Transcranial static magnetic stimulation reduces seizures in a mouse model of Dravet syndrome.

Dravet syndrome is a rare form of severe genetic epilepsy characterized by recurrent and long-lasting seizures. It appears around the first year of life, with a quick evolution toward an increase in the frequency of the seizures, accompanied by a delay in motor and cognitive development, and does not respond well to antiepileptic medication. Most patients carry a mutation in the gene SCN1A encoding the α subunit of the voltage-gated sodium channel Nav1.1, resulting in hyperexcitability of neural circuits and seizure onset. In this work, we applied transcranial static magnetic stimulation (tSMS), a non-invasive, safe, easy-to-use and affordable neuromodulatory tool that reduces neural excitability in a mouse model of Dravet syndrome. We demonstrate that tSMS dramatically reduced the number of crises. Furthermore, crises recorded in the presence of the tSMS were shorter and less intense than in the sham condition. Since tSMS has demonstrated its efficacy at reducing cortical excitability in humans without showing unwanted side effects, in an attempt to anticipate a possible use of tSMS for Dravet Syndrome patients, we performed a numerical simulation in which the magnetic field generated by the magnet was modeled to estimate the magnetic field intensity reached in the cerebral cortex, which could help to design stimulation strategies in these patients. Our results provide a proof of concept for nonpharmacological treatment of Dravet syndrome, which opens the door to the design of new protocols for treatment.

Transplant of GABAergic precursors restores hippocampal inhibitory function in a mouse model of seizure susceptibility.

Defects in GABAergic function can cause epilepsy. In the last years, cell-based therapies have attempted to correct these defects with disparate success on animal models of epilepsy. Recently, we demonstrated that medial ganglionic eminence (MGE)-derived cells grafted into the neonatal normal brain migrate and differentiate into functional mature GABAergic interneurons. These cells are able to modulate the local level of GABA-mediated synaptic inhibition, which suggests their suitability for cell-based therapies. However, it is unclear whether they can integrate in the host circuitry and rescue the loss of inhibition in pathological conditions. Thus, as proof of principle, we grafted MGE-derived cells into a mouse model of seizure susceptibility caused by specific elimination of GABAergic interneuron subpopulations in the mouse hippocampus after injection of the neurotoxic saporin conjugated to substance P (SSP-Sap). This ablation was associated with significant decrease in inhibitory postsynaptic currents (IPSC) on CA1 pyramidal cells and increased seizure susceptibility induced by pentylenetetrazol (PTZ). Grafting of GFP(+) MGE-derived cells in SSP-Sap-treated mice repopulates the hippocampal ablated zone with cells expressing molecular markers of mature interneurons. Interestingly, IPSC kinetics on CA1 pyramidal cells of ablated hippocampus significantly increased after transplantation, reaching levels similar to the normal mice. More importantly, this was associated with reduction in seizure severity and decrease in postseizure mortality induced by PTZ. Our data show that MGE-derived cells fulfill most of the requirements for an appropriate cell-based therapy, and indicate their suitability for neurological conditions where a modulation of synaptic inhibition is needed, such as epilepsy.

Thyroid hormone regulates TAG-1 expression in the developing rat brain.

TAG-1 is a member of the immunoglobulin superfamily of cell adhesion molecules thought to play important roles in neuronal differentiation and the establishment of connectivity during brain development. Because these are processes also affected by hypothyroidism, we studied the effects of thyroid hormone deprivation and administration on TAG-1 expression in the developing rat brain. By in situ hybridization, immunohistochemistry and Western blotting we found that TAG-1 RNA and protein levels are upregulated in the hypothyroid brain. From embryonic day 20 to postnatal day (P) 15, elevated TAG-1 RNA was found in several areas including the cerebral cortex, hippocampus and olfactory bulb. In agreement with this, TAG-1 protein was overexpressed in the major fibre tracts arising from these structures, including the corpus callosum, anterior and hippocampal commissures and lateral olfactory tract. A similar overexpression of TAG-1 by hypothyroidism was detected in the cerebellum, but starting only at P15. In all cases, elevation of TAG-1 RNA and protein expression could be reversed by thyroid hormone treatment. These results show that the deregulation of TAG-1 might contribute to the alterations caused by the lack of thyroid hormone during brain development.

Thyroid hormone regulates the obesity gene tub.

