Pain is more than a symptom of osteoarthritis, it is an inherent and damaging part of the disease itself, according to a study published in the journal Arthritis and Rheumatism. More specifically, the study revealed that pain signals originating in arthritic joints, and the biochemical processing of those signals as they reach the spinal cord, worsen and expand arthritis. In addition, researchers found that “crosstalk” nerve pathways carrying pain signals transfer inflammation from arthritic joints to the spine and back again, causing disease at both ends.

Specifically, the research team genetically engineered a mouse where they could turn up on command the production of IL-1? in the jaw joint, a common site of arthritis. Experiments showed for the first time that turning up IL-1? in a peripheral joint caused higher levels of IL-1? to be produced in the dorsal horns of the spinal cord as well.
Using a second, even more elaborately engineered mouse model, the team also demonstrated for the first time that creating higher levels of IL-1? in cells called astrocytes in the spinal cord caused more osteoarthritic symptoms in joints.

The study’s authors explain that astrocytes, non-nerve cells (glia) in the central nervous system that provide support for the spinal cord and brain, also serve as the immune cells of CNS organs. Among other things, they release cytokines like IL-1? to fight disease when triggered. The same cytokines released from CNS glia may also be released from neurons in joints, possibly explaining how crosstalk carries pain, inflammation and hyper-sensitivity back and forth.

“Until relatively recently, osteoarthritis was believed to be due solely to wear and tear, and inevitable part of aging,” explains study researcher, Stephanos Kyrkanides, DDS, PhD. “Recent studies have revealed, however, that specific biochemical changes contribute to the disease, changes that might be reversed by precision-designed drugs. Our study provides the first solid proof that some of those changes are related to pain processing, and suggests the mechanisms behind the effect.”