A new study contradicts a provocative theory that a protein found in young blood reverses some aging processes in older mice.
Scientists were excited by the discovery of a potential age-mitigating substance, reported in the past few years by Amy Wagers and colleagues at Harvard University. These researchers improved the heart, brain, and muscle function of elderly mice by attaching the rodents’ circulatory systems to those of young mice (C&EN, May 13, 2013, page 41, and May 12, 2014, page 29).
The Harvard scientists went on to identify protein growth differentiation factor 11 (GDF11) as the source of the rejuvenation, reporting that levels of this protein decreased as mice aged and that giving them doses of GDF11 improved muscle and nerve cell growth.
But the Harvard team may have been fooled by their immunoassays, says a Novartis group that also researches aging. That team reports that GDF11 levels do not decrease in aging mice (Cell Metab. 2015, DOI: 10.1016/j.cmet.2015.05.010). What’s more, the muscles of mice given doses of GDF11 deteriorate, rather than improve says team leader David Glass, executive director of the muscle diseases group at Novartis Institutes for BioMedical Research in Cambridge, Mass.
The Novartis researchers say they were prompted to test whether GDF11 has rejuvenating powers because the protein myostatin, which is almost identical to GDF11, has long been known to inhibit skeletal muscle growth. In fact, Novartis’s drug bimagrumab, which is currently in clinical trials, is an antibody designed to treat muscle wasting by blocking myostatin.
On the basis of their experiments, Glass and his group conclude that the Harvard researchers’ tests could not distinguish between myostatin and GDF11. Indeed, the lack of specificity among antibody reagents used in such immunoassays is an epidemic problem in biological research, scientists are realizing (C&EN, Feb. 23, page 39). The Novartis team also developed a GDF11-specific immunoassay and found that GDF11 did not decrease, and possibly even increased, as mice aged.
These disparate results are causing a dustup among researchers. In a commentary accompanying the Novartis paper, Caroline E. Brun and Michael A. Rudnicki, from the University of Ottawa, bluntly state, “Clearly, like the mythical fountain of youth, GDF11 is not the long-sought rejuvenation factor.”
But Wagers notes that the Novartis group used very different methodologies than her group, including the GDF11 dosage administered, in its experiments. She also says that GDF11 may exist in a number of different forms, some not detectable by certain assays.
Nevertheless, Wagers says, “we remain convinced that at least one form of GDF11 declines in blood with age, and that maintaining GDF11 levels in an appropriate physiological range is essential for muscle health.”
Her lab is gearing up for the next salvo. “We are looking forward to addressing the differences in the studies with additional data very soon,” she says.