Changes in Transcriptome-Wide Gene Expression of Anterior Cruciate Ligament Tears Based on Time From Injury

Background: Anterior cruciate ligament (ACL) tears are a common injury. The healing potential of the injured ACL is poorly understood and is considered limited. Therefore, most ACL tears that are treated surgically undergo reconstruction rather than repair. However, there has been renewed interest recently in repairing ACL tears despite unanswered questions regarding the healing capacity of the ACL. Hypothesis: Gene expression in the injured ACL varies with time from injury. Study Design: Descriptive laboratory study. Methods: Transcriptome-wide expression profiles of 24 human ACL remnants recovered at the time of surgical reconstruction were analyzed using the Agilent human 8x60K microarray platform. Gene ontology was performed on differentially expressed transcripts based on time from injury (acute, <3 months; intermediate, 3-12 months; chronic, >12 months). A subset of transcripts with large fold changes in expression between any 2 categories was validated via microfluidic digital polymerase chain reaction. Results: Numerous transcripts representing important biological processes were differentially expressed by time from injury. The most significant changes were noted between the acute and chronic groups. Expression of several extracellular matrix genes namely, POSTN, COL5A1, COL1A1, and COL12A1was lower in the chronic tears compared with acute and intermediate tears. In acute tears, processes representing angiogenesis and stem cell differentiation were affected. In intermediate tears, processes representing stem cell proliferation concomitant with cellular component organization/cellular localization were altered. In ACL tears more than 12 months out from injury, processes denoting myosin filament organization, cellular component organization/cell localization, and extracellular matrix organization were affected. Conclusion: These findings are consistent with initial repair activity in the injured ACL, which declines with time from injury. Individual genes identified in this study, such as periostin, deserve further investigation into their role in tissue repair. Clinical Relevance: The decreased healing capacity of ACL tears over time is relevant to the development of effective techniques for repairing ACL tears and may have some significance for ACL reconstruction techniques as well. The potential for healing appears to be greatest in acute ACL tears, suggesting this window should be the focus of research for ACL repair.