Important Role of Superoxide Dismutase (SOD) in the Regeneration of Spirometra mansoni sparganum: Comparative Transcriptome Analysis

The heads of Spirometra mansoni spargana exhibit a strong ability to regenerate. However, the molecular regulatory mechanisms underlying this regeneration remain poorly understood. This study presents the first comparative transcriptome analysis of the germinal layer part (GLP) and body part (BP) of S. mansoni sparganum. We identified that the MAPK signaling pathway is related to regeneration and that superoxide dismutase (SOD) is the key gene critical for plerocercoid regeneration through pathway inhibition experiments. The genetic structure and expression patterns of the SOD gene family were subsequently analyzed. Finally, the representative member Sm SOD2 was cloned, expressed and identified, and its function in plerocercoid regeneration was systematically evaluated. Comparative transcriptome analysis revealed 1,930 differentially expressed genes (DEGs). Both KEGG enrichment and protein‒protein interaction (PPI) analyses indicated that the MAPK pathway is closely related to plerocercoid regeneration. After pathway inhibition, SOD transcription significantly increased ( P  < 0.01), suggesting that it may play a critical role in the MAPK pathway. A total of 10 S. mansoni SOD ( Sm SOD) family members were identified, among which Sm SOD2 was significantly more highly expressed in the GLP than in the BP and contains completely conserved domains (CDD). Therefore, Sm SOD2 was selected as a representative member for molecular characterization. After treatment with the inhibitor 2-ME, the transcription of Sm SOD2 decreased by 65.14% ( P  < 0.05), the expression of the encoded protein significantly decreased, and SOD enzymatic activity decreased by 38.76% ( P  < 0.001). EdU and H3P labeling experiments demonstrated a significant reduction in the number of proliferating cells in the GLP of the inhibitor-treated group ( P  < 0.05), with the density of H3P⁺ cells decreasing from 131 to 16 cells/mm ² . In vitro regeneration experiments showed significant reductions in plerocercoid activity, regenerated length and regenerated tissue area in the inhibitor-treated group compared with the control group ( P  < 0.001); additionally, the worm body was prone to rupture, indicating serious impairment of regenerative capacity. Based on the experimental results at the molecular, cellular, tissue and organismal levels, inhibition of Sm SOD2 sequentially induces redox imbalance, cell cycle arrest, tissue structure destruction and the loss of regenerative ability. Sm SOD2 may drive the plerocercoid regeneration process by maintaining intracellular redox homeostasis and ensuring cell proliferation in the GLP.