Mitochondrial dysfunction has long been associated with aging, making preventing or reversing the organelle’s decay a high priority for longevity researchers. One key target for such work is the decline in the organelle’s membrane potential: the difference in electrical charge between each side of the inner mitochondrial membrane that is essential for energy production. Now, research published May 12 as a bioRxiv preprint that has not yet been peer reviewed demonstrates that it’s possible to genetically engineer a light-activated proton pump into the mitochondria of Caenorhabditis elegans that maintains the voltage across the inner mitochondrial membrane as the worms age—and doing so, prolongs the animals’ lifespan.
“There are some interventions targeted to mitochondria that are able to extend [the] lifespan of diverse species,” says Universidade Federal de São Paulo biochemist Fernanda Marques da Cunha, who did not participate in this study. “But this is a little bit different because they pinpoint a specific mitochondrial parameter, so they increase the membrane potential in a clean way,” without affecting other aspects of the organelles, she adds. This makes the achievement “very interesting.”
The underlying technology was first described in 2020 research, in which University of Rochester Medical Center mitochondria researcher Andrew Wojtovich and his colleagues uncovered the proton pump’s impact on mitochondria. When they engineered the pump—naturally found in the cells of a fungus—into C. elegans, the animals’ mitochondrial membrane potential was increased, which ramped up the production of molecular fuel. The process, they showed, required neither metabolic substrates like glucose nor oxygen. Instead, the pump used light to fuel the movement of protons across the inner membrane, driving the synthesis of ATP. The team named this tool mitochondria-ON (mtON), which only works if the gene-edited animals are treated with light and supplemented with a vitamin A derivative called all-trans retinal, which acts as a cofactor for the pump.
Shahaf Peleg, an aging researcher at the Research Institute for Farm Animal Biology in Dummerstorf, Germany, who did not participate in the development of the tool, says that he was astounded when he first saw that paper. He tells The Scientist he reasoned that mtON was not only controlling the mitochondria, it was also allowing the animals to harness light to “generate energy without consuming food.” Based on the well-known associations between mitochondrial function and aging, he immediately thought of the tool’s potential to prolong life. He says he contacted Wojtovich the next day, and they soon started to collaborate on a project testing whether the engineered proton pump could indeed delay aging in an animal. In the new preprint, they report the first results of this collaboration.
Using two groups of gene edited worm strains, one that had the pump integrated into their mitochondria by DNA injection and the other through CRISPR/Cas9, the researchers tested their hypothesis by exposing the worms to light, supplementing them with the required cofactor, and assessing how long they lived. They found that activating mtON with all-trans retinal supplementation increased lifespan by 6 to 38 percent compared to those same engineered worms that weren’t given all-trans retinal, depending on the strain and the light intensity. All experiments were performed in two different labs (Wojtovich’s and Matt Kaeberlein’s at the University of Washington).
“They took some care in replicating the lifespan extension in different backgrounds and different laboratories,” says Marques da Cunha, “this is not so common [and] it’s good.”
Shane Rea, an aging researcher at the University of Washington who was not involved in this study but has collaborated with Kaeberlein on other projects, notes it would be important to add another control: wild-type worms exposed to light and supplemented with all-trans retinal to be certain that the proton pump, and not the light and the cofactor, is responsible for the lifespan extension in engineered worms. Brandon Berry, first author of the paper reporting the tool and the recently posted preprint, explains to The Scientist over email that the team has done pilot experiments addressing this—not included in the preprint—and they have found that administering the light and the all-trans retinal cofactor without engineering the pump had no effect on worm longevity. He adds that similar experiments indicate “these mitochondrial optogenetic tools function through membrane potential and not off target effects.”
The team showed in the preprint that the intervention does not adversely affect the worms’ health, and preliminary tests suggest that it could actually improve it, even beyond the increased lifespan. They specifically assessed how well the worms could thrash in liquid, finding that activating mtON increased their ability to move as they aged compared to worms not supplemented with the cofactor.
University of Massachusetts Chan Medical School cell biologist Cole Haynes, who was not involved in the work, says that the thrashing rate is a good measurement for overall health and neuromuscular function in the worms. Peleg adds that this is “very early physiological evidence” of healthier animals, but that more work is needed to understand if the tool also improves other aspects of health.
Peleg explains that he, Wojtovoch, and Berry are coapplicants on a patent based on the findings that mtON can extend lifespan. He says the team is further testing these questions in other model organisms, such as flies and mice, to assess whether mtON “works beyond worms.”
If the results reported in the preprint are correct, Rea adds, it would suggest that maintaining the membrane potential is sufficient to extend the lifespan of an organism, which is information that might also apply to humans. It shows “what problem needs to be solved,” and may open doors to novel approaches for addressing health decline in humans by maintaining mitochondrial membrane potential.
Haynes expresses similar sentiments, saying that the results may motivate the search for small molecules that can increase the mitochondrial membrane potential in humans, similar to how mtON works in worms. “It’s a target for drug development . . . with some promise,” he adds. “The idea is pretty exciting,” Haynes concludes.