Interaction of RAGE with its ligands can promote tumor progression, invasion and angiogenesis. Although blocking RAGE signaling has been proposed as a potential anti-cancer strategy, functional contributions of RAGE expression in the tumor microenvironment (TME) has not been investigated in detail. Here, we evaluated the effect of genetic depletion of RAGE in TME on the growth of gliomas. In both invasive and non-invasive glioma models, animal survival was prolonged in RAGE knockout (Ager−/−) mice. However, the improvement in survival in Ager−/− mice was not due to changes in tumor growth rate but rather to a reduction in tumor-associated inflammation. Furthermore, RAGE ablation in the TME abrogated angiogenesis by downregulating the expression of pro-angiogenic factors which prevented normal vessel formation, thereby generating a leaky vasculature. These alterations were most prominent in non-invasive gliomas, where the expression of VEGF and pro-inflammatory cytokines were also lower in tumor-associated macrophages (TAM) in Ager−/− mice. Interestingly, reconstitution of Ager−/− TAM with wild-type microglia or macrophages normalized tumor vascularity. Our results establish that RAGE signaling in glioma-associated microglia and TAM drives angiogenesis, underscoring the complex role of RAGE and its ligands in gliomagenesis.

Purpose S100B is member of a multigenic family of Ca2+-binding proteins that is overexpressed by gliomas. Recently, we demonstrated that low concentrations of S100B attenuated microglia activation through the induction of Stat3. We hypothesized that overexpression of S100B in gliomas could promote tumor growth by modulating the activity of tumor-associated macrophages (TAMs). Experimental Design We stably transfected GL261 glioma cell lines with constructs that overexpressed (S100Bhigh) or underexpressed (S100Blow) S100B and compared their growth characteristics to intracranial wild-type (S100Bwt) tumors. Results Downregulation of S100B in gliomas had no impact on cell division in vitro but abrogated tumor growth in vivo. Interestingly, compared to S100Blow tumors, S100Bwt and S100Bhigh intracranial gliomas exhibited higher infiltration of TAMs, stronger inflammatory cytokine expression, and increased vascularity. To identify the potential mechanisms involved, the expression of the S100B receptor, RAGE (receptor for advanced glycation end products), was evaluated in gliomas. Although S100B expression induced RAGE in vivo, RAGE ablation in mice did not significantly inhibit TAM infiltration into gliomas, suggesting that other pathways were involved in this process. To evaluate other mechanisms responsible for TAM chemoattraction, we then examined chemokine pathways and found that CCL2 was upregulated in S100Bhigh tumors. Furthermore, analysis of TCGA’s glioma data bank demonstrated a positive correlation between S100B and CCL2 expression in human proneural and neural glioma subtypes, supporting our finding. Conclusions These observations suggest that S100B promotes glioma growth by TAM chemoattraction through upregulation of CCL2 and introduces the potential utility of S100B inhibitors for glioma therapy.