| 1. |
- Cacciani, Nicola, et al.
(author)
-
Chaperone co-inducer BGP-15 mitigates early contractile dysfunction of the soleus muscle in a rat ICU model
- 2020
-
In: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 229:1
-
Journal article (peer-reviewed)abstract
- Aim Critical illness myopathy (CIM) represents a common consequence of modern intensive care, negatively impacting patient health and significantly increasing health care costs; however, there is no treatment available apart from symptomatic and supportive interventions. The chaperone co-inducer BGP-15 has previously been shown to have a positive effect on the diaphragm in rats exposed to the intensive care unit (ICU) condition. In this study, we aim to explore the effects of BGP-15 on a limb muscle (soleus muscle) in response to the ICU condition. Methods Sprague-Dawley rats were subjected to the ICU condition for 5, 8 and 10 days and compared with untreated sham-operated controls. Results BGP-15 significantly improved soleus muscle fibre force after 5 days exposure to the ICU condition. This improvement was associated with the protection of myosin from post-translational myosin modifications, improved mitochondrial structure/biogenesis and reduced the expression of MuRF1 and Fbxo31 E3 ligases. At longer durations (8 and 10 days), BGP-15 had no protective effect when the hallmark of CIM had become manifest, that is, preferential loss of myosin. Unrelated to the effects on skeletal muscle, BGP-15 had a strong positive effect on survival compared with untreated animals. Conclusions BGP-15 treatment improved soleus muscle fibre and motor protein function after 5 days exposure to the ICU condition, but not at longer durations (8 and 10 days) when the preferential loss of myosin was manifest. Thus, long-term CIM interventions targeting limb muscle fibre/myosin force generation capacity need to consider both the post-translational modifications and the loss of myosin.
|
|
| 2. |
- Cacciani, Nicola, et al.
(author)
-
A prospective clinical study on the mechanisms underlying critical illness myopathy : A time-course approach
- 2022
-
In: Journal of Cachexia, Sarcopenia and Muscle. - : John Wiley & Sons. - 2190-5991 .- 2190-6009. ; 13:6, s. 2669-2682
-
Journal article (peer-reviewed)abstract
- Background: Critical illness myopathy (CIM) is a consequence of modern critical care resulting in general muscle wasting and paralyses of all limb and trunk muscles, resulting in prolonged weaning from the ventilator, intensive care unit (ICU) treatment and rehabilitation. CIM is associated with severe morbidity/mortality and significant negative socioeconomic consequences, which has become increasingly evident during the current COVID-19 pandemic, but underlying mechanisms remain elusive.Methods: Ten neuro-ICU patients exposed to long-term controlled mechanical ventilation were followed with repeated muscle biopsies, electrophysiology and plasma collection three times per week for up to 12 days. Single muscle fibre contractile recordings were conducted on the first and final biopsy, and a multiomics approach was taken to analyse gene and protein expression in muscle and plasma at all collection time points.Results: (i) A progressive preferential myosin loss, the hallmark of CIM, was observed in all neuro-ICU patients during the observation period (myosin:actin ratio decreased from 2.0 in the first to 0.9 in the final biopsy, P < 0.001). The myosin loss was coupled to a general transcriptional downregulation of myofibrillar proteins (P < 0.05; absolute fold change >2) and activation of protein degradation pathways (false discovery rate [FDR] <0.1), resulting in significant muscle fibre atrophy and loss in force generation capacity, which declined >65% during the 12 day observation period (muscle fibre cross-sectional area [CSA] and maximum single muscle fibre force normalized to CSA [specific force] declined 30% [P < 0.007] and 50% [P < 0.0001], respectively). (ii) Membrane excitability was not affected as indicated by the maintained compound muscle action potential amplitude upon supramaximal stimulation of upper and lower extremity motor nerves. (iii) Analyses of plasma revealed early activation of inflammatory and proinflammatory pathways (FDR < 0.1), as well as a redistribution of zinc ions from plasma.Conclusions: The mechanical ventilation-induced lung injury with release of cytokines/chemokines and the complete mechanical silencing uniquely observed in immobilized ICU patients affecting skeletal muscle gene/protein expression are forwarded as the dominant factors triggering CIM.
