Recapitulation of dyssynchrony-associated contractile impairment in asymmetrically paced engineered heart tissue.

BACKGROUND: One third of heart failure patients exhibit dyssynchronized electromechanical activity of the heart (evidenced by a broad QRS-complex). Cardiac resynchronization therapy (CRT) in the form of biventricular pacing improves cardiac output and clinical outcome of responding patients. Technically demanding and laborious large animal models have been developed to better predict responders of CRT and to investigate molecular mechanisms of dyssynchrony and CRT. The aim of this study was to establish a first humanized in vitro model of dyssynchrony and CRT. METHODS: Cardiomyocytes were differentiated from human induced pluripotent stem cells and cast into a fibrin matrix to produce engineered heart tissue (EHT). EHTs were either field stimulated in their entirety (symmetrically) or excited locally from one end (asymmetrically) or they were allowed to beat spontaneously. RESULTS: Asymmetrical pacing led to a depolarization wave from one end to the other end, which was visualized in human EHT transduced with a fast genetic Ca2+-sensor (GCaMP6f) arguing for dyssynchronous excitation. Symmetrical pacing in contrast led to an instantaneous (synchronized) Ca2+-signal throughout the EHT. To investigate acute and long-term functional effects, spontaneously beating human EHTs (0.5-0.8 Hz) were divided into a non-paced control group, a symmetrically and an asymmetrically paced group, each stimulated at 1 Hz. Symmetrical pacing was clearly superior to asymmetrical pacing or no pacing regarding contractile force both acutely and even more pronounced after weeks of continuous stimulation. Contractile dysfunction that can be evoked by an increased afterload was aggravated in the asymmetrically paced group. Consistent with reports from paced dogs, p38MAPK and CaMKII-abundance was higher under asymmetrical than under symmetrical pacing while pAKT was considerably lower. CONCLUSIONS: This model allows for long-term pacing experiments mimicking electrical dyssynchrony vs. synchrony in vitro. Combined with force measurement and afterload stimulus manipulation, it provides a robust new tool to gain insight into the biology of dyssynchrony and CRT.

Physioxia rewires mitochondrial complex composition to protect stem cell viability.

Human induced pluripotent stem cells (hiPSCs) are an invaluable tool to study molecular mechanisms on a human background. Culturing stem cells at an oxygen level different from their microenvironmental niche impacts their viability. To understand this mechanistically, dermal skin fibroblasts of 52 probands were reprogrammed into hiPSCs, followed by either hyperoxic (20 % O2) or physioxic (5 % O2) culture and proteomic profiling. Analysis of chromosomal stability by Giemsa-banding revealed that physioxic -cultured hiPSC clones exhibited less pathological karyotypes than hyperoxic (e.g. 6 % vs. 32 % mosaicism), higher pluripotency as evidenced by higher Stage-Specific Embryonic Antigen 3 positivity, higher glucose consumption and lactate production. Global proteomic analysis demonstrated lower abundance of several subunits of NADH:ubiquinone oxidoreductase (complex I) and an underrepresentation of pathways linked to oxidative phosphorylation and cellular senescence. Accordingly, release of the pro-senescent factor IGFBP3 and ß-galactosidase staining were lower in physioxic hiPSCs. RNA- and ATAC-seq profiling revealed a distinct hypoxic transcription factor-binding footprint, amongst others higher expression of the HIF1α-regulated target NDUFA4L2 along with increased chromatin accessibility of the NDUFA4L2 gene locus. While mitochondrial DNA content did not differ between groups, physioxic hiPSCs revealed lower polarized mitochondrial membrane potential, altered mitochondrial network appearance and reduced basal respiration and electron transfer capacity. Blue-native polyacrylamide gel electrophoresis coupled to mass spectrometry of the mitochondrial complexes detected higher abundance of NDUFA4L2 and ATP5IF1 and loss of incorporation into complex IV or V, respectively. Taken together, physioxic culture of hiPSCs improved chromosomal stability, which was associated with downregulation of oxidative phosphorylation and senescence and extensive re-wiring of mitochondrial complex composition.

Harnessing the power of RNA therapeutics in treating ischemic heart failure: the TRAIN-HEART story.

Ischemic heart disease (IHD) is one of the world's foremost killers, accounting for 16% of all deaths worldwide. IHD is the main cause of heart failure (HF), as it leads to pathological changes in the heart, improper pumping function and eventual death. Therapeutic interventions usually follow a systemic general strategy for all heart failure subtypes due to the lack of a deep understanding of the disease mechanisms. Hence, HF and IHD therapeutics need groundbreaking concepts to guide the development of a new therapeutics class that tackles the disease at a molecular level. The TRAIN-HEART consortium, a Marie Sklodowska-Curie Actions Innovative Training Network (MSCA-ITN) funded by the European Commission, was established with the goal of filling that gap and developing RNA-based cardiovascular therapeutics. Created in the context of the Horizon 2020 research and innovation program, TRAIN-HEART comprises three key work packages (WPs) focusing on the pathogenesis of heart disease (WP1), the therapeutic potential of RNA therapeutics (WP2), and the development of new efficient delivery systems (WP3). Fifteen international early stage researchers (ESRs) from multiple complementary scientific disciplines were recruited to collaborate with a network of PIs from nine academic and eight non-academic partners in various disciplines to fully harness their collective potential for the betterment of HF treatment. This article provides an overview of the benefits of being part of an MSCA-ITN, with its different training and networking opportunities, maximizing ESRs' potential and broadening collaborative research possibilities. Finally, it describes what was like to do a PhD during the COVID-19 pandemic, with all the uncertainty and concern attached to it. Luckily, TRAIN-HEART stood out as a proactive network, finding new initiatives and alternatives to promote scientific and personal development. By bringing together leading academic teams, (biotech) companies, and highly motivated researchers, TRAIN-HEART is expanding scientific horizons and accelerating future development of effective RNA-based therapies to treat IHD.