Development and Evaluation of a Parallel Reaction Monitoring Strategy for Large-Scale Targeted Metabolomics Quantification

Recent advances in mass spectrometers which have yielded higher resolution and faster scanning speeds have expanded their application in metabolomics of diverse diseases. Using a quadrupole-Orbitrap LC–MS system, we developed an efficient large-scale quantitative method targeting 237 metabolites involved in various metabolic pathways using scheduled, parallel reaction monitoring (PRM). We assessed the dynamic range, linearity, reproducibility, and system suitability of the PRM assay by measuring concentration curves, biological samples, and clinical serum samples. The quantification performances of PRM and MS1-based assays in Q-Exactive were compared, and the MRM assay in QTRAP 6500 was also compared. The PRM assay monitoring 237 polar metabolites showed greater reproducibility and quantitative accuracy than MS1-based quantification and also showed greater flexibility in postacquisition assay refinement than the MRM assay in QTRAP 6500. We present a workflow for convenient PRM data processing using Skyline software which is free of charge. In this study we have established a reliable PRM methodology on a quadrupole-Orbitrap platform for evaluation of large-scale targeted metabolomics, which provides a new choice for basic and clinical metabolomics study

Citric Acid-Assisted Two-Step Enrichment with TiO₂ Enhances the Separation of Multi- and Monophosphorylated Peptides and Increases Phosphoprotein Profiling

Phosphopeptide enrichment is essential for large-scale phosphoprotein profiling. Titanium dioxide (TiO₂) is widely used in phosphopeptide enrichment, but it is limited in the isolation of multiphosphorylated peptides due to their strong binding. In this study, we found that citric acid greatly affects the binding of mono- and multiphosphopeptides with TiO₂, which can be used for stepwise phosphopeptide separation coupled with mass spectrum (MS) identification. We first loaded approximately 1 mg of peptide mixture of HeLa cell digests onto TiO₂ beads in highly concentrated citric acid (1 M). Then the flow-through fraction was diluted to ensure low concentration of citric acid (50 mM) and followed by loading onto another aliquot of TiO₂ beads. The two eluted fractions were subjected to nanoLC–MS/MS analysis. We identified 1,500 phosphorylated peptides, of which 69% were multiphosphorylated after the first enrichment. After the second enrichment, 2,167 phosphopeptides, of which 92% were monophosphorylated, were identified. In total, we successfully identified 3,136 unique phosphopeptides containing 3,973 phosphosites utilizing this strategy. Finally, more than 37% of the total phosphopeptides and 2.6-fold more of the multiphosphorylated peptides were identified as compared to the frequently used DHB/TiO₂ enrichment strategy. Combining SCX with CATSET, we identified 14,783 phosphopeptides and 15,713 phosphosites, of which 3,678 were unrecorded in PhosphoSitePlus database. This two-step separation procedure for sequentially enriching multi- and monophosphorylated peptides by using citric acid is advantageous in multiphosphorylated peptide separation, as well as for more comprehensive phosphoprotein profiling

Citric Acid-Assisted Two-Step Enrichment with TiO₂ Enhances the Separation of Multi- and Monophosphorylated Peptides and Increases Phosphoprotein Profiling

