Characterizing Nociceptor-Macrophage-Periodontal Ligament Cell Crosstalk in Inflammation.

Objectives: This study aims to characterize the mechanism of interaction between nociceptors, macrophages, and periodontal ligament cells in inflammation.
Methods: To assess neuronal response to inflammation, conditioned media from LPS-treated human periodontal ligament (hPDL) cells and macrophages (MQ) were applied to hPDL-derived nociceptors (hPDL-N). Conditioned media from LPS-treated-hPDL-N were applied to hPDL cells and MQ to assess the effect of nociceptors on these cells. Expression of Substance P (SP), CGRP, TNF-α, IL-1β, IL-6, TGF-β1, and IL-10 were assessed at 1h and 3h. Statistical analyses t-test and one-way ANOVA with Tukey's multiple comparisons test were used (p< 0.05).
Results: LPS-treated hPDL monocultures and MQ monocultures increased SP/CGRP ratio in hPDL-N. hPDL monocultures did not elicit IL-1β and TNF-α expression in hPDL-N, however, MQ monocultures increased hPDL-N expression of TNF-α as TGF-β1 levels remained unchanged. hPDL-MQ cocultures resulted in increased SP/CGRP ratio, IL-1β , TNF-α, and IL-6 in hPDL-N at 3h indicating a delayed proinflammatory response.

hPDL-N did not trigger CGRP expression in hPDL or MQ monocultures but resulted in increased SP expression in hPDL cells. hPDL levels of TGF-β1 and IL-6 were downregulated, and these did not express any IL-1β and TNF-α when subject to hPDL-N+LPS. MQ monocultures released IL-1β with unchanged levels of TNF-α, IL-10 at 3h. TGF-β1 levels were downregulated in this group. hPDL-MQ cocultures expressed SP and CGRP and showed increased TNF-α, IL-1β expression at 3h. IL-6 expressions remained low in all groups at both time points.
Conclusions: This study highlights immunomodulatory effects of nociceptors in periodontitis, which is influenced by crosstalk with macrophages and periodontal ligament cells. SP and CGRP regulate the expression of IL-1β, TNF-α, and TGF-β1 such that there is an early immunosuppressive effect in the presence of nociceptors.