scRNA-seq of periodontal granulation tissue and periodontally inflamed gingiva

Periodontal granulation tissue is formed during the wound healing process and contributes to subsequent repair or regeneration. However, periodontitis causes the presence of unwanted mass of persistently inflamed granulation tissues in periodontal osseous defects, are routinely eliminated and discarded for anticipated better treatment outcomes. Nevertheless, the emerging evidence of microbiome and histological profiles strongly encourages further studies on this considerable issue and the potential clinical implications. Here, we collected the granulation tissues from pocket wall via excision (PT) and osseous defect (GT) during periodontal surgery, and those attaching on the extracted root surfaces (RT) and remaining in the extraction sockets (ST) during tooth extraction. Subsequently, these samples were used for histological assessment, 16S rRNA sequencing of intra-tissue microbiome and single-cell sequencing (scRNA-seq). The origin-based distinguishment of granulation tissue was well reflected by the clinical and biological characteristics. Conceivably, the periodontal parameters at the involved teeth of RT and ST were more deteriorated than those of GT and PT, which was also reflected with the enrichment of genera of periodontopathogens like Porphyromonas and the depletion of commensals such as Rothia and Neisseria in RT and ST. Further scRNA-seq revealed higher proportion of mesenchymal stem cells and fibroblasts while fewer natural killer cells in GT than those in both PT and ST, in line with elevated wound healing scores and decreased inflammatory response scores. Pseudotime trajectory analysis demonstrated the apparent differentiation of stroma cells among these tissues. Histological examination exhibited a less extent of inflammatory infiltration and CD4+ and NKG2D+ immunoreaction in GT, as compared to other tissue types. Collectively, these findings show the salubriousness of osseous GT and deleteriousness of socket-originated RT and ST in terms of clinical, microbiome and cellular attributes. This work could facilitate the development of novel strategies for potentiating and enhancing periodontal treatment outcomes.