Sex, collagen expression, and anterior cruciate ligament strength in rats

Context: Sex-specific responses to steroid sex hormones have been suggested as a potential cause for the disparate anterior cruciate ligament (ACL) injury rates between male and female athletes. Type 1 collagen (T1C) and type 3 collagen (T3C) are crucial structural components that define the ligament's ability to withstand tensile loads. Messenger RNA (mRNA) is an important mediator of downstream collagen synthesis and remodeling, but the sex-specific mechanisms of collagen mRNA expression and ACL strength are unknown. Objective: To examine the influence of sex on T1C and T3C mRNA expression and mass-normalized stiffness and peak failure load in the ACLs of skeletally mature rats. Design: Observational study. Setting: Basic sciences and biomechanical testing laboratories. Patients or Other Participants: Nineteen 12-week-old male (n = 9) and female (n = 10) Sprague Dawley rats. Main Outcome Measure(s): We used real-time polymerase chain reaction to determine T1C and T3C mRNA expression and a hydraulic materials testing device to measure ACL stiffness and failure load. Nonparametric Wilcoxon rank sum tests were used to compare the groups. Results: Female rats had lower amounts of T3C mRNA expression and higher normalized ACL tangent stiffness and failure load than male rats. Conclusions: These findings suggest that sex-specific differences in T1C and T3C mRNA expression may play an important role in the downstream mechanical properties of the ACL.