INTRODUCTION: Alpha-actinin-3 is a Z-disc protein that is expressed only in type II muscle fibers. Common null polymorphism in the ACTN3 gene (R577X) results in lack of this protein in XX-genotypes. In sprint/power oriented elite athletes the prevalence of the X-allele is much lower than in control populations. That implies that lack of alpha-actinin-3 is detrimental for these athletes but a mechanistic link is not fully established. We have previously shown that ACTN3 genotype modulates skeletal muscle hypertrophy signaling in response to sprint exercise in moderately trained subjects. PURPOSE: To examine the impact of ACTN3 genotype on changes in fiber dimensions from adolescence to adulthood. METHODS: 63 male and female subjects (13 XX, 29 RX, 21 RR) from the general Swedish population were studied at 16 and 27 years of age. Their physical activity level was estimated by a questionnaire. Muscle samples were obtained from vastus lateralis muscle by needle biopsy technique. The samples were analyzed histochemically for fiber types (I, IIA, IIB). Cross-sectional area (CSA) of the different fiber types was measured from histological sections by planimetry. DNA was extracted from muscle samples and the genotyping was performed by allelic discrimination. Statistical analyses of the effect of ACTN3 and sex on changes in CSA with age were performed by ANOVA and multiple regression analysis. RESULTS: A significant difference in the relative change of CSA with age, across ACTN3 genotypes was observed in type IIA fibers (ANOVA P=0.02) but not in type I fibers and type IIB fibers. The change, expressed as 27-16 years/16-years value, was in type IIA fibers -4.2%, -2.5% and 7.7% in XX, RX and RR respectively and in type IIB -3.0%, -3.4%, and 9.9% in XX, RX and RR respectively. Multiple regression analysis showed that the change in CSA of type IIA fibers was dependent on ACTN3 genotype, while the change in CSA of type IIB was equally dependent on ACTN3 genotype and sex. No ACTN3 genotype effect was observed for the CSA change in type I fibers where alpha-actinin-3 is not expressed. No significant differences in CSA were detected across ACTN3 genotypes either at 16 or 27 years. CONCLUSION: ACTN3 genotype is strongly suggested to be a determinant of dimensions of type II skeletal muscle fibers in humans which supports the findings in ACNT3 knock out mice.

Objective Skeletal muscle weakness is a prominent clinical feature in patients with rheumatoid arthritis (RA), but the underlying mechanism(s) is unknown. Here we investigate the mechanisms behind arthritis-induced skeletal muscle weakness with special focus on the role of nitrosative stress on intracellular Ca2+ handling and specific force production. Methods Nitric oxide synthase (NOS) expression, degree of nitrosative stress and composition of the major intracellular Ca2+ release channel (ryanodine receptor 1, RyR1) complex were measured in muscle. Changes in cytosolic free Ca2+ concentration ([Ca2+]i) and force production were assessed in single-muscle fibres and isolated myofibrils using atomic force cantilevers. Results The total neuronal NOS (nNOS) levels were increased in muscles both from collagen-induced arthritis (CIA) mice and patients with RA. The nNOS associated with RyR1 was increased and accompanied by increased [Ca2+]i during contractions of muscles from CIA mice. A marker of peroxynitrite-derived nitrosative stress (3-nitrotyrosine, 3-NT) was increased on the RyR1 complex and on actin of muscles from CIA mice. Despite increased [Ca2+]i, individual CIA muscle fibres were weaker than in healthy controls, that is, force per cross-sectional area was decreased. Furthermore, force and kinetics were impaired in CIA myofibrils, hence actin and myosin showed decreased ability to interact, which could be a result of increased 3-NT content on actin. Conclusions Arthritis-induced muscle weakness is linked to nitrosative modifications of the RyR1 protein complex and actin, which are driven by increased nNOS associated with RyR1 and progressively increasing Ca2+ activation.

