Heat stress-induced mitochondrial dysfunction activates the cGAS-STING innate immune pathway and inflammatory injury in the intestine of razor clam Sinonovacula constricta

Global climate change has led to rising marine temperatures, making high temperature (HT) a major threat to bivalve aquaculture. This study investigated the effects of HT on intestinal damage, microbiota, immune responses, and molecular mechanisms in the razor clam (Sinonovacula constricta), aiming to provide a theoretical basis for understanding bivalve adaptation to heat stress and informing aquaculture management. The results showed that HT significantly inhibited the filter-feeding activity of clams. Within one week of continuous HT, the mortality rate of clams reached 42%. HT caused severe damage to the mucosal ridges. HT significantly increased malondialdehyde content, suppressed superoxide dismutase activity, and reduced the activities of intestinal immune-related enzymes (lysozyme, acid phosphatase, and alkaline phosphatase). Additionally, HT reshaped the intestinal microbial composition and reduced microbial abundance. Intestinal transcriptome analysis revealed that HT significantly inhibited the intestinal oxidative phosphorylation process, leading to mitochondrial dysfunction, while the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) innate immune pathway and inflammation-related genes were significantly upregulated. Further verification experiments showed that HT significantly reduced the intestinal adenosine triphosphate content and increased the content of cyclic guanosine monophosphate-adenosine monophosphate. HT caused obvious morphological damage to intestinal mitochondria. These results confirmed the activation of the STING signaling pathway and its downstream inflammatory response. This study systematically reveals the impact mechanism of HT on the intestinal physiology and molecular regulation of razor clam, enriches the theoretical research on the environmental stress response of bivalves, and provides theoretical support for the prevention and control of HT, optimization of aquaculture environments, and breeding of stress-resistant varieties during razor clam aquaculture.