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Miyata T, Shogatsudani A, Igarashi A, Tsutiya H, Yoshida K. Differences in exercise capacity and muscle glycogen metabolism in C57BL/6J and BALB/cA mice. Exp Anim 2024; 73:101-108. [PMID: 37704434 PMCID: PMC10877153 DOI: 10.1538/expanim.23-0074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Accepted: 09/05/2023] [Indexed: 09/15/2023] Open
Abstract
This study compared differences in exercise capacity as well as muscle glycogen content and degradation, and mitochondrial enzyme activity between C57BL/6J and BALB/cA mice. In exercise tests, grip strength was higher in BALB/cA mice. In Rotarod and Inverted screen test, C57BL/6J mice had significantly longer exercise durations and showed differences in motor function and muscle endurance time. Glycogen in the liver and muscle of C57BL/6J mice was significantly decreased after 20 min of swimming. Muscle glycogen content in BALB/cA mice was higher than in C57BL/6J, but swimming induced no decrease in glycogen content. Glycogen phosphorylase in muscle was inactive in the absence of AMP, and its activity increased in a concentration-dependent manner with the addition of AMP in C57BL/6J mice. In BALB/cA mice, phosphorylase activity was increased by AMP, but not further increased by higher concentrations of AMP. The citrate synthase activity in muscle did not differ between C57BL/6J and BALB/cA mice. The results of this study suggested that the reactivity of muscle glycogen phosphorylase to AMP differs among strains of mice and affects glycogen availability during exercise.
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Affiliation(s)
- Tohru Miyata
- Department of Agri-Production Sciences, College of Agriculture, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
- Biosystems & Biofunctions Research Center, Tamagawa University Research Institute, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
| | - Akira Shogatsudani
- Department of Bioresource Sciences, College of Agriculture, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
| | - Ayaka Igarashi
- Department of Bioresource Sciences, College of Agriculture, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
| | - Haruna Tsutiya
- Department of Bioresource Sciences, College of Agriculture, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
| | - Kyouka Yoshida
- Department of Bioresource Sciences, College of Agriculture, Tamagawa University, 6-1-1 Tamagawa-gakuen, Machida, Tokyo 194-8610, Japan
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Štursová P, Budinská X, Nováková Z, Dobšák P, Babula P. Sports activities and cardiovascular system change. Physiol Res 2023; 72:S429-S444. [PMID: 38165749 PMCID: PMC10861254 DOI: 10.33549/physiolres.935238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 09/24/2023] [Indexed: 02/01/2024] Open
Abstract
Sports activity is generally considered to be beneficial to health. The World Health Organization (WHO) recommends physical activity as part of a healthy lifestyle. Sports activities significantly affect the cardiovascular system. A number of studies show that they significantly reduce the risk of cardiovascular disease as well as decrease cardiovascular mortality. This review discusses changes in various cardiovascular parameters in athletes - vagotonia/bradycardia, hypertrophy of heart, ECG changes, blood pressure, and variability of cardiovascular parameters. Because of its relationship to the cardiovascular system, VO2max, which is widely used as an indicator of cardiorespiratory fitness, is also discussed. The review concludes with a discussion of reactive oxygen species (ROS) and oxidative stress, particularly in relation to changes in the cardiovascular system in athletes. The review appropriately summarizes the above issues and points out some new implications.
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Affiliation(s)
- P Štursová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.
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3
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Fernandes MS, Sabino-Arias IT, Dionizio A, Fabricio MF, Trevizol JS, Martini T, Azevedo LB, Valentine RA, Maguire A, Zohoori FV, L. Amaral S, Buzalaf MAR. Effect of Physical Exercise and Genetic Background on Glucose Homeostasis and Liver/Muscle Proteomes in Mice. Metabolites 2022; 12:metabo12020117. [PMID: 35208192 PMCID: PMC8878675 DOI: 10.3390/metabo12020117] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Accepted: 01/22/2022] [Indexed: 02/01/2023] Open
Abstract
We compared the parameters related to glucose homeostasis, and liver and muscle proteomes in fluorosis-susceptible (A/J; S) and fluorosis-resistant (129P3/J; R) mice in response to fluoride (F) exposure and exercise. Ninety male mice (45 R-mice and 45 S-mice) were randomized into three groups: (SI; RI) No-F, No-Exercise, (SII; RII) 50 ppm F, No-Exercise, (SIII; RIII) 50 ppm F, Exercise. Overall, mean F concentrations in the plasma and femur were significantly higher in R-mice compared with S-mice. In R-mice, exercise resulted in an increase in F accumulation in the femur. In S-mice, the mean plasma glucose level was significantly higher in Group II compared with Groups I and III. There was an increase in liver proteins involved in energy flux and antioxidant enzymes in non-exercise groups (I, II) of S-mice in comparison with the corresponding groups of R-mice. The results also showed a decrease in muscle protein expression in Group I S-mice compared with their R-mice counterparts. In conclusion, the findings suggest an increased state of oxidative stress in fluorosis-susceptible mice that might be exacerbated by the treatment with F. In addition, fluorosis-susceptible mice have plasma glucose levels higher than fluorosis-resistant mice on exposure to F, and this is not affected by exercise.
