Periodontitis is the most common chronic inflammatory disease caused by complex interaction between the microbial biofilm and host immune responses. In the present study, high-throughput RNA sequencing was utilized to systemically and precisely identify gene expression profiles and alternative splicing. The pooled RNAs of 10 gingival tissues from both healthy and periodontitis patients were analyzed by deep sequencing followed by computational annotation and quantification of mRNA structures. The differential expression analysis designated 400 up-regulated genes in periodontitis tissues especially in the pathways of defense/immunity protein, receptor, protease, and signaling molecules. The top 10 most up-regulated genes were CSF3, MAFA, CR2, GLDC, SAA1, LBP, MME, MMP3, MME-AS1, and SAA4. The 62 down-regulated genes in periodontitis were mainly cytoskeletal and structural proteins. The top 10 most down-regulated genes were SERPINA12, MT4, H19, KRT2, DSC1, PSORS1C2, KRT27, LCE3C, AQ5, and LCE6A. The differential alternative splicing analysis revealed unique transcription variants in periodontitis tissues. The EDB exon was predominantly included in FN1, while exon 2 was mostly skipped in BCL2A1. These findings using RNA sequencing provide novel insights into the pathogenesis mechanism of periodontitis in terms of gene expression and alternative splicing.

Periodontitis is caused by an oral microbial dysbiosis-mediated imbalance of the local immune microenvironment, which is promoted by insulin resistance and obesity. The prevalence and severity of periodontitis is higher in patients with type 2 diabetes than in healthy individuals, possibly because of differences in immune responses. The level of glycemic control also affects the saliva profile, which may further promote periodontal disease in diabetes patients. Therefore, we compared the salivary exosomal miRNA profiles of patients with type 2 diabetes with those of healthy individuals, and we found that exosomal miR-25-3p in saliva is significantly enriched (by approximately 2-fold, p < 0.01) in obese patients with type 2 diabetes. We also identified CD69 mRNA as a miR-25-3p target that regulates both activation of γδ T cells and the inflammatory response. Knockdown of CD69 increased (by approximately 2-fold) interleukin-17A production of γδ T cells in vitro. To evaluate the role of exosomal miRNA on progression of periodontitis, we analyzed regional immune cells in both periodontal tissues and lymph nodes from mice with periodontitis. We found that diet-induced obesity increased the population of infiltrating pro-inflammatory immune cells in the gingiva and regional lymph nodes of these mice. Treatment with miR-25-3p inhibitors prevented the local in vivo inflammatory response in mice with periodontitis and diet-induced obesity. Finally, we showed that suppression of interleukin 17-mediated local inflammation by a miR-25-3p inhibitor alleviated (by approximately 34%) ligature-induced periodontal alveolar bone loss in mice. Taken together, these data suggest that exosomal miR-25-3p in saliva contributes to development and progression of diabetes-associated periodontitis. Discovery of additional miR-25-3p targets may provide critical insights into developing drugs to treat periodontitis by regulating γδ T cell-mediated local inflammation.

Background: Although increasing evidence indicates that serotonin (SER; 5‐hydroxytrypamine [5‐HT]) is involved in the regulation of bone metabolism, conflicting data exist regarding whether SER promotes or inhibits osteoblast differentiation and bone formation. Regeneration of functional bone is required for proper osseointegration of dental implants. Noticeably, the use of selective SER reuptake inhibitors was recently associated with the failure of osseointegrated dental implants. The present study examines the direct role of peripheral SER on the regulation of bone regeneration.Methods: The effect of SER on osteoblast differentiation and bone regeneration was examined using rat calvarial cell cultures in vitro and a rat critical‐sized calvarial defect model in vivo.Results: Rat calvarial cells expressed SER receptors Htr1 (5‐HT1) and Htr2 (5‐HT2), which are known to transmit signals in bone cells. In vitro, SER significantly reduced osteogenic differentiation and mineralization of rat calvarial cells with concomitant reduction of osteoblast marker genes including alkaline phosphatase (Alpl), osterix (Sp7), and osteocalcin (Bglap). Histologic and radiologic analyses using the rat critical‐sized calvarial defect model revealed that the existence of SER significantly inhibited β‐phase tricalcium phosphate–induced bone regeneration.Conclusion: Results suggest that SER in the local bone microenvironment might play a negative role in osteoblast differentiation and bone formation in rats.

Lee JE, et al. J Periodontal Implant Sci. 2017 Jun;47(3):134-142. https://doi.org/10.5051/jpis.2017.47.3.134