Rationale: Calpain activation contributes to the development of infection induced diaphragm weakness, but the mechanisms by which infections activate calpain are poorly understood. We postulated that skeletal muscle calcium-dependent phospholipase A2 (cPLA2) is activated by cytokines and has downstream effects that induce calpain activation and muscle weakness. Objectives: We determined if cPLA2 activation mediates cytokine induced calpain activation in isolated skeletal muscle (C2C12) cells and infection induced diaphragm weakness in mice. Methods: C2C12 cells were treated with: (a) vehicle, (b) cytomix (TNFα 20 ng/ml, IL1β 50 U/ml, IFNγ 100 U/ml, LPS 10 μg/ml), (c) cytomix + AACOCF3, a cPLA2 inhibitor (10 µM), or (d) AACOCF3 alone. At 24 hours, we assessed cell cPLA2 activity, mitochondrial superoxide generation, calpain activity, and calpastatin activity. We also determined if SS31 (10 µg/ml), a mitochondrial superoxide scavenger, reduced cytomix mediated calpain activation. Finally, we determined if CDIBA (10 μM), a cPLA2 inhibitor, reduced diaphragm dysfunction due to CLP (cecal ligation puncture) in mice. Results: Cytomix increased C2C12 cell cPLA2 activity (p<0.001) and superoxide generation; AACOCF3 and SS31 blocked increases in superoxide generation (p<0.001). Cytomix also activated calpain (p< 0.001) and inactivated calpastatin (p<0.01); both AACOCF3 and SS31 prevented these changes. CLP reduced diaphragm force in mice, and CDIBA prevented this reduction (p<0.001). Conclusions: cPLA2 modulates cytokine induced calpain activation in cells and infection induced diaphragm weakness in animals. We speculate that therapies which inhibit cPLA2 may prevent diaphragm weakness in infected, critically ill patients.
- diaphragm weakness
- Copyright © 2015, American Journal of Physiology - Lung Cellular and Molecular Physiology