|
|
| 3. |
- Qaisar, Rizwan, 1982-
(author)
-
Myonuclear Organization and Regulation of Muscle Contraction in Single Muscle Fibres : Effects of Ageing, Gender, Species, Endocrine Factors and Muscle Size
- 2012
-
Doctoral thesis (other academic/artistic)abstract
- The skeletal muscle fibre is a syncitium where each myonucleus regulates the gene products in a finite volume of cytoplasm i.e., the myonuclear domain (MND). A novel image analysis algorithm applied to confocal images, analyzing MND size and myonuclear spatial distribution in 3-dimensions in single skeletal muscle fibres has been used in this project. The goal was to explore the modulation of myonuclei count and MND size in response to muscle adaptation processes. The effects of ageing, gender, hormones, muscle hypertrophy and body size were investigated on MND size. A strong linear relationship was found between MND size and body size in the muscle fibres from mammals representing a 100,000-fold difference in body size. Independent of species, MND size was highly dependent on MyHC isoform type and mitochondrial contents of skeletal muscle fibres. In hypertrophic mice, a significant effect of MND size on specific force and myosin content was observed. This effect was muscle fibre type-specific and shows that the bigger MNDs in fast-twitch EDL muscle fibres are optimally tuned for force production while smaller MNDs in slow-twitch soleus muscle fibres have a much more dynamic range of hypertrophy without functional compromise. This indicates a critical volume individual myonuclei can support efficiently for a proportional gain in muscle fibre force and size. In human muscle fibres, spatial organization of myonuclei was affected by both ageing and MyHC isoform expression. In fibres expressing type I MyHC isoform, an increased MND size variability and myonuclear aggregates were observed in old age although average MND size was unchanged. In contrast, in type IIa fibres, the average MND size was smaller reflecting smaller size of muscle fibres. Those changes may influence the transcriptional activity per myonucleus and/or local cooperatively of myonuclei in a gender and muscle fibre-type specific manner. Finally, hormone replacement therapy was shown to negate menopause-related functional impairment in skeletal muscle fibres. The positive effect on force was due to quantitative effect in fibres expressing fast myosin isoform while the effect was both quantitative and qualitative in fibres expressing slow myosin isoform. The effect on MND size was fibre type dependent and was achieved by significantly reducing domain size in slow- but not the fast-twitch muscle fibres. Together, our data suggest that modulation of myonuclei count and MND size is a mechanism contributing to remodelling of skeletal muscle in muscle adaptation process. These findings should be considered when developing therapeutic approaches towards restoring muscle mass and strength in muscle wasting conditions.
|
|
| 4. |
- Corpeno, Rebeca, et al.
(author)
-
Time-course analysis of mechanical ventilation-induced diaphragm contractile muscle dysfunction in the rat
- 2014
-
In: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 592:17, s. 3859-3880
-
Journal article (peer-reviewed)abstract
- Controlled mechanical ventilation (CMV) plays a key role in triggering the impaired diaphragm muscle function and the concomitant delayed weaning from the respirator in critically ill intensive care unit (ICU) patients. To date, experimental and clinical studies have primarily focused on early effects on the diaphragm by CMV, or at specific time points. To improve our understanding of the mechanisms underlying the impaired diaphragm muscle function in response to mechanical ventilation, we have performed time‐resolved analyses between 6 h and 14 days using an experimental rat ICU model allowing detailed studies of the diaphragm in response to long‐term CMV. A rapid and early decline in maximum muscle fibre force and preceding muscle fibre atrophy was observed in the diaphragm in response to CMV, resulting in an 85% reduction in residual diaphragm fibre function after 9–14 days of CMV. A modest loss of contractile proteins was observed and linked to an early activation of the ubiquitin proteasome pathway, myosin:actin ratios were not affected and the transcriptional regulation of myosin isoforms did not show any dramatic changes during the observation period. Furthermore, small angle X‐ray diffraction analyses demonstrate that myosin can bind to actin in an ATP‐dependent manner even after 9–14 days of exposure to CMV. Thus, quantitative changes in muscle fibre size and contractile proteins are not the dominating factors underlying the dramatic decline in diaphragm muscle function in response to CMV, in contrast to earlier observations in limb muscles. The observed early loss of subsarcolemmal neuronal nitric oxide synthase activity, onset of oxidative stress, intracellular lipid accumulation and post‐translational protein modifications strongly argue for significant qualitative changes in contractile proteins causing the severely impaired residual function in diaphragm fibres after long‐term mechanical ventilation. For the first time, the present study demonstrates novel changes in the diaphragm structure/function and underlying mechanisms at the gene, protein and cellular levels in response to CMV at a high temporal resolution ranging from 6 h to 14 days.
|
|
| 5. |
- Addinsall, Alex B., et al.
