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SUMMARY Alveolar epithelial type I cells (AT1s) line the gas exchange barrier of the distal lung and have been historically challenging to isolate or maintain in cell culture. Here,we engineer a human in vitro AT1 model system via directed differentiation of induced pluripotent stem cells (iPSCs). We use primary adult AT1 global transcriptomes to suggest benchmarks and pathways,such as Hippo-LATS-YAP/TAZ signaling,enriched in these cells. Next,we generate iPSC-derived alveolar epithelial type II cells (AT2s) and find that nuclear YAP signaling is sufficient to promote a broad transcriptomic shift from AT2 to AT1 gene programs. The resulting cells express a molecular,morphologic,and functional phenotype reminiscent of human AT1 cells,including the capacity to form a flat epithelial barrier producing characteristic extracellular matrix molecules and secreted ligands. Our results provide an in vitro model of human alveolar epithelial differentiation and a potential source of human AT1s. In brief Kotton and colleagues generate human alveolar epithelial type I cells (AT1s) from induced pluripotent stem cells (iPSCs). The resulting cells can be grown as 3D organoids or in 2D air-liquid interface cultures,displaying many of the molecular,morphologic,and functional phenotypes of primary AT1s. Graphical abstract View Publication

Human brain development relies on a finely tuned balance between the proliferation and differentiation of neural progenitor cells,followed by the migration,differentiation,and connectivity of post-mitotic neurons with region-specific identities. These processes are orchestrated by gradients of morphogens,such as FGF8. Disruption of this developmental balance can lead to brain malformations,which underlie a range of complex neurodevelopmental disorders,including epilepsy,autism,and intellectual disabilities. Studying the early stages of human brain development,whether under normal or pathological conditions,remains challenging due to ethical and technical limitations inherent to working with human fetal tissue. Recently,human brain organoids have emerged as a powerful in vitro alternative,allowing researchers to model key aspects of early brain development while circumventing many of these constraints. Unlike traditional 2D cultures,where neural progenitors and neurons are grown on flat surfaces,3D organoids form floating self-organizing aggregates that better replicate the cellular diversity and tissue architecture of the developing brain. However,3D organoid protocols often suffer from significant variability between batches and individual organoids. Furthermore,few existing protocols directly manipulate key morphogen signaling pathways or provide detailed analyses of the resulting effects on regional brain patterning. • To address these limitations,we developed a hybrid 2D/3D approach for the rapid and efficient induction of telencephalic organoids that recapitulate major steps of anterior brain development. Starting from human induced pluripotent stem cells (hiPSCs),our protocol begins with 2D neural induction using small-molecule inhibitors to achieve fast and homogenous production of neural progenitors (NPs). After dissociation,NPs are reaggregated in Matrigel droplets and cultured in spinning mini-bioreactors,where they self-organize into neural rosettes and neuroepithelial structures,surrounded by differentiating neurons. Activation of the FGF signaling pathway through the controlled addition of FGF8 to the culture medium will modulate regional identity within developing organoids,leading to the formation of distinct co-developing domains within a single organoid. Our protocol combines the speed and reproducibility of 2D induction with the structural and cellular complexity of 3D telencephalic organoids. The ability to manipulate signaling pathways provides an additional opportunity to further increase system complexity,enabling the simultaneous development of multiple distinct brain regions within a single organoid. This versatile system facilitates the study of key cellular and molecular mechanisms driving early human brain development across both telencephalic and non-telencephalic areas. Key features • This protocol builds on the method established by Chambers et al. [1] for generating 2D neural progenitors,followed by dissociation and reaggregation into 3D brain organoids. • For optimal growth and maturation,telencephalic organoids are cultured in spinning mini-bioreactors [2] or on orbital shakers. • The protocol enables the generation of telencephalic neural progenitors in 10 days and produces 3D telencephalic organoids containing neocortical neurons within one month of culture. • Addition of morphogens in the culture medium (example: FGF8) enhances cellular heterogeneity,promoting the emergence of distinct brain domains within a single organoid. View Publication

Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses a spectrum of hepatic disorders,ranging from simple steatosis to steatohepatitis,with the most severe outcomes including cirrhosis,liver failure,and hepatocellular carcinoma. Notably,MASLD prevalence is lower in premenopausal women than in men,suggesting a potential protective role of estrogens in mitigating disease onset and progression. In this study,we utilized preclinical in vitro models—immortalized cell lines and hepatocyte-like cells derived from human embryonic stem cells—exposed to clinically relevant steatotic-inducing agents. These exposures led to lipid droplet (LD) accumulation,increased reactive oxygen species (ROS) levels,and mitochondrial dysfunction,along with decreased expression of markers associated with hepatocyte functionality and differentiation. Estrogen treatment in steatotic-induced liver cells resulted in reduced ROS levels and LD content while preserving mitochondrial integrity,mediated by the upregulation of mitochondrial thioredoxin 2 (TRX2),an antioxidant system regulated by the estrogen receptor. Furthermore,disruption of TRX2,either pharmacologically using auranofin or through genetic interference,was sufficient to counteract the protective effects of estrogens,highlighting a potential mechanism through which estrogens may prevent or slow MASLD progression. View Publication

Background: Pulmonary fibrosis is a major disease that leads to the progressive loss of lung function. The disease manifests early,resulting in type 2 respiratory failure. This is likely due to the bronchocentric fibrosis around the major airways,which causes airflow limitation. It affects approximately three million patients worldwide and has a poor prognosis. Skin fibroblasts isolated from patients offer valuable insights into understanding the disease mechanisms,identifying the genetic causes,and developing personalized therapies. However,the use of skin fibroblasts to study a disease that exclusively impacts the lungs is often questioned,particularly since lung fibrosis primarily affects the alveolar epithelium. Method: We report the reprogramming of skin fibroblasts from patients with an atypical early-onset form of lung fibrosis into induced pluripotent stem cells (iPSCs) and subsequently into alveolar epithelial cells. This was achieved using a Sendai virus approach. Results: We show that the reprogrammed cells carry mutations in the calcium-binding protein genes S100A3 and S100A13,leading to diminished protein expression,thus mimicking the patients’ cells. Additionally,we demonstrate that the generated patient iPSCs exhibit aberrant calcium and mitochondrial functions. Conclusions: Due to the lack of a suitable animal model that accurately resembles the human disease,generating patient lung cells from these iPSCs can provide a valuable “disease in a dish” model for studying the atypical form of inherited lung fibrosis. This condition is associated with mutations in the calcium-binding protein genes S100A3 (NM_002960) and S100A13 (NM_001024210),aiding in the understanding of its pathogenesis. View Publication

Animal models have proven integral to broadening our understanding of complex cardiac diseases but have been hampered by significant species-dependent differences in cellular physiology. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have shown great promise in the modelling of cardiac diseases despite limitations in functional and structural maturity. 3D stem cell-derived cardiac models represent a step towards mimicking the intricate microenvironment present in the heart as an in vitro model. Incorporation of non-myocyte cell types,such as cardiac fibroblasts,into engineered heart tissue models (EHTs) can help better recapitulate the cell-to-cell and cell-to-matrix interactions present in the human myocardium. Integration of human-induced pluripotent stem cell-derived cardiac fibroblasts (hiPSC-CFs) and hiPSC-CM into EHT models enables the generation of a genetically homogeneous modelling system capable of exploring the abstruse structural and electrophysiological interplay present in cardiac pathophysiology. Furthermore,the construction of more physiologically relevant 3D cardiac models offers great potential in the replacement of animals in heart disease research. Here we describe efficient and reproducible protocols for the differentiation of hiPSC-CMs and hiPSC-CFs and their subsequent assimilation into EHTs. The resultant EHT consists of longitudinally arranged iPSC-CMs,incorporated alongside hiPSC-CFs. EHTs with both hiPSC-CMs and hiPSC-CFs exhibit slower beating frequencies and enhanced contractile force compared to those composed of hiPSC-CMs alone. The modified protocol may help better characterise the interplay between different cell types in the myocardium and their contribution to structural remodelling and cardiac fibrosis. View Publication

