Mechanism of glioma stem cells with high expression of PTPRZ1 inducing TAMs polarization to M2 immunosuppressive phenotype

To explore the effect of glioma stem cells with high expression of protein tyrosin phosphatase receptor type Z1 (PTPRZ1) on the phenotypic polarization and phagocytosis of tumor-associated macrophages and its regulatory mechanism.

GSCs and non-stem tumor cells (NSTCs) were screened out from human glioblastoma (GBM) specimens using flow cytometry, and the PTPRZ1 expression in paired GSCs and NSTCs were detected. Human peripheral blood mononuclear cells (PBMC)-derived CD14⁺ monocytes were exposed to the conditioned medium from glioma cells or recombinant chemokine C-C motif ligand 20 (CCL20) for TAM polarization. Stable PTPRZ1 knockout GSCs (PTPRZ1-KO GSCs) were constructed using CRISPR/Cas9. TAM phagocytosis to GSCs, NSTCs, PTPRZ1-Control GSCs (PTPRZ1-Ctrl GSCs) and PTPRZ1-KO GSCs and the expression of immunosuppressive phenotype (M2) polarization marker CD163 were examined using flow cytometry. Differentially expressed genes (DEGs) between paired GSCs and NSTCs were determined using a bulk RNA-sequencing dataset (GSE54791) from Gene Expression Omnibus (GEO). A gene set informing worse outcome of patients with GBM was generated using The Cancer Genome Atlas (TCGA)-GBM cohort. By intersecting the aforementioned gene set with the gene set that encodes for humanmembrance proteins, the PTPRZ1 gene is obtained. Gene set enrichment analysis (GSEA) was used for pathway enrichment analysis to compare the differentially regulated pathways between GBMs with high or low PTPRZ1 expression. Bulk RNA sequencing, qRT-PCR and Western blotting were used to identify the DEGs between PTPRZ1-KO GSCs and PTPRZ1-Ctrl GSCs.

GSCs were more capable of escaping from TAM phagocytosis than NSTCs (P<0.05) and had specifically up-regulated PTPRZ1 expression. PTPRZ1-KO significantly suppressed GSCs escaping from TAM phagocytosis (P<0.01). GBMs with high PTPRZ1 expression showed significant inhibition of pathways mediating phagocytosis (P<0.05). The expression of CCL20 as a M2 TAM polarization chemokine was significantly down-regulated in PTPRZ1-KO GSCs (P<0.05). Treatment with recombinant CCL20 up-regulated the expression of CD163 as a M2 TAM marker in TAM.

PTPRZ1⁺ GSCs mediate M2 TAM polarization and inhibit TAM phagocytosis, which may be related to the up-regulation of CCL20 in PTPRZ1⁺ GSCs.