(author)
-
Electrical stimulated GLUT4 signalling attenuates critical illness-associated muscle wasting
- 2022
-
In: Journal of Cachexia, Sarcopenia and Muscle. - : John Wiley & Sons. - 2190-5991 .- 2190-6009. ; 13:4, s. 2162-2174
-
Journal article (peer-reviewed)abstract
- Background Critical illness myopathy (CIM) is a debilitating condition characterized by the preferential loss of the motor protein myosin. CIM is a by-product of critical care, attributed to impaired recovery, long-term complications, and mortality. CIM pathophysiology is complex, heterogeneous and remains incompletely understood; however, loss of mechanical stimuli contributes to critical illness-associated muscle atrophy and weakness. Passive mechanical loading and electrical stimulation (ES) therapies augment muscle mass and function. While having beneficial outcomes, the mechanistic underpinning of these therapies is less known. Therefore, here we aimed to assess the mechanism by which chronic supramaximal ES ameliorates CIM in a unique experimental rat model of critical care. Methods Rats were subjected to 8 days of critical care conditions entailing deep sedation, controlled mechanical ventilation, and immobilization with and without direct soleus ES. Muscle size and function were assessed at the single cell level. RNAseq and western blotting were employed to understand the mechanisms driving ES muscle outcomes in CIM. Results Following 8 days of controlled mechanical ventilation and immobilization, soleus muscle mass, myosin : actin ratio, and single muscle fibre maximum force normalized to cross-sectional area (CSA; specific force) were reduced by 40-50% (P < 0.0001). ES significantly reduced the loss of soleus muscle fibre CSA and myosin : actin ratio by approximately 30% (P < 0.05) yet failed to effect specific force. RNAseq pathway analysis revealed downregulation of insulin signalling in the soleus muscle following critical care, and GLUT4 trafficking was reduced by 55% leading to an 85% reduction of muscle glycogen content (P < 0.01). ES promoted phosphofructokinase and insulin signalling pathways to control levels (P < 0.05), consistent with the maintenance of GLUT4 translocation and glycogen levels. AMPK, but not AKT, signalling pathway was stimulated following ES, where the downstream target TBC1D4 increased 3 logFC (P = 0.029) and AMPK-specific P-TBC1D4 levels were increased approximately two-fold (P = 0.06). Reduction of muscle protein degradation rather than increased synthesis promoted soleus CSA, as ES reduced E3 ubiquitin proteins, Atrogin-1 (P = 0.006) and MuRF1 (P = 0.08) by approximately 50%, downstream of AMPK-FoxO3. Conclusions ES maintained GLUT4 translocation through increased AMPK-TBC1D4 signalling leading to improved muscle glucose homeostasis. Soleus CSA and myosin content was promoted through reduced protein degradation via AMPK-FoxO3 E3 ligases, Atrogin-1 and MuRF1. These results demonstrate chronic supramaximal ES reduces critical care associated muscle wasting, preserved glucose signalling, and reduced muscle protein degradation in CIM.
|
|
| 6. |
- Addinsall, Alex B., et al.
