Background: Cardiovascular diseases such as myocardial infarction (MI) remain a leading cause of death in the world. Matrix metalloproteinases (MMPs) are not only essential for the cleavage of collagen but are also modifying inflammatory cytokines. Thus, MMPs are playing a substantial role in the context of fibrotic as well as inflammatory processes in tissue remodelling after MI.

 

Purpose: Mmp13 is the highest expressed collagenase in the murine left ventricle (LV). Previous results of our group revealed, that Mmp13 is highly upregulated in the LV after 1 day until at least 5 days post-MI in mice. Therefore, the aim of this study was to characterize the role of MMP13 in MI and to evaluate its potential for treatment options. In the human LV, the highest expressed collagenase is MMP1. Single nucleotide polymorphisms (SNPs) in the promotor region of MMP1 can lead to alterations in gene expression level. Therefore, we analysed the genotype of 3 SNPs in approximately 2000 patients admitted to the emergency department with suspected MI to reveal associations with the development of MI and outcome after MI. 

 

Results: To determine the cellular origin of elevated Mmp13 levels after MI, Mmp13 expression in different cardiac cell types, such as cardiomyocytes, fibroblasts and immune cells was accessed under ischaemic conditions. After activation with ischeamic secretome of cardiomyocytes, the Mmp13 expression of macrophages (6.6-fold to control; p=0.0286) and fibroblasts (4.9-fold; p=0.0079) was significantly increased. Under stimulation with ischaemic secretome of fibroblasts, Mmp13 expression of macrophages (4.3-fold; p=0.0286) and leukocytes (2.3-fold; p=0.0260) was significantly elevated. Additionally to the in vitro experiments, the cellular origin of Mmp13 was investigated on tissue sections using RNAscope in situ-hybridization. To investigate the functional role of MMP13 during MI, MMP13-knockout (KO) mice were compared to wildtype (WT) littermates after MI induction. While the survival of WT mice was about 50%, only very few KO mice died after MI (p=0.0107). Most WT mice died due to cardiac rupture between day 3 and 8 after MI. Therefore, we investigated the gene expression of WT and KO mice at day 5 post-MI via RNA sequencing, revealing differences in inflammatory as well as remodelling processes. Moreover, MMP13-KO-mice showed benefits in cardiac function measured by hemodynamic compared to WT littermates 28 days post-MI.

For the human cohort study, two patient groups (non-MI and MI) were restricted out of the BACC cohort at the University Heart and Vascular Centre Hamburg. In these groups, genotypes for 3 SNPs were distinguished. Hazard ratios adjusted to age and male sex were assessed, to evaluate risk for MI and risk for death after MI in dependency of the allele. Risk for death was significantly altered between the investigated genotypes in 2 of 3 investigated SNPs, indicating a role of MMP1 in the remodelling process after myocardial infarction.

 

Conclusion: High levels of Mmp13 after MI originate mainly from activated macrophages and from activated fibroblasts. MMP13-deficiency is beneficial for mice after MI, leading to less cardiac inflammation on gene expression level and to an improved cardiac function 28 days post-MI compared to WT controls. Analysis of SNPs of the human functional homologue of Mmp13 – MMP1 – revealed an association of MMP1 with remodelling processes after MI.