PIK3C2B inhibition improves function and prolongs survival in myotubular myopathy animal models
Nesrin Sabha, … , Eva L. Feldman, James J. Dowling
Nesrin Sabha, … , Eva L. Feldman, James J. Dowling
Published August 22, 2016
Citation Information: J Clin Invest. 2016;126(9):3613-3625. https://doi.org/10.1172/JCI86841.
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Research Article Muscle biology

PIK3C2B inhibition improves function and prolongs survival in myotubular myopathy animal models

Abstract

Myotubular myopathy (MTM) is a devastating pediatric neuromuscular disorder of phosphoinositide (PIP) metabolism resulting from mutations of the PIP phosphatase MTM1 for which there are no treatments. We have previously shown phosphatidylinositol-3-phosphate (PI3P) accumulation in animal models of MTM. Here, we tested the hypothesis that lowering PI3P levels may prevent or reverse the MTM disease process. To test this, we targeted class II and III PI3 kinases (PI3Ks) in an MTM1-deficient mouse model. Muscle-specific ablation of Pik3c2b, but not Pik3c3, resulted in complete prevention of the MTM phenotype, and postsymptomatic targeting promoted a striking rescue of disease. We confirmed this genetic interaction in zebrafish, and additionally showed that certain PI3K inhibitors prevented development of the zebrafish mtm phenotype. Finally, the PI3K inhibitor wortmannin improved motor function and prolonged lifespan of the Mtm1-deficient mice. In all, we have identified Pik3c2b as a genetic modifier of Mtm1 mutation and demonstrated that PIK3C2B inhibition is a potential treatment strategy for MTM. In addition, we set the groundwork for similar reciprocal inhibition approaches for treating other PIP metabolic disorders and highlight the importance of modifier gene pathways as therapeutic targets.

Authors

Nesrin Sabha, Jonathan R. Volpatti, Hernan Gonorazky, Aaron Reifler, Ann E. Davidson, Xingli Li, Nadine M. Eltayeb, Claudia Dall’Armi, Gilbert Di Paolo, Susan V. Brooks, Ana Buj-Bello, Eva L. Feldman, James J. Dowling

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Figure 7

Treatment with pan-PI3K inhibitors improves the mtm zebrafish phenotype.

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Treatment with pan-PI3K inhibitors improves the mtm zebrafish phenotype....
(A) Severity of fin fold phenotype in 4-dpf mtm mutants is significantly improved after treatment with 5 μM LY294002, 50 nM wortmannin, or 250 nM PI-103 (***P < 0.001), but not by inhibition of class III PI3K with 500 nM VPS34-IN1 (P = 0.4955) or class I PI3Ks with 500 nM GDC-0941 (P = 0.3494). From left to right: n = 92, 110, 108, 97, 92, 94; Kruskal-Wallis test, followed by Dunn’s post-test. (B) At 7 dpf, the mean distance traveled in a 30-second optovin-induced photoactivation period by mtm larvae treated with DMSO alone is 57% that of WT siblings (P < 0.001). Class I inhibition with GDC-0941 does not improve mtm motor function (45% WT, P < 0.001). In contrast, mtm motor function is improved relative to cognate-treated WT siblings by treatment with LY294002 (74% WT, P = 0.0059), wortmannin (70% WT, P = 0.0012), and, surprisingly, VPS34-IN1 (73% WT, P = 0.0155). Though these groups remained significantly different from WT, this improvement suggests an mtm-specific chemical effect for this phenotype (**P < 0.01, ***P < 0.001). Notably, mutants treated with PI-103 are statistically indistinguishable from PI-103–treated WT siblings (80% WT) and move significantly better than DMSO-treated mtm (*P < 0.0171). n = 24 each group; 2-way ANOVA, followed by Tukey’s post-test. (C) Kaplan-Meier survival curve showing that treatment with LY294002, wortmannin, and PI-103 improves median survival from 8 to 9 days and maximum survival from 9 to 11 to 12 days in comparison with DMSO-treated mtm larvae (P < 0.001 compared with mtm DMSO, Mantel-Cox or Gehan-Breslow-Wilcoxon tests). Inset legend top to bottom: n = 132, 43, 46, 47, 44.