DPP4 and glioblastoma: Immunohistochemical staining of the GBM tissue chip showed that the protein levels of ANPEP and ENPEP were significantly increased in GBM (Figure 2C), although the mRNA levels of ACE2, DPP4, ANPEP, and ENPEP were upregulated in GBM according to the UALCAN server (Figure 2B).