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 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 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 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.
