Novel role of LOXL2 in TMJ and knee OA cartilage in vitro and in vivo

Abstract

BACKGROUND: Osteoarthritis (OA) is the most common degenerative joint disease which affects the joint structures leading to disability. Studies in the last 20 years have documented the increased prevalence of knee pain and symptomatic knee OA. Similarly, of temporomandibular joint (TMJ) disorders OA is the most common. Lysyl oxidase like-2 (LOXL2) is a copper-dependent amine oxidase. previous studies showed that LOXL2 is elevated during mouse fracture healing. Our hypothesis that LOXL2 acts as a specific anabolic factor in chondrocytes METHODS: The activity of LOXL2 in human articular and TMJ chondrocytes was assessed by cell-based assays and RT-qPCR, and LOXL2-mediated activation of NF-κB and extracellular signal-related kinase (ERK) signaling pathways was measured by western blotting. To examine LOXL2-induced effect in vivo, we implanted Matrigel-imbedded human chondrocytes into nude mice and exposed them to exogenous LOXL2 for 6 weeks. We also examined if LOXL2 induces the proliferation of OA chondrocytes. RESULTS: LOXL2 staining was detected in damaged regions of human TMJ, hip and knee joints affected by OA. Stimulation with transforming growth factor (TGF)-β1 upregulated LOXL2 expression, while pro-inflammatory cytokines IL-1β and TNF-α downregulated LOXL2, in human chondrocytes. LOXL2 expression also inhibited IL-1β-induced phospho-NF-κB/p65 and TGF-β1-induced ERK1/2 phosphorylation. Matrigel constructs of human chondrocytes from the knee joint and TMJ implanted in nude mice showed anabolic responses after LOXL2 transduction, including increased expression of SOX9, ACAN, and COL2A1. We have found that LOXL2 does not induce the proliferation of human TMJ or knee OA chondrocytes. CONCLUSIONS: We showed that LOXL2 induces differentiation and attenuates OA related catabolic signaling pathways