Restoring mitofusin balance prevents axonal degeneration in a Charcot-Marie-Tooth type 2A model
Yueqin Zhou, … , Cathleen M. Lutz, Robert H. Baloh
Yueqin Zhou, … , Cathleen M. Lutz, Robert H. Baloh
Published March 18, 2019
Citation Information: J Clin Invest. 2019;129(4):1756-1771. https://doi.org/10.1172/JCI124194.
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Research Article Neuroscience

Restoring mitofusin balance prevents axonal degeneration in a Charcot-Marie-Tooth type 2A model

Abstract

Mitofusin-2 (MFN2) is a mitochondrial outer-membrane protein that plays a pivotal role in mitochondrial dynamics in most tissues, yet mutations in MFN2, which cause Charcot-Marie-Tooth disease type 2A (CMT2A), primarily affect the nervous system. We generated a transgenic mouse model of CMT2A that developed severe early onset vision loss and neurological deficits, axonal degeneration without cell body loss, and cytoplasmic and axonal accumulations of fragmented mitochondria. While mitochondrial aggregates were labeled for mitophagy, mutant MFN2 did not inhibit Parkin-mediated degradation, but instead had a dominant negative effect on mitochondrial fusion only when MFN1 was at low levels, as occurs in neurons. Finally, using a transgenic approach, we found that augmenting the level of MFN1 in the nervous system in vivo rescued all phenotypes in mutant MFN2R94Q-expressing mice. These data demonstrate that the MFN1/MFN2 ratio is a key determinant of tissue specificity in CMT2A and indicate that augmentation of MFN1 in the nervous system is a viable therapeutic strategy for the disease.

Authors

Yueqin Zhou, Sharon Carmona, A.K.M.G. Muhammad, Shaughn Bell, Jesse Landeros, Michael Vazquez, Ritchie Ho, Antonietta Franco, Bin Lu, Gerald W. Dorn II, Shaomei Wang, Cathleen M. Lutz, Robert H. Baloh

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Figure 4

Model of dominant negative function by MFN2R94Q mutation and effect of conformation-altering peptides and MFN1 complementation.

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Model of dominant negative function by MFN2R94Q mutation and effect of c...
(A) Model of MFN2R94Q mutant dominant negative function and effect of allosteric peptide TAT-MP1Gly. Alteration of GTPase activity does not affect initial mitochondrial tethering (mediated by HR2 domain), but leads to inability to fuse after tethering. TAT-MP1Gly peptide drives the tethering permissive state in this model by blocking HR1-HR2 interaction. (B) Mitochondrial fusion defects caused by MFN2R94Q are only rescued by TAT-MP1Gly in the presence of Mfn1 in MEFs. MEFs lacking either Mfn2 alone or both Mfn1 and Mfn2 were infected with MFN2R94Q lentivirus and imaged with MitoTracker Green and TMRE to label mitochondria. Scale bar: 10 μM. (C) Quantification of B. Mitochondrial fusion is presented as mitochondrial aspect ratio measurement (mitochondrial length/width). TAT-MP1Gly only improved mitochondrial fusion in the presence of functioning Mfn1, but not in cells lacking all functional Mfns. Data are represented as mean ± SEM (n = 3 repeat experiments). Student’s 2-tailed t test. *P < 0.05. (D) MFN2R94Q-induced mitochondrial aggregation was enhanced by TAT-MP1Gly peptide in a neuronal cell line (SH-SY5Y cells) and rescued by increased MFN1 expression. MFNs were expressed by lentivirus, with mito-RFP to visualize mitochondria. Original magnification, ×20 (upper panels). Inset boxes are shown at higher magnification below (×3 magnification). Scale bar: 100 μM. Representative of 3 repeat experiments. (E) Quantification of D. Data are represented as mean ± SEM (n = 5). One-way ANOVA with Tukey’s test was used for multiple comparisons. **P < 0.01; ****P < 0.0001.