Differential response of cardiac fibroblasts from young adult and senescent rats to ANG II

The intracardiac ANG II-forming pathway is activated in the senescent myocardium, raising the possibility of enhanced ANG II effects on cardiac fibroblasts. This study established an in vitro model of cultured cardiac fibroblasts from aged rats to examine if the response of these cells to ANG II is modified in the aged heart. Levels of mRNA encoding renin, angiotensinogen, and the AT₁ receptor subtype in cardiac fibroblasts from young adult and senescent rats were quantified by RT-PCR, net collagen production by a hydroxyproline-based assay, and transforming growth factor (TGF)-β levels using a commercial kit. In cardiac fibroblasts from young adult rats, ANG II significantly enhanced AT₁ mRNA levels, net collagen production, and TGF-β production. In fibroblasts from the aged myocardium, ANG II downregulated AT₁ mRNA expression, had a less pronounced effect on net collagen production, and had no effect on TGF-β production. Such age-related modification of the response of cardiac fibroblasts to ANG II may counteract the effects of augmented intracardiac ANG II production in the senescent heart, limiting fibrogenesis.