Spatial neuroproteomics using imaging mass spectrometry

Spatial neurolipidomics-MALDI mass spectrometry imaging of lipids in brain pathologies

Given the complexity of nervous tissues, understanding neurochemical pathophysiology puts high demands on bioanalytical techniques with respect to specificity and sensitivity. Mass spectrometry imaging (MSI) has evolved to become an important, biochemical imaging technology for spatial biology in biological and translational research. The technique facilitates comprehensive, sensitive elucidation of the spatial distribution patterns of drugs, lipids, peptides, and small proteins in situ. Matrix-assisted laser desorption ionization (MALDI)-based MSI is the dominating modality due to its broad applicability and fair compromise of selectivity, sensitivity price, throughput, and ease of use. This is particularly relevant for the analysis of spatial lipid patterns, where no other comparable spatial profiling tools are available. Understanding spatial lipid biology in nervous tissue is therefore a key and emerging application area of MSI research. The aim of this review is to give a concise guide through the MSI workflow for lipid imaging in central nervous system (CNS) tissues and essential parameters to consider while developing and optimizing MSI assays. Further, this review provides a broad overview of key developments and applications of MALDI MSI-based spatial neurolipidomics to map lipid dynamics in neuronal structures, ultimately contributing to a better understanding of neurodegenerative disease pathology.

Mass Spectrometry Imaging in Alzheimer's Disease

Introduction: Amyloid-beta (Aβ) pathology is the precipitating histopathological characteristic of Alzheimer's disease (AD). Although the formation of amyloid plaques in human brains is suggested to be a key factor in initiating AD pathogenesis, it is still not fully understood the upstream events that lead to Aβ plaque formation and its metabolism inside the brains. Methods: Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) has been successfully introduced to study AD pathology in brain tissue both in AD mouse models and human samples. By using MALDI-MSI, a highly selective deposition of Aβ peptides in AD brains with a variety of cerebral amyloid angiopathy (CAA) involvement was observed. Results: MALDI-MSI visualized depositions of shorter peptides in AD brains; Aβ1-36 to Aβ1-39 were quite similarly distributed with Aβ1-40 as a vascular pattern, and deposition of Aβ1-42 and Aβ1-43 was visualized with a distinct senile plaque pattern distributed in parenchyma. Moreover, how MALDI-MSI covered in situ lipidomics of plaque pathology has been reviewed, which is of interest as aberrations in neuronal lipid biochemistry have been implicated in AD pathogenesis. Discussion: In this study, we introduce the methodological concepts and challenges of MALDI-MSI for the studies of AD pathogenesis. Diverse Aβ isoforms including various C- and N-terminal truncations in AD and CAA brain tissues will be visualized. Despite the close relationship between vascular and plaque Aβ deposition, the current strategy will define cross talk between neurodegenerative and cerebrovascular processes at the level of Aβ metabolism.

Recent advances in mass spectrometry analysis of neuropeptides

Due to their involvement in numerous biochemical pathways, neuropeptides have been the focus of many recent research studies. Unfortunately, classic analytical methods, such as western blots and enzyme-linked immunosorbent assays, are extremely limited in terms of global investigations, leading researchers to search for more advanced techniques capable of probing the entire neuropeptidome of an organism. With recent technological advances, mass spectrometry (MS) has provided methodology to gain global knowledge of a neuropeptidome on a spatial, temporal, and quantitative level. This review will cover key considerations for the analysis of neuropeptides by MS, including sample preparation strategies, instrumental advances for identification, structural characterization, and imaging; insightful functional studies; and newly developed absolute and relative quantitation strategies. While many discoveries have been made with MS, the methodology is still in its infancy. Many of the current challenges and areas that need development will also be highlighted in this review.

Perinatal exposure to a glyphosate-based herbicide causes dysregulation of dynorphins and an increase of neural precursor cells in the brain of adult male rats

Glyphosate, the most used herbicide worldwide, has been suggested to induce neurotoxicity and behavioral changes in rats after developmental exposure. Studies of human glyphosate intoxication have reported adverse effects on the nervous system, particularly in substantia nigra (SN). Here we used matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) to study persistent changes in peptide expression in the SN of 90-day-old adult male Wistar rats. The animals were perinatally exposed to 3 % GBH (glyphosate-based herbicide) in drinking water (corresponding to 0.36 % of glyphosate) starting at gestational day 5 and continued up to postnatal day 15 (PND15). Peptides are present in the central nervous system before birth and play a critical role in the development and survival of neurons, therefore, observed neuropeptide changes could provide better understanding of the GBH-induced long term effects on SN. The results revealed 188 significantly altered mass peaks in SN of animals perinatally exposed to GBH. A significant reduction of the peak intensity (P < 0.05) of several peptides from the opioid-related dynorphin family such as dynorphin B (57 %), alpha-neoendorphin (50 %), and its endogenous metabolite des-tyrosine alpha-neoendorphin (39 %) was detected in the GBH group. Immunohistochemical analysis confirmed a decreased dynorphin expression and showed a reduction of the total area of dynorphin immunoreactive fibers in the SN of the GBH group. In addition, a small reduction of dynorphin immunoreactivity associated with non-neuronal cells was seen in the hilus of the hippocampal dentate gyrus. Perinatal exposure to GBH also induced an increase in the number of nestin-positive cells in the subgranular zone of the dentate gyrus. In conclusion, the results demonstrate long-term changes in the adult male rat SN and hippocampus following a perinatal GBH exposure suggesting that this glyphosate-based formulation may perturb critical neurodevelopmental processes.

