Anis Feki

The first reported generation of several induced pluripotent stem cell lines from homozygous and heterozygous Huntington's disease patients demonstrates mutation related enhanced lysosomal activity

Neuronal disorders, like Huntingtons disease (HD), are difficult to study, due to limited cell accessibility, late onset manifestations, and low availability of material. The establishment of an in vitro model that recapitulates features of the disease may help understanding the cellular and molecular events that trigger disease manifestations. Here, we describe the generation and characterization of a series of induced pluripotent stem (iPS) cells derived from patients with HD, including two rare homozygous genotypes and one heterozygous genotype. We used lentiviral technology to transfer key genes for inducing reprogramming. To confirm pluripotency and differentiation of iPS cells, we used PCR amplification and immunocytochemistry to measure the expression of marker genes in embryoid bodies and neurons. We also analyzed teratomas that formed in iPS cell-injected mice. We found that the length of the pathological CAG repeat did not increase during reprogramming, after long term growth in vitro, and after differentiation into neurons. In addition, we observed no differences between normal and mutant genotypes in reprogramming, growth rate, caspase activation or neuronal differentiation. However, we observed a significant increase in lysosomal activity in HD-iPS cells compared to control iPS cells, both during self-renewal and in iPS-derived neurons. In conclusion, we have established stable HD-iPS cell lines that can be used for investigating disease mechanisms that underlie HD. The CAG stability and lysosomal activity represent novel observations in HD-iPS cells. In the future, these cells may provide the basis for a powerful platform for drug screening and target identification in HD.

Domains of genome-wide gene expression dysregulation in Down’s syndrome

Trisomy 21 is the most frequent genetic cause of cognitive impairment. To assess the perturbations of gene expression in trisomy 21, and to eliminate the noise of genomic variability, we studied the transcriptome of fetal fibroblasts from a pair of monozygotic twins discordant for trisomy 21. Here we show that the differential expression between the twins is organized in domains along all chromosomes that are either upregulated or downregulated. These gene expression dysregulation domains (GEDDs) can be defined by the expression level of their gene content, and are well conserved in induced pluripotent stem cells derived from the twins’ fibroblasts. Comparison of the transcriptome of the Ts65Dn mouse model of Down’s syndrome and normal littermate mouse fibroblasts also showed GEDDs along the mouse chromosomes that were syntenic in human. The GEDDs correlate with the lamina-associated (LADs) and replication domains of mammalian cells. The overall position of LADs was not altered in trisomic cells; however, the H3K4me3 profile of the trisomic fibroblasts was modified and accurately followed the GEDD pattern. These results indicate that the nuclear compartments of trisomic cells undergo modifications of the chromatin environment influencing the overall transcriptome, and that GEDDs may therefore contribute to some trisomy 21 phenotypes.

Identification of BARD1 as Mediator between Proapoptotic Stress and p53-Dependent Apoptosis

The BRCA1-associated protein BARD1 is a putative tumor suppressor. We suggest that BARD1 is a mediator of apoptosis since (1) cell death in vivo (ischemic stroke) and in vitro is accompanied by increased levels of BARD1 protein and mRNA; (2) overexpression of BARD1 induces cell death with all features of apoptosis; and (3) BARD1-repressed cells are defective for the apoptotic response to genotoxic stress. The proapoptotic activity of BARD1 involves binding to and elevations of p53. BRCA1 is not required for but partially counteracts apoptosis induction by BARD1. A tumor-associated mutation Q564H of BARD1 is defective in apoptosis induction, thus suggesting a role of BARD1 in tumor suppression by mediating the signaling from proapoptotic stress toward induction of apoptosis.

Xeno-free derivation and culture of human embryonic stem cells: current status, problems and challenges

Human embryonic stem cells (hESC) not only hold great promise for the treatment of degenerative diseases but also provide a valuable tool for developmental studies. However, the clinical applications of hESC are at present limited by xeno-contamination during the in vitro derivation and propagation of these cells. In this review, we summarize the current methodologies for the derivation and the propagation of hESC in conditions that will eventually enable the generation of clinical-grade cells for future therapeutic applications.

