title: Transglutaminase 2 as a biomarker of osteoarthritis: an update.
abstract: Osteoarthritis is a progressive joint disease characterized by cartilage degradation and bone remodelling. Under physiologic conditions, articular cartilage displays a stable chondrocyte phenotype, whereas in osteoarthritis a chondrocyte hypertrophy develops near the sites of cartilage surface damage and associates to the pathologic expression of type X collagen. Transglutaminases (TGs) include a family of Ca(2+)-dependent enzymes that catalyze the formation of γ-glutamyl cross-links. Their substrates include a variety of intracellular and extracellular macromolecular components. TGs are ubiquitously and abundantly expressed and implicated in a variety of physiopathological processes. TGs activity is modulated by inflammatory cytokines. TG2 (also known as tissue transglutaminase) mediates the hypertrophic differentiation of joint chondrocytes and interleukin-1-induced calcification. Histomorphometrical and biomolecular investigations document increased TG2 expression in human and experimental osteoarthritis. Consequently, the level of TG2 expression may represent an adjuvant additional marker to monitor tissue remodelling occurring in osteoarthritic joint tissue. Experimental induction of osteoarthritis in TG2 knockout mice is followed from reduced cartilage destruction and increased osteophyte formation compared to wild-type mice, suggesting a different influence on joint bone and cartilage remodelling. The capacity of transamidation by TG2 to regulate activation of latent TGF-β seems to have a potential impact on the regulation of inflammatory response in osteoarthritic tissues. Additional studies are needed to define TG2-regulated pathways that are differently modulated in osteoblasts and chondrocytes during osteoarthritis.
authors.affiliation: Orthopaedics and Traumatology, University of Rome Tor Vergata, Viale Oxford 81, 00133 Rome, Italy.
authors.forename: Umberto
authors.initials: U
authors.lastname: Tarantino
authors.forename: Amedeo
authors.initials: A
authors.lastname: Ferlosio
authors.forename: Gaetano
authors.initials: G
authors.lastname: Arcuri
authors.forename: Luigi Giusto
authors.initials: LG
authors.lastname: Spagnoli
authors.forename: Augusto
authors.initials: A
authors.lastname: Orlandi
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002358:Cartilage, Articular / Q000201:enzymology / Q000473:pathology; D005270:Femur Head / Q000201:enzymology / Q000473:pathology; D019204:GTP-Binding Proteins; D006801:Humans; D007719:Knee Joint / Q000201:enzymology / Q000473:pathology; D010003:Osteoarthritis / Q000201:enzymology* / Q000473:pathology; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D016212:Transforming Growth Factor beta / Q000378:metabolism; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D016212:Transforming Growth Factor beta; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins