Porphyromonas gingivalis is a keystone pathogen of periodontitis. Outer membrane vesicles (OMVs) have been considered as both offense and defense components of this bacterium. Previous studies indicated that like their originating cells, P. gingivalis vesicles, are able to invade oral epithelial cells and gingival fibroblasts, in order to promote aggregation of some specific oral bacteria and to induce host immune responses. In the present study, we investigated the invasive efficiency of P. gingivalis OMVs and compared results with that of the originating cells. Results revealed that 70–90% of human primary oral epithelial cells, gingival fibroblasts, and human umbilical vein endothelial cells carried vesicles from P. gingivalis 33277 after being exposed to the vesicles for 1 h, while 20–50% of the host cells had internalized P. gingivalis cells. We also detected vesicle-associated DNA and RNA and a vesicle-mediated horizontal gene transfer in P. gingivalis strains, which represents a novel mechanism for gene transfer between P. gingivalis strains. Moreover, purified vesicles of P. gingivalis appear to have a negative impact on biofilm formation and the maintenance of Streptococcus gordonii. Our results suggest that vesicles are likely the best offence weapon of P. gingivalis for bacterial survival in the oral cavity and for induction of periodontitis.

The association between mucosal microbiota and HIV-1 infection has garnered great attention in the field of HIV-1 research. Previously, we reported a receptor-independent HIV-1 entry into epithelial cells mediated by a Gram-negative invasive bacterium, Porphyromonas gingivalis. Here, we present evidence showing that P. gingivalis outer membrane vesicles (OMVs) promote mucosal transmission of HIV-1. We demonstrated, using the Dynabeads technology, a specific interaction between HIV-1 and P. gingivalis OMVs which led to an OMV-dependent viral entry into oral epithelial cells. HIV-1 was detected in human oral keratinocytes (HOKs) after a 20 minute exposure to the HIV-vesicle complexes. After entry, most of the complexes appeared to dissociate, HIV-1 was reverse-transcribed, and viral DNA was integrated into the genome of HOKs. Meanwhile, some of the complexes exited the original host and re-entered neighboring HOKs and permissive cells of HIV-1. Moreover, P. gingivalis vesicles enhanced HIV-1 infection of MT4 cells at low infecting doses that are not able to establish an efficient infection alone. These findings suggest that invasive bacteria and their OMVs with ability to interact with HIV-1 may serve as a vehicle to translocate HIV through the mucosa, establish mucosal transmission of HIV-1, and enhance HIV-1 infectivity.

Hydroxyurea (HU), the first of two drugs approved by the US Food and Drug Administration for treating patients with sickle cell disease (SCD), produces anti-sickling effect by re-activating fetal γ-globin gene to enhance production of fetal hemoglobin. However, approximately 30% of the patients do not respond to HU therapy. The molecular basis of non-responsiveness to HU is not clearly understood. To address this question, we examined HU-induced changes in the RNA and protein levels of transcription factors NF-Y, GATA-1, -2, BCL11A, TR4, MYB and NF-E4 that assemble the γ-globin promoter complex and regulate transcription of γ-globin gene. In erythroblasts cultured from peripheral blood CD34+ cells of patients with SCD, we found that HU-induced changes in the protein but not the RNA levels of activator GATA-2 and repressors GATA-1, BCL11A and TR4 correlated with HU-induced changes in fetal hemoglobin (HbF) levels in the peripheral blood of HU high and low responders. However, HU did not significantly induce changes in the protein or RNA levels of activators NF-Y and NF-E4. Based on HU-induced changes in the protein levels of GATA-2, -1 and BCL11A, we calculated an Index of Hydroxyurea Responsiveness (IndexHU-3). Compared to the HU-induced fold changes in the individual transcription factor protein levels, the numerical values of IndexHU-3 statistically correlated best with the HU-induced peripheral blood HbF levels of the patients. Thus, IndexHU-3 can serve as an appropriate indicator for inherent HU responsiveness of patients with SCD.