2015 ISAKOS Biennial Congress ePoster #304
Relaxin Signaling in Female Verses Male Human Anterior Cruciate Ligament Tenocytes
Jason L. Dragoo, MD, Englewood, CO UNITED STATES
Malcolm DeBaun, MD, Palo Alto, CA UNITED STATES
Ross Bathgate, PhD, Victoria AUSTRALIA
Stanford University, palo Alto, CA, USA
FDA Status Not Applicable
Summary: These results support our hypothesis that relaxin induces increased intracellular signaling and decreased collagen expression in female tenocytes, when compared to males.
Women are more likely to injure their anterior cruciate ligament (ACL) than men. Preclinical and clinical data suggests relaxin is a collagenlytic hormone that may contribute to the gender discrepancy in the incidence of anterior cruciate ligament (ACL) injury. We hypothesize: 1) relaxin binding induces cellular activity as measured by cyclic adenosine monophosphate (cAMP) production in ACL tenocytes and decreases collagen expression; 2) this response is gender dependent.
After Institutional Review Board approval, female and male ACL tissue was harvested. Tenocytes were isolated and expanded in vitro. To test cAMP production, cells were primed with 1µM forskolin and stimulated with 10 pM relaxin in the presence of 50 µM of 3-isobutyl-1-methylxanthine. After a 30 minute incubation, cells were lysed and intracellular cAMP levels were determined using a cAMP enzyme linked immunoassay. To test collagen expression, cells were incubated in the presence of relaxin at different concentrations for 72 hours. Before relaxin incubation, cells were primed with 1µM 17b-estradiol for 72 hours. After incubation with hormone, cells were lysed and analyzed for collagen type I and collagen type III mRNA expression using real-time reverse-transcription polymerase chain reaction.
After exposure to relaxin, cyclic AMP production was significantly increased in female ACL cells primed with forskolin when compared to male cells (Figure 1). Relaxin decreased collagen type I and collagen type III expression in female ACL cells at various concentrations (Figure 2), but not in male ACL cells (Figure 3).
Discussion And Conclusion
This study provides further evidence that relaxin may contribute to the 2-9 fold increased risk of female athlete ACL injury when compared to males. To our knowledge, this data is the first to provide evidence that relaxin induces intracellular changes in ACL cells. These results support our hypothesis that relaxin induces increased intracellular signaling and decreased collagen expression in female tenocytes, when compared to males. Relaxin sensitization may be a hormonal and potentially modifiable risk factor that contributes to the gender difference in ACL injury incidence.