Scientific Resources

The optical isomers of the 1,4-dihydropyridine BAY K 8644 were studied in isolated rabbit aorta and heart preparations. The (-)-enantiomer has the known vasoconstricting and positive inotropic properties of the Ca agonistic compound. In contrast,its antipode shows at about 10-50 times higher concentrations the vasodilating and negative inotropic effects of Ca antagonistic drugs. It is concluded that neither simple chemical nor physical actions can be responsible for the opposite effects of Ca antagonistic and Ca agonistic dihydropyridines. View Publication

Neutrophils are recruited from the blood to sites of inflammation,where they contribute to immune defense but may also cause tissue damage. During inflammation,neutrophils roll along the microvascular endothelium before arresting and transmigrating. Arrest requires conformational activation of the integrin lymphocyte function-associated antigen 1 (LFA-1),which can be induced by selectin engagement. Here,we demonstrate that a subset of P-selectin glycoprotein ligand-1 (PSGL-1) molecules is constitutively associated with L-selectin. Although this association does not require the known lectin-like interaction between L-selectin and PSGL-1,the signaling output is dependent on this interaction and the cytoplasmic tail of L-selectin. The PSGL-1-L-selectin complex signals through Src family kinases,ITAM domain-containing adaptor proteins,and other kinases to ultimately result in LFA-1 activation. The PSGL-1-L-selectin complex-induced signaling effects on neutrophil slow rolling and recruitment in vivo demonstrate the functional importance of this pathway. We conclude that this is a signaling complex specialized for sensing adhesion under flow. View Publication

Induced pluripotent stem cells (iPSC) offer a unique opportunity for developmental studies,disease modeling and regenerative medicine approaches in humans. The aim of our study was to create an in vitro 'patient-specific cell-based system' that could facilitate the screening of new therapeutic molecules for the treatment of catecholaminergic polymorphic ventricular tachycardia (CPVT),an inherited form of fatal arrhythmia. Here,we report the development of a cardiac model of CPVT through the generation of iPSC from a CPVT patient carrying a heterozygous mutation in the cardiac ryanodine receptor gene (RyR2) and their subsequent differentiation into cardiomyocytes (CMs). Whole-cell patch-clamp and intracellular electrical recordings of spontaneously beating cells revealed the presence of delayed afterdepolarizations (DADs) in CPVT-CMs,both in resting conditions and after $\$-adrenergic stimulation,resembling the cardiac phenotype of the patients. Furthermore,treatment with KN-93 (2-[N-(2-hydroxyethyl)]-N-(4methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine),an antiarrhythmic drug that inhibits Ca(2+)/calmodulin-dependent serine-threonine protein kinase II (CaMKII),drastically reduced the presence of DADs in CVPT-CMs,rescuing the arrhythmic phenotype induced by catecholaminergic stress. In addition,intracellular calcium transient measurements on 3D beating clusters by fast resolution optical mapping showed that CPVT clusters developed multiple calcium transients,whereas in the wild-type clusters,only single initiations were detected. Such instability is aggravated in the presence of isoproterenol and is attenuated by KN-93. As seen in our RyR2 knock-in CPVT mice,the antiarrhythmic effect of KN-93 is confirmed in these human iPSC-derived cardiac cells,supporting the role of this in vitro system for drug screening and optimization of clinical treatment strategies. View Publication

The restoration of pluripotency circuits by the reactivation of endogenous stemness factors,such as SOX2,may provide a new paradigm in cancer development. The tumoral stem cell reprogramming hypothesis,i.e.,the ability of stemness factors to redirect normal and differentiated tumor cells toward a less-differentiated and stem-like state,adds new layers of complexity to cancer biology,because the effects of such reprogramming may remain dormant until engaged later in response to (epi)genetic and/or (micro)environmental events. To test this hypothesis,we utilized an in vitro model of a SOX2-overexpressing cancer stem cell (CSC)-like cellular state that was recently developed in our laboratory by employing Yamanaka's nuclear reprogramming technology in the estrogen receptor $$ (ER$$)-positive MCF-7 breast cancer cell line. Despite the acquisition of distinct molecular features that were compatible with a breast CSC-like cellular state,such as strong aldehyde dehydrogenase activity,as detected by ALDEFLUOR,and overexpression of the SSEA-4 and CD44 breast CSC markers,the tumor growth-initiating ability of SOX2-overexpressing CSC-like MCF-7 cells solely occurred in female nude mice supplemented with estradiol when compared with MCF-7 parental cells. Ser118 phosphorylation of estrogen receptor $$ (ER$$),which is a pivotal integrator of the genomic and nongenomic E 2/ER$$ signaling pathways,drastically accumulated in nuclear speckles in the interphase nuclei of SOX2-driven CSC-like cell populations. Moreover,SOX2-positive CSC-like cells accumulated significantly higher numbers of actively dividing cells,and the highest levels of phospho-Ser118-ER$$ occurred when chromosomes lined up on a metaphase plate. The previously unrecognized link between E 2/ER$$ signaling and SOX2-driven stem cell circuitry may significantly impact our current understanding of breast cancer initiation and progression,i.e.,SOX2 can promote non-genomic E 2 signaling that leads to nuclear phospho-Ser118-ER$$,which ultimately exacerbates genomic ER signaling in response to E 2. Because E 2 stimulation has been recently shown to enhance breast tumor-initiating cell survival by downregulating miR-140,which targets SOX2,the establishment of a bidirectional cross-talk interaction between the stem cell self-renewal regulator,SOX2,and the local and systemic ability of E 2 to increase breast CSC activity may have profound implications for the development of new CSC-directed strategies for breast cancer prevention and therapy. View Publication

