A Novel Mechanism for Bone Loss: Platelet Count Negatively Correlates with Bone Mineral Density via Megakaryocyte-Derived RANKL.

A potential association between hematopoietic stem cell status in bone marrow and surrounding bone tissue has been hypothesized, and some studies have investigated the link between blood count and bone mineral density (BMD), although their exact relationship remains controversial. Moreover, biological factors linking the two are largely unknown. In our present study, we found no clear association between platelet count and BMD in the female group, with aging having a very strong effect on BMD. On the other hand, a significant negative correlation was found between platelet count and BMD in the male group. As a potential mechanism, we examined whether megakaryocytes, the source of platelet production, secrete cytokines that regulate BMD, namely OPG, M-CSF, and RANKL. We detected the production of these cytokines by megakaryocytes derived from bone marrow mononuclear cells, and found that RANKL was negatively correlated with BMD. This finding suggests that RANKL production by megakaryocytes may mediate the negative correlation between platelet count and BMD. To our knowledge, this is the first report to analyze bone marrow cells as a mechanism for the association between blood count and BMD. Our study may provide new insights into the development and potential treatment of osteoporosis.

Dynamics of laser-induced cavitation bubble during expansion over sharp-edge geometry submerged in liquid - an inside view by diffuse illumination.

Laser ablation in liquids is growing in popularity for various applications including nanoparticle production, breakdown spectroscopy, and surface functionalization. When laser pulse ablates the solid target submerged in liquid, a cavitation bubble develops. In case of "finite" geometries of ablated solids, liquid dynamical phenomena can occur inside the bubble when the bubble overflows the surface edge. To observe this dynamics, we use diffuse illumination of a flashlamp in combination with a high-speed videography by exposure times down to 250 ns. The developed theoretical modelling and its comparison with the experimental observations clearly prove that this approach widens the observable area inside the bubble. We thereby use it to study the dynamics of laser-induced cavitation bubble during its expansion over a sharp-edge ("cliff-like" 90°) geometry submerged in water, ethanol, and polyethylene glycol 300. The samples are 17 mm wide stainless steel plates with thickness in the range of 0.025-2 mm. Bubbles are induced on the samples by 1064-nm laser pulses with pulse durations of 7-60 ns and pulse energies of 10-55 mJ. We observe formation of a fixed-type secondary cavity behind the edge where low-pressure area develops due to bubble-driven flow of the liquid. This occurs when the velocity of liquid overflow exceeds ~20 m s-1. A re-entrant liquid injection with up to ~40 m s-1 velocity may occur inside the bubble when the bubble overflows the edge of the sample. Formation and characteristics of the jet evidently depend on the relation between the breakdown-edge offset and the bubble energy, as well as the properties of the surrounding liquid. Higher viscosity of the liquid prevents the generation of the jet.

Role of F225 in O-phosphoserine sulfhydrylase from Aeropyrum pernix K1.

O-Phosphoserine sulfhydrylase (OPSS) synthesizes cysteine from O-phospho-L-serine (OPS) and sulfide. We have determined the three-dimensional structures of OPSS from hyperthermophilic archaeon Aeropyrum pernix K1 (ApOPSS) in complex with aminoacrylate intermediate (AA) formed from pyridoxal 5'-phosphate with OPS or in complex with cysteine and compared them with that of ApOPSS. We found an orientational change of F225 at the active-site entrance and constructed an F225A mutant to examine its activities and AA stability and clarify the role of F225 in ApOPSS. The OPS and O-acetyl-L-serine (OAS) sulfhydrylase activities of the F225A mutant decreased by 4.2- and 15-fold compared to those of the wild-type (wt) ApOPSS, respectively. The ability of OPS and OAS to form AA also decreased by 12- and 27-fold, respectively. AA was less stable in the F225A mutant than in the wt ApOPSS. Simulated docking showed that leaving groups, such as phosphate and acetate, were oriented to the inside of the active site in the F225A mutant, whereas they were oriented to the entrance in the wt ApOPSS. These results suggest that F225 in ApOPSS plays important roles in maintaining the hydrophobic environment of AA from solvent water and in controlling the orientation of leaving groups.

Thermostability and reactivity in organic solvent of O-phospho-L-serine sulfhydrylase from hyperthermophilic archaeon Aeropyrum pernix K1.

O-phospho-l-serine sulfhydrylase (OPSS) from archaeon Aeropyrum pernix K1 is able to synthesize l-cysteine even at 80 °C. In this article, we compared thermal stability and reactivity in organic solvent of OPSS with those of O-acetyl-l-serine sulfhydrylase B (OASS-B) from Escherichia coli. As a result, the thermostability of OPSS was much higher than that of OASS-B. Moreover, the activity of OPSS increased in the reaction mixture containing the organic solvent, such as N, N'-dimethyl formamide and 1,4-dioxane, whereas that of OASS-B gradually decreased as the content of organic solvent increased. From the crystal structural analysis, the intramolecular electrostatic interactions of N-terminal domain in OPSS seemed to be correlated with the tolerance of OPSS to high temperature and organic solvent. These results indicate that OPSS is more superior to OASS-B for the industrial production of l-cysteine and unnatural amino acids that are useful pharmaceuticals in the presence of organic solvent.

Structural analysis of the substrate recognition mechanism in O-phosphoserine sulfhydrylase from the hyperthermophilic archaeon Aeropyrum pernix K1.

L-Cysteine is synthesized from O-acetyl-L-serine (OAS) and sulfide by O-acetylserine sulfhydrylase (OASS; EC 2.5.1.47) in plants and bacteria. O-phosphoserine sulfhydrylase (OPSS; EC 2.5.1.65) is a novel enzyme from the hyperthermophilic aerobic archaeon Aeropyrum pernix K1 (2003). OPSS can use OAS or O-phospho-L-serine (OPS) to synthesize L-cysteine. To elucidate the mechanism of the substrate specificity of OPSS, we analyzed three-dimensional structures of the active site of the enzyme. The active-site lysine (K127) of OPSS forms an internal Schiff base with pyridoxal 5'-phosphate. Therefore, crystals of the complexes formed by the K127A mutant with the external Schiff base of pyridoxal 5'-phosphate with either OPS or OAS were prepared and examined by X-ray diffraction analysis. In contrast to that observed for OASS, no significant difference was seen in the overall structure between the free and complexed forms of OPSS. The side chains of T152, S153, and Q224 interacted with the carboxylate of the substrates, as a previous study has suggested. The side chain of R297 has been proposed to recognize the phosphate group of OPS. Surprisingly, however, the position of R297 was significantly unchanged in the complex of the OPSS K127A mutant with the external Schiff base, allowing enough space for an interaction with OPS. The positively charged environment around the entrance of the active site including S153 and R297 is important for accepting negatively charged substrates such as OPS.