Faculty Bibliography

Glioblastoma (GBM) is a deadly primary brain malignancy with extensive intratumoral hypoxia. Hypoxic regions of GBM contain stem-like cells and are associated with tumor growth and angiogenesis. The molecular mechanisms that regulate tumor growth in hypoxic conditions are incompletely understood. Here, we use primary human tumor biospecimens and cultures to identify GPR133 (ADGRD1), an orphan member of the adhesion family of G-protein-coupled receptors, as a critical regulator of the response to hypoxia and tumor growth in GBM. GPR133 is selectively expressed in CD133+ GBM stem cells (GSCs) and within the hypoxic areas of PPN in human biospecimens. GPR133 mRNA is transcriptionally upregulated by hypoxia in hypoxia-inducible factor 1alpha (Hif1alpha)-dependent manner. Genetic inhibition of GPR133 with short hairpin RNA reduces the prevalence of CD133+ GSCs, tumor cell proliferation and tumorsphere formation in vitro. Forskolin rescues the GPR133 knockdown phenotype, suggesting that GPR133 signaling is mediated by cAMP. Implantation of GBM cells with short hairpin RNA-mediated knockdown of GPR133 in the mouse brain markedly reduces tumor xenograft formation and increases host survival. Analysis of the TCGA data shows that GPR133 expression levels are inversely correlated with patient survival. These findings indicate that GPR133 is an important mediator of the hypoxic response in GBM and has significant protumorigenic functions. We propose that GPR133 represents a novel molecular target in GBM and possibly other malignancies where hypoxia is fundamental to pathogenesis.

Study question: What do RNA seq-profiles tell us about gene activity in preimplantation embryos known to be normal vs. trisomic for chromosomes 21, 18, 15 and 22. Summary answer: RNA-Seq profiles are karyotype-dependent and appear to correlate with viability. X and Y transcription is surprisingly active at the preimplantation stage. What is known already: Embryonic karyotypic abnormalities are the most common cause of implantation failure and miscarriage. Some such embryos can progress to viability as evidenced by the birth of children with Trisomy 21, 18 and 15. An abnormal karyotype dictates developmental aberrations, and for these differences to affect phenotype, variations in gene expression must occur in the developing embryo. We set out to determine if such changes could be identified in embryos as early as the pre-implantation stage. Study design, size, duration: We used a cohort of 19 pre-implantation embryos (day 5 and 6 blastocysts); three being normal, five trisomy 15, two trisomy 22, three trisomy 21 and three trisomy 18, and three of unknown karyotype. Participants/materials, setting, methods: After written consent, analysis was performed on high quality embryos that previously underwent trophectoderm biopsy with array comparative genomic hybridization (aCGH) or next generation sequencing (NGS) for 24-chromosome aneuploidy screening and vitrified. Blastocysts were lysed immediately after thawing, and cDNA was synthesized and amplified, followed by RNA-Seq library preparation for deep Illuminabased sequencing. Sex and chromosomal aneuploidy were used as parameters for comparative analysis using a bioinformatics pipeline using a sensitivity of 0.05. Main results and the role of chance: Principal Component analysis (PCA) revealed that normal embryos clustered in proximity to trisomies 21 and 18, while 15 and 22 clustered separately. This suggested that early gene expression may correlate with viability. PCA did not distinguish between male and female embryos. Differential gene expression was calculated using DESEQ2, an R package that estimates the variance-mean dependence and tests for differential expression using a model using the negative binomial distribution. A comparison of sex-specific gene expression showed that the top differentially expressed genes were on the sex chromosomes, including various Y-linked transcription factors, helicases, and ribosomal proteins, as well as a testis-specific regulatory transcript, and >200 X-chromosome genes. Trisomy 21 embryos were the closest to normal embryos, with only 3 genes on chromosome 21 expressed more highly in the trisomic embryos. In contrast, trisomy 22 embryos (non viable), had 684 differentially expressed genes, 32 of which on chromosome 22. Trisomy 18 embryos had only one highly expressed significant gene, and it is located on chromosome 18. Trisomy 15 embryos had 829 differentially expressed genes, of which 83 were in chromosome 15. Our results suggest that the less viable trisomies have bigger gene expression differences, even at this very early stage. Limitations, reasons for caution: While the karyotypes were analyzed by stringent methods, embryos may have had elements of mosaicism or chromosomal structural abnormalities. The genes identified by RNA-Seq need to be validated using orthogonal methods. Wider implications of the findings: We have expanded the knowledge of the transcriptome of the human pre-implantation embryo as they relate to aneuploidy and sex. This information can now be used to further our understanding of early embryonic development and stem cell biology, and to identify biomarkers for non-invasive preimplantation genomic screening