Aging muscle exhibits a progressive decline in mass and strength, known as sarcopenia, and a decrease in the adaptive response to contractile activity. The molecular mechanisms mediating this reduced plasticity have yet to be elucidated. The purposes of this study were 1) to determine whether denervation-induced muscle disuse would increase the expression of autophagy genes and 2) to examine whether selective autophagy pathways (mitophagy) are altered in aged animals. Denervation reduced muscle mass in young and aged animals by 24 and 16%, respectively. Moreover, young animals showed a 50% decrease in mitochondrial content following denervation, an adaptation that was not matched by aged animals. Basal autophagy protein expression was higher in aged animals, whereas young animals exhibited a greater induction of autophagy proteins following denervation. Localization of LC3II, Parkin, and p62 was significantly increased in the mitochondrial fraction of young and aged animals following denervation. Moreover, the unfolded protein response marker CHOP and the mitochondrial dynamics protein Fis1 were increased by 17-and 2.5-fold, respectively, in aged animals. Lipofuscin granules within lysosomes were evident with aging and denervation. Thus reductions in the adaptive plasticity of aged muscle are associated with decreases in disuse-induced autophagy. These data indicate that the expression of autophagy proteins and their localization to mitochondria are not decreased in aged muscle; however, the induction of autophagy in response to disuse, along with downstream events such as lysosome function, is impaired. This may contribute to an accumulation of dysfunctional mitochondria in aged muscle. reactive oxygen species; muscle atrophy; mitochondria; mitophagy; apoptosis SKELETAL MUSCLE IS A REMARKABLY plastic tissue that undergoes a striking transformation in response to decreases in contractile activity. This distinctive response is attributable to the multinucleated composition of muscle fibers and the coordinated activation of several catabolic signaling pathways. Although muscle retains its adaptability throughout the life of an organism, tissue malleability is reduced with advancing age (4, 22). Aged muscle is further affected by an age-associated loss of skeletal muscle mass and strength, a condition known as sarcopenia (8,22,42). Although the precise cellular mechanisms responsible for mediating sarcopenia have yet to be fully elucidated, several studies have implicated decreases in mitochondrial function and a corresponding increase in mitochondrially mediated cell death (apoptosis) as factors contributing to this age-induced decline (4, 8). Indeed, mitochondrially mediated apoptosis can be activated by increases in reactive oxygen species (ROS), which have also been associated with several other deleterious effects, including the oxidation of mitochondrial DNA, lipids, and proteins (10, 39). Our laboratory has shown that mitochondria from aged muscle generate more ROS, possess a lower mitochondrial membrane pot...

Chronic muscle use increases the ratio of fusion:fission proteins, leading to reticular mitochondria, whereas muscle disuse and aging result in a decrease in this ratio, culminating in fragmented organelles.

Although trace levels of phosphorylated ␣-synuclein (␣-syn) are detectable in normal brains, nearly all ␣-syn accumulated within Lewy bodies in Parkinson disease brains is phosphorylated on serine 129 (Ser-129). The role of the phosphoserine residue and its effects on ␣-syn structure, function, and intracellular accumulation are poorly understood. Here, co-expression of ␣-syn and polo-like kinase 2 (PLK2), a kinase that targets Ser-129, was used to generate phosphorylated ␣-syn for biophysical and biological characterization. Misfolding and fibril formation of phosphorylated ␣-syn isoforms were detected earlier, although the fibrils remained phosphatase-and protease-sensitive. Membrane binding of ␣-syn monomers was differentially affected by phosphorylation depending on the Parkinson disease-linked mutation. WT ␣-syn binding to presynaptic membranes was not affected by phosphorylation, whereas A30P ␣-syn binding was greatly increased, and A53T ␣-syn was slightly lower, implicating distal effects of the carboxyl-on amino-terminal membrane binding. Endocytic vesicle-mediated internalization of pre-formed fibrils into non-neuronal cells and dopaminergic neurons matched the efficacy of ␣-syn membrane binding. Finally, the disruption of internalized vesicle membranes was enhanced by the phosphorylated ␣-syn isoforms, a potential means for misfolded extracellular or lumenal ␣-syn to access cytosolic ␣-syn. Our results suggest that the threshold for vesicle permeabilization is evident even at low levels of ␣-syn internalization and are relevant to therapeutic strategies to reduce intercellular propagation of ␣-syn misfolding.

Oestrogen may augment increases in muscle satellite cells following exercise through OR-mediated mechanisms; furthermore, the attenuation of post-exercise muscle damage and leucocyte infiltration by oestrogen appears to be a non-OR-mediated process.

