iPSC-derived Endothelial Cells Research Articles

Protection of cell therapeutics from antibody-mediated killing by CD64 overexpression

Allogeneic cell therapeutics for cancer therapy or regenerative medicine are susceptible to antibody-mediated killing, which diminishes their efficacy. Here we report a strategy to protect cells from antibody-mediated killing that relies on engineered overexpression of the IgG receptor CD64. We show that human and mouse iPSC-derived endothelial cells (iECs) overexpressing CD64 escape antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity from IgG antibodies in vitro and in ADCC-enabled mice. When CD64 expression was combined with hypoimmune genetic modifications known to protect against cellular immunity, B2M−/−CIITA−/− CD47/CD64-transgenic iECs were resistant to both IgG antibody-mediated and cellular immune killing in vitro and in humanized mice. Mechanistic studies demonstrated that CD64 or its intracellularly truncated analog CD64t effectively capture monomeric IgG and occupy their Fc, and the IgG bind and occupy their target antigens. In three applications of the approach, human CD64t-engineered thyroid epithelial cells, pancreatic beta cells and CAR T cells withstood clinically relevant levels of graft-directed antibodies and fully evaded antibody-mediated killing.

IPSC-Derived Corneal Endothelial Cells.

The corneal endothelium is the innermost monolayer of the cornea that maintains corneal transparency and thickness. However, adult human corneal endothelial cells (CECs) possess limited proliferative capacity, and injuries can only be repaired by migration and enlargement of resident cells. When corneal endothelial cell density is lower than the critical level (400-500 cells/mm2) due to disease or trauma, corneal endothelial dysfunction will occur and lead to corneal edema. Corneal transplantation remains the most effective clinical treatment therapy but is limited by the global shortage of healthy corneal donors. Recently, researchers have developed several alternative strategies for the treatment of corneal endothelial disease, including the transplantation of cultured human CECs and artificial corneal endothelial replacement. Early-stage results show that these strategies can effectively resolve corneal edema and restore corneal clarity and thickness, but the long-term efficacy and safety remain to be further validated. Induced pluripotent stem cells (iPSCs) represent an ideal cell source for the treatment and drug discovery of corneal endothelial diseases, which can avoid the ethical-related and immune-related problems of human embryonic stem cells (hESCs). At present, many approaches have been developed to induce the differentiation of corneal endothelial-like cells from human induced pluripotent stem cells (hiPSCs). Their safety and efficacy for the treatment of corneal endothelial dysfunction have been confirmed in rabbit and nonhuman primate animal models. Therefore, the iPSC-derived corneal endothelial cell model may provide a novel effective platform for basic and clinical research of disease modeling, drug screening, mechanistic investigation, and toxicology testing.

Abstract 10096: Genetic Control of Lysosomal Dysfunction Reprograms Sterol Metabolism in Pulmonary Arterial Hypertension

Background : Vascular inflammation critically regulates endothelial pathophenotypes, yet causative mechanisms remain incompletely defined, particularly in pulmonary arterial hypertension (PAH). Immune dysregulation and metabolic reprogramming are recognized tenets of PAH pathogenesis, but a unifying theory connecting the two has not been established. Methods & Results: Guided by an unbiased, metabolome-wide association study from the multicenter PAH Biobank cohort (N=2,666) that identified a proinflammatory sterol and bile acid metabolite plasma signature significantly associated with PAH mortality (adjusted P values<1.1x10 -6 ), we found in pulmonary arterial endothelial cells (ECs) that induction of the nuclear receptor coactivator 7 (NCOA7) tempered the generation of proinflammatory sterols by bolstering lysosomal acidification and constraining EC immunoactivation. Conversely, reduced NCOA7 promoted lysosomal dysfunction, resulting in sterol- and bile acid-driven inflammation and EC phenotypes consistent with PAH. Notably, the common variant intronic SNP rs11154337 in NCOA7 was found to control NCOA7 levels, lysosome activity, sterol and bile acid production, and EC immunoactivation in isogenic, CRISPR-Cas9, SNP-edited, iPSC-derived ECs, indicating a potentially widespread genetic predisposition to NCOA7 deficiency. Correspondingly, SNP rs11154337 was associated with PAH severity as noted by six-minute walk distance ( P =0.0130, β=58.15, 95% CI [14.45-119.36]) and mortality ( P =0.0250; hazard ratio=0.4368, 95% CI [0.21-0.90]) in an independent, single-center PAH cohort (N=93). In vivo , mice deficient for Ncoa7 or treated with exogenous 7α-hydroxy-3-oxo-4-cholestenoic acid (7HOCA)—chosen as a representative metabolite from the sterol signature associated with mortality in the PAH Biobank—demonstrated worsened hemodynamic and histological indices of PAH. Conclusions: Our work establishes a genetic and metabolic paradigm that links lysosomal biology and sterol and bile acid processes with EC inflammation. This paradigm carries broad implications not only on molecular diagnostic and therapeutic development in PAH but also in other vascular disorders dependent upon acquired and innate immune regulation.

