Tissue inhibitor of metalloproteinases (TIMPs) can mediate myocardial remodelling, hypertrophy, and fibrosis in heart disease. We investigated the impact of TIMP2 vs. TIMP3 deficiency in angiotensin II (Ang II)-induced myocardial remodelling and cardiac dysfunction.Methods and results
TIMP2−/−, TIMP3−/−, and wild-type (WT) mice received Ang II/saline (Alzet pump) for 2 weeks. Ang II infusion resulted in enhanced myocardial hypertrophy and lack of fibrosis in TIMP2−/−, and conversely, excess fibrosis without hypertrophy in TIMP3−/− mice. Echocardiographic imaging revealed preserved ejection fraction in all groups; however, exacerbated left ventricular (LV) diastolic dysfunction was detected in Ang II-infused TIMP2−/− and TIMP3−/− mice, despite the suppressed Ang II-induced hypertension in TIMP3−/− mice. Enhanced hypertrophy in TIMP2−/− mice impaired active relaxation, while excess fibrosis in TIMP3−/− mice increased LV passive stiffness. Adult WT cardiomyocytes, only when co-cultured with cardiac fibroblasts, exhibited Ang II-induced hypertrophy which was suppressed in TIMP3−/− cardiomyocytes. In vitro studies on adult cardiofibroblasts (quiescent and cyclically stretched), and in vivo analyses, revealed that the increased fibrosis in TIMP3−/−-Ang II hearts is due to post-translational stabilization and deposition of collagen by matricellular proteins [osteopontin and Secreted Protein Acidic and Rich in Cysteine (SPARC)], which correlated with increased inflammation, rather than increased de novo synthesis. Reduced cross-linking enzymes, LOX and PLOD1, could underlie suppressed collagen deposition in TIMP2−/−-Ang II hearts.Conclusion
TIMP2 and TIMP3 play fundamental and differential roles in mediating pathological remodelling, independent from their MMP-inhibitory function. TIMP2−/− and TIMP3−/− mice provide a unique opportunity to study myocardial hypertrophy and fibrosis independently, and their impact on cardiac dysfunction.