ETV6::RUNX1,the most common oncogenic fusion in pediatric B cell precursor acute lymphoblastic leukemia (BCP-ALL),induces a clinically silent preleukemic state that can persist in carriers for over a decade and may progress to overt leukemia upon acquisition of secondary lesions. The mechanisms contributing to quiescence of ETV6::RUNX1+ preleukemic cells still remain elusive. In this study,we identify linker histone H1-0 as a critical mediator of the ETV6::RUNX1+ preleukemic state by employing human -induced pluripotent stem cell (hiPSC) models engineered by using CRISPR/Cas9 gene editing. Global gene expression analysis revealed upregulation of H1-0 in ETV6::RUNX1+ hiPSCs that was preserved upon hematopoietic differentiation. Moreover,whole transcriptome data of 1,727 leukemia patient samples showed significantly elevated H1-0 levels in ETV6::RUNX1+ BCP-ALL compared to other leukemia entities. Using dual-luciferase promoter assays,we show that ETV6::RUNX1 induces H1-0 promoter activity. We further demonstrate that depletion of H1-0 specifically inhibits ETV6::RUNX1 signature genes,including RAG1 and EPOR. Single-cell sequencing showed that H1-0 is highly expressed in quiescent hematopoietic cells. Importantly,H1-0 protein levels correspond to susceptibility of BCP-ALL cells towards histone deacetylase inhibitors (HDACis) and combinatorial treatment using the H1-0-inducing HDACi Quisinostat showed promising synergism with established chemotherapeutic drugs. Taken together,our data identify H1-0 as a key regulator of the ETV6::RUNX1+ transcriptome and indicate that the addition of Quisinostat may be beneficial to target non-responsive or relapsing ETV6::RUNX1+ BCP-ALL. View Publication

Induced pluripotent stem cell (iPSC) derived endothelial cells (iECs) have emerged as a promising tool for studying vascular biology and providing a platform for modelling various vascular diseases,including those with genetic origins. Currently,primary ECs are the main source for disease modelling in this field. However,they are difficult to edit and have a limited lifespan. To study the effects of targeted mutations on an endogenous level,we generated and characterized an iPSC derived model for venous malformations (VMs). CRISPR-Cas9 technology was used to generate a novel human iPSC line with an amino acid substitution L914F in the TIE2 receptor,known to cause VMs. This enabled us to study the differential effects of VM causative mutations in iECs in multiple in vitro models and assess their ability to form vessels in vivo. The analysis of TIE2 expression levels in TIE2L914F iECs showed a significantly lower expression of TIE2 on mRNA and protein level,which has not been observed before due to a lack of models with endogenous edited TIE2L914F and sparse patient data. Interestingly,the TIE2 pathway was still significantly upregulated and TIE2 showed high levels of phosphorylation. TIE2L914F iECs exhibited dysregulated angiogenesis markers and upregulated migration capability,while proliferation was not affected. Under shear stress TIE2L914F iECs showed reduced alignment in the flow direction and a larger cell area than TIE2WT iECs. In summary,we developed a novel TIE2L914F iPSC-derived iEC model and characterized it in multiple in vitro models. The model can be used in future work for drug screening for novel treatments for VMs.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10456-024-09925-9. View Publication