Trans-interaction of risk loci 6p24.1 and 10q11.21 is associated with endothelial damage in coronary artery disease

Background and aimsSingle nucleotide polymorphism rs6903956 has been identified as one of the genetic risk factors for coronary artery disease (CAD). However, rs6903956 lies in a non-coding locus on chromosome 6p24.1. We aim to interrogate the molecular basis of 6p24.1 containing rs6903956 risk alleles in endothelial disease biology. Methods and ResultsWe generated induced pluripotent stem cells (iPSCs) from CAD patients (AA risk genotype at rs6903956) and non-CAD subjects (GG non-risk genotype at rs6903956). CRISPR-Cas9-based deletions (Δ63-89bp) on 6p24.1, including both rs6903956 and a short tandem repeat variant rs140361069 in linkage disequilibrium, were performed to generate isogenic iPSC-derived endothelial cells. Edited CAD endothelial cells, with removal of ‘A’ risk alleles, exhibited a global transcriptional downregulation of pathways relating to abnormal vascular physiology and activated endothelial processes. A CXC chemokine ligand on chromosome 10q11.21, CXCL12, was uncovered as a potential effector gene in CAD endothelial cells. Underlying this effect was the preferential inter-chromosomal interaction of 6p24.1 risk locus to a weak promoter of CXCL12, confirmed by chromatin conformation capture assays on our iPSC-derived endothelial cells. Functionally, risk genotypes AA/AG at rs6903956 were associated significantly with elevated levels of circulating damaged endothelial cells in CAD patients. Circulating endothelial cells isolated from patients with risk genotypes AA/AG were also found to have 10 folds higher CXCL12 transcript copies/cell than those with non-risk genotype GG. ConclusionsOur study reveals the trans-acting impact of 6p24.1 with another CAD locus on 10q11.21 and is associated with intensified endothelial injury.

RNA-sequencing reveals significant differences in the inflammatory response of iPSC-derived endothelial cells from ACS patients and healthy controls

Abstract Background Coronary artery disease (CAD) and cardiovascular diseases (CVD) in general still represent the leading cause of death worldwide. As a multifactorial disease entity, genetic predisposition and lifestyle strongly impact disease development and progression. Here, induced pluripotent stem cells (iPSC) are an ideal tool to differentiate (epi-)genetic from lifestyle disease risk modulation and identify the underlying molecular mechanisms. Aim This study aims to determine differences in iPSC-derived endothelial cell (iPSC-EC) characteristics and functionality between healthy donors and high-risk CAD patients. Methods IPSC from participants with similar lifestyle but different disease status (healthy >65 y/o, n=5, acute coronary syndrome (ACS) <65y/o, n=6) were differentiated into iPSC-EC. Cells were exposed to inflammatory stimulation with tumour necrosis factor alpha (TNF-a) followed by bulk RNA-seq. Monocyte (THP-1) recruitment was assessed under protective and atherogenic flow conditions. Mitotic age was calculated based on DNA-methylation via Hannum estimate (1) for each donor at the iPSC and iPSC-EC (passage 4) stage. Results ACS-iPSC-EC had significantly higher upregulation of E-selectin upon TNF-a stimulation on mRNA level (ACS: 532.1-fold±48.7 vs healthy: 322.3-fold±55.7 with p=0.02). Similarly, ICAM1 protein upregulation was higher in ACS-iPSC-EC compared to healthy iPSC-EC as determined by flow cytometry (ACS: 1.4-fold±0.01 vs healthy: 1.1-fold±0.0007; p<0.001). ACS-iPSC-EC recruited significantly more THP-1 per view field under protective (high shear stress, laminar) flow conditions (ACS: 78.4±20.7 vs healthy: 33.25±12.3 with p=0.04) compared to healthy iPSC-EC. While both groups recruited significantly more THP-1 under atherogenic than protective conditions (ACS: 302±38.9 with p=0.0055 vs healthy: 340±70.4 with p=0.0005), there was no difference between the donor groups (p=0.43). Analysis of bulk RNA-seq data showed significant differences in TNF-a-induced transcriptome changes. Gene set enrichment analysis identified differences in signalling pathways related to leukocyte and lymphocyte-mediated immunity, adaptive immune response, cytokine activity, and many more as shown in Figure 1 (p.adj ≤1e-10). IPSC of both groups had a negative calculated mitotic age (in years) which significantly increased after endothelial differentiation and four population doublings (ACS-iPSC: −14.1±0.7 vs ACS-EC: −0.1±1.1, p<0.0001 and healthy-iPSC: −13.7±0.8 vs healthy-EC: 2.5±1.5, p=0.0001). Conclusion The higher rate of basal THP-1 recruitment and upregulation of adhesion molecules on mRNA and protein level and the distinct transcriptome changes suggest intrinsic differences between patient and healthy iPSC-EC both in the basal state and in inflammatory response. Furthermore, this demonstrates iPSC as a viable in vitro model also for polygenetic diseases such as CAD. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): German Cardiac Society, Research Scholarship

