Chronic pain is one of medicine’s most stubborn puzzles. A sprained back, a surgical incision or a pinched nerve heals – and yet, for millions of people, the pain never fully goes away. Why some injuries fade into memory while others evolve into a lifelong condition has remained largely a mystery.
A new study from researchers at the University of California, Irvine offers a striking possible answer, and it comes from an unexpected direction: the same amyloid biology long associated with Alzheimer’s disease. The study, which appears in Science Translational Medicine, suggests that chronic pain may be driven by a distinct biological process that begins shortly after injury. If the same pathway is confirmed in people, future treatments might aim to prevent pain from becoming long-lasting rather than only managing it after it’s established.
Led by Daniele Piomelli, Distinguished Professor of anatomy and neurobiology, the research team used mice to trace how an injury sets off a chain reaction in the spinal cord. Days after a hind paw injection designed to mimic tissue injury, a class of cells called oligodendrocytes, whose normal job is to maintain the fatty insulation around nerve fibers, began behaving strangely – cutting back on the machinery needed to produce that insulating material, called myelin.
That shift didn’t stay contained. Nearby nerve fibers began to lose structural integrity, and neurons responded by churning out amyloid precursor proteins that generate beta-amyloid 42. These sticky protein fragments are notorious for clumping into the plaques found in Alzheimer’s-affected brains. In the mice, elevated beta-amyloid appeared in the spinal cord precisely during the window when pain was shifting from a temporary nuisance to a lasting condition.
“We were not looking for a connection to amyloid biology; it emerged from following the data,” Piomelli said. “What surprised us most was how central this pathway turned out to be. It wasn’t just present alongside chronic pain. When we blocked it, the chronic pain simply didn’t develop.”
Finding a solution
To test whether beta-amyloid was a bystander or a driver, the researchers intervened in several independent ways. Genetically engineered mice lacking the amyloid precursor protein were explored, as well as an antibody that neutralizes beta-amyloid. Another approach used either three chemically distinct drugs or the removal of a gene that blocks amyloid precursor protein production. In every case, thwarting amyloid production during the critical early window prevented the mice from developing the lasting, centrally driven hypersensitivity that marks chronic pain in this model while leaving their initial, acute response to injury intact.
The team also pinpointed an upstream culprit: an enzyme called N-acylethanolamine acid amidase, which becomes active in oligodendrocytes after injury. Mice bred to lack this enzyme specifically in these cells were shielded from the rise in beta-amyloid and did not go on to develop chronic pain – a result the researchers also confirmed in a separate model of nerve injury, suggesting that the mechanism wasn’t a one-off quirk of a single animal model.
“This gives us a mechanistic explanation for why the transition to chronic pain happens when it does and a real handle on how to intervene,” Piomelli said. “The goal isn’t simply to treat pain once it has become chronic; it’s to catch the process while it’s still reversible.”
A new approach to pain management
The implications, if the findings hold up in people, could be significant. Nearly all current pain treatments target pain after it has already become chronic. This research suggests a different approach: identifying and treating the biological process during a brief postinjury window, potentially preventing chronic pain from ever taking hold. It also raises intriguing questions about whether chronic pain and neurodegenerative disease share more biology than previously thought – months after injury, the mice developed spinal deposits resembling Alzheimer’s-related plaques.
Piomelli said the next steps include determining whether the same pathway operates in humans and whether it can be safely targeted. He noted that existing Alzheimer’s or amyloid-targeting drugs should not be used off-label for pain.
The National Institute on Aging and the National Institute of Diabetes and Digestive and Kidney Diseases supported the research.
About the University of California, Irvine: Founded in 1965, UC Irvine is a member of the prestigious Association of American Universities and is ranked among the nation’s top 10 public universities by U.S. News & World Report. The campus has produced five Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UC Irvine has more than 36,000 students and offers 224 degree programs. It’s located in one of the world’s safest and most economically vibrant communities and is Orange County’s second-largest employer, contributing $7 billion annually to the local economy and $8 billion statewide. For more on UC Irvine, visit www.uci.edu.
