Distinct gene expression profiles provoked by polyacrylamide beads (Biogel) during chronic and acute inflammation in mice selected for maximal and minimal inflammatory responses

Alveolar bone healing in mice genetically selected in the maximum (AIRmax) or minimum (AIRmin) inflammatory reaction

The exact role of inflammatory immune response in bone healing process is still unclear, but the success of the alveolar bone healing process seems to be associated with a moderate and transitory inflammatory response, while insufficient or exacerbated responses seems to have a detrimental influence in the healing outcome. In this context, we performed a comparative analysis of mice strains genetically selected for maximum (AIRmax) or minimum (AIRmin) acute inflammatory response to address the influence of inflammation genes in alveolar bone healing outcome. Experimental groups comprised 8-week-old male or female AIRmax and AIRmin submitted to extraction of upper right incisor, and evaluated at 0, 3, 7, 14 and 21 days after upper incision extraction by micro-computed tomography (μCT), histomorphometry, birefringence, immunohistochemistry and molecular (PCRArray) analysis. Overall, the results demonstrate a similar successful bone healing outcome at the endpoint was evidenced in both AIRmin and AIRmax strains. The histormophometric analysis reveal a slight but significant decrease in blood clot and inflammatory cells density, as well a delay in the bone formation in AIRmax strain in the early times, associated with a decreased expression of BMP2, BMP4, BMP7, TGFb1, RUNX2, and ALP. The evaluation of inflammatory cells nature reveals increased GR1+ cells counts in AIRmax strain at 3d, associated with increased levels of neutrophil chemoattractants such as CXCL1 and CXCL2, and its receptor CXCR1, while F4/80+ cell prevails in AIRmin strain at 7d. Also, our results demonstrate a relative predominance of M2 macrophages in AIRmin strain, associated with an increased expression of ARG1, IL10, TGFb, while M1 macrophages prevail in AIRmax, which parallel with increased IL-1B, IL-6 and TNF expression. At late repair stage, AIRmax presents evidences of increased bone remodeling, characterized by increased density of blood vessels and osteoclasts in parallel with decreased bone matrix density, as well increased levels of MMPs, osteoclastogenic and osteocyte markers. In the view of contrasting inflammatory and healing phenotypes of AIRmin and AIRmax strains in other models, the unpredicted phenotype observed suggests the existence of specific QTLs (Quantitative trait loci) responsible for the regulation 'sterile' inflammation and bone healing events. Despite the similar endpoint healing, AIRmax strain delayed repair was associated with increased presence of neutrophils and M1 macrophages, supporting the association of M2 cells with faster bone healing. Further studies are required to clarify the elements responsible for the regulation of inflammatory events at bone healing sites, as well the determinants of bone healing outcome.

miRNA Expression and Interaction with Genes Involved in Susceptibility to Pristane-Induced Arthritis

Pristane-induced arthritis (PIA) in mice is an experimental model that resembles human rheumatoid arthritis, a chronic autoimmune disease that affects joints and is characterized by synovial inflammation and articular cartilage and bone destruction. AIRmax and AIRmin mouse lines differ in their susceptibility to PIA, and linkage analysis in this model mapped arthritis severity QTLs in chromosomes 5 and 8. miRNAs are a class of small RNA molecules that have been extensively studied in the development of arthritis. We analyzed miRNA and gene expression profiles in peritoneal cells of AIRmax and AIRmin lines, in order to evaluate the genetic architecture in this model. Susceptible AIRmax mice showed higher gene (2025 vs 1043) and miRNA (240 vs 59) modulation than resistant AIRmin mice at the onset of disease symptoms. miR-132-3p/212-3p, miR-106-5p, miR-27b-3p, and miR-25-3p were among the miRNAs with the highest expression in susceptible animals, showing a negative correlation with the expression of predicted target genes (Il10, Cd69, and Sp1r1). Our study showed that global gene and miRNA expression profiles in peritoneal cells of susceptible AIRmax and resistant AIRmin lines during pristane-induced arthritis are distinct, evidencing interesting targets for further validation.