Sobrevivendo ao ambiente amazônico: Mecanismos mitocondriais de resposta à hipóxia e reoxigenação em peixes da Amazônia

Abstract

The floodplain areas of the Amazon often present hypoxic conditions, in addition to oxygen gradients that are known to reach concentrations close to zero, especially at night, directly affecting the survival capacity of fish. The present thesis aims to evaluate the effects of hypoxia, as well as reoxygenation on the metabolic responses of Amazonian fish, ranging from respiratory rates of oxygen consumption to cellular mechanisms of redox status regulation and mitochondrial quality control. Both hypoxia and reoxygenation often produce significant changes in metabolic processes as a whole, which includes the production of reactive oxygen species (ROS) in large amounts, resulting in harmful damage to cellular processes. ROS can oxidize and damage mitochondrial membranes as well as the system of transport of electrons and tricarboxylic acid (TCA), leading to suppression of OXPHOS and overproduction of more ROS molecules. Our results showed that Amazonian fish have a high cardiac tolerance to hypoxia under natural environmental conditions. However, important metabolic organs such as the liver are more compromised in terms of their catalytic ability to generate energy. Despite this, highly hypoxia-tolerant fish, such as A. ocellatus, have mitochondrial skills to neutralize ROS content both during hypoxia and after reoxygenation. As far as we know, this work presents, for the first time, mechanisms of mitochondrial respiration never before described for the Amazon fish species living in hypoxia, relating these responses to patterns of oxygen consumption rate, and shedding light on the cellular tolerance of Amazonian fish to their natural environments.