Proceedings of The Physiological Society

University of Manchester (2010) Proc Physiol Soc 19, PC66

Poster Communications

LG/J and SM/J strains as a model for exploration of the genetic effects on muscle fibre properties.

A. M. Carroll1, J. E. Lim2, A. A. Palmer3,4, A. Lionikas1

1. School of Medical Sciences, University of Aberdeen, Aberdeen, Scotland, United Kingdom. 2. Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina, United States. 3. Department of Medicine, Section for Genetic Medicine, University of Chicago, Chicago, Illinois, United States. 4. Department of Psychiatry and Behavioral Neuroscience, University of Chicago, Chicago, Illinois, United States.

Skeletal muscle plays important roles in metabolism, thermoregulation and mobility (2). The functional properties of skeletal muscles are affected by the number, size and type of muscle fibres, all of which vary considerably among individuals. The genetic factors account for a substantial portion of that variation; however, specific mechanisms are poorly understood. Therefore, we aimed at identifying a mouse model which could lead to the discovery of genes influencing characteristics of muscle fibres. We examined soleus fibre properties in two strains of mice divergently selected for large (LG/J) and small (SM/J) body size and their F1 hybrid (1, 3). Solei were dissected from 90 day old mice, transversely cross-sectioned and stained for myosin ATPase. Presented values are mean ± SD. For comparisons, 2-way ANOVA and t-test were used where appropriate. There was no difference in the total number of muscle fibres between the LG/J and SM/J strains across sex (569 ± 95, n=14; versus 540 ± 119, n=13 respectively; P = 0.724). Percentage of type I fibres was higher in LG/J than SM/J in both males (45 ± 3, n=7; versus 37 ± 4, n=9 respectively; P < 0.001) and females (58 ± 4, n=9; versus 41 ± 3, n=7; P < 0.001). Within the females, F1 mice had a higher percentage of type I fibres (50 ± 5, n=5) than SM/J (P<0.01) but lower than LG/J (P<0.01). Male F1 mice had a higher percentage of type I fibres (42 ± 2, n=10) than SM/J males (P<0.01), but showed no difference from LG/J (P = 0.336). This shows an additive effect of the LG/J allele on percentage of type I fibres in females, but a dominant effect in males. Type I fibre area was greater in the LG/J than SM/J strain (P < 0.001) in males (1405 ± 299 μm2, n=7; versus 875 ± 190 μm2, n=9, respectively) and females (1349 ± 279 μm2, n=9 versus 701 ± 247 μm2, n=7, respectively). The LG/J allele showed a dominant effect. Type I fibre area was larger in males than females across strains (P < 0.01). The area of type IIA fibres was higher in the LG/J than SM/J strain across sex (P<0.001): males (1423 ± 262 μm2, n=7; versus 957 ± 195 μm2, n=9 respectively) and females (1304 ± 269 μm2, n=9; versus 713 ± 220 μm2, n=7). The type IIA fibre area was higher in males than females in SM/J (P < 0.05), however, no difference was seen within the LG/J strain (P = 0.390). In conclusion, there are significant differences in the properties of soleus muscle fibres between the LG/J and SM/J strains, providing a useful model to map genes underlying this variation. This may lead to a better understanding of the biological pathways controlling muscle fibre properties and new pharmacological targets for the treatment of musculoskeletal disorders.

Where applicable, experiments conform with Society ethical requirements