A protein believed to induce youth may in fact do more damage by inhibiting the ability of the cells to repair themselves, says new research.
The protein GDF11 was believed to be the reason for the parabiosis effect, where a young mouse and an old mouse sharing a circulatory system seemed to rejuvenate the old mouse, regenerating its wasting muscles and restoring its cognitive abilities.
Amy Wagers, a stem-cell researcher at Harvard University in Cambridge, Massachusetts, offered the explanation for the blood-doping effect by showing that injecting GDF11, which decreased in the blood of mice as they grew older, helped them became 'younger'.
A team from Novartis Institutes for Biomedical Research in Cambridge, Massachusetts has now pointed out that the protein actually increases with age, and does more harm to the tissues than rejuvenation.
They showed that the reagents used by Wagers' group to measure GDF11 levels cannot distinguish between myostatin and GDF11.
Myostatin prevents muscle stem cells from differentiating into mature muscle, reports Nature.
Using a more specific reagent to measure GDF11 levels in the blood of both rats and humans, they found that GDF11 levels actually increased with age.
The researchers regularly injected the animal with three times as much GDF11 as the earlier experiment had, and showed the deleterious effect on the muscles.
The study has been published in Cell Metabolism.
The Novartis team however does not have any explanation for the parabiosis effect seen in mice.
Bimagrumab, an experimental Novartis treatment for muscle weakness and wasting, works by blocking myostatin and possibly GDF11 as well, they say.
Wagers however suggests that there could be multiple forms of GDF11 and that perhaps only one decreases with age. Both papers suggest that having either too much or too little GDF11 could be harmful.
She notes that the Novartis team damaged the mice muscles extensively and then treated them with higher levels of the protein, and hence cannot be compared with her results.