Heat Shock Protein 70 Regulates Tumor Necrosis Factor-Alpha and Myogenin in Skeletal Muscle Following Chemical-Induced Injury

Skeletal muscle injury results in functional deficits that can take several weeks to fully recover. Ultimate recovery of function is dependent on the muscle’s ability to regenerate, a highly coordinated process that involves transient muscle inflammation and the replacement of damaged myofibers. Instrumental in the inflammatory response, is the pro-inflammatory cytokine TNF-α. Expression of TNF-α is thought to be regulated, in part, by the stress sensing 70 kDa heat shock protein (Hsp70). However, it remains unclear how Hsp70 alters TNF-α following injury, and if so, how these changes affect skeletal muscle repair. Therefore, we up-regulated Hsp70 expression using 17-allylamino-17-demethoxygeldanamycin (17-AAG) prior to and following BaCl2-induced injury, and assessed TNF-α and myogenin content. Regenerating fiber cross-sectional area (CSA) and in vivo isometric torque were also analyzed in the weeks following the injury. Treatment of 17-AAG resulted in a ~5 fold increase in Hsp70 of the uninjured muscle, but did not affect any other biochemical, morphological or functional variables compared to controls. In the days following the injury, TNF-α and myogenin were elevated and directly correlated. At these earlier time points (≤7 days), treatment of 17-AAG increased TNF-α above that of the injured controls and resulted in a sustained increase in myogenin. However, no differences were observed in regenerating fiber CSA or in vivo torque production between the groups. Together, these data suggest that Hsp70 induction increases TNF-α and myogenin content following BaCl2-induced injury, but does not appear to alter skeletal muscle regeneration or attenuate functional deficits in otherwise healthy young mice

Identifying characteristics of frailty in female mice using a phenotype assessment tool

Preclinical studies are important in identifying the underlying mechanisms contributing to frailty. Frailty studies have mainly focused on male rodents with little directed at female rodents. Therefore, the purposes of this study were to identify the onset and prevalence of frailty across the life span in female mice, and to determine if frailty predicts mortality. Female C57BL/6 (n = 27) mice starting at 17 months of age were assessed across the life span using a frailty phenotype, which included body weight, walking speed, strength, endurance, and physical activity. The onset of frailty occurred at approximately 17 months (1/27 mice), with the prevalence of frailty increasing thereafter. At 17 months, 11.1% of the mice were pre-frail and by 26 months peaked at 36.9%. The percentage of frail mice progressively increased up to 66.7% at 32 months. Non-frail mice lived to 29 months whereas frail/pre-frail mice lived only to 26 months (p = .04). In closing, using a mouse frailty phenotype, we are able to identify that the prevalence of frailty in female mice increases across the life span and accurately predicts mortality. Together, this frailty phenotype has the potential to yield information about the underlying mechanisms contributing to frailty.T32 AG029796 - NIA NIH HHSPublished versio

Sex-specific components of frailty in C57BL/6 mice.

Many age-related biochemical, physiological and behavioral changes are known to be sex-specific. However, how sex influences frailty status and mortality risk in frail rodents has yet to be established. The purpose of this study was therefore to characterize sex differences in frail mice across the lifespan. Male (n=29) and female (n=27) mice starting at 17 months of age were assessed using a frailty phenotype adjusted according to sex, which included body weight, walking speed, strength, endurance and physical activity. Regardless of sex, frail mice were phenotypically dysfunctional compared to age-matched non-frail mice, while non-frail females generally possessed a higher body fat percentage and were more physically active than non-frail males (p≤0.05). The prevalence of frailty was greater in female mice at 26 months of age (p=0.05), but if normalized to mean lifespan, no sex differences remained. No differences were detected in the rate of death or mean lifespan between frail male and female mice (p≥0.12). In closing, these data indicate that sexual differences exist in aging C57BL/6 mice and if the frailty criteria are adjusted according to sex, the prevalence of frailty increases across age with frail mice dying early in life, regardless of sex.T32 AG029796 - NIA NIH HHS; T32 AR007612 - NIAMS NIH HHSPublished versio

Aerobic And Anaerobic Changes In Collegiate Male Runners Across A Cross-Country Season

