Response mechanism to heat and hypoxia stress in hard clam: insights from antioxidation and lipid metabolism

BACKGROUND: The hard clam (Mercenaria mercenaria) is native to the coast of the United States and Canada. Following its introduction to China, it has become an economically important bivalve species cultured in ponds. Extreme heat and hypoxia events severely impact the physiological status of marine organisms. Excess reactive oxygen species produced by environmental stress can lead to antioxidant stress response and lipid remodeling. Antioxidant stress response and lipid metabolism can reveal the response mechanism and adaptation ability of organisms to environmental changes. RESULTS: In the present study, coupled lipidomic and biochemical approaches were employed to reveal the response mechanism to heat and hypoxia stress at the antioxidant stress and lipid metabolism level in the hard clam. The antioxidant system was enhanced showing stress-specific to increase total antioxidant capacity (T-AOC) capacity and maintain relatively stable malondialdehyde (MDA) level. 913 lipid metabolites were identified by widely targeted lipidomic analysis. Glycerophospholipids (GP), glycerolipids (GL), and sphingolipids (SP) were the main differential expression lipid metabolites. Lipid remodeling of the gill tissue was mainly caused by GP, GL and SP metabolism in the hard clam. CONCLUSION: Activation of the antioxidant system which evidenced by elevated T-AOC, can alleviate oxidative damage, thereby preventing excessive accumulation of MDA under environmental stress. Concurrently, increased abundances of GP and SP metabolites drive remodeling of membrane lipids, which is critical for maintaining membrane fluidity and structural integrity during stress. Furthermore, the accumulation of GL metabolites functions as thermos-protectant. This study expands our understanding of hard clam responses to heat and hypoxia stress at the antioxidant and lipid metabolism level.