Identification of stable housekeeping genes for induced pluripotent stem cells and -derived endothelial cells for drug testing

There are no validated housekeeping genes in induced pluripotent stem cells (iPSC) and derived endothelial iPSC (iPSC-EC). Thus a comparison of gene expression levels is less reliable, especially during drug treatments. Here, we utilized transcriptome sequencing data of iPSC and iPSC-EC with or without CRISPR-Cas9 induced translocation to identify a panel of 15 candidate housekeeping genes. For comparison, five commonly used housekeeping genes (B2M, GAPDH, GUSB, HMBS, and HPRT1) were included in the study. The panel of 20 candidate genes were investigated for their stability as reference genes. This panel was analyzed and ranked based on stability using five algorithms, delta-Ct, bestkeeper, geNorm, Normfinder, and Reffinder. Based on the comprehensive ranking of Reffinder, the stability of the top two genes—RPL36AL and TMBIM6, and the bottom two genes—UBA1 and B2M, were further studied in iPSC-EC with and without genetic manipulation, and after treatment with telatinib. Using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR), it was shown that gene expression of the top two housekeeping genes, RPL36AL and TMBIM6, remained stable during drug treatment. We identified a panel of housekeeping genes that could be utilized in various conditions using iPSC and iPSC-derived endothelial cells as well as genetically modified iPSC for drug treatment.

Flow-induced glycocalyx formation and cell alignment of HUVECs compared to iPSC-derived ECs for tissue engineering applications.

The relevance of cellular in vitro models highly depends on their ability to mimic the physiological environment of the respective tissue or cell niche. Static culture conditions are often unsuitable, especially for endothelial models, since they completely neglect the physiological surface shear stress and corresponding reactions of endothelial cells (ECs) such as alignment in the direction of flow. Furthermore, formation and maturation of the glycocalyx, the essential polysaccharide layer covering all endothelial surfaces and regulating diverse processes, is highly dependent on applied fluid flow. This fragile but utterly important macromolecular layer is hard to analyze, its importance is often underestimated and accordingly neglected in many endothelial models. Therefore, we exposed human umbilical vein ECs (HUVECs) and human induced pluripotent stem cell-derived ECs (iPSC-ECs) as two relevant EC models in a side-by-side comparison to static and physiological dynamic (6.6 dyn cm−2) culture conditions. Both cell types demonstrated an elongation and alignment along the flow direction, some distinct changes in glycocalyx composition on the surface regarding the main glycosaminoglycan components heparan sulfate, chondroitin sulfate or hyaluronic acid as well as an increased and thereby improved glycocalyx thickness and functionality when cultured under homogeneous fluid flow. Thus, we were able to demonstrate the maturity of the employed iPSC-EC model regarding its ability to sense fluid flow along with the general importance of physiological shear stress for glycocalyx formation. Additionally, we investigated EC monolayer integrity with and without application of surface shear stress, revealing a comparable existence of tight junctions for all conditions and a reorganization of the cytoskeleton upon dynamic culture leading to an increased formation of focal adhesions. We then fabricated cell sheets of EC monolayers after static and dynamic culture via non-enzymatic detachment using thermoresponsive polymer coatings as culture substrates. In a first proof-of-concept we were able to transfer an aligned iPSC-EC sheet to a 3D-printed scaffold thereby making a step in the direction of vascular modelling. We envision these results to be a valuable contribution to improvements of in vitro endothelial models and vascular engineering in the future.

Using CRISPR/Cas9 genome editing in human iPSCs for deciphering the pathogenicity of a novel CCM1 transcription start site deletion.

