Atsushi Tachibana

Novel MRI Contrast Agent from Magnetotactic Bacteria Enables In Vivo Tracking of iPSC-derived Cardiomyocytes

Therapeutic delivery of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iCMs) represents a novel clinical approach to regenerate the injured myocardium. However, methods for robust and accurate in vivo monitoring of the iCMs are still lacking. Although superparamagnetic iron oxide nanoparticles (SPIOs) are recognized as a promising tool for in vivo tracking of stem cells using magnetic resonance imaging (MRI), their signal persists in the heart even weeks after the disappearance of the injected cells. This limitation highlights the inability of SPIOs to distinguish stem cell viability. In order to overcome this shortcoming, we demonstrate the use of a living contrast agent, magneto-endosymbionts (MEs) derived from magnetotactic bacteria for the labeling of iCMs. The ME-labeled iCMs were injected into the infarcted area of murine heart and probed by MRI and bioluminescence imaging (BLI). Our findings demonstrate that the MEs are robust and effective biological contrast agents to track iCMs in an in vivo murine model. We show that the MEs clear within one week of cell death whereas the SPIOs remain over 2 weeks after cell death. These findings will accelerate the clinical translation of in vivo MRI monitoring of transplanted stem cell at high spatial resolution and sensitivity.

Paracrine Effects of the Pluripotent Stem Cell-Derived Cardiac Myocytes Salvage the Injured MyocardiumNovelty and Significance

Rationale: Cardiac myocytes derived from pluripotent stem cells have demonstrated the potential to mitigate damage of the infarcted myocardium and improve left ventricular ejection fraction. However, the mechanism underlying the functional benefit is unclear. Objective: To evaluate whether the transplantation of cardiac-lineage differentiated derivatives enhance myocardial viability and restore left ventricular ejection fraction more effectively than undifferentiated pluripotent stem cells after a myocardial injury. Herein, we utilize novel multimodality evaluation of human embryonic stem cells (hESCs), hESC-derived cardiac myocytes (hCMs), human induced pluripotent stem cells (iPSCs), and iPSC-derived cardiac myocytes (iCMs) in a murine myocardial injury model. Methods and Results: Permanent ligation of the left anterior descending coronary artery was induced in immunosuppressed mice. Intramyocardial injection was performed with (1) hESCs (n=9), (2) iPSCs (n=8), (3) hCMs (n=9), (4) iCMs (n=14), and (5) PBS control (n=10). Left ventricular ejection fraction and myocardial viability, measured by cardiac magnetic resonance imaging and manganese-enhanced magnetic resonance imaging, respectively, was significantly improved in hCM- and iCM-treated mice compared with pluripotent stem cell- or control-treated mice. Bioluminescence imaging revealed limited cell engraftment in all treated groups, suggesting that the cell secretions may underlie the repair mechanism. To determine the paracrine effects of the transplanted cells, cytokines from supernatants from all groups were assessed in vitro. Gene expression and immunohistochemistry analyses of the murine myocardium demonstrated significant upregulation of the promigratory, proangiogenic, and antiapoptotic targets in groups treated with cardiac lineage cells compared with pluripotent stem cell and control groups. Conclusions: This study demonstrates that the cardiac phenotype of hCMs and iCMs salvages the injured myocardium effectively than undifferentiated stem cells through their differential paracrine effects.

In vivo multi-modality tracking of the regenerative effects of the human induced pluripotent stem cell-derived cardiomyocytes (iCMs)

Background In vivo multi-modality cellular and molecular imaging of the engrafted iCMs is necessary to characterize the engraftment and the regional effects on the viability of the injured myocardium. Zinc finger nuclease (ZFN)mediated integration of the reporter gene into the AAVS1 locus in the iCMs and manganese enhanced MRI (MEMRI) should allow precise in vivo detection of myocardial regeneration.

Cardiac MRI detection of infarct size reduction with hypothermia in porcine ischemia reperfusion injury model

Background Hypothermia has been shown to provide cardiac protection after a STEMI insult in prior animal and post-hoc human studies. However, the influence of pre-reperfusion temperature on myocardial infarct size is not fully characterized. We employed cardiac MRI to determine the impact of moderate hypothermia (32C) upon infarct size in a porcine ischemia-reperfusion injury (IR) model using an endovascular cooling catheter. Methods

INCREASED MYOCARDIAL VIABILITY AND FUNCTION MEASURED BY MANGANESE-ENHANCED MRI (MEMRI) DEMONSTRATE MYOCARDIAL REGENERATION BY HUMAN PLURIPOTENT STEM CELL DERIVED CARDIOMYOCYTES (HPCMS)

background: Human pluripotent stem cell derived cardiomyocytes (hPCMs) hold the potential to regenerate the myocardium and enable restoration. Manganese-enhanced MRI (MEMRI) allows direct evaluation of myocardial viability. Persistent engraftment of the hPCMs associated with viability and LVEF increase suggests regenerative changes. This study evaluates whether the hPCMs generate regenerative changes in the murine model of myocardial injury.

THERAPEUTIC HYPOTHERMIA DOSE RESPONSE ON INFARCT SIZE IN ACUTE MYOCARDIAL INFARCTION USING ENDOVASCULAR COOLING AND REWARMING

Hypothermia treatment can provide substantial cardiac protection after ischemic insult and before reperfusion. However, there is insufficient data on the relationship between myocardial salvage and degree of cooling. We evaluated the effect of mild hypothermia dose on reduction of acute infarct size

Direct measurement of myocardial viability by manganese-enhanced MRI (MEMRI) tracks the regenerative effects by human pluripotent stem cell derived cardiomyocytes (hPCMs)

Background Human pluripotent stem cell derived cardiomyocytes (hPCMs) may regenerate the myocardium to restore the cardiac function. Manganese-enhanced MRI (MEMRI) enters the cardiomyocytes via calcium channel to generate viability signal directly. Persistent engraftment of the hPCMs associated with increased myocardial viability and LVEF suggests regeneration. This study tests the hypothesis that hPCMs regenerate the injured murine myocardium.