Differential gene expression in response to ventricular unloading in rat and human myocardium

Objectives: Left ventricular unlaoding by mechanical assist devices induces mycardial atrophy. We aimed to systematically identify differentially expressed myocardial genes in a model of physiological atrophy (unloading of healthy rat myocardium) and compare these changes to those in unloaded, failing human heart.

Material and Methods: Atrophy in rat hearts was induced by heterotopic transplantation of a donor heart into the abdomen of an isogenic recipient. After one week, donor and recipient RNA was isolated. Differential gene expression was assessed by subtractive hybridization. Two screens with radioactive probes were performed to verify differentially expressed clones. Positive clones were sequenced and genes with known homology were used as probes for hybridization with RNA from seperate atrophied rat hearts as well as human tissue from normal, failing or failing and unloaded left ventricle.

Results: We picked 1880 clones from the subtractive hybridization procedure (940/940: forward/reverse runs assessing up- or downregulation). The first screen verified 465/140, the second screen 67/30 clones. 24/23 clones were sequenced and 10/14 homologies to know genes were found. In the atrophied heart, mostly respiratory chain and metabolic genes were downregulated (NADH-DH, cytochrome c oxidase, acetyl-CoA synthetase, myoglobin) and cellular recognition and stress genes are upregulated (MHC1 and 2, β2-microglobulin, HSP70). In failing human heart, cytochrome c oxidase, acetyl-CoA synthetase and myoglobin were upregulated. Unloading resulted in upregulation of β2-microglobulin and HSP70. There was no downregulation of the respiratory chain genes.

Conclusions: The genetic response of failing human myocardium to unloading differs significantly from unloading under phyisological conditions.