Modulation of a7nAChR receptor expression by inflammatory processes and the effect on the activity of hypothalamic neurons that participate in energy homeostasis

Abstract

The hypothalamus express different neuropeptides that control different aspects of body homeostasis. The arcuate nucleus is a hypothalamic region composed of two populations of neurons involved with energy homeostasis: orexigenic (NPY/AGRP), which stimulate food intake and anorectic (POMC/CART), which inhibit food intake. Leptin, one of the signaling hormones of these neurons, acts through its receptor (LepR). Activation of this receptor results in the activation of JAK2/STAT3 pathway. Studies show that short-term consumption of a diet rich in saturated fatty acids activates inflammatory pathways in the hypothalamus, showing that inflammatory processes have a fundamental role in the development of metabolic disorders that are associated with hypothalamic activity. Nicotinic acetylcholine receptors (nAChRs) have wide expression in the central nervous system and recent studies showed their ability to modulate the activity of neurons related to the control of intake. In a recent study our group showed that activation of the a7nAChR receptor in the mouse hypothalamus reduces the expression of AGRP/NPY, increases the expression of POMC and reduces food intake and the activation of hypothalamic AMPK. Other important feature of a7nAChR receptors is the ability of these receptors to activate signal transduction pathways that result in inhibition of the transcription of inflammatory cytokines. This mechanism is called cholinergic anti-inflammatory reflex. The cholinergic anti-inflammatory reflex has been studied as a therapeutic target for diseases associated with nutritional disorders such as Obesity and Diabetes. Recently we showed that consumption of a high-fat diet for three days was able to reduce the hypothalamic expression of the a7nAChR receptor and still makes the hypothalamus more susceptible to inflammatory damage. The expression and activity of the a7nAChR receptor depends on several cellular mechanisms that can act by stimulating or inhibiting the expression of the Chrna7 gene or by controlling the presence and activity of the receptor on the membrane, such as methylation, maturation involving chaperone proteins and the ubiquitin-proteasome system (mechanisms pre-transcriptional and post-translational). Although many studies have investigated the cellular signaling to control energy homeostasis, as well as the effects of inflammatory processes on cellular activity, the role of the a7nAChR receptor in this context has been little investigated. Thus, we intend to investigate whether exposure to inflammatory conditions activates cellular mechanisms (pre-transcriptional and/or post-translational) that act early and lead to reduced expression and/or the presence of the a7nAChR receptor on the cell membrane. Furthermore, we also aim to assess whether these events make the CNS more susceptible to inflammatory processes leading to damage in signaling that participates in the control of homeostasis. For this, we will use microglia and neuronal cell lines exposed to inflammatory agents and mice model exposed to high fat diet. In cultured cells we intend to use the CRISPR-Cas9 technology to delete the expression of the a7nAChR receptor. Molecular analyzes of a7nAChR receptor expression, presence of chaperones, expression of inflammatory markers, presence of methylation, participation of the ubiquitin-proteasome system, modulation of neuropeptides by exposure to leptin and a7nAChR receptor agonist will be performed using RT-PCR, Western Blot, Immunoprecipitation and ELISA protocols. (AU)