Development of Tissue-Engineered Ligaments: Elastin Promotes Regeneration of the Rabbit Medial Collateral Ligament.

When ligaments are injured, reconstructive surgery is sometimes required to restore function. Methods of reconstructive surgery include transplantation of an artificial ligament and autotransplantation of a tendon. However, these methods have limitations related to the strength of the bone-ligament insertion and biocompatibility of the transplanted tissue after surgery. Therefore, it is necessary to develop new reconstruction methods and pursue the development of artificial ligaments. Elastin is a major component of elastic fibers and ligaments. However, the role of elastin in ligament regeneration has not been described. Here, we developed a rabbit model of a medial collateral ligament (MCL) rupture and treated animal knees with exogenous elastin [100 µg/(0.5 mL·week)] for 6 or 12 weeks. Elastin treatment increased gene expression and protein content of collagen and elastin (gene expression, 6-fold and 42-fold, respectively; protein content, 1.6-fold and 1.9-fold, respectively), and also increased the elastic modulus of MCL increased with elastin treatment (2-fold) compared with the controls. Our data suggest that elastin is involved in the regeneration of damaged ligaments.

The behavior of ligament cells cultured on elastin and collagen scaffolds.

The ruptured anterior cruciate ligament (ACL) does not heal spontaneously. Therefore, the development of new healing techniques employing tissue engineering is vital. One of the aspects related to tissue-engineered artificial ligaments is the type of cell to be used for the artificial ligament. In this study, ligament cells from the ACL and periodontal ligament (PDL) were evaluated. In addition, we prepared highly oriented extracellular matrix (ECM) fiber scaffolds that mimicked the structure of the ligament and examined the cellular responses to these scaffolds. Elastin-A and collagen were used as the ECM proteins. Although the cells from the PDL (PDL fibroblasts [PDLFs]) showed approximately 2.1-fold higher expression of alkaline phosphatase (ALP; marker of osteogenic differentiation) than the ACL cells, the expression of ligament-related genes (for type I collagen, type III collagen, and tenomodulin) did not differ between PDLFs and ACL cells. Furthermore, the cellular responses (expression pattern of ligament-related genes and ALP activity) to the ECM were similar between ACL cells and PDLFs. In particular, elastin-A upregulated ALP and downregulated tenomodulin (TeM; a ligament marker) in ligament cells. In contrast, collagen maintained TeM expression in ligament cells. These results suggest that elastin-A promotes the osteogenic differentiation of ligament cells and that collagen maintains the phenotype of ligament cells.