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During liver development, bipotential progenitor cells called hepatoblasts differentiate into hepatocytes or cholangiocytes. Hepatocyte differentiation is uniquely associated with multi-axial polarity, enabling the anisotropic expansion of apical lumina between adjacent cells and formation of a three-dimensional network of bile canaliculi. Cholangiocytes, the cells forming the bile ducts, exhibit the vectorial polarity characteristic of epithelial cells. Whether cell polarization feeds back on the gene regulatory pathways governing hepatoblast differentiation is unknown. Here, we used primary mouse hepatoblasts to investigate the contribution of anisotropic apical expansion to hepatocyte differentiation. Silencing of the small GTPase Rab35 caused isotropic lumen expansion and formation of multicellular cysts with the vectorial polarity of cholangiocytes. Gene expression profiling revealed that these cells express reduced levels of hepatocyte markers and upregulate genes associated with cholangiocyte identity. Timecourse RNA sequencing demonstrated that loss of lumen anisotropy precedes these transcriptional changes. Independent alterations in apical lumen morphology induced either by modulation of the subapical actomyosin cortex or by increased intraluminal pressure caused similar transcriptional changes. These findings suggest that cell polarity and lumen morphogenesis feed back to hepatoblast-to-hepatocyte differentiation. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs) have emerged as important mediators of intercellular communication in the heart under homeostatic and pathological conditions, such as myocardial infarction (MI). However, the basic mechanisms driving cardiomyocyte‐derived EV (CM‐EV) production following stress are poorly understood. In this study, we generated human induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) that express NanoLuc‐tetraspanin reporters. These modified hiPSC‐CMs allow for quantification of tetraspanin‐positive CM‐EV secretion from small numbers of cells without the need for time‐consuming EV isolation techniques. We subjected these cells to a panel of small molecules to study their effect on CM‐EV biogenesis and secretion under basal and stress‐associated conditions. We observed that EV biogenesis is context‐dependent in hiPSC‐CMs. Nutrient starvation decreases CM‐EV secretion while hypoxia increases the production of CM‐EVs in a nSmase2‐dependent manner. Moreover, the inflammatory cytokine TNF‐α increased CM‐EV secretion through a process involving NLRP3 inflammasome activation and mTOR signalling. Here, we detailed for the first time the regulatory mechanisms of EV biogenesis in hiPSC‐CMs upon MI‐associated stressors. [ABSTRACT FROM AUTHOR]

The G protein–coupled receptor (GPCR) US28 encoded by the human cytomegalovirus (HCMV) is associated with accelerated progression of glioblastomas, aggressive brain tumors with a generally poor prognosis. Here, we showed that US28 increased the malignancy of U251 glioblastoma cells by enhancing signaling mediated by sphingosine-1-phosphate (S1P), a bioactive lipid that stimulates oncogenic pathways in glioblastoma. US28 expression increased the abundance of the key components of the S1P signaling axis, including an enzyme that generates S1P [sphingosine kinase 1 (SK1)], an S1P receptor [S1P receptor 1 (S1P1)], and S1P itself. Enhanced S1P signaling promoted glioblastoma cell proliferation and survival by activating the kinases AKT and CHK1 and the transcriptional regulators cMYC and STAT3 and by increasing the abundance of cancerous inhibitor of PP2A (CIP2A), driving several feed-forward signaling loops. Inhibition of S1P signaling abrogated the proliferative and anti-apoptotic effects of US28. US28 also activated the S1P signaling axis in HCMV-infected cells. This study uncovers central roles for S1P and CIP2A in feed-forward signaling that contributes to the US28-mediated exacerbation of glioblastoma. Editor's summary: US28 is a GPCR encoded by the β-herpesvirus human cytomegalovirus (HCMV) whose expression is associated with glioblastoma progression and contributes to the tumorigenic properties of HCMV. Bergkamp et al. showed that US28 expression was associated with increased signaling through the sphingosine-1-phosphate (S1P) pathway, a potent driver of gliomagenesis. US28 stimulated sphingosine kinase 1, which generates S1P, and activated STAT3 signaling in an S1P-dependent manner, leading to the increased proliferation and survival of glioblastoma cells. This work provides insight into how manipulating host cell signaling enables HCMV to promote glioblastoma progression. —Amy E. Baek [ABSTRACT FROM AUTHOR]

Background: Tau pathology and endolysosomal alterations co‐occur in brains of Alzheimer's Disease and other tauopathy patients, but the relationship between these two pathological features is currently not understood. Method: Tau pathology can be modeled in vitro by seeding recombinant tau fibrils on human tau expressing cells, recapitulating tau hyperphosphorylation, misfolding and aggregation. The present study addressed how the seeding of tau pathology impacts the endolysosomal systemin various cell models. Cells expressing human GFP‐tau‐P301L were seeded with pre‐aggregated tau and fixed after 10 days for confocal and 3D‐STED analysis. Result: Tau seeds were observed in early and late endosomal/lysosomal compartments. In iPSC‐derived human neurons, the seeding of tau pathology decreased the number, size and EEA1 labelling intensity of EEA1‐positive early endosomes. The effect on early endosomes was specific as the morphology of LAMP1‐positive late endosomes was not affected. Our data however did indicate a decreased proteolytic activity of these compartments suggesting that tau pathology seeding can causally affect endolysosomal function. Conclusion: The seeding of tau pathology can causally induce changes in the endolysosomal system, both on the morphological and the functional level. Such disturbances of this important recycling pathway in neurons may play a critical role in neurodegeneration observed in tauopathies. [ABSTRACT FROM AUTHOR]