Porphyromonas gingivalis hydrogen sulfide enhances methyl mercaptan-induced pathogenicity in mouse abscess formation.

Porphyromonas gingivalis produces hydrogen sulfide (H2S) from l-cysteine. However, the role of H2S produced by P. gingivalis in periodontal inflammation is unclear. In this study, we identified the enzyme that catalyses H2S production from l-cysteine and analysed the role of H2S using a mouse abscess model. The enzyme identified was identical to methionine γ-lyase (PG0343), which produces methyl mercaptan (CH3SH) from l-methionine. Therefore, we analysed H2S and CH3SH production by P. gingivalis W83 and a PG0343-deletion mutant (ΔPG0343) with/without l-cysteine and/or l-methionine. The results indicated that CH3SH is produced constitutively irrespective of the presence of l-methionine, while H2S was greatly increased by both P. gingivalis W83 and ΔPG0343 in the presence of l-cysteine. In contrast, CH3SH production by ΔPG0343 was absent irrespective of the presence of l-methionine, and H2S production was eliminated in the absence of l-cysteine. Thus, CH3SH and H2S production involves different substrates, l-methionine or l-cysteine, respectively. Based on these characteristics, we analysed the roles of CH3SH and H2S in abscess formation in mice by P. gingivalis W83 and ΔPG0343. Abscess formation by P. gingivalis W83, but not ΔPG0343, differed significantly in the presence and absence of l-cysteine. In addition, the presence of l-methionine did not affect the size of abscesses generated by P. gingivalis W83 and ΔPG0343. Therefore, we conclude that H2S produced by P. gingivalis does not induce inflammation; however, H2S enhances inflammation caused by CH3SH. Thus, these results suggest the H2S produced by P. gingivalis plays a supportive role in inflammation caused by methionine γ-lyase.

Bone Formation Is Coupled to Resorption Via Suppression of Sclerostin Expression by Osteoclasts.

Bone formation is coupled to bone resorption throughout life. However, the coupling mechanisms are not fully elucidated. Using Tnfrsf11b-deficient (OPG-/- ) mice, in which bone formation is clearly coupled to bone resorption, we found here that osteoclasts suppress the expression of sclerostin, a Wnt antagonist, thereby promoting bone formation. Wnt/ß-catenin signals were higher in OPG-/- and RANKL-transgenic mice with a low level of sclerostin. Conditioned medium from osteoclast cultures (Ocl-CM) suppressed sclerostin expression in UMR106 cells and osteocyte cultures. In vitro experiments revealed that osteoclasts secreted leukemia inhibitory factor (LIF) and inhibited sclerostin expression. Anti-RANKL antibodies, antiresorptive agents, suppressed LIF expression and increased sclerostin expression, thereby reducing bone formation in OPG-/- mice. Taken together, osteoclast-derived LIF regulates bone turnover through sclerostin expression. Thus, LIF represents a target for improving the prolonged suppression of bone turnover by antiresorptive agents. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Aberrant TRPV1 expression in heat hyperalgesia associated with trigeminal neuropathic pain.

Trigeminal neuropathic pain is a facial pain syndrome associated with trigeminal nerve injury. However, the mechanism of trigeminal neuropathic pain is poorly understood. This study aimed to determine the role of transient receptor potential vanilloid 1 (TRPV1) in heat hyperalgesia in a trigeminal neuropathic pain model. We evaluated nociceptive responses to mechanical and heat stimuli using a partial infraorbital nerve ligation (pIONL) model. Withdrawal responses to mechanical and heat stimuli to vibrissal pads (VP) were assessed using von Frey filaments and a thermal stimulator equipped with a heat probe, respectively. Changes in withdrawal responses were measured after subcutaneous injection of the TRP channel antagonist capsazepine. In addition, the expression of TRPV1 in the trigeminal ganglia was examined. Mechanical allodynia and heat hyperalgesia were observed in VP by pIONL. Capsazepine suppressed heat hyperalgesia but not mechanical allodynia. The number of TRPV1-positive neurons in the trigeminal ganglia was significantly increased in the large-diameter-cell group. These results suggest that TRPV1 plays an important role in the heat hyperalgesia observed in the pIONL model.

Conversion of the metal-specific activity of Escherichia coli Mn-SOD by site-directed mutagenesis of Gly165Thr.

Glycine 165, which is located near the active site metal, is mostly conserved in aligned amino acid sequences of manganese-containing superoxide dismutase (Mn-SOD) proteins, but is substituted to threonine in most iron-containing SODs (Fe-SODs). Because threonine 165 is located between Trp128 and Trp130, and Trp128 is one of the metal-surrounding aromatic amino acids, the conversion of this amino acid may affect the metal-specific activity of Escherichia coli Mn-SOD. In order to clarify this possibility, we prepared a mutant of E. coli Mn-SOD with the replacement of Gly165 by Thr. The ratio of the specific activities of Mn- to Fe-reconstituted enzyme increased from 0.006 in the wild-type to 0.044 in the mutant SOD; therefore, the metal-specific SOD was converted to a metal-tolerant SOD. The visible absorption spectra of the Fe- and Mn-reconstituted mutant SODs indicated the loss of Mn-SOD character. It was concluded that Gly at position 165 plays a catalytic role in maintaining the integrity of the metal specificity of Mn-SOD.

Effects of substrate analogues and pH on manganese superoxide dismutases.

