Abstract
Fragile X syndrome results from a loss of the RNA-binding protein fragile X mental retardation protein (FMRP). How FMRP regulates neuronal development and function remains unclear. Here we show that FMRP-deficient immature neurons exhibit impaired dendritic maturation, altered expression of mitochondrial genes, fragmented mitochondria, impaired mitochondrial function, and increased oxidative stress. Enhancing mitochondrial fusion partially rescued dendritic abnormalities in FMRP-deficient immature neurons. We show that FMRP deficiency leads to reduced Htt mRNA and protein levels and that HTT mediates FMRP regulation of mitochondrial fusion and dendritic maturation. Mice with hippocampal Htt knockdown and Fmr1-knockout mice showed similar behavioral deficits that could be rescued by treatment with a mitochondrial fusion compound. Our data unveil mitochondrial dysfunction as a contributor to the impaired dendritic maturation of FMRP-deficient neurons and suggest a role for interactions between FMRP and HTT in the pathogenesis of fragile X syndrome.
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Code availability
Transcriptome data for this project are available on the Gene Expression Omnibus (accession number GSE117111). We have used only published software and freely accessible software for data analyses. Further details can be requested from the corresponding author.
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Acknowledgements
We thank Y. Xing, S. Malone, H. Zhao, E. Berndt, Y. Zhao, J. Le, Y. Sun, J. Hoang, Y. Tao, J. Wang, and R. Spitzer for technical assistance; Q. Bu, A. Wang, Q. Chang, D. Joshi, S. Shapiro, and W. Qiu for help with mitochondrial analysis; K. Knobel, J. Pinnow, H. Mitchell at the Waisman IDD Model Core; UW Carbone Cancer Center Flow Cytometry lab for help with cell isolation; and S. Splinter-BonDurant and the UW-Madison Biotechnology Center for next generation sequencing services. We also thank U. Mueller (Scripps Institute, San Diego, CA) for Tg(Dcx -CreERT2) mice and D. Lie (Friedrich-Alexander University, Erlangen, Germany) and C. Chang for viral vectors expressing mitochondrial markers. This work was supported by grants from the National Institutes of Health (R01MH078972, R56MH113146, R01NS105200 and R01MH116582 to X.Z., P30HD03352, U54HD090256 to the Waisman Center, MH061876 and NS097362 to E.R.C., F32NS098604 to J.D.V.), UW Vilas Trust (Kellett Mid-Career Award) and UW-Madison and Wisconsin Alumni Research Foundation (to X.Z.), Jenni and Kyle Professorship (to X.Z.), John Merck Fund (to X.Z, and A.B)., and in part by the National Institute on Aging, Intramural Research Program (to H.v.P.).
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Contributions
X.Z. conceived and designed the project, approved the experimental plans, kept track of the project, wrote and submitted the manuscript. M.S. designed the experiments, collected and analyzed data for most figures, kept track of the progress of the project, wrote and submitted the manuscript. F.W. designed the experiments, collected and analyzed data in Fig. 1 and performed FACS-seq in Fig. 3. M.L. created sgRNA/dCas9 system and helped with bioinformatics analysis and human iPSC differentiation. M.E.S. collected some of the qPCR, western blotting and confocal microscopy data for phenotypic analysis of both mouse and human neurons. J.J.T. collected data for in vivo analysis in Fig. 1. T.K. performed quantitative analysis of most of the in vitro neuronal dendrites, S.K. collected data for retroviral-labeled neurons. Y.G. created retroviral and lentiviral Cre and shRNA constructs. N.S. and H.v.P. performed electrophysiological analysis. J.D.V. and E.R.C. analyzed mitochondria dynamics using live imaging. A.B. worked with M.S. in human iPSC differentiation and transplantation.
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Supplementary information
Supplementary Figures 1–25
Supplementary Figures 1–25
Supplementary Note
Information on antibodies.
Supplementary Table 1
DE genes in Fmr1-KO Dcx-DsRed neurons.
Supplementary Table 2
WebGestalt enrichment.
Supplementary Table 3
PANTHER GO analysis.
Supplementary Table 4
Shared targets among published FMRP targets.
Supplementary Table 5
Physical and genetic interactions among all mouse genes (Mus musculus Version 3.4.161) as determined by BIOGRID.
Supplementary Table 6
FMRP targets interacting with DE genes in KO.
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Shen, M., Wang, F., Li, M. et al. Reduced mitochondrial fusion and Huntingtin levels contribute to impaired dendritic maturation and behavioral deficits in Fmr1-mutant mice. Nat Neurosci 22, 386–400 (2019). https://doi.org/10.1038/s41593-019-0338-y
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DOI: https://doi.org/10.1038/s41593-019-0338-y
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