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Affiliation(s)
- Mileni S. Fernandes
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
| | - Isabela T. Sabino-Arias
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
| | - Aline Dionizio
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
| | - Mayara F. Fabricio
- Department of Physical Education, School of Sciences, São Paulo State University, Bauru 17033-360, SP, Brazil; (M.F.F.); (S.L.A.)
| | - Juliana S. Trevizol
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
| | - Tatiana Martini
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
| | - Liane B. Azevedo
- School of Human and Health Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK;
| | - Ruth A. Valentine
- Centre for Oral Health Research, School of Dental Sciences, Newcastle University, Newcastle upon Tyne NE2 4BW, UK; (R.A.V.); (A.M.)
| | - Anne Maguire
- Centre for Oral Health Research, School of Dental Sciences, Newcastle University, Newcastle upon Tyne NE2 4BW, UK; (R.A.V.); (A.M.)
| | - Fatemeh V. Zohoori
- School of Health and Life Sciences, Teesside University, Middlesbrough TS1 3BA, UK
- Correspondence: (F.V.Z.); (M.A.R.B.)
| | - Sandra L. Amaral
- Department of Physical Education, School of Sciences, São Paulo State University, Bauru 17033-360, SP, Brazil; (M.F.F.); (S.L.A.)
| | - Marília A. R. Buzalaf
- Bauru School of Dentistry, University of São Paulo, Bauru 17012-901, SP, Brazil; (M.S.F.); (I.T.S.-A.); (A.D.); (J.S.T.); (T.M.)
- Correspondence: (F.V.Z.); (M.A.R.B.)
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Hwang DJ, Kwon KC, Choi DH, Song HK, Kim KS, Jung YS, Hwang DY, Cho JY. Comparison of intrinsic exercise capacity and response to acute exercise in ICR (Institute of Cancer Research) mice derived from three different lineages. Lab Anim Res 2021; 37:21. [PMID: 34348800 PMCID: PMC8335942 DOI: 10.1186/s42826-021-00094-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Accepted: 06/26/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND As a laboratory animal resource, the ICR mouse is commonly used in a variety of research fields. However, information on differences in exercise-related characteristics in ICR mice derived from different lineages and the underlying mechanisms remains to be elucidated. In this study, we investigated the intrinsic exercise capacity and a magnitude of response to acute exercise, and sought to identify mechanisms contributing to difference in Korl:ICR (a novel ICR lineage recently established by the National Institute of Food and Drug Safety Evaluation, Korea) and two commercialized ICR lineages derived from different origins (viz., A:ICR mouse from Orient Bio Com, the United States, and B:ICR mouse from Japan SLC Inc., Japan). RESULTS Results showed that despite no significant difference in body weight and weight-proportioned tissue mass of heart and skeletal muscles among groups, the relatively low intrinsic exercise capacity and exaggerated response to acute exercise were identified in B:ICR comparted with Korl:ICR and A:ICR, as reflected by total work and lactate threshold (LT). Also, the mitochondrial efficiency expressed as the complex 1 and complex 1 + 2 respiratory control ratio (RCR) values for cardiac mitochondrial O2 consumption in B:ICR was significantly lower than that in Korl:ICR with higher level of state 2 respiration by glutamate/malate and UCP3 expression in cardiac muscle. CONCLUSIONS Taken together, these results indicate that the intrinsic exercise capacity of ICR mouse varies according to lineages, suggesting the role of cardiac mitochondrial coupling efficiency as a possible mechanism that might contribute to differences in the intrinsic exercise capacity and magnitude of response to exercise.
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Affiliation(s)
- Dong-Joo Hwang
- Exercise Biochemistry Laboratory, Korea National Sport University, Yangjae-daero, Songpa-gu, Seoul, Republic of Korea
| | - Ki-Chun Kwon
- Exercise Biochemistry Laboratory, Korea National Sport University, Yangjae-daero, Songpa-gu, Seoul, Republic of Korea
| | - Dong-Hun Choi
- Exercise Biochemistry Laboratory, Korea National Sport University, Yangjae-daero, Songpa-gu, Seoul, Republic of Korea
| | - Hyun-Keun Song
- Department of Microbiology and Immunology, INJE University College of Medicine, Inje-ro, Gimhae-si, Gyeongsangnam-do, Republic of Korea
| | - Kil-Soo Kim
- College of Veterinary Medicine, Kyungpook National University, Daehak-ro, Buk-gu, Daegu, Republic of Korea
| | - Young-Suk Jung
- College of Pharmacy, Pusan National University, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan, Republic of Korea
| | - Dae-Youn Hwang
- Department of Biomaterials Science, College of Natural Resources and Life Science/Life and Industry Convergence Research Institute, Pusan National University, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan, Republic of Korea
| | - Joon-Yong Cho
- Exercise Biochemistry Laboratory, Korea National Sport University, Yangjae-daero, Songpa-gu, Seoul, Republic of Korea.