SummaryCryosectioning remains the gold standard for antibody and transcriptomic/in situ hybridization tissue analysis. However,tissue processing is time-consuming and costly,limiting routine and diagnostic use. Currently,no commercially available protocols or products exist for multiplexing this process. Here,we introduce multiplexed tissue molds (MTMs) that enable high-throughput cryoprocessing—cutting costs and workload by up to 96% while permitting the processing of tissues of various sizes and origins. We demonstrate compatibility with heterogeneous tissues by processing 19 different adult mouse tissues in parallel. Furthermore,we process up to ?110 neural organoids of different ages and sizes simultaneously and assess their neural differentiation marker expression. MTMs allow sectioning-based tissue analysis when labor,time,and cost are limiting factors. MTMs could be used to compare high specimen numbers in histopathological settings,organism-wide antigen and antibody targeting studies,high-throughput tissue screens,and defined tissue section positioning for,e.g.,spatial transcriptomics experiments. Graphical abstract Highlights•Multiplexed tissue molds (MTMs) drastically upscale cryosectioning procedures•MTMs can simultaneously accommodate up to 19 mouse organs and ?110 cerebral organoids•MTMs reduce analysis costs and processing times of tissues by up to 96%•MTMs could be used to reduce diagnostic costs and for spatial transcriptomics MotivationEfficient cryosectioning remains a critical yet labor- and cost-intensive step for immunohistochemistry and in situ hybridization,limiting routine diagnostic and research applications. The increasing demand for high-throughput tissue analysis—driven by advances in organoid and three-dimensional (3D) culture systems and tissue analysis for diagnostics—necessitates methods capable of processing numerous heterogeneous samples simultaneously. Current protocols lack multiplexing capabilities,leading to variability and extended processing times. Our work introduces multiplexed tissue molds (MTMs),a scalable solution that drastically reduces costs and labor by up to 96% while maintaining tissue integrity and consistency,thereby enabling large-scale (>100 tissues) comparative analyses and enhanced experimental reproducibility as well as access to tissue analysis,where cost is a restrictive factor. Reumann et al. develop multiplexed tissue molds (MTMs),which allow upscaling of tissue processing (up to 19 mouse organs or ?110 cerebral organoids simultaneously) while reducing workload and associated analysis costs by up to 96%. MTMs allow cryosection-based tissue analysis when labor,time,and cost are limiting factors and could be used for patient sample analysis as well as spatial transcriptomics approaches. View Publication

Aging is one of the most prominent risk factors for neurodegeneration,yet the molecular mechanisms underlying the deterioration of old neurons are mostly unknown. To efficiently study neurodegeneration in the context of aging,we transdifferentiated primary human fibroblasts from aged healthy donors directly into neurons,which retained their aging hallmarks,and we verified key findings in aged human and mouse brain tissue. Here we show that aged neurons are broadly depleted of RNA-binding proteins,especially spliceosome components. Intriguingly,splicing proteins—like the dementia- and ALS-associated protein TDP-43—mislocalize to the cytoplasm in aged neurons,which leads to widespread alternative splicing. Cytoplasmic spliceosome components are typically recruited to stress granules,but aged neurons suffer from chronic cellular stress that prevents this sequestration. We link chronic stress to the malfunctioning ubiquitylation machinery,poor HSP90? chaperone activity and the failure to respond to new stress events. Together,our data demonstrate that aging-linked deterioration of RNA biology is a key driver of poor resiliency in aged neurons. Rhine et al. find that neuronal aging leads to widespread dysregulation of RNA biology,including mislocalization of splicing proteins like TDP-43,chronic cellular stress and reduced resiliency. View Publication

