Scientific Resources

Long-chain bases are present in the oral cavity. Previously we determined that sphingosine,dihydrosphingosine,and phytosphingosine have potent antimicrobial activity against oral pathogens. Here,we determined the cytotoxicities of long-chain bases for oral cells,an important step in considering their potential as antimicrobial agents for oral infections. This information would clearly help in establishing prophylactic or therapeutic doses. To assess this,human oral gingival epithelial (GE) keratinocytes,oral gingival fibroblasts (GF),and dendritic cells (DC) were exposed to 10.0-640.0 μM long-chain bases and glycerol monolaurate (GML). The effects of long-chain bases on cell metabolism (conversion of resazurin to resorufin),membrane permeability (uptake of propidium iodide or SYTOX-Green),release of cellular contents (LDH),and cell morphology (confocal microscopy) were all determined. GE keratinocytes were more resistant to long-chain bases as compared to GF and DC,which were more susceptible. For DC,0.2-10.0 μM long-chain bases and GML were not cytotoxic; 40.0-80.0 μM long-chain bases,but not GML,were cytotoxic; and 80.0 μM long-chain bases induced cellular damage and death in less than 20 min. The LD50 of long-chain bases for GE keratinocytes,GF,and DC were considerably higher than their minimal inhibitory concentrations for oral pathogens,a finding important to pursuing their future potential in treating periodontal and oral infections. View Publication

Many acute and chronic anaemias,including haemolysis,sepsis and genetic bone marrow failure diseases such as Diamond-Blackfan anaemia,are not treatable with erythropoietin (Epo),because the colony-forming unit erythroid progenitors (CFU-Es) that respond to Epo are either too few in number or are not sensitive enough to Epo to maintain sufficient red blood cell production. Treatment of these anaemias requires a drug that acts at an earlier stage of red cell formation and enhances the formation of Epo-sensitive CFU-E progenitors. Recently,we showed that glucocorticoids specifically stimulate self-renewal of an early erythroid progenitor,burst-forming unit erythroid (BFU-E),and increase the production of terminally differentiated erythroid cells. Here we show that activation of the peroxisome proliferator-activated receptor α (PPAR-α) by the PPAR-α agonists GW7647 and fenofibrate synergizes with the glucocorticoid receptor (GR) to promote BFU-E self-renewal. Over time these agonists greatly increase production of mature red blood cells in cultures of both mouse fetal liver BFU-Es and mobilized human adult CD34(+) peripheral blood progenitors,with a new and effective culture system being used for the human cells that generates normal enucleated reticulocytes. Although Ppara(-/-) mice show no haematological difference from wild-type mice in both normal and phenylhydrazine (PHZ)-induced stress erythropoiesis,PPAR-α agonists facilitate recovery of wild-type but not Ppara(-/-) mice from PHZ-induced acute haemolytic anaemia. We also show that PPAR-α alleviates anaemia in a mouse model of chronic anaemia. Finally,both in control and corticosteroid-treated BFU-E cells,PPAR-α co-occupies many chromatin sites with GR; when activated by PPAR-α agonists,additional PPAR-α is recruited to GR-adjacent sites and presumably facilitates GR-dependent BFU-E self-renewal. Our discovery of the role of PPAR-α agonists in stimulating self-renewal of early erythroid progenitor cells suggests that the clinically tested PPAR-α agonists we used may improve the efficacy of corticosteroids in treating Epo-resistant anaemias. View Publication

Environmental influences and insults by reproductive toxicant exposure can lead to impaired spermatogenesis or infertility. Understanding how toxicants disrupt spermatogenesis is critical for determining how environmental factors contribute to impaired fertility. While current animal models are available,understanding of the reproductive toxic effects on human fertility requires a more robust model system. We recently demonstrated that human pluripotent stem cells can differentiate into spermatogonial stem cells/spermatogonia,primary and secondary spermatocytes,and haploid spermatids; a model that mimics many aspects of human spermatogenesis. Here,using this model system,we examine the effects of 2-bromopropane (2-BP) and 1,2,dibromo-3-chloropropane (DBCP) on in vitro human spermatogenesis. 2-BP and DBCP are non-endocrine disrupting toxicants that are known to impact male fertility. We show that acute treatment with either 2-BP or DBCP induces a reduction in germ cell viability through apoptosis. 2-BP and DBCP affect viability of different cell populations as 2-BP primarily reduces spermatocyte viability,whereas DBCP exerts a much greater effect on spermatogonia. Acute treatment with 2-BP or DBCP also reduces the percentage of haploid spermatids. Both 2-BP and DBCP induce reactive oxygen species (ROS) formation leading to an oxidized cellular environment. Taken together,these results suggest that acute exposure with 2-BP or DBCP causes human germ cell death in vitro by inducing ROS formation. This system represents a unique platform for assessing human reproductive toxicity potential of various environmental toxicants in a rapid,efficient,and unbiased format. View Publication

