Cell-integrated serum-induced signalling patterns can differentiate between hand and knee osteoarthritis patients.

Objective: OA is a very heterogeneous disease. Here, we aimed to differentiate OA patients based on their serum-induced cell-integrated signalling patterns.

Design: In order to monitor the activity of different cellular homeostasis-regulating pathways in response to patient serum, we analysed the response of human OA serum samples to sixteen cell-based transcription factor luciferase reporter assays. In this study we compared serum samples from 55 patients with knee OA, 56 patients with hand OA and 42 healthy controls.

Results: Differential serum-induced pathway activity was observed between samples from healthy controls, knee OA and hand OA patients: Serum of hand OA patients induced high MAPK-related AP1 activity whereas serum of knee OA patients induced more SRE, ISRE and SOX9 activity, which is related to ELK1-SRF, STAT1-STAT2 and SOX9 activity respectively. Principal component analysis revealed that these differences differentiate hand OA from knee OA. Both hand and knee OA clustered clearly in 2 different endotypes each, but no principle component could be identified of these subtypes within either the hand OA or the knee OA sample group.

Conclusion: This study demonstrates that serum from hand OA and knee OA patients evokes diverse cellular signalling patterns that differentiates hand OA, knee OA and healthy controls. This underlines that the pathomolecular mechanisms of OA are likely significantly different between hand and knee OA, a finding that could lead to new insight into the pathobiology of OA endotypes and joint-specific therapies.