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Massett MP, Courtney SM, Kim SK, Avila JJ. Contribution of Chromosome 14 to Exercise Capacity and Training Responses in Mice. Front Physiol 2019; 10:1165. [PMID: 31572215 PMCID: PMC6753330 DOI: 10.3389/fphys.2019.01165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 08/28/2019] [Indexed: 11/22/2022] Open
Abstract
Quantitative trait loci for exercise capacity and training-induced changes in exercise capacity were identified previously on mouse Chromosome 14. The aim of this study was to further investigate the role of Chromosome 14 in exercise capacity and responses to training in mice. Exercise phenotypes were measured in chromosome substitution strain mice carrying Chromosome 14 from the PWD/PhJ donor strain on the genetic background of a host C57BL/6J (B6) strain (B6.PWD14). Eight week old female and male mice from both strains completed a graded exercise test to exhaustion to assess intrinsic or baseline exercise capacity. A separate group of 12-week old female and male mice, randomly assigned to sedentary control (SED) or exercise training (EX) groups, completed a graded exercise test before and after a 4-week exercise training period. EX mice completed a 4-week training program consisting of treadmill running 5 days/week, 60 min/day at a final intensity of approximately 65% of maximum. For intrinsic exercise capacity, exercise time and work were significantly greater in female and male B6.PWD14 than sex-matched B6 mice. In the training study, female B6.PWD14 mice had higher pre-training exercise capacity than B6 mice. In contrast, there were no significant differences for pre-training exercise capacity between male B6 and B6.PWD14 mice. There were no significant strain differences for responses to training. These data demonstrate that PWD/PhJ alleles on Chromosome 14 significantly affect intrinsic exercise capacity. Furthermore, these results support continued efforts to identify candidate genes on Chromosome 14 underlying variation in exercise capacity.
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Sokołowska E, Błachnio-Zabielska AU. A Critical Review of Electroporation as A Plasmid Delivery System in Mouse Skeletal Muscle. Int J Mol Sci 2019; 20:ijms20112776. [PMID: 31174257 PMCID: PMC6600476 DOI: 10.3390/ijms20112776] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 06/03/2019] [Accepted: 06/04/2019] [Indexed: 12/13/2022] Open
Abstract
The gene delivery to skeletal muscles is a promising strategy for the treatment of both muscular disorders (by silencing or overexpression of specific gene) and systemic secretion of therapeutic proteins. The use of a physical method like electroporation with plate or needle electrodes facilitates long-lasting gene silencing in situ. It has been reported that electroporation enhances the expression of the naked DNA gene in the skeletal muscle up to 100 times and decreases the changeability of the intramuscular expression. Coelectransfer of reporter genes such as green fluorescent protein (GFP), luciferase or beta-galactosidase allows the observation of correctly performed silencing in the muscles. Appropriate selection of plasmid injection volume and concentration, as well as electrotransfer parameters, such as the voltage, the length and the number of electrical pulses do not cause long-term damage to myocytes. In this review, we summarized the electroporation methodology as well as the procedure of electrotransfer to the gastrocnemius, tibialis, soleus and foot muscles and compare their advantages and disadvantages.
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Affiliation(s)
- Emilia Sokołowska
- Department of Hygiene, Epidemiology and Metabolic Disorders, Medical University of Bialystok, 15-222 Bialystok, Poland.
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Graber TG, Fandrey KR, Thompson LV. Novel individualized power training protocol preserves physical function in adult and older mice. GeroScience 2019; 41:165-183. [PMID: 31076998 PMCID: PMC6544743 DOI: 10.1007/s11357-019-00069-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 04/16/2019] [Indexed: 11/27/2022] Open
Abstract
Sarcopenia, the age-related loss of muscle mass and strength, contributes to frailty, functional decline, and reduced quality of life in older adults. Exercise is a recognized therapy for sarcopenia and muscle dysfunction, though not a cure. Muscle power declines at an increased rate compared to force, and force output declines earlier than mass. Thus, there is a need for research of exercise focusing on improving power output and functionality in older adults. Our primary purpose was proof-of-concept that a novel individualized power exercise modality would induce positive adaptations in adult mice, before the exercise program was applied to an aged cohort. We hypothesized that after following our protocol, both adult and older mice would show improved function, though there would be evidence of anabolic resistance in the older mice. Male C57BL/6 mice (12 months of age at study conclusion) were randomized into control (n = 9) and exercise (n = 6) groups. The trained group used progressive resistance (with a weighted harness) and intensity (~ 4-10 rpm) on a custom motorized running wheel. The mice trained similarly to a human workout regimen (4-5 sets/session, 3 sessions/week, for 12 weeks). We determined significant (p < 0.05) positive adaptations post-intervention, including: neuromuscular function (rotarod), strength/endurance (inverted cling grip test), training physiology (force/power output per session), muscle size (soleus mass), and power/velocity of contraction (in vitro physiology). Secondly, we trained a cohort of older male mice (28 months old at conclusion): control (n = 12) and exercised (n = 8). While the older exercised mice did preserve function and gain benefits, they also demonstrated evidence of anabolic resistance.
