Abstract
BACKGROUND AND AIM: Glioma is a highly aggressive malignancy of the central nervous system with a poor prognosis. The nucleoside-binding oligomerization domain-containing protein 1 (NOD1)/receptor-interacting protein 2 (RIP2) pathway is involved in various inflammatory responses and is closely associated with microglial polarization. Microglial M2 polarization alters the glioma microenvironment, promoting tumor growth. This study aimed to investigate the role of the NOD1/RIP2 pathway in glioma progression. METHODS: We explored the mechanism of NOD1/RIP2 in glioma progression through bioinformatics analysis, clinical sample evaluation, and in vivo and in vitro experiments. Bioinformatics analysis was conducted to assess NOD1 expression in glioma tissues. Multiparameter MRI and histologic analyses were performed on human tissues, and the correlation between the relative apparent diffusion coefficient (rADC) and NOD1 expression was analyzed. C6 and U251 glioma cells were treated with ML130, a NOD1 inhibitor, and assessed using 5-ethynyl-2'-deoxyuridine (EdU), plate cloning, Transwell, and wound healing assays. Key molecules of the NOD1/RIP2 pathway were examined through immunofluorescence and Western blotting. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect Arg1 and CD206 expression in BV2 mouse microglia cultured with C6-derived conditioned medium (CM). The changes in glioma cell biologic behavior were assessed using C6/BV2-derived CM through EdU, wound healing, and Transwell assays. Finally, the role and mechanism of NOD1 in glioma growth were evaluated using a rat glioma model. RESULTS: Bioinformatics analysis showed that NOD1 was highly expressed in glioma tissues and strongly correlated with glioma grade. Human brain glioma samples exhibited increased expression of NOD1, RIP2, Iba1, interleukin-1β, and CD206, with higher expression in high-grade gliomas compared to low-grade gliomas. The NOD1 expression was negatively correlated with rADC values. Treatment with ML130 inhibited glioma cell proliferation, migration, and invasion while reducing NOD1 and RIP2 expression. The expression levels of Arg1 and CD206 in BV2 cells cultured with C6-derived CM decreased in both ML130 and GSK-583 groups, while the expression levels increased in the ie-DAP group. Compared with the control group, the expressions of Arg1 and CD206 in microglia in the GSK-583 + ML130 and GSK-583 + ie-DAP groups were inhibited, and the inhibitory effect in the GSK-583 + ML130 group was more significant. Furthermore, after culturing with C6/BV2 derived CM, the activity of C6 cells was significantly inhibited in the ML130 group, while the activity increased in the ie-DAP group. The activity of C6 cells in the GSK-583 + ML130 and GSK-583 + ie-DAP groups was significantly decreased, and this effect was more pronounced in the GSK-583 + ML130 group. ML130-treated glioma-bearing rats exhibited reduced tumor growth, suppressed NOD1/RIP2 pathway activation, and inhibited microglial M2 polarization. However, the results observed in the ie-DAP group were opposite. CONCLUSIONS: NOD1 is an effective predictor of preoperative glioma grade and prognosis. It facilitates glioma progression by promoting microglial M2 polarization through the NOD1/RIP2 pathway.