Background: Electronic cigarettes (e-cigarettes) have experienced a tremendous increase in use. Unlike cigarette smoking, the effects of e-cigarettes and their constituents on mediating vascular health remain understudied. However, given their increasing popularity, it is imperative to evaluate the health risks of e-cigarettes, including the effects of their ingredients, especially nicotine and flavorings. Objectives: To investigate the effects of flavored e-cigarette liquids (e-liquids) and serum isolated from e-cigarette users on endothelial health and endothelial cell dependent macrophage activation. Methods: We used human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) and a high-throughput screening approach to assess endothelial integrity following exposure to 6 different e-liquids with varying nicotine concentrations and to serum from e-cigarette users. Results: The cytotoxicity of the e-liquids varied considerably, with the cinnamon-flavored product being most potent and leading to significantly decreased cell viability, increased reactive oxygen species (ROS) levels, caspase 3/7 activity, and low-density lipoprotein uptake, activation of oxidative stress-related pathway, and impaired tube formation and migration, confirming endothelial dysfunction. Upon exposure of ECs to e-liquid, conditioned media induced macrophage polarization into a pro-inflammatory state, eliciting the production of interleukin-1β (IL-1β) and IL-6, leading to increased ROS. After exposure of iPSC-ECs to serum of e-cigarette users, we observed increased ROS linked to endothelial dysfunction, as indicated by impaired pro-angiogenic properties. We also noted an increase in inflammatory cytokine expression in serum of e-cigarette users. Conclusions: Acute exposure to flavored e-liquids or e-cigarette use exacerbates endothelial dysfunction, which often precedes cardiovascular diseases.Abbreviations CRP = c-reactive protein CVD = cardiovascular disease E-cigarette = electronic cigarette E-liquids = electronic cigarette liquids iPSC-ECs = induced pluripotent stem cell-derived endothelial cells PG = propylene glycol PLT = platelet ROS = reactive oxygen species VG = vegetable glycerin Condensed Abstract E-cigarettes have seen a rapid increase in use although their effects on vascular health remain understudied. Here, we investigated the effects of flavored e-cigarette liquids (e-liquids) on endothelial health by exposing human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) to different e-liquids with varying nicotine concentrations. While cytotoxicity varied among the tested flavors, the cinnamon-flavored product was most potent leading to decreased cell viability, increased oxidative stress and caspase activity, and impaired tube formation confirming endothelial dysfunction; results which were further corroborated using e-cigarette

Highlights d TBX5 Clover2 and NKX2-5 TagRFP reporter enables purification of 4 cardiac subpopulations d Different cardiac lineages differentiate into specific cardiac cell types d CORIN is a cell-surface marker for the TBX5+NKX2-5+ subpopulation d Lineage-specific cardiomyocyte subtypes can be used for precise drug testing

Inhibition of Mek/Erk signaling by pharmacological Mek inhibitors promotes self-renewal and pluripotency of mouse embryonic stem cells (ESCs). Intriguingly, Erk signaling is essential for human ESC selfrenewal. Here we demonstrate that Erk signaling is critical for mouse ESC self-renewal and genomic stability. Erk-depleted ESCs cannot be maintained. Lack of Erk leads to rapid telomere shortening and genomic instability, in association with misregulated expression of pluripotency genes, reduced cell proliferation, G1 cell-cycle arrest, and increased apoptosis. Erk signaling is also required for the activation of differentiation genes but not for the repression of pluripotency genes during ESC differentiation. Furthermore, we find an Erk-independent function of Mek, which may explain the diverse effects of Mek inhibition and Erk knockout on ESC self-renewal. Together, in contrast to the prevailing view, Erk signaling is required for telomere maintenance, genomic stability, and self-renewal of mouse ESCs.Erk | Mek | embryonic stem cells | self-renewal | genomic stability E mbryonic stem cells (ESCs) are pluripotent and, hence, promising donor cell sources for regenerative medicine. Transcriptional regulation plays an essential role in pluripotency maintenance of ESCs, and a transcriptional regulation network for pluripotency has been characterized (1, 2). The core component of the pluripotency transcriptional regulation network is a feed-forward selfregulating circuitry formed by transcription factors Oct4, Sox2, and Nanog (3, 4). ESCs are cultured in media supplemented with growth factors. Through signaling pathways, growth factors affect the pluripotency transcriptional regulation network and regulate the self-renewal and differentiation of ESCs. For example, LIF and BMP signaling controls the transcriptional activities of the downstream effectors Stat3 and Smad1 to promote the self-renewal of mouse ESCs (5-7).The extracellular signal-regulated kinase (Erk)/mitogen-activated protein kinase (MAPK) signal-transduction cascade mediates the effect of growth factors by sequential activation of Ras-like GTPase, Raf kinase, serine/threonine protein kinase Mek, and Erk to regulate cell-cycle progression, proliferation, differentiation, and carcinogenesis (8, 9). Erk signaling also plays a pivotal role in pluripotency maintenance. Inhibition of Mek/Erk signaling constrains the differentiation of mouse ESCs (10). Mouse ESCs can be derived and maintained in medium supplemented with inhibitors of Mek and Gsk3 signaling (2i) (11). Moreover, inhibition of Mek facilitates the conversion of mouse epiblast stem cells (epiSCs) to ESC-like cells (12). Similarly, the Mek inhibitor PD0325901 is used in establishing and maintaining human ground-state pluripotent stem cells (13-16). Conversely, activation of Mek/Erk signaling promotes the differentiation of ESCs. Ectopic expression of an activated H-RAS mutant leads to mouse ESC differentiation toward the trophectodermal lineage. Mek/Erk signaling is the downstream effector of Ras medi...