Resolution phase agonists &bone remodeling
Authors: Παπαθανασίου Ευάγγελος 
Published: September 2021

Periodontitis is the 6th most prevalent disease in the world and the primary cause for tooth loss in adults. The host immune response plays a key role in bacteria-induced alveolar bone resorption. Endogenous control of the magnitude and duration of inflammatory signaling is considered an important determinant of the extent of periodontal pathology. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine signaling pathways and may play a role in controlling periodontal inflammation. SOCS proteins are also considered crucial intracellular mediators of the anti-inflammatory actions of lipid mediator agonists including resolvins such as RvE1. We hypothesized that SOCS-3 regulates inflammatory cytokine signaling and alveolar bone loss in experimental periodontitis and that the anti-inflammatory actions of RvE1 are SOCS-3 dependent. Periodontal bone loss was induced in myeloid-specific SOCS-3-knockout (KO) and SOCS-3-wild-type (WT) C57Bl6-B.129 mice by oral inoculation with 1×109 colony-forming units (CFU) P. gingivalis A7436 using an oral gavage model for periodontitis. Sham controls for both types of mice received vehicle without bacteria. The mice were euthanized 6 weeks after the last oral inoculation. Morphometric, histomorphometric, and µCT analyses were performed to assess alveolar bone loss. Peritoneal macrophages were elicited with 4% thioglycolate broth and isolated from myeloid SOCS-3-KO and SOCS-3-WT mice by differential centrifugation. Macrophages were cultured at a concentration of 1.5×106 cells/ml in 6-well plates. After 2 hours, non-adherent cells were discarded and the remaining adherent cells were treated with either culture medium alone (control) or with 100 ng/ml P. gingivalis A7436 LPS or with culture medium and 100nM RvE1 or with 100 ng/ml P. gingivalis A7436 LPS and RvE1 100nM (n≥3 wells per group). Supernatants and cells were collected after 12 hours. Cytokine levels were assessed using Luminex multiplex bead immunoassay and RNA was extracted by Trizol and processed for qRT-PCR. Increased bone loss was demonstrated in P. gingivalis-infected SOCS-3- KO mice compared to P. gingivalis-infected WT mice by direct morphological measurements, µCT analyses and quantitative histology. Loss of SOCS-3 function resulted in increased number of alveolar bone osteoclasts and increased RANKL expression after P. gingivalis infection. SOCS-3 deficiency in myeloid cells also promoted a higher P. gingivalis LPS-induced inflammatory response by inducing a higher secretion of IL-1β, IL-6, TNF-α and KC (IL-8) by peritoneal macrophages from SOCS-3-KO mice. 100nM RvE1 resulted in a significant decrease in P. gingivalis LPS-induced secretion of IL-6, TNF-α and IL-8 by increasing mRNA expression of SOCS-3 and ERV1 in macrophages from SOCS-3-WT mice compared to macrophages from myeloid SOCS-3-KO ones. Our data implicate SOCS-3 as a critical negative regulator of alveolar bone loss in experimental periodontitis and P. gingivalis LPS-induced inflammatory response. SOCS-3 regulates the anti-inflammatory actions of RvE1 on P. gingivalis LPS-induced inflammatory cytokines in macrophages. Understanding further the role of SOCS proteins in regulating periodontal inflammation may provide novel pathways of host susceptibility to periodontitis and new therapeutic targets for modulating the immune response to achieve successful resolution of periodontal inflammation.