Effects of Environmental Hypoxia on Serum Hematological and Biochemical Parameters, Hypoxia-Inducible Factor (hif) Gene Expression and HIF Pathway in Hybrid Sturgeon (Acipenser schrenckii ♂ × Acipenser baerii ♀)

Abstract

Hypoxia is a globally pressing environmental problem in aquatic ecosystems. In the present study, a comprehensive analysis was performed to evaluate the effects of hypoxia on physiological responses (hematology, cortisol, biochemistry, hif gene expression and the HIF pathway) of hybrid sturgeons (Acipenser schrenckii ♂ × Acipenser baerii ♀). A total of 180 hybrid sturgeon adults were exposed to dissolved oxygen (DO) levels of 7.00 ± 0.2 mg/L (control, N), 3.5 ± 0.2 mg/L (moderate hypoxia, MH) or 1.00 ± 0.1 mg/L (severe hypoxia, SH) and were sampled at 1 h, 6 h and 24 h after hypoxia. The results showed that the red blood cell (RBC) counts and the hemoglobin (HGB) concentration were significantly increased 6 h and 24 h after hypoxia in the SH group. The serum cortisol concentrations gradually increased with the decrease in the DO levels. Moreover, several serum biochemical parameters (AST, AKP, HBDB, LDH, GLU, TP and T-Bil) were significantly altered at 24 h in the SH group. The HIFs are transcription activators that function as master regulators in hypoxia. In this study, a complete set of six hif genes were identified and characterized in hybrid sturgeon for the first time. After hypoxia, five out of six sturgeon hif genes were significantly differentially expressed in gills, especially hif-1α and hif-3α, with more than 20-fold changes, suggesting their important roles in adaptation to hypoxia in hybrid sturgeon. A meta-analysis indicated that the HIF pathway, a major pathway for adaptation to hypoxic environments, was activated in the liver of the hybrid sturgeon 24 h after the hypoxia challenge. Our study demonstrated that hypoxia, particularly severe hypoxia (1.00 ± 0.1 mg/L), could cause considerable stress for the hybrid sturgeon. These results shed light on their adaptive mechanisms and potential biomarkers for hypoxia tolerance, aiding in aquaculture and conservation efforts.

Keywords: HIF pathway; hybrid sturgeon; hypoxia; hypoxia-induced factor; physiological response.

Figure 1

Effect of hypoxia on (A) red blood cell (RBC) counts, (B) hemoglobin (HGB) concentrations and (C) cortisol concentrations in hybrid sturgeons. Different letters represented significant differences (p < 0.05).

Figure 2

Phylogenetic relationships of hif genes in hybrid sturgeon and selected species. Multiple sequence alignments of hif amino acid sequences were performed using MUSCLE, and this phylogenetic tree was constructed using MEGA7 by the neighbor-joining (NJ) method and the Jones–Taylor–Thornton (JTT) model with 1000 bootstrap replicates. Different hif genes were classified into their corresponding clades with different colors, and the hif genes of hybrid sturgeon were labeled with red dots.

Figure 3

Expression patterns of hif-1α (A), hif-2α (B), hif-3α (C), hif-1β (D), hif-2β (E) and hif-3β (F) in gill tissues of hybrid sturgeon after hypoxia stress. Different letters represented significant differences (p < 0.05).

Figure 4

Schematic diagram of HIF pathway in liver of hybrid sturgeon 24 h after hypoxia challenge. The expressions of HIF pathway−related genes were determined by meta−analysis of RNA−Seq datasets. The specific expression levels of these function genes were determined in the SH group (n = 2) relative to N group (n = 2) based on the mapped reads using DESeq2 R package and shown in Table S2. They are shown with continuous colors, from blue to red.