The purpose of this study was to assess the physiological characteristics of trained NCAA Division III male runners across a competitive season of cross-country. Eight male distance runners (age 20.6±1.4 y) were administered a battery of aerobic and anaerobic laboratory tests at the beginning and end of an 8-10 week racing season. Aerobic testing included maximal oxygen uptake (VO2max), running economy (RE), ventilatory threshold (VT) and the onset of blood lactate accumulation (OBLA). Anaerobic testing consisted of the vertical jump (VJ) and the Wingate test. Final testing revealed anaerobic Wingate peak power significantly declined (11.8±1.1 to 10.7±1.0 W·kg-1) (P = 0.006), while no significant changes were seen in VJ or any aerobic parameters (P \u3e 0.05). These results indicate that a competitive cross-country season of training and racing diminished anaerobic peak power and failed to elicit quantifiable aerobic adaptations in previously trained collegiate distance runners

Downhill exercise alters immunoproteasome content in mouse skeletal muscle

Content of the immunoproteasome, the inducible form of the standard proteasome, increases in atrophic muscle suggesting it may be associated with skeletal muscle remodeling. However, it remains unknown if the immunoproteasome responds to stressful situations that do not promote large perturbations in skeletal muscle proteolysis. The purpose of this study was to determine how an acute bout of muscular stress influences immunoproteasome content. To accomplish this, wildtype (WT) and immunoproteasome knockout lmp7-/-/mecl1-/-(L7M1) mice were run downhill on a motorized treadmill. Soleus muscles were excised 1 and 3 days post-exercise and compared to unexercised muscle(control). Ex vivophysiology, histology and biochemical analyses were used to assess the effects of immunoproteasome knockout and unaccustomed exercise. Besides L7M1 muscle being LMP7/MECL1deficient, no other major biochemical, histological or functional differences were observed between the control muscles. In both strains, the downhill run shifted the force-frequency curve to the right and reduced twitch force, however did not alter tetanic force or inflammatory markers. In the days post-exercise, several of the proteasome 's catalytic subunits were upregulated. Specifically, WT muscle increased LMP7 while L7M1 muscle instead increased ≤ 5. These findings indicate that running mice downhill results in subtle contractile characteristics that correspond to skeletal muscle injury, yet does not appear to induce a significant inflammatory response. Interestingly, this minor stress activated the production of specific immunoproteasome subunits; that if knocked out, were replaced by components of the standard proteasome. These data suggest that the immunoproteasome may be involved in maintaining cellular homeostasis.This study was supported by the Elaine and Robert Larson Endowed Vision Research Chair (to DAF), the National Institutes of Health/National Institute of Aging (T32-AG29796 to CWB), an anonymous benefactor for Macular Degeneration Research, the Lindsay Family Foundation and an unrestricted grant from Research to Prevent Blindness to the Department of Ophthalmology and Visual Neurosciences. The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript. (Elaine and Robert Larson Endowed Vision Research Chair; T32-AG29796 - National Institutes of Health/National Institute of Aging; Lindsay Family Foundation; Research to Prevent Blindness)Accepted manuscrip

Denervation-induced activation of the standard proteasome and immunoproteasome

The standard 26S proteasome is responsible for the majority of myofibrillar protein degradation leading to muscle atrophy. The immunoproteasome is an inducible form of the proteasome. While its function has been linked to conditions of atrophy, its contribution to muscle proteolysis remains unclear. Therefore, the purpose of this study was to determine if the immunoproteasome plays a role in skeletal muscle atrophy induced by denervation. Adult male C57BL/6 wild type (WT) and immunoproteasome knockout lmp7-/-/mecl-1-/- (L7M1) mice underwent tibial nerve transection on the left hindlimb for either 7 or 14 days, while control mice did not undergo surgery. Proteasome activity (caspase-, chymotrypsin-, and trypsin- like), protein content of standard proteasome (β1, β5 and β2) and immunoproteasome (LMP2, LMP7 and MECL-1) catalytic subunits were determined in the gastrocnemius muscle. Denervation induced significant atrophy and was accompanied by increased activities and protein content of the catalytic subunits in both WT and L7M1 mice. Although denervation resulted in a similar degree of muscle atrophy between strains, the mice lacking two immunoproteasome subunits showed a differential response in the extent and duration of proteasome features, including activities and content of the β1, β5 and LMP2 catalytic subunits. The results indicate that immunoproteasome deficiency alters the proteasome's composition and activities. However, the immunoproteasome does not appear to be essential for muscle atrophy induced by denervation.T32 AG029796 - NIA NIH HH

Age-induced oxidative stress: how does it influence skeletal muscle quantity and quality?

