Sarcomeric Actin Research Articles

Towards a Tissue-Engineered Contractile Fontan-Conduit: The Fate of Cardiac Myocytes in the Subpulmonary Circulation.

The long-term outcome of patients with single ventricles improved over time, but remains poor compared to other congenital heart lesions with biventricular circulation. Main cause for this unfavourable outcome is the unphysiological hemodynamic of the Fontan circulation, such as subnormal systemic cardiac output and increased systemic-venous pressure. To overcome this limitation, we are developing the concept of a contractile extracardiac Fontan-tunnel. In this study, we evaluated the survival and structural development of a tissue-engineered conduit under in vivo conditions. Engineered heart tissue was generated from ventricular heart cells of neonatal Wistar rats, fibrinogen and thrombin. Engineered heart tissues started beating around day 8 in vitro and remained contractile in vivo throughout the experiment. After culture for 14 days constructs were implanted around the right superior vena cava of Wistar rats (n = 12). Animals were euthanized after 7, 14, 28 and 56 days postoperatively. Hematoxylin and eosin staining showed cardiomyocytes arranged in thick bundles within the engineered heart tissue-conduit. Immunostaining of sarcomeric actin, alpha-actin and connexin 43 revealed a well -developed cardiac myocyte structure. Magnetic resonance imaging (d14, n = 3) revealed no constriction or stenosis of the superior vena cava by the constructs. Engineered heart tissues survive and contract for extended periods after implantation around the superior vena cava of rats. Generation of larger constructs is warranted to evaluate functional benefits of a contractile Fontan-conduit.

Cardiomyogenesis of periodontal ligament-derived stem cells by dynamic tensile strain.

Cellular therapies for the treatment of myocardial infarction have proven to be an invaluable tool in recent years and provide encouraging evidence for the possibility to restore normal heart function. However, questions still remain as to the optimal cell source, pre-conditioning methods and delivery techniques for such an application. This study explores the use of a population of stem cells arising from the neural crest and isolated from adult human periodontal ligament along with short-term mechanical strain as an inducer of cardiomyogenesis and possibly pre-conditioning stimulus for cellular cardiomyoplasty. Cells were subjected to a short-term dynamic mechanical tension in our custom-built bioreactor and analyzed for cardiomyogenic commitment. Mechanical strain elicited a cardiomyogenic response from the cells following just 2h of stimulation. Mechanical strain activated and translocated cardiac-specific transcription factors GATA4, MEF2C and Nkx2.5, and induced expression of the sarcomeric actin and cardiac troponin T proteins. Mechanical strain induced production of significantly higher levels of nitric oxide when compared to static controls. Elimination of elevated ROS levels by free radical scavengers completely abolished the cardiomyogenic response of the cells. MicroRNA profile changes in stretched cells were detected for 39 miRNAs with 16 of the differentially expressed miRNAs related to heart development. The use of stem cells in combination with mechanical strain prior to their delivery in vivo may pose a valuable alternative for the treatment of myocardial infarction and merits further exploration for its capacity to augment the already observed beneficial effects of cellular therapies.

Loss of CDKN2A Promoter Methylation Coincides With the Epigenetic Transdifferentiation of Uterine Myosarcomatous Cells.

Leiomyosarcoma is the most common type of uterine sarcoma and usually displays typical morphology. Heterologous leiomyosarcoma is the rarest variant, in which the tumor contains liposarcomatous, osteosarcomatous, or rhabdomyosarcomatous components. We have investigated the largest series of uterine leiomyosarcoma with a rhabdomyosarcomatous component and we have disclosed a molecular finding, which coincides to the process of transdifferentiation from smooth muscle into striated muscle phenotype. The surgical specimens of 5 rare cases of uterine leiomyosarcoma with a rhabdomyosarcomatous component were formalin fixed and paraffin embedded. In addition to hematoxylin/eosin stains, phosphotungstic acid hematoxylin staining, immunohistochemistry, and methylation-specific polymerase chain reaction the CDKN2A promoter region were performed. Leiomyosarcomatous cells were found to be strongly immunoreactive for both desmin and α-smooth muscle actin. Rhabdomyosarcomatous cells were immunoreactive for sarcomeric actin, desmin, vimentin, CD10, and p16. The methylation-specific polymerase chain reaction revealed the presence of a methylated allele and an unmethylated allele in the microdissected samples, coming from leiomyosarcomatous cells. On the contrary, 2 unmethylated alleles, molecular expression of a loss of heterozygosity, were detected in all the microdissected samples in the rhabdomyosarcomatous cells. The loss of heterozygosity methylation in the promoter region of the CDKN2A gene, occurred only in the rhabdomyosarcomatous cells with increases in both p16 and p14 expression. This event may result in an inhibition of cdk4/cdk6 activity, stabilizes the tumor suppressor protein p53, and coincides with the transdifferentiation from smooth muscle into striated muscle.

