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Loss of the Chr16p11.2 candidate gene QPRT leads to aberrant neuronal differentiation

ABSTRACT: Background: Altered neuronal development is discussed as underlying pathogenic mechanism of Autism Spectrum Disorders (ASD). Copy number variations of 16p11.2 have recurrently been identified in individuals with ASD. Of the 29 genes within this region quinolinate phosphoribosyltransferase (QPRT) showed the strongest regulation during in-vitro neuronal differentiation. We hypothesized a causal relation between this tryptophan related enzyme and neuronal differentiation. We thus analyzed the effect of QPRT on differentiation of a neuronal cell line and specifically focused on neuronal morphology, metabolites of the tryptophan pathway and the neurodevelopmental transcriptome. Methods: The gene dosage dependent change of QPRT expression following Chr16p11.2 deletion was investigated in a lymphoblastoid cell line (LCL) of a deletion carrier and compared to his non-carrier parents. Expression of QPRT was tested for correlation with neuromorphology in SH-SY5Y cells. QPRT function was inhibited in SH-SY5Y neuroblastoma cells using (i) siRNA knockdown (KD), (ii) chemical inhibition, and (iii) complete CRISPR/Cas9 induced knockout (KO). QPRT-KD cells underwent morphological analysis. Chemically inhibited and QPRT-KO cells were characterized using viability assays. Additionally, QPRT-KO cells underwent metabolite and whole transcriptome analyses. Genes differentially expressed upon KO of QPRT were tested for enrichment in biological processes and co-regulated gene-networks of the human brain. Results: QPRT expression was reduced in the LCL of the deletion carrier and significantly correlated with neurite maturation in SH-SY5Y cells. The reduction of QPRT altered neuronal morphology of differentiated SH-SY5Y cells. Chemical inhibition as well as complete KO of the gene were lethal upon induction of neuronal differentiation, but not proliferation. The QPRT associated tryptophan pathway was not affected by KO. At the transcriptome level neuronal processes like “synapse organization” were affected. Differentially regulated genes were enriched for ASD-candidates and co-regulated gene networks were implicated in the development of the dorsolateral prefrontal cortex, the hippocampus, and the amygdala. Conclusions: In this study QPRT was causally related to in vitro neuronal differentiation and affected the regulation of genes and gene-networks that were previously implicated in ASD. Thus, our data suggest that QPRT may play an important role in the pathogenesis of ASD in Chr16p11.2 deletion carriers.

ORGANISM(S): Homo sapiens

PROVIDER: GSE113734 | GEO | 2018/11/20

REPOSITORIES: GEO

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Project description:Background: SH-SY5Y cells exhibit a neuronal phenotype when treated with all-trans retinoic acid (RA), but the molecular mechanism of activation in the signaling pathway mediated by phosphatidylinositol 3-kinase (PI3K) is not sufficiently understood. To shed new light on the mechanism, we comprehensively compared the gene expression profiles between SK-N-SH cells and two subtypes of SH-SY5Y cells (SH-SY5Y-A and SH-SY5Y-E), each of which showed a different phenotype during RA-mediated differentiation. Results: SH-SY5Y-A cells differentiated in the presence of RA, whereas RA-treated SH-SY5Y-E cells required additional treatment with brain-derived neurotrophic factor (BDNF) for full differentiation. In combination with perturbation using a PI3K inhibitor, LY294002, we identified 386 genes and categorized them into two clusters dependent on the PI3K signaling pathway during RA-mediated differentiation in SH-SY5Y-A cells. Transcriptional regulation of the gene cluster was greatly reduced in SK-N-SH cells or partially impaired in SH-SY5Y-E cells in coincidence with a defect in the neuronal phenotype of these cell lines. Additional stimulation with BDNF induced a set of neural genes which were down-regulated in RA-treated SH-SY5Y-E cells but were abundant in the differentiated SH-SY5Y-A cells. Conclusions: We identified the gene clusters controlled by PI3K- and TRKB-mediated signaling pathways during differentiation in two subtypes of SH-SY5Y cells. TRKB-mediated bypass pathway compensates for the impaired neural functions generated by defects in several signaling pathways including PI3K in SH-SY5Y-E cells. The expression profiling data are useful for further studies to elucidate the signal transduction-transcriptional network including PI3K and/or TRKB. Experiment Overall Design: Human neuroblastomas, SK-N-SH (HTB-11) and SH-SY5Y-A cells (CRL-2266) were obtained from the American Type Culture Collection (ATCC). We also obtained SH-SY5Y-E cells (EC94030304) from the European Collection of Cell Cultures (ECACC). Tissue culture cells were maintained in D-MEM/F12 1:1 mixture supplemented with 15% FBS (Fetal Bovine Serum) and 1% NEAA (Non-essential amino acid) in a 5% CO2 humidified incubator at 37oC. The culture medium was changed twice a week. For the RA-inducible experiment, random culture cells from two clone subtypes of SH-SY5Y and SK-N-SH were seeded in laminin coated culture dishes (BioCoat Laminin Cellware; BD Biosciences, Billerica, MA, USA) for 1 day and then transferred to a medium containing 10 μM of RA in the presence or the absence of LY294002 (10μM) for five days. For BDNF-induced sequential differentiation of the SH-SY5Y-E strain, cells were washed with D-MEM/F12 twice after five days in the presence of RA and then incubated with 50 ng/ml of BDNF in D-MEM/F12 without serum for three days.

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Loss of the Chr16p11.2 candidate gene QPRT leads to aberrant neuronal differentiation

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