Date of Award

1-1-2021

Embargo Period

9-14-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oral Health Sciences

College

College of Graduate Studies

First Advisor

Özlem Yilmaz

Second Advisor

Besim Ogretmen

Third Advisor

Adam Smolka

Fourth Advisor

Adviye Ergul

Fifth Advisor

Andrew Jakymiw

Abstract

Porphyromonas gingivalis (P.g) is an important opportunistic pathogen and etiological agent in chronic periodontitis. As a major colonizer of oral mucosa, P.g uses multiple mechanisms to survive in human gingival epithelial cells (GECs), key initial defense cells of the oral cavity. Cell surface nucleotide-metabolizing enzyme, ectonucleotidase-CD73, has emerged as a central component of the homeostatic-machinery that counterbalances the danger-molecule, ATP-driven proinflammatory response in immune cells. While the importance of CD73 in microbial host fitness and symbiosis is gradually being unraveled, there remains a significant gap in knowledge of CD73 and its role in epithelial cells. Upon invasion of GECs, P.g significantly elevates host CD73 activity/expression concurrent with treatment of AMP. Enhanced induction of active CD73 increases P.g intracellular growth. Inhibition of CD73 markedly increases ROS generation upon eATP treatment in GECs, indicating active CD73 can function as a negative regulator of ROS. Interestingly, CD73 and P.g cross-modulation significantly abrogates pro-inflammatory IL-6 in GECs and exogenous IL-6 treatment to infected GECs suppresses the intracellular bacteria via amplified ROS production. However, CD73 overexpression significantly restores the reduced bacterial levels in GECs. Furthermore, temporal studies revealed CD73 suppresses pro-inflammatory STAT3 activation while P.g significantly decreases IL-6-induced STAT3 activation/phosphorylation in GECs. Functional studies via cellular transfection of GECs with recombinant P.g tyrosine-phosphatases showed significantly increased STAT3-dephosphorylation. When infected by isogenic P.g mutants lacking tyrosine-phosphatases, time-dependent STAT3-dephosphorylation by wildtype P.g is significantly reversed. Confocal microscopy further indicated P.g specifically utilizes the enzymes to deactivate phosphorylated STAT3 localized around the perinuclear space of GECs. Interestingly, isogenic P.g tyrosine-phosphatase mutants induce significantly elevated IL-6 production by GECs compared to wildtype P.g, resulting in compromised long-term intracellular survival. Together, these findings illuminate 1) the local extracellular-purine-metabolism, in which CD73 serves as a core molecular switch, can alter intracellular microbial colonization resistance; 2) host-adaptive pathogens such as P.g can target host ectonucleotidases, as well as pro-inflammatory cytokine IL-6 production via STAT3 activation; and 3) utilize bacterial tyrosine-phosphatases to disarm specific innate defenses for successful intracellular persistence in mucosal epithelia. Thus, we depict novel and specific cell-microbe adaptation mechanisms that can drive oral microbial-dysbiosis and may be targeted therapeutically in mucosa.

Rights

All rights reserved. Copyright is held by the author.

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Available for download on Monday, September 14, 2026

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