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Rare coding mutations cause ~45% of congenital heart disease (CHD). Noncoding mutations that perturb cis-regulatory elements (CREs) likely contribute to the remaining cases, but their identification has been problematic. Using a lentiviral massively parallel reporter assay (lentiMPRA) in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we functionally evaluated 6,590 noncoding de novo variants (ncDNVs) prioritized from the whole-genome sequencing of 750 CHD trios. A total of 403 ncDNVs substantially affected cardiac CRE activity. A majority increased enhancer activity, often at regions with undetectable reference sequence activity. Of ten DNVs tested by introduction into their native genomic context, four altered the expression of neighboring genes and iPSC-CM transcriptional state. To prioritize future DNVs for functional testing, we used the MPRA data to develop a regression model, EpiCard. Analysis of an independent CHD cohort by EpiCard found enrichment of DNVs. Together, we developed a scalable system to measure the effect of ncDNVs on CRE activity and deployed it to systematically assess the contribution of ncDNVs to CHD.

Preclinical data have confirmed that human pluripotent stem cell-derived cardiomyocytes (PSC-CMs) can remuscularize the injured or diseased heart, with several clinical trials now in planning or recruitment stages. However, because ventricular arrhythmias represent a complication following engraftment of intramyocardially injected PSC-CMs, it is necessary to provide treatment strategies to control or prevent engraftment arrhythmias (EAs). Here, we show in a porcine model of myocardial infarction and PSC-CM transplantation that EAs are mechanistically linked to cellular heterogeneity in the input PSC-CM and resultant graft. Specifically, we identify atrial and pacemaker-like cardiomyocytes as culprit arrhythmogenic subpopulations. Two unique surface marker signatures, signal regulatory protein ? (SIRPA)+CD90?CD200+ and SIRPA+CD90?CD200?, identify arrhythmogenic and non-arrhythmogenic cardiomyocytes, respectively. Our data suggest that modifications to current PSC-CM-production and/or PSC-CM-selection protocols could potentially prevent EAs. We further show that pharmacologic and interventional anti-arrhythmic strategies can control and potentially abolish these arrhythmias. Selvakumar, Clayton et al. use a porcine model of myocardial infarction and PSC-CM transplantation and identify atrial and pacemaker-like cardiomyocytes as the cause of engraftment arrhythmias and surface marker signatures to distinguish between arrhythmogenic and non-arrhythmogenic cardiomyocytes.

Nuclear speckles are membraneless organelles that associate with active transcription sites and participate in post-transcriptional mRNA processing. During the cell cycle, nuclear speckles dissolve following phosphorylation of their protein components. Here, we identify the PP1 family as the phosphatases that counteract kinase-mediated dissolution. PP1 overexpression increases speckle cohesion and leads to retention of mRNA within speckles and the nucleus. Using APEX2 proximity labeling combined with RNA-sequencing, we characterize the recruitment of specific RNAs. We find that many transcripts are preferentially enriched within nuclear speckles compared to the nucleoplasm, particularly chromatin- and nucleus-associated transcripts. While total polyadenylated RNA retention increases with nuclear speckle cohesion, the ratios of most mRNA species to each other are constant, indicating non-selective retention. We further find that cellular responses to heat shock, oxidative stress, and hypoxia include changes to the phosphorylation and cohesion of nuclear speckles and to mRNA retention. Our results demonstrate that tuning the material properties of nuclear speckles provides a mechanism for the acute control of mRNA localization. Here the authors study how interactions with nuclear speckles help localize mRNA in cells. They find that modifications of the proteins in these structures affects their cohesion and can modulate mRNA retention under stress.

PurposeLittle is known about the development of Bruch's membrane (BrM), the structure separating and supporting the retina and choroid, nor whether differentiation of human pluripotent stem cell (hPSC)-derived retinal pigment epithelium (RPE) accurately replicates BrM. This has relevance for tissue engineering strategies, both in the development of accurate in vitro models, and effective RPE transplant strategies. Here, we investigated BrM-associated protein production in human fetal tissue and hPSC-derived RPE.MethodsThe presence of laminin, elastin, fibronectin, and types I/III/IV collagen was examined in human fetal eyes at 6 to 21 post-conception weeks (PCWs) and hPSC-derived RPE cultures at 1 to 6 weeks in culture using immunohistochemistry/immunocytochemistry and quantitative PCR (qPCR).ResultsIn human fetal retina, laminin and fibronectin were present from 6 PCW, type IV collagen from 8 PCW, elastin from 12 PCW, type I collagen by 17 PCW, and type III collagen from 21 PCW. BrM layering was discernible from 12 PCW, becoming distinct by 17 PCW. In hPSC-derived RPE cultures, basement membranes containing laminin and fibronectin were present from week 1, type IV collagen from week 2, and type I collagen from week 4. Type III collagen was present at all timepoints, although not localized as a basement membrane. Elastin was absent at all timepoints.ConclusionsBrM-like membrane synthesis in hPSC-derived RPE largely recapitulates the temporal sequence seen in human development, excluding elastin. These support the utility of hPSC-derived RPE in in vitro systems to model RPE/retina interactions in health and disease, and inform cell therapy approaches, as de novo BrM-like membrane has the potential to support transplanted donor RPE.

