Interleukin-33 Deficiency Exacerbates Bone Loss Associated with Porphyromonas Gingivalis-Induced Experimental Periodontitis in Female Mice.

BACKGROUND/AIMS: Interleukin 33 (IL-33) plays a significant role in immunity but its role in bone physiology and periodontitis needs to be further investigated. The aim of this study was to decipher the contribution of IL-33 to bone homeostasis under physiological conditions, and to alveolar bone loss associated with experimental periodontitis (EP) in IL-33 knockout (KO) mice and their wildtype (WT) littermates. METHODS: The bone phenotype of IL-33 KO mice was studied in the maxilla, femur, and fifth lumbar vertebra by micro-computed tomography (micro-CT). EP was induced by a ligature soaked with the periopathogen Porphyromonas gingivalis (Pg) around a maxillary molar. Alveolar bone loss was quantified by micro-CT. The resorption parameters were assessed via toluidine blue staining on maxillary sections. In vitro osteoclastic differentiation assays using bone marrow cells were performed with or without lipopolysaccharide from Pg (LPS-Pg). RESULTS: First, we showed that under physiological conditions, IL-33 deficiency increased the trabecular bone volume/total volume ratio (BV/TV) of the maxillary bone in male and female mice, but not in the femur and fifth lumbar vertebra, suggesting an osteoprotective role for IL-33 in a site-dependent manner. The severity of EP induced by Pg-soaked ligature was increased in IL-33 KO mice but in female mice only, through an increase in the number of osteoclasts. Moreover, osteoclastic differentiation from bone marrow osteoclast progenitors in IL-33-deficient female mice is enhanced in the presence of LPS-Pg. CONCLUSION: Taken together, our data demonstrate that IL-33 plays a sex-dependent osteoprotective role both under physiological conditions and in EP with Pg.

Dendritic-cell-derived osteoclasts: a new game changer in bone-resorption-associated diseases.

Bone-resorbing cells, osteoclasts (OCs), and antigen-presenting cells, dendritic cells (DCs), share several features. They are derived from a common hematopoietic precursor, exhibit phagocytic activities and their functions are dependent upon receptor activator of nuclear factor κB ligand (RANKL). Upon inflammatory conditions, DCs can transdifferentiate toward functional OCs in the presence of RANKL. It has then been assumed that the increase in proinflammatory cytokines could provide a supportive environment for this transdifferentiation. In this review, we emphasize the molecular mechanisms underlying the potential for DCs to give rise to resorbing OCs in the context of bone-destruction-associated diseases upon inflammatory conditions. Whether these mechanisms reveal new strategies for the discovery of therapeutic targets and drugs is discussed extensively.

Interleukin-33 and RANK-L Interplay in the Alveolar Bone Loss Associated to Periodontitis.

INTRODUCTION: Chronic Periodontitis (CP) is an inflammatory disease of bacterial origin that results in alveolar bone destruction. Porphyromonas gingivalis (Pg), one of the main periopathogens, initiates an inflammatory cascade by host immune cells thereby increasing recruitment and activity of osteoclasts, the bone resorbing cells, through enhanced production of the crucial osteoclastogenic factor, RANK-L. Antibodies directed against some cytokines (IL-1ß, IL-6 and TNF-α) failed to exhibit convincing therapeutic effect in CP. It has been suggested that IL-33, could be of interest in CP. OBJECTIVE: the present study aims to analyze whether and how IL-33 and RANK-L and/or their interplay are involved in the bone destruction associated to CP. MATERIAL AND METHODS: mRNAs and protein expressions of IL-33 and RANK-L were analyzed in healthy and CP human gingival samples by immunohistochemistry (IHC) and RT-qPCR. Murine experimental periodontitis (EP) was induced using Pg infected ligature and Pg free ligature around the first maxillary molar. Alveolar bone loss was recorded by µCT. Mouse gingival explants were stimulated for 24 hours with IL-33 and RANK-L mRNA expression investigated by RT-qPCR. Human oral epithelial cells were infected by Pg for 6, 12; 24 hours and IL-33 and RANK-L mRNA expressions were analyzed by RT-qPCR. RESULTS: IL-33 is overexpressed in gingival epithelial cells in human affected by CP as in the murine EP. In human as in murine gingival cells, RANK-L was independently induced by Pg and IL-33. We also showed that the Pg-dependent RANK-L expression in gingival epithelial cells occured earlier than that of IL-33. CONCLUSION: Our results evidence that IL-33 overexpression in gingival epithelial cells is associated with CP and may trigger RANK-L expression in addition to a direct effect of Pg. Finally, IL-33 may act as an extracellular alarmin (danger signal) showing proinflammatory properties in CP perpetuating bone resorption induced by Pg infection.

Osteoprotegerin, pericytes and bone-like vascular calcification are associated with carotid plaque stability.

BACKGROUND AND PURPOSE: Vascular calcification, recapitulating bone formation, has a profound impact on plaque stability. The aim of the present study was to determine the influence of bone-like vascular calcification (named osteoid metaplasia = OM) and of osteoprotegerin on plaque stability. METHODS: Tissue from carotid endarterectomies were analysed for the presence of calcification and signs of vulnerability according to AHA grading system. Osteoprotegerin (OPG), pericytes and endothelial cells were sought using immuno-histochemistry. Symptoms and preoperative imaging findings (CT-scan, MRI and Doppler-scan) were analyzed. Human pericytes were cultured to evaluate their ability to secrete OPG and to influence mineralization in the plaque. RESULTS: Seventy-three carotid plaques (49 asymptomatic and 24 symptomatic) were harvested. A significantly higher presence of OM (18.4% vs 0%, p<0.01), OPG (10.2% of ROI vs 3.4% of ROI, p<0.05) and pericytes (19% of ROI vs 3.8% of ROI, p<0.05) were noted in asymptomatic compared to symptomatic plaques. Consistently, circulating OPG levels were higher in the plasma of asymptomatic patients (3.2 ng/mL vs 2.5 ng/mL, p = 0.05). In vitro, human vascular pericytes secreted considerable amounts of OPG and underwent osteoblastic differentiation. Pericytes also inhibited the osteoclastic differentiation of CD14+ cells through their secretion of OPG. CONCLUSIONS: OPG (intraplaque an plasmatic) and OM are associated with carotid plaque stability. Pericytes may be involved in the secretion of intraplaque OPG and in the formation of OM.