Thyroid hormone T3/T4 is a major regulator of energy metabolism in vertebrates, and defects in thyroid status are frequently associated with changes in body weight. It is demonstrated here that thyroid hormone regulates in vivo and in vitro the tub gene, which when mutated in tubby mice causes obesity, insulin resistance and sensory deficits. Hypothyroidism in rats altered tub mRNA and protein in discrete brain areas. These changes could be attributed to thyroid hormone deficiency since T3/T4 treatment restored normal tub expression. T3 also upregulated tub mRNA within 4-6 h in neuronal cells in culture, suggesting that T3 is a positive regulator of tub gene expression. Thus, these results establish a novel pathway of T3 action and provide an important molecular link between thyroid status and the tubby-associated syndrome.

Effect of hypothyroidism on G protein-coupled receptor kinase 2 expression levels in rat liver, lung, and heart.

GRK2 is a member of the G protein-coupled receptor kinase family that phosphorylates the activated form of beta-adrenergic and other G protein-coupled receptors and plays an important role in their desensitization and modulation. Alterations in thyroid hormone levels have been reported to lead to important changes in adrenergic receptor responsiveness and signaling in a variety of tissues. In this context, we have explored the effects of experimental hypothyroidism on GRK2 protein levels in rat heart, lung, and liver using a specific antibody. Hypothyroid animals show significant up-regulation ( approximately 50% increase compared with controls) in GRK2 levels in heart and lung at 60 days after birth, whereas a 50% reduction is detected in the liver at this stage. These alterations are selective, as beta-adrenergic receptors or other G protein-coupled receptor regulatory proteins, such as G protein-coupled receptor kinase 5 or beta-arrestin-1, display a different pattern of expression changes in the hypothyroid animals. The reported changes in GRK2 levels and in the receptor/kinase ratio predict alterations in adrenergic receptor desensitization and signal transduction efficacy consistent with those observed in thyroid disorders, thus suggesting a relevant role for the modulation of GRK2 expression in this physiopathological condition.

Regulation of the L1 cell adhesion molecule by thyroid hormone in the developing brain.

Thyroid hormone is essential for brain maturation, regulating neuronal differentiation and migration, myelination, and synaptogenesis. Mutations in the cell adhesion molecule L1 cause severe neurological abnormalities in humans. We studied the effect of thyroid hormone deprivation and administration on L1 expression. Northern and in situ hybridization studies showed that hypothyroidism induces a marked increase in L1 mRNA levels in the caudate putamen, cerebral cortex, amygdala, and some thalamic nuclei. L1 protein was overexpressed in embryonic and newborn hypothyroid rats in the caudate putamen, internal capsule, habenula, and neocortex. Later in development, an abnormally high L1 expression was found in the cortical and cerebellar white matter, corpus callosum, anterior commissure, thalamocortical projections, and striatal fiber tracts of hypothyroid animals. Thyroid hormone administration reversed the upregulation of L1 expression in vivo and in cultured cells. Thus, alterations of L1 expression may contribute to the profound abnormalities caused by hypothyroidism in the developing brain.

Expression patterns of the regulatory proteins G protein-coupled receptor kinase 2 and beta-arrestin 1 during rat postnatal brain development: effect of hypothyroidism.

G protein-coupled receptor kinase 2 (GRK2) and beta-arrestin 1 are key regulatory proteins that modulate the desensitization and resensitization of a wide variety of G protein-coupled receptors (GPCRs) involved in brain functions. In this report, we describe the postnatal developmental profile of the mRNA and protein levels of GRK2 and beta-arrestin 1 in rat brain. The expression levels of GRK2 and beta-arrestin 1 display a marked increase at the second and third week after birth, respectively, consistent with an involvement of these proteins in brain maturation processes. However, the expression attained at birth and during the first postnatal week with respect to adult values (45-70% for GRK2, approximately 30% for beta-arrestin 1) is relatively high compared to that reported for several GPCRs, indicating the existence of changes in the ratio of receptors to their regulatory proteins during brain development. On the other hand, we report that experimental hypothyroidism results in changes in the patterns of expression of GRK2 and beta-arrestin 1 in cerebral cortex, leading to a 25-30% reduction in GRK2 levels at several stages of development. Such changes could help to explain the alterations in GPCR signaling that occur during this pathophysiological condition.

Identification of a mammalian homologue of the fungal Tom70 mitochondrial precursor protein import receptor as a thyroid hormone-regulated gene in specific brain regions.

