Progression of glioblastoma downregulates neprilysin levels and enhances expression of oncogenic mediators in a rodent model

Abstract In various cancers, tumor suppressor neprilysin plays a crucial role in preventing tumorigenesis. Neprilysin levels are decreased in various cancers and neuronal disorders. In the brain, NEP is expressed by astrocytes. However, the neprilysin levels with the oncogenic markers in glioblastoma has not been explored. In this study, we investigated the possible effects of glioblastoma progression on neprilysin signalling using a rat glioblastoma model. The western blot analysis of PTEN, AKT, p53, Pro-caspase-3 and VEGF-A, and immunofluorescence analysis of GFAP, FAK, FGF-2, EGFR and VEGFR-2 were performed. Neprilysin protein levels and activity were attenuated in the tumor tissues as well as the cerebrum of the glioblastoma-induced animals, consistent with reduced MME expression in the TCGA glioblastoma cohort. Hypoxia is recognized as a contributor to neprilysin downregulation, and hypoxic histopathological regions in tumor tissues were associated with elevated pro-caspase-3 levels and reduced NEP expression. Neprilysin protein levels were positively correlated with PTEN and p53 tumor suppressor proteins, which were also attenuated in glioblastoma. In addition, AKT, EGFR, VEGFR-2 and GFAP surface expressions were negatively correlated with neprilysin. Also, the neprilysin substrate- FGF-2, and its downstream effector FAK, were increased in the tumor tissues. These correlations were further supported by analysis of human glioma transcriptomic data from TCGA, examining MME expression and marker associations in glioblastoma. Within the TCGA glioblastoma cohort, only PTEN , AKT1 , and EGFR showed significant correlations with MME expression. The study findings suggest that modulation of neprilysin signalling may serve as a potential therapeutic strategy for glioblastoma.