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Catalase is a crucial enzyme of the antioxidant defense system responsible for the maintenance of cellular redox homeostasis. The aim of the present study was to evaluate the molecular regulation of catalase (Hdh-CAT) in stress physiology, innate immunity, testicular development, metamorphosis, and cryopreserved sperm of Pacific abalone. Hdh-CAT gene was cloned from the digestive gland (DG) of Pacific abalone. The 2894 bp sequence of Hdh-CAT had an open reading frame of 1506 bp encoding 501 deduced amino acids. Fluorescence in situ hybridization confirmed Hdh-CAT localization in the digestive tubules of the DG. Hdh-CAT was induced by different types of stress including thermal stress, H2O2 induction, and starvation. Immune challenges with Vibrio, lipopolysaccharides, and polyinosinic–polycytidylic acid sodium salt also upregulated Hdh-CAT mRNA expression and catalase activity. Hdh-CAT responded to cadmium induced-toxicity by increasing mRNA expression and catalase activity. Elevated seasonal temperature also altered Hdh-CAT mRNA expression. Hdh-CAT mRNA expression was relatively higher at the trochophore larvae stage of metamorphosis. Cryopreserved sperm showed significantly lower Hdh-CAT mRNA expression levels compared with fresh sperm. Hdh-CAT mRNA expression showed a relationship with the production of ROS. These results suggest that Hdh-CAT might play a role in stress physiology, innate immunity, testicular development, metamorphosis, and sperm cryo-tolerance of Pacific abalone.

The Pacific abalone Haliotis discus hannai is a highly commercialized seafood in Southeast Asia. The aim of the present study was to determine the antioxidant activity and oxidative stress-oriented apoptosis pathway in saccharides supplemented cryopreserved sperm of Pacific abalone. Cryopreserved sperm showed impaired antioxidant defenses due to the reduced mRNA abundance of antioxidant genes (CAT, Cu/Zn-SOD, Mn-SOD, GPx, GR, and BCL-2), apoptosis inhibitor (HSP70, and HSP90) gene, and enzymatic antioxidant activity compared to fresh sperm. Such impaired antioxidant defenses caused an increase in the mRNA expression of apoptosis genes (Bax, and Caspase-3), finally leading to apoptosis. The impaired antioxidant defense also increased O2•− production and lipid peroxidation (MDA) levels, which further accelerated apoptosis. Considering all the experimental findings, an apoptosis pathway of cryopreserved sperm has been adopted for the first time. Specifically, sperm cryopreserved using 3% sucrose combined with 8% dimethyl sulfoxide (DMSO) showed improved mRNA stability, enzymatic activity, and DNA integrity with reduced O2•− production and MDA levels compared to sperm cryopreserved with the other types of examined cryoprotectants (8% ethylene glycol + 1% glucose, 6% propylene glycol + 2% glucose, 2% glycerol + 3% glucose, and 2% methanol + 4% trehalose). The present study suggests that 3% sucrose combined with 8% DMSO is suitable to cryopreserve the sperm of this valuable species for molecular conservation.