Thyroid hormone is an important regulator of mammalian brain maturation. By differential display PCR, we isolated a cDNA clone (S2) that is specifically up-regulated in the striatum of neonatal hypothyroid rats. S2 was identified as KIAA0719, the first human gene distantly homologous to the fungal Tom70, which encodes a member of the translocase mitochondrial outer membrane complex involved in the import of preproteins into the mitochondria. By northern and in situ hybridization studies, KIAA0719 was found to be up-regulated in the striatum, nucleus accumbens, and discrete cortical layers of 15-day-old hypothyroid rats. In contrast, lower expression was found in the olfactory tubercle, whereas no differences were detected in other brain regions. Significantly, treatment of hypothyroid animals with single injections of thyroxine restored the normal levels of KIAA0719 expression. Moreover, treatment of control animals with thyroxine led to a reduced expression, demonstrating a negative hormonal regulation in vivo. Thus, KIAA0719 gene expression is regulated by thyroid hormone in the neonatal rat brain in a region-specific fashion. Given the role of the homologous Tom70 gene, the alteration of KIAA0719 expression may contribute to the changes in mitochondrial morphology and physiology caused by hypothyroidism in the developing rat brain.

Retinoic acid and 1,25-dihydroxyvitamin D3 inhibit tenascin-C expression in rat glioma C6 cells.

Tenascin-C (Tn-C) is an extracellular matrix protein with growth-, invasive-, and angiogenesis-promoting activities. Tn-C is upregulated during wound healing, tumorigenesis, and other pathological conditions. Highly malignant gliomas with poor prognosis exhibit high levels of Tn-C expression. Here we demonstrate that Tn-C RNA expression in glioma C6 cells is inhibited in a dose-dependent manner by retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (1,25-D3). No additive or synergistic effects were found. Inhibition is maximum 24 hr after RA or 1,25-D3 treatment, prior to a delayed cytotoxic effect starting at day 4-5 of treatment, and correlates with a reduction in the synthesis of Tn-C protein. Tn-C expression is also inhibited, but to a lesser extent by prostaglandin D2 (PGD2). Furthermore, both RA and 1,25-D3, but not PGD2 abolish the induction of Tn-C by the tumor promoter 12-O-tetradecanoyl phorbol 13-acetate. The inhibition of Tn-C expression might be relevant for the anti-cancer activity of RA and 1,25-D3.

Thyroid hormone regulates reelin and dab1 expression during brain development.

The reelin and dab1 genes are necessary for appropriate neuronal migration and lamination during brain development. Since these processes are controlled by thyroid hormone, we studied the effect of thyroid hormone deprivation and administration on the expression of reelin and dab1. As shown by Northern analysis, in situ hybridization, and immunohistochemistry studies, hypothyroid rats expressed decreased levels of reelin RNA and protein during the perinatal period [embryonic day 18 (E18) and postnatal day 0 (P0)]. The effect was evident in Cajal-Retzius cells of cortex layer I, as well as in layers V/VI, hippocampus, and granular neurons of the cerebellum. At later ages, however, Reelin was more abundant in the cortex, hippocampus, cerebellum, and olfactory bulb of hypothyroid rats (P5), and no differences were detected at P15. Conversely, Dab1 levels were higher at P0, and lower at P5 in hypothyroid animals. In line with these results, reelin RNA and protein levels were higher in cultured hippocampal slices from P0 control rats compared to those from hypothyroid animals. Significantly, thyroid-dependent regulation of reelin and dab1 was confirmed in vivo and in vitro by hormone treatment of hypothyroid rats and organotypic cultures, respectively. In both cases, thyroid hormone led to an increase in reelin expression. Our data suggest that the effects of thyroid hormone on neuronal migration may be in part mediated through the control of reelin and dab1 expression during brain ontogenesis.

Inhibition of tenascin-C expression in mammary epithelial cells by thyroid hormone.

Multiple data suggest a relationship between thyroid hormone (triiodothyronine (T3)) and carcinogenesis. Studies on breast cancer have been inconclusive, suggesting contradictory effects of thyroid status and diseases. Recently, we reported that expression of the extracellular matrix glycoprotein tenascin-C is modulated by T3 during rat brain development. Because tenascin-C has been reported to have growth-, motility-, and angiogenic-promoting activities and to become upregulated during tumorigenesis in breast carcinoma and stromal cells, we analyzed the effects of T3 on tenascin-C expression in mammary epithelial cells. In this study, we showed that tenascin-C RNA expression was inhibited by T3 in normal un-transformed EpH4 mouse mammary epithelial cells expressing appropriate receptors. T3's action appeared to be due to a decreased half-life of the tenascin-C mRNA, with a maximum effect (85% at 100 nM) 48 h after addition. T3 also downregulated tenascin-C in the human mammary tumor cell line SKBR-3, which expresses endogenous thyroid receptors. Immunoprecipitation experiments confirmed that tenascin-C protein content was also decreased by T3 in EpH4 cells (70% reduction at 100 nM). Dexamethasone had a similar inhibitory effect (70% at 100 nM), whereas estradiol, the antiestrogen ICI 164,384, progesterone, and all-trans retinoic acid did not alter tenascin-C expression. Our data demonstrate an inhibitory action of T3 on tenascin-C expression in mammary epithelial cells that may play a role in the physiological regulation of this gene and in neoplastic processes.

