Transcriptional Response of Mouse Fibroblasts to Porphyromonas gingivalis Infection

Objectives: A complex set of interactions between the host and Porphyromonas gingivalis exists, however to date, these remain poorly understood. Especially the response of non-immune cells such as fibroblasts and epithelial cells is under investigated. We are comprehensively characterizing the fibroblast response to P. gingivalis W83. In addition, we want to characterize the contribution of the metabolic state of the bacteria to the host response.

Methods: For our studies we used murine NIH3T3 fibroblasts. The cells were infected with P. gingivalis at MOI of 1:100 for 4h, 8h, and 21h. RNA was isolated from infected cells and analyzed using spotted oligonucleotide microarrays containing probes for all open reading frames predicted to be present on the mouse genome. RNA derived from live and heat-killed bacteria was quantified using qRT-PCR arrays.

Results: A greater number of genes are regulated in the bacteria-challenged cells at the 21 hour time point than at the 8 hour time point post infection. Interestingly, even though the response is delayed, expression of approximately 600 genes was altered after 21 hours of challenge with P. gingivalis. Furthermore, we found morphological as well as transcriptional differences between live- and heat killed-bacteria infected cells. Some genes were up-regulated at the 4 hour time point and then down-regulated at 21 hours post-infection, and the expression of others was unchanged for the heat-killed bacteria challenged cells and significantly changed for live-bacteria infected cells.

Conclusions: The fibroblast response to P. gingivalis infection is time dependent. Also, metabolically active bacteria elicit different response when compared with heat-killed bacteria. We expect this work will lead to a better understanding of the host response to P. gingivalis and ultimately will assist in development of new treatments of periodontal diseases.

These studies were supported from VCU A.D. Williams Fellowship to Poonum Bharal and 5RO1DE016124 to J.P. Lewis.