Enhanced Laterally Resolved ToF-SIMS and AFM Imaging of the Electrically Conductive Structures in Cable Bacteria

Cable bacteria are electroactive bacteria that form a long, linear chain of ridged cylindrical cells. These filamentous bacteria conduct centimeter-scale long-range electron transport through parallel, interconnected conductive pathways of which the detailed chemical and electrical properties are still unclear. Here, we combine time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM) to investigate the structure and composition of this naturally occurring electrical network. The enhanced lateral resolution achieved allows differentiation between the cell body and the cell-cell junctions that contain a conspicuous cartwheel structure. Three ToF-SIMS modes were compared in the study of so-called fiber sheaths (i.e., the cell material that remains after the removal of cytoplasm and membranes, and which embeds the electrical network). Among these, fast imaging delayed extraction (FI-DE) was found to balance lateral and mass resolution, thus yielding the following multiple benefits in the study of structure-composition relations in cable bacteria: (i) it enables the separate study of the cell body and cell-cell junctions; (ii) by combining FI-DE with in situ AFM, the depth of Ni-containing protein-key in the electrical transport-is determined with greater precision; and (iii) this combination prevents contamination, which is possible when using an ex situ AFM. Our results imply that the interconnects in extracted fiber sheaths are either damaged during extraction, or that their composition is different from fibers, or both. From a more general analytical perspective, the proposed methodology of ToF-SIMS in the FI-DE mode combined with in situ AFM holds great promise for studying the chemical structure of other biological systems.

Animal- free skin permeation analysis using mass spectrometry imaging

Here we demonstrate an animal-free skin permeation analytical approach suitable for testing pharmaceuticals, cosmetics, occupational skin hazards and skin allergens. The method aims to replace or significantly reduce existing in-vivo models and improve on already established in-vitro models. This by offering a more sensitive and flexible analytical approach that can replace and/or complement existing methods in the OECD guidelines for skin adsorption (no 427 and no 428) and measure multiple compounds simultaneously in the skin while being able to also trace endogenous effects in cells. We demonstrate this here by studying how active ingredients in sunscreen permeate through left-over human skin, from routine surgery, in a in a Franz-cell permeation model. Two common sunscreens were therefore applied to the human skin and Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to trace the molecules through the skin. We show that that ToF-SIMS imaging can be applied in visualizing the distribution of Avobenzone, Bemotrizinol, Biscotrizole and Ethyl hexyl triazine at subcellular resolution in the skin. The UV-blockers could be visualized at the same time in one single experiment without any probes or antibodies used. The UV-blockers mostly remained in the stratum corneum. However, in certain features of the skin, such as sebaceous glands, the penetration of the UV-blockers was more prominent, and the compounds reached deeper into the epidermis.

ToF-SIMS mediated analysis of human lung tissue reveals increased iron deposition in COPD (GOLD IV) patients

Chronic obstructive pulmonary disease (COPD) is a debilitating lung disease that is currently the third leading cause of death worldwide. Recent reports have indicated that dysfunctional iron handling in the lungs of COPD patients may be one contributing factor. However, a number of these studies have been limited to the qualitative assessment of iron levels through histochemical staining or to the expression levels of iron-carrier proteins in cells or bronchoalveolar lavage fluid. In this study, we have used time of flight secondary ion mass spectrometry (ToF-SIMS) to visualize and relatively quantify iron accumulation in lung tissue sections of healthy donors versus severe COPD patients. An IONTOF 5 instrument was used to perform the analysis, and further multivariate analysis was used to analyze the data. An orthogonal partial least squares discriminant analysis (OPLS-DA) score plot revealed good separation between the two groups. This separation was primarily attributed to differences in iron content, as well as differences in other chemical signals possibly associated with lipid species. Further, relative quantitative analysis revealed twelve times higher iron levels in lung tissue sections of COPD patients when compared to healthy donors. In addition, iron accumulation observed within the cells was heterogeneously distributed, indicating cellular compartmentalization.

