Primary Cilium in the Human Thyrocyte: Changes in Frequency and Length in Relation to the Functional Pathology of the Thyroid Gland.

BACKGROUND: Primary cilia (PC) are conserved structures in the adult thyroid gland of different mammals. It was recently described that in humans, PC are usually present as a single copy per follicular cell emerging from the follicular cell apex into the follicular lumen. METHODS: To understand the role developed by PC in thyroid hormonogenesis better, their changes in different human functional thyroid diseases (diffuse toxic hyperplasia/Graves' disease [GD] and nodular hyperplasia [NH]/nodular goiter), in comparison to normal thyroid tissue, were investigated using immunofluorescence, morphometry, and electron microscopy analyses. RESULTS: Significantly decreased ciliary frequencies were found in both NH (51.16 ± 11.69%) and GD (44.43 ± 23.70%) compared to normal thyroid tissue (76.09 ± 7.31%). Similarly, PC lengths were also significantly decreased in both NH (2.02 ± 0.35 µm) and GD (2.4 ± 0.48 µm) compared to normal glands (3.93 ± 0.90 µm). Moreover, in GD patients, hyperactive-follicle foci always showed diminished ciliary frequency and length compared to any other thyroid follicle pattern, independent of their thyroid status. Finally, in GD, the percentage of thyrocytes exhibiting PC in the "normal-appearance areas" was significantly lower in correspondence with the subsistence of signs of thyroid biosynthetic hyperactivity after long-term antithyroid drug treatment. CONCLUSIONS: The results suggest a direct relationship between ciliogenesis and both follicle activity and tissue heterogeneity in the functional pathology of the thyroid gland.

Melatonin-synthesizing enzymes and melatonin receptor in rat thyroid cells.

Melatonin is an indoleamine with a wide spectrum of biological activities other than transmitting photoperiod information, including antioxidant, oncostatic, anti-aging and immunomodulatory properties. Although melatonin is synthesized mainly in the pineal gland, other tissues have the same capacity. In the present study, we examined whether two key enzymes in melatonin biosynthesis, arylalkylamine Nacetyltransferase (AANAT) and hydroxyindole-O-methyltransferase (HIOMT) and its receptor MT1 are expressed in the two endocrine thyroid cells of the rat, follicular cells and C cells. Reverse transcriptase polymerase chain reaction analyses demonstrated that both AANAT and HIOMT mRNAs are expressed in the rat thyroid C-cells, and MT1 expression has been detected in C cells and follicular cells. Immunofluorescence revealed that AANAT protein is localized in C-cell cytoplasm, and MT1 protein in both cell populations. These findings demonstrate that the rat thyroid expresses AANAT, HIOMT, and its receptor MT1, showing that C cells are the main melatonin-synthesizing sites in the thyroid. This local C-cell-secreted melatonin may protect follicular cells from the oxidative stress inherent to the thyroid gland, and could also have paracrine and autocrine functions.