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 3

Restoration of PI3P levels in the Pik3c2b Mtm1 dKO mice.

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Restoration of PI3P levels in the Pik3c2b Mtm1 dKO mice. (A) PI3P levels...
(A) PI3P levels are normalized in the dKO animals, as determined using a PI3P ELISA kit [purified lipid (pmol)/mass (g) of muscle tissue]. PI3P levels in WT muscle = 58 ± 21 pmol/g (n = 3), Mtm1 KO = 140 ± 20 pmol/g (n = 5, ***P = 0.01 vs. WT, **P = 0.01 vs. dKO), Pik3c2b KO = 68 ± 24 pmol/g (n = 3), and dKO = 56 ± 8 pmol/g (n = 4, P = 0.87 vs. WT, 1-way ANOVA followed by Dunnett’s multiple comparison test). (B) PI3P subcellular localization by IHC on tibialis anterior muscle. Labeling in WT and Pik3c2b KO is observed faintly in the perinuclear and membrane compartment, while staining in Mtm1 KO is seen diffusely, with intense intracellular staining in the sarcolemma of several myofibers (arrow). dKO muscle shows staining similar to WT, though with areas of mildly increased labeling within the sarcolemma of selected myofibers (arrowhead). Scale bars: 20 μm.