Abstract
Maintaining a good health requires the maintenance of a body homeostasis which largely depends on correct functioning of thyroid gland. The cells of the thyroid tissue are strongly sensitive to hypogravity, as already proven in mice after returning to the earth from long-term space missions. Here we studied whether hypergravity may be used to counteract the physiological deconditioning of long-duration spaceflight. We investigated the influence of hypergravity on key lipids and proteins involved in thyroid tissue function. We quantified cholesterol (CHO) and different species of sphingomyelin (SM) and ceramide, analysed thyrotropin (TSH) related molecules such as thyrotropin-receptor (TSHR), cAMP, Caveolin-1 and molecule signalling such as Signal transducer and activator of transcription-3 (STAT3). The hypergravity treatment resulted in the upregulation of the TSHR and Caveolin-1 and downregulation of STAT3 without changes of cAMP. TSHR lost its specific localization and spread throughout the cell membrane; TSH treatment facilitated the shedding of α subunit of TSHR and its releasing into the extracellular space. No specific variations were observed for each species of SM and ceramide. Importantly, the level of CHO was strongly reduced. In conclusion, hypergravity conditions induce change in CHO and TSHR of thyroid gland. The possibility that lipid rafts are strongly perturbed by hypergravity-induced CHO depletion by influencing TSH-TSHR interaction was discussed.
Highlights
Life on earth has been and is constantly evolving for the variations of different environmental factors, with the exception of the gravitational force that has remained constant over time
Reagent Anti- Signal transducer and activator of transcription-3 (STAT3), anti-TSHR, anti-Caveolin 1, fluorescein isothiocyanate (FITC)-conjugated secondary antibody were obtained from Santa Cruz Biotechnology, Inc. (California, USA); SDS-PAGE molecular weight standards were purchased from Bio-Rad Laboratories (Hercules, CA, USA)
Since TSHRs were G protein-coupled receptors [16] which were localized in membrane microdomains, including caveolae and lipid rafts enriched in SM and CHO content [17,18], we considered if the distribution of TSHR over the entire cell surface in hypergravity conditions could be due to the alteration of lipid component of cell membrane
Summary
Life on earth has been and is constantly evolving for the variations of different environmental factors, with the exception of the gravitational force that has remained constant over time. Sphingomyelinase (SMase) and sphingomyelinsynthase (SM-synthase), enzymes involved in cell signaling, were overexpressed [9] It seems that hypogravity and hypergravity would generate opposite results on thyroid gland, but some key results of our previous hypogravity studies were surprisingly similar. In hypergravity the SMase expression did change as in hyporgravity but the nucleus-cytoplasm translocation was similar in the two experimental conditions, suggesting that alteration of gravity conditions might be responsible for molecular remodellings which might influence the cell fate [9] Both hypogravity and hypergravity induced loss of the parafollicular cells within the thyroid gland, with consequent reduction of calcitonin production, suggesting a potential implication of the mechanical forces in the regulation of bone homeostasis via thyroid gland [10]. In this study we investigated the influence of complex mechanical effects of hypergravity on key proteins and lipids of signal transduction in thyroid gland in vivo
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