To characterize the expression profiles of two nuclear-encoded mitochondrial genes previously associated with chronic pain, the translocator protein (TSPO) and family with sequence similarity 173B (FAM173B), in different knee compartments from patients with painful knee OA. Also, to examine their association with the joint expression of inflammatory cytokines/chemokines and clinical symptoms.
The study was performed on 40 knee OA patients and 19 postmortem (PM) controls from which we collected the knee tissues: articular cartilage (AC), synovial membrane (SM) and subchondral bone (SB). Quantitative real-time polymerase chain reaction was used to determine the relative mRNA levels of TSPO, FAM173B, and inflammatory mediators IL6, IL8, IL10, IL12, MCP1, CCL11 and CCL17. OA patients rated their pain intensity (visual analogue scale), severity of knee-related outcomes (KOOS) and pain sensitivity assessed by pressure algometry.
The gene expression of TSPO in SM was elevated in OA patients compared with control subjects while there were no group differences in AC and SB. Expression of FAM173B was reduced in SM but elevated in SB in OA patients compared with controls. The expression of TSPO and FAM173B in SM and SB was associated with the expression of inflammatory substances, but not in AC. Synovial expression of TSPO correlated with lower pain intensity and FAM173B with increased pressure pain sensitivity in OA.
Our results suggest that altered expression of TSPO and FAM173B is associated with joint expression of inflammatory mediators and with clinical symptoms indicating the relevance for the pathophysiology of knee OA.