Integrin and fibronectin guide bridging movement of remnants during anterior cruciate ligament spontaneous healing in rat model

Introduction/Background Cells communicate with extracellular matrix (ECM) through the some essential components of mechano-biological factors. Integrin and fibronectin are known as a connecting organizer between ECM and the cells. Moreover, these are also known as a sensor of mechanical cues. In this study, we focus the function of this sensor of mechanical cue to elucidate the mechanism of anterior cruciate ligaments. Material and method All experiment used 10-week-old male Wistar rats after more than 2 weeks of acclimatization. Initially, 4 rats had their ACL transected, which were divided into 2 groups: ACL transection (ACL-T) groups and ACL transection and controlled abnormal tibial translation (CATT) groups. These rats were then used for a microarray analysis. Next, 40 rats were distributed across the 4 groups based on two factors for comparing controlled abnormal tibial translation and treadmill exercise (sedentary and exercise): ACL transection sedentary or exercise groups (ACLT-Sed or ACLT-Ex), or the controlled abnormal tibia translation sedentary or exercise groups (CATT-Sed or CATT-Ex). Contralateral knees (intact ACL [IN]) of ACLT-Sed rats were used as controls. These rats were used in RT-qPCR. Results The relative expression of ACL remnants had no remarkable changes between groups. However, the relative mRNA expression of infra-patellar fat pad in the both CATT groups had an increasing trend compared to the both non-exercise group. Conclusion Integrin and fibronectin have a key role in ACL spontaneous healing as a sensor of mechanical cues. These protein works at the infra-patellar fad pad, not at ACL remnants. These results suggest that infra-patellar fad pad works mechanosensor in knee joint, and in detail, these functions may support by the integrin and fibronectin.