Molecular Characterization of Anion Exchanger 2 in Litopenaeus vannamei and Its Role in Nitrite Stress

Anion exchanger 2 (AE2) mediates the Cl^-/HCO₃^- transmembrane exchange process and regulates intracellular pH homeostasis. In this study, the AE2 gene (GenBank: PQ073349) was cloned and characterized from Litopenaeus vannamei using the rapid amplification of cDNA ends (RACE) technique. Employing bioinformatics, real-time fluorescence quantitative PCR, and RNA interference, we explored the gene's sequence characteristics, tissue distribution, and the effects of nitrite on shrimp survival, physiology, and tissue damage following gene silencing. The results showed that AE2 cDNA was 5134 bp in length, encoding 1293 amino acids, which includes both the Band3 and HCO₃^- structural domains. AE2 was expressed in all tissues, with the highest expression in muscle. After silencing AE2, shrimp survival increased and hemolymph nitrite levels decreased. Notably, the oxidative stress enzyme system was not severely affected, and gill tissue damage was reduced. In addition, the expression level of Na⁺/K⁺/2Cl^- cotransporter 1 (NKCC1) was significantly reduced (p < 0.05). These findings suggest that AE2 and NKCC1 are jointly involved in regulating the physiological process of nitrite entry into the shrimp body through gill tissue. Overall, this study provides a crucial experimental foundation for addressing the toxicity concerns associated with nitrite.