CXCL12 alone is insufficient for gliomagenesis in Nf1 mutant mice

Abstract

Tumorigenesis requires interactions between tumor progenitors and their microenvironment. We found that low cAMP levels were sufficient for tumorigenesis in a mouse model of Neurofibromatosis-1 (NF1)-associated optic pathway glioma (OPG). We hypothesized that the distinct pattern of glioma in NF1 reflected spatiotemporal differences in CXCL12 effects on cAMP levels. Thus, we sought to alter the pattern of gliomagenesis through manipulation of CXCL12-CXCR4 pathway activation in Nf1 OPG mice. Forced CXCL12 expression induced glioma at a low frequency. Further, treatment of Nf1 OPG mice with AMD3100, a CXCR4 antagonist, did not attenuate glioma growth. Thus, it appears, CXCL12 alone cannot promote gliomagenesis in NF1 mice.

Figure 1. Bioluminescence imaging (BLI) of murine Nf1 OPG

BLI of (A) CXCL12 virus-injected mice (n = 5) and (B) Control virus-injected mice (n = 5). For each animal, BLI data were normalized to the initial post-injection BLI measurement.

Figure 2. Histological features of the single CXCL12-induced glioma

(A) The injection site from the single mouse diagnosed with glioma (TU: tumor) was characterized by increased cellularity with evidence for nuclear atypia and abnormal cell clusters. No remarkable hypercellularity was observed in non-tumor brain (NT: Non-Tumor) Scale bar = 20 μm. (B) CXCL12 expression was increased at the injection sites in both tumor-bearing and non-tumor-bearing brains. Scale bar = 80 μm. (C) Glial Fibrillary Acidic Protein (GFAP)-immunoreactive piloid cells were present within the hypercellular lesion in the brain tumor (asterisk). Only normal (stellate) astrocyte morphologies were found in the non-tumoral brain. Scale bar = 20 μm. (D) There was increased Olig2 expression within the hypercellular lesion in the brain tumor. Scale bar = 40 μm. (E) Infiltrating microglia were identified in brain tumor (IBA-1 staining). Scale bar = 40 μm. (F) A significant degree of angiogenesis was evident by Endoglin staining in the brain tumor. Scale bar = 40 μm. Positive cells appear brown in panels B–F.

Figure 3. AMD3100 did not attenuate optic pathway glioma (OPG) growth

(A) The volumes of the optic nerves were determined as described in Materials and Methods section. There was no difference in optic nerve volumes between mice treated with AMD3100 versus vehicle (PBS) control. (B) AMD had no effect on the mitotic index as measured by Ki-67 labeling. (C) AMD3100 had no significant effect on apoptosis as determined by TUNEL staining. (P > 0.5 in all analyses by two-tailed t-test)