Regulation of Glycosaminoglycan Synthesis by Thyroid Hormone in Vitro

Terry J. Smith; Yoshiharu Murata; Allen L. Horwitz; Louis Philipson; Samuel Refetoff

doi:10.1172/JCI110694

Regulation of Glycosaminoglycan Synthesis by Thyroid Hormone in Vitro

Terry J. Smith, Yoshiharu Murata, Allen L. Horwitz, Louis Philipson, and Samuel Refetoff

Published November 1, 1982 - More info

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Abstract

Human skin fibroblasts synthesize and accumulate glycosaminoglycans (GAG). Recently, we reported that fibroblasts incubated in thyroid hormone-deficient media accumulate more GAG than do cultures incubated in the same media enriched with 0.1 μM triiodothyronine (T₃) (1981. Endocrinology. 108: 2397). The current study characterizes that enhanced accumulation. Confluent cultures were maintained in thyroid hormone-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 μM 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 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 acid-precipitable 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.