Gene expression of catabolic inflammatory cytokines peak before anabolic inflammatory cytokines after ACL injury in a preclinical model.
BACKGROUND
The response of the joint to anterior cruciate ligament (ACL) injury has not been fully characterized. In particular, the characterization of both catabolic factors, including interleukin-6 (IL-6), interleukin-8 (IL-8), and markers of ongoing tissue damage (CRP), and anabolic factors, including vascular endothelial growth factor (VEGF), transforming growth factor β-induced (TGFβI), and the presence of CD163+ macrophages, have not been well defined. In this study, we hypothesized ACL injury would catalyze both catabolic and anabolic processes and that these would have different temporal profiles of expression.


METHODS
Adolescent Yucatan minipigs were subjected to ACL transection. Within the joint, gene expression levels of IL-6, IL-8, VEGF, and TGFβI were quantified in the synovium, ligament, and provisional scaffold located between the torn ligament ends at days 1, 5, 9, and 14 post-injury. Macrophage infiltration was also assessed in the joint tissues over the two week period. Serum C-reactive protein (CRP) levels were measured at multiple time points between 1 hour to 14 days after injury.


RESULTS
Increases in IL-6 and IL-8 gene expression peaked at day 1 after injury in the synovium and ligament. CRP levels were significantly increased at day 3 before returning to pre-injury levels. VEGF and TGFβI gene expression did not significantly increase until day 9 in the synovium and were unchanged in the other tissues. CD163+ macrophages increased in the ligament and synovium until day 9.


CONCLUSIONS
Taken together, these results suggest that the response within the joint is primarily catabolic in the first three days after injury, switching to a more anabolic phase by nine days after injury. The effect of medications which alter these processes may thus depend on the timing of administration after injury.
Department of Orthopaedic Surgery, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115 USA.
Carla M
CM
Haslauer
Department of Orthopaedic Surgery, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115 USA.
Benedikt L
BL
Proffen
Department of Anesthesiology, Boston Children's Hospital, Boston, MA USA.
Victor M
VM
Johnson
Department of Orthopaedic Surgery, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115 USA ; Department of Genetics, Harvard Medical School, Boston, MA USA.
Adele
A
Hill
Department of Orthopaedic Surgery, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115 USA.
Martha M
MM
Murray
ACL; Anabolic; CRP; Catabolic; Inflammation; Injury; Macrophage; Wound healing