Abstract
Glioblastoma multiforme (GBM) present with an abundant tumour neo-vasculature and a high degree of tumour cell infiltration into the parenchyma. In a serial implantation model recapitulating the angiogenic switch of human GBM we found that the expression levels of the proangiogenic receptor APLNR and its cognate ligand APLN strongly increase with the onset of tumour-vascularisation. Screening a set of murine and human GBM stem cell (GSC) cultures of different genetic subtypes we consistently detected APLN/APLNR expression. Knockdown of APLN (AKD) in these GSCs and subsequent orthotopic implantation in mice massively reduced the GBM vascularisation, as compared to tumours generated by control GSCs. Injection of AKD-GSCs into APLN-knockout mice further normalised the intratumoural vascular network to a level otherwise observed in the tumour-free brain. Infusion of the APLNR-agonist apelin-13 restored angiogenesis in APLN-deficient tumours. In stereotactic biopsies of GBM patients we found an upregulation of APLNR in the tumour infiltrative zone (lacking aberrant vascularisation), which points towards an additional role for APLNR in tumor cells. In a series of cell culture and in vivo experiments we observed that autocrine APLN signalling promotes GSC-invasion. Importantly, application of an APLNR antagonist was able to block both tumour angiogenesis and GBM cell invasion in vivo. In summary, we show that APLN-APLNR signalling induces GBM neo-vascularization as well as GSC-invasion and that both pathological features are blunted by APLNR-blockade. We propose APLNR inhibition as a new strategy for combined anti-angiogenic and anti-invasive GBM treatment, which may provide therapeutic benefits for a broad range of GBM subsets.