Dietary phosphate disturbs of gut microbiome in mice.

Disorder of phosphate metabolism is a common pathological condition in chronic kidney disease patients. Excessive intake of dietary phosphate deteriorates chronic kidney disease and various complications including cardiovascular and infectious diseases. Recent reports have demonstrated that gut microbiome disturbance is associated with both the etiology and progression of chronic kidney disease. However, the relationship between dietary phosphate and gut microbiome remains unknown. Here, we examined the effects of excessive intake of phosphate on gut microbiome. Five-week-old male C57BL/6J mice were fed either control diet or high phosphate diet for eight weeks. Analysis of the gut microbiota was carried out using MiSeq next generation sequencer, and short-chain fatty acids were determined with GC-MS. In analysis of gut microbiota, significantly increased in Erysipelotrichaceae and decreased in Ruminococcaceae were observed in high phosphate diet group. Furthermore, high phosphate diet induced reduction of microbial diversity and decreased mRNA levels of colonic tight junction markers. These results suggest that the excessive intake of dietary phosphate disturbs gut microbiota and affects intestinal barrier function.

Altered Fecal Microbiotas and Organic Acid Concentrations Indicate Possible Gut Dysbiosis in University Rugby Players: An Observational Study.

Gut eubiosis is essential for the host's health. In athletes, the gut microbiota can be altered by several factors, including diets. While eubiotic gut microbiota in elite rugby players has been reported, our survey found that university rugby players suffered from loose stools and frequent urgency to defecate. To establish the causes of the condition, the microbiota and the concentrations of organic acids in fecal samples of university male rugby players (URP) were analyzed and compared with those of age-matching, non-rugby playing males (control). Body mass indices were significantly (p < 0.05) different between groups. Chao1 index was significant (p < 0.05) lower in URP than in control. The relative abundances of phyla Firmicutes and Bacteroidetes were significantly (p < 0.05) higher and lower, respectively, in URP than in control. Potential pathobiont genera Collinsella, Enterobacter, and Haemophilus were significantly (p < 0.05) abundant, whereas beneficial Akkermansia was lower (p < 0.05) in URP than in control. Succinate, a potential causative of gut inflammation, was five-fold higher in URP than in controls. Our findings all but confirmed that the dysbiotic status of gut in URP.

Dietary phosphate exacerbates intestinal inflammation in experimental colitis.

The recent widespread consumption of Western diets and food additives worldwide is associated with excessive inorganic phosphate intake. However, researchers have known little about the impact of dietary phosphate intake on the development of inflammatory bowel disease to date. In this study, we investigated the effects of dietary phosphate on intestinal inflammation in experimental colitis. Sprague-Dawley rats were fed different phosphate diets (0.5%, 1.0% and 1.5% phosphate) with or without dextran sulfate sodium. For in vitro study, the effects of phosphate on proinflammatory cytokine induction and reactive oxygen species production in RAW264.7 macrophage were examined. Dietary phosphate exacerbated intestinal inflammation in experimental colitis in a dose-dependent manner, as assessed by the clinical disease activity score, colon length, and histology. Furthermore, the high phosphate diet increased myeloperoxidase activity and proinflammatory cytokine mRNA expression through the activation of nuclear factor κB in the inflamed colon. In addition, high phosphate loading in RAW264.7 cells directly enhanced reactive oxygen species production and proinflammatory cytokine gene expression. Our results demonstrated that the high phosphate diet exacerbated intestinal inflammation in experimental colitis. These findings have important therapeutic implications for inflammatory bowel disease patients.

Self-repairing filamentous actin hydrogel with hierarchical structure.

A chemically cross-linked filamentous actin (F-actin) gel consisting of globular actin (G-actin) as repeating units was prepared. The F-actin gel was cross-linked by covalent bonds, and the main chain is represented by the self-assembly of G-actin with a high-ordered hierarchical structure. The gel exhibited good mechanical performance with a storage modulus >1 kPa and undergoes reversible sol-gel transitions in response to changes in the salt concentration (chemical-induced sol-gel transition) as well as to shear strain (mechanical-induced sol-gel transition). Therefore, the gel exhibits self-repairing ability through dynamic polymerization and depolymerization across the structure hierarchies under repeated shear stress.

Thermoresponsive microtubule hydrogel with high hierarchical structure.

A thermoresponsive 3D microtubule hydrogel (MT gel) was prepared by simultaneous polymerization and chemical cross-linking of tubulins. The main chain of this gel is composed of cross-linked MTs, which consists of a cylindrical assembly of tubulin covalently connected by polyethylene glycol. This gel, which contains 10 mg/mL of tubulin, exhibits a storage modulus G' as high as 1 × 10(3), which is 10 times higher than the loss modulus G'' over a wide range of frequencies. The MT gel exhibits a reversible sol-gel transition by temperature changes at 4-37 °C via depolymerization and polymerization of the MT network. Notable effects of the presence of the cross-linkage on the process of polymerization and depolymerization of tubulin were experimentally observed, and the role of the cross-linkage was discussed.

