cyclin-d1 and Hypothyroidism

3,5,3'-L-triiodothyronine (T3) is a potent inducer of hepatocyte proliferation via the Wnt/β-catenin signaling pathway. Previous studies suggested the involvement of rapid noncanonical thyroid hormone receptor (TR) β signaling, directly activating hepatic Wnt/β-catenin signaling independent from TRβ DNA binding. However, the mechanism by which T3 increases Wnt/β-catenin signaling in hepatocytes has not yet been determined.. We aimed to determine whether DNA binding of TRβ is required for stimulation of hepatocyte proliferation by T3.. Wild-type (WT) mice, TRβ knockout mice (TRβ KO), and TRβ mutant mice with either specifically abrogated DNA binding (TRβ GS) or abrogated direct phosphatidylinositol 3 kinase activation (TRβ 147F) were treated with T3 for 6 hours or 7 days. Hepatocyte proliferation was assessed by Kiel-67 (Ki67) staining and apoptosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Activation of β-catenin signaling was measured in primary murine hepatocytes. Gene expression was analyzed by microarray, gene set enrichment analysis (GSEA), and quantitative reverse transcription polymerase chain reaction.. T3 induced hepatocyte proliferation with an increased number of Ki67-positive cells in WT and TRβ 147F mice (9.2% ± 6.5% and 10.1% ± 2.9%, respectively) compared to TRβ KO and TRβ GS mice (1.2% ± 1.1% and 1.5% ± 0.9%, respectively). Microarray analysis and GSEA showed that genes of the Wnt/β-catenin pathway-among them, Fzd8 (frizzled receptor 8) and Ctnnb1 (β-catenin)-were positively enriched only in T3-treated WT and TRβ 147F mice while B-cell translocation gene anti-proliferation factor 2 was repressed. Consequently, expression of Ccnd1 (CyclinD1) was induced.. Instead of directly activating Wnt signaling, T3 and TRβ induce key genes of the Wnt/β-catenin pathway, ultimately stimulating hepatocyte proliferation via CyclinD1. Thus, canonical transcriptional TRβ action is necessary for T3-mediated stimulation of hepatocyte proliferation.

Topics: Animals; Binding Sites; Cell Proliferation; Cyclin D1; DNA; Gene Expression; Hepatocytes; Hypothyroidism; Male; Mice; Mice, Knockout; Mice, Mutant Strains; Mutation; Signal Transduction; Thyroid Hormone Receptors beta; Triiodothyronine; Wnt Signaling Pathway

Hypothyroidism affects neuron population dynamics in the hippocampus of the adult rat, with neuronal damage as the main feature of its effect. This effect is prevented by the blockade of NMDA receptors, which suggests that glutamatergic activity mediates cell death in this condition. Glutamate can also stimulate cell proliferation and survival of newborn neurons, indicating that it can affect different stages of the cell cycle. In this work we measured the expression of specific proteins that control cell proliferation (cycline-D1), cell arrest (p21), damage (p53) or apoptosis (Bax and Bcl2) in the hippocampus of hypothyroid rats treated with the NMDA receptor (NMDAR) blocker MK-801 during the induction of hypothyroidism. The results show that hypothyroidism increases the expression of markers of DNA damage, cell arrest, and apoptosis, but does not affect the marker of cell proliferation. NMDAR blockade prevents the increase on markers of DNA damage and apoptosis, but does not influence cell arrest or cell proliferation. This suggests that hypothyroidism promotes cell death mainly by an excitotoxic effect of glutamate.

Topics: Analysis of Variance; Animals; Antithyroid Agents; Apoptosis; bcl-2-Associated X Protein; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p21; Disease Models, Animal; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Hippocampus; Hypothyroidism; Methimazole; Proto-Oncogene Proteins c-bcl-2; Rats; Tumor Suppressor Protein p53

We have shown in vitro that thyroid hormones (THs) regulate the balance between proliferation and apoptosis of T lymphoma cells. The effects of THs on tumor development have been studied, but the results are still controversial. Herein, we show the modulatory action of thyroid status on the in vivo growth of T lymphoma cells. For this purpose, euthyroid, hypothyroid, and hyperthyroid mice received inoculations of EL4 cells to allow the development of solid tumors. Tumors in the hyperthyroid animals exhibited a higher growth rate, as evidenced by the early appearance of palpable solid tumors and the increased tumor volume. These results are consistent with the rate of cell division determined by staining tumor cells with carboxyfluorescein succinimidyl ester. Additionally, hyperthyroid mice exhibited reduced survival. Hypothyroid mice did not differ significantly from the euthyroid controls with respect to these parameters. Additionally, only tumors from hyperthyroid animals had increased expression levels of proliferating cell nuclear antigen and active caspase 3. Differential expression of cell cycle regulatory proteins was also observed. The levels of cyclins D1 and D3 were augmented in the tumors of the hyperthyroid animals, whereas the cell cycle inhibitors p16/INK4A (CDKN2A) and p27/Kip1 (CDKN1B) and the tumor suppressor p53 (TRP53) were increased in hypothyroid mice. Intratumoral and peritumoral vasculogenesis was increased only in hyperthyroid mice. Therefore, we propose that the thyroid status modulates the in vivo growth of EL4 T lymphoma through the regulation of cyclin, cyclin-dependent kinase inhibitor, and tumor suppressor gene expression, as well as the stimulation of angiogenesis.

