Calsarcin-2 deficiency increases exercise capacity in mice through calcineurin/NFAT activation
Norbert Frey, … , Hugo A. Katus, Eric N. Olson
Norbert Frey, … , Hugo A. Katus, Eric N. Olson
Published October 9, 2008
Citation Information: J Clin Invest. 2008;118(11):3598-3608. https://doi.org/10.1172/JCI36277.
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Research Article

Calsarcin-2 deficiency increases exercise capacity in mice through calcineurin/NFAT activation

Abstract

The composition of skeletal muscle, in terms of the relative number of slow- and fast-twitch fibers, is tightly regulated to enable an organism to respond and adapt to changing physical demands. The phosphatase calcineurin and its downstream targets, transcription factors of the nuclear factor of activated T cells (NFAT) family, play a critical role in this process by promoting the formation of slow-twitch, oxidative fibers. Calcineurin binds to calsarcins, a family of striated muscle–specific proteins of the sarcomeric Z-disc. We show here that mice deficient in calsarcin-2, which is expressed exclusively by fast-twitch muscle and encoded by the myozenin 1 (Myoz1) gene, have substantially reduced body weight and fast-twitch muscle mass in the absence of an overt myopathic phenotype. Additionally, Myoz1 KO mice displayed markedly improved performance and enhanced running distances in exercise studies. Analysis of fiber type composition of calsarcin-2–deficient skeletal muscles showed a switch toward slow-twitch, oxidative fibers. Reporter assays in cultured myoblasts indicated an inhibitory role for calsarcin-2 on calcineurin, and Myoz1 KO mice exhibited both an excess of NFAT activity and an increase in expression of regulator of calcineurin 1-4 (RCAN1-4), indicating enhanced calcineurin signaling in vivo. Taken together, these results suggest that calsarcin-2 modulates exercise performance in vivo through regulation of calcineurin/NFAT activity and subsequent alteration of the fiber type composition of skeletal muscle.

Authors

Norbert Frey, Derk Frank, Stefanie Lippl, Christian Kuhn, Harald Kögler, Tomasa Barrientos, Claudia Rohr, Rainer Will, Oliver J. Müller, Hartmut Weiler, Rhonda Bassel-Duby, Hugo A. Katus, Eric N. Olson

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Figure 6

Fiber type shift seen in skeletal muscle of Myoz1 KO mice.

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Fiber type shift seen in skeletal muscle of Myoz1 KO mice. (A) Immun...
(A) Immuno­fluorescence histochemistry for type IIa fibers using SC-71 antibody (green, FITC-labeled lectin). (B) An increase of 56.2% was found in the number of type IIa fibers/mm2 in the gastrocnemius of Myoz1 KO mice compared with WT littermates (n = 6–7 animals). (C) The cross-sectional area of type IIa fibers remained unchanged. (D) SDH staining of gastrocnemius showed an increase of SDH-positive fibers in Myoz1 KO mice compared with WT controls. (E) Quantification of SDH-positive fibers shows a 2.58-fold increase in Myoz1 KO mice compared with WT (n = 4 mice per group). (F) Immunofluorescence histochemistry for type IIb fibers using BF-F3 antibody (green, FITC-labeled lectin). (G) The number of type IIb fibers/mm2 increased in Myoz1 KO mice. (H) A reduction was found in the cross-sectional area of type IIb fibers (n = 105–178 cells). (I) Immunofluorescence histochemistry for type I fibers using NOQ7.5.4D antibody. (J) The number of type I fibers/mm2 increased in the soleus of Myoz1 KO mice compared with WT littermates (n = 4–6 mice). (K) Cross-sectional area of type I fibers increased in the soleus in Myoz1 KO mice compared with WT controls (n = 143–260 fibers). Scale bars: 100 μm. *P < 0.05, †P < 0.01, ‡P < 0.001.