Thyroid Hormone Protects from Fasting-Induced Skeletal Muscle Atrophy by Promoting Metabolic Adaptation.

Thyroid hormones regulate a wide range of cellular responses, via non-genomic and genomic actions, depending on cell-specific thyroid hormone transporters, co-repressors, or co-activators. Skeletal muscle has been identified as a direct target of thyroid hormone T3, where it regulates stem cell proliferation and differentiation, as well as myofiber metabolism. However, the effects of T3 in muscle-wasting conditions have not been yet addressed. Being T3 primarily responsible for the regulation of metabolism, we challenged mice with fasting and found that T3 counteracted starvation-induced muscle atrophy. Interestingly, T3 did not prevent the activation of the main catabolic pathways, i.e., the ubiquitin-proteasome or the autophagy-lysosomal systems, nor did it stimulate de novo muscle synthesis in starved muscles. Transcriptome analyses revealed that T3 mainly affected the metabolic processes in starved muscle. Further analyses of myofiber metabolism revealed that T3 prevented the starvation-mediated metabolic shift, thus preserving skeletal muscle mass. Our study elucidated new T3 functions in regulating skeletal muscle homeostasis and metabolism in pathological conditions, opening to new potential therapeutic approaches for the treatment of skeletal muscle atrophy.

Thyroid hormones induce cell proliferation and survival in ovarian granulosa cells COV434.

Numerous evidences indicate that thyroid hormones exert an important role in the regulation of the reproductive system in the adult female. Although a clear demonstration of the thyroid-ovarian interaction is still lacking, it is conceivable that thyroid hormones might have a direct role in ovarian physiology via receptors in granulosa cells. In this study we analyzed if thyroid hormone treatment could affect cell proliferation and survival of COV434 cells. To this aim cell growth experiments and cell cycle analyses by flow cytometry were performed. Secondly the T(3) survival action was tested by TUNEL assay and MD30 cleavage analysis. We showed that T(3), and not T(4), can protect ovarian granulosa cells COV434 from apoptosis, regulating cell cycle and growth in the same cells. The increase in cell growth resulted in an augmented percentage of the cells in the S phase and, in a reduction of the doubling time (18%). Subsequently apoptotic pathway induced by serum deprivation has been evaluated in the cells exposed or not to thyroid hormone treatment. The T(3) treatment was able to remarkably counteract the apoptotic process. Even at the ultrastructural level there was an evident protective effect of T(3) in the cells that, besides the maintenance of the original morphology and, the absence of basophilic cytoplasm, conserved normal junctional areas. Furthermore, the protective T(3) effect evaluated by FACS analysis in the presence of a PI3K inhibitor revealed, as also confirmed by Western Blot on pAkt, that the PI3K pathway is crucial in T(3) survival action.

The TRbeta1 is essential in mediating T3 action on Akt pathway in human pancreatic insulinoma cells.

Thyroid hormone action, widely recognized on cell proliferation and metabolism, has recently been related to the phosphoinositide 3 kinase (PI3K), an upstream regulator of the Akt kinase and the involvement of the thyroid hormone receptor beta1 has been hypothesized. The serine-threonine kinase Akt can regulate various substrates that drive cell mass proliferation and survival. Its action has also been characterized in pancreatic beta-cells. We previously demonstrated that Akt activity and its activation in the insulinoma cell line hCM could be considered a specific target of the non-genomic action of T3. In this study we analyzed the molecular pathways involved in the regulation of cell proliferation, survival, size, and protein synthesis by T3 in a stable TRbeta1 interfered insulinoma cell line, derived from the hCM, and evidenced a strong regulation of both physiological and molecular events by T3 mediated by the thyroid hormone receptor beta1. We showed that the thyroid receptor beta1 mediates the T3 regulation of the cdk4.cyc D1.p21(CIP1).p27(KIP1) complex formation and activity. In addition TRbeta1 is essential for the T3 upregulation of the Akt targets beta-catenin, p70S6K, and for the phosphorylation of Bad and mTOR. We demonstrated that the beta1 receptor mediates the T3 upregulation of protein synthesis and cell size, together with the cell proliferation and survival, playing a crucial role in the T3 regulation of the PI3K/Akt pathway.

Thyroid hormones (T3 and T4): dual effect on human cancer cell proliferation.

Several findings suggest that the patient's hormonal context plays a crucial role in determining cancer outcome. The exact nature of thyroid hormone action on tumour growth has not been established yet, in fact contrasting data show thyroid hormones have a promotory or an inhibitory action on cancer cell proliferation depending on the case. We hypothesized that not only tissue specificity, but also specific mutations occurring during tumoral development in different thyroid hormone cellular targets are responsible for this dual effect. To test our hypothesis we analysed, by time-course and bromodeoxyuridine assay, thyroid hormone effects on the proliferation of six cancer cell lines originating from the same tissue or organ but carrying different mutations (in phospho-inositide 3 kinase or ß-catenin genes). The data obtained in this study show how mutations that affect the balance between degradation and stabilization of ß-catenin assume a remarkable importance in determining the cell-specific thyroid hormone effect on cell growth.

Thyroid hormone T3 counteracts STZ induced diabetes in mouse.

This study intended to demonstrate that the thyroid hormone T3 counteracts the onset of a Streptozotocin (STZ) induced diabetes in wild type mice. To test our hypothesis diabetes has been induced in Balb/c male mice by multiple low dose Streptozotocin injection; and a group of mice was contemporaneously injected with T3. After 48 h mice were tested for glucose tolerance test, insulin serum levels and then sacrificed. Whole pancreata were utilized for morphological and biochemical analyses, while protein extracts and RNA were utilized for expression analyses of specific molecules. The results showed that islets from T3 treated mice were comparable to age- and sex-matched control, untreated mice in number, shape, dimension, consistency, ultrastructure, insulin and glucagon levels, Tunel positivity and caspases activation, while all the cited parameters and molecules were altered by STZ alone. The T3-induced pro survival effect was associated with a strong increase in phosphorylated Akt. Moreover, T3 administration prevented the STZ-dependent alterations in glucose blood level, both during fasting and after glucose challenge, as well as in insulin serum level. In conclusion we demonstrated that T3 could act as a protective factor against STZ induced diabetes.

The thyroid hormone T3 improves function and survival of rat pancreatic islets during in vitro culture.

Ex vivo islet cell culture in the presence of stimulating factors prior to transplantation is considered a good strategy in contrast to the short conclusion of islets transplantation. Previously, we demonstrated how T3 can increase b-cell function via specific activation of Akt; therefore we hypothesized that thyroid hormone T3 can be considered a promising candidate for the in vitro expansion of islet cell mass. Rat pancreatic islets have been isolated by the collagenase digestion and cultured in the presence or not of the thyroid hormone T3 10⁻7 M. Islets viability has been evaluated by the use of two different dyes, one cell-permeable green fluorescent dye and propidium iodide, and by the analysis of core cell damage upcoming. Moreover, islets function has been evaluated by insulin secretion. The ability of b-cells to counteract apoptosis induced by streptozotocin has been analyzed by TUNEL assay. We demonstrated that treatment of primary cultures of rat pancreatic islets with T3 results in augmented ß-cell vitality with an increase of their functional properties. In addition, a sensible reduction of the core cell damage has been observed in the T3 treated islets, suggesting the preservation of the ß-cells integrity during the culture period. Nonetheless, the insulin secretion is sensibly augmented after T3 stimulation. The strong increment shown in Akt activation suggests the involvement of this pathway in the observed phenomena. In conclusion we indicate T3 as a good factor to improve ex vivo islets cell culture.