Maternal-effect mutations in NLRP7 cause rare biparentally inherited hydatidiform moles (BiHMs),abnormal pregnancies containing hypertrophic vesicular trophoblast but no embryo. BiHM trophoblasts display abnormal DNA methylation patterns affecting maternally methylated germline differentially methylated regions (gDMRs),suggesting that NLRP7 plays an important role in reprogramming imprinted gDMRs. How NLRP7—a component of the CATERPILLAR family of proteins involved in innate immunity and apoptosis—causes these specific DNA methylation and trophoblast defects is unknown. Because rodents lack NLRP7,we used human embryonic stem cells to study its function and demonstrate that NLRP7 interacts with YY1,an important chromatin-binding factor. Reduced NLRP7 levels alter DNA methylation and accelerate trophoblast lineage differentiation. NLRP7 thus appears to function in chromatin reprogramming and DNA methylation in the germline or early embryonic development,functions not previously associated with members of the NLRP family. View Publication

AIMS: Mesenchymal stem cells (MSCs) are widely used for cell therapy,particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity,critical elements for their survival and differentiation,have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and,more generally,to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation. METHODS AND RESULTS: MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes,a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand,A-769662,a well-characterized AMPK activator,was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice,providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation,we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved,whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation. CONCLUSION: MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation,p27 being involved in this regulation. View Publication

Aldehyde dehydrogenase (ALDH) has been identified in stem cells from both normal and cancerous tissues. This study aimed to evaluate the potential of ALDH as a universal brain tumour initiating cell (BTIC) marker applicable to primary brain tumours and their biological role in maintaining stem cell status. Cells from various primary brain tumours (24paediatric and 6 adult brain tumours) were stained with Aldefluor and sorted by flow cytometry. We investigated the impact of ALDH expression on BTIC characteristics in vitro and on tumourigenic potential in vivo. Primary brain tumours showed universal expression of ALDH,with 0.3-28.9% of the cells in various tumours identified as ALDH(+). The proportion of CD133(+) cells within ALDH(+) is higher than ALDH cells. ALDH(+) cells generate neurospheres with high proliferative potential,express neural stem cell markers and differentiate into multiple nervous system lineages. ALDH(+) cells tend to show high expression of induced pluripotent stem cell-related genes. Notably,targeted knockdown of ALDH1 by shRNA interference in BTICs potently disturbed their self-renewing ability. After 3months,ALDH(+) cells gave rise to tumours in 93% of mice whereas ALDH cells did not. The characteristic pathology of mice brain tumours from ALDH(+) cells was similar to that of human brain tumours,and these cells are highly proliferative in vivo. Our data suggest that primary brain tumours contain distinct subpopulations of cells that have high expression levels of ALDH and BTIC characteristics. ALDH might be a potential therapeutic target applicable to primary brain tumours. View Publication

Regulatory T cell (Treg) therapy has the potential to induce transplantation tolerance so that immunosuppression and associated morbidity can be minimized. Alloantigen-reactive Tregs (arTregs) are more effective at preventing graft rejection than polyclonally expanded Tregs (PolyTregs) in murine models. We have developed a manufacturing process to expand human arTregs in short-term cultures using good manufacturing practice-compliant reagents. This process uses CD40L-activated allogeneic B cells to selectively expand arTregs followed by polyclonal restimulation to increase yield. Tregs expanded 100- to 1600-fold were highly alloantigen reactive and expressed the phenotype of stable Tregs. The alloantigen-expanded Tregs had a diverse TCR repertoire. They were more potent than PolyTregs in vitro and more effective at controlling allograft injuries in vivo in a humanized mouse model. View Publication

Hybridomas producing mouse monoclonal antibodies to antigens of the human mammary carcinoma cell line,MCF-7,have been generated by electric field-mediated fusion at a frequency ten times higher than by polyethylene glycol. One of the monoclonal antibodies obtained recognizes a cytoskeletal structure restricted to epithelial cells and carcinomas with a distribution pattern resembling cytokeratin 19. View Publication

A prerequisite for the realization of human pluripotent stem cell (hPSC) therapies is the development of bioprocesses for generating clinically relevant quantities of undifferentiated hPSCs and their derivatives under xeno-free conditions. Microcarrier stirred-suspension bioreactors are an appealing modality for the scalable expansion and directed differentiation of hPSCs. Comparative analyses of commercially available microcarriers clearly show the need for developing synthetic substrates supporting the adhesion and growth of hPSCs in three-dimensional cultures under agitation-induced shear. Moreover,the low seeding efficiencies during microcarrier loading with hPSC clusters poses a significant process bottleneck. To that end,a novel protocol was developed increasing hPSC seeding efficiency from 30% to over 80% and substantially shortening the duration of microcarrier loading. Importantly,this method was combined with the engineering of polystyrene microcarriers by surface conjugation of a vitronectin-derived peptide,which was previously shown to support the growth of human embryonic stem cells. Cells proliferated on peptide-conjugated beads in static culture but widespread detachment was observed after exposure to stirring. This prompted additional treatment of the microcarriers with a synthetic polymer commonly used to enhance cell adhesion. hPSCs were successfully cultivated on these microcarriers in stirred suspension vessels for multiple consecutive passages with attachment efficiencies close to 40%. Cultured cells exhibited on average a 24-fold increase in concentration per 6-day passage,over 85% viability,and maintained a normal karyotype and the expression of pluripotency markers such as Nanog,Oct4,and SSEA4. When subjected to spontaneous differentiation in embryoid body cultures or directed differentiation to the three embryonic germ layers,the cells adopted respective fates displaying relevant markers. Lastly,engineered microcarriers were successfully utilized for the expansion and differentiation of hPSCs to mesoderm progeny in stirred suspension vessels. Hence,we demonstrate a strategy for the facile engineering of xeno-free microcarriers for stirred-suspension cultivation of hPSCs. Our findings support the use of microcarrier bioreactors for the scalable,xeno-free propagation and differentiation of human stem cells intended for therapies. View Publication

The p53 tumor suppressor protein is a major sensor of cellular stresses,and upon stabilization,activates or represses many genes that control cell fate decisions. While the mechanism of p53-mediated transactivation is well established,several mechanisms have been proposed for p53-mediated repression. Here,we demonstrate that the cyclin-dependent kinase inhibitor p21 is both necessary and sufficient for the downregulation of known p53-repression targets,including survivin,CDC25C,and CDC25B in response to p53 induction. These same targets are similarly repressed in response to p16 overexpression,implicating the involvement of the shared downstream retinoblastoma (RB)-E2F pathway. We further show that in response to either p53 or p21 induction,E2F4 complexes are specifically recruited onto the promoters of these p53-repression targets. Moreover,abrogation of E2F4 recruitment via the inactivation of RB pocket proteins,but not by RB loss of function alone,prevents the repression of these genes. Finally,our results indicate that E2F4 promoter occupancy is globally associated with p53-repression targets,but not with p53 activation targets,implicating E2F4 complexes as effectors of p21-dependent p53-mediated repression. View Publication

Applications of human induced pluripotent stem cell derived-cardiac myocytes (hiPSC-CMs) would be strengthened by the ability to generate specific cardiac myocyte (CM) lineages. However,purification of lineage-specific hiPSC-CMs is limited by the lack of cell marking techniques. Here,we have developed an iPSC-CM marking system using recombinant adenoviral reporter constructs with atrial- or ventricular-specific myosin light chain-2 (MLC-2) promoters. MLC-2a and MLC-2v selected hiPSC-CMs were purified by fluorescence-activated cell sorting and their biochemical and electrophysiological phenotypes analyzed. We demonstrate that the phenotype of both populations remained stable in culture and they expressed the expected sarcomeric proteins,gap junction proteins and chamber-specific transcription factors. Compared to MLC-2a cells,MLC-2v selected CMs had larger action potential amplitudes and durations. In addition,by immunofluorescence,we showed that MLC-2 isoform expression can be used to enrich hiPSC-CM consistent with early atrial and ventricular myocyte lineages. However,only the ventricular myosin light chain-2 promoter was able to purify a highly homogeneous population of iPSC-CMs. Using this approach,it is now possible to develop ventricular-specific disease models using iPSC-CMs while atrial-specific iPSC-CM cultures may require additional chamber-specific markers. ?? 2013 Elsevier B.V. View Publication