LOXL2 Deletion Triggers TMJ Osteoarthritis While Overexpression Protects Against NF-κB-Induced Chondrocyte Apoptosis

Temporomandibular joint osteoarthritis (TMJ-OA) affects a significant proportion of the population worldwide. However, there has been no substantial progress in the development of FDA-approved drugs for treatment due to a lack of understanding of the specific factors regulating key TMJ-OA molecular mechanisms. Lysyl Oxidase Like-2 (LOXL2) promotes knee joint cartilage protection, and it is downregulated in TMJ-OA animal model. We evaluated the role of LOXL2 in TMJ cartilage, its molecular mechanism and gene networks using in vivo Loxl2 knockout mice (Acan-Cre; Loxl2flox/flox) and ex vivo goat TMJ cartilage. Our results show that Loxl2 knockout in mice cartilage upregulates Il1b, Mmp9, Mmp13, Adamts4, and Adamts5, whereas it reduces the levels of aggrecan and proteoglycan. Loxl2 deleted TMJ cartilage show a higher enrichment of inflammatory response, TNFA signaling via NF-kB, extracellular matrix (ECM), and collagen degradation pathway network. Conversely, LOXL2 treatment reduces interleukin-1 beta (IL-1{beta})-induced expression of Mmp13, protects mitochondrial function and ECM from degeneration. Importantly, LOXL2 attenuates IL-1{beta}-induced chondrocyte apoptosis via phosphorylation of NF-{kappa}B and expression of pain-related gene PTGS2 (encodes COX2). Taken together, Loxl2 knockout mice exacerbate TMJ-OA through cartilage/ECM degradation, mitochondrial dysfunction, chondrocyte apoptosis, and inflammatory gene expression, whereas LOXL2 treatment mitigates these effects. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/653519v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@cb7540org.highwire.dtl.DTLVardef@17ebe2eorg.highwire.dtl.DTLVardef@1f7fd59org.highwire.dtl.DTLVardef@19fdd7_HPS_FORMAT_FIGEXP M_FIG C_FIG