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1.  The role of cell death and myofibrillar damage in contractile dysfunction of long-term cultured adult cardiomyocytes exposed to doxorubicin 
Cytotechnology  2009;61(1-2):25-36.
In failing hearts cardiomyocytes undergo alterations in cytoskeleton structure, contractility and viability. It is not known presently, how stress-induced changes of myofibrils correlate with markers for cell death and contractile function in cardiomyocytes. Therefore, we have studied the progression of contractile dysfunction, myofibrillar damage and cell death in cultured adult cardiomyocytes exposed to the cancer therapy doxorubicin. We demonstrate, that long-term cultured adult cardiomyocytes, a well-established model for the study of myofibrillar structure and effects of growth factors, can also be used to assess contractility and calcium handling. Adult rat ventricular myocytes (ARVM) were isolated and cultured for a total of 14 days in serum containing medium. The organization of calcium-handling proteins and myofibrillar structure in freshly isolated and in long-term cultured adult cardiomyocytes was studied by immunofluorescence and electron microscopy. Excitation contraction-coupling was analyzed by fura 2 and video edge detection in electrically paced cardiomyocytes forming a monolayer, and cell death and viability was measured by TUNEL assay, LDH release, MTT assay, and Western blot for LC3. Adult cardiomyocytes treated with Doxo showed apoptosis and necrosis only at supraclinical concentrations. Treated cells displayed merely alterations in cytoskeleton organization and integrity concomitant with contractile dysfunction and up-regulation of autophagosome formation, but no change in total sarcomeric protein content. We propose, that myofibrillar damage contributes to contractile dysfunction prior to cell death in adult cardiomyocytes exposed to clinically relevant concentrations of anthracyclines.
PMCID: PMC2795142  PMID: 19890731
Cardiomyocytes; Doxorubicin; Contractility; Apoptosis; Necrosis; Autophagy
2.  Alterations at the Intercalated Disk Associated with the Absence of Muscle Lim Protein 
The Journal of Cell Biology  2001;153(4):763-772.
In this study, we investigated cardiomyocyte cytoarchitecture in a mouse model for dilated cardiomyopathy (DCM), the muscle LIM protein (MLP) knockout mouse and substantiated several observations in a second DCM model, the tropomodulin-overexpressing transgenic (TOT) mouse. Freshly isolated cardiomyocytes from both strains are characterized by a more irregular shape compared with wild-type cells. Alterations are observed at the intercalated disks, the specialized areas of mechanical coupling between cardiomyocytes, whereas the subcellular organization of contractile proteins in the sarcomeres of MLP knockout mice appears unchanged. Distinct parts of the intercalated disks are affected differently. Components from the adherens junctions are upregulated, desmosomal proteins are unchanged, and gap junction proteins are downregulated. In addition, the expression of N-RAP, a LIM domain– containing protein located at the intercalated disks, is upregulated in MLP knockout as well as in TOT mice. Detailed analysis of intercalated disk composition during postnatal development reveals that an upregulation of N-RAP expression might serve as an early marker for the development of DCM. Altered expression levels of cytoskeletal proteins (either the lack of MLP or an increased expression of tropomodulin) apparently lead to impaired function of the myofibrillar apparatus and to physiological stress that ultimately results in DCM and is accompanied by an altered appearance and composition of the intercalated disks.
PMCID: PMC2192386  PMID: 11352937
dilated cardiomyopathy; N-RAP; tropomodulin; adherens junction; gap junction
3.  Point Mutations in Human β Cardiac Myosin Heavy Chain Have Differential Effects on Sarcomeric Structure and Assembly: An ATP Binding Site Change Disrupts Both Thick and Thin Filaments, Whereas Hypertrophic Cardiomyopathy Mutations Display Normal Assembly 
The Journal of Cell Biology  1997;137(1):131-140.
Hypertrophic cardiomyopathy is a human heart disease characterized by increased ventricular mass, focal areas of fibrosis, myocyte, and myofibrillar disorganization. This genetically dominant disease can be caused by mutations in any one of several contractile proteins, including β cardiac myosin heavy chain (βMHC). To determine whether point mutations in human βMHC have direct effects on interfering with filament assembly and sarcomeric structure, full-length wild-type and mutant human βMHC cDNAs were cloned and expressed in primary cultures of neonatal rat ventricular cardiomyocytes (NRC) under conditions that promote myofibrillogenesis. A lysine to arginine change at amino acid 184 in the consensus ATP binding sequence of human βMHC resulted in abnormal subcellular localization and disrupted both thick and thin filament structure in transfected NRC. Diffuse βMHC K184R protein appeared to colocalize with actin throughout the myocyte, suggesting a tight interaction of these two proteins. Human βMHC with S472V mutation assembled normally into thick filaments and did not affect sarcomeric structure. Two mutant myosins previously described as causing human hypertrophic cardiomyopathy, R249Q and R403Q, were competent to assemble into thick filaments producing myofibrils with well defined I bands, A bands, and H zones. Coexpression and detection of wild-type βMHC and either R249Q or R403Q proteins in the same myocyte showed these proteins are equally able to assemble into the sarcomere and provided no discernible differences in subcellular localization. Thus, human βMHC R249Q and R403Q mutant proteins were readily incorporated into NRC sarcomeres and did not disrupt myofilament formation. This study indicates that the phenotype of myofibrillar disarray seen in HCM patients which harbor either of these two mutations may not be directly due to the failure of the mutant myosin heavy chain protein to assemble and form normal sarcomeres, but may rather be a secondary effect possibly resulting from the chronic stress of decreased βMHC function.
PMCID: PMC2139848  PMID: 9105042
4.  Different Domains of the M-Band Protein Myomesin Are Involved in Myosin Binding and M-Band TargetingV⃞ 
Molecular Biology of the Cell  1999;10(5):1297-1308.
Myomesin is a 185-kDa protein located in the M-band of striated muscle where it interacts with myosin and titin, possibly connecting thick filaments with the third filament system. By using expression of epitope-tagged myomesin fragments in cultured cardiomyocytes and biochemical binding assays, we could demonstrate that the M-band targeting activity and the myosin-binding site are located in different domains of the molecule. An N-terminal immunoglobulin-like domain is sufficient for targeting to the M-band, but solid-phase overlay assays between individual N-terminal domains and the thick filament protein myosin revealed that the unique head domain contains the myosin-binding site. When expressed in cardiomyocytes, the head domains of rat and chicken myomesin showed species-specific differences in their incorporation pattern. The head domain of rat myomesin localized to a central area within the A-band, whereas the head domain of chicken myomesin was diffusely distributed in the cytoplasm. We therefore conclude that the head domain of myomesin binds to myosin but that this affinity is not sufficient for the restriction of the domain to the M-band in vivo. Instead, the neighboring immunoglobulin-like domain is essential for the precise incorporation of myomesin into the M-band, possibly because of interaction with a yet unknown protein of the sarcomere.
PMCID: PMC25262  PMID: 10233145

Results 1-4 (4)