SPECIES-SPECIFIC EXPRESSION OF TYPE-II TGF-BETA RECEPTOR ISOFORMS BY ARTICULAR CHONDROCYTES - EFFECT OF PROTEOGLYCAN DEPLETION AND AGING

Recently, a new isoform of the type II transforming growth factor beta receptor (TGF-beta RII) was identified. This isoform (TGF-beta RII2) contains an insertion of 25 amino acids in the extracellular domain of the receptor, Using RT-PCR the authors demonstrated that both TGF-bet a RII1 and TGF-beta RII2 are expressed by chondrocytes in murine and h uman articular cartilage. Bovine articular chondrocytes expressed TGF- beta RII1 mRNA but did not express detectable levels of TGF-beta RII2 mRNA, suggesting that the new isoform does not play an important role in normal bovine cartilage physiology, Because TGF-beta responses seem to be age related and differential TGF-beta responses have been descr ibed between normal cartilage and cartilage undergoing repair the auth ors studied if the relative mRNA expression between these isoforms is altered during cartilage repair and aging. No differences in the relat ive mRNA expression of the two isoforms of the type II TGF-beta recept or could be demonstrated in murine cartilage during aging or during th e repair phase after mild PG depletion indicating that it is unlikely that age-related TGF-beta responses and differential TGF-beta response s between normal cartilage and cartilage undergoing repair are the res ult of differences in the relative expression of the two TGF-beta RII isoforms. (C) 1997 Academic Press Limited.