Molecular mechanisms mediating stiffening in the mechanically adaptable connective tissues of sea cucumbers

Abstract In most animals, connective tissues such as the dermis or tendons present invariant mechanical properties, fine-tuned for their structural function. However, echinoderms, a group of sea creatures including sea cucumbers, possess the ability to voluntarily modify the mechanical properties of their connective tissues, which are therefore called mutable collagenous tissues (MCT). Understanding the molecular mechanism underlying MCT mutability is a prerequisite for the development of biomimetic smart dynamic materials. The stiffening and softening cycles of MCTs are made possible by the release of specialized effector proteins. We identified a stiffening factor from the dermis of Holothuria forskali, Hf-(D)Tensilin, and showed that it is localized in the secretory granules of juxtaligamental-like cells, a MCT specific cell type. Using recombinant proteins, we confirmed its effect on the dermis and its aggregation effect on extracted collagen fibrils. A model is proposed for the molecular interactions which mediate collagen fibrils cross-linking by tensilin.