Monoclonal antibodies against muscle actin isoforms: epitope identification and analysis of isoform expression by immunoblot and immunostaining in normal and regenerating skeletal muscle.

Higher vertebrates (mammals and birds) express six different highly conserved actin isoforms that can be classified in three subgroups: 1) sarcomeric actins, α-skeletal (α-SKA) and α-cardiac (α-CAA), 2) smooth muscle actins (SMAs), α-SMA and γ-SMA, and 3) cytoplasmic actins (CYAs), β-CYA and γ-CYA. The variations among isoactins, in each subgroup, are due to 3-4 amino acid differences located in their acetylated N-decapeptide sequence. The first monoclonal antibody (mAb) against an actin isoform (α-SMA) was produced and characterized in our laboratory in 1986 (Skalli et al., 1986). We have further obtained mAbs against the 5 other isoforms. In this report, we focus on the mAbs anti-α-SKA and anti-α-CAA obtained after immunization of mice with the respective acetylated N-terminal decapeptides using the Repetitive Immunizations at Multiple Sites Strategy (RIMMS). In addition to the identification of their epitope by immunoblotting, we describe the expression of the 2 sarcomeric actins in mature skeletal muscle and during muscle repair after micro-lesions. In particular, we analyze the expression of α-CAA, α-SKA and α-SMA by co-immunostaining in a time course frame during the muscle repair process. Our results indicate that a restricted myocyte population expresses α-CAA and suggest a high capacity of self-regeneration in muscle cells. These antibodies may represent a helpful tool for the follow-up of muscle regeneration and pathological changes.

Monoclonal antibodies against muscle actin isoforms: epitope identification and analysis of isoform expression by immunoblot and immunostaining in normal and regenerating skeletal muscle

Higher vertebrates (mammals and birds) express six different highly conserved actin isoforms that can be classified in three subgroups: 1) sarcomeric actins, α-skeletal (α-SKA) and α-cardiac (α-CAA), 2) smooth muscle actins (SMAs), α-SMA and γ-SMA, and 3) cytoplasmic actins (CYAs), β-CYA and γ-CYA. The variations among isoactins, in each subgroup, are due to 3-4 amino acid differences located in their acetylated N-decapeptide sequence. The first monoclonal antibody (mAb) against an actin isoform (α-SMA) was produced and characterized in our laboratory in 1986 (Skalli et al., 1986) . We have further obtained mAbs against the 5 other isoforms. In this report, we focus on the mAbs anti-α-SKA and anti-α-CAA obtained after immunization of mice with the respective acetylated N-terminal decapeptides using the Repetitive Immunizations at Multiple Sites Strategy (RIMMS). In addition to the identification of their epitope by immunoblotting, we describe the expression of the 2 sarcomeric actins in mature skeletal muscle and during muscle repair after micro-lesions. In particular, we analyze the expression of α-CAA, α-SKA and α-SMA by co-immunostaining in a time course frame during the muscle repair process. Our results indicate that a restricted myocyte population expresses α-CAA and suggest a high capacity of self-regeneration in muscle cells. These antibodies may represent a helpful tool for the follow-up of muscle regeneration and pathological changes.

Neck Kaposiform haemangioendothelioma in a Fischer’s lovebird (Agapornis fischeri)

