PARATHYROID HORMONE-RELATED PROTEIN (PTHRP) ACTION IN RAT ARTICULAR CHONDROCYTES - COMPARISON OF PTH(1-34), PTHRP(1-34), PTHRP(1-141), PTHRP(100-114) AND ANTISENSE OLIGONUCLEOTIDES AGAINST PTHRP

Parathyroid hormone-related protein (PTHrP) is thought to be an import ant autocrine/paracrine factor ibr chondrocyte metabolism since mice l acking the PTHrP gene exhibit abnormal cartilage development. To deter mine the biological role of PTHrP in chondrocytes, we first compared t he agonist potency of human (h) PTHrP(1-34) with hPTH(1-34) in culture d rat articular chondrocytes. Neither hPTHrP(1-34) nor hPTH(1-34) alte red basal DNA synthesis, but attenuated the stimulatory effect of tran sforming growth factor beta (TGF-beta). Both agents suppressed the exp ression of alpha(1) type II collagen mRNA in a dose-response fashion w ith the same potency. In addition, the action of exogenously added hPT HrP(1-34) and hPTH(1-34) on intracellular cAMP and [Ca2+](i) levels wa s similar. We next compared the effect of PTHrP within its entire amin o acid sequence (1-141). With regard to thymidine incorporation, alpha (1) type II collagen gene expression and accumulation of cAMP and [Ca2 +](i) level, there was no significant difference between hPTHrP(1-34) and hPTHrP(1-141). PTHrP C-terminal (100-114) did not show any functio n. further investigate PTHrP function, intracellular PTHrP translation was inhibited by a transgene of antisense oligonucleotides against PT HrP. Antisense oligonucleotides decreased PTHrP mRNA translation, spec ifically inhibited DNA synthesis in control as well. as TGF-beta-treat ed chondrocytes and enhanced alpha(1) type II collagen mRNA expression in TGF-beta-treated chondrocytes. These results suggest that there is no significant difference between exogenously added hPTH(1-34), hPTHr P(1-34) and PTHrP(1-141) with regard to the biological action of these agents, including cell growth, differentiation and second messenger p athway. However, the result of DNA synthesis in the antisense PTHrP-in hibition study suggests that intracellular PTHrP may have an as yet un known biological role, in addition to a classical PTH/PTHrP receptor-m ediated function in the rat articular chondrocyte.