Hypertrophy-associated Gene Induction after β -Adrenergic Stimulation in Adult Cardiomyocytes

In isolated cardiomyocytes, hypertrophic responsiveness to β -adrenergic stimulation can be induced by pre-exposure of the cells to TGF- β. To characterize genes involved in β -adrenergically mediated hypertrophy, mRNA expression patterns in isoprenaline-stimulated cardiomyocytes which were pre-exposed to TGF-β were analysed by differential display RT-PCR analysis. Eighteen fragments, upregulated by isoprenaline, were identified. Six of them, which code for proteins with known function, were further analysed by RT-PCR (1) to verify their induction after β -adrenergic stimulation, (2) to restrict their number to genes only upregulated after hypertrophy inducingβ -adrenergic stimulation, and (3) to study their expression in stroke-prone spontaneous hypertrophic rats (SHR-sp), an in vivo model of myocardial hypertrophy, in which elevated levels of TGF- β are found. Induction by isoprenaline could be proved for all but one of the six genes. Further analysis of these genes in freshly isolated myocytes, which respond with hypertrophic growth only to α - but not β -adrenergic stimulation, revealed that three of them, coding for the translation initiation factor sui 1, the cis-golgi transport protein p28 and the mitochondrial NADH-dehydrogenase II subunit, are specifically induced in TGF- β -pre-exposed cardiomyocytes after β -adrenergic stimulation. Their induction is therefore closely associated with a β -adrenergic growth response in isolated cardiomyocytes. p28-mRNA is also markedly increased in SHR-sp rats. Antisense experiments revealed a functional importance of p28 for the β -adrenergic growth response in isolated cardiomyocytes. Therefore, p28 seems causally involved in this β -adrenergic growth response.