Iqbal S, Hood DA. Oxidative stress-induced mitochondrial fragmentation and movement in skeletal muscle myoblasts. Am J Physiol Cell Physiol 306: C1176 -C1183, 2014. First published April 16, 2014; doi:10.1152/ajpcell.00017.2014.-Mitochondria are dynamic organelles, capable of altering their morphology and function. However, the mechanisms governing these changes have not been fully elucidated, particularly in muscle cells. We demonstrated that oxidative stress with H2O2 resulted in a 41% increase in fragmentation of the mitochondrial reticulum in myoblasts within 3 h of exposure, an effect that was preceded by a reduction in membrane potential. Using live cell imaging, we monitored mitochondrial motility and found that oxidative stress resulted in a 30% reduction in the average velocity of mitochondria. This was accompanied by parallel reductions in both organelle fission and fusion. The attenuation in mitochondrial movement was abolished by the addition of N-acetylcysteine. To investigate whether H2O2-induced fragmentation was mediated by dynaminrelated protein 1, we incubated cells with mDivi1, an inhibitor of dynamin-related protein 1 translocation to mitochondria. mDivi1 attenuated oxidative stress-induced mitochondrial fragmentation by 27%. Moreover, we demonstrated that exposure to H2O2 upregulated endoplasmic reticulum-unfolded protein response markers before the initiation of mitophagy signaling and the mitochondrial-unfolded protein response. These findings indicate that oxidative stress is a vital signaling mechanism in the regulation of mitochondrial morphology and motility. mitochondria; mitochondrial movement; oxidative stress; mitochondrial morphology MITOCHONDRIA ARE ESSENTIAL ORGANELLES for the life and death of eukaryotic cells. They play key roles in aerobic energy production, apoptosis, mitophagy, and cellular signaling. These versatile organelles were once thought to be static and rigid structures. More recently, mitochondria have been appreciated for their dynamic nature. They can change their distribution by moving along cytoskeletal tracks or change their overall morphology. The maintenance and appropriate networking of mitochondria within the cell is mediated by fusion and opposing fission processes. Fusion involves the mixing of mitochondrial material, whereas fission divides the organelle into smaller components. Disruptions in either of these opposing events can lead to developmental defects and disease (29), suggesting that the proper maintenance of mitochondrial morphology is critical for normal cell function.Mitochondrial fission is orchestrated, in part, by dynaminrelated protein 1 (Drp1) (4, 25), a protein that is a GTPase of the dynamin family. All dynamin members are structurally similar but functionally diverse GTP-binding proteins. Drp1 assists in mitochondrial fission by polymerizing into a ring-like structure around the organelle. The cross-bridging of the GTPase domains of adjacent Drp1 proteins results in GTP hydrolysis, constriction, and the ultimate severing of mitochon...

The tumor suppressor protein p53 is recognized to contribute significantly to the regulation of mitochondrial content. Mice without p53 have reduced endurance capacity and muscle performance. However, the function of p53 in muscle remains to be fully established. Understanding how p53 coordinates mitochondrial homeostasis will facilitate a better comprehension of how exercise could constitute as a therapy for cancer treatment.

PGC‐1α is an important transcriptional coactivator that plays a key role in mediating mitochondrial biogenesis. Within seconds of the onset of contractile activity, a number of rapid cellular events occur that form part of the initial signaling processes involved in PGC‐1α gene regulation, such as elevations in cytoplasmic calcium, AMPK and p38 activation, and elevated ROS production. We observed that basal levels of PGC‐1α promoter activity were more sensitive to resting Ca2+ levels, compared to ROS, p38 or, AMPK signaling. Moreover, enhanced PGC‐1α transcription and post‐translational activity on DNA were a result of the activation of multiple signal transduction pathways during contractile activity of myotubes. AMPK, ROS, and Ca2+ appear to be necessary for the regulation of contractile activity‐induced PGC‐1α gene expression, governed partly through p38 MAPK and CaMKII activity. Whether these signaling pathways are arranged as a linear sequence of events, or as largely independent pathways during contractile activity, remains to be determined.

Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficient to fulfill the projected global demand generated by increased populations. For wheat, global production will need to be increased by 60% to fulfill the estimated demand in 2050. Until recently, global wheat production increased mostly in response to development of improved cultivars and farming practices and technologies. Production is now limited by biotic and abiotic constraints, including diseases, nematodes, insect pests, weeds, and climate. Among these constraints, plant-parasitic nematodes alone are estimated to reduce production of all world crops by 10%. Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals. Heavily invaded young plants are stunted and their lower leaves are often chlorotic, forming pale green patches in the field. Mature plants are also stunted, have a reduced number of tillers, and the roots are shallow and have a “bushy-knotted” appearance. CCNs comprise a number of closely-related species and are found in most regions where cereals are produced.