Cerebral cavernous malformations are clusters of aberrant vessels that can lead to severe neurological complications. Pathogenic loss-of-function variants in the CCM1, CCM2, or CCM3 gene are associated with the autosomal dominant form of the disease. While interpretation of variants in protein-coding regions of the genes is relatively straightforward, functional analyses are often required to evaluate the impact of non-coding variants. Because of multiple alternatively spliced transcripts and different transcription start points, interpretation of variants in the 5′ untranslated and upstream regions of CCM1 is particularly challenging. Here, we identified a novel deletion of the non-coding exon 1 of CCM1 in a proband with multiple CCMs which was initially classified as a variant of unknown clinical significance. Using CRISPR/Cas9 genome editing in human iPSCs, we show that the deletion leads to loss of CCM1 protein and deregulation of KLF2, THBS1, NOS3, and HEY2 expression in iPSC-derived endothelial cells. Based on these results, the variant could be reclassified as likely pathogenic. Taken together, variants in regulatory regions need to be considered in genetic CCM analyses. Our study also demonstrates that modeling variants of unknown clinical significance in an iPSC-based system can help to come to a final diagnosis.

Abstract 195: A focused ultrasound blood brain barrier disruption model to test the influence of tight junction genes to treat brain tumors

Abstract A major hindrance to advances in the care of patients with malignant gliomas is the presence of the blood brain barrier (BBB) and blood-brain tumor barrier (BBTB) that greatly restricts drug access from the plasma to the tumor cells. Bubble-assisted Focused Ultrasound (BAFUS) has proven effective in opening the BBB for treatment of glial tumors in adults and pediatric cases. BAFUS has been previously shown to disrupt noninvasively, selectively, and transiently the BBB in small animals in vivo. However, there is a lack of an in vitro preclinical model suitable for testing the genetic determinants of endothelial cell tight junction integrity and vulnerability to the physical disruption. Our BBB organ-on-chip platform will enable precision medicine of brain cancers through identifying patient-specific parameters by which to open the BBB allowing use of drugs and drug combinations otherwise unsuitable. We intend to sequence these in vitro models to verify that the genotype (alleles/SNPs) of tight junction proteins contribute to BBB structure and integrity. To initiate this effort, we report the development of an ultrasound transparent organ-on-chip model populated by iPSC-derived endothelial cells (iPSC-EC) co-cultured with astrocytes. Western blot, immunocytochemistry, permeability, and transelectrical endothelial resistance (TEER) studies all convey expression of key EC proteins and marked barrier integrity. Further benchmarking of device-ultrasound interactions, successful iPSC differentiation, tight junction formation, and fabrication of nanobubbles and their assistance in ultrasound BBB disruption will be presented. Efforts are underway to analyze nine characteristic BBB tight junction genes from WGS data to determine associations between iPSC-EC genotype and phenotype. Citation Format: Jayashree Iyer, Adam Akkad, Nanyun Tang, Sen Peng, Michael Berens, Frederic Zenhausern, Jian Gu. A focused ultrasound blood brain barrier disruption model to test the influence of tight junction genes to treat brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 195.

Generation of Complex Syngeneic Liver Organoids from Induced Pluripotent Stem Cells to Model Human Liver Pathophysiology.

The study of human liver pathophysiology has been hampered for decades by the lack of easily accessible, robust, and representative in vitro models. The discovery of induced pluripotent stem cells (iPSCs)-which can be generated from patients' somatic cells, engineered to harbor specific mutations, and differentiated into hepatocyte-like cells-opened the way to more meaningful modeling of liver development and disease. Nevertheless, representative modeling of many complex liver conditions requires the recreation of the interplay between hepatocytes and nonparenchymal liver cells. Here we describe protocols we developed to generate and characterize complex human liver organoids composed of iPSC-derived hepatic, endothelial, and mesenchymal cells. With all cell types derived from the same iPSC population, such organoids reproduce the liver niche, allowing for the study of liver development and the modeling of complex inflammatory and fibrotic conditions. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Differentiation of human iPSCs into hepatic progenitor cells (hepatoblasts) Basic Protocol 2: Differentiation of human iPSCs into endothelial progenitor cells Support Protocol 1: Characterization of iPSC-derived endothelial progenitor cells Basic Protocol 3: Differentiation of human iPSCs into mesenchymal progenitor cells Support Protocol 2: Characterization of iPSC-derived mesenchymal progenitor cells Basic Protocol 4: Generation of complex syngeneic liver organoids.

Erratum: Standardized and Scalable Assay to Study Perfused 3D Angiogenic Sprouting of iPSC-derived Endothelial Cells In Vitro.

