NF1 germline mutation differentially dictates optic glioma formation and growth in neurofibromatosis-1

Neurofibromatosis type 1 (NF1) is a common neurogenetic condition characterized by significant clinical heterogeneity. A major barrier to developing precision medicine approaches for NF1 is an incomplete understanding of the factors that underlie its inherent variability. To determine the impact of the germline NF1 gene mutation on the optic gliomas frequently encountered in children with NF1, we developed genetically engineered mice harboring two representative NF1-patient-derived Nf1 gene mutations (c.2542G>C;p.G848R and c.2041C>T;p.R681X). We found that each germline Nf1 gene mutation resulted in different levels of neurofibromin expression. Importantly, only R681X^CKO but not G848R^CKO, mice develop optic gliomas with increased optic nerve volumes, glial fibrillary acid protein immunoreactivity, proliferation and retinal ganglion cell death, similar to Nf1 conditional knockout mice harboring a neomycin insertion (neo) as the germline Nf1 gene mutation. These differences in optic glioma phenotypes reflect both cell-autonomous and stromal effects of the germline Nf1 gene mutation. In this regard, primary astrocytes harboring the R681X germline Nf1 gene mutation exhibit increased basal astrocyte proliferation (BrdU incorporation) indistinguishable from neo^CKO astrocytes, whereas astrocytes with the G848R mutation have lower levels of proliferation. Evidence for paracrine effects from the tumor microenvironment were revealed when R681X^CKO mice were compared with conventional neo^CKO mice. Relative to neo^CKO mice, the optic gliomas from R681X^CKO mice had more microglia infiltration and JNK^{Thr183/Tyr185} activation, microglia-produced Ccl5, and glial AKT^Thr308 activation. Collectively, these studies establish that the germline Nf1 gene mutation is a major determinant of optic glioma development and growth through by both tumor cell-intrinsic and stromal effects.