chain replacement in the heart.

Myosin-actin cross-bridge kinetics are an important determinant for cardiac systolic and diastolic function. We compared the effects of myosin light chain substitutions on the ability of the fibers to contract in response to calcium and in their ability to produce power. Transgenesis was used to effect essentially complete replacement of the target contractile protein isoform specifically in the heart. Atrial and ventricular fibers derived from the various transgenic (TG) lines were skinned, and the force-velocity relationships, unloaded shortening velocities, and Ca(2+)-stimulated Mg(2+)-ATPase activities were determined. Replacement with an ectopic isoform resulted in significant changes in cross-bridge cycling kinetics but without any overt effects on morbidity or mortality. To confirm that this result was not light chain specific, a modified alpha-myosin heavy chain isoform that resulted in significant changes in force development was also engineered. The animals appeared healthy and have normal lifespans, and the changes in force development did not result in significant remodeling or overt hypertrophy. We conclude that myosin light chains can control aspects of cross-bridge cycling and alter force development. The myosin heavy chain data also show that changes in the kinetics of force development and power output do not necessarily lead to activation of the hypertrophic response or significant cardiac remodeling.

In vivo analysis of an essential myosin light chain mutation linked to familial hypertrophic cardiomyopathy.

Mutations in cardiac motor protein genes are associated with familial hypertrophic cardiomyopathy. Mutations in both the regulatory (Glu22Lys) and essential light chains (Met149Val) result in an unusual pattern of hypertrophy, leading to obstruction of the midventricular cavity. When a human genomic fragment containing the Met149Val essential myosin light chain was used to generate transgenic mice, the phenotype was recapitulated. To unambiguously establish a causal relationship for the regulatory and essential light chain mutations in hypertrophic cardiomyopathy, we generated mice that expressed either the wild-type or mutated forms, using cDNA clones encompassing only the coding regions of the gene loci. Expression of the proteins did not lead to a hypertrophic response, even in senescent animals. Changes did occur at the myofilament and cellular levels, with the myofibrils showing increased Ca(2+) sensitivity and significant deficits in relaxation in a transgene dose-dependent manner. Clearly, mice do not always recapitulate important aspects of human hypertrophy. However, because of the discordance of these data with data obtained in transgenic mice containing the human genomic fragment, we believe that the concept that these point mutations by themselves can cause hypertrophic cardiomyopathy should be revisited.

A preliminary report on the effect of measured strength training in adolescent idiopathic scoliosis.

The authors studied 12 adolescent patients with scoliosis (10 girls and 2 boys) who were 11 to 16 years old and had curvatures ranging from 20 degrees to 60 degrees. Seven were right thoracic curves and five were thoracolumbar with double curves. When tested on the MedX Torso Rotation Machine, both sides were unequal in their torso rotation strength all patients. Myoelectric activity was asymmetric in both sides and in abdominal and paraspinal muscles of all patients. These asymmetries were corrected completely with torso rotation, which was associated with significant strength gains. Strength gains ranged from 12% to 40%. A 16-year-old girl with a 60 degree lumbar curve progressed and had surgery. None of the remaining patients progressed, and 4 of the 12 had decreases in their curvatures from 20 degrees to 28 degrees. None of the patients used braces during this study.

Abnormal cardiac structure and function in mice expressing nonphosphorylatable cardiac regulatory myosin light chain 2.

A role for myosin phosphorylation in modulating normal cardiac function has long been suspected, and we hypothesized that changing the phosphorylation status of a cardiac myosin light chain might alter cardiac function in the whole animal. To test this directly, transgenic mice were created in which three potentially phosphorylatable serines in the ventricular isoform of the regulatory myosin light chain were mutated to alanines. Lines were obtained in which replacement of the endogenous species in the ventricle with the nonphosphorylatable, transgenically encoded protein was essentially complete. The mice show a spectrum of cardiovascular changes. As previously observed in skeletal muscle, Ca(2+) sensitivity of force development was dependent upon the phosphorylation status of the regulatory light chain. Structural abnormalities were detected by both gross histology and transmission electron microscopic analyses. Mature animals showed both atrial hypertrophy and dilatation. Echocardiographic analysis revealed that as a result of chamber enlargement, severe tricuspid valve insufficiency resulted in a detectable regurgitation jet. We conclude that regulated phosphorylation of the regulatory myosin light chains appears to play an important role in maintaining normal cardiac function over the lifetime of the animal.

