Regulation of antisense RNA expression during cardiac MHC gene switching in response to pressure overload

Hypertension has been shown to cause cardiac hypertrophy and a shift in myosin heavy chain ( MHC) gene expression from the faster alpha- to slower beta- MHC isoform. The expression of the beta- and alpha- MHC pre- mRNAs, mRNAs, as well as the newly discovered antisense beta- RNA were analyzed in three regions of the normal control ( NC) and 12- day pressure- overloaded ( AbCon) hearts: the left ventricle apex, left ventricle base, and the septum. The RNA analyses in the AbCon heart targeted both the 5 ' and the 3 ' ends of each RNA molecule. beta- MHC mRNA expression significantly increased relative to control in all three regions, regardless of the target site ( 5 ' or 3 ; end). In contrast, alpha- MHC pre- mRNA expression in the AbCon heart depended on the site of the measurement ( 5 ' vs. 3 ' end). For example, whereas the pre- mRNA did not change when targeted at the 3 ' end ( last intron), it increased significantly in the AbCon heart when measurement targeted the 5 ' end ( 2nd intron) of the 25- kb molecule. Analyses of the antisense beta- RNA revealed that its expression in the AbCon heart was significantly decreased relative to control regardless of its measurement site. A negative correlation was observed between the beta- mRNA expression and the antisense beta- RNA ( P < 0.05), suggesting an inhibitory role of antisense RNA on the sense beta- MHC gene expression. In contrast, a positive correlation was observed between the antisense beta- RNA and the alpha- MHC pre- mRNA ( P < 0.05). This latter observation along with the beta- MHC gene position relative to that of the beta- antisense suggest that the alpha- MHC sense and beta- antisense transcription are coregulated likely via common intergenic regulatory sequences. Our results suggest that the increased beta- MHC expression in the AbCon heart not only is the result of increased beta- MHC transcription but also involves an antisense beta- RNA regulation scheme. Although the exact mechanism concerning antisense regulation is not clear, it could involve modulation of both transcriptional activity of the beta- MHC gene and posttranscriptional processing.