A new study finds that nearly one in five people lack a certain protein in their muscles that gives them better resistance to the cold.
The study was published February 17 in the American Journal of Human Genetics.
The protein α-actinin-3, which is found only in fast-twitch fibers, is missing by almost 20% the human.
The absence of this protein is due to a mutation in the gene that codes for it. From an evolutionary perspective, the presence of the mutant gene increased as humans migrated from Africa to the colder climates of central and northern Europe.
Some humans are naturally better at keeping warm
“This suggests that people lacking α-actinin-3 are better at keeping warm and endure a harsher climate in terms of energy,” said co-author Håkan Westerblad of Karolinska Institutet. “But so far there has been no direct experimental evidence for this.”
“We can now show that the loss of this protein confers greater resistance to cold,” said Westerblad. “And we also found a possible mechanism for this.”
For the study, 42 healthy males between the ages of 18 and 40 sat in cold water (14°C or 57°F) until their body temperature dropped to 35.5°C (96°F). . .
During the immersion in the cold water, the researchers measured the subjects’ electrical muscle activity using electromyography (EMG). They also took muscle biopsies to examine protein content and fiber type composition.
The results showed that the skeletal muscle of people lacking α-actinin-3 had a greater proportion of slow-twitch fibers. When cooling down, these people were more energy efficient in maintaining their body temperature.
Instead of activating fast-twitch fibers, leading to apparent tremors, they increased activation of slow-twitch fibers, which generate heat by increasing baseline contraction (tone). .
“The mutation likely conferred an evolutionary advantage during migration to a colder climate,” Westerblad said. But today, he said, that ability to conserve energy could instead increase the risk of some “affluence diseases.”
Examples include type 2 diabetes, asthma and heart disease.
A genetic mutation for endurance sports
Another interesting question is how the lack of α- Actinin-3 affects the body’s response to exercise.
“People who lack α-actinin-3 rarely succeed in sports that require strength and explosiveness, while those in the A trend toward more capacity was observed in endurance sports,” Westerblad said.
Selection for cold resistance
In conclusion, the researchers write that people lacking α-actinin-3 “show improved cold tolerance during cold water immersion.” This is in part associated with “an energetically effective, heat-producing increase in muscle tone, rather than overt tremors.”
These results provide a mechanism for the increase in the frequency of this mutation “as modern humans migrated from Africa to the colder climates of central and northern Europe over 50,000 years ago.”
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Study: “Loss of α-Actinin-3 during human evolution provides superior cold resilience and muscle heat generation.”Authors: 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, and Håkan WesterbladPublished in: American Journal of Human GeneticsPublished date: February 17, 2021DOI: http://dx.doi.org/10.1016/j.ajhg. 2021.01.013Photo: by Free-q1Photos from Pixabay