Biology subjects

Geertz, B.

Publications and source records attributed to Geertz, B..

5 recordsLinked to original sources

bioRxiv2023

Impulse initiation in engrafted pluripotent stem cell-derived cardiomyocytes can stimulate the recipient heart.

Transplantation of pluripotent stem cell-derived cardiomyocytes is a novel promising cell-based therapeutic approach for patients with heart failure. However, engraftment arrhythmias are a predictable life-threatening complication and represent a major hurdle for clinical translation. Catheter-based electrophysiological analysis suggested that the ventricular arrhythmias were caused by an automaticity of the transplanted cells, but whether impulse generation by transplanted cardiomyocytes can propagate to the host myocardium and override the recipient rhythm has not been directly assessed experimentally. We used optogenetics to specifically activate engrafted cardiomyocytes, which resulted in impulse generation in the engrafted cardiomyocytes and stimulated the recipient heart (4/9 hearts). Thus, our study shows that transplanted cardiomyocytes can electrically couple to the host myocardium and stimulate the recipient heart, providing experimental evidence that cardiomyocyte automaticity can serve as a trigger for ventricular arrhythmias.

pharmacology and toxicology↗

bioRxiv2023

Reducing microtubule detyrosination improves heart function in HCM mice and human iPSC-engineered heart tissues

RationaleHypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and associated with left ventricular (LV) hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with the findings that -tubulin detyrosination (dTyr-tub) is markedly elevated in heart failure. Acute reduction of dTyr-tub by inhibition of the detyrosinase (VASH/SVBP complex) or activation of the tyrosinase (tubulin tyrosine ligase, TTL) markedly improved contractility and reduced stiffness in human failing cardiomyocytes, and thus poses a new perspective for HCM treatment. ObjectiveIn this study, we tested the impact of chronic tubulin tyrosination in a HCM mouse model (Mybpc3-knock-in; KI), in human HCM cardiomyocytes and in SVBP-deficient human engineered heart tissues (EHTs). Methods and ResultsAAV9-mediated TTL transfer was applied in neonatal wild-type (WT) rodents and 3-week-old KI mice and in HCM human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. We show that i) TTL for 6 weeks dose-dependently reduced dTyr-tub and improved contractility without affecting cytosolic calcium transients in WT cardiomyocytes; ii) TTL for 12 weeks improved diastolic filling, cardiac output and stroke volume and reduced stiffness in KI mice; iii) TTL for 10 days normalized cell hypertrophy in HCM hiPSC-cardiomyocytes; iv) TTL induced a marked transcription and translation of several tubulins and modulated mRNA or protein levels of components of mitochondria, Z-disc, ribosome, intercalated disc, lysosome and cytoskeleton in KI mice; v) SVBP-deficient EHTs exhibited reduced dTyr-tub levels, higher force and faster relaxation than TTL-deficient and WT EHTs. RNA-seq and mass spectrometry analysis revealed distinct enrichment of cardiomyocyte components and pathways in SVBP-KO vs. TTL-KO EHTs. ConclusionThis study provides the first proof-of-concept that chronic activation of tubulin tyrosination in HCM mice and in human EHTs improves heart function and holds promise for targeting the non-sarcomeric cytoskeleton in heart disease.

physiology↗

bioRxiv2022

Immature human engineered heart tissues engraft in a guinea pig chronic injury model

AO_SCPLOWBSTRACTC_SCPLOWEngineered heart tissue (EHT) transplantation represents an innovative, regenerative approach for heart failure patients. Late preclinical trials are underway, and the first clinical trial has started in 2021. Preceding studies revealed functional recovery after implantation of in vitro-matured EHT in the subacute stage while transplantation in a chronic injury setting was less efficient. We hypothesized that the use of immature EHT patches (EHTIm) could improve cardiomyocytes (CM) engraftment. Chronic myocardial injury was induced in a guinea pig model (n=14). EHTIm (15x106 cells) were transplanted directly after casting. Functional consequences were assessed by serial echocardiography. Animals were sacrificed four weeks after transplantation and hearts were excised for histological analysis. Cryo-injury lead to large transmural scars amounting to 26% of the left ventricle. Grafts were identified by a positive staining for human Ku80 and dystrophin, remuscularizing 9% of the scar area on average. The CM density in the graft was higher compared to previous studies with in vitro-matured EHTs and showed a greater population of immature CM. Echocardiographic analysis showed a small improvement of left ventricular function after EHTIm transplantation. In a small translational proof-of-concept study human scale EHTIm patches (4.5x108 cells) were epicardially implanted on healthy pig hearts (n=2). In summary, we provide evidence that transplantation of immature EHT patches without pre-cultivation results in better cell engraftment.

pharmacology and toxicology↗

bioRxiv2021

Contractile force of transplanted cardiomyocytes contributes to heart function after injury

Transplantation of pluripotent stem cell-derived cardiomyocytes represents an innovative therapeutic strategy for heart failure. Studies in small and large animals have demonstrated functional recovery of left ventricular function after cardiomyocyte transplantation1-4, and first clinical studies are currently underway5. Yet, the mechanism of action underlying graft-induced benefit is unknown6. Here we demonstrate that transplanted cardiomyocytes actively contribute to heart function. We transplanted cardiomyocytes with an optogenetic off-on switch in a guinea pig cardiac injury model. Light-induced inhibition of engrafted cardiomyocyte contractility resulted in a rapid decrease of left ventricular function that was fully reversible with the offset of photostimulation. Hence, our optogenetic approach demonstrated that transplanted cardiomyocytes actively participate in heart function, supporting the hypothesis that the delivery of new force-generating myocardium can serve as a regenerative therapeutic strategy.

pharmacology and toxicology↗

bioRxiv2021

Human engineered heart tissue transplantation in a guinea pig chronic injury model

AO_SCPLOWBSTRACTC_SCPLOWMyocardial injury leads to an irreversible loss of cardiomyocytes (CM). The implantation of human engineered heart tissue (EHT) has become a promising regenerative approach. Previous studies exhibited beneficial, dose-dependent effects of human induced pluripotent stem cell (hiPSC)-derived EHT patch transplantation in a guinea pig model in the subacute phase of myocardial injury. Yet, advanced heart failure often results from a chronic remodeling process. Therefore, from a clinical standpoint it is worthwhile to explore the ability to repair the chronically injured heart. In this study human EHT patches were generated from hiPSC-derived CMs (15x106 cells) and implanted epicardially four weeks after injury in a guinea-pig cryo-injury model. Cardiac function was evaluated by echocardiography after a follow-up period of four weeks. Hearts revealed large transmural myocardial injuries amounting to 27% of the left ventricle. EHT recipient hearts demonstrated compact muscle islands of human origin in the scar region, as indicated by a positive staining for human Ku80 and dystrophin, remuscularizing 5% of the scar area. Echocardiographic analysis demonstrated no significant difference between animals that received EHT patches and animals in the control group (fractional area change 36% vs. 34%). Thus, EHT patches engrafted in the chronically injured heart but in contrast to the subacute model, grafts were smaller and EHT patch transplantation did not improve left ventricular function, highlighting the difficulties for a regenerative approach.

pharmacology and toxicology↗