A six-year-old female Fischer's lovebird (Agapornis fischeri) presented at necropsy with a cutaneous mass on the neck, 3.5cm in diameter, yielding and with blood content. Histopathological findings showed a neoplasm characterized by proliferation of vascular endothelial cells. The histology of the mass revealed a multinodular, focally infiltrating tumor. Deeper dermal nodules were made of spindle cells forming vascular slits reminiscent of the histology seen in Kaposi's sarcoma (KS). More superficially located dermal nodules consisted of small blood vessels, with histology resembling capillary hemangioma. The spindle cells and capillaries were strongly positive for Vimentin, endothelial cell marker CD31, and negative for sarcomeric α-smooth muscle actin (α-SMA). Intravascular platelet trapping and Periodic acid-Schiff (PAS)-positive hyaline globules were also observed. Differential diagnosis included Kaposi's sarcoma, capillary haemangioma, spindle cell haemangioendothelioma, and epithelioid haemangioendothelioma. Based on morphological and immunohistochemical findings, the tumor was diagnosed as a cutaneous Kaposiform haemangioendothelioma (KHE), a rare, low-grade malignant vascular neoplasm. Other organs showed no abnormalities. PCR amplifications, conducted using Kaposi's sarcoma-associated herpesvirus (KSHV)-specific primers and degenerate sets of primers designed to detect and characterize members of the Herpesviridae, on DNA extracted from tumor tissue and from whole blood failed to amplify any KSHV-related sequence. Moreover, no specific signal was obtained using primers for detection of psittacine herpesvirus, known to be linked to Pacheco's disease in parrots. To the best of our knowledge, this unusual case is the third report of KHE in a non-human animal species, the first described in a bird.

Monoclonal antibodies against muscle actin isoforms: epitope identification and analysis of isoform expression by immunoblot and immunostaining in normal and regenerating skeletal muscle

Higher vertebrates express six different highly conserved actin isoforms that can be classified in three subgroups: 1) sarcomeric actins, α-skeletal (α-SKA) and α-cardiac (α-CAA), 2) smooth muscle actins (SMAs), α-SMA and γ-SMA, and 3) cytoplasmic actins (CYAs), β-CYA and γ-CYA. The variations among isoactins, in each subgroup, are due to 3-4 amino acid differences located in their acetylated N-decapeptide sequence. The first monoclonal antibody (mAb) against an actin isoform (α-SMA) was produced and characterized in our laboratory in 1986 (Skalli et al., 1986). We have further obtained mAbs against the 5 other isoforms. In this report, we focus on the mAb anti-α-SKA and anti-α-CAA obtained after immunization of mice with the respective acetylated N-terminal decapeptides using the Repetitive Immunizations at Multiple Sites Strategy (RIMMS). In addition to the identification of their epitope by immunoblotting, we describe the expression of the 2 sarcomeric actins in mature skeletal muscle and during muscle repair after micro-lesions. In particular, we analyze the expression of α-CAA, α-SKA and α-SMA by co-immunostaining in a time course frame during the muscle repair process. Our results indicate that a restricted myocyte population expresses α-CAA and suggest a high capacity of self-renewal in muscle cells. These antibodies may represent a helpful tool for the follow-up of muscle regeneration and pathological changes.

Growth on elastic silicone substrate elicits a partial myogenic response in periodontal ligament derived stem cells

The processes of cellular differentiation and phenotypic maintenance can be influenced by stimuli from a variety of different factors. One commonly overlooked factor is the mechanical properties of the growth substrate in which stem cells are maintained or differentiated down various lineages. Here we explored the effect that growth on an elastic silicone substrate had on the myogenic expression and cytoskeletal morphology of periodontal ligament derived stem cells. Cells were grown on either collagen I coated tissue culture polystyrene plates or collagen I coated elastic silicone membranes for a period of 4 days without further induction from soluble factors in the culture media. Following the 4-day growth, gene expression and immunohistochemical analysis for key cardiomyogenic markers was performed along with a morphological assessment of cytoskeletal organization. Results show that cells grown on the elastic substrate significantly upregulate key markers associated with contractile activity in muscle tissues. Namely, the myosin light chain polypeptides 2 and 7, as well as the myosin heavy chain polypeptide 7 genes underwent a statistically significant upregulation in the cells grown on elastic silicone membranes. Similarly, the cells on the softer elastic substrate stained positive for both sarcomeric actin and cardiac troponin t proteins following just 4 days of growth on the softer material. Cytoskeletal analysis showed that substrate stiffness had a marked effect on the organization and distribution of filamentous actin fibers within the cell body. Growth on silicone membranes produced flatter and shorter cellular morphologies with filamentous actin fibers projecting anisotropically throughout the cell body. These results demonstrate how crucial the mechanical properties of the growth substrate of cells can be on the ultimate cellular phenotype. These observations highlight the need to further optimize differentiation protocols to enhance the application of cellular products in the fields of regenerative medicine and stem cell therapies.