An erratum was issued for:Standardized and Scalable Assay to Study Perfused 3D Angiogenic Sprouting of iPSC-derived Endothelial Cells In Vitro. The Protocol section wasupdated. Step 2.6 of the Protocol was updated from: Add 50 µL of 10 µg/mL FN coating solution to the outlet well of the top perfusion channel of every microfluidic unit (Figure 1b, well A3). Press the pipette tip against the side of the well for correct filling of the well without trapping air bubbles (see Figure 2b). The channel should fill, and the liquid should pin on the outlet (well C1) without filling the outlet well. to: Add 50 µL of 10 µg/mL FN coating solution to the outlet well of the top perfusion channel of every microfluidic unit (Figure 1b, well A3). Press the pipette tip against the side of the well for correct filling of the well without trapping air bubbles (see Figure 2b). The channel should fill, and the liquid should pin on the inlet (well A1) without filling the inlet well. Step 3.7 of the Protocol was updated from: Aspirate FN-coating solution from the perfusion inlet (well A1). Add 25 µL of basal medium in the inlet wells (well A1). to: Aspirate FN-coating solution from the perfusion outlet well (A3) and replace with 25 µL of basal medium in the outlet well (well A3).

Efficient generation of endothelial cells from induced pluripotent stem cells derived from a patient with peripheral arterial disease.

Peripheral arterial disease (PAD) is caused by atherosclerotic plaque accumulation, which results in ischemia in lower extremity ischemia. Cell-based therapy using endothelial progenitor cells (EPCs) or endothelial cells (ECs) has been challenging due to an insufficient number and replicative senescence of primary cells isolated from patients. To overcome this limitation, we generated induced pluripotent stem cells (iPSCs) from a patient with PAD for the first time. The patient-specific iPSCs have unlimited proliferation and can be used to generate a clinically relevant number of functional ECs. Here we developed a strategy to efficiently generate high EC yields within 5days of differentiation. The generated iPSC-derived ECs from a PAD patient were phenotypically and functionally similar to the primary blood outgrowth endothelial cells (BOECs) and iPSC-ECs derived from healthy donors as evidenced by expression of EC-specific markers, capillary-like tube-forming potential, and the ability to uptake acetylated low-density lipoprotein (Ac-LDL). Our approach may provide an alternative renewable source of large-scale ECs for regenerative therapy. This study represents the first step toward the development of an autologous cell-based strategy for the treatment of PAD in the future.

3003 – TARGETED CRISPR-MEDIATED GENE ACTIVATION DURING IN VITRO IPSCS DIFFERENTIATION SUCCESSFULLY EXPANDS ARTERIAL-FATED CELLS IN ASSOCIATION WITH HIGHER PROGENITOR ACTIVITY.

Hematopoietic stem and progenitor cells develop from hemogenic endothelium located in various sites during development. Particularly, Hematopoietic Stem Cells (HSCs) develop from specialised endothelial cells within the wall of the dorsal aorta. This process has proven especially challenging to recapitulate in vitro from pluripotent stem cells. Here, we compared iPSC-derived (PSD) endothelial cells and in vivo (IV) hemogenic endothelium and identified 9 transcription factors expressed at significantly lower levels in vitro. We then developed a novel DOX-inducible CRISPR activation system to induce the expression of those genes during in vitro differentiation. We then employed single-cell RNA sequencing to study the phenotypical changes induced by the target genes. Furthermore, by engineering the gRNA we were able to detect them within the sequencing pipeline. Our data showed a significant expansion of arterial-fated endothelial cells with associated higher in vitro progenitor activity. Interestingly, the expanded arterial cluster is distinct from that expressing hemogenic markers, suggesting that the arterial cells might play a supportive role in the emergence of progenitor cells from the hemogenic endothelium. Hematopoietic stem and progenitor cells develop from hemogenic endothelium located in various sites during development. Particularly, Hematopoietic Stem Cells (HSCs) develop from specialised endothelial cells within the wall of the dorsal aorta. This process has proven especially challenging to recapitulate in vitro from pluripotent stem cells. Here, we compared iPSC-derived (PSD) endothelial cells and in vivo (IV) hemogenic endothelium and identified 9 transcription factors expressed at significantly lower levels in vitro. We then developed a novel DOX-inducible CRISPR activation system to induce the expression of those genes during in vitro differentiation. We then employed single-cell RNA sequencing to study the phenotypical changes induced by the target genes. Furthermore, by engineering the gRNA we were able to detect them within the sequencing pipeline. Our data showed a significant expansion of arterial-fated endothelial cells with associated higher in vitro progenitor activity. Interestingly, the expanded arterial cluster is distinct from that expressing hemogenic markers, suggesting that the arterial cells might play a supportive role in the emergence of progenitor cells from the hemogenic endothelium.