BackgroundThe causal relationship between the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and the preservation of SERCA2a function in mitigating myocardial ischemia–reperfusion (mI/R) injury, along with the associated regulatory mechanisms, remains incompletely understood. This study aims to unravel how NRF2 directly or indirectly influences SERCA2a function and its regulators, phospholamban (PLN) and Dwarf Open Reading Frame (DWORF), by testing the pharmacological repositioning of AEOL-10150 (AEOL) in the context of mI/R injury.MethodsC57BL6/J, Nrf2 knockout (Nrf2?/?), and wild-type (Nrf2+/+) mice, as well as human induced pluripotent stem cell-derived cardiomyocytes (hiPSCMs) were subjected to I/R injury. Gain/loss of function techniques, RT-qPCR, western blotting, LC/MS/MS, and fluorescence spectroscopy were utilized. Cardiac dimensions and function were assessed by echocardiography.ResultsIn the early stages of mI/R injury, AEOL administration reduced mitochondrial ROS production, decreased myocardial infarct size, and improved cardiac function. These effects were due to NRF2 activation, leading to the overexpression of the micro-peptide DWORF, consequently enhancing SERCA2a activity. The cardioprotective effect induced by AEOL was diminished in Nrf2?/? mice and in Nrf2/Dworf knockdown models in hiPSCMs subjected to simulated I/R injury. Our data show that AEOL-induced NRF2-mediated upregulation of DWORF disrupts the phospholamban-SERCA2a interaction, leading to enhanced SERCA2a activation and improved cardiac function.ConclusionsTaken together, our study reveals that AEOL-induced NRF2-mediated overexpression of DWORF enhances myocardial function through the activation of the SERCA2a offering promising therapeutic avenues for mI/R injury.Supplementary InformationThe online version contains supplementary material available at 10.1186/s10020-025-01242-1. Highlights• Novel AEOL-10150 therapeutic potential. AEOL-10150 demonstrates promise in activating NRF2 and mitigating myocardial ischemia-reperfusion injury.• DWORF overexpression breakthrough. Overexpression of DWORF significantly contributes to preserving cardiac function and reducing myocardial injury through the NRF2-DWORF pathway.• Enhanced cardiac protection mechanisms. The study highlights the dual role of AEOL-10150 and DWORF in enhancing cardiac protection and preventing heart failure.• Future research directions. Additional studies are required to validate the long-term efficacy of AEOL-10150 and the regulatory effects of NRF2-DWORF axis in clinical applications.Supplementary InformationThe online version contains supplementary material available at 10.1186/s10020-025-01242-1.

Human pluripotent stem cells (hPSCs) and their differentiated derivatives represent valuable tools for studying development, modeling diseases, and advancing cell therapy. Recent improvements in genome engineering allow for precise modifications of hPSCs, further enhancing their utility in basic and translational research. Here we describe a Recombinase-Mediated Cassette Exchange (RMCE) platform in hPSCs that allows for the highly efficient, rapid, and specific integration of transgenes. The RCME-mediated DNA integration process is nearly 100% efficient, without negatively affecting the pluripotency or karyotypic stability of hPSCs. Taking advantage of this convenient system, we first established a dual inducible expression system based on the Tet-On and Cumate-On systems, allowing for the inducible expression of two transgenes independently. Secondly, we incorporated a Tet-on inducible system, driving the expression of three genes simultaneously. However, two genes also contain independent degron sequences, allowing for precise control over the expression of each gene individually. We demonstrated the utility of these systems in hPSCs, as well as their functionality after differentiation into cells that were representative of the three germ layers. Lastly, we used the triple inducible system to investigate the lineage commitment induced by the pancreatic transcription factors NKX6.1 and PDX1. We found that controlled dual expression, but not individual expression, biases hPSC embryoid body differentiation towards the pancreatic lineage by inducing the expression of the NeuroD program. In sum, we describe a novel genetic engineering platform that allows for the efficient and fast integration of any desired transgene(s) in hPSCs using RMCE. We anticipate that the ability to modulate the expression of three transgenes simultaneously will further accelerate discoveries using stem cell technology.