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Affiliation(s)
- Ted G. Graber
- Department of Nutrition and Metabolism, Division of Rehabilitation Science, University of Texas Medical Branch, Galveston, TX USA
| | - Katie R. Fandrey
- Program in Physical Therapy, University of Minnesota-Twin Cities, Minneapolis, MN USA
| | - LaDora V. Thompson
- Department of Physical Therapy & Athletic Training, Boston University, Boston, MA USA
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Low Citrate Synthase Activity Is Associated with Glucose Intolerance and Lipotoxicity. J Nutr Metab 2019; 2019:8594825. [PMID: 30944739 PMCID: PMC6421790 DOI: 10.1155/2019/8594825] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Accepted: 01/12/2019] [Indexed: 11/18/2022] Open
Abstract
Citrate synthase (CS) is a key mitochondrial enzyme. The aim of this study was to test the hypothesis that low CS activity impairs the metabolic health of mice fed a high fat diet (HFD) and promotes palmitate-induced lipotoxicity in muscle cells. C57BL/6J (B6) mice and congenic B6.A-(rs3676616-D10Utsw1)/KjnB6 (B6.A), a strain which carries the A/J allele of CS on the B6 strain background, were fed HFD (45% kcal from fat) for 12 weeks. C2C12 mouse muscle cells were used to investigate effects of CS knockdown on cell viability and signalling after incubation in 0.8 mM palmitate. CS activity, but not that of β-hydroxyacyl-coenzyme-A dehydrogenase was lower in the gastrocnemius muscle and heart of B6.A mice compared to B6 mice (P < 0.001). During HFD feeding, glucose tolerance of mice decreased progressively and to a greater extent in B6.A females compared to B6 females, with males showing a similar trend. Body weight and fat gain did not differ between B6.A and B6 mice. After an 18 h incubation in 0.8 mM palmitate C2C12 muscle cells with ∼50% shRNA mediated reduction in CS activity showed lower (P < 0.001) viability and increased (P < 0.001) levels of cleaved caspase-3 compared to the scramble shRNA treated C2C12 cells. A/J strain variant of CS is associated with low enzyme activity and impaired metabolic health. This could be due to impaired lipid metabolism in muscle cells.
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9
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Satkunskiene D, Ratkevicius A, Kamandulis S, Venckunas T. Effects of myostatin on the mechanical properties of muscles during repeated active lengthening in the mouse. Appl Physiol Nutr Metab 2018; 44:381-388. [PMID: 30222937 DOI: 10.1139/apnm-2018-0369] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of the present study was to investigate how myostatin dysfunction affects fast and slow muscle stiffness and viscosity during severe repeated loading. Isolated extensor digitorum longus (EDL) and soleus muscles of young adult female mice of the BEH (dysfunctional myostatin) and BEH+/+ (functional myostatin) strains were subjected to 100 contraction-stretching loading cycles during which contractile and mechanical properties were assessed. BEH mice exhibited greater exercise-induced muscle damage, although the effect was muscle- and age-dependent and limited to the early phases of simulated exercise. The relative reduction of the EDL muscle isometric force recorded during the initial 10-30 loading cycles was greater in BEH mice than in BEH+/+ mice and exceeded that of the soleus muscle of either strain. The induced damage was associated with lower muscle stiffness. The effects of myostatin on the mechanical properties of muscles depend on muscle type and maturity.
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Affiliation(s)
- Danguole Satkunskiene
- Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania.,Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania
| | - Aivaras Ratkevicius
- Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania.,Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania
| | - Sigitas Kamandulis
- Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania.,Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania
| | - Tomas Venckunas
- Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania.,Institute of Sports Science and Innovation, Lithuanian Sports University, Kaunas, Lithuania
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Vellers HL, Kleeberger SR, Lightfoot JT. Inter-individual variation in adaptations to endurance and resistance exercise training: genetic approaches towards understanding a complex phenotype. Mamm Genome 2018; 29:48-62. [PMID: 29356897 PMCID: PMC5851699 DOI: 10.1007/s00335-017-9732-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 12/27/2017] [Indexed: 12/21/2022]
Abstract
Exercise training which meets the recommendations set by the National Physical Activity Guidelines ensues a multitude of health benefits towards the prevention and treatment of various chronic diseases. However, not all individuals respond well to exercise training. That is, some individuals have no response, while others respond poorly. Genetic background is known to contribute to the inter-individual (human) and -strain (e.g., mice, rats) variation with acute exercise and exercise training, though to date, no specific genetic factors have been identified that explain the differential responses to exercise. In this review, we provide an overview of studies in human and animal models that have shown a significant contribution of genetics in acute exercise and exercise training-induced adaptations with standardized endurance and resistance training regimens, and further describe the genetic approaches which have been used to demonstrate such responses. Finally, our current understanding of the role of genetics and exercise is limited primarily to the nuclear genome, while only a limited focus has been given to a potential role of the mitochondrial genome and its interactions with the nuclear genome to predict the exercise training-induced phenotype(s) responses. We therefore discuss the mitochondrial genome and literature that suggests it may play a significant role, particularly through interactions with the nuclear genome, in the inherent ability to respond to exercise.