Biochemical Activities of the Wiskott-Aldrich Syndrome Homology Region 2 Domains of Sarcomere Length Short (SALS) Protein

Drosophila melanogaster sarcomere length short (SALS) is a recently identified Wiskott-Aldrich syndrome protein homology 2 (WH2) domain protein involved in skeletal muscle thin filament regulation. SALS was shown to be important for the establishment of the proper length and organization of sarcomeric actin filaments. Here, we present the first detailed characterization of the biochemical activities of the tandem WH2 domains of SALS (SALS-WH2). Our results revealed that SALS-WH2 binds both monomeric and filamentous actin and shifts the monomer-filament equilibrium toward the monomeric actin. In addition, SALS-WH2 can bind to but fails to depolymerize phalloidin- or jasplakinolide-bound actin filaments. These interactions endow SALS-WH2 with the following two major activities in the regulation of actin dynamics: SALS-WH2 sequesters actin monomers into non-polymerizable complexes and enhances actin filament disassembly by severing, which is modulated by tropomyosin. We also show that profilin does not influence the activities of the WH2 domains of SALS in actin dynamics. In conclusion, the tandem WH2 domains of SALS are multifunctional regulators of actin dynamics. Our findings suggest that the activities of the WH2 domains do not reconstitute the presumed biological function of the full-length protein. Consequently, the interactions of the WH2 domains of SALS with actin must be tuned in the cellular context by other modules of the protein and/or sarcomeric components for its proper functioning.

A simplified protocol for the isolation and culture of cardiomyocytes and progenitor cells from neonatal mouse ventricles

The neonatal heart is a very useful tool for the study of biochemical pathways and properties of cardiomyocytes and as it has the potential to regenerate for a brief period of time from birth; it is also useful to study cardiac regeneration. However, as the heart matures, this proficiency for regeneration is reduced. This regenerative potential may be influenced by the microenvironment of the heart in the early stages of postnatal development and therefore, cell cultures derived at this stage may contain functional cardiomyocytes and progenitor cells. The aim of this study was to identify key steps in the isolation and culture of such early stage—neonatal mouse hearts to allow maximum migration of cardiomyocytes from the explant and their maintenance as functional, long term cultures. Explant cultures of mouse ventricles preserved 3-dimensional structure and generated migrating layers of cardiomyocytes that expressed alpha sarcomeric actin which could be further sub-cultured by enzymatic dissociation. Western blotting demonstrated expression of c-KIT, GATA4, alpha sarcomeric actin and connexin43 proteins after 20 days of explant culture. ACTA1, GATA4, and CX43 continued to express in five weeks old explant cultures while the c-KIT protein was expressed up to two passages during sub-culture. Real time PCR and SQRT PCR also demonstrated gene expression of cardiomyocyte markers in long term cultures. Migrating cells from the explants assembled into contracting spheroids after subculture and expressed the c-KIT protein. Progenitor markers CD44, CD90, and extracellular proteins, periostin and vimentin demonstrated the preservation of cellular heterogeneity in such cultures. Supplementation with Hydrocortisone maintained a cardioprotective environment and reduced the non-myocyte population. This is an optimized and efficient method for the generation of neonatal heart cultures that is not labor intensive and does not require supplementation with cytokines.

Rhabdomyosarcoma of Soft Tissues in an Adult Brook Trout (Salvelinus fontinalis)

This report describes a spontaneously arising rhabdomyosarcoma of soft tissues in a brook trout (Salvelinus fontinalis). The lesion was examined by means of histology, immunohistochemistry (IHC) and transmission electron microscopy (TEM). The cross-reactivity of the primary antibodies used in the IHC was investigated in silico using the Protein Blast system. Microscopically, the lesion appeared as a 'small round cell' undifferentiated sarcoma with rare myotube formation. IHC identified expression of sarcomeric actin and vimentin and these molecules showed the highest protein sequence identity. Lower protein sequence identity coincided with negative immunolabelling for desmin, MyoD1, myogenin and CD3. TEM revealed myofibrils, but without a defined sarcomeric architecture. The diagnosis of solid alveolar rhabdomyosarcoma of soft tissues was achieved on the basis of histological and ultrastructural findings.

