Researchers led by the Harvard Stem Cell Institute and Brigham and Women's Hospital have identified a protein — GDF11 — using Somalogic's Somascan technology, that they showed can reverse features of age-related heart disease in mice.
The group published the results of their study this week in Cell. According to the researchers, the study started with an initial hypothesis that proteins in the circulatory system of young mice might be able to influence aging tissues in old mice. After showing this to be the case by connecting the circulatory systems of young mice to older mice surgically, the group moved on to try to identify a specific molecule or other factor associated with this change.
Using Somalogic's apatamer-based technology to scan for the presence of over 1,000 analytes, the group identified a single circulating protein — GDF11, a member of the TGF-beta superfamily — with higher levels in young, healthy mice than old mice with cardiac hypertrophy, a major factor of diastolic heart failure, the most common form of human heart failure in the United States.
When the researchers then treated older mice with the protein to restore youthful GDF11 levels, they saw a reversal of signs of the disease, akin to what they observed when the young mice were surgically bound to the older diseased mice.
"We designed the initial experiments, and they were stunningly positive from the outset," one of the study's two lead authors, Richard Lee said in a conference call discussing the results this week.
"So then we worked for several years on this concept, that there was something in the young blood that could take the older heart and turn the clock back. … We started the search for what that could be, and it was unsuccessful for quite a while, [but then] we developed a collaboration with Somalogic and we identified a factor that right away was a candidate for this effect."
"We found that [GDF11] circulates in the blood of young mice, and then goes down over time so that old mice have much lower levels. [But] when we give old mice this factor to bring levels up to the level of young mice, the heart goes back to the appearance of the young mouse," Lee said in the call.
"I think it was a good day for proteomics," Somalogic Chief Medical Officer Steve Williams told ProteoMonitor this week. "Some of the things we say are special about proteins are clearly demonstrated by this study— first, that they change with age, and second, that they carry real biological signals. From the results, it's clear that this GDF11 has to be on, or close to the causal pathway for cardiac hypertrophy."
While the research doesn't have any direct implications for humans, GDF11 has been found in other studies to be linked with human heart disease risk, which suggests that the finding could have relevance for human health if the team is able to validate and expand their research.
In the study, the Harvard researchers first demonstrated that they could reverse age-related cardiac hypertrophy by comparing heterochronic, or young-old surgical pairs, to controls of either young-young, or old-old isochronic pairs, as well as sham pairs, connected surgically through the skin, but not the circulatory system.
According to the study authors, the effect of a young circulation was "striking" and immediately apparent on visual inspection, with the hearts from the exposed older mice shrinking in size compared to controls. This visual observation was confirmed by measuring the heart weight relative to tibia length in the mice, as well as by histologic analysis and molecular analysis, which revealed a reduction in both atrial natriuretic peptide and brain natriuretic peptide — molecular markers of myocyte hypertrophy — in mice surgically joined to a young circulatory system.
To find a molecule potentially responsible for this regression, the researchers initially tried metabolomic and lipidomic profiling, but were unable to identify any candidates. The group then turned to Somalogic's Somascan assay to quantitatively evaluate plasma from 10 young mice and 10 old mice.
On the call this week, Lee told ProteoMonitor that the researchers presented to Somalogic the problem of scanning for a protein that could explain the effect of youthful mouse circulation on older mice, and that the company was excited to see if the Somascan technology could help.
"We had a conversation with Somalogic and it became clear that they had some very powerful technology. We presented this problem to them as one we were trying to solve, and they said, 'Wow, that's cool. Let's try to see if we can help you fish things out,'" Lee said.
Somalogic's Somamer technology uses modified aptamers as an alternative to antibodies for protein discovery and identification, offering multiplexing ability significantly greater than with traditional ELISA platforms.
The company analyzed samples sent by the researchers in its Boulder, Colo. lab, Williams said. This scan identified 13 candidate analytes that reliably distinguished the young mice from the old. One — GDF11 — was confirmed to be associated with a more youthful expression profile in the heterochronic mouse pairs, and was reduced in old-old versus young-young isochronic pairs.
Finally, the researchers tested whether increasing GDF11 could reverse signs of age-related cardiac hypertrophy first in vitro, and then in a randomized, blinded in vivo study.
The results showed that old mice treated to increase GDF11 had significantly lower ratios of heart weight to tibia length compared to those injected with placebo saline. On the molecular level, both BNP and ANP were also reduced in the treated mice.
"If you take a two-year-old mouse, which is a pretty old mouse, and you give the factor for four weeks, it turns the heart into the same shape and the cells to the same size they were when the mouse was two months old," Lee said.
"If you just looked at the heart … it was quite obvious that something dramatic had occurred. There are a lot of things in science that are subtle, and this was not one of them," he added.
Future studies will be necessary to establish whether the finding holds true across species, and whether GDF11 could be useful as a therapy in humans.
On the call, Lee explained that the TGF-b class of proteins, which have diverse roles and effects in the body, is well studied, but not as much is known about GDF11 specifically. "It is a protein that has an effect in development in utero, but its role in adults has not really been that explored," he said.
Somalogic's Williams said that in a study presented last year by UCSF's Peter Ganz at the annual meeting of the American Heart Association, researchers used the same version of the Somascan assay on samples from nearly 1,000 people and found that low levels of GDF11 were associated with greater risk of death in those with stable coronary artery disease.
"In that study, we used the exact same technique, the same version of the assay on those people, and we also found GDF11 deficiency relating to cardiovascular risk in those subjects," Williams said.
"Of course, we have to validate that finding in an independent set, but since we found that association independently from this mouse study, it looks like it is a nice corroboration. I think it's more than a coincidence that the same analyte in the same assay was deficient in humans at high risk," he added.
According to the study authors, the Harvard group is now planning to move GDF11 toward human clinical trials, which they believe could begin within four to five years.
"In humans we'd like to get evidence as quickly as possibly that this pathway is participating in diseases of aging," Lee said. "There is no assay for this so we are developing that now, [and] we believe that in a short period of time we should be able to get the answer to that question."
"We've also called in a lot of collaborators at the Stem Cell Institute to look at what other organ systems this may play a role in," Lee said.
The researchers have collected preliminary evidence that young blood may also influence aging phenotypes in other types of tissue, such as skeletal muscle and the spinal cord. They plan to do further research to see if GDF11 plays a role in these other systems, as well.
According to Williams, Somalogic has expanded Somascan since the Harvard research to include 1,129 analytes.