Abstract 11425: Vascular Organ-Chips Made from Blood

Introduction: Organ-on-chip technology has accelerated in vitro preclinical research of the vascular system, and a key strength of this platform is its promise to impact personalized medicine by providing a primary human cell-culture environment where endothelial cells are directly biopsied from individual tissue or differentiated through stem cell biotechniques. But these methods are difficult to adopt in labs and limit the power of organ-chips in making accurate physiological predictions. Hypothesis: In this study, we report Blood Outgrowth Endothelial Cells as a suitable alternative to primary and iPSC-derived endothelial cells. Through organ-chip and RNA sequencing, we further demonstrate that patient-blood derived BOECs are disease-specific and can differentiate sickle cell disease (SCD) patients. Methods: We isolate BOECs from healthy blood samples and compare their genotype, phenotype and organ-chip functional characteristics against commercially available and most commonly used HUVECs and iPSC-derived endothelial cells. To study patient-specificity, we isolate BOECs from two clinically distinct SCD patients and compare the presence of proinflammatory and endothelial activation pathways as predicted by RNA sequencing of autologous BOECs. Finally, we study the differences in thromboinflammation and endothelial activation between patient BOECs through vessel-chips. Results: Blood-derived endothelial cells exhibit the gold-standard hallmarks of typical endothelial cells. BOECs exhibit the classic endothelial “cobblestone” morphology in vitro and exhibit growth rates, migration abilities, de novo vessel formation, response to fluid shear and exogenous cytokine stimulation in a manner comparable to HUVECs and iECs. When isolated from SCD patients, BOECs exhibit an activated state as predicted by differential gene expression (DGE) and pathway analysis. Finally, real-time healthy whole blood perfusion through endothelialized vessel-chips with BOECs from more severe SCD patient yielded higher platelet adhesion compared to patient with mild severity. Conclusions: Blood-derived endothelial cells may be employed in preclinical research for developing more robust and personalized next-generation disease models.

Abstract 10410: Human Stem Cell-Derived Endothelial Cells Suppress Automaticity of Stem Cell-Derived Cardiomyocytes

Clinical translation of stem cell therapies for heart disease is limited by a risk of potentially life-threatening ventricular arrhythmias seen following cardiomyocyte delivery in large animal models. Enhancing cardiomyocyte maturation may reduce this arrhythmogenic risk by reducing automaticity of delivered cardiomyocytes. We tested whether human induced pluripotent stem cell (hiPSC)-derived endothelial cells can enhance maturation and suppress automaticity of iPSC-derived cardiomyocytes in vitro. We found that co-culture of hiPSC-derived endothelial cells with hiPSC-derived cardiomyocytes significantly increased protein expression of cardiac troponin T, cardiac troponin I, Kir2.1, connexin 43, and CD36. In addition, using a stretchable mesh nanoelectronics device, we found that hiPSC-derived endothelial cells accelerated electrical maturation of hiPSC-derived cardiomyocytes and progressively suppressed cardiomyocyte automaticity in vitro (Figure). Using single cell RNA-seq, we identified a subpopulation of hiPSC-derived cardiomyocytes that is eliminated upon co-culture with hiPSC-derived endothelial cells. Further work will investigate whether this subpopulation of cardiomyocytes is responsible for automaticity of cardiomyocyte cultures. Figure. Induced pluripotent stem cell (iPSC)-derived cardiomyocytes alone (CM only) or iPSC-derived cardiomyocytes co-cultured with iPSC-derived endothelial cells (CM+EC) were seeded onto a stretchable mesh nanoelectronics device. Unstimulated voltage tracings at day 30 of cardiomyocyte differentiation show cardiomyocytes with a slower beating rate and more narrow action potential when co-cultured with iPSC-derived endothelial cells compared to iPSC-derived cardiomyocytes alone.

