Cellular oncogene expression in the idiopathic cardiomyopathic hamster heart during the growing process

Cardiac Tumors and Dysrhythmias in Transgenic Mice

Transgenic mice expressing atrial natriuretic factor-SV40 T-antigen fusion genes (ANF-TAG) developed cardiac tumors asymmetrically in the right atrium. Features associated with cardiac failure, including increased plasma creatine kinase activity (MM and MB) and ventricular dysrhythmias, also were associated with atrial tumor growth. These atrial tumors were able to grow at histocompatible sites (subcutaneously in syngeneic animals) for protracted periods of time yielding a series of transplantable atrial tumor lineages. The transplantable tumors displayed several cardiac-specific characteristics, such as endogenous electrical activity and expression of cardiac-specific proteins. These transplantable atrial tumors constitute a novel experimental resource for developing cell lines which display an adult cardiac phenotype.

Expression of proto-oncogenes and gene mutation of sarcomeric proteins in patients with hypertrophic cardiomyopathy

Several mutations of cardiac beta-myosin heavy chain (beta-MHC) gene were reported in patients with hypertrophic cardiomyopathy (HCM). Involvement of proto-oncogenes has been shown in the mechanism of experimental cardiac hypertrophy. This study sought to examine the effects of c-H-ras and c-myc expression in the steady-state myocardium on hypertrophic changes and to evaluate the possible interaction between beta-MHC mutation and proto-oncogene expression in HCM. Endomyocardial biopsy was performed in 17 HCM patients (5 beta-MHC mutations and 1 troponin T mutation) and 7 control subjects (no mutation). Reverse transcription-polymerase chain reaction analysis revealed c-H-ras expression in all members of both groups. Cardiomyocyte size was correlated with the expression level of c-H-ras (P<0.001), and c-H-ras expression was upregulated in HCM patients (P<0.01). HCM patients with a beta-MHC mutation had the higher c-H-ras expression than did control subjects or patients without a mutation (P<0.01). c-myc mRNA was expressed in 7 of 17 HCM patients but not in control subjects. Myocyte size was greater in c-myc-positive HCM patients than in control subjects and c-myc-negative HCM patients (P<0.001 and P<0.05, respectively). The proto-oncogene expression did not affect clinical findings, myocardial fibrosis, or disarray. In conclusion, c-H-ras and c-myc expression in the steady-state myocardium may play a role in the hypertrophic mechanism in HCM. It is possible that ss-MHC gene mutation has some effect on the regulation of proto-oncogene expression in HCM.

Immunocytochemical detection of enhanced expression of c-myc protein in the heart of cardiomyopathic hamster

An immunocytochemical study was performed to examine the expression of cellular c-myc protein in the heart of 30-, 120- and 180-day-old cardiomyopathic Syrian UM-X7.1 hamsters. The heart of age- and sex-matched BIO-RB hamster was used as normal control. In paraffin sections, an immunostaining for c-myc was markedly increased in cytoplasm of cells from the UM-X7.1 heart as compared with that of the BIO-RB heart which showed a weak staining. However, c-myc was localized in nuclei of cells in frozen sections of the heart. Specific cell types of the heart were differentiated with anti-vimentin, and we found that the increased expression of c-myc was present in nuclei of muscle cells of the UM-X7.1 myocardium. A quantitative study of c-myc-positive nuclei of muscle and nonmuscle cells was carried out by a video micrometer. The mean number of c-myc-positive nuclei of muscle cells was significantly higher in the cardiomyopathic heart than in the control heart from hamsters of all ages studied. These results suggest that the increase of c-myc protein may relate to the pathological state or pathogenesis of the hereditary cardiomyopathy.

Alteration of extracellular matrix in dilated cardiomyopathic hamster heart

The purpose of this study was to characterize the collagen in hereditary dilated cardiomyopathic hamster hearts, and to examine the participation of the collagen in the occurrence and progression of cardiomyopathy. BIO 53.58 hamsters (5, 10, 20 weeks old) were used as the model of dilated cardiomyopathy. Flb hamsters were used as controls. The collagen content was almost constant at any age in the Flb hamsters, but increased with age in BIO 53.58 hamsters. Type III collagen increased significantly in BIO 53.58 hamsters at 10 weeks. The acetic acid solubility of collagen decreased in BIO 53.58 hamsters as the fibrosis progressed, but was unchanged in controls. Reducible crosslinks showed a tendency to decrease progressively in BIO 53.58 hamsters. There were no differences between Flb and BIO 53.58 hamsters at 5 weeks, but its expression in BIO 53.58 hamsters at 10 and 20 weeks of age increased compared to Flb controls. These findings indicate that in the early phase of cardiomyopathy the extracellular matrix of the myocardium is rich in type III collagen. In the later phase, the matrix resembles that of hard tissues, whose collagen is mainly of type I collagen and is insoluble. These data suggest that the increased collagen synthesis may impair the cardiac function in the development of cardiomyopathy.

Morphometric analysis of cultured normal and cardiomyopathic hamster heart cells after immunofluorescent staining for tubulin and alpha-actinin

The cardiomyopathic (CM) hamster (Strain UM X7.1) develops a progressive cardiomyopathy characterized by cellular necrosis, hypertrophy and congestive heart failure. To better understand these abnormalities, this study was undertaken to investigate possible abnormalities in the morphology and distributions of cytoskeletal proteins in normal and cardiomyopathic hamster heart cells in vitro. Primary cultures of cardiac myocytes from normal and CM newborn hamsters were analyzed and compared by indirect immunofluorescent microscopy after 3, 5, 7 and 9 days in culture. The distributions of the cytoskeletal proteins, alpha-actinin and tubulin, were examined in cultured hamster cardiac myocytes. After the cells attach to coverslips, both normal and CM myocytes appear rounded in shape. After 5 days in culture, CM myocytes show fewer cytoplasmic projections than normal. To assess this phenomenon, the area and perimeter dimensions of normal and CM myocytes were analyzed by morphometric methods. It was determined that cardiomyopathic cells in culture become progressively larger in area but smaller than normal in their perimeter dimensions. A statistically significant difference was noted from day 3 onward. This result confirms that cardiomyopathic cells have abnormal shapes in vitro. It is conceivable that a reduction of the perimeter dimension in CM cells may be related to the reported calcium overload or to other biochemical or physiological lesions. In addition, the greatest density of tubulin staining is present immediately around the nucleus, with fluorescent "rays" radiating out to the cell periphery. Most of the myofibrils labelled by anti-alpha-actinin antibody showed parallel arrangements with respect to each other in normal myocytes whereas in CM heart cells the myofibrils were disarrayed. There were no differences in the distributions of tubulin and alpha-actinin in normal and cardiomyopathic myocytes in culture.