In vitro effects of oral bacteria on mesenchymal stem cells

The loss of periodontal tissues is considered as the critical manifestation of periodontitis. Numerous different therapies have been developed, including surgical strategies, grafts, membranes, and the application of growth factors. Nevertheless, complete regeneration is still a challenge. Recent studies showed that stem cell-based-therapies become a promising strategy. The immunomodulatory functions, the self renewal capacity and the potential to differentiate into several types of tissue cells make mesenychmal stem cells (MSC) an interesting therapeutical tool. However, for their potential application in periodontal regeneration therapies the effect of physiological and pathogenic oral bacteria on MSC has to be elucidated. Objectives: In this study we tried to establish a model to investigate the interaction of oral bacteria with MSC. Methods: Porphyromonas gingivalis (Pg), Fusobacterium nucleatum (Fn) and two strains of Aggregatibacter actinomycetemcomitans (Aa and AaHK) were chosen as periodontal pathogens. As representatives for the physiological flora the two strains Streptococcus sanguinis Sang and SangSK were tested. The viability of cells and bacteria was pretested under aerobic and anaerobic conditions. After this the microorganisms were inoculated to a monolayer of MSC and cultivated under anaerobic conditions. The cell and bacteria mortality was determined by Fluorescence microscopy after LIVE/DEAD staining. To document morphological aspects safranin staining and scanning electron microscopy was applied. Cytotoxic effects of the bacteria on MSC were analyzed by Lactat-Dehydrogenase (LDH) measurement. Furthermore, adherence to and internalization into MSC was tested. Results: We were able to show that MSC can survive under anaerobic conditions for more than three days. The co-cultivation of MSC with S. sanguinis resulted in a good adherence of S. sang to the MSC. Conclusion: Overall, our results revealed species specific bacterial interactions with human mesenchymal stem cells. To elucidate the underlying mechanisms will be part of future studies.