Hemodynamic unloading via heterotopic cardiac transplantation resulted in a 53% decrease in the rate of myosin heavy chain synthesis and a shift from alpha to beta myosin heavy chain mRNA expression.
Does hemodynamic unloading via heterotopic transplantation reduce myosin heavy chain synthesis and alter gene expression in rat hearts?
Hemodynamic unloading of the heart leads to rapid cardiac atrophy characterized by decreased myosin heavy chain synthesis due to translational changes and a shift from alpha to beta MHC isoform expression.
Effect estimate: 53% decrease
Absolute Event Rate: 0.46% vs 0.97%
p-value: p=<0.05
Cardiac work is a major determinant of heart size and growth. Heterotopic cardiac isografts are hemodynamically unloaded and undergo atrophy. To determine the molecular changes that occur as a result of hemodynamic unloading, we have studied the rate of synthesis of total cardiac proteins and myosin heavy chain (MHC) and the expression of the myosin heavy chain gene as reflected in the messenger RNA levels for alpha- and beta-MHC isoforms. 72 h after transplantation there is a significant decrease in left ventricular size accompanied by a 27% decrease in the rate of total cardiac protein synthesis and a 53% decrease in the rate of myosin heavy chain synthesis. In contrast to isografts 14 d after transplantation which have a decrease in protein synthetic capacity, simultaneous measurements of 18S ribosomal RNA and myosin messenger RNA suggest that after 3 d the decrease in synthesis is due to a change in the efficiency of protein translation. While the working in situ heart expresses primarily alpha-MHC mRNA (97%) hemodynamic unloading leads to a 43% decrease in alpha-MHC mRNA concentration and the de novo expression of the beta-MHC mRNA. Total MHC mRNA (alpha plus beta) concentration analyzed by a quantitative S1 nuclease protection assay was similar in the two groups of hearts. Thus, in association with hemodynamic unloading there are changes in cardiac myosin heavy chain content as a result of both gene transcription and protein translation mechanisms.
Klein et al. (Wed,) conducted a other in Hemodynamic unloading (cardiac atrophy). Heterotopic cardiac transplantation (hemodynamic unloading) vs. In situ (host) working heart was evaluated on Myosin heavy chain (MHC) protein synthetic rate (mg/d per LV) at 72 hours (53% decrease, p=<0.05). Hemodynamic unloading via heterotopic cardiac transplantation resulted in a 53% decrease in the rate of myosin heavy chain synthesis and a shift from alpha to beta myosin heavy chain mRNA expression.