Dental caries, one of the most prevalent infectious diseases worldwide, affects approximately 80% of children and the majority of adults. Dental caries may result in endodontic disease, leading to dental pulp necrosis, periapical inflammation and bone resorption, severe pain, and tooth loss. Periapical inflammation may also increase inflammation in other parts of the body. Although many studies have attempted to develop therapies for this disease, there is still an urgent need for effective treatments. In this study, we applied a novel gene therapeutic approach using recombinant adeno-associated virus (AAV)-mediated RNAi knockdown of Cathepsin K (Ctsk) gene expression, to target osteoclasts and periapical bone resorption in a mouse model. We found that AAV-sh-Cathepsin K (AAV-sh-Ctsk) impaired osteoclast function in vivo and furthermore reduced bacterial infection-stimulated bone resorption by 88%. Reduced periapical lesion size was accompanied by decreases in mononuclear leukocyte infiltration and inflammatory cytokine expression. Our study shows that AAV-RNAi silencing of Cathepsin K in periapical tissues can significantly reduce endodontic disease development, bone destruction, and inflammation in the periapical lesion. This is the first demonstration that AAV-mediated RNAi knockdown gene therapy may significantly reduce the severity of endodontic disease.

Background and Objective Periodontitis is a serious disease that affects the majority of adult population around the world. While great efforts have been devoted toward understanding the pathogenesis of periodontitis, there remains a pressing need for developing potent therapeutic strategies for targeting this dreadful disease. In this study, we utilized adeno-associated virus (AAV) expressing Cathepsin K (Ctsk) shRNA (AAV-sh-Ctsk) to silence Ctsk in vivo and subsequently evaluated its impact in periodontitis as a potential therapeutic strategy for this disease. Material and Methods We used a known mouse model of periodontitis, in which wild-type BALB/cJ mice were infected with Porphyromonas gingivalis W50 (P. gingivalis) in the maxillary and mandibular periodontium to induce the disease. AAV-sh-Ctsk was then administrated locally into the periodontal tissues in vivo, followed by analyses to assess the progression of the disease. Results AAV-mediated Ctsk silencing drastically protected mice (>80%) from P. gingivalis-induced bone resorption by osteoclasts. Also, AAV-sh-Ctsk administration drastically reduced inflammation by impacting the expression of many inflammatory cytokines as well as T cell and dendritic cell numbers in periodontal lesions. Conclusion AAV-mediated Ctsk silencing can simultaneously target both the inflammation and bone resorption associated with periodontitis through its inhibitory effect on immune cells and osteoclast function. Thereby, AAV-sh-Ctsk administration can efficiently protect against periodontal tissue damage and alveolar bone loss, establishing this AAV-mediated local silencing of Ctsk as an important therapeutic strategy for potently treating periodontal disease.