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Affiliation(s)
- Heather L Vellers
- Immunity, Inflammation and, Disease Laboratory, National Institute of Environmental Health Sciences, 111 T.W. Alexander Dr., Building 101, E-224, Research Triangle Park, NC, 27709, USA.
| | - Steven R Kleeberger
- Immunity, Inflammation and, Disease Laboratory, National Institute of Environmental Health Sciences, 111 T.W. Alexander Dr., Building 101, E-224, Research Triangle Park, NC, 27709, USA
| | - J Timothy Lightfoot
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, 77843, USA
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11
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Avila JJ, Kim SK, Massett MP. Differences in Exercise Capacity and Responses to Training in 24 Inbred Mouse Strains. Front Physiol 2017; 8:974. [PMID: 29249981 PMCID: PMC5714923 DOI: 10.3389/fphys.2017.00974] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Accepted: 11/15/2017] [Indexed: 01/13/2023] Open
Abstract
Changes in cardiorespiratory fitness in response to a standardized exercise training protocol differ substantially between individuals. Results from cross-sectional, twin, and family studies indicate genetics contribute to individual differences in both baseline exercise capacity and the response to training. Exercise capacity and responses to training also vary between inbred strains of mice. However, such studies have utilized a limited number of inbred strains. Therefore, the aim of this study was to characterize exercise-training responses in a larger number of genetically diverse strains of inbred mice and estimate the contribution of genetic background to exercise training responses. Eight-week old male mice from 24 inbred strains (n = 4–10/strain) performed a graded exercise test before and after 4 weeks of exercise training. Before training, exercise capacity was significantly different between strains when expressed as time (range = 21–42 min) and work performed (range = 0.42–3.89 kg·m). The responses to training also were significantly different between strains, ranging from a decrease of 2.2 min in NON/ShiLtJ mice to an increase of 8.7 min in SWR/J mice. Changes in work also varied considerably between the lowest (−0.24 kg·m in NON/ShiLtJ) and highest (+2.30 kg·m in FVB/NJ) performing strains. Heart and skeletal muscle masses also varied significantly between strains. Two broad sense heritability estimates were calculated for each measure of exercise capacity and for responses to training. For change in run time, the intraclass correlation between mice within the same inbred strain (rI) was 0.58 and the coefficient of genetic determination (g2) was 0.41. Heritability estimates were similar for the change in work: rI = 0.54 and g2 = 0.37. In conclusion, these results indicate genetic background significantly influences responses to exercise training.
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Affiliation(s)
- Joshua J Avila
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
| | - Seung Kyum Kim
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
| | - Michael P Massett
- Department of Health and Kinesiology, Texas A&M University, College Station, TX, United States
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12
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Gabriel BM, Al-Tarrah M, Alhindi Y, Kilikevicius A, Venckunas T, Gray SR, Lionikas A, Ratkevicius A. H55N polymorphism is associated with low citrate synthase activity which regulates lipid metabolism in mouse muscle cells. PLoS One 2017; 12:e0185789. [PMID: 29095821 PMCID: PMC5667803 DOI: 10.1371/journal.pone.0185789] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 09/19/2017] [Indexed: 11/18/2022] Open
Abstract
The H55N polymorphism in the Cs gene of A/J mice has been linked to low activity of the enzyme in skeletal muscles. The aim of the study was to test this hypothesis and examine effects of low citrate synthase (CS) activity on palmitate metabolism in muscle cells. Results of the study showed that carriers of the wild type (WT) Cs (C57BL/6J and Balb/cByJ mouse strains) had higher CS activity (p < 0.01) than carriers of the A/J variant (B6.A-(rs3676616-D10Utsw1)/KjnB6 and A/J mouse strains) in the heart, liver and gastrocnemius muscle. Furthermore, the recombinant CS protein of WT showed higher CS activity than the A/J variant. In C2C12 muscle cells the shRNA mediated 47% knockdown of CS activity reduced the rate of fatty acid oxidation compared to the control cells. In summary, our results are consistent with the hypothesis that H55N substitution causes a reduction in CS activity. Furthermore, low CS activity interferes with metabolic flexibility of muscle cells.
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Affiliation(s)
- Brendan M. Gabriel
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Aberdeen, Scotland, United Kingdom
- Integrative Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - Mustafa Al-Tarrah
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Aberdeen, Scotland, United Kingdom
| | - Yosra Alhindi
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Aberdeen, Scotland, United Kingdom
| | - Audrius Kilikevicius
- Department of Applied Biology and Rehabilitation, Lithuanian Sports University, Kaunas, Lithuania
| | - Tomas Venckunas
- Department of Applied Biology and Rehabilitation, Lithuanian Sports University, Kaunas, Lithuania
| | - Stuart R. Gray
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom
| | - Arimantas Lionikas
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Aberdeen, Scotland, United Kingdom
| | - Aivaras Ratkevicius
- Department of Applied Biology and Rehabilitation, Lithuanian Sports University, Kaunas, Lithuania
- * E-mail:
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13
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Kvedaras M, Minderis P, Fokin A, Ratkevicius A, Venckunas T, Lionikas A. Forced Running Endurance Is Influenced by Gene(s) on Mouse Chromosome 10. Front Physiol 2017; 8:9. [PMID: 28167917 PMCID: PMC5253375 DOI: 10.3389/fphys.2017.00009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/05/2017] [Indexed: 01/10/2023] Open
Abstract
Phenotypic diversity between laboratory mouse strains provides a model for studying the underlying genetic mechanisms. The A/J strain performs poorly in various endurance exercise models. The aim of the study was to test if endurance capacity and contractility of the fast- and slow-twitch muscles are affected by the genes on mouse chromosome 10. The C57BL/6J (B6) strain and C57BL/6J-Chr 10A/J/NaJ (B6.A10) consomic strain which carries the A/J chromosome 10 on a B6 strain background were compared. The B6.A10 mice compared to B6 were larger in body weight (p < 0.02): 27.2 ± 1.9 vs. 23.8 ± 2.7 and 23.4 ± 1.9 vs. 22.9 ± 2.3 g, for males and females, respectively, and in male soleus weight (p < 0.02): 9.7 ± 0.4 vs. 8.6 ± 0.9 mg. In the forced running test the B6.A10 mice completed only 64% of the B6 covered distance (p < 0.0001). However, there was no difference in voluntary wheel running (p = 0.6) or in fatigability of isolated soleus (p = 0.24) or extensor digitorum longus (EDL, p = 0.7) muscles. We conclude that chromosome 10 of the A/J strain contributes to reduced endurance performance. We also discuss physiological mechanisms and methodological aspects relevant to interpretation of these findings.
