The expression of cyclic GMP–AMP synthase in human apical periodontitis: A laboratory investigation

Abstract Aim As a key DNA sensor, cyclic GMP–AMP synthase (cGAS) has emerged as a major mediator of innate immunity and inflammation. Human apical periodontitis has yet to be studied for the presence of cGAS. This investigation was conducted to determine if cGAS is involved in the pathological process of human apical periodontitis. Methodology Sixty four human periapical lesions, comprising 20 periapical granulomas and 44 radicular cysts, were employed in this investigation. Healthy gingiva ( n = 6), dental pulp ( n = 3), and apical papilla ( n = 3) were used as control samples. The expression of cGAS in the periapical tissues was discovered using immunohistochemical staining. mRNA‐Sequencing and qRT‐PCR were utilized to determine the differentially expressed genes (DEGs) associated with DNA‐sensing signalling in periapical lesions compared to the healthy control. Immunofluorescence labelling was used to identify the co‐expression of cGAS, interleukin‐1β, and interleukin‐18. Results A significantly greater expression level of cGAS was discovered in the periapical lesions, with no significant difference between radicular cysts and periapical granulomas. mRNA‐Sequencing analysis and qRT‐PCR identified differentially expressed mRNA, such as cGAS and its downstream DEGs, between periapical lesions and healthy control tissues. Immunofluorescence labelling further revealed that cGAS, interleukin‐1, and interleukin‐18 were co‐localized. Conclusions These observations imply that along with the synthesis of interleukin‐1 and interleukin‐18, cGAS may be involved in the aetiology of apical periodontitis.