Molecular imaging mass spectrometry for probing protein dynamics in neurodegenerative disease pathology

Recent advances in the understanding of basic pathological mechanisms in various neurological diseases depend directly on the development of novel bioanalytical technologies that allow sensitive and specific chemical imaging at high resolution in cells and tissues. Mass spectrometry-based molecular imaging (IMS) has gained increasing popularity in biomedical research for mapping the spatial distribution of molecular species in situ. The technology allows for comprehensive, untargeted delineation of in situ distribution profiles of metabolites, lipids, peptides and proteins. A major advantage of IMS over conventional histochemical techniques is its superior molecular specificity. Imaging mass spectrometry has therefore great potential for probing molecular regulations in CNS-derived tissues and cells for understanding neurodegenerative disease mechanism. The goal of this review is to familiarize the reader with the experimental workflow, instrumental developments and methodological challenges as well as to give a concise overview of the major advances and recent developments and applications of IMS-based protein and peptide profiling with particular focus on neurodegenerative diseases. This article is part of the Special Issue "Proteomics".

Applications of MALDI-TOF mass spectrometry in clinical proteomics

INTRODUCTION

The development of precision medicine requires advanced technologies to address the multifactorial disease stratification and to support personalized treatments. Among omics techniques, proteomics based on Mass Spectrometry (MS) is becoming increasingly relevant in clinical practice allowing a phenotypic characterization of the dynamic functional status of the organism. From this perspective, Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) MS is a suitable platform for providing a high-throughput support to clinics. Areas covered: This review aims to provide an updated overview of MALDI-TOF MS applications in clinical proteomics. The most relevant features of this analysis have been discussed, highlighting both pre-analytical and analytical factors that are crucial in proteomics studies. Particular emphasis is placed on biofluids proteomics for biomarkers discovery and on recent progresses in clinical microbiology, drug monitoring, and minimal residual disease (MRD). Expert commentary: Despite some analytical limitations, the latest technological advances together with the easiness of use, the low time and low cost consuming and the high throughput are making MALDI-TOF MS instruments very attractive for the clinical practice. These features offer a significant potential for the routine of the clinical laboratory and ultimately for personalized medicine.

High resolution imaging and 3D analysis of Ag nanoparticles in cells with ToF-SIMS and delayed extraction

Within this study, the authors use human mesenchymal stem cells incubated with silver nanoparticles (AgNPs) as a model system to systematically investigate the advantages and drawbacks of the fast imaging delayed extraction mode for two-dimensional and three-dimensional (3D) analyses at the cellular level. The authors compare the delayed extraction mode with commonly employed measurement modes in terms of mass and lateral resolution, intensity, and dose density. Using the delayed extraction mode for single cell analysis, a high mass resolution up to 4000 at m/z = 184.08 combined with a lateral resolution up to 360 nm is achieved. Furthermore, the authors perform 3D analyses with Ar-clusters (10 keV) and O₂⁺ (500 eV) as sputter species, combined with Bi₃⁺ and delayed extraction for analysis. Cell compartments like the nucleus are visualized in 3D, whereas no realistic 3D reconstruction of intracellular AgNP is possible due to the different sputter rates of inorganic and organic cell materials. Furthermore, the authors show that the sputter yield of Ag increases with the decreasing Ar-cluster size, which might be an approach to converge the different sputter rates.

Novel Trimodal MALDI Imaging Mass Spectrometry (IMS3) at 10 μm Reveals Spatial Lipid and Peptide Correlates Implicated in Aβ Plaque Pathology in Alzheimer's Disease

Multimodal chemical imaging using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) can provide comprehensive molecular information in situ within the same tissue sections. This is of relevance for studying different brain pathologies such as Alzheimer's disease (AD), where recent data suggest a critical relevance of colocalizing Aβ peptides and neuronal lipids. We here developed a novel trimodal, high-resolution (10 μm) MALDI imaging MS (IMS) paradigm for negative and positive ion mode lipid analysis and subsequent protein ion imaging on the same tissue section. Matrix sublimation of 1,5-diaminonaphthalene (1,5-DAN) enabled dual polarity lipid MALDI IMS on the same pixel points at high spatial resolutions (10 μm) and with high spectral quality. This was followed by 10 μm resolution protein imaging on the same measurement area, which allowed correlation of lipid signals with protein distribution patterns within distinct cerebellar regions in mouse brain. The demonstrated trimodal imaging strategy (IMS3) was further shown to be an efficient approach for simultaneously probing Aβ plaque-associated lipids and Aβ peptides within the hippocampus of 18 month-old transgenic AD mice (tgArcSwe). Here, IMS3 revealed a strong colocalization of distinct lipid species including ceramides, phosphatidylinositols, sulfatides (Cer 18:0, PI 38:4, ST 24:0) and lysophosphatidylcholines (LPC 16:0, LPC 18:0) with plaque-associated Aβ isoforms (Aβ 1-37, Aβ 1-38, Aβ 1-40). This highlights the potential of IMS3 as an alternative, superior approach to consecutively performed immuno-based Aβ staining strategies. Furthermore, the IMS3 workflow allowed for multimodal in situ MS/MS analysis of both lipids and Aβ peptides. Altogether, the here presented IMS3 approach shows great potential for comprehensive, high-resolution molecular analysis of histological features at cellular length scales with high chemical specificity. It therefore represents a powerful approach for probing the complex molecular pathology of, e.g., neurodegenerative diseases that are characterized by neurotoxic protein aggregation.