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Affiliation(s)
- Mindaugas Kvedaras
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Petras Minderis
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Andrej Fokin
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Aivaras Ratkevicius
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Tomas Venckunas
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Arimantas Lionikas
- School of Medicine, Medical Sciences and Nutrition, College of Life Sciences and Medicine, University of Aberdeen Aberdeen, UK
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14
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Carroll AM, Cheng R, Collie-Duguid ESR, Meharg C, Scholz ME, Fiering S, Fields JL, Palmer AA, Lionikas A. Fine-mapping of genes determining extrafusal fiber properties in murine soleus muscle. Physiol Genomics 2017; 49:141-150. [PMID: 28087756 PMCID: PMC5374456 DOI: 10.1152/physiolgenomics.00092.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Revised: 12/07/2016] [Accepted: 12/12/2016] [Indexed: 02/08/2023] Open
Abstract
Muscle fiber cross-sectional area (CSA) and proportion of different fiber types are important determinants of muscle function and overall metabolism. Genetic variation plays a substantial role in phenotypic variation of these traits; however, the underlying genes remain poorly understood. This study aimed to map quantitative trait loci (QTL) affecting differences in soleus muscle fiber traits between the LG/J and SM/J mouse strains. Fiber number, CSA, and proportion of oxidative type I fibers were assessed in the soleus of 334 genotyped female and male mice of the F34 generation of advanced intercross lines (AIL) derived from the LG/J and SM/J strains. To increase the QTL detection power, these data were combined with 94 soleus samples from the F2 intercross of the same strains. Transcriptome of the soleus muscle of LG/J and SM/J females was analyzed by microarray. Genome-wide association analysis mapped four QTL (genome-wide P < 0.05) affecting the properties of muscle fibers to chromosome 2, 3, 4, and 11. A 1.5-LOD QTL support interval ranged between 2.36 and 4.67 Mb. On the basis of the genomic sequence information and functional and transcriptome data, we identified candidate genes for each of these QTL. The combination of analyses in F2 and F34 AIL populations with transcriptome and genomic sequence data in the parental strains is an effective strategy for refining QTL and nomination of the candidate genes.
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Affiliation(s)
- A M Carroll
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill Aberdeen, United Kingdom.,The New Zealand Institute for Plant & Food Research Limited, Palmerston North, New Zealand
| | - R Cheng
- Research School of Biology, Australian National University, Acton, Australia
| | - E S R Collie-Duguid
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill Aberdeen, United Kingdom.,Centre for Genome Enabled Biology and Medicine, University of Aberdeen, Old Aberdeen, Aberdeen, United Kingdom
| | - C Meharg
- Institute for Global Food Security, Queen's University Belfast, Belfast, United Kingdom
| | - M E Scholz
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill Aberdeen, United Kingdom
| | - S Fiering
- Department of Microbiology/Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire; and
| | - J L Fields
- Department of Microbiology/Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire; and
| | - A A Palmer
- Department of Psychiatry, University of California San Diego, La Jolla, California
| | - A Lionikas
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Foresterhill Aberdeen, United Kingdom;
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15
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Wang Q, Du L, Wang Y, Xu C, Sun Z, Fu Y, Yang B, Wang Y, Mu C, Fan S, Cai L, Katsube T, Liu Q. The development and biological characteristics of a novel potentially radioresistant inbred mouse strain. Mol Med Rep 2016; 15:759-767. [PMID: 28035407 PMCID: PMC5364868 DOI: 10.3892/mmr.2016.6066] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 11/15/2016] [Indexed: 02/03/2023] Open
Abstract
The growth of biomedical research over the previous decades has been accompanied by an increase in the number, complexity and diversity of experimental animals developed as research tools, and inbred mice are some of the most widely used. However, thus far, no inbred mice have exhibited strong radioresistance for use in radiation‑damage research. To develop a radioresistant mouse model, a female Japanese outbreeding strain ICR/JCL mouse was mated with a male Chinese inbred strain 615 mouse. From the F1 generation, the mouse line was maintained by brother‑to‑sister mating. A novel mouse strain was established over >20 continuous generations and designated the Institute of Radiation Medicine-2 (IRM-2) mouse. The biological characteristics, genetic characteristics and susceptibility to radiation of these mice were determined. The IRM‑2 mice inherited traits from the parents, including strong reproductive capacity, stable physiological and biochemical indices and few differences among individuals. According to the genetic results, the IRM‑2 mice exhibited homozygosity, isogenicity and consistency, in agreement with international standards for inbred strains. Radiosensitivity studies have previously suggested that the lethal dose (LD)50 values for IRM‑2 mice were 7.17 Gy (male) and 7.5 Gy (female), resulting in a dose reduction factor value of 1.39 (male) and 1.37 (female). The mortality of IRM‑2 mice irradiated with 8 Gy total body irradiation was 15% at day 9 and 90% at day 15 after radiation. The number of nucleated cells in bone marrow, DNA content and colony‑forming unit‑spleen counts in IRM‑2 mice after exposure to γ‑ray irradiation were markedly higher than the corresponding values for the parental strains, suggesting that the IRM‑2 mice exhibit high resistance to ionizing radiation. Thus, it is suggested that this novel inbred mouse strain may be developed as an animal model of radioresistance for future use in radiation research.
