1p/19q co-deletion status is associated with distinct tumor-associated macrophage infiltration in IDH mutated lower-grade gliomas

Background Tumor-associated macrophages (TAM)s are critical regulators of glioma progression. As yet, however, TAMs in isocitrate dehydrogenase (IDH) mutated lower-grade gliomas (LGGs) have not been thoroughly investigated. The aim of this study was to determine whether 1p/19q co-deletion status affects the TAM phenotype or its prevalence in IDH mutated LGGs. Methods TAMs in IDH mutated LGGs were analyzed using transcriptome data from 230 samples in the TCGA database in combination with transcriptome data from single-cell RNA sequencing of IDH-mutated LGGs. Proteins potentially involved in TAM regulation were examined by immuno-staining in primary LGG samples harboring IDH mutations. Essential signaling pathways regulating TAM phenotypes were investigated in a glioma mouse model using small molecule inhibitors. Results Most of the TAMs in IDH-mutated LGGs expressed the M1 activation markers CD86 and TNF, whereas a subset of individual TAMs co-expressed both M1 and M2-related markers. Bioinformatics analysis in combination with immuno-staining of IDH-mutated patient samples revealed higher amounts of TAMs expressing M2-related markers in 1p/19q non-codeletion IDH-mutated LGGs compared to 1p/19q codeletion LGGs. The levels of transforming growth factor beta 1 (TGF beta 1) and macrophage colony-stimulating factor (M-CSF) were significantly higher in 1p/19q non-codeletion LGGs than in 1p/19q codeletion LGGs. M-CSF and TGF beta 1 signal inhibition decreased tumor growth and modulated the TAM phenotype in a glioma mouse model. Conclusions Our data indicate that 1p/19q co-deletion status relates to distinct TAM infiltration in gliomas, which is likely mediated by M-CSF and TGF beta 1 signaling. M-CSF and TGF beta 1 signaling may play a pivotal role in regulating the TAM phenotype in glioma.

Automated summary

This study found that in IDH-mutated LGGs, most TAMs expressed M1 activation markers CD86 and TNF, with some TAMs co-expressing both M1 and M2-related markers. Higher levels of TAMs expressing M2-related markers were observed in 1p/19q non-codeletion IDH-mutated LGGs compared to 1p/19q codeletion LGGs. Inhibition of M-CSF and TGF beta 1 signaling decreased tumor growth and modulated TAM phenotype in a glioma mouse model, indicating a potential role of these proteins in regulating TAM phenotype in glioma.