Role of adenosine-mediated signaling in neuron-glia interactions in the brainstem during hypoxia and acidification.

• Grant number: 23/14990-4
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: March 28, 2024
• End date: March 27, 2025
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal Investigator: Benedito Honorio Machado
• Grantee: Karla Lima Rodrigues
• Supervisor: Alexander Gourine
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Institution abroad: University College London (UCL), England
• Associated to the scholarship: 21/08833-8 - Possible role of astrocytes in the brainstem regions in the respiratory changes observed in mice submitted to sustained hypoxia, BP.DR

Abstract

Hypoxic challenge can activate peripheral and central chemoreceptors and recruit brainstem sites directly involved with the generation/modulation of autonomic and respiratory functions in order to bring the PaO2 back to the normal level. Previous studies from our laboratory showed that C57BL/6 mice submitted to sustained hypoxia (SH, FiO2 0.1 for 24h) presented significant changes in the respiratory pattern, an increase in vagal drive but no changes in the sympathetic activity. In a recent study performed in conscious freely moving adenosine A2A receptors knockout (KOA2A) mice, we verified significant changes in the baseline ventilatory parameters, indicating a relevant role for these receptors in modulation of the respiratory frequency. This finding in KOA2A mice is consistent with the concept that adenosine is a modulator of the brainstem neurons and that the activation of its A2A receptors modulates the synaptic transmission in the neural pathways mediating cardiovascular and respiratory reflexes. Experiments performed in in situ preparation (WHBP) demonstrated that KOA2A mice presented a higher baseline frequency of phrenic nerve discharge (PND) and a reduction in the Late-E incidence in relation to control mice. These data, support the concept that adenosine acting on A2A receptors plays an important role in the modulation of the respiratory frequency as well as in the generation of active expiration. In another series of studies performed in rats, we observed that glial cells/astrocytes are directly involved in the modulation of synaptic transmission at the NTS level. In this context, it is possible that the changes in the respiratory pattern in mice submitted to sustained hypoxia are related to changes in the astrocytic modulation via adenosine and its A2A and A2B receptors at the NTS as well as in the neurons of the ventral medulla involved in the generation and modulation of the respiratory rhythm and pattern. The main goal of this BEPE project is to use novel experimental approaches to critically evaluate the involvement of adenosine and its receptors in modulation of the respiratory responses to hypoxia and acidosis (CO2/[H+]) in the brainstem respiratory nuclei (BotC/preBotC and RTN/vlPF). To reach this goal we will prepare brainstem slices containing BotC/preBotC and RTN/vlPF and specific biosensors of ATP and adenosine will be placed in this region of the ventral medulla to evaluate the release of these purines under challenging conditions such as hypoxia and hypercapnia/acidosis in wild-type mice (Figure A). We will also evaluate changes in in vitro imaging of astrocytes Ca2+ waves in response to adenosine in wild-type and A2B receptors deficient mice in order to evaluate the role of these receptors in astrocyte modulation (Figure B). This project will help in the understanding of how adenosine signaling mechanisms are necessary in situations of hypoxia, hypercapnia and acidosis (CO2/[H+]) in brainstem sites directly involved with the generation/modulation of autonomic and respiratory functions. Furthermore, the international experience in a reference laboratory in studies of neuronal and astrocyte interaction in conditions of metabolic changes will bring to my academic and laboratory routine innovative techniques and concepts that will be very important for the final steps of this Ph.D. project.