To cite: Yamada T, Fedotovskaya O, Cheng AJ, et al. Ann Rheum Dis 2015;74:1907–1914. ABSTRACT Objective Skeletal muscle weakness is a prominent clinical feature in patients with rheumatoid arthritis (RA), but the underlying mechanism(s) is unknown. Here we investigate the mechanisms behind arthritis-induced skeletal muscle weakness with special focus on the role of nitrosative stress on intracellular Ca handling and specific force production. Methods Nitric oxide synthase (NOS) expression, degree of nitrosative stress and composition of the major intracellular Ca release channel (ryanodine receptor 1, RyR1) complex were measured in muscle. Changes in cytosolic free Ca concentration ([Ca]i) and force production were assessed in single-muscle fibres and isolated myofibrils using atomic force cantilevers. Results The total neuronal NOS (nNOS) levels were increased in muscles both from collagen-induced arthritis (CIA) mice and patients with RA. The nNOS associated with RyR1 was increased and accompanied by increased [Ca]i during contractions of muscles from CIA mice. A marker of peroxynitrite-derived nitrosative stress (3-nitrotyrosine, 3-NT) was increased on the RyR1 complex and on actin of muscles from CIA mice. Despite increased [Ca]i, individual CIA muscle fibres were weaker than in healthy controls, that is, force per crosssectional area was decreased. Furthermore, force and kinetics were impaired in CIA myofibrils, hence actin and myosin showed decreased ability to interact, which could be a result of increased 3-NT content on actin. Conclusions Arthritis-induced muscle weakness is linked to nitrosative modifications of the RyR1 protein complex and actin, which are driven by increased nNOS associated with RyR1 and progressively increasing Ca activation.

α-Actinin-3 is a Z-disc protein expressed only in type II muscle fibers. A polymorphism in the ACTN3 gene (R577X) results in lack of α-actinin-3 in XX genotype. The prevalence of the mutated X-allele is lower among power/sprint oriented athletes compared with controls, indicating that the lack of α-actinin-3 is detrimental in these sports, but a mechanistic link has not been established. Results from Actn3-knockout (KO) mouse model suggest that α-actinin-3 may affect muscle mass and muscle glycogen levels. In the present investigation we examined muscle fiber type composition, cross-sectional fiber area (CSA), and muscle glycogen levels at baseline in 143 human subjects with different ACTN3 genotypes. In addition, hypertrophy signaling and glycogen utilization in response to sprint exercise were studied in a subset of subjects. Glycogen utilization was analyzed in separate pools of type I and type II fibers. No differences in fiber type composition, CSA, or muscle glycogen levels were observed at baseline across the ACTN3 genotypes. However, the sprint exercise-induced increase in phosphorylation of mTOR and p70S6k was smaller in XX than in RR+RX (P = 0.03 and P = 0.01, respectively), indicating a less pronounced activation of hypertrophy signaling in XX. Glycogen utilization during sprint exercise varied across ACTN3 genotypes in type II fibers (P = 0.03) but not in type I fibers (P = 0.38). The present results are in accordance with findings from the KO mice and reinforce the hypothesis that ACTN3 genotype-associated differences in muscle mass and glycogen utilization provide a mechanistic explanation for the modulation of human performance by the ACTN3 genotype.

PURPOSE:The purpose of the study was to examine muscle strength and pain sensitivity in postmenopausal women with and without RA.METHODS:Ten women with and ten without early RA were recruited. All were postmenopausal, and did not use hormone replacement therapy. Measurements of isokinetic muscle strength in knee flexors/extensors, hand grip strength, timed standing, pressure pain thresholds (PPT), suprathreshold pressure pain, and segmental and plurisegmental endogenous pain inhibitory mechanisms during muscle contraction were assessed.RESULTS:Participants with early RA were weaker in knee flexors, in hand grip strength and they needed more time for the timed standing. Women with early RA had higher sensitivity to threshold pain and suprathreshold pressure pain compared to women without RA. PPTs increased in the contracting muscle as well as in a distant resting muscle during static contractions in both groups.CONCLUSIONS:Our results indicate differences in muscular strength between postmenopausal women with and without RA. Furthermore, women with RA had decreased PPT and hyperalgesia, but no dysfunction of segmental or plurisegmental pain inhibitory mechanisms during static exercise compared to healthy controls. The normal function of endogenous pain inhibitory mechanisms despite chronic pain in women with RA might contribute to the good effects of physical activity previously reported.

