Mechanical ventilation (MV) is a life-saving intervention for many
critically ill patients. Unfortunately, an unintended consequence of prolonged MV is the rapid development of diaphragmatic
atrophy and contractile dysfunction, known as
ventilator-induced diaphragm dysfunction (VIDD). Although the mechanism(s) responsible for VIDD are not fully understood, abundant evidence reveals that oxidative stress leading to the activation of the major proteolytic systems (i.e., autophagy,
ubiquitin-
proteasome,
caspase, and
calpain) plays a dominant role. Of the proteolytic systems involved in VIDD,
calpain has received limited experimental attention due to the longstanding dogma that
calpain plays a minor role in inactivity-induced
muscle atrophy. Guided by preliminary experiments, we tested the hypothesis that activation of calpains play an essential role in MV-induced oxidative stress and the development of VIDD. This premise was rigorously tested by transgene overexpression of
calpastatin, an endogenous inhibitor of calpains. Animals with/without transfection of the
calpastatin gene in diaphragm muscle fibers were exposed to 12 h of MV. Results confirmed that overexpression of
calpastatin barred MV-induced activation of
calpain in diaphragm fibers. Importantly, deterrence of
calpain activation protected the diaphragm against MV-induced oxidative stress, fiber
atrophy, and contractile dysfunction. Moreover, prevention of
calpain activation in the diaphragm forstalled MV-induced
mitochondrial dysfunction and prevented MV-induced activation of
caspase-3 along with the transcription of muscle specific E3
ligases. Collectively, these results support the hypothesis that
calpain activation plays an essential role in the early development of VIDD. Further, these findings provide the first direct evidence that
calpain plays an important function in inactivity-induced
mitochondrial dysfunction and oxidative stress in skeletal muscle fibers.