Contractile weakness and loss of muscle mass are critical features of the aging process in mammalians. Age-related fibre wasting has a profound effect on muscle metabolism, fibre type distribution and the overall physiological integrity of the neuromuscular system. This study has used mass spectrometry-based proteomics to investigate the fate of the aging rat muscle proteome. Using nonionic detergent phase extraction, this report shows that the aged gastrocnemius muscle exhibits a generally perturbed protein expression pattern in both the detergent-extracted fraction and the aqueous protein complement from senescent muscle tissue. In the detergent-extracted fraction, the expression of ATP synthase, isocitrate dehydrogenase, enolase, tropomyosin and beta-actin was increased. Different isoforms of creatine kinase and prohibitin showed differential changes. In the aqueous fraction, malate dehydrogenase, sulfotransferase, triosephosphate isomerase, aldolase, cofilin-2 and lactate dehydrogenase showed increased levels. Interestingly, differential effects on dissimilar 2-D spots of the same protein species were shown for Cu/Zn superoxide dismutase, albumin, annexin A4 and phosphoglycolate phosphatase. Mitochondrial Hsp60, Hsp71 and nucleoside diphosphate kinase B exhibited a reduced abundance in aged muscle. The majority of altered proteins were found to be involved in mitochondrial metabolism, glycolysis, metabolic transportation, regulatory processes, the cellular stress response, detoxification mechanisms and muscle contraction.

Abstract. in order to increase our understanding of diabetes-related muscle weakness, we carried out a mass spectrometry-based proteomic analysis of skeletal muscle preparations from the Goto-Kakizaki rat model of type-2 diabetes. Fluorescence difference in-gel electrophoresis was performed to determine potential differences in the global protein expression profile of muscle extracts. Besides changes in contractile proteins and metabolic enzymes, the abundance of the small stress proteins αB-crystallin and Hsp27 was significantly increased. The up-regulation of the lowmolecular-mass heat shock protein Hsp27 was confirmed by an alternative fluorescent staining method of two-dimensional gels and immunoblotting. The observed protein alterations in the cellular stress response, distinct metabolic pathways, regulatory mechanisms and the contractile apparatus might be directly or indirectly associated with peripheral resistance to insulin signalling, making these newly identified muscle proteins potential biomarkers of type-2 diabetes. increased levels of molecular chaperones suggest considerably enhanced cellular stress levels in diabetic muscle fibres. IntroductionThe application of gel electrophoresis-based proteomics in diabetes research is a fast growing field (1), including the proteomic analysis of diabetic skeletal muscle tissues (2-7). Since diabetes is increasingly prevalent in the general population, research into the complex pathophysiological mechanisms that underlie abnormal signaling in crucial target organs, such as skeletal muscle, is of central importance (8-10). It is now clear that type-2 diabetes mellitus represents a group of heterogeneous disorders with abnormal expression patterns in various genes and protein products (11-13). Peripheral insulin resistance in the liver, adipose tissue and muscles, as well as impaired pancreatic β-cell functioning, are the principal features of type-2 diabetes (11). The worldwide incidence of type-2 diabetes is dramatically increasing (14) and it has been estimated that the incidence of diabetes will rise to a staggering 4.4% by the year 2030, with 366 million affected patients (15). Importantly, type-2 diabetes is associated with a loss of skeletal muscle mass and contractile strength (16-19) warranting detailed investigations into diabetes-related muscle weakness (20). In this respect, large-scale biochemical approaches, such as gel electrophoresis-based proteomics, are ideal analytical tools for an unbiased identification of novel protein factors that are associated with abnormal functioning in diabetic fibres.High-resolution two-dimensional gel electrophoresis has long been established as one of the most powerful biochemical techniques for the comparative analysis of large protein complements (21-23). The more recent combination of advanced gel electrophoretic methods with mass spectrometry has further reinforced the central importance of gel electrophoretic techniques for analytical protein chemistry (24-26). The unprecedented advancements of mass spectrome...

