Today in Nature, University of Pittsburgh researchers describe for the first time a pathway by which cells repair damaged lysosomes, structures that contribute to longevity by recycling cellular trash. The findings are an important step towards understanding and treating age-related diseases driven by leaky lysosomes.
“Lysosome damage is a hallmark of aging and many diseases, particularly neurodegenerative disorders such as Alzheimer’s,” said lead author Jay Xiaojun Tan, Ph.D., assistant professor of cell biology at Pitt’s School of Medicine and member of the Aging Institute, a partnership between Pitt and UPMC. “Our study identifies a series of steps that we believe is a universal mechanism for lysosomal repair, which we named the PITT pathway as a nod to the University of Pittsburgh.”
As the cell’s recycling system, lysosomes contain potent digestive enzymes that degrade molecular waste. These contents are walled off from damaging other parts of the cell with a membrane that acts like a chain link fence around a hazardous waste facility. Although breaks can occur in this fence, a healthy cell quickly repairs the damage. To learn more about this repair process, Tan teamed up with senior author Toren Finkel, M.D., Ph.D., director of the Aging Institute and distinguished professor of medicine at Pitt’s School of Medicine.
First, Tan experimentally damaged lysosomes in lab-grown cells and then measured the proteins that arrived on the scene. He found that an enzyme called PI4K2A accumulated on damaged lysosomes within minutes and generated high levels of a signaling molecule called PtdIns4P.
“PtdIns4P is like a red flag. It tells the cell, ‘Hey, we have a problem here,'” said Tan. “This alert system then recruits another group of proteins called ORPs.”
ORP proteins work like tethers, Tan explained. One end of the protein binds to the PtdIns4P red flag on the lysosome, and the other end binds to the endoplasmic reticulum, the cellular structure involved in synthesis of proteins and lipids.
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