NEURONAL DEVELOPMENT. Glycerophospholipid regulation of modality-specific sensory axon guidance in the spinal cord.

Glycerophospholipids, the structural components of cell membranes, have not been considered to be spatial cues for intercellular signaling because of their ubiquitous distribution. We identified lyso-phosphatidyl-ß-D-glucoside (LysoPtdGlc), a hydrophilic glycerophospholipid, and demonstrated its role in modality-specific repulsive guidance of spinal cord sensory axons. LysoPtdGlc is locally synthesized and released by radial glia in a patterned spatial distribution to regulate the targeting of nociceptive but not proprioceptive central axon projections. Library screening identified the G protein-coupled receptor GPR55 as a high-affinity receptor for LysoPtdGlc, and GPR55 deletion or LysoPtdGlc loss of function in vivo caused the misallocation of nociceptive axons into proprioceptive zones. These findings show that LysoPtdGlc/GPR55 is a lipid-based signaling system in glia-neuron communication for neural development.

GPRC5B activates obesity-associated inflammatory signaling in adipocytes.

A genome-wide association study identified a strong correlation between body mass index and the presence of a 21-kb copy number variation upstream of the human GPRC5B gene; however, the functional role of GPRC5B in obesity remains unknown. We report that GPRC5B-deficient mice were protected from diet-induced obesity and insulin resistance because of reduced inflammation in their white adipose tissue. GPRC5B is a lipid raft-associated transmembrane protein that contains multiple phosphorylated residues in its carboxyl terminus. Phosphorylation of GPRC5B by the tyrosine kinase Fyn and the subsequent direct interaction with Fyn through the Fyn Src homology 2 (SH2) domain were critical for the initiation and progression of inflammatory signaling in adipose tissue. We demonstrated that a GPRC5B mutant lacking the direct binding site for Fyn failed to activate a positive feedback loop of nuclear factor κB-inhibitor of κB kinase ε signaling. These findings suggest that GPRC5B may be a major node in adipose signaling systems linking diet-induced obesity to type 2 diabetes and may open new avenues for therapeutic approaches to diabetic progression.

The novel neutrophil differentiation marker phosphatidylglucoside mediates neutrophil apoptosis.

A new type of glycolipid, phosphatidylglucoside (PtdGlc), was identified as a component of raft-like membrane domains of the human leukemia cell line HL-60. In this study, we show that PtdGlc forms functional domains that are different from those produced by lactosylceramide (LacCer)-enriched lipid rafts. These rafts initiate neutrophil apoptosis. Neutrophils are the only type of human peripheral blood leukocyte or monocyte-derived dendritic cell to express large amounts of PtdGlc on their cell surfaces. PtdGlc was not colocalized with LacCer. Anti-PtdGlc IgM DIM21 did not induce neutrophil chemotaxis or superoxide generation, whereas anti-LacCer IgM T5A7 induced these activities. DIM21, but not T5A7, significantly induced neutrophil apoptosis. DIM21-induced apoptosis was inhibited by specific inhibitors of cysteine-containing aspartate-specific proteases (caspases)-8, -9, and -3 but not by the Src family kinase inhibitor PP1, PIP(3) kinase inhibitor LY294002, NADPH oxidase inhibitor diphenyleneiodonium, superoxide dismutase, or catalase. PtdGlc was colocalized with Fas on the neutrophil plasma membrane. DIM21 and the agonist anti-Fas Ab DX2 induced the formation of large Fas-colocalized clusters of PtdGlc on the plasma membrane. Furthermore, the antagonistic anti-Fas Ab ZB4 significantly inhibited DIM21-induced neutrophil apoptosis. These results suggest that PtdGlc is specifically expressed on neutrophils and mediates apoptosis of these cells, and that the Fas-associated death signal may be involved in PtdGlc-mediated apoptosis.

Improved method of phosphopeptides enrichment using biphasic phosphate-binding tag/C18 tip for versatile analysis of phosphorylation dynamics.

