The effect of tumor formation and treatment on retinal dysfunction in mouse models of Neurofibromatosis type 1 (NF1)-associated optic glioma.

Abstract

Purpose: Neurofibromatosis type 1 (NF1) is an autosomal dominant cancer predisposition syndrome, affecting 1 in 2,500 people worldwide. Approximately 15-20% of children with NF1 develop low-grade gliomas of the optic pathway (OPG), leading to visual imparment in 30-50% of affected children. While bi-allelic inactivation of the NF1 gene is the most common cause of OPG, a small group of patients with OPGs have additional genetic alterations resulting in greater tumor volume and proliferation. Our aim was to determine the impact of optic glioma formation on retinal dysfunction utilizing genetically engineered mouse (GEM) models. Additionally, we tested the outcome of tumor treatment on retinal function.

Methods: Mice used in the study were Nf1 ^flox/mut; GFAP-Cre (FMC) Nf1flox^/mut; f-BRAF; GFAP-Cre mice (FMBC) and Nf1^flox/mut; Pten ^flox/wt; GFAP-Cre (FMPC) mice. Mice were perfused at 3 months of age and processed for paraffin embedding. Immunohistochemistry was performed on paraffin sections using antibodies Brn3a and SMI-32. TUNEL staining was also performed. 3 month old FMC mice were treated for 4 weeks with PD901, BKM120, or vehicle controls via oral gavage (n=6).

Results: FMC, FMBC, and FMPC retinae had a 6-fold (±5.6% -6.9%) increase in RGC death and a 31-45% reduction in RGCs compared to controls. While all of the Nf1-OPG mouse strains had decreased RNFL thickness, FMPC mice had 3-fold decreased RNFL thickness in comparison with 2-fold reductions observed in FMC and FMBC mice. We found an inverse correlation (R² = 0.803) between RGC death and RNFL thickness among all 3 mouse models. Following treatment with either BKM120 or PD901 which each reduced FMC-OPG volume to wild-type levels, we found 1.9-fold and 4.9 -fold decreases in TUNEL⁺ cells in BKM120-treated and PD901-treated mice, respectively. Similarly, BKM120-treated and PD901-treated mice retained 40% (± 14%-57%) and 50% (± 34%-60%) more RGCs than controls. Lastly, RNFL thickness following BKM120 and PD901 treatment was increased by 1.6-fold and 2.3-fold, respectively, compared to vehicle-treated FMC mice.

Conclusions: The results from this study show that a larger, more proliferative OPG leads to increased retinal dysfunction. Likewise, using biological targets that inhibit tumor growth reversed these effects. These findings have implications for assessing visual outcome in children with NF1-OPG.