(author)
-
Ruxolitinib Prevents Ventilator Induced Diaphragm Dysfunction
- 2022
-
In: The FASEB Journal. - : John Wiley & Sons. - 0892-6638 .- 1530-6860. ; 36:S1
-
Journal article (peer-reviewed)abstract
- Mechanical ventilation (MV), however brief results in the loss of diaphragm muscle mass and strength, termed ventilator induced diaphragm dysfunction (VIDD). VIDD increases dependence, complicates and prolongs weaning and significantly increases discharge mortality rate and health care costs worldwide. The Janus kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) pathway was recently identified as an important signalling pathway implicated in VIDD, upregulated in the diaphragm following MV and limb muslces during critical care. Regulation of STAT3 is imperritve to skeletal muscle mass and function, as STAT3 is required in proper muscle growth and regeneration, while chronic activation of STAT3 is implicated in muscle dysfunction. As JAK/STAT pathway inhibition can restrict the development of chronic muscle wasting conditons, this study aimed to explore the therapeutic potential of Ruxolitinib, an approved JAK1/2 inhibitor for myelofibrosis, for treatment of CIM. We hypothesised Ruxolitinib would reduce loss of muscle mass and function associated with VIDD. Here, rats were subjected to five days controlled MV (CMV) with and without daily Ruxolitinib gavage. Five-days CMV significantly reduced diaphragm muscle size and impaired specific force, which was associated with 2-fold upregulation of P-STAT3, disrupted mitochondrial structure and respiratory function. Expression of the motor protein myosin was not affected, however CMV may alter myosin function through deamidation post translational modification. Ruxolitinib increases five-day survival rate, restored P-STAT3 expression and preserved diaphragm muscle size and specific force. These functional improvements were associated with improved mitochondrial structure, augmented mitochondrial respiratory function and reversal or augmentation of myosin deamidations. These results provide evidence of the preclinical potential of repurposing Ruxolitinib for the treatment of VIDD.
|
|
| 7. |
- Cristea, Alexander, et al.
(author)
-
Effects of aging and gender on the spatial organization of nuclei in single human skeletal muscle cells
- 2010
-
In: Aging Cell. - : Wiley. - 1474-9718 .- 1474-9726. ; 9:5, s. 685-697
-
Journal article (peer-reviewed)abstract
- The skeletal muscle fibre is a syncitium where each myonucleus regulates the gene products in a finite volume of the cytoplasm, i.e., the myonuclear domain (MND). We analysed aging- and gender-related effects on myonuclei organization and the MND size in single muscle fibres from six young (21–31 years) and nine old men (72–96 years), and from six young (24–32 years) and nine old women (65–96 years), using a novel image analysis algorithm applied to confocal images. Muscle fibres were classified according to myosin heavy chain (MyHC) isoform expression. Our image analysis algorithm was effective in determining the spatial organization of myonuclei and the distribution of individual MNDs along the single fibre segments. Significant linear relations were observed between MND size and fibre size, irrespective age, gender and MyHC isoform expression. The spatial organization of individual myonuclei, calculated as the distribution of nearest neighbour distances in 3D, and MND size were affected in old age, but changes were dependent on MyHC isoform expression. In type I muscle fibres, average NN-values were lower and showed an increased variability in old age, reflecting an aggregation of myonuclei in old age. Average MND size did not change in old age, but there was an increased MND size variability. In type IIa fibres, average NN-values and MND sizes were lower in old age, reflecting the smaller size of these muscle fibres in old age. It is suggested that these changes have a significant impact on protein synthesis and degradation during the aging process.
|
|
| 8. |
- Larsson, Lars, 1952-, et al.
(author)
-
Adaptation by alternative RNA splicing of slow troponin T isoforms in type 1 but not type 2 Charcot-Marie-Tooth disease
- 2008
-
In: American Journal of Physiology - Cell Physiology. - : American Physiological Society. - 0363-6143 .- 1522-1563. ; 295:3, s. 722-731
-
Journal article (peer-reviewed)abstract
- Slow troponin T (TnT) plays an indispensable role in skeletal muscle function. Alternative RNA splicing in the NH2-terminal region produces high-molecular-weight (HMW) and low-molecular-weight (LMW) isoforms of slow TnT. Normal adult slow muscle fibers express mainly HMW slow TnT. Charcot-Marie-Tooth disease (CMT) is a group of inherited peripheral polyneuropathies caused by various neuronal defects. We found in the present study that LMW slow TnT was significantly upregulated in demyelination form type 1 CMT (CMT1) but not axonal form type 2 CMT (CMT2) muscles. Contractility analysis showed an increased specific force in single fibers isolated from CMT1 but not CMT2 muscles compared with control muscles. However, an in vitro motility assay showed normal velocity of the myosin motor isolated from CMT1 and CMT2 muscle biopsies, consistent with their unchanged myosin isoform contents. Supporting a role of slow TnT isoform regulation in contractility change, LMW and HMW slow TnT isoforms showed differences in the molecular conformation in conserved central and COOH-terminal regions with changed binding affinity for troponin I and tropomyosin. In addition to providing a biochemical marker for the differential diagnosis of CMT, the upregulation of LMW slow TnT isoforms under the distinct pathophysiology of CMT1 demonstrates an adaptation of muscle function to neurological disorders by alternative splicing modification of myofilament proteins.