The liver is the main organ responsible for the modification,clearance,and transformational toxicity of most xenobiotics owing to its abundance in cytochrome P450 (CYP450) enzymes. However,the scarcity and variability of primary hepatocytes currently limits their utility. Human pluripotent stem cells (hPSCs) represent an excellent source of differentiated hepatocytes; however,current protocols still produce fetal-like hepatocytes with limited mature function. Interestingly,fetal hepatocytes acquire mature CYP450 expression only postpartum,suggesting that nutritional cues may drive hepatic maturation. We show that vitamin K2 and lithocholic acid,a by-product of intestinal flora,activate pregnane X receptor (PXR) and subsequent CYP3A4 and CYP2C9 expression in hPSC-derived and isolated fetal hepatocytes. Differentiated cells produce albumin and apolipoprotein B100 at levels equivalent to primary human hepatocytes,while demonstrating an 8-fold induction of CYP450 activity in response to aryl hydrocarbon receptor (AhR) agonist omeprazole and a 10-fold induction in response to PXR agonist rifampicin. Flow cytometry showed that over 83% of cells were albumin and hepatocyte nuclear factor 4 alpha (HNF4α) positive,permitting high-content screening in a 96-well plate format. Analysis of 12 compounds showed an R(2) correlation of 0.94 between TC50 values obtained in stem cell-derived hepatocytes and primary cells,compared to 0.62 for HepG2 cells. Finally,stem cell-derived hepatocytes demonstrate all toxicological endpoints examined,including steatosis,apoptosis,and cholestasis,when exposed to nine known hepatotoxins. CONCLUSION: Our work provides fresh insights into liver development,suggesting that microbial-derived cues may drive the maturation of CYP450 enzymes postpartum. Addition of these cues results in the first functional,inducible,hPSC-derived hepatocyte for predictive toxicology. (Hepatology 2015). View Publication

The mechanisms by which neutralizing antibodies inhibit Marburg virus (MARV) are not known. We isolated a panel of neutralizing antibodies from a human MARV survivor that bind to MARV glycoprotein (GP) and compete for binding to a single major antigenic site. Remarkably,several of the antibodies also bind to Ebola virus (EBOV) GP. Single-particle EM structures of antibody-GP complexes reveal that all of the neutralizing antibodies bind to MARV GP at or near the predicted region of the receptor-binding site. The presence of the glycan cap or mucin-like domain blocks binding of neutralizing antibodies to EBOV GP,but not to MARV GP. The data suggest that MARV-neutralizing antibodies inhibit virus by binding to infectious virions at the exposed MARV receptor-binding site,revealing a mechanism of filovirus inhibition. View Publication

Endogenous molecular and cellular mediators modulate tissue repair and regeneration. We have recently described antibody mediated osseous regeneration (AMOR) as a novel strategy for bioengineering bone in rat calvarial defect. This entails application of anti-BMP-2 antibodies capable of in vivo capturing of endogenous osteogenic BMPs (BMP-2,BMP-4,and BMP-7). The present study sought to investigate the feasibility of AMOR in other animal models. To that end,we examined the efficacy of a panel of anti-BMP-2 monoclonal antibodies (mAbs) and a polyclonal Ab immobilized on absorbable collagen sponge (ACS) to mediate bone regeneration within rabbit calvarial critical size defects. After 6 weeks,de novo bone formation was demonstrated by micro-CT imaging,histology,and histomorphometric analysis. Only certain anti-BMP-2 mAb clones mediated significant in vivo bone regeneration,suggesting that the epitopes with which anti-BMP-2 mAbs react are critical to AMOR. Increased localization of BMP-2 protein and expression of osteocalcin were observed within defects,suggesting accumulation of endogenous BMP-2 and/or increased de novo expression of BMP-2 protein within sites undergoing bone repair by AMOR. Considering the ultimate objective of translation of this therapeutic strategy in humans,preclinical studies will be necessary to demonstrate the feasibility of AMOR in progressively larger animal models. View Publication

