Long-term effects of fatty acids on cell viability and gene expression of neonatal cardiac myocytes.

Fatty acids are the most important source of energy for the adult heart. However, cardiac substrate preference changes during development and alters in pathophysiological states. Fatty acids have also been shown to be involved in signal transduction pathways, thereby affecting gene expression in various cell systems. In the present paper the significance of changes in substrate preference and the potential role of fatty acids in signal transduction in the cardiomyocyte are briefly reviewed. Furthermore, the development of a cellular model system, useful in exploring the long-term effects of fatty acids on the normal and hypertrophic cardiomyocyte, is described. Some aspects of this model system are illustrated by showing the effects of different fatty acid species on cell viability and the effects of fatty acids on the expression of heart type fatty acid-binding protein (H-FABP), a 15 kDa protein thought to be involved in intracellular trafficking of fatty acids. To this end primary cultures of rat neonatal ventricular myocytes were kept in defined medium containing various (combinations of) substrates for up to 48 h. First, the effects of prolonged exposure to different fatty acid species, complexed to BSA, on cell viability were investigated. Exposure of the cells to saturated fatty acids (C16:0 or C18:0), but not mono-unsaturated (C16:1 or C18:1) fatty acids, resulted in cell death, as evidenced by the release of intracellular proteins like lactate dehydrogenase. The detrimental effects of saturated fatty acids were nullified by the co-addition of mono-unsaturated fatty acids. Accordingly, the combination of C16:0/C18:1 was used to examine the effects of fatty acids on the expression of H-FABP. Therefore, the cells were incubated with either (i) glucose only, (ii) fatty acids only, or (iii) glucose plus fatty acids. Incubation with fatty acids (with or without glucose) resulted in a nearly four-fold increase of the H-FABP mRNA level. Similarly, at the protein level the cellular H-FABP/LDH ratio increased almost two-fold. In hypertrophic cardiomyocytes (stimulated with the alpha1-adrenergic agonist phenylephrine) the stimulatory effect of fatty acids on H-FABP expression was mitigated. These findings strongly suggest that fatty acids are able to modulate gene expression in the context of the cardiac muscle cell.