Ghrelin-mediated inhibition of the TSH-stimulated function of differentiated human thyrocytes ex vivo

Abstract

Ghrelin is a peptide hormone produced mainly in the gastrointestinal tract known to regulate several physiological functions including gut motility, adipose tissue accumulation and hunger sensation leading to increased bodyweight. Studies have found a correlation between the plasma levels of thyroid hormones and ghrelin, but an effect of ghrelin on the human thyroid has never been investigated even though ghrelin receptors are present in the thyroid. The present study shows a ghrelin-induced decrease in the thyroid-stimulating hormone (TSH)-induced production of thyroglobulin and mRNA expression of thyroperoxidase in a primary culture of human thyroid cells obtained from paranodular tissue. Accordingly, a trend was noted for an inhibition of TSH-stimulated expression of the sodium-iodine symporter and the TSH-receptor. Thus, this study suggests an effect of ghrelin on human thyrocytes and thereby emphasizes the relevance of examining whether ghrelin also influences the metabolic homeostasis through altered thyroid hormone production.

Fig 1. Ghrelin receptor (GhrR) mRNA expression level.

GhrR mRNA expression level in relation to the reference gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA expression level in human brain, thyroid tissue and cell cultures measured by real-time quantitative polymerase chain reaction (RT-qPCR). n = 2.

Fig 2. The influence of ghrelin on the thyroid-stimulating hormone (TSH)-induced increase in thyroglobulin (Tg) and cAMP production.

The influence of ghrelin on the TSH-induced increase in Tg and cAMP production at three different concentrations of TSH (0.1 IU/L, 0.5 IU/L and 1 IU/L). The basal levels, i.e. the values in the absence of TSH, were subtracted, before the groups were compared. Grey = vehicle, pattern = ghrelin (100 nM). Means (+SEM). *P < 0.05 compared to the control (vehicle). A) Ghrelin inhibited the TSH-induced increase in Tg production measured by enzyme-linked immunosorbent assay (ELISA) in primary cultures of human thyroid cells for the TSH concentration of 0.1 IU/L. n = 8 (0.1 IU/L) and n = 6 (0.5 and 1 IU/L) in triplets. Two patient samples were excluded due to lack of basal TSH-induced Tg production. B) No influence of ghrelin on the TSH-induced increase in cAMP production at three different concentrations of TSH (0.1 IU/L, 0.5 IU/L and 1 IU/L) measured by a competitive protein binding method in primary cultures of human thyroid cells. n = 8 (0.1 IU/L and 1 IU/L) and n = 6 (0.5 IU/L) in triplets.

Fig 3. The influence of ghrelin on the thyroid-stimulating hormone (TSH)-induced (0.1 IU/L) mRNA expression of four thyroid components.

The expression of the TSH receptor (TSH-R), thyroperoxidase (TPO), thyroglobulin (Tg) and sodium iodide symporter (NIS) measured by real-time quantitative polymerase chain reaction (RT-qPCR) in a primary culture of human thyroid cells in presence and absence of ghrelin. Indicated as fold change of mRNA expression compared to basal level (dashed line). IL-6 was used as a negative control. Grey = vehicle, pattern = ghrelin (100 nM). Means (±SEM), n = 6. *P < 0.05 compared to the control (vehicle). Two patients were excluded due to unknown sample material.