The experimental study of mir‐99a‐5p negative regulation of TLR8 receptor mediated‐mediated innate immune response in rabbit knee cartilage injury

Abstract Background Traumatic cartilage injury is an important cause of osteoarthritis (OA) and limb disability, and toll‐like receptors (TLRs) mediated innate immune response has been confirmed to play a crucial role in cartilage injury. In the previous study, we found that the activation of TLR8 molecules in injured articular cartilage was more obvious than other TLRs by establishing an animal model of knee impact injury in rabbits, and the changes of TLR8 molecules could significantly affect the process of articular cartilage injury and repair. Objective To verify how mir‐99a‐5p regulates TLR8 receptor mediated innate immune response to treat traumatic cartilage injury. Methods The impact of a heavy object on the medial condyle of the rabbit's knee joint caused damage to the medial condylar cartilage. Through pathological and imaging analysis, it was demonstrated whether the establishment of an animal model of traumatic cartilage injury was successful. Establishing a cell model by virus transfection of chondrocytes to demonstrate the role of TLR8 in the innate immune response to impact cartilage injury. Through transcriptome sequencing, potential targets of TLR8, mir‐99a‐5p, were predicted, and basic experiments were conducted to demonstrate how they interact with innate immune responses to impact cartilage damage. Results TLR8 is a receptor protein of the immune system, which is widely expressed in immune cells. In our study, we found that TLR8 expression is localized in lysosomes and endosomes. Mir‐99a‐5p can negatively regulate TLR8 to activate PI3K‐AKT molecular pathway and aggravate cartilage damage. Inhibiting TLR8 expression can effectively reduce the incidence of articular cartilage damage. Conclusion Based on the results from this study, mir‐99a‐5p may be an effective molecular marker for predicting traumatic cartilage injury and targeting TLR8 is a novel and promising approach for the prevention or early treatment of cartilage damage.