Evidence for Minimal Cardiogenic Potential of Sca-1 Positive Cells in the Adult Mouse Heart

Thesis (Master's)--University of Washington, 2018Despite modern pharmacotherapy, heart failure remains a major medical burden. The heart has a limited regenerative capacity, and bolstering regeneration might represent new therapeutic approaches for heart failure patients. Various progenitor cells have been proposed to have cardiomyogenic properties, but this evidence is based mostly on cell culture and transplantation studies. One population of interest is characterized by the expression of Stem Cell Antigen-1 (Sca-1). Here we tested the hypothesis that Sca-1+ cells are endogenous progenitors for cardiomyocytes. We evaluated the innate cardiogenic potential of Sca-1 positive cells in vivo by generating a novel mouse model to genetic lineage-trace the fate of Sca-1+ cells. This was accomplished by introducing a tamoxifen-inducible Cre-recombinase into the Sca-1 locus (Sca-1mCm/+). Crossing this mouse line to a Cre dependent tdTomato reporter line allowed for genetic lineage-tracing of endogenous Sca-1+ cells (Sca-1mCmtdTomato). We validated the genetic lineage tracing mouse model in bone marrow and heart. Unlike previous publications suggesting significant cardiogenic potential, we found that less than 0.1% of cardiomyocytes were derived from Sca-1+ cells in the adult heart under homeostatic conditions and there was no significant change in contribution to cardiomyoctyes six months after myocardial infarction. Our results show that Sca-1+ cells in the adult heart have minimal cardiogenic potential under homeostatic conditions or in response to myocardial infarction

Quantitative Analyses of the Left Ventricle Volume and Cardiac Function in Normal and Infarcted Yucatan Minipigs

(1) Background: The accuracy of the left ventricular volume (LVV) and contractility measurements with cardiac magnetic resonance imaging (CMRI) is decreased if the papillary muscles are abnormally enlarged, such as in hypertrophic cardiomyopathy in human patients or in pig models of human diseases. The purpose of this work was to establish the best method of LVV quantification with CMRI in pigs. (2) Methods: The LVV in 29 Yucatan minipig hearts was measured using two different techniques: the “standard method”, which uses smooth contouring along the endocardial surface and adds the papillary volume to the ventricular cavity volume, and the “detailed method”, which traces the papillary muscles and trabeculations and adds them to the ventricular mass. (3) Results: Papillary muscles add 21% to the LV mass in normal and infarcted hearts of Yucatan minipigs. The inclusion or exclusion of these from the CMRI analysis significantly affected the study results. In the normal pig hearts, the biggest differences were found in measurements of the LVV, ejection fraction (EF), LV mass and indices derived from the LV mass (p < 0.001). The EF measurement in the normal pig heart was 11% higher with the detailed method, and 19% higher in the infarcted pig hearts (p < 0.0001). The detailed method of endocardium tracing with CMRI closely represented the LV mass measured ex vivo. (4) Conclusions: The detailed method, which accounts for the large volume of the papillary muscles in the pig heart, provides better accuracy and interobserver consistency in the assessment of LV mass and ejection fraction, and might therefore be preferable for these analyses

Pharmacologic therapy for engraftment arrhythmia induced by transplantation of human cardiomyocytes

Heart failure remains a significant cause of morbidity and mortality following myocardial infarction. Cardiac remuscularization with transplantation of human pluripotent stem cell-derived cardiomyocytes is a promising preclinical therapy to restore function. Recent large animal data, however, have revealed a significant risk of engraftment arrhythmia (EA). Although transient, the risk posed by EA presents a barrier to clinical translation. We hypothesized that clinically approved antiarrhythmic drugs can prevent EA-related mortality as well as suppress tachycardia and arrhythmia burden. This study uses a porcine model to provide proof-of-concept evidence that a combination of amiodarone and ivabradine can effectively suppress EA. None of the nine treated subjects experienced the primary endpoint of cardiac death, unstable EA, or heart failure compared with five out of eight (62.5%) in the control cohort (hazard ratio = 0.00; 95% confidence interval: 0–0.297; p = 0.002). Pharmacologic treatment of EA may be a viable strategy to improve safety and allow further clinical development of cardiac remuscularization therapy