Hybrid Optical and CT Imaging reveals increased Matrix Metalloprotease Activity and Apoptosis Preceding Cardiac Failure in Progeroid Ercc1 mice

In this study, we tested the use of functional micro-Computed Tomography (microCT) imaging combined with near infrared fluorescent (NIRF) probes to directly report the in vivo activity of key biomarkers of age-related cardiac failure using progeroid Ercc1 mouse models. Mutations in the ERCC1 gene causes diminished DNA damage repair and an accelerated aging phenotype in mice, including cardiovascular aging. We tested the effect and kinetics of diminished DNA damage repair on protease activity and apoptosis and possible subsequent cardiac failure in vivo. Full body Ercc1, cardiomyocyte-specific Ercc1 and their Ercc1-proficient controls were imaged with contrast enhanced microCT for anatomical reference and to assess cardiac morphology and function. The NIRF probes MMPSense680TM and Annexin-Vivo750TM were used to image matrix metalloprotease activity and apoptosis, respectively. Functional microCT analysis was compared to ultrasound imaging and results were validated by histology. Ercc1 deficiency resulted in changes in left ventricular geometry and functioning at 24 weeks of age; an increase in left ventricular end-diastolic and left ventricular end-systolic volume was observed, thereby leading to an overall decrease in stroke volume and a substantial reduction in left ventricular ejection fraction. Ercc1-proficient mice showed relative stable volumes over time. Moreover, Ercc1 deficiency leads to increased myocardial apoptosis at 12 and 24 weeks of age, and a gradual increase of MMP activity already starting at 6 weeks, suggesting that these processes precede cardiac failure in these progeroid Ercc1 mice. Cardiomyocyte-specific inactivation of Ercc1 also led to impaired cardiac functioning and increased myocardial apoptosis and MMP activity, indicating that Ercc1 deficiency in cardiomyocytes is associated with adverse cardiac remodeling and poor cardiac functioning. In conclusion, combined microCT and optical imaging allows simultaneous analysis of molecular and functional changes in mouse models for accelerated aging and shows that gradual increases in matrix metalloprotease activity is followed by apoptosis and cardiac functional decline in progeroid Ercc1 mice. 2 Erasmus Medical Center Rotterdam