Regulation of Glycosaminoglycan Synthesis

0.1 ,uM triiodothyronine (T3) (1981. Endocrinology. 108: 2397). The current study characterizes that enhanced accumulation. Confluent cultures were maintained in thyroid hormnone-deficient media without or with added T3, labeled with [3H]acetate and analyzed for total [3H]GAG and [3H]hyaluronic acid content. Addition of T3 to thyroid hormone-depleted media consistently inhibited the incorporation of [3H]acetate into GAG by 28-60% in fibroblast cultures from four different normal human donors. Maximal inhibitory effect was observed within 3 d after hormone addition at concentrations > 1 nM. 73% of the maximal inhibitory effect was observed in the presence of physiologic concentrations of T3 (0.16 nM total T3 or 1.4 pM free T3). The following observations indicated that T3 inhibition of [3H]GAG accumulation is most likely due to a decrease in GAG synthesis rather than to changes in the acetate pool or GAG degradation: (a) Addition of 0, 100, 500, and 2,500,uM unlabeled acetate progressively decreased [3H]acetate incorporation into GAG, up to 80%, without altering the further inhibitory effect of T3 (35-40%); (b). A similar effect of T3 on GAG (32% inhibition) was observed using [3H]glucosamine as substrate; (c) T3 decreased hyaluronate synthetase activity by 32%; and (d) There was no effect of T3 on GAG degradation in a pulse-chase experiment. The Portions of this work were presented at the 63rd Annual Meeting of The Endocrine Society, Cincinnati, OH, 17-19 June 1981. Address reprint requests to Dr. Smith. His present address is The Rockefeller University, New York 10021. Received for publication 8 September 1981 and in revised form 14 July 1982. effect of T3 on [3H]GAG accumulation appears to be quite specific, since the hormone had no effect on the incorporation of [3H]leucine into trichloroacetic acidprecipitable material. Thus, thyroid hormone inhibits GAG accumulation in a dose-, time-dependent, and reversible manner. This inhibition is apparently due to specific effects on the rate of macromolecular synthesis.