Transgenic over-expression of a motor protein at high levels results in severe cardiac pathology.

Transgenesis has become a useful tool in effecting a complete or partial remodeling of the cardiac contractile apparatus. Although gene dosage effects were initially a concern, recent data showed that the heart is able to accommodate varying levels of transgenic over-expression without detectable ill effects. The present study was designed to test the limits of the transgenic paradigm in terms of the production of a cardiac phenotype due simply to the over-expression of a contractile protein. To this end, eight lines of mice which express an isoform of the essential myosin light chain 1 that is normally found in the adult ventricle (ELC1v) were generated. Overt phenotype was correlated both with the level of expression/protein replacement and copy number of the transgene. Two of the lines showed essentially complete replacement of the atrial isoform (ELC1a) with ELC1v. However, the phenotypes of the two lines differed dramatically. The line with the lower copy number (37 copies), and moderate over-expression (16 fold) showed no overt pathology while a line with very high copy number (94 copies) and extremely high levels of over-expression (27-50 fold) developed a significant atrial hypertrophy, dilation and cardiomyopathy. These data indicate that very high expression levels of a contractile protein can cause a cardiac pathology that is unrelated to its degree of replacement in the sarcomere and the unique role(s) it may assume in motor protein function.

Effects of total replacement of atrial myosin light chain-2 with the ventricular isoform in atrial myocytes of transgenic mice.

BACKGROUND: In contrast to their well-known and critical role in excitation-contraction coupling of vascular smooth muscle, the effects of the myosin light chains on cardiomyocyte mechanics are poorly understood. Accordingly, we designed the present experiment to define the cardiac chamber-specific functional effects of the ventricular isoform of the regulatory myosin light chain (MLC2v). METHODS AND RESULTS: Postnatal transgenic cardiac-specific overexpression of MLC2v was achieved by use of the alpha-myosin heavy chain promoter. Enzymatically disaggregated atrial and ventricular mouse myocytes were field-stimulated at multiple frequencies, and mechanical properties and calcium kinetics were studied by use of video edge detection and FURA 2-AM, respectively. MLC2v overexpression resulted in complete replacement of the atrial with the ventricular isoform of the regulatory myosin light chain at the steady-state mRNA and protein levels in the atria of transgenic mice. Mechanical properties of transgenic atrial myocytes were enhanced to the level of ventricular myocytes of control animals in association with modest decreases in the amplitude of the calcium transient. CONCLUSIONS: MLC2v modulates chamber-specific contractility by enhanced calcium sensitivity and/or improved cross-bridge cycling of the thin and thick filaments of the cardiomyocyte.

Relationships between myoelectric activity, strength, and MRI of lumbar extensor muscles in back pain patients and normal subjects.

Eight normal individuals and eight patients with chronic back pain were evaluated. They undertook a treatment program lasting 8 weeks, with two exercise sessions each week. Myoelectric activity, lumbar extensor strength, and cross-sectional magnetic resonance imaging appearance of the lumbar paraspinal extensor muscles was assessed at the beginning and end of the program. Initial baseline and final extensor strength measurements were done isometrically at seven points through full range. Surface myoelectric activity was monitored during both flexion and extension exercise. Subsequently, electromyographic (EMG) signals were analyzed for mean frequency (MPF) and amplitude (RMS). An average functional improvement of 65% and reduction of pain complaint of 41% occurred in the eight patients with chronic low back pain. Extensor strength improved an average of 48% contrasted to 6% for the normal subjects. Four patients who showed severe fatty infiltration in the extensors had a decrease in the degree of infiltration and no change in muscle mass. Changes in fatty infiltration did not correlate with strength changes. The dynamic EMG changes documented a decrease in amplitude (RMS) and a smaller decrease in frequency (MPF) for the same resistance when used at the beginning and end of the program. Structural changes in the muscles are not always needed to achieve strength gains or symptomatic improvement.

