A vida é bela

Abstract

Glial cells are responsible for several roles that guarantee homeostasis of the central nervous system (CNS), including its immunoprotection. Glia responds to tissue aggressions through intense morphofunctional modifications, known as gliosis. Neospora caninum (Nc), an intracelular protozoan, infects several animal species, and it has a special tropism for nervous tissue and has been used as a model of neuroinflammation, with particular focus on the analysis of glia-neuron interaction aspects. Literature data shows that glial cells from rats infected with Nc tachyzoites release IL-10, which modulates the inflammatory response and may participate in the preservation of nerve tissue mechanism. Studies also indicate that parasites, by infecting nervous tissue in an attempt to survive, induce the release of neurotrophic factors. The objective of the present study was to investigate the modulatory activity of glial cells of rats infected with Nc tachyzoites, in induction of neuronal differentiation. The methodology consisted on performing primary cultures of glial cell of Wistar rats, under conditions: control, stimulated by IFN-γ, infected by Nc, and under IFN-γ stimulation and Nc infection. Each medium conditioned by the respective treatment was used to cultivate neurons, in co-cultures, for 24 hours. Subsequently, were evaluated by immunocytochemistry astrocyte and neuronal phenotypic profiles, marked respectively with GFAP and β-III-tubulin. Mitochondrial dehydrogenases activity was also evaluated by MTT assay, while the expression of the neurotrophic factors NGF, BDNF, GDNF, NTF4 and the NTRK2 gene, were evaluated by qRT-PCR. The presence of nitrite was inspected in the supernatants using a colorimetric assay based on the Griess method. The results presented astrogliosis in the primary culture in all conditions, when compared to the control group. The increased mitochondrial dehydrogenases activity was observed in the culture infected by Nc. Regarding neurotrophic factors, the infection with Nc induced greater NGF expression and reduced BNDF expression. On the other hand, the co-cultures showed astrocytic reactivity only when treated with the IFN-γ conditioned medium. In addition, there was an increase in the dehydrogenase activity in the Nc conditioned medium, in comparison to control, as well as NTRK2 gene expression increment in all groups. This study data allow to conclude that Nc infection in glial cells induced astrogliosis, promoted neuronal differentiation and stimulated NGF and NTRK2 expressions. These findings may justify nervous system protection in favor of maintaining the parasitosis in neural environment.

Key words: Glia. NGF. BDNF. NTRK2. Neospora caninum. Astrogliosis. Neuritogenesis.

Introdução

Neospora caninum (Nc) é um protozoário coccídio intracelular obrigatório do filo Apicomplexa, que possui tropismo por tecidos diversos, inclusive o tecido nervoso (DUBEY et al., 1998). Estudos sobre a caracterização da resposta imune glial foram desenvolvidos por Pinheiro et al. (2010) através de culturas primárias infectadas por esse parasito e dosagem de citocinas inflamatórias. Esses autores indicaram que a produção de altos níveis de IL-6 e IL-10 seria sugestiva de uma ação protetora glial no SNC, criando um ambiente imunologicamente privilegiado, enquanto que TNF e NO atuariam no controle da proliferação parasitária.

Posteriormente, Jesus et al. (2014) avaliaram co-culturas (glia-neurônio) estimuladas com IFN-γ infectadas com Nc e observaram ausência de NO, liberação de IL-10 e preservação neuronal.

Além das citocinas inflamatórias, existem fatores que também atuam na preservação do tecido nervoso, a exemplo das neurotrofinas, que promovem a diferenciação e sobrevivência de neurônios e participam na modulação da transmissão e plasticidade sináptica.

Mecanismos imunomodulatórios já caracterizados pela literatura remetem à presença de fatores neurotróficos liberados pelo protozoário T. cruzi no Sistema Nervoso Central para promoção da integridade neural (CHUENKOVA; PEREIRA, 2003). Fatores neurotróficos são polipeptídios que auxiliam no processo regenerativo. Constituem basicamente um conjunto de famílias de moléculas e de seus receptores responsáveis por manter o crescimento e a sobrevivência dos axônios e neurônios após danos teciduais (SEBBEN et al., 2011).

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