Divergent physiological characteristics and responses to endurance training among inbred mouse strains

Abstract

Both baseline values and adaptive changes in mice can vary depending on the genetic background. We aimed to assess variation in a battery of variables and their adaptations to endurance training in six inbred mouse strains. Males, n = 184, from A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J, and PWD/PhJ strains were assigned to a control or an endurance group (5 weeks swimming exercise). Enzyme activity, histology of soleus (SOL) muscle, swimming endurance, cardiac ventricular and hind limb muscle weight, and femur length were examined. Endurance capacity, morphological and histological variables, and enzyme activity substantially differed among strains. For example, SOL weight was twofold higher and cross-sectional area (CSA) of fibers was ≈ 30% greater in C57BL/6J than in PWD/PhJ strain. The CSA of type 1 fibers were larger than type 2A in PWD/PhJ (P < 0.01); however, the reverse was true in DBA/2J and BALB/cByJ strains (P < 0.05). Swimming endurance in DBA/2J strain was ≈ 9 times better than in BALB/cByJ. Endurance training increased the activity of citrate synthase in gastrocnemius across strains (P < 0.01), however, changes in endurance were strain-specific; the C57BL/6J and DBA/2J strains improved substantially, whereas A/J and BALB/cByJ strains did not. In conclusion, genetic background is a potent determinant of the physiological characteristics and adaptations to training in mice.

Baseline Muscle Mass Is a Poor Predictor of Functional Overload-Induced Gain in the Mouse Model

“…However, such a model is not consistent with our findings (Figure 2). The D2 strain soleus increased 1.7-fold compared to ~1.3-fold for the DUHi or BEH (this strain's soleus contains ~1063 fibers; Kilikevicius et al, 2013; Lionikas et al, 2013a,b). Thus, it is not the number of fibers per se , that is positively associated with muscle mass gain.…”

“…For instance, there is a considerable difference in the number of soleus fibers among the studied strains, ranging from ~760 in the D2 through ~1249 in the DUHi (Kilikevicius et al, 2013; Lionikas et al, 2013a,b). It is reasonable to hypothesize that, other factors remaining constant, more numerous fibers should confer greater gains due to a cumulative effect of fiber hypertrophy.…”

“…This permitted exploration of the role of genetic variability in compensatory growth and assessment of the influence of pre-existing morphological differences. There were three classical inbred strains, C57BL/6J (B6, n = 17), BALB/cByJ (BALB, n = 7), DBA/2J (D2, n = 12), which vary in muscle fiber properties and in adaptation to endurance training (Kilikevicius et al, 2013). A consomic C57BL/6J-Chr10 A/J /NaJ (B6.A10, n = 8) and congenic B6.A-( rs3676616-D10Utsw1 )/Kjn (B6.A, n = 9) strains derived from the B6 (host) and A/J strains (donor) were also included.…”

“…Comparison of relevant traits between animals of different strains reared under the same environmental conditions permits assessment of the role of the genetic background. Up to a 10-fold difference in muscle mass has been reported between inbred strains (Kilikevicius et al, 2013; Lionikas et al, 2013a,b). The number of fibers can differ by over two-fold (Lionikas et al, 2013b).…”

“…In addition to the baseline properties, the ability to adapt to endurance type of training is also affected by genetic background; strains such as A/J show a very limited improvement in endurance capacity while the C57BL/6J and DBA/2J strains can progress substantially (Kilikevicius et al, 2013). Considering the extent of differences in muscle mass and fiber properties between inbred strains, it is reasonable to expect that their ability to adapt to resistance type of training would differ as well.…”