Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin Induces Cellugyrin-(Synaptogyrin 2) Dependent Cellular Senescence in Oral Keratinocytes

Abstract

Recently, we reported that oral-epithelial cells (OE) are unique in their response to Aggregatibacter actinomycetemcomitans cytolethal distending toxin (Cdt) in that cell cycle arrest (G2/M) occurs without leading to apoptosis. We now demonstrate that Cdt-induced cell cycle arrest in OE has a duration of at least 7 days with no change in viability. Moreover, toxin-treated OE develops a new phenotype consistent with cellular senescence; this includes increased senescence-associated β-galactosidase (SA-β-gal) activity and accumulation of the lipopigment, lipofuscin. Moreover, the cells exhibit a secretory profile associated with cellular senescence known as the senescence-associated secretory phenotype (SASP), which includes IL-6, IL-8 and RANKL. Another unique feature of Cdt-induced OE senescence is disruption of barrier function, as shown by loss of transepithelial electrical resistance and confocal microscopic assessment of primary gingival keratinocyte structure. Finally, we demonstrate that Cdt-induced senescence is dependent upon the host cell protein cellugyrin, a homologue of the synaptic vesicle protein synaptogyrin. Collectively, these observations point to a novel pathogenic outcome in oral epithelium that we propose contributes to both A. actinomycetemcomitans infection and periodontal disease progression.

Cellugyrin (synaptogyrin-2) dependent pathways are used by bacterial cytolethal distending toxin and SARS-CoV-2 virus to gain cell entry

“…Recently, we determined that cellugyrin plays a requisite role in the internalization and endosomal trafficking of Cdts ( Boesze-Battaglia et al., 2016 ; Boesze-Battaglia et al., 2017 ; Boesze-Battaglia et al., 2020 ). To date, we have demonstrated that cellugyrin expression in human lymphocytes, macrophages and, more recently, oral keratinocytes is required for toxin entry and subsequent intoxication of these cells ( Boesze-Battaglia et al., 2016 ; Boesze-Battaglia et al., 2017 ; Boesze-Battaglia et al., 2020 ; Shenker et al, 2024 ). Cdts are produced by more than 30 γ- and ϵ-Proteobacteria; indeed, we have shown that cellugyrin is required for at least three Cdts produced by Aggregatibacter actinomycetemcomitans ( Aa Cdt), Haemophilus ducreyi ( Hd Cdt) and Campylobacter jejuni ( Cj Cdt) ( Boesze-Battaglia et al., 2017 ; Boesze-Battaglia et al., 2020 ; Huang et al., 2021 ).…”