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Skeletal muscle calcineurin: influence of phenotype adaptation and atrophy
E E Spangenburg1, J H Williams, R R Roy
1Muscle Function Laboratory, Department of Human Nutrition, Foods, and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
Abstract:
Calcineurin (CaN) has been implicated as a signaling molecule that can transduce physiological stimuli (e.g., contractile activity) into molecular signals that initiate slow-fiber phenotypic gene expression and muscle growth. To determine the influence of muscle phenotype and atrophy on CaN levels in muscle, the levels of soluble CaN in rat muscles of varying phenotype, as assessed by myosin heavy chain (MHC)-isoform proportions, were determined by Western blotting. CaN levels were significantly greater in the plantaris muscle containing predominantly fast (IIx and IIb) MHC isoforms, compared with the soleus (predominantly type I MHC) or vastus intermedius (VI, contains all 4 adult MHC isoforms). Three months after a complete spinal cord transection (ST), the CaN levels in the VI muscle were significantly reduced, despite a significant increase in fast MHC isoforms. Surprisingly, the levels of CaN in the VI were highly correlated with muscle mass but not MHC isoform proportions in ST and control rats. These data demonstrate that CaN levels in skeletal muscle are highly correlated to muscle mass and that the normal relationship with phenotype is lost after ST.
Insights
Calcineurin (CaN) levels in skeletal muscle correlate with muscle mass, not fiber type, after spinal cord injury. This suggests CaN signaling
Area of Science:
- Skeletal muscle physiology
- Molecular signaling
- Neuroscience
Background:
- Calcineurin (CaN) acts as a signaling molecule, linking physiological stimuli like muscle activity to gene expression and muscle growth.
- Understanding CaN's role in different muscle types and during atrophy is crucial for muscle health research.
Purpose of the Study:
- To investigate the impact of muscle phenotype and atrophy on calcineurin (CaN) levels in rat skeletal muscles.
- To determine the relationship between CaN levels, muscle mass, and myosin heavy chain (MHC) isoform proportions following spinal cord transection (ST).
Main Methods:
- Western blotting was used to quantify soluble CaN levels in rat muscles with varying myosin heavy chain (MHC) isoform compositions.
- Muscles analyzed included plantaris, soleus, and vastus intermedius (VI) from control and ST-induced atrophied rats.
Main Results:
- CaN levels were higher in fast-twitch (plantaris) muscles compared to slow-twitch (soleus) or mixed-fiber (VI) muscles.
- Following spinal cord transection (ST), CaN levels in VI muscle decreased significantly, despite an increase in fast MHC isoforms.
- CaN levels in VI muscle strongly correlated with muscle mass but not MHC isoform proportions in both control and ST rats.
Conclusions:
- Skeletal muscle calcineurin (CaN) levels are primarily associated with muscle mass.
- The typical correlation between CaN levels and muscle fiber type (phenotype) is disrupted after spinal cord transection (ST).