|
|
| 9. |
- Li, Mingxin, 1964-
(author)
-
Celluar and Molecular Mechanisms Underlying Regulation of Skeletal Muscle Contraction in Health and Disease
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- Morphological changes, genetic modifications, and cell functional alterations are not always parallel. Therefore, assessment of skeletal muscle function is an integral part of the etiological approach. The general objective of this thesis was to look into the cellular and molecular events occurring in skeletal muscle contraction in healthy and diseased condition, using a single fiber preparation and a single fiber in vitro motility assay, in an attempt to approach the underlying mechanisms from different physiological angles. In a body size related muscle contractility study, scaling of actin filament sliding speed and its temperature sensitivity has been investigated in mammals covering a 5,500-fold difference in body mass. A profound temperature dependence of actin filament sliding speed over myosin head was demonstrated irrespective of MyHC isoform expression and species. However, the expected body size related scaling within orthologus myosin isoforms between species failed to be maintained at any temperature over 5,500-fold range in body mass, with the larger species frequently having faster in vitro motility speeds than the smaller species. This suggest that apart from the MyHC iso-form expression, other factors such as thin filament proteins and myofilament lattice spacing, may contribute to the scaling related regulation of skeletal muscle contractility. A study of a novel R133W β-tropomyosin mutation on regulation of skeletal muscle contraction in the skinned single fiber prepration and single fiber in vitro motility assay suggested that the mutation induced alteration in myosin-actin kinetics causing a reduced number of myosin molecules in the strong actin binding state, resulting in overall muscle weakness in the absence of muscle wasting. A study on a type IIa MyHC isoform missense mutation at the motor protein level demonstrated a significant negative effect on the function of the IIa MyHC isoform while other myosin isoforms had normal function. This provides evidence that the pathogenesis of the MyHC IIa E706K myopathy involves defective function of the mutated myosin as well as alterations in the structural integrity of all muscle irrespective of MyHC isoform expression.
|
|
| 10. |
- Li, Meishan, et al.
(author)
-
Force-generating capacity of human myosin isoforms extracted from single muscle fibre segments
- 2010
-
In: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 588:24, s. 5105-5114
-
Journal article (peer-reviewed)abstract
- Muscle, motor unit and muscle fibre type-specific differences in force-generating capacity have been investigated for many years, but there is still no consensus regarding specific differences between slow- and fast-twitch muscles, motor units or muscle fibres. This is probably related to a number of different confounding factors disguising the function of the molecular motor protein myosin. We have therefore studied the force-generating capacity of specific myosin isoforms or combination of isoforms extracted from short single human muscle fibre segments in a modified single fibre myosin in vitro motility assay, in which an internal load (actin-binding protein) was added in different concentrations to evaluate the force-generating capacity. The force indices were the x-axis intercept and the slope of the relationship between the fraction of moving filaments and the α-actinin concentration. The force-generating capacity of the β/slow myosin isoform (type I) was weaker (P < 0.05) than the fast myosin isoform (type II), but the force-generating capacity of the different human fast myosin isoforms types IIa and IIx or a combination of both (IIax) were indistinguishable. A single fibre in vitro motility assay for both speed and force of specific myosin isoforms is described and used to measure the difference in force-generating capacity between fast and slow human myosin isoforms. The assay is proposed as a useful tool for clinical studies on the effects on muscle function of specific mutations or post-translational modifications of myosin.Myosin is the molecular motor protein in skeletal muscle that generates force and movement. It is expressed in multiple isoforms that have different enzymatic properties. There are isoform specific differences in contractile speed, but there is no consensus if the force generating capacity differs between isoforms. In this study we have modified a single fibre in vitro motility assay to measure both force and speed generated by specific myosin isoforms extracted from short single human muscle fibre segments. It is shown that human slow myosin is weaker and slower than fast myosin. This assay is put forward as a useful tool for future investigations on myosin function in response to modifications associated with muscle disease or ageing.
|
|