A number of factors including low stoichiometry of phosphorylation, ion suppression, and reduced peptide backbone fragmentation interfere with precise identification of proteins in phosphoproteomic analysis by MS. Therefore, enrichment of phosphopeptides is an important process for subsequent mass spectrometric analysis. Here, we have developed a simple and efficient method for phosphopeptides enrichment, which employs a biphasic phosphate-binding tag (Phos-tag)/C18 tip consisting of overlaid Phos-tag on the C18 resin in a pipet tip. The improvement in selectivity for phosphopeptides was achieved by using a 40% ACN solution under the phosphopeptides binding conditions. We also assessed the adequacy of Phos-tag/C18 tip for quantitative phosphoproteomic analysis using the iTRAQ technology. After protein digestion and subsequent iTRAQ labeling, interfering substances including excess iTRAQ reagent were directly removed by Phos-tag/C18 tip in a single step. Applying this method, phosphoproteomic analysis of HeLa cells stimulated with tumor necrosis factor -alpha was rapidly and successfully achieved.

Quantitative analysis of a novel glucosylated phospholipid by liquid chromatography-mass spectrometry.

Building upon the demonstrated presence of a new glyceroglycolipid, phosphatidylglucoside (PtdGlc), in rat embryonic brain tissues, we have developed a method to identify minute amounts of PtdGlc in cultured cells by using nano-flow high-performance liquid chromatography and negative-ion-mode electrospray linear-ion trap time-of-flight mass spectrometry (LC-MS). A normal-phase silica gel-based column enabled us to separate PtdGlc from other lipid classes. PtdGlc was identified from its tandem mass spectrometry spectrum and from its retention time in the column. Using an internal standard collection and LC-MS, we obtained the linearity of PtdGlc at a range of 6.3-800 fmol per injection. We applied this method to analyze quantitative changes in PtdGlc in C6 glioma cells after cellular differentiation into GFAP-positive glial cells. PtdGlc in C6 glioma cells consisted exclusively of C18:0/C20:0 fatty acyl chains. Differentiation induced by the addition of anti-PtdGlc antibody plus cAMP in culture medium significantly increased the glycolipid content.

Proteomic analysis of livers of patients with primary hepatolithiasis.

Primary hepatolithiasis or intrahepatic calculi (IHC), which is characterized by the formation of gallstones in the intrahepatic bile duct, is an intractable liver disease and suspected to be one of the causes of cholangiocellular carcinoma. To obtain an insight into the disease, we performed proteomic analysis of liver tissue specimens of paired affected and unaffected hepatic segments from patients with primary hepatolithiasis by two-dimensional gel electrophoresis followed by identification of proteins. For the specimens from the unaffected segments, 125 spots out of 613 spots were identified, defining 83 unique protein names. For the specimens from the affected segments, 102 spots out of 671 spots were identified, defining 74 unique protein names. To further precisely compare, we used two-dimensional fluorescence difference gel electrophoresis. Consequently we identified 12 up-regulated proteins and 21 down-regulated proteins. The up-regulated proteins contained the proteins related to liver fibrosis and to cellular oxidoreduction. The down-regulated proteins contained RAF kinase inhibitor protein, chaperonin and proteins related to principal liver function.

Two-dimensional electrophoretic profiling of normal human kidney glomerulus proteome and construction of an extensible markup language (XML)-based database.

To contribute to physiology and pathophysiology of the glomerulus of human kidney, we have launched a proteomic study of human glomerulus, and compiled a profile of proteins expressed in the glomerulus of normal human kidney by two-dimensional gel electrophoresis (2-DE) and identification with matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and/or liquid chromatography-tandem mass spectrometry (LC-MS/MS). Kidney cortices with normal appearance were obtained from patients under surgical nephrectomy due to renal tumor, and glomeruli were highly purified by a standard sieving method followed by picking-up under a phase-contrast microscope. The glomerular proteins were separated by 2-DE with 24 cm immobilized pH gradient strips in the 3-10 range in the first dimension and 26 x 20 cm sodium dodecyl sulfate polyacrylamide electrophoresis gels of 12.5% in the second dimension. Gels were silver-stained, and valid spots were processed for identification through an integrated robotic system that consisted of a spot picker, an in-gel digester, and a MALDI-TOF MS and / or a LC-MS/MS. From 2-DE gel images of glomeruli of four subjects with no apparent pathologic manifestations, a synthetic gel image of normal glomerular proteins was created. The synthetic gel image contained 1713 valid spots, of which 1559 spots were commonly observed in the respective 2-DE gels. Among the 1559 spots, 347 protein spots, representing 212 proteins, have so far been identified, and used for the construction of an extensible markup language (XML)-based database. The database is deposited on a web site (http://www.sw.nec.co.jp/bio/rd/hgldb/index.html) in a form accessible to researchers to contribute to proteomic studies of human glomerulus in health and disease.