Mithramycin A Alleviates Osteoarthritic Cartilage Destruction by Inhibiting HIF-2α Expression

Abstract

Osteoarthritis (OA) is the most common and increasing joint disease worldwide. Current treatment for OA is limited to control of symptoms. The purpose of this study was to determine the effect of specificity protein 1 (SP1) inhibitor Mithramycin A (MitA) on chondrocyte catabolism and OA pathogenesis and to explore the underlying molecular mechanisms involving SP1 and other key factors that are critical for OA. Here, we show that MitA markedly inhibited expressions of matrix-degrading enzymes induced by pro-inflammatory cytokine interleukin-1β (IL-1β) in mouse primary chondrocytes. Intra-articular injection of MitA into mouse knee joint alleviated OA cartilage destruction induced by surgical destabilization of the medial meniscus (DMM). However, modulation of SP1 level in chondrocyte and mouse cartilage did not alter catabolic gene expression or cartilage integrity, respectively. Instead, MitA significantly impaired the expression of HIF-2α known to be critical for OA pathogenesis. Such reduction in expression of HIF-2α by MitA was caused by inhibition of NF-κB activation, at least in part. These results suggest that MitA can alleviate OA pathogenesis by suppressing NF-κB-HIF-2α pathway, thus providing insight into therapeutic strategy for OA.

Antiosteoarthritic Effect of Morroniside in Chondrocyte Inflammation and Destabilization of Medial Meniscus-Induced Mouse Model

“…The meniscus is a fibrocartilaginous tissue that extends mechanical integrity to the knee [ 45 ]. The loss of the meniscal function triggers increased mechanical stress in the articular cartilage, resulting in subchondral bone degeneration [ 46 ]. Furthermore, mechanical stress induces inflammatory responses in the articular cartilage via the secretion of IL-1β in the synovial region [ 47 ].…”

NF-κB Signaling Pathways in Osteoarthritic Cartilage Destruction

“…Several pharmacologic inhibitors have been shown to be effective in in vitro or in vivo OA models, with some executing their functions through NF-κB inhibition. The inhibitors reported have been developed against protein kinase Czeta (PKCzeta) [155,156], purinergic P2X7 receptor (P2X7R) [157], specificity protein 1 (SP1) [158], and receptor-interacting protein kinase 1 (RIPK1) [159]. Similar to the anti-catabolic effects of the pharmacologic PKCzeta inhibitor, inhibition of PKCzeta using molecular approaches, such as siRNA-mediated KD and the overexpression of dominant negative PKCzeta, also suppressed ECM degradation in inflammatory cytokine-treated chondrocytes [155,156].…”

“…Similar to the anti-catabolic effects of the pharmacologic PKCzeta inhibitor, inhibition of PKCzeta using molecular approaches, such as siRNA-mediated KD and the overexpression of dominant negative PKCzeta, also suppressed ECM degradation in inflammatory cytokine-treated chondrocytes [155,156]. In contrast, the SP1 inhibitor mithramycin A showed anti-catabolic effects in chondrocytes by primarily suppressing the NF-κB-HIF2-α axis rather than by targeting SP1, as SP1 KD had minimal effects on catabolic gene expression in IL-1β-treated chondrocytes [158]. Collectively, these studies identified potential signaling pathways and targets for NF-κB inhibition.…”

Intra-Articular Administration of Cramp into Mouse Knee Joint Exacerbates Experimental Osteoarthritis Progression

“…The experimental design of IA injection with peptide concentration and injection period is shown in each figure. For the experimental OA study, DMM surgery was performed as described previously [ 56 ]. Seven days after DMM surgery, the vehicle or Cramp peptide (10 μL of 25 μM; approximately 1 μg) was first injected into mice by IA injection, and then injected weekly a total of seven times before the mice were sacrificed at 9 weeks for histological analysis.…”