Cytokine Secretion, Viability, and Real-Time Proliferation of Apical-Papilla Stem Cells Upon Exposure to Oral Bacteria

Abstract

The use of stem cells from the apical papilla (SCAPs) has been proposed as a means of promoting root maturation in permanent immature teeth, and plays a significant role in regenerative dental procedures. However, the role of SCAPs may be compromised by microenvironmental factors, such as hypoxic conditions and the presence of bacteria from infected dental root canals. We aim to investigate oral bacterial modulation of SCAP in terms of binding capacity using flow cytometry and imaging, real-time cell proliferation monitoring, and cytokine secretion (IL-6, IL-8, and TGF-β isoforms) under anaerobic conditions. SCAPs were exposed to key species in dental root canal infection, namely Actinomyces gerensceriae, Slackia exigua, Fusobacterium nucleatum, and Enterococcus faecalis, as well as two probiotic strains, Lactobacillus gasseri strain B6 and Lactobacillus reuteri (DSM 17938). We found that A. gerensceriae, S. exigua, F. nucleatum, and E. faecalis, but not the Lactobacillus probiotic strains bind to SCAPs on anaerobic conditions. Enterococcus faecalis and F. nucleatum exhibited the strongest binding capacity, resulting in significantly reduced SCAP proliferation. Notably, F. nucleatum, but not E. faecalis, induce production of the proinflammatory chemokine IL-8 and IL-10 from SCAPs. Production of TGF-β1 and TGF-β2 by SCAPs was dependent on species, cell line, and time, but secretion of TGF-β3 did not vary significantly over time. In conclusion, SCAP response is compromised when exposed to bacterial stimuli from infected dental root canals in anaerobic conditions. Thus, stem cell-mediated endodontic regenerative studies need to include microenvironmental conditions, such as the presence of microorganisms to promote further advantage in the field.

Combined Transcriptomic and Protein Array Cytokine Profiling of Human Stem Cells from Dental Apical Papilla Modulated by Oral Bacteria

“…In agreement with our previous findings [22] using a V-PLEX human biomarker multiplex assay, F. nucleatum, but not E. faecalis, induced cytokine production of the proinflammatory chemokines IL-8 and IL-10 in SCAP. In the current study, we showed that viable F. nucleatum upregulated the secretion of chemokines and cytokines such as GM-CSF, GROα, IL-6, IL-8, MCP-1, and VCAM-1, as detected by microarray and transcriptomics.…”

“…This pathway leads to a decrease in the immune response [44]. The pathway is activated by a TGF-β cytokine that was not included in the set of 105 cytokines applied on the membrane, but its secretion was analyzed in an earlier study [22].…”

“…Moreover, E. faecalis and F. nucleatum exhibited the strongest binding capacities, resulting in significantly reduced SCAP proliferation. Notably, F. nucleatum, but not E. faecalis, induced production of the proinflammatory chemokines IL-8 and IL-10 from SCAP [22]. Accordingly, results from the analyzed cytokines should be expanded and the effects of a broad variety of inflammatory cytokines further explored.…”

“…Clinical isolates of F. nucleatum subsp. polymorphum and Enterococcus faecalis were used in this study for their impact on SCAP [22].…”

Molecular Biological Comparison of Dental Pulp- and Apical Papilla-Derived Stem Cells

“…In contrast, IL-8 was released only in low levels by DPSC as well as SCAP under standard conditions; however, a considerable increase was observed during osteogenic differentiation, especially in SCAP. Interestingly, a recent study also measured high levels of proinflammatory cytokines such as IL-8 released by SCAP exposed to different anaerobic oral bacteria [ 46 ]. In general, IL-8 promotes osteoclastogenesis and is associated with bone resorption [ 47 ].…”