Physiological responses of Holothuria grisea during a wound healing event: An integrated approach combining tissue, cellular and humoral evidence

Due to their tissue structure similar to mammalian skin and their close evolutionary relationship with chordates, holothurians (Echinodermata: Holothuroidea) are particularly interesting for studies on wound healing. However, previous studies dealing with holothuroid wound healing have had limited approaches, being restricted to tissue repair or perivisceral immune response. In this study, we combined tissue, cellular and humoral parameters to study the wound healing process of Holothuria grisea. The immune responses of the perivisceral coelom were assessed by analyzing the number, proportion and viability of coelomocytes and the volume and protein concentration of the coelomic fluid. Additionally, the morphology of the healing tissue and number of coelomocytes in the connective tissue of different body wall layers were examined over 30 days. Our results showed that perivisceral reactions started 3 h after injury and decreased to baseline levels within 24 h. In contrast, tissue responses were delayed, beginning after 12 h and returning to baseline levels only after day 10. The number of coelomocytes in the connective tissue suggests a potential cooperation between these cells during wound healing: phagocytes and acidophilic spherulocytes act together in tissue clearance/homeostasis, whereas fibroblast-like and morula cells cooperate in tissue remodeling. Finally, our results indicate that the major phases observed in mammalian wound healing are also observed in H. grisea, despite occurring at a different timing, which might provide insights for future studies. Based on these data, we propose a model that explains the entire healing process in H. grisea.