Abstract 11407: E-Cigarettes Induce Dysregulation of Autophagy Leading to Endothelial Dysfunction in an Ipsc Model of Pulmonary Arterial Hypertension

Introduction: Given the increasing popularity of electronic-cigarettes (e-cigs), it is imperative to evaluate the potential health risks of e-cigs especially in users with pre-existing health concerns. Although we have recently demonstrated that acute exposure to e-cig exacerbates endothelial dysfunction, a prominent feature of pulmonary arterial hypertension (PAH), it is currently unknown whether the use of e-cig represents an even higher risk factor in PAH patients. The aim of the present study is to assess if differential susceptibility exists between healthy and PAH patients following e-cig exposure and mechanisms contributing to it. Methods and Results: Using patient-specific induced pluripotent stem cells (iPSCs) derived from both PAH patients and healthy controls, we showed that PAH iPSC-derived endothelial cells (iPSC-ECs) exhibited increased susceptibility against e-cig exposure compared to healthy iPSC-ECs leading to significantly decreased cell viability, increased reactive oxygen species generation and apoptosis, and reduced tube formation and migration. Transcriptomic analyses revealed that differential expression of AKT3 may be responsible for triggering enhanced autophagic flux impairment in PAH iPSC-ECs compared to healthy iPSC-ECs which underlies increased susceptibility upon e-cig exposure. Consistent with sequencing data, western blot confirmed that AKT3 level was decreased in PAH iPSC-ECs following e-cig exposure and AKT3 proteasomal degradation was mediated by K48-linked ubiquitination. Moreover, knockdown of AKT3 in healthy iPSC-ECs significantly induced autophagic flux impairment and increased endothelial dysfunction and these vascular toxicities were further increased when exposed to e-cig, thus mimicking the PAH cell phenotype after e-cig exposure. Finally, rapamycin treatment reversed e-cig-induced decreased AKT3 level, endothelial dysfunction, and autophagy impairment in PAH iPSC-ECs. Conclusions: Taken together, these data suggest a potential link between autophagy and Akt3-mediated increased susceptibility to e-cig in PAH.

Abstract 11757: Telomerase Treatment Restores Transcriptional Profile and Epigenetic Landscape in Progeria Vascular Cells

Hutchinson-Gilford progeria syndrome (HGPS) is a model of accelerated vascular aging caused by a de novo mutation of a single nucleotide in the Lamin A gene. The accumulation of abnormal lamin A (progerin) in the nuclear envelope induces a nuclear dysmorphology associated with global gene dysregulation, increased expression of inflammatory cytokines, impaired vascular function, and accelerated telomere erosion. These individuals succumb to myocardial infarction or stroke in their mid-teens. We hypothesized that restoration of telomere length might reverse some of the observed derangements in cell function, transcriptional profile and epigenetic alterations. Accordingly, we generated iPSC-derived endothelial cells (ECs) from HGPS children and their unaffected parents. By comparison to the parental controls, HGPS ECs have severely impaired replicative capacity, cellular functions (e.g. NO synthesis, acLDL uptake, network formation, cytokine secretion) and severe telomere shortening. We observed that transient transfection with mRNA encoding human telomerase (hTERT) increases telomere length, restores cellular replicative capacity and improves HGPS-EC functions. Notably, RNAseq studies revealed that that approximately 1200 genes were dysregulated in Progeria, most of which were improved by hTERT treatment, among which approximately 250+ genes were fully normalized. Intriguingly, hTERT treatment reduces DNA damage signals (γH2Ax) and reverses the aberrant chromatin accessibility observed in HGPS-ECs, as assessed by a reduction in the activating histone mark H3K4me3; an increase in the suppressive mark H3K4me3; and normalizes the level of heterochromatin markers HP1, Histone H1 and H3. Preliminary results from ChIPseq studies targeting histone marks characteristic of activators, repressors and enhancers as well as chromatin remodeling proteins; together with Hi-C analyses indicate that there are global changes in topologically associated domains (TADs) and other features of the chromatin landscape in HGPS ECs, which are partially restored by hTERT treatment. We conclude that hTERT treatment has surprisingly global effects on transcriptional profile and epigenetic landscape in addition to telomere extension.

EXTH-17. A FOCUSED ULTRASOUND BLOOD BRAIN BARRIER DISRUPTION MODEL TO TEST THE INFLUENCE OF TIGHT JUNCTION GENES TO TREAT BRAIN TUMORS

