Meeting Abstract
The property of muscle stiffness, though extensively studied, is poorly understood. Past experiments have described the stiffness in whole muscles, muscle tendon units, and individual muscle fibers. Muscle stiffness plays a role in stabilizing muscles during force production and reducing energy costs. In this study, the effects of titin and age on both active and passive muscle stiffness were tested using an eccentric workloop technique. The soleus and extensor digitorum longus muscles from wildtype, muscular dystrophy with myositis (mdm), and aged mice were extracted to determine how titin and age affect whole muscle stiffness. The stiffness of the muscle was assessed calculating effective Young’s Modulus. The effects of age, genotype, and stimulation were analyzed using 3-way ANOVA and ANCOVA tests comparing age, genotype, and stimulation. Wildtype mice had a larger active stiffness for both EDL and soleus than mutants (p<0.0001). For passive muscle, the mutant EDL was significantly stiffer than other muscles (p<0.0001). The EDL increased in stiffness up to 250 days (p=0.0009) before it dropped by almost 50% at 400 days. In the soleus, the stiffness was still increasing at 400 days (p=0.0013), but at a slower rate than 30-250 days. The genotype data show that a deletion in the N2A region of titin significantly affects muscle properties like stiffness, though the mechanism by which this happens is yet unexplained. With age, the rise in muscle stiffness may also be due to an increase in connective tissues such as collagen, with the disparity seen between the two muscle types attributable to either differing muscle fiber types, titin isoforms, or both. Overall, this study opens the way to further investigation of the effects of titin on muscle stiffness and the mechanism responsible for enhanced muscle properties in healthy muscles.