There is an urgent need for new and advanced approaches to modeling the pathological mechanisms of complex human neurological disorders. This is underscored by the decline in pharmaceutical research and development efficiency resulting in a relative decrease in new drug launches in the last several decades. Induced pluripotent stem cells represent a new tool to overcome many of the shortcomings of conventional methods,enabling live human neural cell modeling of complex conditions relating to aberrant neurodevelopment,such as schizophrenia,epilepsy and autism as well as age-associated neurodegeneration. This review considers the current status of induced pluripotent stem cell-based modeling of neurological disorders,canvassing proven and putative advantages,current constraints,and future prospects of next-generation culture systems for biomedical research and translation. View Publication

Emerging hepatic models for the study of drug-induced toxicity include pluripotent stem cell-derived hepatocyte-like cells (HLCs) and complex hepatocyte-non-parenchymal cellular coculture to mimic the complex multicellular interactions that recapitulate the niche environment in the human liver. However,a specific marker of hepatocyte perturbation,required to discriminate hepatocyte damage from non-specific cellular toxicity contributed by non-hepatocyte cell types or immature differentiated cells is currently lacking,as the cytotoxicity assays routinely used in in vitro toxicology research depend on intracellular molecules which are ubiquitously present in all eukaryotic cell types. In this study,we demonstrate that microRNA-122 (miR-122) detection in cell culture media can be used as a hepatocyte-enriched in vitro marker of drug-induced toxicity in homogeneous cultures of hepatic cells,and a cell-specific marker of toxicity of hepatic cells in heterogeneous cultures such as HLCs generated from various differentiation protocols and pluripotent stem cell lines,where conventional cytotoxicity assays using generic cellular markers may not be appropriate. We show that the sensitivity of the miR-122 cytotoxicity assay is similar to conventional assays that measure lactate dehydrogenase activity and intracellular adenosine triphosphate when applied in hepatic models with high levels of intracellular miR-122,and can be multiplexed with other assays. MiR-122 as a biomarker also has the potential to bridge results in in vitro experiments to in vivo animal models and human samples using the same assay,and to link findings from clinical studies in determining the relevance of in vitro models being developed for the study of drug-induced liver injury. View Publication

Extracellular vesicles (EVs) are phospholipid-based particles endogenously produced by cells. Their natural composition and selective cell interactions make them promising drug carriers. However,in order to harness their properties,efficient exogenous drug encapsulation methods need to be investigated. Here,EVs from various cellular origins (endothelial,cancer and stem cells) were produced and characterised for size and composition. Porphyrins of different hydrophobicities were employed as model drugs and encapsulated into EVs using various passive and active methods (electroporation,saponin,extrusion and dialysis). Hydrophobic compounds loaded very efficiently into EVs and at significantly higher amounts than into standard liposomes composed of phosphocholine and cholesterol using passive incubation. Moreover,loading into EVs significantly increased the cellular uptake by textgreater60% and the photodynamic effect of hydrophobic porphyrins in vitro compared to free or liposome encapsulated drug. The active encapsulation techniques,with the saponin-assisted method in particular,allowed an up to 11 fold higher drug loading of hydrophilic porphyrins compared to passive methods. EVs loaded with hydrophilic porphyrins induced a stronger phototoxic effect than free drug in a cancer cell model. Our findings create a firm basis for the development of EVs as smart drug carriers based on straightforward and transferable methods. View Publication

