Proteomic profiling reveals matrix remodeling and metabolic homeostasis in sea cucumber mutable collagenous tissue

Mutable Collagenous Tissue (MCT) is an echinoderm-specific connective tissue, capable of rapidly altering its mechanical properties under neural regulation. Although several potential effector proteins have been identified, the overall molecular network governing the transition between the stiffened and softened states of MCT remains unclear. To uncover potential mechanisms, we performed iTRAQ-based quantitative proteomics on MCT from Stichopus chloronotus under stiffened and softened conditions. A total of 1653 proteins were identified, with 160 differentially abundant proteins detected between stiffened and softened tissues. Functional enrichment analysis revealed that the stiffened state was significantly associated with upregulation of vesicle-mediated transport systems and glycosaminoglycan metabolism, supporting the hypothesis of secretion-driven matrix remodeling. The softened state was characterized by enrichment in protein synthesis, ribosome biosynthesis, and oxidative phosphorylation pathways. Additionally, enrichment of Hippo signaling and DNA damage response terms was observed in the softened condition. Collectively, these data provide a proteomic resource for MCT state transitions and suggest that stiffening is associated with matrix remodeling. In contrast, softening is accompanied by shifts in metabolic homeostasis and stress-response programs. This research provides a systematic understanding of MCT's rapid reversibility and may inform the design of bioinspired mechanically adaptable materials.