Cardiomyocyte‐Specific Transgenic MMP9 Overexpression Induces Cardiac Remodeling

Abstract

Objective Activated matrix metalloproteinase-9 (MMP9), a collagenase, promotes cardiac remodeling leading to dysfunction. MMP9 is secreted by a wide variety of cells including cardiomyocytes. Although the role of MMP9 secreted from leukocytes and fibroblasts have been studied, very little is known about the role of cardiomyocyte-specific MMP9. Hypothesis Cardiomyocyte-specific MMP9 overexpression induces cardiac remodeling. Materials and Methods We have developed a novel cardiomyocytes-specific MMP9 transgenic (M9Tg) mouse strain. We used alpha-myosin heavy chain promoter and knocked in MMP9 gene using CRISPR-Cas9 method. After validation through genotyping, we performed gravimetric analyses and evaluated cardiac function by M-Mode echocardiography (short-axis), and hemodynamic changes by pressure-volume loop (open-chest, 4mm catheter, Transonic) studies. Results Eighteen-week old male M9Tg mice had a higher body weight and other organ's weight compared to the sibling WT. In four mice, the comparison of M9Tg/WT: body weight (g) = 26.8/24.8, heart weight (mg) = 119.0/107.0, Liver (mg) = 1309.5/1203.3, Kidney (mg) = 159.6/141.6, lung (mg) = 154.8/141.3). There was no significant change in the size of these organs relative to their body weight in M9Tg mice. The M-mode echocardiography analysis of three mice showed a decrease in cardiac output (WT= 15.8 ± 1.1, M9Tg =13.5 ± 0.8, P= 0.038) and a trend of decrease in fractional shortening (WT =27.4 ± 3.6, M9Tg = 24.9 ± 2.0, P = 0.231) and an increase in left ventricular mass (WT = 75.1 ± 4.1, M9Tg = 80.5 ± 3.8, P = 0.12). The pressure-volume loop study with two WT and three M9Tg mice showed an increase in dp/dt max (average, WT =5881.5, M9Tg = 7211.3 mmHg/s) and decrease in end systolic volume (WT = 22.1, M9Tg = 17.4 µL), suggesting a potential increase in cardiac contractility. Conclusion Cardiomyocyte-specific overexpression of MMP9 potentially increased left ventricular mass and cardiac contractility without altering fractional shortening. Further studies are ongoing to increase the sample size and examine the changes in the heart at the histological and molecular levels.