TGF-β1 secreted by M2 phenotype macrophages enhances the stemness and migration of glioma cells via the SMAD2/3 signalling pathway

The positive correlation between the number of M2 phenotype TAMs (M2‑TAMs) and tumour development suggests a supportive role of M2‑TAMs in glioma progression. In the present study, the molecular link between glioma cells and M2‑TAMs was investigated and it was demonstrated that transforming growth factor‑β1 (TGF‑β1) secreted by M2‑TAMs is key in facilitating the stemness and migration of glioma cells. Cluster of differentiation (CD)133 and CD44, markers for the M2 phenotype, were assessed by western blotting. A sphere formation assay and trans‑well assay were applied to test the stemness and migration abilities of glioma cells following co‑cultured with M2‑TAMs. Stemness markers CD133 and CD44, epithelial‑mesenchymal transition‑associated markers and mothers against decapentaplegic homolog (SMAD)2/3 and sex determining region Y‑box 4/2 (SOX4/2) levels were also evaluated by western blotting. A xenograft tumor mouse model was used to demonstrate the tumor forming ability of glioma cells. The results showed that the U251 glioma cells co‑cultured with M2‑TAMs exhibited high level of sphere formation, stemness and migration ability. Recombinant TGF‑β1 protein treatment was able to achieve the same effects on U251 cells, whereas a TGF‑β pathway inhibitor reversed the stemness and migration abilities of the glioma cells induced by M2‑TAMs. It was also demonstrated that TGF‑β1 secreted by M2‑TAMs upregulated the phosphorylation of SMAD2/3 and the expression of SOX4/2 in glioma cells. In a mouse xenograft model, solid tumours formed by U251 cells co‑cultured with M2‑TAMs or pre‑treated with TGF‑β1 were larger in size and had a higher growth rate. Taken together, results of the present study demonstrated that M2‑TAMs promoted the stemness and migration abilities of glioma cells by secreting TGF‑β1, which activated the SMAD2/3 pathway and induced the expression of SOX4 and SOX2. These results highlight the mechanism by which M2‑TAMs and glioma interact and demonstrate potential therapeutic strategies for glioma treatment.