Abstract 283: Gender Modulates the Effects of Tissue Factor Deficiency on Myocardial Matrix Remodelling and Urokinase Plasminogen Activator Expression
Tissue factor (TF) null mice with low-level expression of a human TF minigene (low-TF mice) develop premature cardiac fibrosis. We investigated the hypothesis that female gender affects the development of fibrosis in low-TF mice through differential protease regulation. Hearts were isolated from male and female low-TF mice and fibrosis was assessed by Trichrome staining of heart tissue sections. Protease expression was evaluated by RT-PCR in low-TF mice and littermate controls at various ages (2–5 [males only], 6–12, 13–18, 19+ weeks; 8–12 per group). Data were analysed by t-test or Kruskal-Wallis test, with results given in arbitrary units as the mean ± SEM. The time-course of cardiac fibrosis development was studied in 24 male and 30 female low-TF mice aged 7–50 weeks. Females showed delayed fibrosis onset, with interstitial collagen deposition evident in male low-TF mice from 9 weeks of age, but not until 19 weeks in females. The degree of fibrosis was also determined by measuring the area of collagen staining in heart tissue sections. At 10 (8.6 ± 5.1% vs 0.3 ± 0.1%; p = 0.005) and 30 (16.6 ± 4.4 vs 6.7 ± 1.5%; p = 0.02) weeks, male low-TF mice showed more extensive fibrosis than females. Female low-TF mice also showed delayed up-regulation of molecular markers of remodelling. MMP-3 and TIMP-1 were up-regulated in male low-TF mice from 6–12 weeks (MMP-3, 0.08 ± 0.02 vs 0.5 ± 0.1, p = 0.002; TIMP-1, 0.09 ± 0.02 vs 1.1 ± 0.3, p = 0.004), but not until after 19 weeks in females (MMP-3, 0.18 ± 0.08 vs 1.0 ± 0.2, p = 0.003; TIMP-1, 0.2 ± 0.06 vs 1.1 ± 0.3, p = 0.02). Up-regulated expression of other profibrotic markers including MT1-MMP, TIMP-2, CTGF, PAI-1 and collagen 1 and 3 was also delayed or not apparent in female low-TF mice compared to males. The only gender difference found prior to fibrosis was the down-regulation of urokinase plasminogen activator (uPA) in low-TF females (0.7 ± 0.1 vs 0.3 ± 0.05; p = 0.003) but not males (0.7 ± 0.05 vs 0.8 ± 0.1; p = 0.3). In conclusion, we have found that female gender provides some protection against the development of cardiac fibrosis in low-TF mice. This may be due to decreased cardiac uPA expression in females, as uPA deficiency has been shown to impair scar formation after myocardial infarction and reduce cardiac fibrosis after acute pressure overload.