| 1. |
- Akkad, Hazem, et al.
(författare)
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Masseter Muscle Myofibrillar Protein Synthesis and Degradation in an Experimental Critical Illness Myopathy Model
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:4, s. e92622-
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Tidskriftsartikel (refereegranskat)abstract
- Critical illness myopathy (CIM) is a debilitating common consequence of modern intensive care, characterized by severe muscle wasting, weakness and a decreased myosin/actin (M/A) ratio. Limb/trunk muscles are primarily affected by this myopathy while cranial nerve innervated muscles are spared or less affected, but the mechanisms underlying these muscle-specific differences remain unknown. In this time-resolved study, the cranial nerve innervated masseter muscle was studied in a unique experimental rat intensive care unit (ICU) model, where animals were exposed to sedation, neuromuscular blockade (NMB), mechanical ventilation, and immobilization for durations varying between 6 h and 14d. Gel electrophoresis, immunoblotting, RT-PCR and morphological staining techniques were used to analyze M/A ratios, myofiber size, synthesis and degradation of myofibrillar proteins, and levels of heat shock proteins (HSPs). Results obtained in the masseter muscle were compared with previous observations in experimental and clinical studies of limb muscles. Significant muscle-specific differences were observed, i.e., in the masseter, the decline in M/A ratio and muscle fiber size was small and delayed. Furthermore, transcriptional regulation of myosin and actin synthesis was maintained, and Akt phosphorylation was only briefly reduced. In studied degradation pathways, only mRNA, but not protein levels of MuRF1, atrogin-1 and the autophagy marker LC3b were activated by the ICU condition. The matrix metalloproteinase MMP-2 was inhibited and protective HSPs were up-regulated early. These results confirm that the cranial nerve innervated masticatory muscles is less affected by the ICU-stress response than limb muscles, in accordance with clinical observation in ICU patients with CIM, supporting the model' credibility as a valid CIM model.
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| 2. |
- Corpeño Kalamgi, Rebeca
(författare)
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Critical illness myopathy : effects of specific intervention strategies and molecular mechanisms
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Skeletal muscles are a tissue with remarkable adaptability and are essential in the body in many aspects. The homeostasis of the muscles is vital for the maintenance of the body, thus muscle damage is associated with several diseases and leads to a poor quality of life. Acquired muscle weaknesses in the intensive care unit (ICU) is a major complication that occurs in severely ill patients and has a significant impact on the immune system, energy metabolism, amino acid reserves and temperature regulation in the body. Critical illness myopathy (CIM) is a myopathy that results from critical illness and is commonly found in mechanically ventilated ICU patients. It is characterized by paralysis of the limb muscles, atrophy and reduced muscle excitability. The exact cause and underlying mechanisms of the disease remain obscure, hence, the aim of this thesis was to achieve a better understanding of the cellular and molecular mechanisms underlying the muscle wasting and weakness seen in ICU patients with CIM. In accordance with this, a rodent ICU model was used to address the mechanistic and therapeutic aspects of the disease. This thesis has investigated the intracellular pathways controlling the mechanisms underlying muscle wasting in an ICU rat model and the effects of passive mechanical loading. Passive mechanical loading induced significant positive effects on muscle function in the limb muscles and was able to attenuate myosin protein loss, associated with mechanical silencing and CIM. It was also demonstrated that both fission and fusion events as well as mitophagy are significantly affected by mechanosensing. Mitochondria dynamic alterations induced by mechanical silencing were completely counteracted by passive mechanical loading. Additionally it is demonstrated that the temporal pattern and the lack of preferential myosin loss observed in the diaphragm in response to CMV and immobilization differs dramatically to what is occurring in the limb muscles. Further, the response of cranial nerve innervated masseter is also different from that of limb and diaphragm muscles. Early activation of heat shock proteins suggest that an enriched antioxidative profile in the masseter may play a role in the mechanism of preserved masticatory function in CIM.
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| 3. |
- Corpeno Kalamgi, Rebeca, et al.
(författare)
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Mechano-signalling pathways in an experimental intensive critical illness myopathy model.
