Abstract
Surgical reconstruction of the anterior cruciate ligament (ACL) has historically been
the only method by which knee stability is restored following ACL rupture. Following
ACL rupture, the torn ends of the ligament are exposed to the synovial environment,
containing hyaluronan (HA), which has been implicated in the poor migratory function
of ACL fibroblasts (ACLF). We hypothesize that the HA in synovial fluid attenuates
the wound healing response of the ACL by inhibition of new focal adhesions between
ACLF and the surrounding environment. Juvenile bovine ACLF were isolated and cultured
in the presence of endogenous and exogenous high molecular weight HA (HMWHA) to monitor
in vitro wound closure. Concurrently, cells were assayed for focal adhesion formation
and adhesion strength. Next, human ACLF were cast into tissue-engineered constructs
to assess their ability to contract within a 3D matrix after treatment with HA. A
cellular viability assay was used to determine the cytotoxicity of HMWHA. Co-culture
of synoviocytes with ACLF wounds demonstrated that HMWHA was the primary cause for
attenuated wound healing. When exogenous HMWHA was cultured with ACLF, a dose-dependent
negative correlation (r = −0.65, p < 0.001) in cell migration was observed. A significant decrease in the number and
strength of focal adhesions was found to mirror the dose-dependent pattern. Collagen
gel contraction was inhibited in the presence of HMWHA. Direct exposure of ACLF to
HMWHA was shown to inhibit ACLF wound healing and contraction. As cytotoxicity remained
unchanged, this decreased healing capacity is attributed to reduced focal adhesion
formation and weakened adhesion strength of ACLF in the presence of HMWHA. This study
identifies HMWHA exclusion as a potential therapeutic strategy and provides insight
into the mechanism by which traditional primary repair of the ACL, as well as graft
reconstructions, may fail.
Keywords
ACL - tissue engineering - cell biology