Two-crystal structures of tropomyosin C-terminal fragment 176-273: exposure of the hydrophobic core to the solvent destabilizes the tropomyosin molecule.

Tropomyosin (Tm) is a two-stranded alpha-helical coiled-coil protein, and when associated with troponin, it is responsible for the actin filament-based regulation of muscle contraction in vertebrate skeletal and cardiac muscles. It is widely believed that Tm adopts a flexible rod-like structure in which the flexibility must play a crucial role in its functions. To obtain more information about the flexibility of Tm, we solved and compared two crystal structures of the identical C-terminal segments, spanning approximately 40% of the entire length. We also compared these structures with our previously reported crystal structure of an almost identical Tm segment in a distinct crystal form. The parameters specifying the local coiled-coil geometry, such as the separation between two helices and the local helical pitch, undulate along the length of Tm in the same way as among the three crystal structures, indicating that these parameters are defined by the amino acid sequence. In the region of increased separation, around Glu-218 and Gln-263, the hydrophobic core is disrupted by three holes. Moreover, for the first time to our knowledge, for Tm, water molecules have been identified in these holes. In some structures, the B-factors are higher around the holes than in the rest of the molecule. The Tm coiled-coil must be destabilized and therefore may be flexible, not only in the alanine clusters but also in the regions of the broken core. A closer look at the local staggering between the two chains and the local bending revealed that the strain accumulates at the alanine cluster and may be relaxed in the broken core region. Moreover, the strain is distributed over a long range, even when a deformation like bending may occur at a limited number of spots. Thus, Tm should not be regarded as a train of short rigid rods connected by flexible linkers, but rather as a seamless rubber rod patched with relatively more flexible regions.

Modulation of Caenorhabditis elegans chemotaxis by cultivation and assay temperatures.

The chemotaxis behaviors of the nematode Caenorhabditis elegans cultivated at various temperatures (15 degrees C, 20 degrees C and 25 degrees C) were examined at various temperatures (10 degrees C, 15 degrees C, 20 degrees C and 25 degrees C) to determine the multi-sensory integration of physical (thermal) and chemical sensory information within its nervous system. Chemotaxis behavior toward sodium acetate and ammonium chloride were differently affected by both assay and cultivation temperatures, suggesting that the temperature effect on chemotaxis is not general, but rather distinctive for each chemosensory pathway. Since thermosensory cues are likely encountered constantly in C. elegans, we supposed that the chemotaxis behaviors of worms are achieved by the integration of chemo- and thermosensory information. To verify the possible contribution of thermosensory function in chemotaxis, we examined the chemotaxis behaviors of ttx-1(p767) mutant worms with defective AFD thermosensory neurons. The chemotaxis behaviors toward sodium acetate or ammonium chloride of mutant worms cultivated at 20 degrees C and 25 degrees C were reduced relative to those of wild-type worms. These results indicate the important role of multi-sensory integration of chemosensory and thermosensory information in chemotaxis behavior of the C. elegans.

Crystal structures of tropomyosin: flexible coiled-coil.

Tropomyosin (Tm) is a 400 angstroms long coiled coil protein, and with troponin it regulates contraction in skeletal and cardiac muscles in a [Ca2+]-dependent manner. Tm consists of multiple domains with diverse stabilities in the coiled coil form, thus providing Tm with dynamic flexibility. This flexibility must play important roles in the actin binding and the cooperative transition between the calcium regulated states of the entire muscle thin filament. In order to understand the flexibility of Tm in its entirety, the atomic coordinates of Tm are needed. Here we report the two crystal structures of Tm segments. One is rabbit skeletal muscle alpha-Tm encompassing residues 176-284 with an N-terminal extension of 25 residues from the leucine zipper sequence of GCN4, which includes the region that interacts with the troponin core domain. The other is alpha-Tm encompassing residues 176-273 with N- and C-terminal extensions of the leucine zipper sequences. These two crystal structures imply that this molecule is a flexible coiled coil. First, Tm's are not homogeneous and smooth coiled coils, but instead they undulate, with highly fluctuating local parameters specifying the coiled coil. Independent fluctuating showed by two crystal structures is important. Second, in the first crystal, the coiled coil is bent by 9 degrees in the region centered about Y214-E218-Y221, where the inter-helical distance has its maximum. On the other hand, no bend is observed at the same region in the second crystal even if its inter-helical distance has also its maximum. E218, an unusual negatively charged residue at the a position in the heptad repeat, seems to play the key role in destabilizing the coiled coil with alanine destabilizing clusters.