Biomimetic reconstruction of the hematopoietic stem cell niche for in vitro amplification of human hematopoietic stem cells

Hematopoietic stem cell transplantation is successfully applied since the late 1950s; however, its efficacy still needs to be increased. A promising strategy is to transplant high numbers of pluripotent hematopoietic stem cells (HSCs). Therefore, an improved ex vivo culture system that supports proliferation and maintains HSC pluripotency would override possible limitations in cell numbers gained from donors. To model the natural HSC niche in vitro, we optimized the HSC medium composition with a panel of cytokines and valproic acid and used an artificial 3D bone marrow-like scaffold made of polydimethylsiloxane (PDMS). This 3D scaffold offered a suitable platform to amplify human HSCs in vitro and, simultaneously, to support their viability, multipotency and ability for self-renewal. Silicon oxide-covering of PDMS structures further improved amplification of CD34+ cells, although the conservation of naïve HSCs was better on non-covered 3D PDMS. Finally, we found that HSC cultivated on non-covered 3D PDMS generated most pluripotent colonies within colony forming unit assays. In conclusion, by combining biological and biotechnological approaches, we optimized in vitro HSCs culture conditions, resulting in improved amplification, multipotency maintenance and vitality of HSCs.

THU0321 URINARY T CELLS IDENTIFY ACTIVE RENAL ANCA ASSOCIATED VASCULITIS

Background:

ANCA-associated vasculitis (AAV) causes necrotizing crescentic glomerulonephritis (NCGN) which is a major contributor to morbidity and mortality in AAV. Since therapy relies on cytotoxic agents with potentially severe adverse effects, a reliable non-invasive biomarker of disease activity is needed to determine the right balance between over- and undertreatment. Using the urine space as a window into the local inflammatory milieu of the kidney, quantification of urinary leukocytes using flow cytometry has become an upcoming marker of various other inflammatory kidney diseases. As recent studies have illuminated the emerging role of T regulatory (Treg) and Th17 cells in the pathogenesis of AAV, these could represent a viable non-invasive biomarker more closely displaying the underlying pathogenic processes than metabolites or epiphenomena of inflammation.

Objectives:

To quantify urinary T cells in active renal AAV and asses their biomarker characteristics.

Methods:

Using flow cytometry, T-lymphocytes and their subsets were quantified in peripheral blood and urine samples from patients with active AAV with or without NCGN, in stable remission with previous NCGN and healthy controls. Concentrations of urinary soluble metabolites and cytokines (Monocyte-attracting protein 1 (MCP-1), sCD163, sCD25 and C5a) were measured using Multiplex analysis. Results were verified in a separate validation cohort.

Results:

Patients with renal active AAV (n = 30) showed significantly higher urinary cell counts of total T cells, CD4+, CD8+, Treg and Th17 subsets than disease (n = 21) and healthy controls (n = 8). Patients with active renal AAV also showed a significantly higher percentage of Tregs in urine than in blood. While Tregs allowed a robust discrimination between active renal AAV and disease controls (receiver operator characteristics (ROC): area under the curve (AUC) 0.93, sensitivity 79%, specificity 95%) quantification of all T cells proved to be slightly more accurate (ROC: AUC 0.95, sensitivity 92%, specificity 95%). Soluble markers showed a slightly inferior discrimination (MCP-1 ROC: AUC 0.90, sensitivity 60%, specificity 100%, sCD163 ROC: AUC 0.92, sensitivity 96%, specificity 85%) while sCD25 and C5a were far less accurate.

Conclusion:

Urinary T cells are significantly elevated in active renal AAV and the increased frequency of Tregs in urine suggests active migration into inflamed glomeruli and thereby the urine rather than mere bleeding of ruptured capillaries. These cells show great potential for a non-invasive biomarker close to the local inflammatory milieu. Particularly the total count of urinary T cells showed slightly superior biomarker characteristics than previously established soluble markers. Further studies are needed to confirm these results and show potential prognostic value of these cellular markers.

