Scientists at the MDI Biological Laboratory, in collaboration with scientists from the Buck Institute for Research on Aging in Novato, Calif., and Nanjing University in China, have identified synergistic cellular pathways for longevity that amplify lifespan fivefold in C. elegans, a nematode worm used as a model in aging research.
The increase in lifespan would be the equivalent of a human living for 400 or 500 years, according to one of the scientists.
The research draws on the discovery of two major pathways governing aging in C. elegans, which is a popular model in aging research because it shares many of its genes with humans and because its short lifespan of only three to four weeks allows scientists to quickly assess the effects of genetic and environmental interventions to extend healthy lifespan.
Because these pathways are “conserved,” meaning that they have been passed down to humans through evolution, they have been the subject of intensive research.
A number of drugs that extend healthy lifespan by altering these pathways are now under development. The discovery of the synergistic effect opens the door to even more effective anti-aging therapies.
The new research uses a double mutant in which the insulin signaling (IIS) and TOR pathways have been genetically altered. Because alteration of the IIS pathways yields a 100 percent increase in lifespan and alteration of the TOR pathway yields a 30 percent increase, the double mutant would be expected to live 130 percent longer. But instead, its lifespan was amplified by 500 percent.
“Despite the discovery in C. elegans of cellular pathways that govern aging, it hasn’t been clear how these pathways interact,” said Hermann Haller, M.D., president of the MDI Biological Laboratory.
“By helping to characterize these interactions, our scientists are paving the way for much-needed therapies to increase healthy lifespan for a rapidly aging population.”
The elucidation of the cellular mechanisms controlling the synergistic response is the subject of a recent paper in the online journal Cell Reports entitled “Translational Regulation of Non-autonomous Mitochondrial Stress Response Promotes Longevity.”
The authors include Jarod A. Rollins, Ph.D., and Aric N. Rogers, Ph.D., of the MDI Biological Laboratory.
“The synergistic extension is really wild,” said Rollins, who is the lead author with Jianfeng Lan, Ph.D., of Nanjing University.
“The effect isn’t one plus one equals two, it’s one plus one equals five. Our findings demonstrate that nothing in nature exists in a vacuum; in order to develop the most effective anti-aging treatments we have to look at longevity networks rather than individual pathways.”
The discovery of the synergistic interaction could lead to the use of combination therapies, each affecting a different pathway, to extend healthy human lifespan in the same way that combination therapies are used to treat cancer and HIV, Pankaj Kapahi, Ph.D., of the Buck Institute, has said. Kapahi is a corresponding author of the paper with Rogers and Di Chen, Ph.D., of Nanjing University.
The synergistic interaction may also may explain why scientists have been unable to identify a single gene responsible for the ability of some people to live to extraordinary old ages free of major age-related diseases until shortly before their deaths.
The paper focuses on how longevity is regulated in the mitochondria, which are the organelles in the cell responsible for energy homeostasis.
Over the last decade, accumulating evidence has suggested a causative link between mitochondrial dysregulation and aging. Rollins’ future research will focus on the further elucidation of the role of mitochondria in aging, he said.
The research was conducted at the MDI Biological Laboratory and Nanjing University using information from double mutants developed by Kapahi. Rollins’ and Rogers’ work was supported by the National Institutes of Health (AG056743), the Morris Scientific Discovery Fund and the National Institute of General Medical Sciences (P20GM103423 and P20GM104318).
What causes cells to age?
To achieve this, lead author Alireza Delfarah, a graduate student in the Graham lab, focused on senescence, a natural process in which cells permanently stop creating new cells. This process is one of the key causes of age-related decline, manifesting in diseases such as arthritis, osteoporosis and heart disease.
“Senescent cells are effectively the opposite of stem cells, which have an unlimited potential for self-renewal or division,” Delfarah said. “Senescent cells can never divide again. It’s an irreversible state of cell cycle arrest.”
The research team discovered that the aging, senescent cells stopped producing a class of chemicals called nucleotides, which are the building blocks of DNA. When they took young cells and forced them to stop producing nucleotides, they became senescent, or aged.
“This means that the production of nucleotides is essential to keep cells young,” Delfarah said. “It also means that if we could prevent cells from losing nucleotide synthesis, the cells might age more slowly.”
Graham’s team examined young cells that were proliferating robustly and fed them molecules labeled with stable isotopes of carbon, in order to trace how the nutrients consumed by a cell were processed into different biochemical pathways.
Scott Fraser and his lab worked with the research team to develop 3D imagery of the results. The images unexpectedly revealed that senescent cells often have two nuclei, and that they do not synthesize DNA.
Before now, senescence has primarily been studied in cells known as fibroblasts, the most common cells that comprised the connective tissue in animals. Graham’s team is instead focusing on how senescence occurs in epithelial cells, the cells that line the surfaces of the organs and structures in the body and the type of cells in which most cancers arise.
Graham said that senescence is most widely known as the body’s protective barrier against cancer: When cells sustain damage that could be at risk of developing into cancer, they enter into senescence and stop proliferating so that the cancer does not develop and spread.
“Sometimes people talk about senescence as a double-edged sword, that it protects against cancer, and that’s a good thing,” Graham said. “But then it also promotes aging and diseases like diabetes, cardiac dysfunction or atherosclerosis and general tissue dysfunction,” he said.
Graham said the goal was not to completely prevent senescence, because that might unleash cancer cells.
“But then on the other hand, we would like to find a way to remove senescent cells to promote healthy aging and better function,” he said.
Graham said that the team’s research has applications in the emerging field of senolytics, the development of drugs that may be able to eliminate aging cells. He said that human clinical trials are still in early stages, but studies with mice have shown that by eliminating senescent cells, mice age better, with a more productive life span.
“They can take a mouse that’s aging and diminishing in function, treat it with senolytic drugs to eliminate the senescent cells, and the mouse is rejuvenated. If anything, it’s these senolytic drugs that are the fountain of youth,” Graham said.
He added that in order for successful senolytic drugs to be designed, it was important to identify what is unique about senescent cells, so that drugs won’t affect the normal, non-senescent cells.
“That’s where we’re coming in — studying senescent cell metabolism and trying to figure out how the senescent cells are unique, so that you could design targeted therapeutics around these metabolic pathways,” Graham said.
- Jianfeng Lan, Jarod A. Rollins, Xiao Zang, Di Wu, Lina Zou, Zi Wang, Chang Ye, Zixing Wu, Pankaj Kapahi, Aric N. Rogers, Di Chen. Translational Regulation of Non-autonomous Mitochondrial Stress Response Promotes Longevity. Cell Reports, 2019; 28 (4): 1050 DOI: 10.1016/j.celrep.2019.06.078