The immune enhancement strategies of Strongylocentrotus intermedius in response to different immunomodulators.

Abstract

The sea urchin Strongylocentrotus intermedius is an economically important aquaculture species in northern China, where bacterial diseases significantly restrict healthy industry development. To counter these pathogens, specific pathogen-associated molecular patterns (PAMPs) are increasingly utilized as immunostimulants to prime the innate immune system. To elucidate the molecular mechanisms underlying early immune enhancement, a de novo transcriptome analysis was performed on sea urchins treated with lipopolysaccharides (LPS), peptidoglycan (PGN), and β-glucan. A total of 1007, 6216, and 2866 differentially expressed genes (DEGs) were identified in LPS, PGN, and β-glucan treatment group, respectively. Functional analyses demonstrated that LPS triggers an early MAPK signaling burst, PGN elicits a massive multi-pronged inflammatory signaling cascade, and β-glucan primarily activates cellular clearance mechanisms via lysosomal degradation pathways. These distinct upstream programs were further corroborated by rapid, stimulus-specific physiological responses, with extracellular SOD and CAT activities being selectively modulated under LPS and PGN stimulation. Notably, co-expression heatmap analyses revealed that these distinct pathway activations are tightly governed by specific, highly synchronized transcription factor (TF) modules. Among these, the transcription factor Runx1 was identified as a shared differentially expressed regulator whose expression was significantly correlated with the activation of numerous immune genes across all three PAMP treatment groups, suggesting that it functions as a universal core regulatory hub bridging these diverse immune stimuli. Despite these divergent upstream regulatory programs, analysis of 241 shared DEGs revealed that the immune response converges on a universal effector baseline centered on the phagosome, lysosome, NOD-like receptor (NLR) signaling, and primitive IL-17-driven pathways. Furthermore, the expression of key core immune genes, including RUNX1, IFITM, and MRC1, was successfully validated by qRT-PCR. These findings provide comprehensive insights into the early regulatory switches and conserved immune priming mechanisms in echinoderms, offering valuable molecular targets for the rational development of broad-spectrum immunostimulants in sea urchin aquaculture.