Contributions of increased osteopontin and hypophosphatemia to dentoalveolar defects in osteomalacic Hyp mice

X-linked hypophosphatemia (XLH) is an inherited disorder caused by inactivating mutations in the PHEX gene leading to renal phosphate wasting, rickets and osteomalacia. XLH is also associated with dentoalveolar mineralization defects in tooth enamel, dentin and cementum, and in alveolar bone, which lead to an increased prevalence of dental abscesses, periodontal disease and tooth loss. Genetic mouse experiments, and deficiencies in XLH patient therapies where treatments do not fully ameliorate mineralization defects, suggest that other pathogenic mechanisms may exist in XLH. The mineralization-inhibiting, secreted extracellular matrix phosphoprotein osteopontin (OPN, gene Spp1) is a substrate for the PHEX enzyme whereby extensive and inactivating degradation of inhibitory OPN by PHEX facilitates mineralization. Conversely, excess OPN accumulation in skeletal and dental tissues - for example in XLH where inactivating mutations in the PHEX gene limit degradation of inhibitory OPN, or as occurs in Fgf23-null mice - contributes to mineralization defects. We hypothesized that Spp1/OPN ablation in Hyp mice (a mouse model for XLH) would reduce dentoalveolar mineralization defects. Immunostaining revealed increased OPN in Hyp vs. wild-type (WT) alveolar bone, particularly in osteocyte lacunocanalicular networks where Hyp mice have characteristic hypomineralized peri-osteocytic lesions (POLs). Micro-computed tomography and histology showed that ablation of Spp1 in Hyp mice (Hyp;Spp1-/-) on a normal diet did not ameliorate bulk defects in enamel, dentin, or alveolar bone. On a high-phosphate diet, both Hyp and Hyp;Spp1-/- mice showed improved mineralization of enamel, dentin, and alveolar bone. Silver staining indicated Spp1 ablation did not improve alveolar or mandibular bone osteocyte POLs in Hyp mice; however, they were normalized by a high-phosphate diet in both Hyp and Hyp;Spp1-/- mice, although inducing increased OPN. Collectively, these data indicate that despite changes in OPN content in the dentoalveolar mineralized tissues, there exist other compensatory mineralization mechanisms that arise from knockout of Spp1/OPN in the Hyp background.

Titanium dioxide nanotubes added to glass ionomer cements affect S. mutans viability and mechanisms of virulence

This in vitro study evaluated the impact of TiO2 nanotubes (n-TiO2) incorporated into glass ionomer cement (GIC) on Streptococcus mutans (S. mutans) characteristics at cellular and molecular levels. n-TiO2, synthesized by the alkaline method (20 nm in size), was added to Ketac Molar EasyMix® at 0%, 3%, 5%, and 7% by weight. S. mutans strains were cultured on GIC disks with addition or not of n-TiO2 for 1, 3, and 7 days and the following parameters were assessed: inhibition halo (mm) (n=3/group); cell viability (live/dead) (n=5/group); cell morphology (SEM) (n=3/group); and gene expression by real-time PCR (vicR, covR, gtfB, gtfC, and gtfD) (n=6/group). The data were analyzed by the Kruskal-Wallis test, repeated-measures ANOVA or two-way ANOVA, and Tukey's and Dunn's post-hoc tests (α=0.05). The agar diffusion test showed a higher antibacterial property for 5% n-TiO2 compared with 3% and 7% (p<0.05) with no effect of time (1, 3, and 7 days). The cell number was significantly affected by all n-TiO2 groups, while viability was mostly affected by 3% and 5% n-TiO2, which also affected cell morphology and organization. Real-time PCR demonstrated that n-TiO2 reduced the expression of covR when compared with GIC with no n-TiO2 (p<0.05), with no effect of time, except for 3% n-TiO2 on vicR expression. Within-group and between-group analyses revealed n-TiO2 did not affect mRNA levels of gtfB, gtfC, and gtfD (p>0.05). Incorporation of n-TiO2 at 3% and 5% potentially affected S. mutans viability and the expression of key genes for bacterial survival and growth, improving the anticariogenic properties of GIC.

Shifts in the bacterial community of saliva give insights on the relationship between obesity and oral microbiota in adolescents

The current study aimed at the determination of the impact of obesity on the salivary microbiome in adolescents. Sixty subjects ranging 14-17 years old were enrolled (obese: n = 30-50% females, and normal weight: n = 30-50% females). Stimulated saliva was collected for denaturing gradient gel electrophoresis (DGGE) band patterns and massive 16S rRNA gene sequencing using the Ion Torrent platform. Overall, data analysis revealed that male subjects harbored a higher diverse salivary microbiome, defined by a significant higher richness (32.48 versus 26.74) and diversity (3.36 versus 3.20), higher Simpson values (0.96 versus 0.95) and distinct bacterial community structure considering either sex or condition (p < 0.05). Bacterial community fingerprinting analysis in human saliva showed a positive correlation with increased body mass index (BMI) in adolescents. Veillonella, Haemophilus and Prevotella occurrence was found to be affected by BMI, whereas Neisseria and Rothia occurrence was significantly impacted by sex in obese subjects. Our findings suggest that male and female adolescents may harbor a naturally distinct salivary microbiota and that obesity may specifically have an impact on their oral bacterial community. The potential dysbiotic oral microbiome in obese adolescents raises new insights on the etiology and prevention of future conditions in these populations.

