Modulación de la neurogénesis y de la conducta por hormonas tiroideas en ratas adultas

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina. Departamento de Bioquímica. Fecha de lectura: 23 de Junio de 200

Adult-Onset Hypothyroidism Enhances Fear Memory and Upregulates Mineralocorticoid and Glucocorticoid Receptors in the Amygdala

Hypothyroidism is the most common hormonal disease in adults, which is frequently accompanied by learning and memory impairments and emotional disorders. However, the deleterious effects of thyroid hormones deficiency on emotional memory are poorly understood and often underestimated. To evaluate the consequences of hypothyroidism on emotional learning and memory, we have performed a classical Pavlovian fear conditioning paradigm in euthyroid and adult-thyroidectomized Wistar rats. In this experimental model, learning acquisition was not impaired, fear memory was enhanced, memory extinction was delayed and spontaneous recovery of fear memory was exacerbated in hypothyroid rats. The potentiation of emotional memory under hypothyroidism was associated with an increase of corticosterone release after fear conditioning and with higher expression of glucocorticoid and mineralocorticoid receptors in the lateral and basolateral nuclei of the amygdala, nuclei that are critically involved in the circuitry of fear memory. Our results demonstrate for the first time that adult-onset hypothyroidism potentiates fear memory and also increases vulnerability to develop emotional memories. Furthermore, our findings suggest that enhanced corticosterone signaling in the amygdala is involved in the pathophysiological mechanisms of fear memory potentiation. Therefore, we recommend evaluating whether inappropriate regulation of fear in patients with post-traumatic stress and other mental disorders is associated with abnormal levels of thyroid hormones, especially those patients refractory to treatment

Thyroid hormones inhibit TGF-β signaling and attenuate fibrotic responses

TGF-β, the most potent profibrogenic factor, acts by activating SMAD (mothers against decapentaplegic) transcription factors, which bind to SMAD-binding elements in target genes. Here, we show that the thyroid hormone triiodothyronine (T3), through binding to its nuclear receptors (TRs), is able to antagonize transcriptional activation by TGF-β/SMAD. This antagonism involves reduced phosphorylation of SMADs and a direct interaction of the receptors with SMAD3 and SMAD4 that is independent of T3-mediated transcriptional activity but requires residues in the receptor DNA binding domain. T3 reduces occupancy of SMADbinding elements in response to TGF-β, reducing histone acetylation and inhibiting transcription. In agreement with this transcriptional cross-talk, T3 is able to antagonize fibrotic processes in vivo. Liver fibrosis induced by carbon tetrachloride is attenuated by thyroid hormone administration to mice, whereas aged TR knockout mice spontaneously accumulate collagen. Furthermore, skin fibrosis induced by bleomycin administration is also reduced by the thyroid hormones. These findings define an important function of the thyroid hormone receptors and suggest TR ligands could have beneficial effects to block the progression of fibrotic diseases.This work was supported by Grants BFU2011-28058 and BFU2014-53610P from Ministerio de Economía y Competitividad; S2011/BMD-2328 TIRONET from the Comunidad de Madrid; and RD12/0036/0030 from the Instituto de Salud Carlos III. The cost of this publication has been paid in part by FEDER fund

Moderate SIRT1 overexpression protects against brown adipose tissue inflammation

Objective: Metainflammation is a chronic low-grade inflammatory state induced by obesity and associated comorbidities, including peripheral insulin resistance. Brown adipose tissue (BAT), a therapeutic target against obesity, is an insulin target tissue sensitive to inflammation. Therefore, it is demanding to find strategies to protect BAT against the effects of inflammation in energy balance. In this study we have explored the impact of moderate Sirtuin 1 (SIRT1) overexpression in insulin sensitivity and β-adrenergic responses in BAT and brown adipocytes (BA) under pro-inflammatory conditions. Methods: The effect of inflammation in BAT functionality was studied in obese db/db mice and lean wild-type (WT) mice or mice with moderate overexpression of SIRT1 (SIRT1Tg+) injected a low dose of bacterial lipopolysaccharide (LPS) to mimic endotoxemia. We also conducted studies in differentiated BA (BA-WT and BA-SIRT1Tg+) exposed to a macrophagederived pro-inflammatory conditioned medium (CM) to evaluate the protection of SIRT1 overexpression in insulin signaling and glucose uptake, mitochondrial respiration, fatty acid oxidation (FAO), as well as norepinephrine (NE)-mediated-modulation of uncoupling protein-1 (UCP-1) expression. Results: BAT from db/db mice was susceptible to metabolic inflammation manifested by activation of pro-inflammatory signaling cascades, increased pro-inflammatory gene expression, tissue-specific insulin resistance and reduced UCP-1 expression. Impairment of insulin and noradrenergic responses were also found in lean WT mice upon LPS injection. By contrast, BAT from mice with moderate overexpression of SIRT1 (SIRT1Tg+) was protected against LPSinduced activation of pro-inflammatory signaling, insulin resistance and defective thermogenicrelated responses upon cold exposure. Importantly, the drop of triiodothyronine (T3) levels both in circulation and intra-BAT after exposure of WT mice to LPS and cold was markedly attenuated in SIRT1Tg+ mice. In vitro experiments in BA from the two genotypes revealed that upon differentiation with a T3-enriched medium and subsequent exposure to a macrophagederived pro-inflammatory CM, only BA-SIRT1Tg+ fully recovered insulin and noradrenergic responses. Conclusion: This study has unraveled the benefit of moderate overexpression of SIRT1 to confer protection against defective insulin and β-adrenergic responses caused by inflammation in BAT. Our results have potential therapeutic value proposing combinatorial therapies of BATspecific thyromimetics and SIRT1 activators to combat metainflammation in this tissue

