Acute hypoxia up-regulates HIF-1α and VEGF mRNA levels in Amazon hypoxia-tolerant Oscar (Astronotus ocellatus)

Abstract

Amazon fish maintain oxygen uptake through a variety of strategies considered evolutionary and adaptive responses to the low water oxygen saturation, commonly found in Amazon waters. Oscar (Astronotus ocellatus) is among the most hypoxia-tolerant fish in Amazon, considering its intriguing anaerobic capacity and ability to depress oxidative metabolism. Previous studies in hypoxia-tolerant and non-tolerant fish have shown that hypoxia-inducible factor-1α (HIF-1α) gene expression is positively regulated during low oxygen exposure, affecting vascular endothelial growth factor (VEGF) transcription and fish development or tolerance in different manners. However, whether similar isoforms exists in tolerant Amazon fish and whether they are affected similarly to others physiological responses to improve hypoxia tolerance remain unknown. Here we evaluate the hepatic HIF-1α and VEGF mRNA levels after 3 h of acute hypoxia exposure (0.5 mgO2/l) and 3 h of post-hypoxia recovery. Additionally, hematological parameters and oxidative enzyme activities of citrate synthase (CS) and malate dehydrogenase (MDH) were analyzed in muscle and liver tissues. Overall, three sets of responses were detected: (1) as expected, hematocrit, hemoglobin concentration, red blood cells, and blood glucose increased, improving oxygen carrying capacity and glycolysis potential; (2) oxidative enzymes from liver decreased, corroborating the tendency to a widespread metabolic suppression; and (3) HIF-1α and VEGF increased mRNA levels in liver, revealing their role in the oxygen homeostasis through, respectively, activation of target genes and vascularization. This is the first study to investigate a hypoxia-related transcription factor in a representative Amazon hypoxia-tolerant fish and suggests that HIF-1α and VEGF mRNA regulation have an important role in enhancing hypoxia tolerance in extreme tolerant species.

Hepatopancreas Transcriptome Profiling Analysis Reveals Physiological Responses to Acute Hypoxia and Reoxygenation in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

“…HIF-1a is an important homeostasis regulatory protein in organisms ( Baptista et al, 2016 ). In this study, the hif-1a gene was up-regulated during hypoxia and down-regulated following reoxygenation ( Figure 7 ), suggesting that a molecular regulatory pathway with HIF-1 signal pathway as the core occurred in PF-carp during the hypoxic and reoxygenation processes ( Zhang et al, 2017b ), thereby triggering a series of metabolic changes that includes energy metabolism ( Goda and Kanai, 2012 ), cell proliferation and apoptosis ( Carmeliet et al, 1998 ), immune response ( Cramer et al, 2005 ) and other metabolic pathway ( Semenza, 1999 ).…”

Ecophysiology, genotoxicity, histopathology, and gene responses of naphthalene injected Colossoma macropomum (Cuvier, 1818) exposed to hypoxia

“…The greater influence of oxygen concentration on hematology is supported by the PCA result, as demonstrated by the clustering of hematological variables determined by oxygen concentration (Figure 6). Hematological changes in Amazonian fish exposed to hypoxia are well reported in the literature (Val and Almeida-Val, 1995; Val, 1996; Baptista et al , 2016). The increase in plasma glucose levels suggests the use of glucose as an anaerobic energy source (Chippari-Gomes et al.…”

Differential survivorship of congeneric ornamental fishes under forecasted climate changes are related to anaerobic potential

“…To validate the normalization calculations, we previously confirmed 18S as a suitable internal control gene due its uniform efficiency and stable expression under experimental climate scenarios (one-way ANOVA, P > 0.05). In addition, 18S ribosomal RNA has been used as endogenous reference gene in previous studies with Amazonian fish ( Anjos et al , 2011 ; Baptista et al , 2016 ; Vásquez KL, 2009, PhD Thesis, Federal University of Amazonas, Manaus; Oliveira CPF, 2010, PhD Thesis, Federal University of Amazonas, Manaus). An untreated control from the baseline scenario was selected as a calibrator sample for qRT-PCR relative quantification assays.…”