Abstract. Serious diabetic complications affect millions of patients worldwide. Skeletal muscle represents the largest insulin-regulated glucose sink in the body, making insulin resistance and abnormal glucose disposal in muscle fibres a critical aspect of diabetes mellitus. Advances in the biomedical analysis of the molecular mechanisms underlying diabetic complications rely heavily on the study of suitable disease models. The Goto-Kakizaki (GK) rat is an established animal model of non-obese type 2 diabetes. This review discusses the recent finding that expression of the dystrophin-dystroglycan complex is drastically altered in diabetic GK skeletal muscle fibres. In normal muscle, the dystrophin-glycoprotein complex provides a stabilizing connection between the actin membrane cytoskeleton and the extracellular matrix component laminin. A reduction in dystrophin-associated proteins may be associated with a weakening of the fibre periphery, abnormal sarcolemmal signaling and/or a decreased cytoprotective mechanism in diabetic skeletal muscle. Stimulation by insulin might be altered due to impaired linkage between the dystrophin-anchored actin cytoskeleton and the intracellular pool of essential glucose transporters. The diminished recruitment of GLUT4 transporter molecules to the sarcolemma may be a key step in the development of insulin resistance in diabetic skeletal muscles. Thus, analogous to certain forms of muscular dystrophy, altered dystrophin levels may have pathological effects in type 2 diabetes. In contrast, the dystrophin-glycoprotein complex does not appear to be altered in diabetic cardiac muscle. However, reduced expression of the sarcoplasmic reticulum Ca 2+ -ATPase isoform SERCA2 is characteristic of cardiac abnormalities in type 2 diabetes. Reduced Ca 2+ removal from the sarcoplasm may be associated with impaired relaxation kinetics, and could therefore play a pathophysiological role in diabetic cardiomyopathy. Here, the potential impact of these molecular alterations in diabetic muscle tissues is discussed and critically examined with respect to the future design of alternative treatment strategies to counteract diabetes-associated muscle weakness.

Abstract. Abnormal glucose handling has emerged as a major clinical problem in millions of diabetic patients worldwide. Insulin resistance affects especially one of the main target organs of this hormone, the skeletal musculature, making impaired glucose metabolism in contractile fibres a major feature of type 2 diabetes. High levels of circulating free fatty acids, an increased intramyocellular lipid content, impaired insulin-mediated glucose uptake, diminished mitochondrial functioning and an overall weakened metabolic flexibility are pathobiochemical hallmarks of diabetic skeletal muscles. In order to increase our cellular understanding of the molecular mechanisms that underlie this complex diabetesassociated skeletal muscle pathology, we initiated herein a mass spectrometry-based proteomic analysis of skeletal muscle preparations from the non-obese Goto-Kakizaki rat model of type 2 diabetes. Following staining of high-resolution two-dimensional gels with colloidal Coomassie Blue, 929 protein spots were detected, whereby 21 proteins showed a moderate differential expression pattern. Decreased proteins included carbonic anhydrase, 3-hydroxyisobutyrate dehydrogenase and enolase. Increased proteins were identified as monoglyceride lipase, adenylate kinase, Cu/Zn superoxide dismutase, phosphoglucomutase, aldolase, isocitrate dehydrogenase, cytochrome c oxidase, small heat shock Hsp27/B1, actin and 3-mercaptopyruvate sulfurtransferase. These proteomic findings suggest that the diabetic phenotype is associated with a generally perturbed protein expression pattern, affecting especially glucose, fatty acid, nucleotide and amino acid metabolism, as well as the contractile apparatus, the cellular stress response, the anti-oxidant defense system and detoxification mechanisms. The altered expression levels of distinct skeletal muscle proteins, as documented in this study, might be helpful for the future establishment of a comprehensive biomarker signature of type 2 diabetes. Reliable markers could be used for improving diagnostics, monitoring of disease progression and therapeutic evaluations.