Developmental expression of the tenascin-C is altered by hypothyroidism in the rat brain.

Tenascin-C is an extracellular matrix glycoprotein involved in cell adhesion and migration, and neurite outgrowth. Since these processes have been found to be under thyroid control in the developing rat brain, we have investigated the effect of congenital hypothyroidism on tenascin-C expression. At birth, in situ hybridization studies in hypothyroid rats show an abnormal up-regulation of tenascin-C in some areas (caudate-putamen, geniculate nuclei, ependymal epithelium of the lateral ventricles, hippocampus) and down-regulation in others (occipital and retrosplenial cortex, subiculum). With subsequent development, hypothyroid animals show higher tenascin-C expression also in the upper layers of the cerebral cortex and subplate, and the Bergmann glia of the cerebellum. Significantly, thyroxine treatment of hypothyroid rats led to normalization of tenascin-C levels in most areas. In agreement with the messenger RNA data, hypothyroid rats contain an uniformly higher level of immunoreactive tenascin-C protein throughout the brain, particularly in the cerebellum. Suggesting a direct cellular effect, thyroid hormone also decreases tenascin-C expression in two glial cell lines (C6, B3.1) expressing thyroid receptors. Our results show that congenital hypothyroidism causes specific alterations in the pattern of tenascin-C expression in the rat brain which may at least partially be responsible for some of the developmental disturbances observed in this syndrome.

1,25-Dihydroxyvitamin D3 inhibits tenascin-C expression in mammary epithelial cells.

Tenascin-C is an extracellular matrix protein with growth-, invasion- and angiogenesis-promoting activities. Tenascin-C is upregulated in breast carcinoma and stromal cells, and in many other cell types during tumorigenesis. We demonstrate that tenascin-C RNA expression is inhibited by 1,25-dihydroxyvitamin D3 (1,25-D3) in a variety of mouse and human mammary epithelial cell lines exhibiting normal or malignant phenotype. In EpH4 cells, the inhibition is maximum 24 h after 1,25-D3 treatment and correlates with a dose-dependent reduction in the synthesis of tenascin-C protein. Furthermore, 1,25-D3 also abolishes the induction of tenascin-C by serum or the tumor promoter 12-O-tetradecanoyl phorbol 13-acetate. The inhibition of tenascin-C expression may be relevant for the anticancer activity of 1,25-D3.

Expression of neurotrophins and the trk family of neurotrophin receptors in normal and hypothyroid rat brain.

Thyroid hormone deficiency has dramatic effects on rat brain maturation. The expression of genes encoding neurotrophins and the trk family of neurotrophin receptors has been evaluated in several brain regions of normal and of neonatal or adult hypothyroid rats to analyze whether they are subject to thyroid hormone action. We found that hypothyroidism decreased trk mRNA levels in its major site of expression, the striatum, on postnatal days 5 (P5; 45%) and 15 (P15; 25%) and also in adults (35%). In contrast, no differences in trkB or trkC mRNAs levels were observed in any brain region at studied ages. According to previous reports, p75LNGFR mRNA was elevated in hypothyroid cerebellum as compared to age-matched controls on P5 and P15. We have also observed a distinct pattern for neurotrophin genes. The level of NGF mRNA was 20-50% lower in the cortex, hippocampus, and cerebellum of hypothyroid rats on neonatal hypothyroid rats on P15 and also after adult-onset hypothyroidism. Treatment of neonatally-induced hypothyroid rats with a single injection of triiodothyronine led to the recovery of hippocampal but not cortex NGF mRNA levels to that of control animals. On the contrary, no differences in the relatively high expression of the two mRNAs encoding BDNF were observed in any brain area. In contrast to a recent report, we did not find a reduction in brain NT-3 mRNA levels in hypothyroid animals. If any, the effect of thyroid deficiency in the hippocampus and cortex seems to be an early upregulation of NT-3 expression.(ABSTRACT TRUNCATED AT 250 WORDS)