- 2016
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Ingår i: Journal of Physiology. - 0022-3751 .- 1469-7793. ; 594:15, s. 4371-88
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Tidskriftsartikel (refereegranskat)abstract
- KEY POINTS: Using an experimental rat intensive care unit (ICU) model, not limited by early mortality, we have previously shown that passive mechanical loading attenuates the loss of muscle mass and force-generation capacity associated with the ICU intervention. Mitochondrial dynamics have recently been shown to play a more important role in muscle atrophy than previously recognized. In this study we demonstrate that mitochondrial dynamics, as well as mitophagy, is affected by mechanosensing at the transcriptional level, and muscle changes induced by unloading are counteracted by passive mechanical loading. The recently discovered ubiquitin ligases Fbxo31 and SMART are induced by mechanical silencing, an induction that similarly is prevented by passive mechanical loading.ABSTRACT: The complete loss of mechanical stimuli of skeletal muscles, i.e. loss of external strain related to weight bearing and internal strain related to activation of contractile proteins, in mechanically ventilated, deeply sedated and/or pharmacologically paralysed intensive care unit (ICU) patients is an important factor triggering the critical illness myopathy (CIM). Using a unique experimental ICU rat model, mimicking basic ICU conditions, we have recently shown that mechanical silencing is a dominant factor triggering the preferential loss of myosin, muscle atrophy and decreased specific force in fast- and slow-twitch muscles and muscle fibres. The aim of this study is to gain improved understanding of the gene signature and molecular pathways regulating the process of mechanical activation of skeletal muscle that are affected by the ICU condition. We have focused on pathways controlling myofibrillar protein synthesis and degradation, mitochondrial homeostasis and apoptosis. We demonstrate that genes regulating mitochondrial dynamics, as well as mitophagy are induced by mechanical silencing and that these effects are counteracted by passive mechanical loading. In addition, the recently identified ubiquitin ligases Fbxo31 and SMART are induced by mechanical silencing, an induction that is reversed by passive mechanical loading. Thus, mechano-cell signalling events are identified which may play an important role for the improved clinical outcomes reported in response to the early mobilization and physical therapy in immobilized ICU patients.
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| 4. |
- Marrero, Humberto D. J. Gonzalez, et al.
(författare)
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Neurogenic vs. Myogenic Origin of Acquired Muscle Paralysis in Intensive Care Unit (ICU) Patients : Evaluation of Different Diagnostic Methods
- 2020
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Ingår i: Diagnostics (Basel). - : MDPI. - 2075-4418. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Introduction. The acquired muscle paralysis associated with modern critical care can be of neurogenic or myogenic origin, yet the distinction between these origins is hampered by the precision of current diagnostic methods. This has resulted in the pooling of all acquired muscle paralyses, independent of their origin, into the term Intensive Care Unit Acquired Muscle Weakness (ICUAW). This is unfortunate since the acquired neuropathy (critical illness polyneuropathy, CIP) has a slower recovery than the myopathy (critical illness myopathy, CIM); therapies need to target underlying mechanisms and every patient deserves as accurate a diagnosis as possible. This study aims at evaluating different diagnostic methods in the diagnosis of CIP and CIM in critically ill, immobilized and mechanically ventilated intensive care unit (ICU) patients. Methods. ICU patients with acquired quadriplegia in response to critical care were included in the study. A total of 142 patients were examined with routine electrophysiological methods, together with biochemical analyses of myosin:actin (M:A) ratios of muscle biopsies. In addition, comparisons of evoked electromyographic (EMG) responses in direct vs. indirect muscle stimulation and histopathological analyses of muscle biopsies were performed in a subset of the patients. Results. ICU patients with quadriplegia were stratified into five groups based on the hallmark of CIM, i.e., preferential myosin loss (myosin:actin ratio, M:A) and classified as severe (M:A < 0.5; n = 12), moderate (0.5 <= M:A < 1; n = 40), mildly moderate (1 <= M:A < 1.5; n = 49), mild (1.5 <= M:A < 1.7; n = 24) and normal (1.7 <= M:A; n = 19). Identical M:A ratios were obtained in the small (4-15 mg) muscle samples, using a disposable semiautomatic microbiopsy needle instrument, and the larger (>80 mg) samples, obtained with a conchotome instrument. Compound muscle action potential (CMAP) duration was increased and amplitude decreased in patients with preferential myosin loss, but deviations from this relationship were observed in numerous patients, resulting in only weak correlations between CMAP properties and M:A. Advanced electrophysiological methods measuring refractoriness and comparing CMAP amplitude after indirect nerve vs. direct muscle stimulation are time consuming and did not increase precision compared with conventional electrophysiological measurements in the diagnosis of CIM. Low CMAP amplitude upon indirect vs. direct stimulation strongly suggest a neurogenic lesion, i.e., CIP, but this was rarely observed among the patients in this study. Histopathological diagnosis of CIM/CIP based on enzyme histochemical mATPase stainings were hampered by poor quantitative precision of myosin loss and the impact of pathological findings unrelated to acute quadriplegia. Conclusion. Conventional electrophysiological methods are valuable in identifying the peripheral origin of quadriplegia in ICU patients, but do not reliably separate between neurogenic vs. myogenic origins of paralysis. The hallmark of CIM, preferential myosin loss, can be reliably evaluated in the small samples obtained with the microbiopsy instrument. The major advantage of this method is that it is less invasive than conventional muscle biopsies, reducing the risk of bleeding in ICU patients, who are frequently receiving anticoagulant treatment, and it can be repeated multiple times during follow up for monitoring purposes.
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