Effect of Resistance Exercise and Endurance Exercise on Muscle and Bone FGF-2 Protein Level in Aged Mice

Abstract

Background: Aging is natural phenomena which all living organism experience. With aging, muscle loss and bone loss occur, and induce functional and physiological impairments. Fibroblast growth factor 2, FGF-2, is potent growth factor which induce muscle regeneration via satellite cell activation and osteogenic differentiation. In normal status, FGF-2 is increased and have beneficial effects on muscle and bone regeneration and osteogenic differentiation. In aged status, FGF-2 in muscle is elevated as cell-autonomous response to repair the aged muscle fibers, however, it induce acceleration of muscle aging by depleting satellite cell, and effect of FGF-2 on bone is known. In spite of difference compared to the normal status, none of the studies investigate the effect of exercise on muscle and bone FGF-2 protein level in aged status. Therefore, in this study, we try to investigate the effect of exercise on muscle and bone FGF-2 protein level.

Method: Twenty 19 months old C57B/6 mice were randomly divided into 3 groups, OCON (old control group, n=7), ORT (old resistance exercise group, n=7) and OET (old endurance exercise group, n=6). 12 weeks of resistance ladder climbing exercise was conducted for ORT group and 12 weeks of treadmill exercise was conducted for OET group 3 days per week. Rough food intake was measured every week, and grip strength was measured every two weeks during intervention period. After the exercise intervention period, body composition was measured by DEXA (Duel Energy X-Ray Absorptiometry), and sacrificed. During sacrifice, soleus muscle (SOL), tibialis anterior muscle (TA) and femur were collected and weighted. Collected muscle tissues and bone tissues were frozen and stored in -70 °C right after the sample collection for protein analysis. ELISA protein assay were performed to measure the muscle and bone FGF-2 protein level. The data were analyzed by using one-way ANOVA, and the post-hoc test were conducted to analyze group difference. Also pearson correlation analysis was conducted to assess correlation between hindlimb lean mass and muscle FGF-2 protein level. The level of significance was set at p<0.05.

Results: Relative grip strength of ORT was increased compared to OCON group (OCON vs. ORT, 6.092±0.145 vs. 7.083±0.194, p<0.05). Appendicular lean mass of ORT were increased compared to OCON (forelimb

OCON vs. ORT, 5.25±0.360 vs 6.3±0.239, hindlimb

OCON vs. ORT, 1.52±0.01 vs. 2.15±0.141, p<0.05), only hindlimb lean mass was increased in OET compared to OCON (1.52±0.01 vs. 2.14±0.167, p<0.05). SOL wet weight of ORT was increased compared to OCON (OCON vs. ORT, 0.313±0.011 vs. 0.35±0.0215, p<0.05). Also appendicular BMC and BMD of ORT group were increased compared to OCON group (BMC

OCON vs. ORT, 0.166±0.00204 vs. 0.283±0.0425, BMD

OCON vs ORT, 0.1089±0.007 vs. 0.1329±0.0045, p<0.05), only BMC of forelimb was increased in OET compared to OCON group (OCON vs. ORT, 0.0152±0.002 vs. 0.423±0.0063, p<0.05). SOL FGF-2 protein level of both ORT and OET group were decreased compared to OCON group muscle (OCON vs. ORT, 1.35±0.1667 vs. 0.9434±0.035, p<0.05

OCON vs. OET, 1.35±0.1667 vs. 0.967±0.030, p<0.05), and only TA FGF-2 level of ORT group was decreased compared to OCON group (OCON vs. ORT, 0.400±0.027 vs. 0.268±0.027, p<0.05). However there was no change of femur FGF-2 protein level among all three groups. Negative correlation was found between SOL FGF-2 protein level and hindlimb lean mass (r2=0.48592, p=0.0012).

Conclusion: 12 weeks of resistance exercise increased appendicular lean mass, BMC and BMD. Also 12 weeks of resistance exercise increased soleus muscle and tibialis anterior muscle wet weight. Also 12 weeks of resistance exercise reduced muscle FGF-2 protein level, but bone FGF-2 protein level. Lastly, there was negative correlation between soleus muscle FGF-2 protein level and hindlimb lean mass.