Lys-specific gingipain (Kgp) of <i>P. gingivalis</i> promotes viral infection by disabling the interferon pathway

Periodontitis (PD) is a chronic inflammatory disease of the periodontium with a high prevalence and is considered a potential risk factor for the development of other diseases. These include viral infections of the upper and lower respiratory tracts, including those caused by the <i>Herpesviridae</i> family, human immunodeficiency virus, hepatitis C and B viruses, influenza virus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which have been identified with greater frequency in patients with PD. The underlying molecular mechanisms that underpin this comorbidity remain to be elucidated; however, the compromised capacity of the oral mucosa-associated antiviral response is a plausible explanation. Driven by clinical data that revealed the <i>Herpesviridae</i> family as the most commonly identified viruses in PD patients, this study was aimed to determine the effect of <i>Porphyromonas gingivalis</i>, the key etiological factor in periodontitis, on the development of herpes simplex virus-1 (HSV-1) infection. Using a model of the human gingiva, it was demonstrated that <i>P. gingivalis</i> significantly increases infection with HSV-1, promoting tissue distribution and propagation of the virus. This phenomenon can be attributed to the impairment of the interferon response, a consequence of proteolytic modifications of major signaling components catalyzed by Kgp gingipain. Furthermore, <i>P. gingivalis</i> infection has been observed to promote reactivation of HSV-1 in neuronal cells but via IFN-independent mechanism. These findings, demonstrating the attenuation of the host defense, expand our basic knowledge of the mechanisms underlying polymicrobial infections and clarify the observed comorbidity of PD with viral disorders.IMPORTANCEPeriodontitis (PD) is a chronic inflammatory disease of the gingiva, with a high prevalence. Clinical reports indicate the significant role of PD in the development of comorbidities, including <i>Herpesviridae</i> infections; however, the molecular basis of this phenomenon has not yet been described. In our work, we uncovered a novel molecular mechanism by which the interferon-dependent antiviral response is tailored by the cysteine protease of <i>P. gingivalis</i>-Kgp. Using gingival keratinocytes and a model of human gingiva, we have demonstrated that lysin-specific gingipain attenuates the antiviral response and promotes the propagation of herpes simplex virus-1, which is one of the most frequently identified viruses in patients suffering from PD. These findings expand our knowledge of the mechanisms underlying polymicrobial infections and may provide a basis for considering PD as a gateway to viral infection.