Oxytocin is a molecule that plays a dual role in your body, functioning both as a hormone and a neurotransmitter. With each warm hug, grasped hand, and loving gaze, it is released from your pituitary gland. Produced in the hypothalamus, it is associated with childbirth and sex as well as more abstract emotional encounters, such as friendship, social bonding, and romance.
Now, researchers at the UC Berkeley are suggesting that oxytocin may serve a more utilitarian purpose. Noting how in mice oxytocin declines with age, they believe it is indispensable for healthy muscle maintenance and repair, and so may become a treatment target for age-related muscle wasting, or sarcopenia. "Aging is a natural process, but I believe that we can meaningfully intervene with age-imposed organ degeneration, thereby slowing down the rate at which we become progressively unhealthy," said Dr. Irina Conboy, associate professor of bioengineering and principal investigator of the study.
Your skeletal muscle regenerates throughout your life, but as you age, your muscles atrophy and their ability to self-repair, especially after injury, diminishes; this is referred to as sarcopenia. For this reason, it is wise to exercise with weights, in order to maintain your muscle as best you can as you age. To regenerate muscle after an injury, your muscle stem cells need to waken from dormancy and begin to multiply, thereby forming new myofibers (the basic cellular unit of muscle tissue) or fuse with damaged ones.
Unexpectedly, some previous studies have suggested that aging muscle’s dwindling regeneration potential is not due to its inability to activate stem cells, but instead may be based on factors having to do with circulation. In animal studies, it has been found that receptors for oxytocin exist in muscle stem cells of old mice compared to young mice, while blood levels of oxytocin generally decline with age. For these reasons, Conboy focused her current study on how oxytocin, flowing in the blood, might affect adult muscle regeneration and repair.
To tease out oxytocin's role in muscle rejuvenation, she and her team of researchers injected oxytocin under the skin of old mice for four days, and then for five days more after the muscles were injured. After the nine-day treatment, they found that the muscles of the mice that had received oxytocin injections healed far better than those of a control group of mice without oxytocin. "The action of oxytocin was fast," said Dr. Christian Elabd, a senior scientist in Conboy's lab and lead author of this study. "The repair of muscle in the old mice was at about 80 percent of what we saw in the young mice."
The team of researchers also found that blocking the effects of oxytocin in young mice rapidly compromised their ability to repair muscle, which resembled old tissue after an injury. Interestingly, giving young mice an extra boost of oxytocin did not seem to cause a significant change in muscle regeneration, further proof that extra oxytocin does not make stem cells divide uncontrollably — a good thing. "Unfortunately, most of the molecules discovered so far to boost tissue regeneration are also associated with cancer, limiting their potential as treatments for humans," said Conboy in a press release.
Following these experiments, the researchers next studied mice whose gene for oxytocin was disabled, comparing them to a group of control mice. At a young age, these mice showed no significant differences in terms of either muscle mass or repair efficiency. In fact, it wasn't until these mice with a disabled oxytocin gene reached adulthood that signs of premature aging began to appear. This finding was unusual because when past studies have disabled other types of genes associated with tissue repair, defects appeared right away. "To our knowledge, the oxytocin gene is the only one whose impact is seen later in life, suggesting that its role is closely linked to the aging process," Conboy said.
Conboy and her colleagues will continue to research oxytocin's effects on muscle repair. Because it already circulates throughout the body, reaching every organ, and is not associated immune system interference or tumors, oxytocin may be the perfect candidate for sustainable long-term treatments for rejuvenating old muscle, Conboy believes. Aging appears to be getting better every day.
Source: Elabd C, Cousin W, Upadhyalula P, et al. Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration. Nature Communications. 2014.