Aims: A selective nonpeptide agonist for the angiotensin AT2 receptor compound 21 (C21) improved cardiac functions 7 days after myocardial infarction (MI). Here, we aimed to investigate what are the cellular mechanisms underlying cardiac protection in the late stage after MI.
Methods and Results: MI was induced in Wistar rats by permanent ligation of the left coronary artery. Treatment with C21 (0.03mg/kg i.p. daily) started 6h after MI and continued for 6 weeks. Hemodynamic parameters were measured via transthoracic Doppler echocardiography and intracardiac Samba catheter. The expression of MMP9, TIMP1, TGF-β1 and collagen content were determined in left ventricle. Anti-proteolytic effects were additionally studied in primary cardiac fibroblasts.
C21 significantly improved systolic and diastolic function 6 weeks after MI in comparison with the vehicle group as shown by ejection fraction (71.2±4.7 % vs. 53.4±7.0%; p<0.001), fractional shortening (40.8±2.3% vs. 30.9±3.1%; p<0.05), LVIDs (4.4±0.5mm vs. 5.2±0.8mm; p<0.05), LV EDP (16.9±1.2mmHg vs. 22.1±1.4mmHg; p<0.05), E/A ratio, dP/dtmax and dP/dtmin (p<0.05). Moreover, C21 improved arterial stiffness parameter (AIx) (18±1.2% vs. 25%±1.8, p<0.05) and reduced collagen content (15%; p<0.05) in postinfarcted myocardium. TIMP1 protein expression in the left ventricle was strongly up-regulated (17.7-fold; p<0.05) whereas MMP9 and TGF-β1 were significantly down-regulated (1.5-fold, p<0.05; 3.4-fold p<0.001, respectively) in the treated group. In cardiac fibroblasts, C21 primarily induced TIMP1 expression followed by attenuated MMP9 secretion and TGF-β1 down-regulation.
Conclusion: C21 improves heart function in the late stage after MI and prevents cardiac remodeling. Activation of TIMP1 and subsequent inhibition of MMP9-mediated proteolysis as well as down-regulation of TGF-β1 followed by decreased collagen accumulation may attenuate disintegration of the extracellular matrix and reduce fibrosis.