Phosphopeptide enrichment is essential for large-scale phosphoprotein profiling. Titanium dioxide (TiO₂) is widely used in phosphopeptide enrichment, but it is limited in the isolation of multiphosphorylated peptides due to their strong binding. In this study, we found that citric acid greatly affects the binding of mono- and multiphosphopeptides with TiO₂, which can be used for stepwise phosphopeptide separation coupled with mass spectrum (MS) identification. We first loaded approximately 1 mg of peptide mixture of HeLa cell digests onto TiO₂ beads in highly concentrated citric acid (1 M). Then the flow-through fraction was diluted to ensure low concentration of citric acid (50 mM) and followed by loading onto another aliquot of TiO₂ beads. The two eluted fractions were subjected to nanoLC–MS/MS analysis. We identified 1,500 phosphorylated peptides, of which 69% were multiphosphorylated after the first enrichment. After the second enrichment, 2,167 phosphopeptides, of which 92% were monophosphorylated, were identified. In total, we successfully identified 3,136 unique phosphopeptides containing 3,973 phosphosites utilizing this strategy. Finally, more than 37% of the total phosphopeptides and 2.6-fold more of the multiphosphorylated peptides were identified as compared to the frequently used DHB/TiO₂ enrichment strategy. Combining SCX with CATSET, we identified 14,783 phosphopeptides and 15,713 phosphosites, of which 3,678 were unrecorded in PhosphoSitePlus database. This two-step separation procedure for sequentially enriching multi- and monophosphorylated peptides by using citric acid is advantageous in multiphosphorylated peptide separation, as well as for more comprehensive phosphoprotein profiling

Citric Acid-Assisted Two-Step Enrichment with TiO₂ Enhances the Separation of Multi- and Monophosphorylated Peptides and Increases Phosphoprotein Profiling

Phosphopeptide enrichment is essential for large-scale phosphoprotein profiling. Titanium dioxide (TiO₂) is widely used in phosphopeptide enrichment, but it is limited in the isolation of multiphosphorylated peptides due to their strong binding. In this study, we found that citric acid greatly affects the binding of mono- and multiphosphopeptides with TiO₂, which can be used for stepwise phosphopeptide separation coupled with mass spectrum (MS) identification. We first loaded approximately 1 mg of peptide mixture of HeLa cell digests onto TiO₂ beads in highly concentrated citric acid (1 M). Then the flow-through fraction was diluted to ensure low concentration of citric acid (50 mM) and followed by loading onto another aliquot of TiO₂ beads. The two eluted fractions were subjected to nanoLC–MS/MS analysis. We identified 1,500 phosphorylated peptides, of which 69% were multiphosphorylated after the first enrichment. After the second enrichment, 2,167 phosphopeptides, of which 92% were monophosphorylated, were identified. In total, we successfully identified 3,136 unique phosphopeptides containing 3,973 phosphosites utilizing this strategy. Finally, more than 37% of the total phosphopeptides and 2.6-fold more of the multiphosphorylated peptides were identified as compared to the frequently used DHB/TiO₂ enrichment strategy. Combining SCX with CATSET, we identified 14,783 phosphopeptides and 15,713 phosphosites, of which 3,678 were unrecorded in PhosphoSitePlus database. This two-step separation procedure for sequentially enriching multi- and monophosphorylated peptides by using citric acid is advantageous in multiphosphorylated peptide separation, as well as for more comprehensive phosphoprotein profiling

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy

Secretome Analyses of Aβ_1–42 Stimulated Hippocampal Astrocytes Reveal that CXCL10 is Involved in Astrocyte Migration

Amyloid-beta (Aβ) aggregation plays an important role in the development of Alzheimer’s disease (AD). In the AD brain, amyloid plaques are surrounded by reactive astrocytes, and many essential functions of astrocytes have been reported to be mediated by protein secretion. However, the roles of activated astrocytes in AD progression are under intense debate. To provide an in-depth view of the secretomes of activated astrocytes, we present in this study a quantitative profile of rat hippocampal astrocyte secretomes at multiple time points after both brief and sustained Aβ_1–42 stimulation. Using SILAC labeling and LC–MS/MS analyses, we identified 19 up-regulated secreted proteins after Aβ_1–42 treatment. These differentially expressed proteins have been suggested to be involved in key aspects of biological processes, such as cell recruitment, Aβ clearance, and regulation of neurogenesis. Particularly, we validated the role played by CXCL10 in promoting astrocyte aggregation around amyloid plagues through <i>in vitro</i> cell migration analysis. This research provides global, quantitative profiling of astrocyte secretomes produced on Aβ stimulation and hence provides a detailed molecular basis for the relationship between amyloid plaques and astrocyte aggregation; the findings thus have important implications for further investigations into AD development and therapy