Red Blood Cells from COVID-19 Patients Show Evidence of Increased Oxidative Stress and Increased Lactate Influx Corona Disease 19 (COVID-19) is caused by SARS-CoV-2, a novel, highly infectious, single stranded RNA virus. In severe cases, excess oxidative stress produced by a 'cytokine storm' may generate excess reactive oxygen species (ROS) and lead to tissue damage in the lungs and elsewhere. As the potential role of RBCs in the pathophysiology of COVID-19 remains controversial (1), we investigated for evidence of increased oxidative stress and increased thrombotic tendency in RBCs from patients with COVID-19 infection. Following ethical approval and written informed consent, we used flow cytometry (BD FACSCanto II) to measure baseline RBC ROS following incubation with 2'-7'-dichlorofluorescein diacetate (DCF). RBC ROS were also measured following pre-incubation with hydrogen peroxide (H2O2) (2mM) +/- antioxidant N-acetyl cysteine (NAC) (0.6mM). We also measured RBC surface expression of adhesion molecules CD44, CD47 and CD242, as well as CD147. Results were expressed as mean +/- standard deviation (SD). RBC ROS were measured in 22 COVID-19 positive patients and in 10 age matched healthy controls. One patient died from respiratory failure, whilst only 3 others required ITU admission for continuous positive airway pressure (CPAP) or intubation. There was no statistical difference in mean basal RBC DCF mean fluorescence intensity (MFI) levels between COVID-19 positive patients and controls. However, mean increase in RBC DCF MFI following H2O2 incubation was significantly higher in the COVID-19 positive group (1105.7+/-336.3) compared to the control group (843.4+/-256.7)( p= 0.042). The increase in RBC DCF MFI in the COVID-19 positive group correlated with CRP (p=0.014) but not with D-dimer, serum ferritin or any complete blood count (CBC) parameters. Incubation of RBC with 0.6 mM NAC for 30 minutes prior to H2O2 exposure caused a mean reduction in DCF MFI of 26.7% in the COVID-19 positive group. RBC expression of CD44, CD47, CD242 and CD147 were measured In a separate cohort of COVID-19 positive patients (n=32), and in 22 age matched controls. There were no statistically significant differences in mean expression levels of CD44, CD47 and CD242 between the 2 groups. However, mean RBC CD147 MFI expression was higher in the COVID-19 group (1319.64+/-374.76) compared to controls (1061.59+/-253.33) (p=0.018). There was no significant correlation between RBC CD147 MFI and D-dimer, CRP, serum ferritin or any CBC parameters in the COVID-19 positive group. However, 21 of the 32 COVID-19 positive patients had blood lactate levels measured and there was a positive correlation between CD147 MFI expression and blood lactate (R=0.56, p=0.0077). Induction of oxidative stress by H2O2 resulted in a greater increase in ROS in RBCs from COVID-19 patients compared to controls and with correlation to CRP, despite the fact that there were very few patients with severe disease in the study. This suggests a role for oxidative stress in disease pathogenesis. Pre-incubation with NAC attenuated this increase in ROS, suggesting a possible role for antioxidants in therapy. Increased RBC cell surface expression of adhesion molecules CD44, CD47 and CD242 can facilitate RBC interaction with platelets and/or endothelial cells, potentially contributing to thrombosis. We found no increase in their expression in COVID-19 patients compared to controls although RBCs may contribute to thrombosis in COVID-19 infection by other means (1). CD147 is tightly associated with and enables proper expression of monocarboxylate transporter 1, the lactate transporter for RBCs. We found increased surface expression of CD147 on RBCs of COVID-19 patients, whilst CD147 expression showed a moderate correlation with serum lactate levels, suggesting that RBCs in COVID-19 infection may be acting as a lactate sink to protect against lactic acidosis. In summary, our study suggests that COVID-19 infection causes increased oxidative stress and increased lactate influx in RBCs. Further studies are warranted into the role of RBCs in COVID-19 infection. Reference: (1) Murphy P, Glavey S, Quinn J. Anemia and red blood cell abnormalities in COVID-19. Leuk Lymphoma 2021;62:1539 Disclosures Quinn: Takeda: Honoraria. Glavey: Abbvie: Research Funding; Celgene and BMS company: Research Funding; Janssen: Honoraria, Research Funding; Amgen: Honoraria, Research Funding.