Hypothyroidism confers tolerance to cerebral malaria

The modulation of the host’s metabolism to protect tissue from damage induces tolerance to infections increasing survival. Here, we examined the role of the thyroid hormones, key metabolic regulators, in the outcome of malaria. Hypothyroidism confers protection to experimental cerebral malaria by a disease tolerance mechanism. Hypothyroid mice display increased survival after infection with Plasmodium berghei ANKA, diminishing intracranial pressure and brain damage, without altering pathogen burden, blood-brain barrier disruption, or immune cell infiltration. This protection is reversed by treatment with a Sirtuin 1 inhibitor, while treatment of euthyroid mice with a Sirtuin 1 activator induces tolerance and reduces intracranial pressure and lethality. This indicates that thyroid hormones and Sirtuin 1 are previously unknown targets for cerebral malaria treatment, a major killer of children in endemic malaria areas.This work was funded by grants SAF2017-83289-R to S.A. and A.A., SAF2017-90604REDT to A.A. supported by the The European Regional Development Fund (FEDER) and BIO2016-77430-R to J.M.B. from the Ministerio de Economía y Competitividad; B2017/BMD-3724 to S.A. and A.A. from the Comunidad de Madrid; and CIBERONC CB/16/00228 to A.A. from the Instituto de Salud Carlos III

Modulación de la neuritogénesis y de la conducta por hormonas tiroideas en ratas adultas

Las alteraciones hormonales están implicadas en muchas patologías asociadas con la edad como las enfermedades neurodegenerativas y los trastornos psiquiátricos. En el adulto, las alteraciones del estado tiroideo cursan con frecuencia con cambios psicológicos y trastornos del estado del ánimo como la depresión. Se ha demostrado que en los mamíferos adultos, incluido el hombre, continúa generándose neuronas a partir de células madre en el giro dentado GD, de la formación del hipocampo. Las neuronas generadas se integran funcionalmente y podrían estar implicadas en procesos de memoria y aprendizaje, así como en el mantenimiento del estado de ánimo. Se ha descrito que una disminución de la neurogénesis en el adulto induce trastornos depresivos y que la eficacia de los antidepresivos depende de la generación de nuevas neuronas en el GD. Por ello, el conocimiento del proceso de adquisición de nuevas neuronas en el adulto y su modulación puede suponer una herramienta importante para paliar daños cerebrales y enfermedades neurodegenerativas y psiquiátricas. Numerosos estudios han demostrado que las hormonas tiroideas HT, son esenciales para la neurogénesis y la gliogénesis durante el desarrollo, pero hay muy pocos trabajos que hayan analizado su función en el adulto. El objetivo de esta tesis fue analizar in vivo la posible modulación de la neurogénesis del adulto en el GD por las HT, así como explorar posibles implicaciones funcionales relacionadas con esta modulación. Los resultados obtenidos indican que el hipotiroidismo durante un corto periodo de tiempo en el adulto disminuye significativamente la capacidad proliferativa del GD, reduciendo tanto el número de precursores neuronales en proliferación, como el número de unidades proliferativas. Además, el hipotiroidismo afecta gravemente a los neuroblastos inmaduros disminuyendo su numero, alterando su distribución y provocando un desarrollo anormal de su árbol dendrítico.Peer reviewe

Divergent expression of type 2 deiodinase and the putative thyroxine-binding protein p29, in rat brain, suggests that they are functionally unrelated proteins

