FOXO1 regulates dendritic cell activity through ICAM-1 and CCR7.

The transcription factor FOXO1 regulates cell function and is expressed in dendritic cells (DCs). We investigated the role of FOXO1 in activating DCs to stimulate a lymphocyte response to bacteria. We show that bacteria induce FOXO1 nuclear localization through the MAPK pathway and demonstrate that FOXO1 is needed for DC activation of lymphocytes in vivo. This occurs through FOXO1 regulation of DC phagocytosis, chemotaxis, and DC-lymphocyte binding. FOXO1 induces DC activity by regulating ICAM-1 and CCR7. FOXO1 binds to the CCR7 and ICAM-1 promoters, stimulates CCR7 and ICAM-1 transcriptional activity, and regulates their expression. This is functionally important because transfection of DCs from FOXO1-deleted CD11c.Cre(+)FOXO1(L/L) mice with an ICAM-1-expressing plasmid rescues the negative effect of FOXO1 deletion on DC bacterial phagocytosis and chemotaxis. Rescue with both CCR7 and ICAM-1 reverses impaired DC homing to lymph nodes in vivo when FOXO1 is deleted. Moreover, Ab production following injection of bacteria is significantly reduced with lineage-specific FOXO1 ablation. Thus, FOXO1 coordinates upregulation of DC activity through key downstream target genes that are needed for DCs to stimulate T and B lymphocytes and generate an Ab defense to bacteria.

FOXO1 deletion reduces dendritic cell function and enhances susceptibility to periodontitis.

The host response plays both protective and destructive roles in periodontitis. FOXO1 is a transcription factor that is activated in dendritic cells (DCs), but its function in vivo has not been examined. We investigated the role of FOXO1 in activating DCs in experimental (CD11c.Cre(+).FOXO1(L/L)) compared with matched control mice (CD11c.Cre(-).FOXO1(L/L)) in response to oral pathogens. Lineage-specific FOXO1 deletion reduced the recruitment of DCs to oral mucosal epithelium by approximately 40%. FOXO1 was needed for expression of genes that regulate migration, including integrins αν and ß3 and matrix metalloproteinase-2. Ablation of FOXO1 in DCs significantly decreased IL-12 produced by DCs in mucosal surfaces. Moreover, FOXO1 deletion reduced migration of DCs to lymph nodes, reduced capacity of DCs to induce formation of plasma cells, and reduced production of bacteria-specific antibody. The decrease in DC function in the experimental mice led to increased susceptibility to periodontitis through a mechanism that involved a compensatory increase in osteoclastogenic factors, IL-1ß, IL-17, and RANKL. Thus, we reveal a critical role for FOXO1 in DC recruitment to oral mucosal epithelium and activation of adaptive immunity induced by oral inoculation of bacteria.

Subgingival microbiome in Chinese patients with generalized aggressive periodontitis compared to healthy controls.

OBJECTIVE: The aim of the study was to profile the subgingival microbiome of Chinese adults with generalized aggressive periodontitis (GAgP) using human oral microbe identification microarray (HOMIM), and to compare the results with matched periodontal healthy controls. DESIGN: 15 subjects with GAgP and 15 age- and gender- matched periodontal healthy controls were included. Subgingival plaque samples were collected from the deepest pockets of patients with GAgP and matched sites in controls and then analyzed by 16S rRNA-based microarrays. Student's paired t-test was used to compare clinical parameters and mean number of bacterial taxa detected between the two groups. Fisher's exact probability test and Wilcoxon Rank Sum were used to compare bacterial species between all samples. A multiple linear regression model was used for correlations among age, gender and bacterial with clinical parameters. RESULTS: From a total sum of 379 strains tested, 171 bacterial strains were detected from subgingival plaques of the GAgP patients, more than the 157 strains detected in control group. Mean number of subgingival bacterial taxa detected in GAgP group was 68 (SD = 21.06) while in control group was 45 (SD = 21.60). 47 bacterial taxa were detected more frequently in GAgP group while 12 taxa were more prevalent in control group. The significantly more prevalent and abundant taxa of bacteria in GAgP group included Filifactor alocis, Desulfobulbus sp., Fretibacterium sp., Porphyromonas gingivalis, Tannerella forsythia, Porphyromon as endodontalis, Peptostreptococcaceae spp., Parvimonas micra, Eubacterium nodatum and Eubacterium saphenum. Meanwhile the more abundant taxa in control group were Streptococcus spp. and Pseudomonas aeruginosa. CONCLUSIONS: There are more taxa of bacteria in subgingival plaques of Chinese patients with GAgP than in healthy controls. F. alocis, Desulfobulbus sp., Fretibacterium sp., P. gingivalis and T. forsythia are strongly associated with GAgP. High-throughout microbiological results may help dentists have a better understanding of subgingival microbiome of GAgP.

