Hypergravity delocalizes thyrotropin receptor (650.3)

Abstract

Thyrotropin receptor (TSHR) is a a heterodimer G protein‐coupled receptor constituted by an α extracellular subunit (53 kDa) interacting with thyrotropin (TSH) and a broad β transmembrane and intracellular subunit (30‐42 kDa) held together by disulphide bridges. TSHR are localized in the basolateral membrane rich in lipid rafts, microdomains with high level of cholesterol and sphingolipids, that provide a platform for the assembly of signaling complexes after TSH‐TSHR interaction. This interaction was perturbed in hypogravity during parabolic flights and longer missions in Space on board the ISS. In the present work the influence of complex mechanical effects of hypergravity on TSHR, cholesterol and sphingolipid in thyroid gland in vivo was investigated. Seven mice were maintained in hypergravity in a 2g centrifuge. Our results show that hypergravity up‐regulated 65% TSHR. TSH treatment did not cause significant changes in the thyroid gland of the control mice and induced about 50% reduction of the α subunit TSHR of 2g animal. TSH‐stimulated cAMP production was similar in control and 2g samples, indicating that even if TSHR is up‐regulated in hypergravity, the loss of its α subunit that binds TSH was responsible for the lack of the expected increased response to hormonal stimulation. Immunofluorescence analysis of TSHR demonstrated that in control samples the receptor was present on the surface of thyrocytes that surrounded follicles with a precise location, whereas in 2g samples the fluorescent signal was higher and spread over the entire surface of thyrocytes. The UFLC‐MS/MS study on lipid fraction of thyroid tissue showed that sphingomyelin and ceramide species remained unchanged whereas cholesterol was reduced 49% in 2g in comparison with control samples. We thus suggest that gravity, by inducing a significant loss of cholesterol, perturbed lipid rafts modifying TSH‐TSHR interaction.Grant Funding Source: Agenzia Spaziale Italiana