Abstract Treating primary or metastatic tumors in the brain (glioblastomas, melanoma, lung cancer, breast cancer) proves challenging by virtue of the protective function of the blood brain barrier (BBB). The tight junction proteins (TJPs) binding the specialized endothelial cells of the BBB largely contribute to the limited permeability of cancer-therapeutic drugs. In both preclinical and clinical models, low intensity focused ultrasound (LIFU) coupled with microbubbles has been proven to safely and transiently open the BBB. Despite this method being established, potential genetic influences on the durability and vulnerability of tight junctions to LIFU have not been elucidated, nor have the determinants of tight junction repair post LIFU been thoroughly investigated. We report the development of an ultrasound transparent organ-on-chip model populated by iPSC-derived endothelial cells (iPSC-EC) co-cultured with astrocytes. We aim to probe the contributions of various tight junction genes to barrier integrity along with the subsequent protein topology involved in reassembly post ultrasound. Thus, this model serves to determine parameters for ultrasound disruption for precision opening of the BBB. The BBB-On-Chip was successfully fabricated and assembled with an optimized technique that has an 80% yield of leak-free devices, with stable cavitation post nanobubble injection. Furthermore, Western blots show expression of claudin-5, a key TJP, in our iPSC-ECs. We have also demonstrated by confocal microscopy that another component of the TJP complex, ZO-1, can be visualized at iPSC-derived cell junctions. Further benchmarking of device-ultrasound interactions, successful iPSC differentiation, tight junction formation, and fabrication of nanobubbles and their assistance in ultrasound BBB disruption will be presented. Efforts are underway to characterize the contributions of tight junction genes and their variations to the integrity and disruption of the BBB.

Towards Biohybrid Lung: Induced Pluripotent Stem Cell Derived Endothelial Cells as Clinically Relevant Cell Source for Biologization.

In order to provide an alternative treatment option to lung transplantation for patients with end-stage lung disease, we aim for the development of an implantable biohybrid lung (BHL), based on hollow fiber membrane (HFM) technology used in extracorporeal membrane oxygenators. Complete hemocompatibility of all blood contacting surfaces is crucial for long-lasting BHL durability and can be achieved by their endothelialization. Autologous endothelial cells (ECs) would be the ideal cell source, but their limited proliferation potential excludes them for this purpose. As induced pluripotent stem cell-derived ECs enable the generation of a large number of ECs, we assessed and compared their capacity to form a viable and confluent monolayer on HFM, while indicating physiologic EC-specific anti-thrombogenic and anti-inflammatory properties. ECs were generated from three different human iPSC lines, and seeded onto fibronectin-coated poly-4-methyl-1-pentene (PMP) HFM. Following phenotypical characterization, ECs were analyzed for their thrombogenic and inflammatory behavior with or without TNFα induction, using FACS and qRT-PCR. Complementary, leukocyte- and platelet adhesion assays were carried out. The capacity of the iPSC-ECs to reendothelialize cell-free monolayer areas was assessed in a scratch assay. ECs sourced from umbilical cord blood (hCBECs) were used as control. iPSC-derived ECs formed confluent monolayers on the HFM and showed the typical EC-phenotype by expression of VE-cadherin and collagen-IV. A low protein and gene expression level of E-selectin and tissue factor was detected for all iPSC-ECs and the hCBECs, while a strong upregulation of these markers was noted upon stimulation with TNFα. This was in line with the physiological and strong induction of leukocyte adhesion detected after treatment with TNFα, iPSC-EC and hCBEC monolayers were capable of reducing thrombocyte adhesion and repopulating scratched areas. iPSCs offer the possibility to provide patient-specific ECs in abundant numbers needed to cover all blood contacting surfaces of the BHL with a viable, non-thrombogenic and non-inflammatory monolayer. iPSC-EC clones can differ in terms of their reendothelialization rate, and pro-inflammatory response. However, a less profound inflammatory response may even be advantageous for BHL application. With the proven ability of the seeded iPSC-ECs to reduce thrombocyte adhesion, we expect that thrombotic events that could lead to BHL occlusion can be avoided, and thus, justifies further studies on enabling BHL long-term application.

Patient-specific iPSC-derived endothelial cells reveal aberrant p38 MAPK signaling in atypical hemolytic uremic syndrome.

SummaryAtypical hemolytic uremic syndrome (aHUS) is a rare disease associated with high morbidity and mortality. Existing evidence suggests that the central pathogenesis to aHUS might be endothelial cell damage. Nevertheless, the role of endothelial cell alterations in aHUS has not been well characterized and the underlying mechanisms remain unclear. Utilizing an induced pluripotent stem cell-derived endothelial cell (iPSC-EC) model, we showed that anti-complement factor H autoantibody-associated aHUS patient-specific iPSC-ECs exhibited an intrinsic defect in endothelial functions. Stimulation using aHUS serums exacerbated endothelial dysfunctions, leading to cell apoptosis in iPSC-ECs. Importantly, we identified p38 as a novel signaling pathway contributing to endothelial dysfunctions in aHUS. These results illustrate that iPSC-ECs can be a reliable model to recapitulate EC pathological features, thus providing a unique platform for gaining mechanistic insights into EC injury in aHUS. Our findings highlight that the p38 MAPK signaling pathway can be a therapeutic target for treatment of aHUS.