Disclosure of Interests:

None declared

p53-dependent and p53-independent anticancer effects of different histone deacetylase inhibitors

Background:

Histone deacetylase inhibitors (HDACi) are promising antineoplastic agents, but their precise mechanisms of actions are not well understood. In particular, the relevance of p53 for HDACi-induced effects has not been fully elucidated. We investigated the anticancer effects of four structurally distinct HDACi, vorinostat, entinostat, apicidin and valproic acid, using isogenic HCT-116 colon cancer cell lines differing in p53 status.

Methods:

Effects were assessed by MTT assay, flow-cytometric analyses of propidium iodide uptake, mitochondrial depolarisation and cell-cycle distribution, as well as by gene expression profiling.

Results:

Vorinostat was equally effective in p53 wild-type and null cells, whereas entinostat was less effective in p53 null cells. Histone deacetylase inhibitors treatment suppressed the expression of MDM2 and increased the abundance of p53. Combination treatments showed that vorinostat enhanced the cytotoxic activity of TRAIL and bortezomib, independent of the cellular p53 status. Investigations into the effects of an inhibitor of the sirtuin class of HDAC, tenovin-1, revealed that tenovin-1-mediated cell death hinged on p53.

Conclusion:

These results demonstrate that vorinostat activates p53, but does not require p53 for inducing its anticancer action. Yet they also demonstrate that entinostat-induced cytotoxic effects partially depend on p53, indicating that different HDACi have a different requirement for p53.

The bisphosphonate pamidronate is a potent inhibitor of human osteosarcoma cell growth in vitro

Bisphosphonates (BPs), such as pamidronate and clodronate, are an important class of drugs for the treatment of bone diseases. It is widely recognized that they inhibit bone resorption by suppressing the action of osteoclasts through antagonizing the mevalonate pathway, thereby reducing osteolytic bone metastases derived from different cancers, i.e. breast carcinoma and multiple myeloma. In contrast, the effects of BPs on primary bone tumors is an issue still to be resolved. Therefore, a systematic approach was set up to test the hypothesis that BPs could act directly on osteosarcoma cells. The effects of pamidronate and clodronate on seven osteosarcoma cell lines (HOS, MG-63, OST, SaOS-2, SJSA-1, U(2)OS and ZK-58) were studied. Pamidronate inhibited cell growth in a time- and dose-dependent manner, and decreased proliferation for up to 73% at 50 microM after 72 h, whereas its monophosphonate analog 3-aminopropyl phosphonate did not reduce cell viability at concentrations up to 2 mM. Clodronate showed less inhibitory effects (maximally 38% reduction at 1 mM after 72 h). Importantly, cell growth of fibroblasts was only very weakly affected by treatment with pamidronate. These results suggest that pamidronate may be a useful agent for the treatment of patients with osteosarcoma.

Apoptotic responsiveness of the Ewing's sarcoma family of tumours to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)

We investigated the cytotoxic responsiveness of 40 cell lines derived from representatives of the Ewing's sarcoma family of tumours (ESFT), i.e., Ewing's sarcoma (ES), peripheral primitive neuroectodermal tumour (pPNET) and Askin tumour (AT), to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). Incubation with TRAIL at 100 ng/ml induced cell death at 24 hr in 19 of 26 ES, 11 of 12 pPNET and 2 of 2 AT cell lines. Half-maximal cell death concentrations (IC(50) values) varied from 0.1 to 20 ng/ml. TRAIL displayed potent cytotoxic activity against freshly derived ESFT cell isolates. Cytotoxicity was associated with phosphatidylserine expression and internucleosomal DNA fragmentation, features characteristic of apoptosis. The apoptotic programme in the sensitive ESFT VH-64 cell line revealed TRAIL-induced activation of FLICE/MACH1 (caspase-8) and CPP32/Yama/apopain (caspase-3) and processing of the prototype caspase substrate poly(ADP-ribose) polymerase. In addition, TRAIL provoked a collapse of the mitochondrial transmembrane potential (DeltaPsi(m)), parallelled by a reduction in ATP levels and release of cytochrome c from mitochondria into the cytosol. Inhibition of caspase-8 and caspase-3 by zIETDfmk and zDEVDfmk, respectively, substantially prevented TRAIL-induced apoptosis. However, zIETDfmk, but not zDEVDfmk, reduced TRAIL-mediated DeltaPsi(m) dissipation, indicating that TRAIL causes mitochondrial dysfunction through caspase-8 acting upstream of mitochondria. While macromolecule synthesis inhibitors (actinomycin D, cycloheximide) augmented susceptibility to TRAIL in TRAIL-responsive cell lines, these agents did not render TRAIL-resistant cell lines susceptible to TRAIL. However, the proteasome inhibitor MG132 sensitised to TRAIL in resistant cell lines. Collectively, these results show that TRAIL initiates effective death in the vast majority (80%) of cell lines derived from ESFT. Since TRAIL provoked cell death in ESFT ex vivo, this cytokine may be a promising drug for the treatment of ESFT in vivo.

