A novel stiffening factor inducing the stiffest state of holothurian catch connective tissue

Abstract

SUMMARYThe dermis of sea cucumbers is a catch connective tissue or mutable collagenous tissue that shows large changes in stiffness. Extensive studies on the dermis revealed that it can adopt three different states having different mechanical properties that can be reversibly converted. These are the stiff, standard and soft states. The standard state is readily produced when a dermal piece is immersed in the sea water containing Ca 2+, whereas the soft state can be produced by removal of Ca 2+. A stiffening protein, tensilin, has been isolated from some sea cucumbers (Cucumaria frondosa and Holothuria leucospilota). Although tensilin converts the state of the dermis from soft to standard, it cannot convert from standard to stiff. In this study, we isolated and partially purified a novel stiffening factor from the dermis of Holothuria leucospilota. The factor stiffened the dermis in normal artificial sea water (ASW) but did not stiffen the soft dermis in Ca 2+ -free ASW. It also stiffened the dermis that had been converted to the standard state in Ca 2+ -free ASW by the action of tensilin. These results suggest that the factor produces the stiff dermis from the standard state but cannot work as a stiffener on the soft dermis. Its addition to longitudinal muscles of the sea cucumber produced no effects, suggesting that its effect is specific to the catch connective tissue. Its stiffening activity was susceptible to trypsin, meaning that it is a polypeptide, and its molecular mass estimated from gel filtration chromatography was 2.4kDa.

Interfibrillar stiffening of echinoderm mutable collagenous tissue demonstrated at the nanoscale

“…These experimental results, showing clear alterations in the deformation at the fibrillar level when MCT is stimulated into its stiff and soft states, can be used to build a simple model that sheds light on the key biophysical mechanisms enabling mutability (31,34,35,37,38). Prior research has proposed, but not directly demonstrated, that certain proteins secreted by JLCs including tensilin (35,37), stiparin (34), and NSF (31) act to cross-link the fibrils.…”

“…Small changes in the mechanical properties of the interfibrillar matrix are thus amplified to apply considerable stress to the elastic fibrils, as a consequence of which the fibrils are more effectively recruited to bear load. Prior biochemical evidence suggests the involvement of proteins like tensilin and NSF in the stiffening of the matrix (31,35,37). It is probable that these proteins physically cross-link to the existing glycosaminoglycans and proteoglycans, which in turn are bound to the gap zones in collagen fibrils.…”

“…It is therefore believed that the ionic treatments directly affect cellular secretion pathways in the JLCs, inducing release of proteins that alter interfibrillar binding, thus changing the stiffness of the tissue (12). Several such proteins, including tensilin, softenin, and novel stiffening factor (NSF), have been identified (31,34,35,37,38). It is believed that the JLCs secrete such effector proteins as a result of external stimuli (such as touch, aggressive attack or alteration in the ionic strength of the sea water around the animal), thereby changing the stiffness of the tissue.…”

“…The changes induced by these chemical methods are within the same order of magnitude as physiologically relevant mechanical changes occurring in MCT in vivo: Under mechanical stimulation (pressing the tissue by hand), starfish body wall MCT stiffens by a factor of ∼3.3 (30), whereas increasing K + concentration leads to an increase of ∼6.1 (30). Conversely, the reduction of stiffness in calcium-free artificial sea water is considerable (31), which is comparable to the reduction to zero in the extreme case of limb autotomy where the tissue disintegrates structurally (32).…”

Coordination between catch connective tissue and muscles through nerves in the spine joint of the sea urchin Diadema setosum

“…Stiffening and de-stiffening proteins have been isolated from the body-wall dermis of sea cucumbers, a well-studied catch connective tissue. NSF (novel stiffening factor) stiffens the dermis in the standard state into a stiff state (Yamada et al, 2010). Tensilin stiffens the dermis in the soft state into the standard state (Tipper et al, 2003) whereas softenin softens dermis in the standard state into a soft state (Takehana et al, 2014).…”