OBJECTIVEProgressive muscle weakness is a common feature in patients with rheumatoid arthritis (RA). However, little is known about whether the intrinsic contractile properties of muscle fibers are affected in RA. This study was undertaken to investigate muscle contractility and the myoplasmic free Ca2+ concentration ([Ca2+](i)) in the soleus, a major postural muscle, in mice with collagen-induced arthritis (CIA).METHODSMuscle contractility and [Ca2+](i) were assessed in whole muscle and intact single-fiber preparations, respectively. The underlying mechanisms of contractile dysfunction were assessed by investigating redox modifications using Western blotting and antibodies against nitric oxide synthase (NOS), superoxide dismutase (SOD), 3-nitrotyrosine (3-NT), carbonyl, malondialdehyde (MDA), and S-nitrosocysteine (SNO-Cys).RESULTSThe tetanic force per cross-sectional area was markedly decreased in the soleus muscle of mice with CIA, and the change was not due to a decrease in the amplitude of [Ca2+](i) transients. The reduction in force production was accompanied by slowing of the twitch contraction and relaxation and a decrease in the maximum shortening velocity. Immunoblot analyses showed a marked increase in neuronal NOS expression but not in inducible or endothelial NOS expression, which, together with the observed decrease in SOD2 expression, favors peroxynitrite formation. These changes were accompanied by increased 3-NT, carbonyl, and MDA adducts content in myofibrillar proteins from the muscles of mice with CIA. Moreover, there was a significant increase in SNO-Cys content in myosin heavy-chain and troponin I myofibrillar proteins from the soleus muscle of mice with CIA.CONCLUSIONThese findings show impaired contractile function in the soleus muscle of mice with CIA and suggest that this abnormality is due to peroxynitrite-induced modifications in myofibrillar proteins.

The purpose of the study was to investigate to what extent the physical activity pattern in adulthood can be predicted by physical characteristics, performance and activity in adolescence. A group of 62 men and 43 women completed a questionnaire concerning physical activity during their leisure time at the ages of 16 and 27 years. An activity index produced from the questionnaire. At the age of 16 years, the subjects were also tested for strength (strength test battery) and running performance (9-min run). Maximal oxygen uptake (\(\dot V{\text{O}}_{{\text{2max}}} \)) was estimated from a submaximal test and a muscle biopsy specimen was taken and analysed for fibre types (percentages of types I, IIA, 1113). The proportion of subjects engaged in some kind of physical activity during their leisure time was approximately 70% among the women and 80% among the men at both ages. The time spent on physical activity (minutes per week) decreased with age for the men but not for the women. The women devoted less time. to physical activity than the men both at age 16 and 27 years. The attitude to endurance activities had changed to a more positive attitude among the women and to a less positive attitude among the men at age 27 years. The aerobic potential (\(\dot V{\text{O}}_{{\text{2max}}} \) and percentage of type I fibre), running performance, strength performance, physical activity and marks in physical education at age 16 years explained 82% of the physical activity level in adulthood for the women and 47% for the men. The aerobic potential at age 16 years alone explained 31% of the adult physical activity level in the women and 24% in the men. Strength performance, physical activity and marks in physical education at age 16 years further increased the predictive value for the physical activity level in adulthood for the women but not for the men. It is suggested that the major portion of the variation in physical activity level in adult women, but not in the adult men, could be predicted from physical characteristics, physical performance, and the activity level in adolescence.

Male skeletal muscles are generally faster and have higher maximum power output than female muscles. Conversely, during repeated contractions, female muscles are generally more fatigue resistant and recover faster. We studied the role of estrogen receptor-beta (ERbeta) in this gender difference by comparing contractile function of soleus (mainly slow-twitch) and extensor digitorum longus (fast-twitch) muscles isolated from ERbeta-deficient (ERbeta(-/-)) and wild-type mice of both sexes. Results showed generally shorter contraction and relaxation times in male compared with female muscles, and ERbeta deficiency had no effect on this. Fatigue (induced by repeated tetanic contractions) and recovery of female muscles were not affected by ERbeta deficiency. However, male ERbeta(-/-) muscles were slightly more fatigue resistant and produced higher forces during the recovery period than wild-type male muscles. In fact, female muscles and male ERbeta(-/-) muscles displayed markedly better recovery than male wild-type muscles. Gene screening of male soleus muscles showed 25 genes that were differently expressed in ERbeta(-/-) and wild-type mice. Five of these genes were selected for further analysis: muscle ankyrin repeat protein-2, muscle LIM protein, calsequestrin, parvalbumin, and aquaporin-1. Expression of these genes showed a similar general pattern: increased expression in male and decreased expression in female ERbeta(-/-) muscles. In conclusion, ERbeta deficiency results in increased performance during fatigue and recovery of male muscles, whereas female muscles are not affected. Improved contractile performance of male ERbeta(-/-) mouse muscles was associated with increased expression of mRNAs encoding important muscle proteins.

