Laboratory mouseIn a bizarre experiment done in the 1950s, it was discovered that connecting the circulatory systems of old and young mice seems to rejuvenate the more elderly animals.  Recently, a handful of labs have been racing to discover what factors explain this effect.  Yet now, a Harvard University group that claims to have found one such anti-aging protein has published a study that counters those critics who dismissed the molecule work as “flawed”.

The researchers claim that a specific protein, GDF11, may explain the beneficial effects of young blood, reporting that blood levels of GDF11 drop in mice as the animals get older and injecting them with GDF11 can partially reverse age-related thickening of the heart.  In two papers that they published last year in the magazine Science, the researchers have also reported that GDF11 can rejuvenate the muscles and brains of rodents as well.  Yet last May, another group of researchers from the Novartis Institutes for Biomedical Research in Cambridge, reported that the antibody used by the Harvard researchers to measure levels of GDF11 also detected myostatin (aka GDF8), a similar protein that hinders muscle growth.  The Novartis researchers concluded that GDF11 levels in blood actually rise with age in rats and people.  And according to their research, GDF11 injections inhibited muscle regeneration in young mice.

Yet now, the Harvard group says that Novartis used a flawed assay to detect GDF11 and GDF8, claiming that the main protein detected by the antibody test is immunoglobulin, another protein that rises in blood level with age.  They reported that mice without the gene for immunoglobulin tested negative for the active form of GDF11/8 that the Novartis assay was thought to reveal.

The paper by the Harvard team also disputes a recent study in which a group at Temple University in Philadelphia found that GDF11 injections don’t have any effect on heart thickness in older mice.  They said the problem was that commercially purchased GDF11 can vary in the actual level and activity of protein.  Such variability, they say, likely explains why the Temple researchers didn’t see any effects from GDF11 at the same apparent dose the Harvard group reported using.  To back up their earlier results, the Harvard researchers pointed out that daily GDF11 injections can shrink heart muscle in both old and new mice, yet also noted that the mice lost weight.  Such findings, they say, suggest that GDF11 could have a “therapeutic window” for beneficial effects, where too much could actually cause harm.

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