MYOTROPHIN IN HUMAN CARDIOMYOPATHIC HEART

Earlier, myotrophin, a factor, has been isolated, purified, and partia lly sequenced from spontaneously hypertensive rat hearts that stimulat ed myocyte growth. To evaluate the role of myotrophin in the initiatio n of the human dilated cardiomyopathic heart, we have isolated and pur ified myotrophin to homogeneity (approximately 50 000-fold) as defined by reverse-phase high-performance liquid chromatography and sodium do decyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). During pu rification, we used a bioassay system in which adult myocardial cells maintained in culture were used to evaluate protein synthesis by the i ncorporation of [H-3]leucine into myocyte protein. Myotrophin purified from human dilated cardiomyopathic hearts is composed of a single pol ypeptide chain having an apparent molecular mass of 12 kD, determined by SDS-PAGE. The partial internal amino acid sequence of human myotrop hin is very similar to that of rat myotrophin peptide T9. Using a rat myotrophin peptide (T26) antibody, we identified human myotrophin on a n immunoblot. These results showed that human myotrophin possesses the T9 and T26 regions of rat myotrophin. Human myotrophin stimulated myo cardial protein synthesis and cell growth, similar to the way in which rat myotrophin stimulated these factors. Western blot analysis showed the presence of myotrophin in both dilated cardiomyopathic and normal human hearts. In addition, we observed significantly elevated levels of myotrophin in dilated cardiomyopathic human hearts when compared wi th age- and sex-matched normal control hearts. From these observations , we conclude that myotrophin is present in normal human hearts, is fo und at higher levels in dilated cardiomyopathic human hearts, and may play a role in the initiation of cardiac hypertrophy as well as in nor mal growth of cardiac myocytes in humans.