Patients affected by osteoporosis have weak bones
A fault in the way the body replenishes bone stem cells could help explain why people develop osteoporosis.
The condition is a weakening of the bones that can lead to breaks which are difficult to heal.
There are two types of osteoporosis; post-menopausal which affects women, and age-related, which affects men and women.
Canadian researchers have discovered a defect in a molecule linked to how the stem cells develop which may contribute to someone developing age-related osteoporosis.
One reason for age-dependent osteoporosis in humans may be defective maintenance of these stem cells
Professor William Stanford, of the University of Toronto
They looked at mice which had been genetically engineered to lack a molecule called Stem Cell Antigen-1 (Sca-1).
In adults, stem cells play key roles in repairing injured organs, making copies of themselves and dividing into other kinds of cells, such as bone cells.
The new study suggests that if the Sca-1 molecule is absent, these mesenchymal stem cells are less likely to make copies.
This means that the number of stem cells will decrease as a person ages, so that there may not be enough stem cells left to make the bone cells needed to maintain bone density.
The genetically engineered mice studied had normal bone development and maintained normal bone density well into adulthood.
But they then showed dramatically decreased bone mass and brittle bones as they aged - similar to the symptoms of age-related osteoporosis in humans.
The number of stem cells they produced declined with age, leading to fewer bone-forming cells.
Professor William Stanford, of the University of Toronto, who led the research, said: "We believe that one reason for age-dependent osteoporosis in humans may be defective maintenance of these stem cells.
"If we can learn how Sca-1 influences the number of stem cells, we may be able to develop new drugs to combat this disabling disease."
He added: "Sca-1 is somehow influencing the decision to make more stem cells when the stem cell divides.
"We think that there are probably many types of proteins or molecules that influence stem cell self-renewal and Sca-1 is one of them.
"We think that Sca-1 is probably important in maintaining the stem cells' ability to make more stem cells and that, with its loss, individuals would probably lose stem cells and bone faster."
Professor Jane Aubin, who also worked on the study, said while there has been a significant amount of research into hormonally driven post-menopausal osteoporosis, there is less understanding of the age-related form of the disease.
She said: "While previous studies have suggested that older individuals - especially those with osteoporosis - have fewer bone-forming cells, this is the first research to say, 'You're running out of bone-forming cells for this stem cell-related reason'."
The research is published online by the journal Proceedings of the National Academy of Sciences.