SummaryDysfunction of the sympathetic nervous system and increased epicardial adipose tissue (EAT) have been independently associated with the occurrence of cardiac arrhythmia. However,their exact roles in triggering arrhythmia remain elusive. Here,using an in vitro coculture system with sympathetic neurons,cardiomyocytes,and adipocytes,we show that adipocyte-derived leptin activates sympathetic neurons and increases the release of neuropeptide Y (NPY),which in turn triggers arrhythmia in cardiomyocytes by interacting with the Y1 receptor (Y1R) and subsequently enhancing the activity of the Na+/Ca2+ exchanger (NCX) and calcium/calmodulin-dependent protein kinase II (CaMKII). The arrhythmic phenotype can be partially blocked by a leptin neutralizing antibody or an inhibitor of Y1R,NCX,or CaMKII. Moreover,increased EAT thickness and leptin/NPY blood levels are detected in atrial fibrillation patients compared with the control group. Our study provides robust evidence that the adipose-neural axis contributes to arrhythmogenesis and represents a potential target for treating arrhythmia. Graphical abstract Highlights•Stem cell-based coculture model can simulate the pathogenesis of cardiac arrhythmia•The adipose-neural axis plays critical roles in cardiac arrhythmias•Leptin,NPY/Y1R,NCX,and CaMKII are potential intervention targets for arrhythmia•Increased EAT thickness and leptin/NPY levels are detected in CS blood of AF patients Fan et al. establish a stem cell-based coculture model to mimic the in vivo cardiac microenvironment and elucidate that the adipose-neural interaction plays a critical role in epicardial adipose tissue-related cardiac arrhythmia through leptin-NPY axis. Their results may provide potential therapeutic targets for treating arrhythmia. View Publication

SUMMARY Elevated interferon (IFN) signaling is associated with kidney diseases including COVID-19,HIV,and apolipoprotein-L1 (APOL1) nephropathy,but whether IFNs directly contribute to nephrotoxicity remains unclear. Using human kidney organoids,primary endothelial cells,and patient samples,we demonstrate that IFN-? induces pyroptotic angiopathy in combination with APOL1 expression. Single-cell RNA sequencing,immunoblotting,and quantitative fluorescence-based assays reveal that IFN-?-mediated expression of APOL1 is accompanied by pyroptotic endothelial network degradation in organoids. Pharmacological blockade of IFN-? signaling inhibits APOL1 expression,prevents upregulation of pyroptosis-associated genes,and rescues vascular networks. Multiomic analyses in patients with COVID-19,proteinuric kidney disease,and collapsing glomerulopathy similarly demonstrate increased IFN signaling and pyroptosis-associated gene expression correlating with accelerated renal disease progression. Our results reveal that IFN-? signaling simultaneously induces endothelial injury and primes renal cells for pyroptosis,suggesting a combinatorial mechanism for APOL1-mediated collapsing glomerulopathy,which can be targeted therapeutically. In brief Juliar et al. address interferon signaling in kidney disease. Organoids,primary cells,and clinical datasets reveal that interferon signaling simultaneously induces APOL1 expression and endothelial cell pyroptosis. This suggests a combinatorial mechanism for APOL1-mediated collapsing glomerulopathy,which can be targeted therapeutically. The findings may also be relevant in other organs. Graphical Abstract View Publication

Prime editing (PE) is a CRISPR-based tool for genome engineering that can be applied to generate human induced pluripotent stem cell (hiPSC)-based disease models. PE technology safely introduces point mutations,small insertions,and deletions (indels) into the genome. It uses a Cas9-nickase (nCas9) fused to a reverse transcriptase (RT) as an editor and a PE guide RNA (pegRNA),which introduces the desired edit with great precision without creating double-strand breaks (DSBs). PE leads to minimal off-targets or indels when introducing single-strand breaks (SSB) in the DNA. Low efficiency can be an obstacle to its use in hiPSCs,especially when the genetic context precludes the screening of multiple pegRNAs,and other strategies must be employed to achieve the desired edit. We developed a PE platform to efficiently generate isogenic models of Mendelian disorders. We introduced the c.25G>A (p.V9M) mutation in the NMNAT1 gene with over 25% efficiency by optimizing the PE workflow. Using our optimized system,we generated other isogenic models of inherited retinal diseases (IRDs),including the c.1481C>T (p.T494M) mutation in PRPF3 and the c.6926A>C (p.H2309P) mutation in PRPF8. We modified several determinants of the hiPSC PE procedure,such as plasmid concentrations,PE component ratios,and delivery method settings,showing that our improved workflow increased the hiPSC editing efficiency. View Publication