Mechanical ventilation-induced diaphragm disuse in humans triggers autophagy.
BACKGROUND
Controlled mechanical ventilation (CMV) results in atrophy of the human diaphragm. The autophagy-lysosome pathway (ALP) contributes to skeletal muscle proteolysis, but its contribution to diaphragmatic protein degradation in mechanically ventilated patients is unknown.


OBJECTIVE
To evaluate the autophagy pathway responses to CMV in the diaphragm and limb muscles of humans and to identify the roles of FOXO transcription factors in these responses.


METHODS
Muscle biopsies were obtained from nine control subjects and nine brain-dead organ donors. Subjects were mechanically ventilated for 2 to 4 hours and 15 to 276 hours, respectively. Activation of the ubiquitin-proteasome system was detected by measuring mRNA expressions of Atrogin-1, MURF1, and protein expressions of UBC2, UBC4, and the α subunits of the 20S proteasome (MCP231). Activation of the ALP was detected by electron microscopy and by measuring the expressions of several autophagy-related genes. Total carbonyl content and HNE-protein adduct formation were measured to assess oxidative stress. Total AKT, phosphorylated and total FOXO1, and FOXO3A protein levels were also measured.


RESULTS
Prolonged CMV triggered activation of the ALP as measured by the appearance of autophagosomes in the diaphragm and increased expressions of autophagy-related genes, as compared with controls. Induction of autophagy was associated with increased protein oxidation and enhanced expression of the FOXO1 gene, but not the FOXO3A gene. CMV also triggered the inhibition of both AKT expression and FOXO1 phosphorylation.


CONCLUSIONS
We propose that prolonged CMV causes diaphragm disuse, which, in turn, leads to activation of the ALP through oxidative stress and the induction of the FOXO1 transcription factor.
Hussain
Sabah N A
SN
McGill University, Montréal, Québec, Canada. sabah.hussain@muhc.mcgill.ca
Mofarrahi
Mahroo
M
Sigala
Ioanna
I
Kim
Ho Cheol
HC
Vassilakopoulos
Theodoros
T
Maltais
Francois
F
Bellenis
Ion
I
Chaturvedi
Rakesh
R
Gottfried
Stewart B
SB
Metrakos
Peter
P
Danialou
Gawiyou
G
Matecki
Stefan
S
Jaber
Samir
S
Petrof
Basil J
BJ
Goldberg
Peter
P
D000368:Aged; D001343:Autophagy; D015153:Blotting, Western; D003964:Diaphragm / Q000378:metabolism / Q000503:physiopathology*; D005260:Female; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D009124:Muscle Proteins / Q000378:metabolism; D009133:Muscular Atrophy / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D018384:Oxidative Stress; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012121:Respiration, Artificial / Q000009:adverse effects*
C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D009124:Muscle Proteins; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex