Functional polymorphisms within the inflammatory pathway regulate expression of extracellular matrix components in a genetic risk dependent model for anterior cruciate ligament injuries.

OBJECTIVES

To investigate the functional effect of genetic polymorphisms of the inflammatory pathway on structural extracellular matrix components (ECM) and the susceptibility to an anterior cruciate ligament (ACL) injury.

DESIGN

Laboratory study, case-control study.

METHODS

Eight healthy participants were genotyped for interleukin (IL)1B rs16944 C>T and IL6 rs1800795 G>C and classified into genetic risk profile groups. Differences in type I collagen (COL1A1), type V collagen (COL5A1), biglycan (BGN) and decorin (DCN) gene expression were measured in fibroblasts either unstimulated or following IL-1β, IL-6 or tumor necrosis factor (TNF)-α treatment. Moreover, a genetic association study was conducted in: (i) a Swedish cohort comprised of 116 asymptomatic controls (CON) and 79 ACL ruptures and (ii) a South African cohort of 100 CONs and 98 ACLs. Participants were genotyped for COL5A1 rs12722 C>T, IL1B rs16944 C>T, IL6 rs1800795 G>C and IL6R rs2228145 G>C.

RESULTS

IL1B high-risk fibroblasts had decreased BGN (p=0.020) and COL5A1 (p=0.012) levels after IL-1β stimulation and expressed less COL5A1 (p=0.042) following TNF-α treatment. Similarly, unstimulated IL6 high-risk fibroblasts had lower COL5A1 (p=0.012) levels than IL6 low-risk fibroblasts. In the genetic association study, the COL5A1-IL1B-IL6 T-C-G (p=0.034, Haplo-score 2.1) and the COL5A1-IL1B-IL6R T-C-A (p=0.044, Haplo-score: 2.0) combinations were associated with an increased susceptibility to ACL injury in the Swedish cohort when only male participants were evaluated.

CONCLUSIONS

This study shows that polymorphisms within genes of the inflammatory pathway modulate the expression of structural and fibril-associated ECM components in a genetic risk depended manner, contributing to an increased susceptibility to ACL injuries.