Mecanismos celulares envolvidos na morte e neuroproteção deneurônios primários infectados pelo vírus da Zika

Abstract

In 2015, Brazil was affected by an outbreak caused by zika virus (ZIKV), which is an arbovirus from the Flaviviridae family. For most individuals, ZIKV infection is asymptomatic and in most symptomatic cases clinical signs are usually mild, including fever, arthralgia, and skin rash.However, ZIKV can trigger serious neurological complications, causing microcephaly among fetuses of infected pregnant women. Is has been demonstrated that the virus is neurotropic, triggering neuroinflammation and the death of neurons and neuronal precursor cells, promoting microcephaly. However, little is known about the mechanism involved in the neurodegeneration triggered by ZIKV infection. Here, we performed viral infection in cultures of C57/BL6 embryos primary neurons to characterize the ZIKV-mediated neuronal death. Our data show that ZIKV infection in primary neurons triggered apoptosismediated neuronal death under a non-autonomous mechanism. Virus-infected neuronal cultures exhibited a significant increase in caspase 3 activation in uninfected neuronal cells that were nearby infected cells, due to increased levels of extracellular glutamate, increased expression of tumor necrosis factor- (TNF-) and increased expression of interleukin-1 (IL- 1) in these cultures. Moreover, we observed increased levels of intracellular Ca2+ on ZIKVinfected neuronal cultures, which correlates with the excitotoxicity observed. At the molecular level, we observed that ZIKV infection promoted significant increase in the expression levels of N-methyl D-aspartate receptor 2-subunit (GluN2B). The activity blockade of TNF- and IL- 1 on these neurons led to decreased intracellular Ca2+ levels, thus preventing ZIKV-mediated neurodegeneration. These results suggest that cytokines and N-Methyl-D-Aspartate (NMDAR) receptors may interact. Furthermore, the blockade of NMDAR containing GluN2B increases the survival rates of ZIKV-infected cells and promotes the activation of neuroprotective biological pathways, such as the extracellular signal-regulated protein kinase (ERK) and cAMP-responsive element binding protein (CREB). Altogether, these results suggest that the excitotoxicity observed following ZIKV infection is mediated by the classical mechanism involving elevated levels of extracellular glutamate and increased release of proinflammatory cytokines by infected neuronal cultures. Besides, the increase in cell viability promoted by NMDAR blockade after virus infection appears to be a good therapeutic strategy to prevent neuronal death mediated by ZIKV.