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ABSTRACTPropionic acidemia (PA) is a metabolic disorder caused by a deficiency of the mitochondrial enzyme propionyl?CoA carboxylase (PCC) due to mutations in the PCCA or PCCB genes, which encode the two PCC subunits. PA may lead to several types of cardiomyopathy and has been linked to cardiac electrical abnormalities such as QT interval prolongation, life?threatening arrhythmias, and sudden cardiac death. To gain insights into the mechanisms underlying PA?induced proarrhythmia, we recorded action potentials (APs) and ion currents using whole?cell patch?clamp in ventricular?like induced pluripotent stem cells?derived cardiomyocytes (hiPSC?CMs) from a PA patient carrying two pathogenic mutations in the PCCA gene (p.Cys616_Val633del and p.Gly477Glufs*9) (PCCA cells) and from a healthy subject (healthy cells). In cells driven at 1?Hz, PCC deficiency increased the latency and prolonged the AP duration (APD) measured at 20% of repolarization, without modifying resting membrane potential or AP amplitude. Moreover, delayed afterdepolarizations appeared at the end of the repolarization phase in unstimulated and paced PCCA cells. PCC deficiency significantly reduced peak sodium current (I Na) but increased the late I Na (I NaL) component. In addition, L?type Ca2+ current (I CaL) density was reduced, while the inward and outward density of the Na+/Ca2+ exchanger current (I NCX) was increased in PCCA cells compared to healthy ones. In conclusion, our results demonstrate that at the cellular level, PCC deficiency can modify the ion currents controlling cardiac excitability, APD, and intracellular Ca2+ handling, increasing the risk of arrhythmias independently of the progressive late?onset cardiomyopathy induced by PA disease.

ABSTRACTRAD50?interacting protein1 (RINT1) deficiency has been implicated in recurrent acute liver failure (RALF) triggered by fever or infections. RINT1, together with neuroblastoma amplified sequence and Zeste White 10 (forming the NRZ complex), localizes at the interface between the endoplasmic reticulum and Golgi apparatus, where it plays a key role in vesicular trafficking. However, the mechanisms by which RINT1 deficiency leads to RALF remain unclear. This study aimed to describe a woman with RALF harboring a homozygous missense mutation in RINT1. Induced pluripotent stem cells (iPSCs) were generated from the patient's mononuclear cells and differentiated into hepatocyte?like cells (HLCs). Upon exposure to high temperature (40°C), RINT1?deficient HLCs exhibited cellular damage characteristic of RALF. Furthermore, these cells also demonstrated heightened sensitivity to cytokines and viral mimetics while showing comparatively lower responsiveness to bacterial infection?related stimuli. Transcriptome sequencing revealed dysregulated gene expression associated with the extracellular matrix (ECM). Additionally, glycosaminoglycan disaccharide analysis revealed abnormal levels of chondroitin sulfate, heparan sulfate, and hyaluronan in RINT1?deficient HLCs. In conclusion, HLCs derived from RINT1?deficient iPSCs serve as a valuable model for investigating RINT1?related liver pathogenesis. The results suggest that cytokine responses, particularly those triggered by viral infections, play a central role in the development of RALF. Furthermore, ECM alterations provided novel insights into the potential role of RINT1 defects in RALF. RAD50?interacting protein1 (RINT1) deficiency causes recurrent acute liver failure (RALF) during fever or infections. To investigate its underlying mechanism, induced pluripotent stem cells were generated from a patient with RINT1 deficiency and differentiated into hepatocyte?like cells (HLCs). RINT1?deficient HLCs exhibited damage resembling RALF when exposed to high temperatures and were more susceptible to cytokines and viral mimetics than to bacterial infection?related factors. Furthermore, RNA?seq and disaccharide analyses revealed dysregulation of extracellular matrix?related genes and abnormalities in extracellular matrix levels.

Remarkable advances in protocol development have been achieved to manufacture insulin-secreting islets from human pluripotent stem cells (hPSCs). Distinct from current approaches, we devised a tunable strategy to generate islet spheroids enriched for major islet cell types by incorporating PDX1+ cell budding morphogenesis into staged differentiation. In this process that appears to mimic normal islet morphogenesis, the differentiating islet spheroids organize with endocrine cells that are intermingled or arranged in a core-mantle architecture, accompanied with functional heterogeneity. Through in vitro modelling of human pancreas development, we illustrate the importance of PDX1 and the requirement for EphB3/4 signaling in eliciting cell budding morphogenesis. Using this new approach, we model Mitchell-Riley syndrome with RFX6 knockout hPSCs illustrating unexpected morphogenesis defects in the differentiation towards islet cells. The tunable differentiation system and stem cell-derived islet models described in this work may facilitate addressing fundamental questions in islet biology and probing human pancreas diseases. The ability to differentiate human pluripotent stem cells (hPSCs) into insulin producing cells holds potential for diabetes treatments, but many of these approaches lack the complexity needed for in vitro disease modeling. Here they develop an hPSC-derived islet spheroid system, offering an experimental model to study pancreatic budding and islet morphogenesis with human cells.

Creatine transporter deficiency (CTD) is an X-linked disease caused by mutations in the Slc6a8 gene. The impaired creatine uptake in the brain leads to developmental delays with intellectual disability. We hypothesized that deficient creatine uptake in CTD cerebral cells impact methylation balance leading to alterations of genes and proteins expression by epigenetic mechanism. In this study, we determined the status of nucleic acid methylation in both Slc6a8 knockout mouse model and brain organoids derived from CTD patients’ cells. We also investigated the effect of dodecyl creatine ester (DCE), a promising prodrug that increases brain creatine content in the mouse model of CTD. The level of nucleic acid methylation was significantly reduced compared to healthy controls in both in vivo and in vitro CTD models. This hypo-methylation tended to be regulated by DCE treatment in vivo. These results suggest that increased brain creatine after DCE treatment restores normal levels of DNA methylation, unveiling the potential of using DNA methylation as a marker to monitor the drug efficacy.