| 1. |
- Banduseela, Varuna C., et al.
(författare)
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Gene expression and muscle fiber function in a porcine ICU model
- 2009
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Ingår i: Physiological Genomics. - : American Physiological Society. - 1094-8341 .- 1531-2267. ; 39:3, s. 141-159
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Tidskriftsartikel (refereegranskat)abstract
- Skeletal muscle wasting and impaired muscle function in response to mechanical ventilation and immobilization in intensive care unit (ICU) patients are clinically challenging partly due to 1) the poorly understood intricate cellular and molecular networks and 2) the unavailability of an animal model mimicking this condition. By employing a unique porcine model mimicking the conditions in the ICU with long-term mechanical ventilation and immobilization, we have analyzed the expression profile of skeletal muscle biopsies taken at three time points during a 5-day period. Among the differentially regulated transcripts, extracellular matrix, energy metabolism, sarcomeric and LIM protein mRNA levels were downregulated, while ubiquitin proteasome system, cathepsins, oxidative stress responsive genes and heat shock proteins (HSP) mRNAs were upregulated. Despite 5 days of immobilization and mechanical ventilation single muscle fiber cross-sectional areas as well as the maximum force generating capacity at the single muscle fiber level were preserved. It is proposed that HSP induction in skeletal muscle is an inherent, primary, but temporary protective mechanism against protein degradation. To our knowledge, this is the first study that isolates the effect of immobilization and mechanical ventilation in an ICU condition from various other cofactors.
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| 2. |
- Ochala, Julien, et al.
(författare)
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Diaphragm muscle weakness in an experimental porcine intensive care unit model
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:6
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Tidskriftsartikel (refereegranskat)abstract
- In critically ill patients, mechanisms underlying diaphragm muscle remodeling and resultant dysfunction contributing to weaning failure remain unclear. Ventilator-induced modifications as well as sepsis and administration of pharmacological agents such as corticosteroids and neuromuscular blocking agents may be involved. Thus, the objective of the present study was to examine how sepsis, systemic corticosteroid treatment (CS) and neuromuscular blocking agent administration (NMBA) aggravate ventilator-related diaphragm cell and molecular dysfunction in the intensive care unit. Piglets were exposed to different combinations of mechanical ventilation and sedation, endotoxin-induced sepsis, CS and NMBA for five days and compared with sham-operated control animals. On day 5, diaphragm muscle fibre structure (myosin heavy chain isoform proportion, cross-sectional area and contractile protein content) did not differ from controls in any of the mechanically ventilated animals. However, a decrease in single fibre maximal force normalized to cross-sectional area (specific force) was observed in all experimental piglets. Therefore, exposure to mechanical ventilation and sedation for five days has a key negative impact on diaphragm contractile function despite a preservation of muscle structure. Post-translational modifications of contractile proteins are forwarded as one probable underlying mechanism. Unexpectedly, sepsis, CS or NMBA have no significant additive effects, suggesting that mechanical ventilation and sedation are the triggering factors leading to diaphragm weakness in the intensive care unit.
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| 3. |
- Ochala, Julien, et al.
(författare)
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Preferential skeletal muscle myosin loss in response to mechanical silencing in a novel rat intensive care unit model : underlying mechanisms
- 2011
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 589:8, s. 2007-2026
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Tidskriftsartikel (refereegranskat)abstract
- Non-technical summary Wasting and severely impaired function of skeletal muscle is frequently observed in critically ill intensive care unit (ICU) patients, with negative consequences for recovery and quality of life. An experimental rat ICU model has been used to study the mechanisms underlying this unique wasting condition in neuromuscularly blocked and mechanically ventilated animals at durations varying between 6 h and 2 weeks. The complete 'mechanical silencing' of skeletal muscle (removal of both weight bearing and activation) resulted in a specific myopathy frequently observed in ICU patients and characterized by a preferential loss of the motor protein myosin. A highly complex and coordinated protein synthesis and degradation system was observed in the time-resolved analyses. It is suggested the 'mechanical silencing' of skeletal muscle is a dominating factor triggering the specific myopathy associated with the ICU intervention, and strongly supporting the importance of interventions counteracting the complete unloading in ICU patients.The muscle wasting and impaired muscle function in critically ill intensive care unit (ICU) patients delay recovery from the primary disease, and have debilitating consequences that can persist for years after hospital discharge. It is likely that, in addition to pernicious effects of the primary disease, the basic life support procedures of long-term ICU treatment contribute directly to the progressive impairment of muscle function. This study aims at improving our understanding of the mechanisms underlying muscle wasting in ICU patients by using a unique experimental rat ICU model where animals are mechanically ventilated, sedated and pharmacologically paralysed for duration varying between 6 h and 14 days. Results show that the ICU intervention induces a phenotype resembling the severe muscle wasting and paralysis associated with the acute quadriplegic myopathy (AQM) observed in ICU patients, i.e. a preferential loss of myosin, transcriptional down-regulation of myosin synthesis, muscle atrophy and a dramatic decrease in muscle fibre force generation capacity. Detailed analyses of protein degradation pathways show that the ubiquitin proteasome pathway is highly involved in this process. A sequential change in localisation of muscle-specific RING finger proteins 1/2 (MuRF1/2) observed during the experimental period is suggested to play an instrumental role in both transcriptional regulation and protein degradation. We propose that, for those critically ill patients who develop AQM, complete mechanical silencing, due to pharmacological paralysis or sedation, is a critical factor underlying the preferential loss of the molecular motor protein myosin that leads to impaired muscle function or persisting paralysis.
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