Dissection of the cAMP induced cytosolic calcium response in Dictyostelium discoideum: the role of cAMP receptor subtypes and G protein subunits

The cAMP signaling cascade leading to changes in [Ca2+]i in Dictyostelium discoideum was analyzed using cell lines overexpressing single cAMP receptor subtypes (cAR1-cAR3) or lacking the G(alpha2) or G(beta) subunit of the G protein. Imaging of fura2-dextran-loaded amoebae revealed cAMP-induced [Ca2+]i changes characteristic for each receptor subtype activated. Cells expressing distinct subtypes sort to defined zones during multicellular development suggesting involvement of the specific [Ca2+]i transients in patterning processes. Whereas generation of the [Ca2+]i increase was G(alpha2)-independent, only few cells devoid of G(beta) displayed a [Ca2+]i change after stimulation indicating its participation in the regulation of the calcium homeostasis.

Fatty acids induce release of Ca2+ from acidosomal stores and activate capacitative Ca2+ entry in Dictyostelium discoideum

cAMP-induced Ca2+ fluxes in Dictyostelium discoideum largely depend on phospholipase A2 activity generating non-esterified fatty acids [Schaloske and Malchow (1997) Biochem. J. 327, 233-238]. In the present study the effect of fatty acids on Ca2+ homoeostasis in D. discoideum was investigated. Cytosolic free Ca2+ concentration ([Ca2+]i) was analysed by digital imaging of single fura2-dextran-loaded cells. Arachidonic acid and linoleic acid induced a transient increase in [Ca2+]i. The concentration of arachidonic acid determined the percentage of responding cells, with the mean height of the increase being dose-independent. In nominally Ca2+-free medium or in the presence of bis-(o-aminophenoxy)ethane-N, N,N',N'-tetra-acetic acid (BAPTA), no [Ca2+]i transient was detectable. In spite of this, we found that (1) arachidonic acid induced Ca2+ release from permeabilized cells and from vesicular fractions at concentrations that elicited Ca2+ influx in intact cells and (2) Ca2+ entry was inhibited by inhibitors of Ca2+-transport ATPases and V-type H+-ATPase, indicating that intracellular Ca2+ release precedes Ca2+ entry. Inhibition studies and mutant analysis point to the acidosomal Ca2+ stores as a target of fatty acids. Although fatty acids can substitute fully for cAMP with respect to Ca2+ influx in wild-type cells, experiments with a mutant strain revealed that cAMP also sensitizes the Ca2+-entry mechanism: cAMP-induced Ca2+ influx was normal in a phospholipase C knockout mutant but influx was fairly insensitive to arachidonic acid in this strain. This defect could be overcome by higher doses of arachidonic acid which cause sufficient Ca2+ to be released from the stores to trigger extracellular Ca2+ entry.

cAMP-induced changes in the cytosolic free Ca2+ concentration in Dictyostelium discoideum are light sensitive