With advancing age, skeletal muscle function declines as a result of strength loss. These strength deficits are largely due to reductions in muscle size (i.e., quantity) and its intrinsic force-producing capacity (i.e., quality). Age-induced reductions in skeletal muscle quantity and quality can be the consequence of several factors, including accumulation of reactive oxygen and nitrogen species (ROS/RNS), also known as oxidative stress. Therefore, the purpose of this mini-review is to highlight the published literature that has demonstrated links between aging, oxidative stress, and skeletal muscle quantity or quality. In particular, we focused on how oxidative stress has the potential to reduce muscle quantity by shifting protein balance in a deficit, and muscle quality by impairing activation at the neuromuscular junction, excitation-contraction (EC) coupling at the ryanodine receptor (RyR), and cross-bridge cycling within the myofibrillar apparatus. Of these, muscle weakness due to EC coupling failure mediated by RyR dysfunction via oxidation and/or nitrosylation appears to be the strongest candidate based on the publications reviewed. However, it is clear that age-associated oxidative stress has the ability to alter strength through several mechanisms and at various locations of the muscle fiber.T32 AG029796 - NIA NIH HHSPublished versio

Eccentric Contractions Disrupt FKBP12 Content in Mouse Skeletal Muscle

Strength deficits associated with eccentric contraction-induced muscle injury stem, in part, from impaired voltage-gated sarcoplasmic reticulum (SR) Ca2+ release. FKBP12 is a 12-kD immunophilin known to bind to the SR Ca2+ release channel (ryanodine receptor, RyR1) and plays an important role in excitation-contraction coupling. To assess the effects of eccentric contractions on FKBP12 content, we measured anterior crural muscle (tibialis anterior [TA], extensor digitorum longus [EDL], extensor hallucis longus muscles) strength and FKBP12 content in pellet and supernatant fractions after centrifugation via immunoblotting from mice before and after a single bout of either 150 eccentric or concentric contractions. There were no changes in peak isometric torque or FKBP12 content in TA muscles after concentric contractions. However, FKBP12 content was reduced in the pelleted fraction immediately after eccentric contractions, and increased in the soluble protein fraction 3 day after injury induction. FKBP12 content was correlated (P = 0.025; R2 = 0.38) to strength deficits immediately after injury induction. In summary, eccentric contraction-induced muscle injury is associated with significant alterations in FKBP12 content after injury, and is correlated with changes in peak isometric torque

Assessing onset, prevalence and survival in mice using a frailty phenotype

Little is known whether frailty assessments in mice are capable of distinguishing important characteristics of the frailty syndrome. The goals of this study were to identify the onset and the prevalence of frailty across the lifespan and to determine if a frailty phenotype predicts mortality. Body weight, walking speed, strength, endurance and physical activity were assessed in male C57BL/6 mice every three months starting at 14 months of age. Mice that fell in the bottom 20% for walking speed, strength, endurance and physical activity, and in the top 20% for body weight were considered to have a positive frailty marker. The onset of frailty occurred at 17 months, and represented only 3.5% of the mouse cohort. The percentage of frail mice increased with age until basically every mouse was identified as frail. Frail, pre-frail, and non-frail mice had mean survival ages of 27, 29 and 34 months, respectively. In closing, frail mice lack resilience; in that, multiple tissue/organ systems may deteriorate at an accelerated rate and ultimately lead to early mortality when compared to non-frail mice. Identifying the onset and prevalence of frailty, in addition to predicting mortality, has potential to yield information about several aging processes.This work was supported by the National Institutes of Health (T32-AG029796 to L.V.T & C.W.B and T32-AR007612 to C.W.B) and Travis Roy Endowed Professorship (to L.V.T). (T32-AG029796 - National Institutes of Health; T32-AR007612 - National Institutes of Health)Published versio

Evodia nishimurae Koidz.

原著和名: ヲガサハラゴシュユ科名: ミカン科 = Rutaceae採集地: 東京都 小笠原村 父島 (小笠原村 父島)採集日: 1971/4/2採集者: 萩庭丈壽整理番号: JH008878国立科学博物館整理番号: TNS-VS-95887