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Affiliation(s)
- Qin Wang
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Liqing Du
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Yan Wang
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Chang Xu
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Zhijuan Sun
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Yue Fu
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Bing Yang
- Department of Cell Biology, Tianjin Medical University, Tianjin 300070, P.R. China
| | - Yueying Wang
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Chuanjie Mu
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Saijun Fan
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
| | - Lu Cai
- Department of Pediatrics, University of Louisville, Louisville, KY 40202, USA
| | - Takanori Katsube
- Radiation Risk Reduction Research Program, National Institute of Radiological Sciences, Anagawa 4‑9‑1, Inage‑ku, Chiba 263‑8555, Japan
| | - Qiang Liu
- Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear Medicine, Institute of Radiation Medicine of Chinese Academy of Medical Science, Tianjin 300192, P.R. China
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16
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Kilikevicius A, Bunger L, Lionikas A. Baseline Muscle Mass Is a Poor Predictor of Functional Overload-Induced Gain in the Mouse Model. Front Physiol 2016; 7:534. [PMID: 27895593 PMCID: PMC5108802 DOI: 10.3389/fphys.2016.00534] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 10/26/2016] [Indexed: 12/15/2022] Open
Abstract
Genetic background contributes substantially to individual variability in muscle mass. Muscle hypertrophy in response to resistance training can also vary extensively. However, it is less clear if muscle mass at baseline is predictive of the hypertrophic response. The aim of this study was to examine the effect of genetic background on variability in muscle mass at baseline and in the adaptive response of the mouse fast- and slow-twitch muscles to overload. Males of eight laboratory mouse strains: C57BL/6J (B6, n = 17), BALB/cByJ (n = 7), DBA/2J (D2, n = 12), B6.A-(rs3676616-D10Utsw1)/Kjn (B6.A, n = 9), C57BL/6J-Chr10A/J/NaJ (B6.A10, n = 8), BEH+/+ (n = 11), BEH (n = 12), and DUHi (n = 12), were studied. Compensatory growth of soleus and plantaris muscles was triggered by a 4-week overload induced by synergist unilateral ablation. Muscle weight in the control leg (baseline) varied from 5.2 ± 07 mg soleus and 11.4 ± 1.3 mg plantaris in D2 mice to 18.0 ± 1.7 mg soleus in DUHi and 43.7 ± 2.6 mg plantaris in BEH (p < 0.001 for both muscles). In addition, soleus in the B6.A10 strain was ~40% larger (p < 0.001) compared to the B6. Functional overload increased muscle weight, however, the extent of gain was strain-dependent for both soleus (p < 0.01) and plantaris (p < 0.02) even after accounting for the baseline differences. For the soleus muscle, the BEH strain emerged as the least responsive, with a 1.3-fold increase, compared to a 1.7-fold gain in the most responsive D2 strain, and there was no difference in the gain between the B6.A10 and B6 strains. The BEH strain appeared the least responsive in the gain of plantaris as well, 1.3-fold, compared to ~1.5-fold gain in the remaining strains. We conclude that variation in muscle mass at baseline is not a reliable predictor of that in the overload-induced gain. This suggests that a different set of genes influence variability in muscle mass acquired in the process of normal development, growth, and maintenance, and in the process of adaptive growth of the muscle challenged by overload.
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Affiliation(s)
- Audrius Kilikevicius
- Institute of Sport Science and Innovations, Lithuanian Sports University Kaunas, Lithuania
| | - Lutz Bunger
- Animal & Veterinary Sciences, Scotland's Rural College, Roslin Institute Building Midlothian, UK
| | - Arimantas Lionikas
- School of Medicine, Medical Sciences and Nutrition, College of Life Sciences and Medicine, University of Aberdeen Aberdeen, UK
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17
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Baltusnikas J, Kilikevicius A, Venckunas T, Fokin A, Lionikas A, Ratkevicius A. Regenerated soleus muscle shows reduced creatine kinase efflux after contractile activity in vitro. Appl Physiol Nutr Metab 2015; 40:129-33. [PMID: 25565131 DOI: 10.1139/apnm-2014-0274] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Regenerated skeletal muscles show less muscle damage after strenuous muscle exercise. The aim of the studies was to investigate if the regeneration is associated with reduced muscle creatine kinase (CK) efflux immediately after the exercise. Cryolesion was applied to the soleus muscle of 3-month-old C57BL/6J male mice. Then total CK efflux was assessed in vitro in the regenerated muscles without exercise or after 100 eccentric contractions. The same measurements were performed in the control muscles, which were not exposed to cryolesion. Regenerated muscles generated weaker (P < 0.05) twitches, but stronger (P < 0.05) 150-Hz and 300-Hz tetani with prolonged (P < 0.01) contraction times compared with the control muscles. There was no difference between regenerated and control muscles in the total CK efflux without exercise, but only control muscles showed an increase (P < 0.001) in the CK efflux after the exercise. Our results suggest that muscle regeneration is associated with modulation of contractile properties and improvement in muscle resistance to damage after eccentric exercise.
