Osteoarthritis year in review 2022: biology

The field of osteoarthritis (OA) biology is rapidly evolving and brilliant progress has been made this year as well. Landmark studies of OA biology published in 2021 and early 2022 were selected through PubMed search by personal opinion. These papers were classified by their molecular mechanisms, and it was largely divided into the intracellular signaling mechanisms and the inter-compartment interaction in chondrocyte homeostasis and OA progression. The intracellular signaling mechanisms involving OA progression included (1) Piezo1/transient receptor potential channels of the vanilloid subtype (TRPV) 4-mediated calcium signaling, (2) mechanical load–F-box and WD repeat domain containing 7 (FBXW7) in chondrocyte senescence, (3) mechanical loading-primary cilia-hedgehog signaling, (4) low grade inflammation by toll-like receptor (TLR)-CD14-lipopolysaccharide-binding protein (LBP) complex and inhibitor of NF-κB kinase (IKK) β–nuclear factor kappa B (NF-κB) signaling, (5) selenium pathway and reactive oxygen species (ROS) production, (6) G protein–coupled receptor (GPCR) and cyclic adenosine monophosphate (cAMP) signaling, (7) peroxisome proliferator-activated receptor α (PPARα)–acyl-CoA thioesterase 12 (ACOT12)-mediated de novo lipogenesis and (8) hypoxia–disruptor of telomeric silencing 1-like (DOT1L)–H3-lysine 79 (H3K79) methylation pathway. The studies on inter-compartment or intercellular interaction in OA progression included the following subjects; (1) the anabolic role of lubricin, glycoprotein from superficial zone cells, (2) osteoclast–chondrocyte interaction via exosomal miRNA and sphingosine 1-phosphate (S1P), (3) senescent fibroblast-like synoviocyte and chondrocyte interaction, (4) synovial macrophage and chondrocyte interaction through Flightless I, (5) αV integrin-mediated transforming growth factor beta (TGFβ) activation by mechanical loading, and (6) osteocytic TGFβ in subchondral bone thickening. Despite the disastrous Covid-19 pandemic, many outstanding studies have expanded the boundary of OA biology. They provide both critical insight into the pathophysiology as well as clues for the treatment of OA.