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Objective : Myocardial fibrosis contributes to the impairing of cardiac function and characterizes ageing, but is also a consequence of atherosclerotic ischemic disease. Since atherosclerosis is a slow progressive disease, which prevails in elderly populations, the aim of this study was to distinguish the contribution of ageing and atherosclerosis to cardiac fibrosis. Methods : Coronary atherosclerosis was induced in 5–6-year-old rabbits by a hyperlipemic diet for 9 months. Left ventricular (LV) collagen was quantified by densitometric analysis after Sirius-Red staining; an immunohistochemical investigation of the interstitium was also performed. Results : Atherosclerosis was associated to a marked increase of left ventricular interstitial collagen with the appearance of fibrotic foci and a decrease of coronary vessel endothelial nitric oxide synthase (eNOS) expression. In fibrotic foci, abundant macrophages co-localized with transforming growth factor beta-1 (TGFβ-1)-positive myofibroblasts and vascular cell adhesion molecule-1 (VCAM-1) positive microvessels (52.3±3.9%). In normocholesterolemic rabbits, ageing resulted in a fourfold increase of myocardial interstitial collagen, with alpha-smooth muscle actin and TGFβ-1 negative fibroblasts and VCAM-1 positive microvessels (19.4±1.2%) without macrophages, suggesting a role of endothelial dysfunction in age-related fibrosis. Conclusions : There is a distinct difference between ageing and coronary atherosclerosis-induced cardiac fibrosis, although the effects may be cumulative. In the cascade of events leading to myocardial remodeling, reparative fibrosis with TGFβ-1-positive myofibroblasts and interstitial inflammation were the major findings in atherosclerotic old rabbits, whereas with ageing alone, interstitial fibrosis with TGFβ-1 negative fibroblasts and VCAM-1 positive microvessels prevailed.

Aims Flt-1 is an fms-like tyrosine kinase receptor which binds to vascular endothelial growth factor (VEGF) and placental growth factor (PlGF). Ligand activation and blocking of flt-1 influence several vascular smooth muscle cell (SMC) functions, including apoptotic susceptibility. However, downstream signal transduction pathways by which flt-1 regulates SMC apoptosis have still to be investigated. Methods and results Flt-1 expression and apoptosis in Wistar rat aortic intimal cells 15 days after ballooning were studied by immunohistochemistry, cytometry, cell sorting, western blotting, and PCR. Anti-flt1 blocking antibody effects were compared with those of anti-PlGF and anti-VEGF antibodies. Rat aortic intimal cells 15 days after injury exhibited increased flt-1 protein and mRNA and lower smooth muscle markers compared with normal media SMCs. Immunoreactivity for flt-1 protein was also observed in apoptotic intimal cells. Anti-flt-1 (EC(50) = 16.5 ng/mL) and anti-PlGF (EC(50) = 20.5 ng/mL) antibodies added to intimal cultures reduced serum-deprived apoptosis but not serum-and PDGF-BB-induced proliferation; the anti-VEGF antibody was ineffective. Sorted flt-1(+) cells were more clonogenic than flt-1 and whole intimal SMC populations. Increased nuclear factor-kappaB (NF-kappa B) and inhibitor of apoptosis protein-1 (IAP-1) and reduced bax levels associated with the anti-flt-1-induced increase of intimal SMC survival; the latter was prevented by NF-kappa B activity inhibitor and IAP-1 interfering RNA (RNAi). Blocking of NF-kappa B activity reduced IAP-1 expression and prevented IAP-1 RNAi effects. Increased flt-1 immunoreaction was also documented in human atheromatous lesions. Conclusion Our results show that anti-flt-1 blocking reduces apoptosis through NF-kappa B and the downstream IAP-1 pathway. The close link between flt-1, PlGF, and apoptotic susceptibility of intimal SMCs suggests new potential strategies aimed at influencing post-injury arterial remodelling.