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Affiliation(s)
- Juozas Baltusnikas
- a Institute of Sports Sciences and Innovation, Lithuanian Sports University, Sporto 6, LT-44221 Kaunas, Lithuania
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Carbonetto P, Cheng R, Gyekis JP, Parker CC, Blizard DA, Palmer AA, Lionikas A. Discovery and refinement of muscle weight QTLs in B6 × D2 advanced intercross mice. Physiol Genomics 2014; 46:571-82. [PMID: 24963006 DOI: 10.1152/physiolgenomics.00055.2014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The genes underlying variation in skeletal muscle mass are poorly understood. Although many quantitative trait loci (QTLs) have been mapped in crosses of mouse strains, the limited resolution inherent in these conventional studies has made it difficult to reliably pinpoint the causal genetic variants. The accumulated recombination events in an advanced intercross line (AIL), in which mice from two inbred strains are mated at random for several generations, can improve mapping resolution. We demonstrate these advancements in mapping QTLs for hindlimb muscle weights in an AIL (n = 832) of the C57BL/6J (B6) and DBA/2J (D2) strains, generations F8-F13. We mapped muscle weight QTLs using the high-density MegaMUGA SNP panel. The QTLs highlight the shared genetic architecture of four hindlimb muscles and suggest that the genetic contributions to muscle variation are substantially different in males and females, at least in the B6D2 lineage. Out of the 15 muscle weight QTLs identified in the AIL, nine overlapped the genomic regions discovered in an earlier B6D2 F2 intercross. Mapping resolution, however, was substantially improved in our study to a median QTL interval of 12.5 Mb. Subsequent sequence analysis of the QTL regions revealed 20 genes with nonsense or potentially damaging missense mutations. Further refinement of the muscle weight QTLs using additional functional information, such as gene expression differences between alleles, will be important for discerning the causal genes.
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Affiliation(s)
| | - R Cheng
- Australian National University, Canberra, Australia
| | - J P Gyekis
- Pennsylvania State University, State College, Pennsylvania; and
| | | | - D A Blizard
- Pennsylvania State University, State College, Pennsylvania; and
| | - A A Palmer
- University of Chicago, Chicago, Illinois
| | - A Lionikas
- University of Aberdeen, Aberdeen, United Kingdom;
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Lionikas A, Smith CJ, Smith TL, Bünger L, Banks RW, Bewick GS. Analyses of muscle spindles in the soleus of six inbred mouse strains. J Anat 2013; 223:289-96. [PMID: 23834369 DOI: 10.1111/joa.12076] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/03/2013] [Indexed: 02/06/2023] Open
Abstract
Adult muscle size and fibre-type composition are heritable traits that vary substantially between individuals. We used inbred mouse strains in which soleus muscle mass varied by an order of magnitude to explore whether properties of muscle spindles can also be influenced by genetic factors. Skip-serial cross-sections of soleus muscles dissected from 15 male mice of BEH, BEL, C57BL/6J, DUH, LG/J and SM/J strains were analysed for number of muscle spindles and characteristics of intrafusal and extrafusal fibres following ATPase staining. The BEL and DUH strains determined the range of: soleus mean size, a 10-fold difference from 2.1 to 22.3 mg, respectively; the mean number of extrafusal fibres, a 2.5-fold difference from 497 to 1249; and mean fibre-cross-sectional area, three-fold difference, e.g. for type 1 fibres, from 678 to 1948 μm². The range of mean proportion of type 1 fibres was determined by C57BL/6J (31%) and DUH (64%) strains. The mean number of spindles per muscle ranged between nine (LG/J) and 13 (BEL) (strain effect P < 0.02). Genetic correlations between spindle count and muscle weight or properties of extrafusal fibres were weak and not statistically significant. However, there was a strong correlation between the proportion of spindles with more than one bag2 fibre and the proportion of extrafusal fibres that were of type 1, and strain-dependent variation in the numbers of such spindles was statistically significant. The numbers of intrafusal fibres per spindle ranged from 2 to 8, with the most common complement of four found in 75.6% of spindles. There were no significant differences between the strains in the mean numbers of intrafusal fibres; however, the variance of the number was significantly less for the C57BL/6J strain than for any of the others. We conclude that abundance of muscle spindles and their intrafusal-fibre composition are substantially determined by genetic factors, which are different from those affecting muscle size and properties of the extrafusal fibres.
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