Development of the Ventricular Conduction System of the Crocodilian Heart

Unlike other cold‐blooded vertebrates, crocodilians have a fully septated heart, similar to birds and mammals. It is not known whether they have a ventricular conduction system (VCS) as wellWe studied a group of 8 embryos of the Siamese and Mugger Crocodile between 3 and 84 days of incubation, and serial early embryo sections with HNK‐1/Hematoxylin staining of the Nile Crocodile. We employed optical mapping, ultrasound biomicroscopy, histo‐ and immunohistochemistry, in situ hybridization and 3D reconstructionAt the pre‐septation stage (12 days of incubation), the ventricular activation pattern progressed in a left‐to‐right sweep, similar to that observed at early stages of avian and mammalian cardiogenesis. At two post‐septation stages investigated (45 and 84 days) , epicardial activation patterns showed dual apical breakthroughs on either side of the interventricular septum. Immunohistochemistry using smooth muscle actin (SMA), sarcomeric actin, periostin and HNK‐1 antibodies showed that myocardial SMA staining was present even after septation, while it disappears in comparable chick or mouse hearts. HNK‐1 staining was prominent in the interventricular septum, similar to the situation in the chick and rat where it is considered a marker of the developing ventricular conduction system. In situ hybridization for Cx40 (VCS marker) showed a uniform expression in the entire trabeculated myocardiumWe conclude that this is an evidence of evolutionary correlation between ventricular septation and presence specialized VCS in vertebratesSupported by PRVOUK P35/LF1/5.

UNC-87 isoforms, Caenorhabditis elegans calponin-related proteins, interact with both actin and myosin and regulate actomyosin contractility.

Calponin-related proteins are widely distributed among eukaryotes and involved in signaling and cytoskeletal regulation. Calponin-like (CLIK) repeat is an actin-binding motif found in the C-termini of vertebrate calponins. Although CLIK repeats stabilize actin filaments, other functions of these actin-binding motifs are unknown. The Caenorhabditis elegans unc-87 gene encodes actin-binding proteins with seven CLIK repeats. UNC-87 stabilizes actin filaments and is essential for maintenance of sarcomeric actin filaments in striated muscle. Here we show that two UNC-87 isoforms, UNC-87A and UNC-87B, are expressed in muscle and nonmuscle cells in a tissue-specific manner by two independent promoters and exhibit quantitatively different effects on both actin and myosin. Both UNC-87A and UNC-87B have seven CLIK repeats, but UNC-87A has an extra N-terminal extension of ~190 amino acids. Both UNC-87 isoforms bind to actin filaments and myosin to induce ATP-resistant actomyosin bundles and inhibit actomyosin motility. UNC-87A with an N-terminal extension binds to actin and myosin more strongly than UNC-87B. UNC-87B is associated with actin filaments in nonstriated muscle in the somatic gonad, and an unc-87 mutation causes its excessive contraction, which is dependent on myosin. These results strongly suggest that proteins with CLIK repeats function as a negative regulator of actomyosin contractility.

Drosophila small heat shock protein CryAB ensures structural integrity of developing muscles, and proper muscle and heart performance.

Molecular chaperones, such as the small heat shock proteins (sHsps), maintain normal cellular function by controlling protein homeostasis in stress conditions. However, sHsps are not only activated in response to environmental insults, but also exert developmental and tissue-specific functions that are much less known. Here, we show that during normal development the Drosophila sHsp CryAB [L(2)efl] is specifically expressed in larval body wall muscles and accumulates at the level of Z-bands and around myonuclei. CryAB features a conserved actin-binding domain and, when attenuated, leads to clustering of myonuclei and an altered pattern of sarcomeric actin and the Z-band-associated actin crosslinker Cheerio (filamin). Our data suggest that CryAB and Cheerio form a complex essential for muscle integrity: CryAB colocalizes with Cheerio and, as revealed by mass spectrometry and co-immunoprecipitation experiments, binds to Cheerio, and the muscle-specific attenuation of cheerio leads to CryAB-like sarcomeric phenotypes. Furthermore, muscle-targeted expression of CryAB(R120G), which carries a mutation associated with desmin-related myopathy (DRM), results in an altered sarcomeric actin pattern, in affected myofibrillar integrity and in Z-band breaks, leading to reduced muscle performance and to marked cardiac arrhythmia. Taken together, we demonstrate that CryAB ensures myofibrillar integrity in Drosophila muscles during development and propose that it does so by interacting with the actin crosslinker Cheerio. The evidence that a DRM-causing mutation affects CryAB muscle function and leads to DRM-like phenotypes in the fly reveals a conserved stress-independent role of CryAB in maintaining muscle cell cytoarchitecture.

