Sustained correction of hippocampal neurogenic and cognitive deficits after a brief treatment by Nutlin-3 in a mouse model of Fragile X Syndrome

Background Fragile X syndrome (FXS), the most prevalent inherited intellectual disability and one of the most common monogenic form of autism, is caused by a loss of FMRP translational regulator 1 (FMR1). We have previously shown that FMR1 represses the levels and activities of ubiquitin ligase MDM2 in young adult FMR1-deficient mice and treatment by a MDM2 inhibitor Nutlin-3 rescues both hippocampal neurogenic and cognitive deficits in FMR1-deficient mice when analyzed shortly after the administration. However, it is unknown whether Nutlin-3 treatment can have long-lasting therapeutic effects. Methods We treated 2-month-old young adult FMR1-deficient mice with Nutlin-3 for 10 days and then assessed the persistent effect of Nutlin-3 on both cognitive functions and adult neurogenesis when mice were 6-month-old mature adults. To investigate the mechanisms underlying persistent effects of Nutlin-3, we analyzed proliferation and differentiation of neural stem cells isolated from these mice and assessed the transcriptome of the hippocampal tissues of treated mice. Results We found that transient treatment with Nutlin-3 of 2-month-old young adult FMR1-deficient mice prevents the emergence of neurogenic and cognitive deficits in mature adult FXS mice at 6-month of age. We further found that the long-lasting restoration of neurogenesis and cognitive function might not be mediated by changing intrinsic properties of adult neural stem cells. Transcriptomic analysis of the hippocampal tissue demonstrated that transient Nultin-3 treatment leads to significant expression changes in genes related to extracellular matrix, secreted factors, and cell membrane proteins in FMR1-deficient hippocampus. Conclusions Our data indicates that transient Nutlin-3 treatment in young adults leads to long-lasting neurogenic and behavioral changes through modulating adult neurogenic niche rather than intrinsic properties of adult neural stem cells. Our results demonstrate that cognitive impairments in FXS may be prevented by an early intervention through Nutlin-3 treatment. ### Competing Interest Statement X.Z. and Y.L. are inventors of a patent (METHODS FOR TREATING COGNITIVE DEFICITS ASSOCIATED WITH FRAGILE X SYNDROME, United States US 9,962,380 B2). The remaining authors declare no competing interests. * ASD : autism spectrum disorder ANOVA : Analysis of variance BrdU : Bromodeoxyuridine cKO : Conditional knockout DEG : Differentially expressed gene CE : Coefficient of error DG : Dentate gyrus ECM : Extracellular matrix Erdr1 : Erythroid differentiation regulator 1 Fig : Figure Fmr1 : Fragile x mental retardation protein 1 FMR1 : Translational regulator 1 (official name) FMRP : Fragile x mental retardation protein (previous name) FXS : Fragile x syndrome GAPDH : Glyceraldehyde-3-phosphate dehydrogenase GC : Granule cell GFP : Green fluorescent protein GFAP : Glial fibrillary acidic protein GO : Gene ontology HDAC1 : Histone deacetylase 1 KO : Knockout qPCR : quantitative polymerase chain reaction MCM2 : Minichromosome maintenance complex component 2 MDM2 : mouse double minute 2 NeuN : Neuronal nuclei antigen NIH : National institute of health NLR : Novel location recognition NOR : Novel object recognition NSPC : Neural stem/progenitor cell NSC : Neural stem cell NP : Neural progenitors Nut3 : Nutlin3 p53 : Protein PFA : Paraformaldehyde RBFOX3 : RNA binding fox-1 homolog 3 RGL : Radial glial like SGZ : Subgranular zone SVZ : Subventricular zone TF : Transcription factor Veh : Vehicle WT : Wild type