8 pages, 4 figures.Deiodinases (D1, D2, and D3) are selenoproteins involved in thyroid hormone metabolism. Generation of the active hormone T3, from T4, is carried out by D1 and D2, whereas D3 degrades both hormones. The identity of the cloned D2 as a selenoprotein is well supported by biochemical and physiological data. However, an alternative view has proposed that type 2 deiodinase is a nonselenoprotein complex containing a putative T4 binding subunit called p29, with an almost identity in sequence with the Dickkopf protein Dkk3. To explore a possible functional relationship between p29 and D2, we have compared their mRNA expression patterns in the rat brain. In brain, parenchyma p29 was expressed in neurons. High expression levels were found in all the regions of the blood-cerebrospinal fluid (CSF) barrier. p29 was present in different types of cells than D2, with the exception of the tanycytes. Our data do not support that p29 has a functional relationship with D2. On the other hand, expression of p29 in the blood-CSF barrier suggests that it might be involved in T4 transport to and from the CSF, but further studies are needed to substantiate this hypothesis.This work was supported by Grants PM980118 and BFI2001-2412 from Ministerio de Ciencia y Tecnología, and QLG3-2000-00930 from the European Union. A.M.-P. is recipient of a fellowship from the Ministry of Science and Technology, Spain. A.G.-F. is recipient of a contract from the Ramón y Cajal Program of the Ministry of Science and Technology, Spain.Peer reviewe

Hippocampal synaptic plasticity characterization of defective deiodinase 2 mice

Resumen del póster presentado al 7th Federation of European Neurosciences Societies (FENS) Forum, celebrado en Amsterdam (Netherlands) del 3 al 7 de julio de 2010.Thyroid hormones (TH) play an important role in Central Nervous System (CNS) development. The thyroid gland produces 30% of the nuclear active form Triiodothyronine (T3) and 70% of the non-nuclear active form Thyroxine (T4). Type 2 deiodinase (D2), that is expressed in the brain, is the main enzyme responsible for T4 deiodination to T3 for local use. The reduction of TH levels in developmental hypothyroidism is associated with neurological disorders in the adult, such as learning and memory impairment. The hippocampus participates in many learning and memory processes and is a target region of TH. In fact, in hypothyroid experimental animals, this brain area shows a severe deficiency in long-term potentiation (LTP), a well accepted cellular model for learning and memory. The goal of this study is to clarify the relation between local deregulation of TH metabolism and the synaptic plasticity capability of the hippocampal CA1 region in D2 deficient mutant mice (D2KO). We have observed a reduction of T3 and T4 levels in several brain regions of the adult D2KO mice. In the hippocampus this reduction reached 40%. We have performed the electrophysiological characterization of D2KO and WT mice stimulating and recording field EPSPs in CA1 region of hippocampal slices. The stimulus/response curve revealed an increment of synaptic responses in D2KO mice while the paired-pulse facilitation ratio, which estimates glutamate release probability, was not altered. However, early and late phases of LTP induced by one or three trains of high frequency stimulation, respectively, were not modified in D2KO mice. Nor did these animals show changes in long-term depression (LTD) induced by 1 Hz synaptic stimulation for 15 min. These results suggest that a 40% reduction in TH levels in the hippocampus affect basal synaptic transmission in CA3 - CA1 synapses but does not modify long-lasting changes of synaptic efficacy evoked by several protocols of synaptic stimulation.Peer Reviewe

Thyroid Hormone Transporters MCT8 and OATP1C1 Are Expressed in Pyramidal Neurons and Interneurons in the Adult Motor Cortex of Human and Macaque Brain

Monocarboxylate transporter 8 (MCT8) and organic anion transporter polypeptide 1C1 (OATP1C1) are thyroid hormone (TH) transmembrane transporters that play an important role in the availability of TH for neural cells, allowing their proper development and function. It is important to define which cortical cellular subpopulations express those transporters to explain why MCT8 and OATP1C1 deficiency in humans leads to dramatic alterations in the motor system. By means of immunohistochemistry and double/multiple labeling immunofluorescence in adult human and monkey motor cortices, we demonstrate the presence of both transporters in long-projection pyramidal neurons and in several types of short-projection GABAergic interneurons in both species, suggesting a critical position of these transporters for modulating the efferent motor system. MCT8 is present at the neurovascular unit, but OATP1C1 is only present in some of the large vessels. Both transporters are expressed in astrocytes. OATP1C1 was unexpectedly found, only in the human motor cortex, inside the Corpora amylacea complexes, aggregates linked to substance evacuation towards the subpial system. On the basis of our findings, we propose an etiopathogenic model that emphasizes these transporters’ role in controlling excitatory/inhibitory motor cortex circuits in order to understand some of the severe motor disturbances observed in TH transporter deficiency syndromes.This research was funded by MCIN/AEI/10.13039/501100011033 (Grant No. SAF2017-86342-R to A.G.-F.); MCIN/AEI/10.13039/501100011033/FEDER “Una manera de hacer Europa” (Grant No PID2020-113139RB-I00 to A.G.-F.); Consejo Superior de Investigaciones Científicas (Grant No. 2020AEP044 to A.G.-F.); the Sherman Foundation (Grant No. OTR02211 to A.G.-F.); Asociación Corriendo con el Corazón por Hugo (Grant No OTR06190 to A.G.-F.), YW is a beneficiary of a fellowship from China Scholarship Council (CSC).Peer reviewe