Transgenic remodeling of the regulatory myosin light chains in the mammalian heart.

The regulatory myosin light chain (MLC) regulates contraction in smooth muscle. However, its function in striated muscle remains obscure, and the different functional activities of the various isoforms that are expressed in the mammalian heart (ventricle- and atrium-specific MLC2) remain undefined. To begin to explore these issues, we used transgenesis to determine the feasibility of effecting a complete or partial replacement of the cardiac regulatory light chains with the isoform that is normally expressed in fast skeletal muscle fibers (fast muscle-specific MLC2). Multiple lines of transgenic mice were generated that expressed the transgene at varying levels in the heart in a copy number-dependent fashion. There is a major discordance in the manner in which the different cardiac compartments respond to high levels of overexpression of the transgene. In atria, isoform replacement with the skeletal protein was quite efficient, even at low copy number. The ventricle is much more refractory to replacement, and despite high levels of transgenic transcript, protein replacement was incomplete. Replacement could be further increased by breeding the transgenic lines with one another. Despite very high levels of transgenic transcript in these mice, the overall level of the regulatory light chain in both compartments remained essentially constant; only the protein isoform ratios were altered. The partial replacement of the ventricular with the skeletal isoform reduced both left ventricular contractility and relaxation, although the unloaded shortening velocity of isolated ventricular cardiomyocytes was not significantly different.

Ablation of the murine alpha myosin heavy chain gene leads to dosage effects and functional deficits in the heart.

The alpha-myosin heavy chain (alpha-MyHC) is the major contractile protein expressed in the myocardium of adult mice. We have produced mice carrying a null mutation of alpha-MyHC by homologous recombination in murine ES cells. Homozygous null animals die between 11 and 12 d in utero of gross heart defects, while alpha-MyHC+/- heterozygotes survive and appear externally normal. The presence of a single functional alpha-MyHC+ allele in heterozygous animals results in reduced levels of the transcript and protein as well as fibrosis and alterations in sarcomeric structure. Examination of heart function using a working heart preparation revealed severe impairment of both contractility and relaxation in a subset of the alpha-MyHC+/- animals. Thus, two alpha-MyHC+ alleles are necessary for normal cardiac development, and hemizygosity for the normal allele can result in altered cardiac function.

Transgenic remodeling of the contractile apparatus in the mammalian heart.

The structure-function relationships of the sarcomeric proteins in the mammalian cardiac compartment remain ill-defined because of the lack of a suitable model in which they can be readily manipulated or exchanged in vivo. To establish the validity of the transgenic paradigm for remodeling the mammalian heart, the murine alpha -cardiac myosin heavy chain gene promoter was used to express a ventricular myosin light chain-2 transgene (MLC2v) in both the atria and ventricles of the adult animal. Expression resulted in high levels of the transgene's transcript in both compartments. In the ventricle, the transgene was expressed against the background expression of the normal isoform. In the atrium, the transgene's expression would be ectopic, in that normally, MLC2v expression is restricted to the ventricle. Ectopic expression of the transgene in the atria resulted in a complete replacement of the atrial myosin light chain-2 protein isoform, although the endogenous isoform's steady state transcript levels were unchanged. In contrast, ventricular expression of the transgene had no effect at the protein level, despite an eightfold increase in MLC2v transcript levels. The data show that sarcomeric protein stoichiometry is maintained rigorously via posttransciptional regulation and that protein replacement can be achieved through a single transgenic manipulation.