The cytosolic free calcium concentration ([Ca2+]i) of the social amoeba Dictyostelium discoideum was analyzed after challenge with the chemoattractant cAMP. [Ca2+]i was measured by digital imaging in single cells loaded with the Ca2+ indicator Fura-2-dextran. Global stimulation with low concentrations of cAMP (0.1-1 microM) led to a global transient [Ca2+]i increase. This increase was abolished when cells were illuminated with high doses of light. However, after a short recovery period of several minutes, the cells again displayed the normal response. Inhibition of the [Ca2+]i elevation depended on the wavelength of illumination light. We compared the required recovery period of cells irradiated with either 340, 380, 405, 450 or 490 nm at defined intensities. Light of 405 nm had a pronounced effect; 340 nm alone or in combination with 380 nm was also effective, but to a lesser extent, whereas neither 450 nm nor 490 nm inhibited the [Ca2+]i increase, even at very high irradiance. The wavelength dependence matched the absorption spectrum of amoebae grown in darkness that contain a photopigment which seems to be responsible for phototaxis of single cells. Cells grown in darkness exhibited an increased sensitivity of the cAMP-induced [Ca2+]i transient towards light compared to light-grown cells. From these data we conclude that phototactic signaling could interfere with chemotactic signaling at the level of [Ca2+]i changes.

Cytosolic nucleoside diphosphate kinase associated with the translation apparatus may provide GTP for protein synthesis

Elongation of nascent polypeptides in a Dictyostelium discoideum in vitro translation system did not require the addition of ATP and GTP when creatine phosphate and creatine phosphokinase were present. However, depletion of the exogenous energy supply completely abolished incorporation of amino acids. Addition of dTTP, a nucleoside triphosphate that can be utilized by nucleoside diphosphate kinase (NDP kinase) to phosphorylate endogenous ADP and GDP, partially restored protein synthesis. Dictyostelium ribosomes were found to contain NDP kinase activity that could not be released by 1 M KCl. Thermal denaturation studies, specific inhibition with antibodies, and Western blotting identify the activity as cytosolic NDP kinase. These data support the idea that GTP can be fed into the translation machinery efficiently by NDP kinase associated with active ribosomes.

Elongation in a Dictyostelium in vitro translation system is affected by calmodulin antagonists

We have previously shown that the Dictyostelium discoideum ribosomal protein L19 specifically binds Ca2+/calmodulin [Sonneman et al. (1991) J. Biol. Chem. 266, 23091-23096]. To investigate the role of calmodulin in the regulation of protein synthesis, we have now established an in vitro protein synthesizing system from Dictyostelium cells which can elongate polypeptide chains with high efficiency. Various calmodulin antagonists affected translation in this system. The inhibitory effects of the antagonists could be partially reversed by addition of calmodulin. A monoclonal antibody against D. discoideum calmodulin also specifically inhibited protein synthesis. Similar effects of calmodulin antagonists were found in a standard wheat germ in vitro translation system.

A ribosomal calmodulin-binding protein from Dictyostelium

Using 125I-calmodulin as a probe, we have recently identified specific Ca2+/calmodulin-binding proteins in cell extracts from the cellular slime mold, Dictyostelium discoideum: a major 22-kDa activity, a soluble 78/80-kDa protein, and several membrane-associated high Mr proteins (Winckler, T., Dammann, H., and Mutzel, R. (1991) Res. Microbiol. 142, 509-519). cDNA clones for at least two of these proteins have been isolated by ligand screening of a lambda gt11 prophage expression library. Antibodies directed against the lacZ-cDNA-encoded fusion protein from one of the clones recognized a single 22-kDa component in D. discoideum extracts which comigrated with the endogenous 22-kDa calmodulin-binding protein. The cDNA-derived nucleotide sequence predicts a protein of Mr 21,659 with 56% sequence identity (69% homology) with rat ribosomal protein L19. The endogenous 22-kDa calmodulin-binding activity was associated with ribosomes. It was found to be an integral constituent of the large ribosomal subunit, since it cosedimented with 60 S ribosomal subunits in sucrose density gradients in the presence of 0.5 M NH4Cl. Our observations point to a physiological role for calmodulin in the Ca2+ regulation of eukaryotic protein synthesis. Support for this comes from recent studies showing inhibition of protein synthesis by calmodulin antagonists in Ehrlich ascites tumor cells (Kumar, R. V., Panniers, R., Wolfman, A., and Henshaw, E.C. (1991) Eur. J. Biochem. 195, 313-319).