Periodontitis in Chédiak-Higashi Syndrome: An Altered Immunoinflammatory Response

Chédiak-Higashi syndrome (CHS), a rare autosomal recessive disorder caused by mutations in the lysosomal trafficking regulator gene (LYST), is associated with aggressive periodontitis. It is suggested that LYST mutations affect the toll-like receptor (TLR)-mediated immunoinflammatory response, leading to frequent infections. This study sought to determine the periodontal status of patients with classic (severe) and atypical (milder) forms of CHS and the immunoregulatory functions of gingival fibroblasts in CHS patients. In contrast to aged-matched healthy controls, atypical (n = 4) and classic (n = 3) CHS patients presented with mild chronic periodontitis with no evidence of gingival ulceration, severe tooth mobility, or premature exfoliation of teeth. As a standard of care, all classic CHS patients had undergone bone marrow transplantation (BMT). Primary gingival fibroblasts obtained from atypical and BMT classic CHS patients displayed higher protein expression of TLR-2 (1.81-fold and 1.56-fold, respectively) and decreased expression of TLR-4 (-2.5-fold and -3.85-fold, respectively) at baseline when compared with healthy control gingival fibroblasts. When challenged with whole bacterial extract of Fusobacterium nucleatum, both atypical and classic CHS gingival fibroblasts failed to up-regulate TLR-2 and TLR-4 expression when compared with their respective untreated groups and control cells. Cytokine multiplex analysis following F. nucleatum challenge showed that atypical CHS gingival fibroblasts featured significantly increased cytokine expression (interleukin [IL]-2, IL-4, IL-5, IL-6, IL-10, IL-12, interferon-γ, tumor necrosis factor-α), whereas classic CHS cells featured similar/decreased cytokine expression when compared with treated control cells. Collectively, these results suggest that LYST mutations in CHS patients affect TLR-2 and TLR-4 expression/function, leading to dysregulated immunoinflammatory response, which in turn may influence the periodontal phenotype noted in CHS patients. Furthermore, our results suggest that atypical CHS patients and classic CHS patients who undergo BMT early in life are less susceptible to aggressive periodontitis and that hematopoietic cells play a critical role in mitigating the risk of aggressive periodontitis in CHS. Knowledge Transfer Statement: Results from this study can be used to create awareness among clinicians and researchers that not all CHS patients exhibit historically reported aggressive periodontitis, especially if they have atypical CHS disease or have received bone marrow transplantation. LYST mutations in CHS patients may affect TLR-2 and TLR-4 expression/function leading to dysregulated immunoinflammatory response, which in turn may influence the periodontal phenotype noted in CHS patients.

Computational analysis for GNAQ mutations: New insights on the molecular etiology of Sturge-Weber syndrome

Somatic activating mutations in the GNAQ have been recently associated with several congenital genetic disorders and tumors; however, the molecular mechanism/etiology that leads to GNAQ somatic mosaic mutation are unknown. Here, we reported a case of Sturge-Weber Syndrome (SWS) manifesting cutaneous vascular malformations (hemifacial Port-wine stain), cerebral and ocular vascular abnormalities (including epilepsy and glaucoma) and harboring a c.548G>A (p.R183Q) somatic mosaic mutation in GNAQ. Computational modeling studies were performed to assistant with the comprehension of the functional impact of p.R183Q and p.Q209L mutations in GNAQ, which encodes a G protein subunit alpha q (Gαq). The p.R183Q mutation was predicted to abolish hydrogen bonds between R183 residue and GDP molecule, destabilizing the inactive GDP-bound conformation of the Gαq mutants. Furthermore, replacement of R183 by Q183 residue was predicted to promote conformation changes in protein surface features affecting the switch I region, a key region that undergoes conformational changes triggered by receptor binding during signal transduction. In addition, replacement of Q209 by L209 residue was predicted to affect the molecular interaction between Gαq and Gβ subunit, impairing formation of the inactive heterotrimeric complex. These findings, in association with PPI network analysis, indicate that p.R183Q and p.Q209L mutations result in the over-activation of different downstream effectors, which in turn will determine the distinct cell responses and phenotype. These findings bring new insights on molecular etiology of vascular malformations associated to SWS and on different mechanisms underlying hyperactivation of downstream pathways to Gαq.