Oxidative proteome alterations during skeletal muscle ageing

Comparative Skeletal Muscle Proteomics Using Two-Dimensional Gel Electrophoresis

The pioneering work by Patrick H. O’Farrell established two-dimensional gel electrophoresis as one of the most important high-resolution protein separation techniques of modern biochemistry (Journal of Biological Chemistry1975, 250, 4007–4021). The application of two-dimensional gel electrophoresis has played a key role in the systematic identification and detailed characterization of the protein constituents of skeletal muscles. Protein changes during myogenesis, muscle maturation, fibre type specification, physiological muscle adaptations and natural muscle aging were studied in depth by the original O’Farrell method or slightly modified gel electrophoretic techniques. Over the last 40 years, the combined usage of isoelectric focusing in the first dimension and sodium dodecyl sulfate polyacrylamide slab gel electrophoresis in the second dimension has been successfully employed in several hundred published studies on gel-based skeletal muscle biochemistry. This review focuses on normal and physiologically challenged skeletal muscle tissues and outlines key findings from mass spectrometry-based muscle proteomics, which was instrumental in the identification of several thousand individual protein isoforms following gel electrophoretic separation. These muscle-associated protein species belong to the diverse group of regulatory and contractile proteins of the acto-myosin apparatus that forms the sarcomere, cytoskeletal proteins, metabolic enzymes and transporters, signaling proteins, ion-handling proteins, molecular chaperones and extracellular matrix proteins.

Bioenergetics of the aging heart and skeletal muscles: Modern concepts and controversies

Age-related alterations in the bioenergetics of the heart and oxidative skeletal muscle tissues are of crucial influence on their performance. Until now the prevailing concept of aging was the mitochondrial theory, the increased production of reactive oxygen species, mediated by deficiency in the activity of respiratory chain complexes. However, studies with mitochondria in situ have presented results which, to some extent, disagree with previous ones, indicating that the mitochondrial theory of aging may be overestimated. The studies reporting age-related decline in mitochondrial function were performed using mainly isolated mitochondria. Measurements on this level are not able to take into account the system level properties. The relevant information can be obtained only from appropriate studies using cells or tissue fibers. The functional interactions between the components of Intracellular Energetic Unit (ICEU) regulate the energy production and consumption in oxidative muscle cells. The alterations of these interactions in ICEU should be studied in order to find a more effective protocol to decelerate the age-related changes taking place in the energy metabolism. In this article, an overview is given of the present theories and controversies of causes of age-related alterations in bioenergetics. Also, branches of study, which need more emphasis, are indicated.

Oxidative stress and lipotoxicity

The α,β polyunsaturated lipid aldehydes are potent lipid electrophiles that covalently modify lipids, proteins, and nucleic acids. Recent work highlights the critical role these lipids play under both physiological and pathological conditions. Protein carbonylation resulting from nucleophilic attack of lysine, histidine, and cysteine residues is a major outcome of oxidative stress and functions as a redox-sensitive signaling mechanism with roles in autophagy, cell proliferation, transcriptional control, and apoptosis. In addition, protein carbonylation is implicated as an initiating factor in mitochondrial dysfunction and endoplasmic reticulum stress, providing a mechanistic connection between oxidative stress and metabolic disease. In this review, we discuss the generation and metabolism of reactive lipid aldehydes, as well as their signaling roles.

Innovative biomarkers for predicting type 2 diabetes mellitus: relevance to dietary management of frailty in older adults

Type 2 diabetes mellitus (T2DM) increases in prevalence in the elderly. There is evidence for significant muscle loss and accelerated cognitive impairment in older adults with T2DM; these comorbidities are critical features of frailty. In the early stages of T2DM, insulin sensitivity can be improved by a "healthy" diet. Management of insulin resistance by diet in people over 65 years of age should be carefully re-evaluated because of the risk for falling due to hypoglycaemia. To date, an optimal dietary programme for older adults with insulin resistance and T2DM has not been described. The use of biomarkers to identify those at risk for T2DM will enable clinicians to offer early dietary advice that will delay onset of disease and of frailty. Here we have used an in silico literature search for putative novel biomarkers of T2DM risk and frailty. We suggest that plasma bilirubin, plasma, urinary DPP4-positive microparticles and plasma pigment epithelium-derived factor merit further investigation as predictive biomarkers for T2DM and frailty risk in older adults. Bilirubin is screened routinely in clinical practice. Measurement of specific microparticle frequency in urine is less invasive than a blood sample so is a good choice for biomonitoring. Future studies should investigate whether early dietary changes, such as increased intake of whey protein and micronutrients that improve muscle function and insulin sensitivity, affect biomarkers and can reduce the longer term complication of frailty in people at risk for T2DM.

Mitochondrial Quality Control and Muscle Mass Maintenance

Loss of muscle mass and force occurs in many diseases such as disuse/inactivity, diabetes, cancer, renal, and cardiac failure and in aging-sarcopenia. In these catabolic conditions the mitochondrial content, morphology and function are greatly affected. The changes of mitochondrial network influence the production of reactive oxygen species (ROS) that play an important role in muscle function. Moreover, dysfunctional mitochondria trigger catabolic signaling pathways which feed-forward to the nucleus to promote the activation of muscle atrophy. Exercise, on the other hand, improves mitochondrial function by activating mitochondrial biogenesis and mitophagy, possibly playing an important part in the beneficial effects of physical activity in several diseases. Optimized mitochondrial function is strictly maintained by the coordinated activation of different mitochondrial quality control pathways. In this review we outline the current knowledge linking mitochondria-dependent signaling pathways to muscle homeostasis in aging and disease and the resulting implications for the development of novel therapeutic approaches to prevent muscle loss.

Single muscle fiber contractile properties in diabetic RAT muscle

INTRODUCTION

Diabetes is associated with accelerated loss of muscle mass and function. We compared the contractile properties of single muscle fibers in young rat soleus muscle of uncontrolled streptozotocin-induced diabetic animals (n = 10) and nondiabetic controls (n = 10).

METHODS

Single fiber maximal force, shortening velocity, and power were assessed during maximal activation with calcium using the slack test 4 weeks after induction. Myosin heavy chain expression was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Oxidized myosin levels were detected by analyzing protein carbonyls in muscle homogenates. All fibers expressed the type I myosin heavy chain isoform.

RESULTS

Diabetic rats had higher blood glucose (537 vs. 175 mg/dl; P < 0.001) and lower body weight (171 vs. 356 g; P < 0.001) than controls. Muscle fibers from diabetic rats showed smaller cross-sectional area (1128 vs. 1812 μm(2) ), lower maximal force (258 vs. 492 μN), and reduced absolute power (182 vs. 388 μN FL/s) (all P < 0.0001). No differences were seen in shortening velocity, specific force or specific power. Myosin carbonylation was higher (P < 0.01) in diabetic rats.

CONCLUSIONS

After 4 weeks of untreated diabetes, there are significant alterations in muscle at the level of isolated single fibers and myosin protein, although some contractile properties seem to be protected. Muscle Nerve, 2015 Muscle Nerve 53: 958-964, 2016.