Immune response of Amphioctopus fangsiao brain to Aggregata sinensis infection: Insights from transcriptomic studies

Cephalopods are susceptible to various pathogens, including bacteria, fungi, viruses, protozoa, and metazoans. Among these, Aggregata is one of the most common and dangerous protozoan parasites. Aggregata can infect the digestive tract of cephalopods, leading to ulceration and atrophy of the host's mucosa, infiltration of blood cells, and malabsorption. This study aims to investigate the impact of Aggregata sinensis infection on the neural function of the brain in Amphioctopus fangsiao. Pathological sections revealed that Aggregata sinensis causes parasite-associated histopathological alterations to the brain. Subsequently, we employed transcriptomic methods to systematically assess the changes in gene expression post-infection through GO/KEGG and WGCNA analyses. Differential expression analysis revealed significant changes in the expression of 858, 749, and 983 genes in the supraesophageal mass (SUP), subesophageal mass (SUB), and optic lobe (OL), respectively. Enrichment analysis uncovered signaling pathways related to inflammation and immune response, particularly in the optic lobe, where an upregulation of inflammation-related genes and a downregulation of neuron-related genes were observed. This alteration had a significant impact on the dopaminergic synapse pathway, indicating that parasitic infection may lead to impairments in neural function. Gene expression network analysis further identified several key immune-related hub genes, suggesting a complex immune regulatory mechanism triggered by the parasitic infection. Overall, Aggregata infection not only triggered significant inflammatory and immune responses but also potentially caused damage to the nervous system of A. fangsiao. This study provides new insights into the immune adaptability of cephalopods under parasitic infection and lays an important foundation for future management of parasitic infections in octopus aquaculture.