Caspase-3 regulation of diaphragm myonuclear domain during mechanical ventilation-induced atrophy.
BACKGROUND
Unloading the diaphragm via mechanical ventilation (MV) results in rapid diaphragmatic fiber atrophy. It is unknown whether the myonuclear domain (cytoplasmic myofiber volume/myonucleus) of diaphragm myofibers is altered during MV.


OBJECTIVE
We tested the hypothesis that MV-induced diaphragmatic atrophy is associated with a loss of myonuclei via a caspase-3-mediated, apoptotic-like mechanism resulting in a constant myonuclear domain.


METHODS
To test this postulate, Sprague-Dawley rats were randomly assigned to a control group or to experimental groups exposed to 6 or 12 h of MV with or without administration of a caspase-3 inhibitor.


RESULTS
After 12 h of MV, type I and type IIa diaphragm myofiber areas were decreased by 17 and 23%, respectively, and caspase-3 inhibition attenuated this decrease. Diaphragmatic myonuclear content decreased after 12 h of MV and resulted in the maintenance of a constant myonuclear domain in all fiber types. Both 6 and 12 h of MV resulted in caspase-3-dependent increases in apoptotic markers in the diaphragm (e.g., number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive nuclei and DNA fragmentation). Caspase-3-dependent increases in apoptotic markers occurred after 6 h of MV, before the onset of myofiber atrophy.


CONCLUSIONS
Collectively, these data support the hypothesis that the myonuclear domain of diaphragm myofibers is maintained during prolonged MV and that caspase-3-mediated myonuclear apoptosis contributes to this process.
McClung
Joseph M
JM
Department of Applied Physiology and Kinesiology, University of Florida, Room 25, Florida Gym, Gainesville, FL 32611, USA.
Kavazis
Andreas N
AN
DeRuisseau
Keith C
KC
Falk
Darin J
DJ
Deering
Melissa A
MA
Lee
Youngil
Y
Sugiura
Takao
T
Powers
Scott K
SK
D000818:Animals; D017209:Apoptosis; D001284:Atrophy / Q000201:enzymology; D015415:Biomarkers / Q000032:analysis / Q000378:metabolism; D053148:Caspase 3 / Q000032:analysis / Q000378:metabolism*; D003964:Diaphragm / Q000201:enzymology* / Q000473:pathology*; D005260:Female; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000009:adverse effects*
D015415:Biomarkers; D053148:Caspase 3