Almost one in five people does not have α-aktinin-3 protein in their muscle fiber. Researchers at the Karolinska Institutet in Sweden now show that more of the skeletal muscle in these individuals comprises slow-twitch muscle fibers, which are more durable and energy efficient and provide better tolerance to low temperatures than muscle fibers of rapid contraction. The results are published in the scientific journal The American Journal of Human Genetics.
Skeletal muscle comprises fast-twitch (white) fibers that tire quickly and slow-twitch (red) fibers that are more resistant to fatigue. The α-aktinina-3 protein, found only in fast-twitch fibers, is absent in almost 20% of people – almost 1.5 billion individuals – due to a mutation in the gene that encodes it. In evolutionary terms, the presence of the mutated gene increased when humans migrated from Africa to the colder climates of central and northern Europe.
“This suggests that people without α-aktinin-3 are better at keeping warm and, in terms of energy, in enduring a more difficult climate, but there has been no direct experimental evidence of this before,” says Håkan Westerblad, a cell phone professor. muscle physiology in the Department of Physiology and Pharmacology, Karolinska Institutet. “Now we can show that the loss of this protein makes the cold more resilient and we also found a possible mechanism for that.”
For the study, 42 healthy men between the ages of 18 and 40 were invited to sit in cold water (14 ° C) until their body temperature dropped to 35.5 ° C. During immersion in cold water, the researchers measured muscle electrical activity with electromyography (EMG) and performed muscle biopsies to study protein content and fiber type composition.
The results showed that the skeletal muscle of people without α-aktinina-3 contains a higher proportion of slow-twitch fibers. In cooling, these individuals were able to maintain body temperature more efficiently in terms of energy. Instead of activating the fast twitch fibers, which results in noticeable tremors, they increased the activation of the slow twitch fibers that produce heat, increasing the basal contraction (tone).
“The mutation probably gave an evolutionary advantage during the migration to a colder climate, but in today’s modern society this energy-saving ability may instead increase the risk of affluent diseases, which is something for which now we want to turn our attention ”, says Professor Westerblad.
Another interesting question is how the lack of α-aktinina-3 affects the body’s response to exercise.
“People lacking α-aktinina-3 are rarely successful in sports that require strength and explosiveness, while a tendency towards greater capacity has been observed in these people in endurance sports,” he explains.
A limitation of the study is that it is more difficult to study mechanisms in human studies at the same level of detail than in experiments with animals and cells. The physiological mechanism presented was not verified with experiments, for example, at the molecular level.
Reference: “The loss of α-actinin-3 during human evolution provides resilience to superior cold and muscle heat generation” by Victoria L. Wyckelsma, Tomas Venckunas, Peter J. Houweling, Maja Schlittler, Volker M Lauschke, Chrystal F. Tiong, Harrison D. Wood, Niklas Ivarsson, Henrikas Paulauskas, Nerijus Eimantas, Daniel C. Andersson, Kathryn N. North, Marius Brazaitis, Håkan Westerblad, February 17, 2021, American Journal of Human Genetics.
DOI: 10.1016 / j.ajhg.2021.01.013.
The study was a collaboration with research groups at the Lithuanian Sports University in Kaunas, Lithuania, and the University of Melbourne, Australia. It was supported by grants from the Swedish Research Council, the Swedish National Sports Research Center, the Lithuanian Research Council, the Swedish Medical Research Society, the Jeansson Foundations, the Swedish Heart and Lung Foundation and Australia’s National Health and Medical Research Council. Co-author Volker Lauschke is the founding CEO and shareholder of HepaPredict AB and was a consultant with EnginZyme AB.