Resistance to Thyroid Hormone Diagnosed by the Reduced Response of Fibroblasts to the Triiodothyronine-Induced Suppression of Fibronectin Synthesis^*

Abstract

The syndrome of generalized resistance to thyroid hormone (GRTH) is due to a defect at the level of target tissues, but its diagnosis is currently based on indirect tests and cumbersome clinical observations. We recently reported that physiological amounts of T3 inhibit fibronectin (Fn) synthesis by human fibroblasts derived from normal donors. The aim of this study was to assess if this observation could be used for the direct tissue diagnosis of GRTH. Skin fibroblasts from seven normal subjects and seven patients with GRTH were grown to confluence and then exposed for 3 days to medium supplemented with 10% thyroidectomized bovine serum with or without added T3. Cells were then labeled with [35S]methionine for 4 h, and the combined medium and cell lysate was examined for the incorporation of [35S]methionine into trichloroacetic acid and anti-Fn-precipitable material, followed by analysis on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. 35S activity in the 230K protein was corrected for trichloroacetic acid-precipitable 35S activity. To assess the selectivity of the T3 effect on Fn in fibroblasts from normal subjects compared to GRTH patients, the responses of Fn to dexamethasone and Na butyrate were also determined. Addition of 10(-9) and 10(-7) M T3 to the medium (free T3, 6 X 10(-12) and 2 X 10(-9) M, respectively) reduced Fn synthesis by 13.2 +/- 3.2% (+/- SD) and 14.3 +/- 8.2%, respectively, in fibroblasts from patients with GRTH, an effect significantly less (P less than 0.02 and P less than 0.005) than the 22.2 +/- 7.4% and 30.2 +/- 5.0% reduction that occurred in fibroblasts from normal subjects. With the exception of one patient with GRTH, individual values from each of the two groups did not overlap; the clinical studies suggested that this patient had a milder form of GRTH. In contrast, dexamethasone and sodium butyrate stimulated Fn synthesis by 25.6 +/- 8.7% and 268 +/- 125%, respectively, in fibroblasts from patients with GRTH compared to 27.6 +/- 7.2% and 304 +/- 125% in fibroblasts from normal subjects. The difference of the responses between the two groups was not significant. The results indicate that measurement of the response of Fn to T3 in cultured fibroblasts can be used for the tissue diagnosis of GRTH.

Generalized resistance to thyroid hormone associated with a mutation in the ligand-binding domain of the human thyroid hormone receptor beta.

“…Triiodothyronine has been shown (31,32) to produce a dose-dependent decrease in fibronectin synthesis in normal fibroblasts, and this response is diminished in fibroblasts cultured from patients with GRTH. In the present study, triiodothyronine added to the medium to a concentration of 10-11 and 10-9 M free hormone produced little suppression of fibronectin synthesis in fibroblasts from the affected proband and his father and normally suppressed fibronectin synthesis in fibroblasts from the mother (Fig.…”

Thyroid Hormone Generalized Resistance

“…It is imperative to compare values obtained in the same indi vidual before and during the administration of graded doses of thyroid hormone rather than to interpret baseline data on the basis of normal values [7], In vitro. T3 does not increase low density lipoprotein (LDL) degradation [ 10] and does not reduce glycosaminoglvcan synthesis [ 11] or fibronectin synthesis [12] in skin fibroblasts of subjects with GRTH.…”

Defective Response of Body Height to Growth Hormone Treatment in Resistance to Thyroid Hormone with Short Stature.

“…It was also recognized that 15% of subjects had a height below the fifth percentile and 8% belos the third percentile [3]. However, most measure ments were obtained in children, and it is not clea7 whether they ultimately achieved a normal height Although attempts to improve growth rate b) TH therapy were reported by several investigator [4][5][6], there have been, as far as we know of, nc reports on GH treatment in patients with resis tance to TH and short stature. In this study, wE have examined the response of height to GH treat ment together with increased doses of TH b) measuring serum concentrations of insulin-likf growth factor-1(IGF-1) during the course of treat ment.…”