Preprint: Legumain is required for scar-free ligament healing in zebrafish

Preprint: Legumain is required for scar-free ligament healing in zebrafish

In a preprint posted on 23 October, biologists described how immune cells help remodel the tissue’s protein network after the intermandibular ligament is cut in adult zebrafish. Fish with a mutation that prevents Legumain production healed with a fibrotic scar.

The intermandibular ligament connects the jaw bones. In a 2023 study, the same group showed that within approximately 28 days after being cut, this ligament regains a structure resembling that of an uninjured ligament. The new preprint examines the protein-level mechanism behind this recovery.

During the first one to three days after injury, the authors detected Legumain and Ctsla in macrophages, immune cells at the wound edge. Legumain and Ctsla break down proteins; tissue staining and RNA analysis showed where these enzymes were located and which cells produced them.

Fibronectin is a component of the extracellular matrix, the network between cells on which other fibers assemble. By day seven, this network had become more uniform in wild-type fish. In mutants, excess fibronectin persisted at the edge of the original ligament, and cells retained features of a mature state for longer. The authors link these findings to an impaired transition into a repair state.

Overall activity of protein-degrading enzymes remained at wild-type levels in mutants, although Ctsla abundance increased. In wild-type fish, Ctsla accumulated at the injury boundary and more often took the form of two linked chains. In mutants, it was distributed throughout the tissue and remained predominantly in its single-chain form. The authors showed that Legumain is required for this processing of Ctsla.

In this adult zebrafish model, the authors link the outcome of healing to local macrophage activity, which remodels the protein network at the wound edge and helps ligament cells enter a repair state.