Expression of hyaluronan synthases in articular cartilage

Objective: To investigate the mRNA expression profiles of three mammalian h yaluronan synthases (HAS1, HAS2 and HAS3) in chondrocytes from normal (undi seased) animal cartilage and osteoarthritic human cartilage maintained in e xperimental culture systems and exposed to catabolic or anabolic stimuli pr ovided by cytokines, growth factors and retinoic acid. Design: Chondrocytes isolated from normal bovine, porcine or from osteoarth ritic human cartilage were cultured as monolayers or embedded in agarose. C ultures were maintained for 3-5 days in the presence or absence of cataboli c stimuli (IL-l, TNF-alpha or retinoic acid) or anabolic stimuli (TGF-beta or IGF-1) followed by extraction of RNA and analysis of HAS mRNA expression by RT-PCR. Results: Whereas mRNA for HAS1 was not detected in any sample, the mRNAs fo r HAS2 and HAS3 were expressed in human, bovine and porcine chondrocytes. H AS2 mRNA was present in chondrocytes from all cartilages and under all cult ure conditions, whereas HAS3 did not show such constitutive expression. In agarose cultures of bovine and porcine chondrocytes HAS2 mRNA was present i n control, IL-l and retinoic acid treated cultures. whereas HAS3 mRNA was o nly detected in IL-l stimulated cultures. Mature bovine chondrocytes cultur ed in monolayers expressed mRNAs for both HAS2 and HAS3 in the presence of IL-l, TNF-alpha, IGF-beta and IGF1, however immature bovine chondrocytes in monolayer cultures displayed virtually no HAS3 mRNA expression in the pres ence of these cytokines and growth factors. HAS2 and HAS3 mRNAs were also e xpressed by bovine chondrocytes isolated from either the superficial or dee p zone of articular cartilage, and by human chondrocytes cultured either in the absence or presence of IL-1 and retinoic acid. Conclusions: Our data indicate that HASP and HAS3 (but not HAS1) mRNAs are expressed in several mammalian cartilages. Chondrocyte HAS2 mRNA appears to be constitutively expressed while chondrocyte HAS3 mRNA expression can be differentially regulated in an age-dependent fashion, and may be affected b y local and/or systemic catabolic or anabolic stimuli provided by cytokines or growth factors. (C) 2000 OsteoArihrjtis Research Society International.