Evaluation of the enzyme AGO2, related to miRNA activity during hippocampus development and in pilocarpine-induced neuronal activation.

• Grant number: 13/06633-5
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2013
• End date: December 31, 2013
• Field of knowledge: Biological Sciences - Biology
• Principal Investigator: Alexandre Hiroaki Kihara
• Grantee: Bianca Araújo dos Santos
• Host Institution: Centro de Matemática, Computação e Cognição (CMCC). Universidade Federal do ABC (UFABC). Santo André , SP, Brazil

Abstract

MicroRNAs (miRNAs) are a class of small non-coding RNAs of approximately 22 nucleotides, which act as post-transcriptional silencing by inhibiting translation of target mRNAs. The production of the miRNAs is highly regulated in several steps, from its biogenesis to degradation and stabilization, including the control of its activity. Studies have indicated that miRNAs control the activity of more than 60% of genes that encode proteins and participate in the regulation of several cellular processes such as proliferation, apoptosis and differentiation. The complex miRNA and RISC (RNA-induced silencing complex) regulates gene expression by deadenilation and degradation of mRNA, and repression of translation of the mRNA. Studies point to the importance of this complex in memory formation and synaptic plasticity processes. Neuronal activity, which is also known to control the activity of specific miRNAs, regulates important processes, from the development of the nervous system to it's function, modulating the translation of protein synthesis. Having in mind that changes in the hippocampus during the development stages, as well as changes in neuronal activity may contribute to the development of pathological conditions, and that dysfunction of miRNAs that act on neurons may contribute to the installation of these conditions, we describe the dynamics of gene and protein expression of AGO2, the main component of the RISC complex, throughout the development of the hippocampus, at ages P0, P5, P10 and P60, and in conditions of high neuronal activation induced by pilocarpine. We observed that the levels of transcripts of Ago2 are present in the hippocampus at all tested ages, although with significantly reduced levels in P0 compared to P60. The protein, also found in all ages evaluated, is located preferentially in mature neurons, with minimal proximity to immature neurons and absent in astrocytes. Ago2 is present in CR and PV-positive cells, suggesting that the activity of miRNAs is necessary to control the transmission of inhibitory neurons in the hippocampus. We also observed that Ago2 transcript levels are not altered in the hippocampus of animals submitted to conditions of high neuronal activation, and there are no changes in the pattern of protein distribution. Thus, the presence of Ago2 is essential in the control of post-transcriptional regulation, including situations involving neuronal activation, such as LTP and development processes of the nervous system.