The immunohistochemical study of the structures of the cardiac conduction system in the case of death from alcoholic cardiomyopathy

The objective of the present study was to study the morphological criteria for toxic cardiopathy with the use of histological and immunohistochemical methods. The results of immunohistochemical studies of the sinoatrial node---???---(SAN) and the working myocardium in the patients presenting with alcoholic cardiomyopathy (ACMP) are presented. It was shown that vimentin expression in the SAN structures and the contractile myocardium is slightly increased whereas the expression of sarcomeric actin is decreased and that of fibrinogen is increased too. The authors put forward an assumption about the role of lesions in the membrane apparatus of the pacemaker cells in the development of arrhythmia characteristic of tanatogenesis associated with alcoholic cardiomyopathy.

Activated macrophages as a feeder layer for growth of resident cardiac progenitor cells.

The adult heart contains a population of cardiac progenitor cells (CPCs). Growing and collecting an adequate number of CPCs demands complex culture media containing growth factors. Since activated macrophages secrete many growth factors, we investigated if activated isolated heart cells seeded on a feeder layer of activated peritoneal macrophages (PM) could result in CPCs and if these, in turn, could exert cardioprotection in rats with myocardial infarction (MI). Heart cells of inbred Wistar rats were isolated by collagenase digestion and cultured on PM obtained 72h after intraperitoneal injection of 12ml thioglycollate. Cells (1×10(6)) exhibiting CPC phenotype (immunohistochemistry) were injected in the periphery of rat MI 10min after coronary artery occlusion. Control rats received vehicle. Three weeks later, left ventricular (LV) function (echocardiogram) was assessed, animals were euthanized and the hearts removed for histological studies. Five to six days after seeding heart cells on PM, spherical clusters composed of small bright and spherical cells expressing mostly c-Kit and Sca-1 antigens were apparent. After explant, those clusters developed cobblestone-like monolayers that expressed smooth muscle actin and sarcomeric actin and were successfully transferred for more than ten passages. When injected in the MI periphery, many of them survived at 21days after coronary ligature, improved LV ejection fraction and decreased scar size as compared with control rats. CPC-derived cells with cardiocyte and smooth muscle phenotypes can be successfully grown on a feeder layer of activated syngeneic PM. These cells decreased scar size and improved heart function in rats with MI.

Diaphragm muscle weakness in mice is early-onset post-myocardial infarction and associated with elevated protein oxidation.

Heart failure induced by myocardial infarction (MI) causes diaphragm muscle weakness, with elevated oxidants implicated. We aimed to determine whether diaphragm muscle weakness is 1) early-onset post-MI (i.e., within the early left ventricular remodeling phase of 72 h); and 2) associated with elevated protein oxidation. Ligation of the left coronary artery to induce MI (n = 10) or sham operation (n = 10) was performed on C57BL6 mice. In vitro contractile function of diaphragm muscle fiber bundles was assessed 72 h later. Diaphragm mRNA and protein expression, enzyme activity, and individual carbonylated proteins (by two-dimensional differential in-gel electrophoresis and mass spectrometry) were subsequently assessed. Infarct size averaged 57 ± 1%. Maximal diaphragm function was reduced (P < 0.01) by 20% post-MI, with the force-frequency relationship depressed (P < 0.01) between 80 and 300 Hz. The mRNA expression of inflammation, atrophy, and regulatory Ca(2+) proteins remained unchanged post-MI, as did the protein expression of key contractile proteins. However, enzyme activity of the oxidative sources NADPH oxidase and xanthine oxidase was increased (P < 0.01) by 45 and 33%, respectively. Compared with sham, a 57 and 45% increase (P < 0.05) was observed in the carbonylation of sarcomeric actin and creatine kinase post-MI, respectively. In conclusion, diaphragm muscle weakness was rapidly induced in mice during the early left ventricular remodeling phase of 72 h post-MI, which was associated with increased oxidation of contractile and energetic proteins. Collectively, these findings suggest diaphragm muscle weakness may be early onset in heart failure, which is likely mediated in part by posttranslational oxidative modifications at the myofibrillar level.

Regulation of structure and function of sarcomeric actin filaments in striated muscle of the nematode Caenorhabditis elegans.