Cellular and Molecular Aspects of Bone Remodeling.

Bone remodeling is a highly coordinated process responsible for bone resorption and formation. It is initiated and modulated by a number of factors including inflammation, changes in hormonal levels and lack of mechanical stimulation. Bone remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix through osteoblasts that subsequently becomes mineralized. In addition to the traditional bone cells (osteoclasts, osteoblasts and osteocytes) that are necessary for bone remodeling, several immune cells such as polymorphonuclear neutrophils, B cells and T cells have also been implicated in bone remodelling. Through the receptor activator of nuclear factor-x03BA;B/receptor activator of the NF-x03BA;B ligand/osteoprotegerin system the process of bone resorption is initiated and subsequent formation is tightly coupled. Mediators such as prostaglandins, interleukins, chemokines, leukotrienes, growth factors, wnt signalling and bone morphogenetic proteins are involved in the regulation of bone remodeling. We discuss here cells and mediators involved in the cellular and molecular machanisms of bone resorption and bone formation.

Bone Remodeling Under Pathological Conditions.

Bone is masterfully programmed to repair itself through the coupling of bone formation following bone resorption, a process referred to as coupling. In inflammatory or other conditions, the balance between bone resorption and bone formation shifts so that a net bone loss results. This review focuses on four pathologic conditions in which remodeling leads to net loss of bone, postmenopausal osteoporosis, arthritis, periodontal disease, and disuse bone loss, which is similar to bone loss associated with microgravity. In most of these there is an acceleration of the resorptive process due to increased formation of bone metabolic units. This initially leads to a net bone loss since the time period of resorption is much faster than the time needed for bone formation that follows. In addition, each of these processes is characterized by an uncoupling that leads to net bone loss. Mechanisms responsible for increased rates of bone resorption, i.e. the formation of more bone metabolic units, involve enhanced expression of inflammatory cytokines and increased expression of RANKL. Moreover, the reasons for uncoupling are discussed which range from a decrease in expression of growth factors and bone morphogenetic proteins to increased expression of factors that inhibit Wnt signaling.

NF-κB Has a Direct Role in Inhibiting Bmp- and Wnt-Induced Matrix Protein Expression.

The host response to pathogens through nuclear factor κB (NF-κB) is an essential defense mechanism for eukaryotic organisms. NF-κB-mediated host responses inhibit bone and other connective tissue synthesis and are thought to affect the transcription of matrix proteins through multiple indirect pathways. We demonstrate that inhibiting NF-κB in osteoblasts increases osteocalcin expression in vivo in mice with periodontal disease. Mutating NF-κB binding sites on osteocalcin (OC) or bone sialoprotein (Bsp) promoters rescues the negative impact of NF-κB on their transcription and that NF-κB can inhibit Wnt- and Bmp-induced OC and Bsp transcription, even when protein synthesis is inhibited, indicating a direct effect of NF-κB. This inhibition depends on p65-p50 NF-κB heterodimer formation and deacetylation by HDAC1 but is not affected by the noncanonical NF-κB pathway. Moreover, NF-κB reduces Runx2 and ß-catenin binding to OC/Bsp promoters independently of their nuclear localization. Thus, inflammatory signals stimulate the direct interaction of NF-κB with response elements to inhibit binding of ß-catenin and Runx2 binding to nearby consensus sites and reduce expression of matrix proteins. This direct mechanism provides a new explanation for the rapid decrease in new bone formation after inflammation-related NF-κB activation.

Osteoblast Lineage Cells Play an Essential Role in Periodontal Bone Loss Through Activation of Nuclear Factor-Kappa B.

Bacterial pathogens stimulate periodontitis, the most common osteolytic disease in humans and the most common cause of tooth loss in adults. Previous studies identified leukocytes and their products as key factors in this process. We demonstrate for the first time that osteoblast lineage cells play a critical role in periodontal disease. Oral infection stimulated nuclear localization of NF-κB in osteoblasts and osteocytes in the periodontium of wild type but not transgenic mice that expressed a lineage specific dominant negative mutant of IKK (IKK-DN) in osteoblast lineage cells. Wild-type mice were also susceptible to bacteria induced periodontal bone loss but transgenic mice were not. The lack of bone loss in the experimental group was linked to reduced RANKL expression by osteoblast lineage cells that led to diminished osteoclast mediated bone resorption and greater coupled new bone formation. The results demonstrate that osteoblast lineage cells are key contributors to periodontal bone loss through an NF-κB mediated mechanism.