Papel de SOCS2 na modulação da resposta imune e perda óssea alveolar durante a infecção periodontal experimental induzida por Aggregatibacter actinomycetemcomitans

Abstract

Periodontal disease is an inflammatory disease that leads to loss of dental support structures. Proinflammatory cytokines play a critical role in the destruction of periodontal tissue. SOCS proteins have been shown to be key negative regulators of cytokine signaling in several tissues and may play a role in restraining periodontal inflammation. The induction of SOCS2 may represent a general pathway responsible for controlling several innate/adptative responses. However, the role of SOCS2 in osteoclastogenesis is still unclear. This study aimed to determine the role of SOCS2 in modulating host responses during experimental periodontal disease induced by Aggregatibacter actinomycetemcomitans (Aa). Alveolar bone loss was induced in 8- wk-old SOCS-2-knockout (Socs2-/- ) and wild-type (WT) mice by oral inoculation with 100 µL of an inoculum containing 109 CFU/mL of Aa with 1.5% of carboximetilcelulose, each 48 h for 7 days. Control mice receive only PBS. Mice were euthanized 30 days after the last oral inoculation. Socs2−/− mice intrinsically exhibited irregular phenotype in maxillary bone. After 30 and 60 days of infection, Socs2-/- mice presented increased alveolar bone loss when compared to infected WT mice. However, Socs2-/- mice had lower levels of pro-inflammatory cytokines such as IL-6 and TNF and showed an increase in levels of anti-inflammatory and pro-resolving mediator, Lipoxin A4. Socs2-/- mice also demonstrated a higher neutrophil influx, however there were no changes in RANKL expression on WT and Socs2-/- neutrophils membrane after LPS-Aa or Aa stimulation. Of note, Socs2-/- deficient neutrophils produced higher levels of TNF after LPS-Aa and Aa stimulus when compared to WT cells. Furthermore, the results showed a higher baseline amount of positive TRAP-positive cells in Socs2-/- mice, and that it remains stable during infection, unlike that observed in WT animals, where there is an increase in TRAPpositive cells during infection. Moreover, no differences in the amount of RANKL was observed after infection in Socs2-/- mice when compared to WT. In vitro studies have shown that bone marrow cells (BMC) from Socs2-/- mice presented higher differentiation in osteoclast than WT BMC. Of note, SOCS2 deficiency promoted lower Aa lipopolysaccharide-induced inflammatory response with lower secretion TNF and IL-6 by osteoclasts, and lower Aa-induced inflammatory response with lower secretion of TNF, IL-6, IL-1β and RANKL by fibroblasts, as compared with WT. BMCs-derived osteoclasts from Socs2−/− mice exhibited similar mRNA expression of Traf6, Cathepsin K, Rank, Ahr, and Myd88 observed in WT cells. However, Socs2−/− mice showed increased mRNA expression of Tlr4 48 h after RANKL+LPS-Aa stimulus. WB analysis of osteoclasts from Socs2-/- mice demonstrates increased baseline levels of TRAF6, c-FOS and NFATc1 that were decreased after stimulation with RANKL and LPS-Aa. Thus, our results suggested that SOCS2 may play an important role controlling alveolar bone loss in experimental periodontal disease induced by Aa, and this mechanism does not seem to be related to the control of inflammation, but it seems to play a direct role in the LPS-Aa signaling and osteocalstogenesis process.