title: Cross-talk between the calpain and caspase-3 proteolytic systems in the diaphragm during prolonged mechanical ventilation.
abstract: OBJECTIVE
  Diaphragmatic weakness, due to both atrophy and contractile dysfunction, is a well-documented response following prolonged mechanical ventilation. Evidence indicates that activation of the proteases calpain and caspase-3 is essential for mechanical ventilation-induced diaphragmatic weakness to occur. We tested the hypothesis that a regulatory cross-talk exists between calpain and caspase-3 in the diaphragm during prolonged mechanical ventilation. To test this prediction, we determined whether selective pharmacological inhibition of calpain would prevent activation of caspase-3 and conversely whether selective inhibition of caspase-3 would abate calpain activation.
  
  
  METHODS
  Animal study.
  
  
  METHODS
  University Research Laboratory.
  
  
  METHODS
  Female Sprague-Dawley rats.
  
  
  METHODS
  Animals were randomly divided into control or one of three 12-hr mechanical ventilation groups that were treated with/without a selective pharmacological protease inhibitor: 1) control, 2) mechanical ventilation, 3) mechanical ventilation with a selective caspase-3 inhibitor, and 4) mechanical ventilation with a selective calpain inhibitor.
  
  
  RESULTS
  Compared to control, mechanical ventilation resulted in calpain and caspase-3 activation in the diaphragm accompanied by atrophy of type I, type IIa, and type IIx/IIb fibers. Independent inhibition of either calpain or caspase-3 prevented this mechanical ventilation-induced atrophy. Pharmacological inhibition of calpain prevented mechanical ventilation-induced activation of diaphragmatic caspase-3 and inhibition of caspase-3 prevented activation of diaphragmatic calpain. Furthermore, calpain inhibition also prevented the activation of caspase-9 and caspase-12, along with the cleavage of Bid to tBid, all upstream signals for caspase-3 activation. Lastly, caspase-3 inhibition prevented the mechanical ventilation-induced degradation of the endogenous calpain inhibitor, calpastatin.
  
  
  CONCLUSIONS
  Collectively, these results indicate that mechanical ventilation-induced diaphragmatic atrophy is dependent on the activation of both calpain and caspase-3. Importantly, these findings provide the first experimental evidence in diaphragm muscle that calpain inhibition prevents the activation of caspase-3 and vice versa and caspase-3 inhibition prevents the activation of calpain. These findings support our hypothesis that a regulatory calpain/caspase-3 cross-talk exists whereby calpain can promote caspase-3 activation and active caspase-3 can enhance calpain activity in diaphragm muscle during prolonged mechanical ventilation.
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA.
authors.forename: W Bradley
authors.initials: WB
authors.lastname: Nelson
authors.forename: Ashley J
authors.initials: AJ
authors.lastname: Smuder
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Hudson
authors.forename: Erin E
authors.initials: EE
authors.lastname: Talbert
authors.forename: Scott K
authors.initials: SK
authors.lastname: Powers
mesh_terms: D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism*; D061945:Caspase Inhibitors; D003964:Diaphragm / Q000201:enzymology* / Q000473:pathology / Q000503:physiopathology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005260:Female; D009133:Muscular Atrophy / Q000209:etiology / Q000503:physiopathology; D059748:Proteolysis; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000009:adverse effects; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D061945:Caspase Inhibitors; D002154:Calpain; D053148:Caspase 3