Muscle Fiber‐type Differences in Mice Selected for Wheel Running Behavior

Abstract

Mammalian skeletal muscle fibers contain varying amounts of myosin isoforms for slow and fast myosin heavy‐chains, (Types 1, 2A, 2X, 2B,). Muscle fibers containing different isoform profiles typically correlate with variable force, speed, and fatigue resistance. We investigated the isoform profiles of various hindlimb muscles in two lines of mice, one of which has been undergoing laboratory selection for high wheel‐running behavior for over 80 generations. We hypothesized that the selected line would typically have the most type 1 or type 2a myosin. This isoform is most often expressed in muscle with higher oxidative capacity and therefore greater fatigue resistance. We collected lower leg muscles including the quadriceps, soleus, medial and lateral gastrocnemius, and plantaris from the breeding pairs of generation 80 from replicated selected and control lines.Some data were previously reported from generations collected over a decade ago, but many muscles were not included, and we wished to see if further changes to the isoform profiles have arisen. SDS PAGE and densitometry were used to quantify the myosin isoforms.Preliminary analysis using densitometry shows that the leg muscles of high‐running mice had a higher concentration of type 1 myosin, or in other cases, a shift towards slower type 2 fibers (i.e. 2x to 2a). The findings were highly muscle‐specific, and indicate shifts in muscle protein expression has resulted from selection.Our new catalog of isoform profiles will serve as a baseline for comparison of two future studies – one following the development and subsequent senescence of muscle function with aging, and the second determining the effect of exercise activity on both selected and control lines.With the aging study we hope to identify whether activity during the lifetime is as important and genetic factors in preventing the decline of muscle performance with age. For the exercise study, we hope to determine the influence of genetics on shaping exercise performance for individuals which descend from sedentary or active lines. All of these data address long‐standing nature vs nurture debates, but also bear on human clinical muscle disease, aging, and activity.Support or Funding InformationThis research was supported by California State University, Long Beach and the National Institute of General Medical Sciences of the National Institutes of Health under Award Numbers; 8UL1GM118979‐02; 8TL4GM118980‐02; 8RL5GM118978‐02. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We would also like to thank Dr. Theodore Garland from University of California, Riverside and Dr. Angela Horner from California State University, San Bernardino.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.