Age-related changes in fibronectin expression in spontaneously hypertensive, Wistar-Kyoto, and Wistar rat hearts

The effects of age and blood pressure on fibronectin expression in the rat heart were studied in the normotensive Wistar and Wistar-Kyoto (WKY) strains and in the spontaneously hypertensive rat (SHR). Fibronectin mRNA expression decreased threefold between 10 and 40 weeks of age in Wistar hearts, with changes of similar magnitude occurring between 6 and 24 weeks in WKY rats. In contrast, no decrease in fibronectin mRNA was observed in SHR hearts during this time span. These results are in contrast to changes observed previously in the aorta, where an increase in fibronectin mRNA occurred with age in all three rat strains. Ribonuclease protection analysis showed a small age-specific increase in the relative content of EIIIA+ fibronectin mRNA isoforms in hearts from Wistar rats, whereas no change was found in the relative amount of either EIIIA or EIIIB isoforms in SHR hearts. Changes similar to those observed for fibronectin mRNA, although of different magnitudes, were observed in mRNA levels for collagen alpha 1(III) and beta 1 integrin. In Wistar hearts, collagen alpha 1(III) mRNA levels decreased fivefold to sixfold between 10 and 40 weeks of age, whereas a twofold to threefold decrease in beta 1 integrin was observed in WKY hearts between 6 and 24 weeks of age. Western blot analysis revealed a positive correlation between fibronectin mRNA and protein for age-dependent changes in ventricular tissue but not in the atria, suggesting that the regulation of fibronectin expression during the changes common to both aging and hypertrophy could involve both transcriptional and posttranscriptional mechanisms.