Cells Carry Memory Of Injury, Reveal Why Chronic Pain Lasts, Study Says

A recent study has offered clue why chronic pain can last even when the injury that caused it has gone. Although the research is just starting, this could explain how small and seemingly harmless injuries leave molecular 'footprints' which add up to more lasting damage, and ultimately chronic pain.

According to Science Daily, chronic pain can have a variety of causes, but would often have the same outcome: an overly sensitive nervous system that responds much more than it normally would. These got people questioning why the nervous system should remain to be this sensitive over long periods of time, most especially in situations where the cause of the pain has already gone.

The study from King's College in London is trying to answer this question by analyzing immune cells in the nervous system of mice, which are known to be important for the generation of persistent pain. In the study, they found that nerve damage changes the epigenetic, the process that determines which gene is expressed and where, marks on some of the genes in immune cells. Some signals have different functional effects, while others are just primers which are flags that indicate a potential to act or be modified.

The cells analyzed in the study behaved normally, but the existence of these novel epigenetic markers may mean that they carry a "memory" of the original injury. Dr Franziska Denk, first author of the study, from the Wolfson Centre for Age Related Diseases at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN), King's College London, said: "We are ultimately trying to reveal why pain can turn into a chronic condition. We already knew that chronic pain patients have nerves that are more active, and we think this is probably due to various proteins and channels in those nerves having different properties."

"However, it is unclear why these nerves should remain in this overactive, highly sensitive state, even when the initial injury or disease has gone: the back pain from two years ago that never quite went away or the joints that are still painful despite your rheumatoid arthritis being in remission," she continued.

Sciencecodex.com also mentioned that Dr. Denk said they want to know why these proteins and channels should maintain their altered function over a long period of time. She also explained that cells have housekeeping systems where the majority of their content are replaced and renewed every few weeks and months. "Our study is the very first step towards trying to answer this question by exploring the possibility that changes in chronic pain may persist because of epigenetics. We hope that future research in this area could help in the search for novel therapeutic targets," said Dr. Denk.

Professor Stephen McMahon from the IoPPN at King's College London said: 'This research raises many interesting questions: do neurons also acquire epigenetic footprints as a result of nerve injury? Do these molecular footprints affect the function of proteins? And are they ultimately the reason that chronic pain persists in patients over such long periods of time?  

 Professor McMahon also said that the last question is particularly hard to answer because in order to study epigenetics, researchers must first be able to access pure cell populations which obviously only accessible in postmortem tissue. But, the professor said his colleagues at King's are already doing this in psychiatry, through studies such as the The PsychENCODE project, so it is possible.