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 7

Calsarcin-2 inhibits calcineurin activity in vitro and in vivo.

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Calsarcin-2 inhibits calcineurin activity in vitro and in vivo. C2C12 ce...
C2C12 cells containing an NFAT reporter plasmid (NFATluc) were transfected with (A) full-length calcineurin A (CnA), an NFAT expression plasmid, and an increasing amount of calsarcin-2 or (B) constitutively active calcineurin (ΔC) and NFAT expression plasmid, resulting in induction of the NFAT-luciferase reporter (P < 0.01). (A) After transfection, cells underwent treatment with the calcineurin stimulators PMA and ionomycin (PMA+Iono). PMA and ionomycin strongly induced NFAT reporter activity, while increasing amounts of calsarcin-2 completely abrogated the increase in reporter gene activity. (B) The presence of calsarcin-2 inhibited the calcineurin activity in a dose-dependent and significant manner. (C) Western blot analysis (left) and densitometric quantification (right) showing induction of the endogenous calcineurin-responsive Rcan1-4 gene in Myoz1 KO mice and (D) an increase of nuclear NFATc4 in the gastrocnemius of Myoz1 KO mice compared with that of WT littermates. *P < 0.05, †P < 0.01, ‡P < 0.001.