Essential role of the N-terminal region of TFII-I in viability and behavior.

BACKGROUND: GTF2I codes for a general intrinsic transcription factor and calcium channel regulator TFII-I, with high and ubiquitous expression, and a strong candidate for involvement in the morphological and neuro-developmental anomalies of the Williams-Beuren syndrome (WBS). WBS is a genetic disorder due to a recurring deletion of about 1,55-1,83 Mb containing 25-28 genes in chromosome band 7q11.23 including GTF2I. Completed homozygous loss of either the Gtf2i or Gtf2ird1 function in mice provided additional evidence for the involvement of both genes in the craniofacial and cognitive phenotype. Unfortunately nothing is now about the behavioral characterization of heterozygous mice. METHODS: By gene targeting we have generated a mutant mice with a deletion of the first 140 amino-acids of TFII-I. mRNA and protein expression analysis were used to document the effect of the study deletion. We performed behavioral characterization of heterozygous mutant mice to document in vivo implications of TFII-I in the cognitive profile of WBS patients. RESULTS: Homozygous and heterozygous mutant mice exhibit craniofacial alterations, most clearly represented in homozygous condition. Behavioral test demonstrate that heterozygous mutant mice exhibit some neurobehavioral alterations and hyperacusis or odynacusis that could be associated with specific features of WBS phenotype. Homozygous mutant mice present highly compromised embryonic viability and fertility. Regarding cellular model, we documented a retarded growth in heterozygous MEFs respect to homozygous or wild-type MEFs. CONCLUSION: Our data confirm that, although additive effects of haploinsufficiency at several genes may contribute to the full craniofacial or neurocognitive features of WBS, correct expression of GTF2I is one of the main players. In addition, these findings show that the deletion of the fist 140 amino-acids of TFII-I altered it correct function leading to a clear phenotype, at both levels, at the cellular model and at the in vivo model.

The vulnerability of striatal projection neurons and interneurons to excitotoxicity is differentially regulated by dopamine during development.

The maturation of striatal projection neurons and interneurons is influenced by the development and integrity of their connectivity. In the present work, we have analyzed the modulation of striatum vulnerability to quinolinate (QUIN)-induced excitotoxicity in different neuronal populations by the nigrostriatal dopaminergic pathway during postnatal development. A single striatal lesion with 6-hydroxydopamine (6-OHDA) at the second postnatal day (P) 2 or QUIN at P7 induced a reduction in the striatal volume at P30, whereas an additive effect was observed when these two lesions were performed in the same animal. The analysis of different striatal neuronal populations showed that the excitotoxic lesion induced by QUIN over projection neurons stained with calbindin was partially reverted by the previous injection of 6-OHDA at P2. However, cholinergic interneurons were affected neither by the lack of dopamine innervation nor by QUIN treatment. This neuronal population also remained intact after the double lesion. In contrast, the number of other type of striatal interneurons, parvalbumin-positive neurons, were reduced by the dopaminergic ablation and also by the QUIN-induced excitotoxicity and this effect was additive after the double lesion when it was measured at P30. On the other hand, we studied the effect on the striatal outputs measuring the density of substance P-positive fibers in the substantia nigra and enkephalin-positive fibers in the globus pallidus. A reduction in substance P-positive fibers was observed in 6-OHDA injected animals, while the density of enkephalin-positive fibers was only decreased after QUIN treatment. The double lesion did not modify the effects of the single lesions. In conclusion, our results show that dopamine modulates the vulnerability to excitotoxicity during striatal postnatal development, and this effect is specific for projection neurons. Furthermore, striatonigral and striatopallidal pathways are differentially regulated by the activation of dopamine or glutamate receptors.

Endogenous brain-derived neurotrophic factor protects dopaminergic nigral neurons against transneuronal degeneration induced by striatal excitotoxic injury.

Injury to the central nervous system causes atrophy or death of connecting neurons and can modify the expression of neurotrophic factors. We observed transneuronal upregulation of brain-derived neurotrophic factor (BDNF) expression in the rat ipsilateral substantia nigra pars compacta after a striatal lesion induced by kainate. This effect is developmentally regulated because the enhancement of nigral BDNF expression was only observed when striatal lesion was performed on postnatal day (P) 15 and in adulthood, but not at P7. Interestingly, the lack of regulation of BDNF was coincident with the transynaptic degeneration of nigral neurons after striatal excitotoxic injury. Hence, the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta decreased when the lesion was performed at P7, but not at P15 or at P30. The analysis of the functional significance of this BDNF upregulation was done using trkB-IgG fusion proteins. After striatal injury, blockade of endogenous BDNF by trkB fusion proteins induced an atrophy of the dopaminergic neurons of the pars compacta. The injection of trkB-IgG fusion proteins did not modify the effects of kainate in the substantia nigra pars reticulata. Thus, our results show that BDNF exerts an autocrine/paracrine protective effect selectively on dopaminergic neurons against the loss of trophic support from the target striatum.

Intranigral infusion of interleukin-1beta activates astrocytes and protects from subsequent 6-hydroxydopamine neurotoxicity.

Activation of glial cells is a prevalent response to neuronal damage in brain disease and ageing, with potential neuroprotective and neurotoxic consequences. We were interested in studying the role of glial activation on dopaminergic neurons of the substantia nigra in an animal model of Parkinson's disease. Thus, we evaluated the effect of a pre-existing glial activation on the dopaminergic neuronal death induced by striatal infusion of 6-hydroxydopamine. We established a model of local glial activation by stereotaxic infusion of interleukin-1beta in the substantia nigra of adult rats. Interleukin-1beta (20 ng) induced a marked activation of astrocytes at days 2, 5 and 10, revealed by heat-shock protein 27 and glial fibrillary acid protein immunohistochemistry, but did not affect the microglial markers OX-42 and heat-shock proteins 32 or 47. Intranigral infusion of interleukin-1beta 5 days before a striatal injection of 6-hydroxydopamine significantly protected nigral dopaminergic cell bodies, but not striatal terminals from the 6-hydroxydopamine lesion. Also, in the animals pre-treated with interleukin-1beta, a significant prevention of 6-hydroxydopamine-induced reduction of adjusting steps, but not of 6-hydroxydopamine-induced amphetamine rotations, were observed. These data show the characterization of a novel model of local astroglial activation in the substantia nigra and support the hypothesis of a neuroprotective role of activated astrocytes in Parkinson's disease.