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 2

Restoration of normal muscle structure in Pik3c2b Mtm1 dKO mice.

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Restoration of normal muscle structure in Pik3c2b Mtm1 dKO mice. (A) Cro...
(A) Cross sections from tibialis anterior muscle tissue of 35-day-old animals stained for H&E, SDH, and dysferlin. Mtm1 KO muscle has centrally located nuclei (arrow in H&E), mitochondrial aggregation and necklace myofibers on SDH staining (arrow), and abnormal distribution of dysferlin staining (double arrow). None of these changes were observed in muscle from dKO animals. Electron microscopic (EM) images reveal normal triad formation (arrowhead) in WT as well as dKO muscle but abnormal triads in Mtm1 KO with formation of longitudinal tubes (L-tubules, arrow) and absence of triads (double arrowhead). Scale bars: 20 μm; for EM: 500 nm. (B) dKO muscle has restored myofiber size, with average myofiber diameter for WT = 39 ± 5.8 μm (n = 6), for Mtm1 KO = 23 ± 4.1 μm (n = 4, **P < 0.01 vs. WT or dKO), and for dKO = 38 ± 4.3 μm (n = 5, P = 0.85 vs. WT). (C) Absence of central nuclei in the dKO. The average percent of central nuclei (per 100 fibers) in WT = 0% (n = 11), in Mtm1 KO = 7.4% ± 1.0% (n = 7, ***P < 0.001 vs. WT or dKO), and in dKO = 0.09% (n = 5, P = 0.2 vs. WT). (D) Quantification of number of triads per field. WT = 34 ± 3.1 (n = 4), Mtm1 KO = 10.7 ± 2.9 (n = 5, ***P < 0.001 vs. WT or dKO ), and dKO = 33 ± 4.6 (n = 5, P = 0.6 vs. WT). All comparisons in B–D done by 1-way ANOVA followed by Dunnett’s multicomparison test. (E) Schematic of the structure of triad with T-tubules, sarcoplasmic reticulum (SR), and the sarcomere ends (Z-line).