RESUMO
Mechanical ventilation (MV) is a life-saving measure in many critically ill patients. However, prolonged MV results in diaphragm dysfunction that contributes to the frequent difficulty in weaning patients from the ventilator. The molecular mechanisms underlying ventilator-induced diaphragm dysfunction (VIDD) remain poorly understood. We report here that MV induces myonuclear DNA fragmentation (3-fold increase; P<0.01) and selective activation of caspase 9 (P<0.05) and Bcl2-interacting mediator of cell death (Bim; 2- to 7-fold increase; P<0.05) in human diaphragm. MV also statistically significantly down-regulates mitochondrial gene expression and induces oxidative stress. In cultured muscle cells, we show that oxidative stress activates each of the catabolic pathways thought to underlie VIDD: apoptotic (P<0.05), proteasomal (P<0.05), and autophagic (P<0.01). Further, silencing Bim expression blocks (P<0.05) oxidative stress-induced apoptosis. Overlapping the gene expression profiles of MV human diaphragm and H2O2-treated muscle cells, we identify Fos, FoxO1, and Stat3 as regulators of Bim expression as well as of expression of the catabolic markers atrogin and LC3. We thus identify a novel Fos/FoxO1/Stat3-Bim intrinsic apoptotic pathway and establish the centrality of oxidative stress in the development of VIDD. This information may help in the design of specific drugs to prevent this condition.
Assuntos
Proteínas Reguladoras de Apoptose/metabolismo , Apoptose/fisiologia , Diafragma/fisiologia , Fatores de Transcrição Forkhead/metabolismo , Proteínas de Membrana/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Fator de Transcrição STAT3/metabolismo , Adolescente , Adulto , Idoso , Proteínas Reguladoras de Apoptose/genética , Proteína 11 Semelhante a Bcl-2 , Caspase 9/metabolismo , Linhagem Celular , Fragmentação do DNA , Diafragma/citologia , Feminino , Proteína Forkhead Box O1 , Fatores de Transcrição Forkhead/genética , Humanos , Masculino , Proteínas de Membrana/genética , Pessoa de Meia-Idade , Mitocôndrias Musculares/metabolismo , Estresse Oxidativo , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas c-fos/genética , Respiração Artificial/efeitos adversos , Fator de Transcrição STAT3/genética , Adulto JovemRESUMO
In this study we examined whether the foraging for artificial blood affected the behavioral responsiveness of leeches to electrical stimulation of the body wall. After foraging for artificial blood, electrical stimulation of the posterior end of the leech significantly increased the percentage of stimulation trials that elicited locomotory activity--swimming and crawling--compared to the behaviors elicited when leeches did not forage or foraged for normal saline. On the other hand, shortening always dominated the behavioral profile of the leech to anterior stimulation even after foraging for artificial blood. In intact anterior end-isolated nerve cord preparations, we also found that application of artificial blood to the intact anterior end was sufficient to modify motor responsiveness to DP nerve stimulation. Full strength artificial blood had an overall negative effect on the likelihood of DP nerve stimulation initiating swimming and on the average length of elicited swim episodes compared to when pond water surrounded the anterior end. Application of a 10% solution of artificial blood to the anterior end led to an increase in the likelihood of DP nerve stimulation eliciting swimming.
