Cardiac MHC gene expression: more complexity and a step forward

摘要

within cardiac muscle, the myosin heavy chain (MHC) protein is a major component of the contractile machinery. MHC provides structural integrity, and its isoform is a major determinant of contractile and functional properties of the myocardium (1, 8). Cardiac MHC isoforms exist as homologous or heterologous dimers, and a unique gene product encodes each. At the genomic level, alpha- and beta-MHC genes are organized in tandem over a 60-kb region on human chromosome 14 (18). At the protein level, the cardiac a- and p-MHC proteins have a high degree (94%) of sequence identity, and divergence only occurs in clusters of functionally important regions such as the ATPase catalytic site (16). Although the human heart expresses predominantly the beta-MHC protein, a small but significant amount of a-MHC is present. The proportion of a-MHC has been shown to decline in the failing human heart, which is likely to contribute to a decline in cardiac performance (14, 17).