AIM There are two known oestrogen receptors (ER), oestrogen receptor alpha (ERalpha) and the recently cloned oestrogen receptor beta (ERbeta). ERalpha mRNA has been detected in mouse, rat, bovine and human skeletal muscle. ERbeta mRNA has been detected in bovine skeletal muscle. To our knowledge, no study has investigated the expression of oestrogen receptor beta in human skeletal muscle. Therefore, the primary aim of the present investigation was to study ERbeta mRNA and protein expression in human skeletal muscle. In addition the ERalpha expression was also studied. METHODS Muscle biopsies were taken from vastus lateralis in six healthy adults (three women and three men). mRNA expression was detected with real-time PCR (TaqMan) and protein localization by immunohistochemistry. RESULTS A clear expression of ERalpha and ERbeta mRNA was seen in skeletal muscle in all subjects. The ERalpha mRNA expression was 180 fold higher compared with that of ERbeta mRNA. Immunohistochemistry demonstrated positive staining for ERbeta, but not for ERalpha, with localization to the nuclei of skeletal muscle fibres. On average, 70% of all nuclei were ERbeta-positive. CONCLUSION The present study shows for the first time ERbeta mRNA and protein expression in human skeletal muscle tissue in both males and females.

Conference Abstract| January 01 1994 Absence of Muscle AMP Deaminase in 2% of a Healthy Population B Norman; B Norman 1Karolinska Institute, Department of Medical Laboratory Science and Technology, Division of Clinical Physiology, Huddinge University Hospital, Huddinge, Sweden Search for other works by this author on: This Site PubMed Google Scholar B Glenmark; B Glenmark 1Karolinska Institute, Department of Medical Laboratory Science and Technology, Division of Clinical Physiology, Huddinge University Hospital, Huddinge, Sweden Search for other works by this author on: This Site PubMed Google Scholar E Jansson E Jansson 1Karolinska Institute, Department of Medical Laboratory Science and Technology, Division of Clinical Physiology, Huddinge University Hospital, Huddinge, Sweden Search for other works by this author on: This Site PubMed Google Scholar Clin Sci (Lond) (1994) 87 (s1): 123–124. https://doi.org/10.1042/cs087s123a Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation B Norman, B Glenmark, E Jansson; Absence of Muscle AMP Deaminase in 2% of a Healthy Population. Clin Sci (Lond) 1 January 1994; 87 (s1): 123–124. doi: https://doi.org/10.1042/cs087s123a Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsClinical Science Search Advanced Search This content is only available as a PDF. © 1994 The Biochemical Society and the Medical Research Society1994 Article PDF first page preview Close Modal You do not currently have access to this content.

The aim of the present study was to reinvestigate muscle strength and the relationship to muscle fibre and the level of physical activity in adult men and women previously studied during adolescence. A group of 55 men and 26 women were tested for maximal strength (handgrip, Sargent jump and two-hand lift) and completed a questionnaire concerning physical activity during their leisure time (activity index) at the ages of 16 and 27 years. Biopsy specimens were taken from the vastus lateralis and analysed for fibre type (percentage of I, IIA, IIB) and fibre area (area I, area IIA, area IIB). The sex differences in strength increased from age 16 to 17 years. Body dimension, sex, percentage of type II, mean fibre area and the activity index contributed to explaining 50-75% of the strength at both ages. Different changes in relationship between fibre type composition and strength in women and men was seen with increasing age. In the women, the relationship between strength and the percentage of type II fibres changed with age (from 16 to 27 years of age) from a positive correlation (only Sargent jump) to negative correlations for all the strength tests, i.e. the more type I fibres the stronger the subject. A positive correlation between strength and the level of physical activity during leisure time was revealed in the women at both ages. The positive correlation between strength and type II fibres in the 16-year-old men had disappeared at age 27. No systematic relationships between strength and the level of physical activity were seen in the men at either 16 or 27 years of age. It is suggested that women may be more dependent on physical activity than adult men to develop strength and the percentage of type I fibres reflects the degree of physical activity among adult women but not among adolescent women.

