Presence of ChAT mRNA and a very marked α7nAChR immunoreaction in the synovial lining layer of the knee joint

Abstract

AimsThe aim was to examine if there is evidence of acetylcholine (ACh) production within the synovial lining layer and to examine the pattern of α7nAChR expression in the layer. This layer is of relevance clinically as it becomes thickened in response to both rheumatoid arthritis (RA) and osteoarthritis (OA) and as it has been shown to produce proteases that are involved in the cartilage destruction. Main methodsSynovial tissue specimens from the knee joint of patients with RA and OA undergoing prosthetic surgery were examined. In situ hybridization and immunohistochemistry were used for the evaluation of ChAT reaction patterns. Immunohistochemistry was utilized for demonstration of activity of α7nAChR. Key findingsThere were ChAT mRNA reactions in the synovial lining layer of both patient categories. On the other hand, no ChAT immunoreactions were detected in the layer. There was a very marked α7nAChR immunoreaction. SignificanceThere is a potential for ACh production within the synovial lining layer as there are ChAT mRNA reactions. However, the level of ACh production is apparently very low. It is thus possible that there is a down-regulation of ACh production but an apparent upregulation in expression level of α7nAChR. Based on the knowledge that the non-neuronal cholinergic system can have anti-inflammatory effects, the low level of ACh production in the synovial lining layer can be a drawback for the arthritic joints.