Brain-wide structural and functional disruption in mice with oligodendrocyte specificNf1deletion is rescued by inhibition of NOS

Abstract

Neurofibromin gene (NF1) mutation causes Neurofibromatosis type 1 (NF1), a disorder in which brain white matter deficits identified by neuroimaging are common, yet of unknown cellular etiology. In mice, Nf1 loss in adult oligodendrocyte causes myelin decompaction, and increases oligodendrocyte nitric oxide (NO) levels. Nitric oxide synthase (NOS) inhibitors rescue this pathology. Whether oligodendrocyte pathology is sufficient to affect brainwide structure and account for NF1 imaging findings is unknown. Here, we show that Nf1 gene inactivation in adult oligodendrocytes (Plp-Nf1 fl/+ mice) results in a motor coordination deficit. Magnetic resonance imaging in awake mice shows that fractional anisotropy is reduced in Plp-Nf1 fl/+ corpus callosum and that interhemispheric functional connectivity in motor cortex is also reduced, consistent with disrupted myelin integrity. Further, NOS-specific inhibition rescued both measures. These results demonstrate that oligodendrocyte defects account for aspects of brain dysfunction in NF1, which can be identified by neuroimaging and ameliorated by NOS inhibition. Significance statementThis study assesses the effects of myelin decompaction on motor behavior and brain-wide structural and functional connectivity, and the effect of nitric oxide synthase (NOS) inhibition by N-nitro-L-arginine methyl ester (L-NAME) on these imaging measures. We report that inducible oligodendrocyte-specific inactivation of the Nf1 gene, which causes myelin decompaction, results in reduced motor coordination. Using diffusion-based MRI we show reduced myelin integrity and using functional MRI we show reduced functional connectivity in awake passive mice. L-NAME administration results in rescue of the pathology at the mesoscopic level using imaging procedures that can be directly applied to humans to study treatment efficacy in clinical trials.

Individual variability in functional connectivity architecture of the mouse brain

“…Future studies can use the individual functional connectome to predict the effect of causal control similar to the way human resting-state fMRI is used to predict individual task fMRI activation pattern 9 , linking the different levels of organization and uncovering sources of individual variation. In addition, rodent models of disease are commonly studied using fcMRI 21,22,29,65 , which allows direct translation to humans 20,28 , as well as studying the relations between functional connectivity and behavior [23][24][25][26] . Such studies can utilize the approach presented here to follow the trajectory of individual animals during development, aging or after treatment, as well as CPM, which provides a data-driven alternative for fcMRI-based behavioral prediction 35 , rather than the hypothesis-driven approach that examines the behavioral correlations of specific functional connections.…”

“…Since this experimental design is hard to achieve in anesthetized animals, such studies can benefit from awake mouse imaging. We have previously established fcMRI experiments in awake head-fixed mice [27][28][29] and used repeatedmeasurement designs to link individual differences in structural and functional connectivity 30 . However, a detailed analysis of individual variability of functional connectivity in the mouse brain and its relevance to behavior has heretofore not been demonstrated.…”

Structural and functional brain-wide alterations in A350V Iqsec2 mutant mice displaying autistic-like behavior

“…Mice of each genotype (n = 13 per group) underwent multiple awake head-fixed fcMRI sessions, as previously described 14,17,40,41 . Imaging of animals in the awake state may be impacted by stress and in group comparisons, genotype-specific response to stress may be raised as a concern.…”

“…Raw data were preprocessed as previously described 14,17,40,41 , including removal of the first two volumes for T1-equilibration effects, compensation of slice dependent time shifts, rigid body correction for head motion, registration to a downsampled version of the AMBC atlas 36,37 , and intensity normalization. Data scrubbing was applied as previously described 14,44 with exclusion criteria of 50 μm framewise displacement and derivative root-mean-square variance over voxels (DVARS) of 150% inter-quartile range (IQR) above the 75th percentile and exclusion of one additional frame after the detected motion.…”

“…All data were analyzed using MATLAB R2018a (The Mathworks, Natick, MA, USA) except for behavioral data in which analysis of variance (ANOVA) was analyzed using jamovi 1.0.7 47 . Sample size was estimated based on previous studies 17,20,40 . The Lilliefors test was used to determine normality.…”