Topics: Animals; Apoptosis; Caspase 3; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Female; Hyperthyroidism; Hypothyroidism; Lymphoma, T-Cell; Mice; Mice, Inbred C57BL; Neoplasm Transplantation; Neovascularization, Pathologic; Proliferating Cell Nuclear Antigen; Thyroid Gland; Tumor Suppressor Protein p53

The onset of adult hypothyroidism causes neuronal damage in the CA3 hippocampal region, which is attenuated by T(4) administration. We analyzed the expression of molecular proliferation markers (Cyclin D1 and PCNA), cellular damage-arrest (p53 and p21), and apoptosis (Bax/Bcl-2 index) in the hippocampus of hypothyroid (methimazole; 60 mg/kg) or thyroid replaced (T(4), 20 microg/kg; MMI+T(4) or T(3), 20 microg/kg; MMI+T(3)) adult male rats. Histological analysis showed that hypothyroid animals exhibit significant neuronal damage in all regions of the hippocampus accompanied by the triggering of the apoptotic pathway (increases in p53, p21 and the Bax/Bcl-2 index) and no changes in proliferation (Cyclin D1 and PCNA). MMI+T(4) replaced animals were completely protected with no changes in molecular markers. In contrast, MMI+T(3) replaced animals showed partial protection in which, although pro-apoptotic effects remained (increase in the Bax/Bcl-2), proliferative mechanisms were triggered (increase in p53, Cyclin D1 and PCNA expression). Our results indicate that thyroid hormones participate in the maintenance of the hippocampal neuronal population even in adulthood, suggesting that THs have different physiological roles as neuronal survival factors: T(4) prevents the activation of apoptotic pathways, whereas T(3) activates cell differentiation and proliferation mechanisms.

Topics: Animals; Antithyroid Agents; bcl-2-Associated X Protein; Cell Cycle; Cell Cycle Proteins; Cell Proliferation; Cell Survival; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p21; Disease Models, Animal; Hippocampus; Hypothyroidism; Male; Methimazole; Proliferating Cell Nuclear Antigen; Proto-Oncogene Proteins c-bcl-2; Pyramidal Cells; Rats; Rats, Wistar; Thyroid Gland; Thyroid Hormones; Tumor Suppressor Protein p53

Although transcriptional effects of thyroid hormones have substantial influence on oxidative metabolism, how thyroid sets basal metabolic rate remains obscure. Compartmental localization of nitric-oxide synthases is important for nitric oxide signaling. We therefore examined liver neuronal nitric-oxide synthase-alpha (nNOS) subcellular distribution as a putative mechanism for thyroid effects on rat metabolic rate. At low 3,3',5-triiodo-L-thyronine levels, nNOS mRNA increased by 3-fold, protein expression by one-fold, and nNOS was selectively translocated to mitochondria without changes in other isoforms. In contrast, under thyroid hormone administration, mRNA level did not change and nNOS remained predominantly localized in cytosol. In hypothyroidism, nNOS translocation resulted in enhanced mitochondrial nitric-oxide synthase activity with low O2 uptake. In this context, NO utilization increased active O2 species and peroxynitrite yields and tyrosine nitration of complex I proteins that reduced complex activity. Hypothyroidism was also associated to high phospho-p38 mitogen-activated protein kinase and decreased phospho-extracellular signal-regulated kinase 1/2 and cyclin D1 levels. Similarly to thyroid hormones, but without changing thyroid status, nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester increased basal metabolic rate, prevented mitochondrial nitration and complex I derangement, and turned mitogen-activated protein kinase signaling and cyclin D1 expression back to control pattern. We surmise that nNOS spatial confinement in mitochondria is a significant downstream effector of thyroid hormone and hypothyroid phenotype.

Topics: Animals; Cyclin D1; Cytosol; Electron Transport Complex I; Electrons; Electrophoresis, Polyacrylamide Gel; HSP90 Heat-Shock Proteins; Hypothyroidism; Immunoblotting; Immunoprecipitation; Liver; Male; MAP Kinase Signaling System; Microscopy, Immunoelectron; Mitochondria; Mitochondria, Liver; Models, Chemical; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Oxidants; Oxygen; p38 Mitogen-Activated Protein Kinases; Peroxynitrous Acid; Phenotype; Protein Isoforms; Protein Transport; Rats; Rats, Wistar; Reactive Oxygen Species; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Subcellular Fractions; Thyroid Hormones; Transcription, Genetic