Myotrophin in human cardiomyopathic heart.

Earlier, myotrophin, a factor, has been isolated, purified, and partially sequenced from spontaneously hypertensive rat hearts that stimulated myocyte growth. To evaluate the role of myotrophin in the initiation of the human dilated cardiomyopathic heart, we have isolated and purified myotrophin to homogeneity (approximately 50,000-fold) as defined by reverse-phase high-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). During purification, we used a bioassay system in which adult myocardial cells maintained in culture were used to evaluate protein synthesis by the incorporation of [3H]leucine into myocyte protein. Myotrophin purified from human dilated cardiomyopathic hearts is composed of a single polypeptide chain having an apparent molecular mass of 12 kD, determined by SDS-PAGE. The partial internal amino acid sequence of human myotrophin is very similar to that of rat myotrophin peptide T9. Using a rat myotrophin peptide (T26) antibody, we identified human myotrophin on an immunoblot. These results showed that human myotrophin possesses the T9 and T26 regions of rat myotrophin. Human myotrophin stimulated myocardial 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 with age- and sex-matched normal control hearts. From these observations, we conclude that myotrophin is present in normal human hearts, is found at higher levels in dilated cardiomyopathic human hearts, and may play a role in the initiation of cardiac hypertrophy as well as in normal growth of cardiac myocytes in humans.