The effect of the substrate analogues azide and fluoride on the manganese(II) zero-field interactions of different manganese-containing superoxide dismutases (SOD) was measured using high-field electron paramagnetic resonance spectroscopy. Two cambialistic types, proteins that are active with manganese or iron, were studied along with two that were only active with iron and another that was only active with manganese. It was found that azide was able to coordinate directly to the pentacoordinated Mn(II) site of only the MnSOD from Escherichia coli and the cambialistic SOD from Rhodobacter capsulatus. The formation of a hexacoordinate azide-bound center was characterized by a large reduction in the Mn(II) zero-field interaction. In contrast, all five SODs were affected by fluoride, but no evidence for hexacoordinate Mn(II) formation was detected. For both azide and fluoride, the extent of binding was no more than 50%, implying either that a second binding site was present or that binding was self-limiting. Only the Mn(II) zero-field interactions of the two SODs that had little or no activity with manganese were found to be significantly affected by pH, the manganese-substituted iron superoxide dismutase from E. coli and the Gly155Thr mutant of the cambialistic SOD from Porphyromonas gingivalis. A model for anion binding and the observed pK involving tyrosine-34 is presented.

Manganese(II) zero-field interaction in cambialistic and manganese superoxide dismutases and its relationship to the structure of the metal binding site.

The Mn(II) high-magnetic-field electron paramagnetic resonance (HFEPR) spectra of five different superoxide dismutases (SODs) were measured at 190 and 285 GHz. The native E. coli manganese SOD was found to be distinct from the other SODs by virtue of its large zero-field E-value. The two wild-type cambialistic proteins from Porphyromonas gingivalis and Rhodobacter capsulatus were also distinct. However, the Gly155Thr mutant of the P. gingivalis SOD changed the Mn(II) spectrum so that it closely resembled the spectrum of manganese reconstituted E. coli iron SOD. This observation paralleled enzyme activity measurements that show that this mutation causes the loss of activity with manganese and enhanced activity with iron indicating a conversion from a cambialistic to an iron-specific protein. The Mn(II) magnetic parameters were determined by simultaneously fitting the multifrequency data. Simulations were carried out by numerically diagonalizing the spin Hamiltonian and explicitly calculating all possible transition probabilities. The relationship between the Mn(II) zero-field interaction and structure of the metal binding site is also discussed.

Pronounced conversion of the metal-specific activity of superoxide dismutase from Porphyromonas gingivalis by the mutation of a single amino acid (Gly155Thr) located apart from the active site.

Glycine 155, which is located approximately 10 A from the active metal sites, is mostly conserved in aligned amino acid sequences of manganese-specific superoxide dismutases (Mn-SODs) and cambialistic SOD (showing the same activity with Fe and Mn) from Porphyromonas gingivalis, but is substituted for threonine in most Fe-SODs. Since Thr155 is located between Trp123 and Trp125, and Trp123 is one member of the metal-surrounding aromatic amino acids, there is a possibility that the conversion of this amino acid may cause a conversion of the metal-specific activity of cambialistic P. gingivalis SOD. To clarify this possibility, we have prepared a mutant of the P. gingivalis SOD with conversion of Gly155 to Thr. The ratios of the specific activities of Fe- to Mn-reconstituted enzyme, which are measured by the xanthine oxidase/cytochrome c method, increased from 0.6 in the wild-type to 11.2 in the mutant SODs, indicating the conversion of the metal-specific activity of the enzyme from a cambialistic type to an Fe-specific type. The visible absorption spectra of the Fe- and Mn-reconstituted mutant SODs closely resembled those of Fe-specific SOD. Furthermore, the EPR spectra of the Fe- and Mn-reconstituted mutant SODs also closely resembled those of Fe-specific SOD. Three-dimensional structures of the Fe-reconstituted wild-type SOD and Mn-reconstituted mutant SOD have been determined at 1.6 A resolution. Both structures have identical conformations, orientations of residues involved in metal binding, and hydrogen bond networks, while the side chain of Trp123 is moved further toward the metal-binding site than in wild-type SOD. A possible contribution of the structural differences to the conversion of the metal-specific activity through rearrangement of the hydrogen bond network among Trp123, Gln70, Tyr35, and the metal-coordinated solvent is discussed.

Osteoprotegerin regulates bone formation through a coupling mechanism with bone resorption.

Deficiency of osteoprotegerin (OPG), a soluble decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL), in mice induces osteoporosis caused by enhanced bone resorption, but also accelerates bone formation. We examined whether bone formation is coupled with bone resorption in OPG-deficient (OPG-/-) mice using risedronate, an inhibitor of bone resorption. Histomorphometric analysis showed that bone formation-related parameters (e.g. mineral apposition rate and osteoblast surface/bone surface) in OPG-/- mice sharply decreased with suppression of bone resorption by daily injection of risedronate for 30 d. OPG-/- mice exhibited high serum alkaline phosphatase activity and osteocalcin concentration, both of which were decreased to the levels in wild-type mice by the risedronate injection. Serum levels of RANKL were markedly elevated in OPG-/- mice, but were unaffected by risedronate. The ectopic bone formation induced by bone morphogenetic protein-2 implantation into OPG-/- mice was not accelerated even with a high turnover rate of bone, but attenuation of mineral density from the ectopic bone was more pronounced than that in wild-type mice. These results suggest that bone formation is coupled with bone resorption at local sites in OPG-/- mice, and that serum RANKL levels do not reflect this coupling.