RECOVERY FROM HYPOXIA AND HYPERCAPNIC HYPOXIA: IMPACTS ON THE TRANSCRIPTION OF KEY ANTIOXIDANTS IN THE SHRIMP Litopenaeus vannamei
Kniffin, Casey Darling
Burnett, Karen G
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The Pacific whiteleg shrimp, Litopenaeus vannamei, inhabits coastal and estuarine waters, which are prone to intermittent bouts of low oxygen (hypoxia) and high carbon dioxide (hypercapnia). The current study assesses the responses of key antioxidants in shrimp during exposure and recovery from hypoxia (H) and hypercapnic hypoxia (HH) by measuring changes in their associated gene transcripts using qPCR. In a typical semidiurnal tidal cycle episodic H and HH (4-6h) are followed by recovery to normal oxygen (normoxia) and carbon dioxide levels (8-12h). Similar oxygen recovery scenarios produce a large number of reactive oxygen species (ROS) in vertebrates as a result of a rapid influx of oxygen into tissues, and thereby oxidative injury can occur. While ROS can be detrimental to cells, they also play an important role in crustacean immune function and are eventually removed through the production of antioxidant (antioxidant) enzymes. In the current study we aimed to determine whether changes in relative gene expression of key antioxidant genes contributed to the ability of shrimp to tolerate fluctuations in oxygen and carbon dioxide. Three antioxidant systems were assessed to address different modes of removal of ROS. qPCR was used to measure relative transcript abundance of MnSOD, GST, GPX, TRX-1, TRX-2, and PRX. After recovery from H and HH it was clear that certain genes have differential expression patterns compared to the time matched normoxia controls. Significant increases in expression of MnSOD occurred after exposure to both H and HH treatment and during recovery from both short and long-term exposure times, providing evidence that MnSOD is a major route of elimination of ROS. However, other antioxidant genes (GST and TRX-1) exhibited decreases in expression or no regulation (PRX) in various treatment groups. Overall, a dynamic pattern of expression of antioxidant genes were observed with marked differences in the short term vs. long term exposure times.