Abstract
IntroductionOsteoarthritis (OA) is an inflammatory disease of the joints that causes progressive disability in the elderly. Reactive oxygen species (ROS) play an important role in OA development; they may activate the NLRP3 inflammasome, thereby inducing the secretion of proinflammatory IL-1β and IL-18, leading to the aggravation of the downstream inflammatory response. Nrf2 is a key transcription factor that regulates the expression of antioxidant enzymes that protect against oxidative stress and tissue damage. We aimed to explore the underlying mechanism of OA development by investigating NLRP3, ASC, Nrf2, and HO-1 expression in synovia and their regulatory networks in OA.MethodsHuman total knee replacement samples were subjected to histology and micro-CT analysis to determine the pathological changes in the cartilage and subchondral bone and to assess the expression of inflammation-related markers in the synovial tissue by immunohistochemistry (IHC), qRT-PCR, and Western blot. To investigate these pathological changes in an OA animal model, adult Sprague-Dawley rats were subjected to anterior cruciate ligament transection and medial meniscectomy. Articular cartilage and subchondral bone changes and synovial tissue were also determined by the same methods used for the human samples. Finally, SW982 cells were stimulated with lipopolysaccharide (LPS) as an in vitro inflammatory cell model. The correlation between NLRP3 and Nrf2 expression was confirmed by knocking down NLRP3 or Nrf2.ResultsCartilage destruction and subchondral bone sclerosis were found in the OA patients and OA model rats. Significantly increased expression levels of NLRP3, ASC, Nrf2, and HO-1 were found in the synovial tissue from OA patients. NLRP3, ASC, Nrf2, and HO-1 expression in the synovium was also upregulated in the OA group compared with the sham group. Furthermore, the NLRP3, Nrf2, HO-1, IL-1β, and IL-18 expression in LPS-treated SW982 cells was increased in a dose-dependent manner. As expected, the expression of NLRP3 was upregulated, and the expression of IL-1β and IL-18 was downregulated after Nrf2 silencing. However, knocking down NLRP3 did not affect the expression of Nrf2.ConclusionsROS-induced oxidative stress may be the main cause of NLRP3 inflammasome activation and subsequent release of downstream factors during OA development. Nrf2/HO-1 signaling could be a key pathway for the activation of the NLRP3 inflammasome, which may contribute to the progression of OA. Herein, we discovered a novel role of Nrf2/HO-1 signaling in the production of NLRP3, which may facilitate the prevention and treatment of OA.
Highlights
Osteoarthritis (OA) is an inflammatory disease of the joints that causes progressive disability in the elderly
Reactive oxygen species (ROS)-induced oxidative stress may be the main cause of Nod-like receptor protein 3 (NLRP3) inflammasome activation and subsequent release of downstream factors during OA development
nuclear factor E2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) signaling could be a key pathway for the activation of the NLRP3 inflammasome, which may contribute to the progression of OA
Summary
Osteoarthritis (OA) is an inflammatory disease of the joints that causes progressive disability in the elderly. Reactive oxygen species (ROS) play an important role in OA development; they may activate the NLRP3 inflammasome, thereby inducing the secretion of proinflammatory IL-1β and IL-18, leading to the aggravation of the downstream inflammatory response. Osteoarthritis (OA), characterized by progressive cartilage degeneration and secondary synovial inflammation, is one of the most common chronic joint diseases affecting people of all ages, especially the elderly, and causes severe pain and physical disability [1]. If patients suffer from severe joint damage or OA fails to respond to the conservative management, surgical treatments such as arthroplasty and osteotomy are generally recommended. Proinflammatory cytokines (e.g., interleukin-1 beta (IL-1β), and IL-18), reactive oxygen species (ROS), inflammatory mediators, and biomechanical stress are regarded to be the major factors contributing to this scenario [4]. Recent studies have demonstrated that dysregulated microRNAs, obesity-related metabolic factors, and inflammasome signaling molecules including Nod-like receptor protein 3 (NLRP3) are involved in the progression of OA [5,6,7,8]
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