Long interspersed element-1 (LINE-1 or L1) retrotransposition induces insertional mutations that can result in diseases. It was recently shown that the copy number of L1 and other retroelements is stable in induced pluripotent stem cells (iPSCs). However,by using an engineered reporter construct over-expressing L1,another study suggests that reprogramming activates L1 mobility in iPSCs. Given the potential of human iPSCs in therapeutic applications,it is important to clarify whether these cells harbor somatic insertions resulting from endogenous L1 retrotransposition. Here,we verified L1 expression during and after reprogramming as well as potential somatic insertions driven by the most active human endogenous L1 subfamily (L1Hs). Our results indicate that L1 over-expression is initiated during the reprogramming process and is subsequently sustained in isolated clones. To detect potential somatic insertions in iPSCs caused by L1Hs retotransposition,we used a novel sequencing strategy. As opposed to conventional sequencing direction,we sequenced from the 3' end of L1Hs to the genomic DNA,thus enabling the direct detection of the polyA tail signature of retrotransposition for verification of true insertions. Deep coverage sequencing thus allowed us to detect seven potential somatic insertions with low read counts from two iPSC clones. Negative PCR amplification in parental cells,presence of a polyA tail and absence from seven L1 germline insertion databases highly suggested true somatic insertions in iPSCs. Furthermore,these insertions could not be detected in iPSCs by PCR,likely due to low abundance. We conclude that L1Hs retrotransposes at low levels in iPSCs and therefore warrants careful analyses for genotoxic effects. View Publication

UNLABELLED: Due to continuous changes to its antigenic regions,influenza viruses can evade immune detection and cause a significant amount of morbidity and mortality around the world. Influenza vaccinations can protect against disease but must be annually reformulated to match the current circulating strains. In the development of a broad-spectrum influenza vaccine,the elucidation of conserved epitopes is paramount. To this end,we designed an immunization strategy in mice to boost the humoral response against conserved regions of the hemagglutinin (HA) glycoprotein. Of note,generation and identification of broadly neutralizing antibodies that target group 2 HAs are rare and thus far have yielded only a few monoclonal antibodies (MAbs). Here,we demonstrate that mouse MAb 9H10 has broad and potent in vitro neutralizing activity against H3 and H10 group 2 influenza A subtypes. In the mouse model,MAb 9H10 protects mice against two divergent mouse-adapted H3N2 strains,in both pre- and postexposure administration regimens. In vitro and cell-free assays suggest that MAb 9H10 inhibits viral replication by blocking HA-dependent fusion of the viral and endosomal membranes early in the replication cycle and by disrupting viral particle egress in the late stage of infection. Interestingly,electron microscopy reconstructions of MAb 9H10 bound to the HA reveal that it binds a similar binding footprint to MAbs CR8020 and CR8043.backslashnbackslashnIMPORTANCE: The influenza hemagglutinin is the major antigenic target of the humoral immune response. However,due to continuous antigenic changes that occur on the surface of this glycoprotein,influenza viruses can escape the immune system and cause significant disease to the host. Toward the development of broad-spectrum therapeutics and vaccines against influenza virus,elucidation of conserved regions of influenza viruses is crucial. Thus,defining these types of epitopes through the generation and characterization of broadly neutralizing monoclonal antibodies (MAbs) can greatly assist others in highlighting conserved regions of hemagglutinin. Here,we demonstrate that MAb 9H10 that targets the hemagglutinin stalk has broadly neutralizing activity against group 2 influenza A viruses in vitro and in vivo. View Publication

Human pluripotent stem cells (hPSCs) tend to acquire genomic aberrations in culture,the most common of which is trisomy of chromosome 12. Here we dissect the cellular and molecular implications of this trisomy in hPSCs. Global gene expression analyses reveal that trisomy 12 profoundly affects the gene expression profile of hPSCs,inducing a transcriptional programme similar to that of germ cell tumours. Comparison of proliferation,differentiation and apoptosis between diploid and aneuploid hPSCs shows that trisomy 12 significantly increases the proliferation rate of hPSCs,mainly as a consequence of increased replication. Furthermore,trisomy 12 increases the tumorigenicity of hPSCs in vivo,inducing transcriptionally distinct teratomas from which pluripotent cells can be recovered. Last,a chemical screen of 89 anticancer drugs discovers that trisomy 12 raises the sensitivity of hPSCs to several replication inhibitors. Together,these findings demonstrate the extensive effect of trisomy 12 and highlight its perils for successful hPSC applications. View Publication