Immortalized human skin fibroblast feeder cells support growth and maintenance of both human embryonic and induced pluripotent stem cells

BACKGROUND Feeder cells are frequently used for the early-stage of derivation and culture of human embryonic stem cell (hESC) lines. METHODS We established a conditionally immortalized human foreskin fibroblast line that secreted basic fibroblast growth factor (bFGF). These cells were used as feeder cells for hESC culture and induced pluripotent stem (iPS) cell derivation and expansion. This conditional immortalization was performed using lentiviral vector (LV) mediated transduction of Bmi-1 and human telomerase reverse transcriptase genes and the resulting cell line was further modified by LV-mediated transduction of a secreted form of bFGF gene product. Three different laboratories have tested whether this feeder cell line could support the maintenance of four different hESC lines. RESULTS Immortalized fibroblasts secreting stable amounts of bFGF supported the growth of all hESC lines, which remained pluripotent and had a normal karyotype for at least 10 passages. Even at high passage (p56), these modified cells, when used as feeders, could support iPS derivation and propagation. Derived iPS cells expressed pluripotency markers, had hESC morphology and produced tissue components of the three germ layers when differentiated in vitro. CONCLUSION These modified fibroblasts are useful as a genetically-defined feeder cell line for reproducible and cost-effective culture of both hESC and iPS cells.

Modelling and rescuing neurodevelopmental defect of Down syndrome using induced pluripotent stem cells from monozygotic twins discordant for trisomy 21

Down syndrome (trisomy 21) is the most common viable chromosomal disorder with intellectual impairment and several other developmental abnormalities. Here, we report the generation and characterization of induced pluripotent stem cells (iPSCs) derived from monozygotic twins discordant for trisomy 21 in order to eliminate the effects of the variability of genomic background. The alterations observed by genetic analysis at the iPSC level and at first approximation in early development illustrate the developmental disease transcriptional signature of Down syndrome. Moreover, we observed an abnormal neural differentiation of Down syndrome iPSCs in vivo when formed teratoma in NOD‐SCID mice, and in vitro when differentiated into neuroprogenitors and neurons. These defects were associated with changes in the architecture and density of neurons, astroglial and oligodendroglial cells together with misexpression of genes involved in neurogenesis, lineage specification and differentiation. Furthermore, we provide novel evidence that dual‐specificity tyrosine‐(Y)‐phosphorylation regulated kinase 1A (DYRK1A) on chromosome 21 likely contributes to these defects. Importantly, we found that targeting DYRK1A pharmacologically or by shRNA results in a considerable correction of these defects.

An effective serum- and xeno-free chemically defined freezing procedure for human embryonic and induced pluripotent stem cells

BACKGROUND Both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) bear a great potential in regenerative medicine. In addition to optimized clinical grade culture conditions, efficient clinical grade cryopreservation methods for these cells are needed. Obtaining good survival after thawing has been problematic. METHODS We used a novel, chemically defined effective xeno-free cryopreservation system for cryostorage and banking of hESCs and iPSCs. The earlier established slow freezing protocols have, even after recent improvements, resulted in low viability and thawed cells had a high tendency to differentiate. The medium is a completely serum and animal substance free product containing dimethylsulfoxide, anhydrous dextrose and a polymer as cryoprotectants. The cells were directly frozen at −70°C, without a programmed freezer. RESULTS The number of frozen colonies versus the number of surviving colonies differed significantly for both HS293 (χ2 = 9.616 with one degree of freedom and two-tailed P = 0.0019) and HS306 (χ2 = 8.801 with one degree of freedom and two-tailed P = 0.0030). After thawing, the cells had a high viability (90–96%) without any impact on proliferation and differentiation, compared with the standard freezing procedure where viability was much lower (49%). The frozen–thawed hESCs and iPSCs had normal karyotype and maintained properties of pluripotent cells with corresponding morphological characteristics, and expressed pluripotency markers after 10 passages in culture. They formed teratomas containing tissue components of the three germ layers. CONCLUSION The defined freezing–thawing system described here offers an excellent simple option for banking of hESCs and iPSCs.

BARD1 induces apoptosis by catalysing phosphorylation of p53 by DNA-damage response kinase.

