gms | German Medical Science

Gremlin was identified as a regulator of growth and development in Xenopus laevis and a transcript downregulated in mos transformed rat cells. Gremlin binds to BMP4 and BMP7 and inhibits their cell differentiating and antiproliferative effects during limb patterning. More recent data demonstrated binding of Gremlin to the VEGF-receptor 2 which has angiogenic effects.

Methylation and expression of Gremlin was studied in gliomas by pyrosequencing and realtime RT-PCR in 63 gliomas, 6 glioblastoma cell lines and 7 stem cell enriched primary glioblastoma cell cultures. Structural alterations were investigated by SNP and high resolution melting analysis. The capacity of focus formation was studied on Gremlin transfected glioblastoma cells. A reporter assay of transfected glioma cells was performed to identify signaling pathways influenced by the expression of Gremlin.

Gliomas showed remarkably reduced mRNA-levels of Gremlin and excessive hypermethylation compared to normal brain tissues. Methylation was found to be more abundant in anaplastic astrocytomas and glioblastomas as compared to low-grade diffuse astrocytomas. There was no significant correlation between Gremlin methylation and IDH1 mutation.

Treatment of glioblastoma cell lines with the demethylating agens 5-aza-2'-deoxycytidine resulted in an increased expression of Gremlin. 23% of informative gliomas revealed LOH at the investigated SNPs. In addition, missense mutations were observed at codon 35 (P35A). Focus formation was significantly reduced in Gremlin transfected glioblastoma cell lines. The reporter array uncovered a significant repression of the Oct4 reporter activity.

Our findings argue for a contribution of Gremlin epigenetic silencing to the molecular pathology of gliomas. The significant impact of Gremlin on Oct4 reporter activity suggests that Gremlin inactivation would enhance Oct4 related molecular events in glioma cells e.g. inhibition of differentiation and elevation of cellular proliferation.