title: Differentiation-dependent effects of IL-1 and TGF-beta on human articular chondrocyte proliferation are related to inducible nitric oxide synthase expression.
abstract: This study analyzed the effect of chondrocyte differentiation on iNOS expression and responses to IL-1 and TGF-beta. During subculturing of chondrocytes, the growth-stimulatory effects of TGF-beta decreased, and cells in later passages even were growth inhibited by TGF-beta. IL-1 beta responses showed an inverse pattern. The antiproliferative effects of IL-1 beta decreased, and, after passage 6, IL-1 beta became a growth stimulator for chondrocytes. This change in growth factor response pattern was associated with a decrease in type II collagen expression. To determine whether these changes in the growth regulatory effects of IL-1 beta and TGF-beta were related to nitric oxide (NO), inducible nitric oxide synthase (iNOS) expression and NO release were analyzed. In primary chondrocytes, TGF-beta did not stimulate iNOS mRNA expression or NO release, and, during co-incubation, it did not detectably alter the IL-1 beta effect. Preincubation with TGF-beta resulted in a time-dependent increase in IL-1-induced NO. With increasing passage number, the IL-1 beta effects decreased, and, after passage 6, IL-1 beta no longer detectably stimulated iNOS expression or NO release. However, TGF-beta increased NO production synergistically with IL-1 beta during the same culture period when it lost its growth-stimulatory effects. The antiproliferative effects of TGF-beta in late passage chondrocytes were reversed by the NO synthase inhibitor NG-monomethylarginine. These results suggest a novel pattern of iNOS regulation by IL-1 and TGF-beta and show that the factors that modulate iNOS expression and proliferation are dependent on the differentiation status of the cells.
authors.affiliation: Sam and Rose Stein Institute for Research on Aging, University of California-San Diego, La Jolla 92093, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Blanco
authors.forename: Y
authors.initials: Y
authors.lastname: Geng
authors.forename: M
authors.initials: M
authors.lastname: Lotz
mesh_terms: D000328:Adult; D000368:Aged; D000594:Amino Acid Oxidoreductases / Q000235:genetics*; D001483:Base Sequence; D002358:Cartilage, Articular / Q000166:cytology* / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007375:Interleukin-1 / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D019001:Nitric Oxide Synthase; D012333:RNA, Messenger / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D017931:DNA Primers; D007375:Interleukin-1; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D003094:Collagen; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases