Déficit cognitivo espacial está relacionado com alteração na concentração do canal aniônico dependente de voltagem no tálamo de ratos deficientes em tiamina

Abstract

Thiamine deficiency (TD) results in biochemical dysfunction that can culminate with the death of neurons, characterizing the process of neurodegeneration, such as occur in Wernicke-Korsakoff's syndrome. Thiamine or vitamin B1, after being captured by the tissues, can be phosphorylated giving rise to different forms including, thiamine pyrophosphate (TPP) which acts as a cofactor of key enzymes in cellular energy metabolism. TD leads to cell loss in various regions of the brain, being the thalamus and mammillary bodies the most affected areas. In both experimental models and in humans, episodes of TD causing, among other effects, motor hypoactivity and cognitive impairments. Various behavioral and neurobiological aspects have been studied in conditions of TD. However, the involvement of specific proteins in the molecular mechanisms responsible for brain damage and which may, as a consequence, generate cognitive alterations remains unclear. The present study aims to: (i) identify and characterize proteins that have altered their expression in the thalamus of rats with severe TD (ii) evaluate the relationship between proteic changes and performance of rats in spatial learning task. The experimental model of TD in diet associated with pyrithiamine (PTD, kinase inhibitor that produces TPP from thiamine) in rats was used. The animals' performance on tasks of spatial navigation was assessed in the Morris Water Maze (MWM). The proteomic profile of the thalamus was analyzed qualitatively and quantitatively by two-dimensional electrophoresis. This detected 320 spots and a significant increase or decrease in seven proteins. Four proteins were correlated to rat behavioral performance in the Morris Water Maze. One of the proteins that have undergone significant changes was identified by mass spectrometry and their respective mRNAs were quantified by real time PCR. Furthermore, the analysis includes immunochemical assays, using the Western Blot. In a previous study in our laboratory, negative correlation (r = -0.83, p = 0.009) was found between the relative volume of one thalamic protein and latency in the third training session. In the present study, the data confirmed that this protein corresponds to the Voltage Dependent Anion Channel (VDAC). VDAC is also known as mitochondrial porin, a channel permeable to anions, cations, ATP, and other metabolites. VDAC has several isoforms, being the most studied VDAC1, VDAC2 and VDAC3. The evaluation by real-time PCR showed no effects of TD on the levels of mRNAs of genes Vdac1, Vdac2 and Vdac3, indicating that the decrease in VDAC expression may be due to post-transcriptional processes. The data suggest that the process of neurodegeneration induced by TD involves serious decrease in VDAC proteic levels in the thalamus, indicating that this protein might play an important role in the initial stage of the spatial learning process.