Pulsed electromagnetic field improves subchondral bone microstructure in knee osteoarthritis rats through a Wnt/-catenin signaling-associated mechanism

Pulsed electromagnetic field (PEMF) is often used for management of osteoarthritis (OA). The aim of the study was to determine whether PEMF can successfully improve subchondral bone microstructure through a Wnt/-catenin signaling-associated pathway in rats with knee OA induced by low-dose monosodium iodoacetate (MIA). Seventy-two 12-week-old male Sprague-Dawley rats were randomly assigned to three groups: OA (n=24), PEMF (n=24), and Control (n=24). OA was induced (OA and PEMF groups) by injecting 0.2mg MIA in rats' right knee joint. The control rats received a single sterile saline injection in the right knee. Rats in the PEMF group were exposed to daily 2h PEMF exposure with 75Hz, 1.6mT for 4 weeks. After 4 weeks, micro-computed tomography (micro-CT), real-time PCR, and immunohistochemistry staining were performed. The PEMF group increased bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), and suppressed bone surface/bone volume (BS/BV) and trabecular separation (Tb.Sp) levels in micro-CT analysis. Real-time PCR analysis showed that PEMF promoted tibial subchondral bone's gene expressions of Wnt3a, -catenin, and OPG, but did not alter LRP5 and RANKL mRNA levels. Similar results involved tibial subchondral bone's protein expressions that were observed in immunohistochemistry staining. These results suggest that PEMF preserved the structural integrity of subchondral bone in knee OA rats by promoting the activation of Wnt/-catenin signaling and OPG/RANKL/RANK signaling. Bioelectromagnetics. 39:89-97, 2018. (c) 2017 Wiley Periodicals, Inc.