Pericytes/vessel-associated mural cells (VAMCs) are the major source of key epithelial-mesenchymal transition (EMT) factors SLUG and TWIST in human glioma.

Lisa Mäder,Simone Niclou,Stefan Liebner,Anna E Blank,Patrick N Harter,Michael Seifert,Michel Mittelbronn,Ulrike Naumann,Peter Baumgarten,Cornelia Zachskorn,Janina Jansong,David Capper,Jakob Ehlers,Naita M Wirsik,Barbara Klink

doi:10.18632/oncotarget.25275

Abstract

Epithelial-to-mesenchymal transition (EMT) is supposed to be responsible for increased invasion and metastases in epithelial cancer cells. The activation of EMT genes has further been proposed to be important in the process of malignant transformation of primary CNS tumors. Since the cellular source and clinical impact of EMT factors in primary CNS tumors still remain unclear, we aimed at deciphering their distribution in vivo and clinico-pathological relevance in human gliomas.We investigated 350 glioma patients for the expression of the key EMT factors SLUG and TWIST by immunohistochemistry and immunofluorescence related to morpho-genetic alterations such as EGFR-amplification, IDH-1 (R132H) mutation and 1p/19q LOH. Furthermore, transcriptional cluster and survival analyses were performed.Our data illustrate that SLUG and TWIST are overexpressed in gliomas showing vascular proliferation such as pilocytic astrocytomas and glioblastomas. EMT factors are exclusively expressed by non-neoplastic pericytes/vessel-associated mural cells (VAMCs). They are not associated with patient survival but correlate with pericytic/VAMC genes in glioblastoma cluster analysis.In summary, the upregulation of EMT genes in pilocytic astrocytomas and glioblastomas reflects the level of activation of pericytes/VAMCs in newly formed blood vessels. Our results underscore that the negative prognostic potential of the EMT signature in the group of diffuse gliomas of WHO grade II-IV does most likely not derive from glioma cells but rather reflects the degree of proliferating mural cells thereby constituting a potential target for future alternative treatment approaches.

Highlights

Our results show that key Epithelial-to-mesenchymal transition (EMT) factors such as SLUG and TWIST are overexpressed in glioblastomas (Figure 1)
In contrast to the hypothesis that the activation of EMT genes might be responsible for the malignant transformation of glioma cells, our results indicate that the central EMT regulators SLUG and TWIST are exclusively expressed by pericytes/vessel associated mural cells (VAMC) of proliferating blood vessels (Figures 1–4) while being absent from glioma cells (Figures 2, 3)
It has been shown that gliomas with a www.oncotarget.com proneural gene expression signature displayed a distinct underlyinggenetic phenotype consisting of a specific glioma-CpG island methylation phenotype (G-CIMP) related to IDH1 mutations [19]

Summary

Introduction

RESULTSThe concept of epithelial-to-mesenchymal transition (EMT) was first reported over 40 years ago [1]. The reactivation of EMT genes is associated with worse patient prognosis in carcinomas [3,4,5,6]. MET induction has been proposed as a promising therapeutic strategy for glioblastomas by potentially reversing the malignancy-associated EMT program thereby reducing glioma cell invasion as well as the survival of gliomainitiating cells. Most studies linking the expression of EMT genes to glioma malignancy analyzed gene expression at mRNA levels but not the related protein expression in vivo [13]. The EMT signature in glioblastoma was primarily ascribed to glioma cells without deciphering the exact cellular sources of the expression of EMT transcription factors. The aim of our study was to dissect the cellular source of expression of key EMT factors and investigate their potential association with patient survival in human gliomas. Among others including the WNT, RTK, TGFβ pathways, are involved in the EMT program, we mainly focused on down-stream EMT transcription factors such as SLUG and TWIST

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