O efeito da hipóxia sobre os parâmetros bioquímicos e a expressão dos genes hif-1α e phd2 do ciclídeo amazônico Astronotus ocellatus (Agassiz, 1831)

Abstract

Variations on dissolved oxygen levels in Amazonian lakes are determinant to the survival of aquatic organisms, which require a variety of adaptive responses to survive such environments, particularly fish. Tolerance to hypoxia is a common feature amoug species of Amazonian fishes, such as Astronotus ocellatus, which presents a series of physiological and biochemical adjustments, aiming to reduce oxygen demand and increase anaerobic metabolism. In this research, we aim to contribute with information about the physiological and molecular responses of Astronotus ocellatus submitted to low oxygen levels. This study is pioneer in evaluating Astronotus ocellatus phd2 mRNA transcripts submitted to hypoxia. Some well-known hypoxia indicators, such as plasma glucose, plasma lactate, hepatic glycogen and transcription of hif-1α and phd2 were investigated after 1, 3 and 5 hours of hypoxia followed by 3 hours of recovery in normoxia. Fishes under hypoxia presented a reduction in liver glycogen levels after 1 hour of hypoxia and an increase in plasma glucose and lactate during hypoxia. The responses of the species Astronotus ocellatus to exposure to different periods of hypoxia, followed by recovery in normoxia, showed that the fish entered hypoxia and the pattern of transcription of phd2 in liver and gills showed that these organs have different molecular responses to cope with hypoxia, although the hif-1α gene kept similar transcription levels in both tissues. The gene phd2 increased its transcripts in gills and decreased, as expected, in liver. These antagonistic responses were explained by a previously published positive feedback mechanism in which the HIF protein controls levels of the phd2 gene.