Washington: Injecting a bone hormone, that is produced during exercise, can help rejuvenate ageing muscles and increase the capacity of performing physical activities, a new study has found.
When we exercise, our bones produce a hormone called osteocalcin that increases muscle performance, researchers have found. Osteocalcin naturally declines in humans as we age, beginning in women at age 30 and in men at age 50.
The study describes the first bone-derived hormone known to affect exercise capacity and shows that injecting it can reverse the age-related exercise capacity decline in mice.
"Our bones are making a hormone called osteocalcin that provides an explanation for why we can exercise," said Gerard Karsenty, from the Columbia University Medical Centre.
"The hormone is powerful enough to reconstitute, in older animals, the muscle function of young animals," said Karsenty.
During exercise in mice and humans, the levels of osteocalcin in the blood increase depending on how old the organism is.
The researchers observed that in 3-month-old adult mice, osteocalcin levels spiked approximately four times the amount that the levels in 12-month-old mice did when the rodents ran for 40 minutes on a treadmill.
The three-month-old mice could run for about 1,200 metres before becoming exhausted, while the 12-month-old mice could only run half of that distance.
To study whether osteocalcin levels were affecting exercise performance, researchers tested mice genetically engineered so the hormone could not signal properly in their muscles.
Without osteocalcin muscle signalling, the mice ran 20-30 per cent less time and distance than their healthy counterparts before reaching exhaustion.
When healthy mice that were 12 and 15 months old - whose osteocalcin levels had naturally decreased with age - were injected with osteocalcin, their running performance matched that of the healthy 3-month-old mice, researchers said.
The older mice were able to run about 1,200 metres before becoming exhausted.
"It was extremely surprising that a single injection of osteocalcin in a 12-month-old mouse could completely restore its muscle function to that of a 3-month-old mouse," said Karsenty.
To determine the cellular mechanisms behind osteocalcins effects, the team measured levels of glycogen, glucose, and acylcarnitines (an indicator of fatty-acid use) in mice with and without osteocalcin.
The researchers determined that the hormone helps muscle fibres uptake and catabolise glucose and fatty acids as nutrients during exercise.
"Osteocalcin is not the only hormone responsible for adaptation to exercise in mice and humans, but it is the only known bone-derived hormone that increases exercise capacity. This may be one way to treat age-related decline in muscle function in humans," said Karsenty.
The study was published in the journal Cell Metabolism.