Remodeling the mammalian heart using transgenesis.

Our objective was to test the hypothesis that, via transgenesis, one can modify the contractile protein complement of the mouse heart. Using a promoter derived from the mouse myosin heavy chain gene (alpha-MyHC), we attempted to remodel the mouse myocardium by ectopically expressing a ventricular form of the myosin light chain 2 (MLC2v) in the atrium. The ability of the heart to maintain contractile isoform stoichiometry was tested by overexpressing the cDNA in both the atria and ventricle. The promoter drove high levels of transgene expression in both cardiac compartments and was controlled in an appropriate manner during development. The data show that ectopic overexpression of a contractile protein isoform can lead to compartment specific replacement. However, if the transgene encodes the isoform that is normally present (e.g., MLC2v expressed in the ventricle), the protein levels remain unaffected, although the transgenic transcript accumulates to very high levels. The basic function and the physiologic or pathophysiologic significance of differential MLC2 isoform content was examined. Using the whole working heart preparation, we show that an MLC2a --> MLC2v shift in the atrium severely affects contractile function and performance.

In vivo analysis of the murine beta-myosin heavy chain gene promoter.

The 5' upstream region of the murine beta-myosin heavy chain (MHC) gene has been isolated and tested for its ability to drive gene expression in transgenic mice. Three classes of transgenic mice were generated. The constructs contained approximately 5000, 2500, and 600 base pairs of beta-MHC upstream sequence fused to the chloramphenicol acetyltransferase gene and were termed beta 5, beta 2.5, and beta .6, respectively. Muscle-specific expression was observed with all three constructs. However, only the beta 5 lines directed high levels of muscle-specific transgene expression in both pre- and postbirth mice. Expression driven by the two shorter constructs was two to three orders of magnitude lower when the chloramphenicol acetyltransferase specific activities were compared. These data suggest that a distal-positive element directs high levels of gene expression in the ventricle and in slow skeletal muscles. Analyses of transgene expression during heart maturation revealed that some of the beta 5 lines were not able to respond in an appropriate manner to developmental transcriptional cues. Unlike the endogenous beta-MHC gene, which is down regulated in the ventricles around the time of birth, reporter gene expression in the majority of the lines generated was not shut off in the ventricles of the adult animals. These data indicate that high levels of muscle-specific beta-MHC gene expression are dependent upon the combinatorial interactions of a number of sequence elements that are distributed over a large region of the gene's upstream sequence.

Transgenic analysis of the thyroid-responsive elements in the alpha-cardiac myosin heavy chain gene promoter.

The role of two putative, cis-acting thyroid hormone-responsive elements, TRE1 and TRE2, located at -129 to -149 and -102 to -120, respectively, on the murine alpha-myosin heavy chain (MHC) gene, has been investigated in transgenic mice. These motifs are present in a 4.5-kilobase fragment lying upstream of the transcriptional start site of the mouse alpha-MHC gene: this fragment directs appropriate expression of a reporter gene in transgenic mice (Subramaniam, A., Jones, W. K., Gulick, J., Wert, S., Neumann, J., and Robbins, J. (1991) J. Biol. Chem. 266, 24613-24620). Here, we independently mutate the TRE1 and TRE2 elements by base substitution. The mice were analyzed for transgene expression in different muscle and non-muscle tissues including the atria and ventricles. Normal levels of transgene expression were observed in euthyroid mice carrying a mutation in TRE1. In contrast to these results, mice in which TRE2 was mutated showed reduced levels of CAT activity in both the atria and ventricles, suggesting a previously undefined role for this element in the constitutive up-regulation of the alpha-MHC gene. In hypothyroid mice carrying either of these mutations, the complete cessation of ventricular expression of the chloramphenicol acetyltransferase transcripts that takes place in the alpha-5.5 (wild type) animals did not occur.