Tiago Santos Pereira

Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons

Proteolytic cleavage of the Na+/Ca2+ exchanger (NCX) by calpains impairs calcium homeostasis, leading to a delayed calcium overload and excitotoxic cell death. However, it is not known whether reversal of the exchanger contributes to activate calpains and trigger neuronal death. We investigated the role of the reversal of the NCX in Ca2+ dynamics, calpain activation and cell viability, in α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-stimulated hippocampal neurons. Selective overactivation of AMPA receptors caused the reversal of the NCX, which accounted for approximately 30% of the rise in intracellular free calcium concentration ([Ca2+]i). The NCX reverse-mode inhibitor, 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R7943), partially inhibited the initial increase in [Ca2+]i, and prevented a delayed increase in [Ca2+]i. In parallel, overactivation of AMPA receptors strongly activated calpains and led to the proteolysis of NCX3. KB-R7943 prevented calpain activation, cleavage of NCX3 and was neuroprotective. Silencing of NCX3 reduced Ca2+ uptake, calpain activation and was neuroprotective. Our data show for the first time that NCX reversal is an early event following AMPA receptor stimulation and is linked to the activation of calpains. Since calpain activation subsequently inactivates NCX, causing a secondary Ca2+ entry, NCX may be viewed as a new suicide substrate operating in a Ca2+-dependent loop that triggers cell death and as a target for neuroprotection.

High glucose and diabetes increase the release of [3H]-D-aspartate in retinal cell cultures and in rat retinas

Several evidences suggest that glutamate may be involved in retinal neurodegeneration in diabetic retinopathy (DR). For that reason, we investigated whether high glucose or diabetes affect the accumulation and the release of [(3)H]-D-aspartate, which was used as a marker of the glutamate transmitter pool. The accumulation of [(3)H]-D-aspartate did not change in cultured retinal neural cells treated with high glucose (30 mM) for 7 days. However, the release of [(3)H]-D-aspartate, evoked by 50 mM KCl, significantly increased in retinal cells exposed to high glucose. Mannitol, which was used as an osmotic control, did not cause any significant changes in both accumulation and release of [(3)H]-D-aspartate. In the retinas, 1 week after the onset of diabetes, both the accumulation and release of [(3)H]-D-aspartate were unchanged comparing to the retinas of age-matched controls. However, after 4 weeks of diabetes, the accumulation of [(3)H]-D-aspartate in diabetic retinas decreased and the release of [(3)H]-D-aspartate increased, compared to age-matched control retinas. These results suggest that high glucose and diabetes increase the evoked release of D-aspartate in the retina, which may be correlated with the hypothesis of glutamate-induced retinal neurodegeneration in DR.

High Glucose Changes Extracellular Adenosine Triphosphate Levels in Rat Retinal Cultures

Diabetic retinopathy (DR) is the leading cause of blindness in adults. In diabetes, there is activation of microglial cells and a concomitant release of inflammatory mediators. However, it remains unclear how diabetes triggers an inflammatory response in the retina. Activation of P2 purinergic receptors by adenosine triphosphate (ATP) may contribute to the inflammatory response in the retina, insofar as it has been shown to be associated with microglial activation and cytokine release. In this work, we evaluated how high glucose, used as a model of hyperglycemia, considered the main factor in the development of DR, affects the extracellular levels of ATP in retinal cell cultures. We found that basal extracellular ATP levels were not affected by high glucose or mannitol, but the extracellular elevation of ATP, after a depolarizing stimulus, was significantly higher in retinal cells cultured in high glucose compared with control or mannitol‐treated cells. The increase in the extracellular ATP was prevented by application of botulinum neurotoxin A or by removal of extracellular calcium. In addition, degradation of exogenously added ATP was significantly lower in high‐glucose‐treated cells. It was also observed that, in retinal cells cultured under high‐glucose conditions, the changes in the intracellular calcium concentrations were greater than those in control or mannitol‐treated cells. In conclusion, in this work we have shown that high glucose alters the purinergic signaling system in the retina, by increasing the exocytotic release of ATP and decreasing its extracellular degradation. The resulting high levels of extracellular ATP may lead to inflammation involved in the pathogenesis of DR.

NPY in rat retina is present in neurons, in endothelial cells and also in microglial and Muller cells

NPY is present in the retina of different species but its role is not elucidated yet. In this work, using different rat retina in vitro models (whole retina, retinal cells in culture, microglial cell cultures, rat Müller cell line and retina endothelial cell line), we demonstrated that NPY staining is present in the retina in different cell types: neurons, macroglial, microglial and endothelial cells. Retinal cells in culture express NPY Y(1), Y(2), Y(4) and Y(5) receptors. Retina endothelial cells express all NPY receptors except NPY Y(5) receptor. Moreover, NPY is released from retinal cells in culture upon depolarization. In this study we showed for the first time that NPY is present in rat retina microglial cells and also in rat Müller cells. These in vitro models may open new perspectives to study the physiology and the potential pathophysiological role of NPY in the retina.

Efficiency of Innovation Systems in Europe: An Institutional Approach to the Diversity of National Profiles

Globalization did not create convergence to a unique economic model among countries. Even in developed countries, the answers to the pressures of markets underline the existence of a variety of capitalisms. The analysis of innovation systems, in particular at the national level, is adequate as a preliminary approach to understand the diversity of profiles and institutional architectures. The article benefits from the broader notion of national innovation system to understand the profiles of 15 European countries. By analysing central building blocks and institutional complementarities through the creation of indexes based on 64 variables and a cluster analysis, it was possible to understand the different levels of institutional efficiency in the analysed dimensions for the selected groups of countries.

Imaginaries of nuclear energy in the Portuguese parliament: Between promise, risk, and democracy

This article explores the evolution of the nuclear energy debate and its associated controversies in the Portuguese parliament. The analysis focuses on the dictatorial regime of the New State (from the beginning of the nuclear program in 1951 until the 1974 revolution) and on the democratic period (post-1974). Portugal, as an exporting country of uranium minerals, significantly invested in the development of a national capacity in nuclear research, but never developed an endogenous nuclear power infrastructure. Through the analysis of parliamentary debates, this article characterizes the dynamic evolution of the Portuguese sociotechnical imaginary on nuclear energy and technology interlinked with ambivalent representations, including the promise of nuclear energy as key for the constitution of a technological Nation or as prompting new sociotechnical risks.