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Molecular mechanisms associated to modulation of alpha7-type nicotinic acetylcholine receptor (alpha7nAChR) expression in the hypothalamus by high fat diet consumption


The fundamental cause of obesity is the imbalance between the ingested calories and the energy expenditure, and the main regulator of this energy balance is the hypothalamus. Nicotinic-type cholinergic receptors play an important role in this process, as they are able to alter neuronal excitability, favoring the neurotransmitters secretion. The nicotinic acetylcholine ±7 cholinergic receptor (±7nAChR) is expressed in glial cells and neurons and, when activated by acetylcholine, inhibits the production of inflammatory cytokines. Recent studies have correlated the activation of this receptor with decreased food intake. However, both high-fat diet consumption and obesity promote a decrease in ±7nAchR expression in the hypothalamus. However, the molecular mechanisms by which ±7nAChR receptors are differentially expressed are not yet known. Studies show that reduced ±7nAchR expression increases tissue susceptibility to damage caused by inflammatory processes. In the hypothalamus, the exacerbation of inflammatory processes is related to the reduction of hormonal signaling, cell death and damage to energy homeostasis and the development of metabolic disorders associated with obesity. It is known that the content of about 60% of metabolically active proteins can be modulated by pre- or post-translational mechanisms, such as ubiquitination, methylation and expression of microRNAs. MicroRNAs are small molecules that are part of ncRNAs (non-coding RNAs), with the ability to regulate gene expression by pairing with the target mRNA, preventing its translation. Through a previous bioinformatics analysis, we identified several microRNAs with the potential to regulate the expression of the Chrna7 gene (the gene encoding the ±7nAchR receptor). Thus, our study hypothesis is that hormonal, nutritional and/or pro-inflammatory factors, which permeate the genesis of obesity, may be involved with the modulation of mechanisms that stimulate the expression of microRNAs, causing the reduced expression of the ±7nAChR receptor in the hypothalamus and thus making the tissue more susceptible to inflammatory processes and cellular damage. To investigate this hypothesis, we will use protocols of in vitro studies with neuronal lineage (mHypoA-Pomc GFP lineage and primary culture of neuroprogenitor cells) after exposure to the serum of mice submitted to a high fat diet, as well as an in vivo protocol through the evaluation of the hypothalamus of animals that consumed the high-fat diet. In these models, we will use methods to confirm the regulation of ±7nAChR by the microRNAs found in the in silico analysis, to evaluate its expression by Real Time PCR (RT-qPCR) and Western Blotting (WB), assays of gain and loss of function with transfection of mimetic or inhibitor of the microRNA of interest, construction of plasmid with luciferase reporter to confirm the microRNA/Chrna7 interaction and Enzyme-linked Immunosorbent Assay (ELISA) to evaluate cytokines. Thus, we hope to elucidate the factors and mechanisms that occur early, resulting from the consumption of a high-fat diet, and that are responsible for the negative modulation of the ±7nAChR receptor in the hypothalamus and its consequent negative impact on energy balance which favors the development of obesity in mice. (AU)

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