A new type of mechanical memory that increases inherent muscle elasticity based on a muscle’s history of stretching has recently been uncovered. Researchers investigated how titin, the largest protein in the body and the primary source of passive muscle elasticity elasticity, is affected by increasing oxidation levels during muscular activity.
“We were expecting some kind of change as the muscle proteins became oxidized, but the magnitude of the effect we measured was quite honestly far beyond what we had anticipated,” Pallav Kosuri, PhD, told Orthopedics Today.
Titin was found to contain an unusually high number of oxidation hotspots, although the majority are inactive, hidden inside molecular folds. Muscular stretching can force titin to unfold, exposing the hotspots and causing titin to become increasingly sensitive to oxidation during stretching. This uncovering from stretching also enabled glutathionylation, which locks the bundles in an unfolded state, causing the stiffness of titin to drop substantially. Unlike without oxidation, the effect of a mechanical force in combination with glutathionylation showed the stiffness of the titin molecules only could be reset by reversing the oxidation.
“Stretching without oxidation causes changes that last only briefly, while oxidation serves to prolong those changes, making them more permanent,” Kosuri told Orthopedics Today. Stretching that primes the muscle for oxidation reactions which lock the muscle proteins unfolded, causing sustained increases in elasticity. The muscle reverts to normal upon the muscle removing the oxidation over several hours following stretching. Researchers speculated this type of mechanical memory could be a common feature of most elastic tissues.
“This is an initial discovery, but the implications are exciting,” Kosuri stated in a press release. “And it shows that we still have much to learn about how our muscles really work.”
Alegre-Cebollada J. Cell. 2014;doi:10.1016/j.cell.2014.01.056
Disclosure: The authors have no relevant financial disclosures.