Fifty-five men and 28 women were tested at age 16 and retested at age 27. Muscle biopsies were taken from m. vastus lateralis to analyse fibre types, fibre areas and enzyme contents. A cycle ergometer test to was used to estimate the maximal oxygen uptake. Physical performance was assessed in an endurance test, where the subjects had to run as far as possible in 9 min on a 400-m track, and in three strength tests designed to test maximal dynamic strength (Sargent jump) and maximal static strength (handgrip test, two-hand lift). The subjects answered a questionnaire concerning physical activity during their leisure time and an activity index was calculated from the answers. The relative proportion of type I fibres (type I%) tended to increase with age in women and decreased in men. At age 27, the type I% was higher in women than in men. Multiple regression analysis indicated that sex per se could explain some of the interindividual variation in the type I% at age 27 and in the changes with age in the type I%, but also factors as physical activity (increase in type I%) and smoking (decrease in type I%) probably contributed to the variation. VO2max (ml.kg-1.min-1) increased with age in women and was unchanged in men so that there was no significant sex difference in VO2max at age 27. Running performance remained unchanged from age 16 to age 27 in both sexes and men performed better than women at both ages. Running performance was directly related to the type I% for both women and men at age 27, a relationship which existed also for men at age 16, but not for women at that age. It seems that the age related changes in relationship between running performance and type I% may be related to the altered choice of physical activity from speed and strength to more endurance demanding activities and the increased VO2max in the women. This may allow an adaptation of the skeletal muscle towards type I fibres in the active ones. The sex differences in strength increased from age 16 to age 27. The relationship between strength and the type II% in the women changed with age from a positive correlation (Sargent jump only, partiell correlation after body dimensions were considered) to negative correlations for all the strength tests, i.e. the more type I fibres the stronger. A positive correlation between strength and activity index was revealed in the women at both ages.(ABSTRACT TRUNCATED AT 400 WORDS)

It has been shown earlier that the proportion of slow twitch (type I) fibres in the leg musculature is directly related to running performance in boys but not in girls at the age of 16. The purpose of the present study was to determine whether this pattern remains in adulthood. Forty-one men and 19 women were tested at the age of 16 and 27 years. Muscle biopsy specimens were obtained from the vastus lateralis and analysed for fibre type (I%, IIA%, IIB%). Maximal oxygen uptake (VO2max) was estimated from a submaximal exercise test. Running performance (9-min run) was assessed in a modified Cooper test. At age 16, the 9-min run was positively correlated with type I% and VO2max for the men. For the women, the 9-min run was positively correlated with VO2max but not with type I%. At age 27, the 9-min run was positively correlated with type I % and VO2max for both men and women. The appearance at the age of 27 of a relationship between running performance and type I% in the women could be related to the increase with age in the VO2max found in the women in the present study. These results support an earlier formulated hypothesis that a certain level of VO2max must be reached before peripheral factors such as the muscle fibre type composition are of any significance for the performance in a 9-min run.

Age-related changes in muscle fibre characteristics have been presented in cross-sectional studies previously. The aim of the present study was to investigate longitudinally whether the muscle fibre type composition and muscle fibre area change from adolescence to adulthood. Fifty-five men and 28 women were studied at the age of 16 and again at the age of 27. Biopsies were taken from the vastus lateralis muscle and analysed for fibre types (I, IIA, IIB, IIC) and fibre areas. Different development of fibre type composition with increased age were seen in women and men: the type I percentage tended to increase in the women (51 +/- 9 to 55 +/- 12) and decrease significantly in the men (55 +/- 12 to 48 +/- 13). The fibre areas remained unchanged in both sexes. It is suggested that there is a sex-related fibre adaptation to increased age.