The BRCA1-associated RING domain protein BARD1 acts with BRCA1 in double-strand break repair and ubiquitination. BARD1 plays a role as mediator of apoptosis by binding to and stabilizing p53, and BARD1-repressed cells are resistant to apoptosis. We therefore investigated the mechanism by which BARD1 induces p53 stability and apoptosis. The apoptotic activity of p53 is regulated by phosphorylation. We demonstrate that BARD1 binds to unphosphorylated and serine-15 phosphorylated forms of p53 in several cell types and that the region required for binding comprises the region sufficient for apoptosis induction. In addition, BARD1 binds to Ku-70, the regulatory subunit of DNA-PK, suggesting that the mechanism of p53-induced apoptosis requires BARD1 for the phosphorylation of p53. Upregulation of BARD1 alone is sufficient for stabilization of p53 and phosphorylation on serine-15, as shown in nonmalignant epithelial cells and ovarian cancer cells, NuTu-19, which are defective in apoptosis induction and express aberrant splice variants of BARD1. Stabilization and phosphorylation of p53 in NuTu-19 cells, as well as apoptosis, can be induced by the exogenous expression of wild-type BARD1, suggesting that BARD1, by binding to the kinase and its substrate, catalyses p53 phosphorylation.

Nuclear-cytoplasmic translocation of BARD1 is linked to its apoptotic activity

The tumor suppressor protein BARD1 plays a dual role in response to genotoxic stress: DNA repair as a BARD1–BRCA1 heterodimer and induction of apoptosis in a BRCA1-independent manner. We have constructed a series of BARD1 deletion mutants and analysed their cellular distribution and capacity to induce apoptosis. As opposed to previous studies suggesting an exclusively nuclear localization of BARD1, we found, both in tissues and cell cultures, nuclear and cytoplasmic localization of BARD1. Enhanced cytoplasmic localization of BARD1, as well as appearance of a 67 kDa C-terminal proteolytic cleavage product, coincided with apoptosis. BARD1 translocates to the nucleus independently of BRCA1. For recruitment to nuclear dots, however, the BRCA1-interacting RING finger domain is required but not sufficient. Protein levels of N-terminal RING finger deletion mutants were much higher than those of full-length BARD1, despite comparable mRNA levels, suggesting that the N-terminal region comprising the RING finger is important for BARD1 degradation. Sequences required for apoptosis induction were mapped between the ankyrin repeats and the BRCT domains coinciding with two known cancer-associated missense mutations. We suggest that nuclear and cytoplasmic localization of BARD1 reflect its dual function and that the increased cytoplasmic localization of BARD1 is associated with apoptosis.

A Teratocarcinoma-Like Human Embryonic Stem Cell (hESC) Line and Four hESC Lines Reveal Potentially Oncogenic Genomic Changes

The first Swiss human embryonic stem cell (hESC) line, CH-ES1, has shown features of a malignant cell line. It originated from the only single blastomere that survived cryopreservation of an embryo, and it more closely resembles teratocarcinoma lines than other hESC lines with respect to its abnormal karyotype and its formation of invasive tumors when injected into SCID mice. The aim of this study was to characterize the molecular basis of the oncogenicity of CH-ES1 cells, we looked for abnormal chromosomal copy number (by array Comparative Genomic Hybridization, aCGH) and single nucleotide polymorphisms (SNPs). To see how unique these changes were, we compared these results to data collected from the 2102Ep teratocarcinoma line and four hESC lines (H1, HS293, HS401 and SIVF-02) which displayed normal G-banding result. We identified genomic gains and losses in CH-ES1, including gains in areas containing several oncogenes. These features are similar to those observed in teratocarcinomas, and this explains the high malignancy. The CH-ES1 line was trisomic for chromosomes 1, 9, 12, 17, 19, 20 and X. Also the karyotypically (based on G-banding) normal hESC lines were also found to have several genomic changes that involved genes with known roles in cancer. The largest changes were found in the H1 line at passage number 56, when large 5 Mb duplications in chromosomes 1q32.2 and 22q12.2 were detected, but the losses and gains were seen already at passage 22. These changes found in the other lines highlight the importance of assessing the acquisition of genetic changes by hESCs before their use in regenerative medicine applications. They also point to the possibility that the acquisition of genetic changes by ESCs in culture may be used to explore certain aspects of the mechanisms regulating oncogenesis.