Scientists at the Wistar Institute say they have discovered that mice lacking a specific protein live longer lives with fewer age-related illnesses. The mice, which lack the TRAP-1 protein, demonstrated less age-related tissue degeneration, obesity, and spontaneous tumor formation when compared to normal mice, according to the researchers, who believe their findings could change how scientists view the metabolic networks within cells.
In healthy cells, TRAP-1 is an important regulator of metabolism and has been shown to regulate energy production in mitochondria, organelles that generate chemically useful energy for the cell. In the mitochondria of cancer cells, TRAP-1 is universally overproduced.
The Wistar team’s report (“Deletion of the Mitochondrial Chaperone TRAP-1 Uncovers Global Reprogramming of Metabolic Networks”), which appears in Cell Reports, shows how "knockout" mice bred to lack the TRAP-1 protein compensate for this loss by switching to alternative cellular mechanisms for making energy.
"We see this astounding change in TRAP-1 knockout mice, where they show fewer signs of aging and are less likely to develop cancers," said Dario C. Altieri. M.D., Robert and Penny Fox Distinguished Professor and director of the Wistar Institute's National Cancer Institute-designated Cancer Center. "Our findings provide an unexpected explanation for how TRAP-1 and related proteins regulate metabolism within our cells. We usually link the reprogramming of metabolic pathways with human diseases, such as cancer. "What we didn't expect to see were healthier mice with fewer tumors."
Dr. Altieri and his colleagues created the TRAP-1 knockout mice as part of their ongoing investigation into the drug Gamitrinib, which targets the protein in the mitochondria of tumor cells. TRAP-1 is a member of the heat shock 90 (HSP90) protein family, which are chaperone proteins that guide the physical formation of other proteins and serve a regulatory function within mitochondria. Tumors use HSP90 proteins like TRAP-1 to help survive therapeutic attack.
"In tumors, the loss of TRAP-1 is devastating, triggering a host of catastrophic defects, including metabolic problems that ultimately result in in death of the tumor cells," continued Dr. Altieri. "Mice that lack TRAP-1 from the start, however, have three weeks in the womb to compensate for the loss of the protein."
The researchers found that in their knockout mice, the loss of TRAP-1 causes mitochondrial proteins to misfold, which then triggers a compensatory response that causes cells to consume more oxygen and metabolize more sugar. This causes mitochondria in knockout mice to produce deregulated levels of ATP, the chemical used as an energy source to power all the everyday molecular reactions that allow a cell to function.
This increased mitochondrial activity actually creates a moderate boost in oxidative stress (free radical damage) and the associated DNA damage. While DNA damage may seem counterproductive to longevity and good health, the low level of DNA damage actually reduces cell proliferation—slowing growth down to allow the cell's natural repair mechanisms to take effect.
"TRAP-1−/− mice are viable and showed reduced incidence of age-associated pathologies including obesity, inflammatory tissue degeneration, dysplasia, and spontaneous tumor formation," wrote the investigators. "This was accompanied by global upregulation of oxidative phosphorylation and glycolysis transcriptomes, causing deregulated mitochondrial respiration, oxidative stress, impaired cell proliferation, and a switch to glycolytic metabolism in vivo. These data identify TRAP-1 as a central regulator of mitochondrial bioenergetics, and this pathway could contribute to metabolic rewiring in tumors."
"Our findings strengthen the case for targeting HSP90 in tumor cells, but it also opens up a fascinating array of questions that may have implications for metabolism and longevity," explained Dr. Altieri. "I predict that the TRAP-1 knockout mice will be a valuable tool for answering these questions."