The nematode Caenorhabditis elegans has been used as a valuable system to study structure and function of striated muscle. The body wall muscle of C. elegans is obliquely striated muscle with highly organized sarcomeric assembly of actin, myosin, and other accessory proteins. Genetic and molecular biological studies in C. elegans have identified a number of genes encoding structural and regulatory components for the muscle contractile apparatuses, and many of them have counterparts in mammalian cardiac and skeletal muscles or striated muscles in other invertebrates. Applicability of genetics, cell biology, and biochemistry has made C. elegans an excellent system to study mechanisms of muscle contractility and assembly and maintenance of myofibrils. This review focuses on the regulatory mechanisms of structure and function of actin filaments in the C. elegans body wall muscle. Sarcomeric actin filaments in C. elegans muscle are associated with the troponin-tropomyosin system that regulates the actin-myosin interaction. Proteins that bind to the side and ends of actin filaments support ordered assembly of thin filaments. Furthermore, regulators of actin dynamics play important roles in initial assembly, growth, and maintenance of sarcomeres. The knowledge acquired in C. elegans can serve as bases to understand the basic mechanisms of muscle structure and function.

Bioreactor for modulation of cardiac microtissue phenotype by combined static stretch and electrical stimulation

We describe here a bioreactor capable of applying electrical field stimulation in conjunction with static strain and on-line force of contraction measurements. It consisted of a polydimethylsiloxane (PDMS) tissue chamber and a pneumatically driven stretch platform. The chamber contained eight tissue microwells (8.05 mm in length and 2.5 mm in width) with a pair of posts (2.78 mm in height and 0.8 mm in diameter) in each well to serve as fixation points and for measurements of contraction force. Carbon rods, stimulating electrodes, were placed into the PDMS chamber such that one pair stimulated four microwells. For feasibility studies, neonatal rat cardiomyocytes were seeded in collagen gels into the microwells. Following 3 days of gel compaction, electrical field stimulation at 3–4 V cm−1 and 1 Hz, mechanical stimulation of 5% static strain or electromechanical stimulation (field stimulation at 3–4 V cm−1, 1 Hz and 5% static strain) were applied for 3 days. Cardiac microtissues subjected to electromechanical stimulation exhibited elevated amplitude of contraction and improved sarcomere structure as evidenced by sarcomeric α-actinin, actin and troponin T staining compared to microtissues subjected to electrical or mechanical stimulation alone or non-stimulated controls. The expression of atrial natriuretic factor and brain natriuretic peptide was also elevated in the electromechanically stimulated group.

Protein kinase C‐site phosphorylation of cardiac myosin binding protein‐C decreases cross‐bridge kinetics (1081.5)

Cardiac myosin binding protein‐C (cMyBP‐C) phosphorylation is necessary for the regulation of sarcomeric structure and myocardial contractility in vivo. Different from skeletal isoforms, cMyBP‐C has M‐domain phosphorylation motifs in which three serines, Ser273, 282 and 302, are known to be substrates for several kinases. Phosphorylation of these M‐domain sites regulates the interaction of cMyBP‐C with thick and thin myofilaments during muscle contraction. While protein kinase C (PKC) is known to phosphorylate Ser273 and Ser302, the precise functional consequences of PKC‐mediated cMyBP‐C phosphorylation are not fully characterized. Therefore, the objective of this study was to determine how PKC‐mediated phosphorylation at Ser273/302 might control the function of cMyBP‐C in the context of thick and thin myofilament regulation and sarcomere contraction. Using recombinant proteins and yeast‐2‐hybrid (Y2H) clones expressing Ser273‐Ser282‐Ser302 (cMyBP‐CWT), Ala273‐Asp282‐Ala302 (cMyBP‐CADA) or Asp273‐Ala282‐Asp302 (cMyBP‐CDAD), cosedimentation of C0C2 and Y2H of C1C2 assays with either cardiac myosin S2 region or sarcomeric actin revealed that PKC phosphorylation of Ser273/Ser302 in cMyBP‐C M‐domain is sufficient to maintain its interaction with myosin S2 region, but diminish its interaction with actin in vitro. Furthermore, mechanical studies using skinned ventricular fibers from cMyBP‐CDAD revealed that PKC phospho‐mimetic exhibits a significant decrease in active force, cross‐bridge kinetics and Mg2+‐ATPase activity and myofilament Ca2+ sensitivity in vitro, compared to the controls. Taken together, our studies demonstrated that two phosphorylatable (by PKC) serines in cMyBP‐C M‐domain enable the interaction between cMyBP‐C protein and myosin S2, but diminishes its interaction with actin, thus affecting the ability of this protein to regulate sarcomere contractility