Imaging mass spectrometry for novel insights into contact allergy - a proof-of-concept study on nickel

BACKGROUND

In spite of extensive regulation to limit exposure, nickel remains the main cause of contact allergy in the general population. More detailed knowledge on the skin uptake of haptens is required. So far, no method exists for the visualization of this clinically relevant hapten and its distribution in the skin.

OBJECTIVES

To show, in terms of a proof of concept, that imaging mass spectrometry [time of flight secondary ion mass spectrometry (ToF-SIMS)] can be applied for investigation of the penetration and distribution of nickel in human skin.

METHOD

Full-thickness human skin obtained from breast reduction surgery was exposed to nickel sulfate (5% in deionized water) for 24 h in Franz-type diffusion cells. Biopsies were obtained from nickel-treated samples and control (deionized water). The tissue was sliced, and analysed with ToF-SIMS, generating high-resolution images of ion distribution in the epidermis and upper dermis.

RESULTS

The skin layers could be discerned from the ToF-SIMS data, particularly on the basis of the collagen signal. Nickel ions were localized to the stratum corneum and upper epidermis.

CONCLUSIONS

This is the first time that ToF-SIMS has been applied to trace the distribution of a hapten in human skin. Proof of principle was shown for nickel, and the technique can, in the future, be expanded for investigation of the skin distribution of clinically relevant sensitizers in general.

Integration of Ion Mobility MSE after Fully Automated, Online, High-Resolution Liquid Extraction Surface Analysis Micro-Liquid Chromatography

Direct analysis by mass spectrometry (imaging) has become increasingly deployed in preclinical and clinical research due to its rapid and accurate readouts. However, when it comes to biomarker discovery or histopathological diagnostics, more sensitive and in-depth profiling from localized areas is required. We developed a comprehensive, fully automated online platform for high-resolution liquid extraction surface analysis (HR-LESA) followed by micro–liquid chromatography (LC) separation and a data-independent acquisition strategy for untargeted and low abundant analyte identification directly from tissue sections. Applied to tissue sections of rat pituitary, the platform demonstrated improved spatial resolution, allowing sample areas as small as 400 μm to be studied, a major advantage over conventional LESA. The platform integrates an online buffer exchange and washing step for removal of salts and other endogenous contamination that originates from local tissue extraction. Our carry over–free platform showed high reproducibility, with an interextraction variability below 30%. Another strength of the platform is the additional selectivity provided by a postsampling gas-phase ion mobility separation. This allowed distinguishing coeluted isobaric compounds without requiring additional separation time. Furthermore, we identified untargeted and low-abundance analytes, including neuropeptides deriving from the pro-opiomelanocortin precursor protein and localized a specific area of the pituitary gland (i.e., adenohypophysis) known to secrete neuropeptides and other small metabolites related to development, growth, and metabolism. This platform can thus be applied for the in-depth study of small samples of complex tissues with histologic features of ∼400 μm or more, including potential neuropeptide markers involved in many diseases such as neurodegenerative diseases, obesity, bulimia, and anorexia nervosa.

Rodent Whole-Body Sectioning and MALDI Mass Spectrometry Imaging

Here, we describe a method for obtaining whole-body MALDI imaging data. MALDI imaging provides chemical compound-specific information not attainable with conventional histology techniques. The specificity of mass spectrometry with the addition of spatial information makes this a very powerful technique, especially for the analysis of endogenous and exogenous small molecules. This chapter will provide the reader with a comprehensive description of the techniques involved in obtaining high-quality MALDI mass spectrometry imaging (MSI) data from large tissue sections.

Selective improvement of peptides imaging on tissue by supercritical fluid wash of lipids for matrix-assisted laser desorption/ionization mass spectrometry

There is a high analytical demand for improving the detection sensitivity for various peptides in matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) because exhaustive distribution analyses of various peptides could help to reveal the function of peptides in vivo. To improve the sensitivity of peptide detection, we used supercritical fluid of CO₂ (scCO₂) as washing solvent for a pretreatment to remove lipids. We evaluated whether our wash method using scCO₂ with an entrainer improved the detection of peptides and suppressed lipid detection in MALDI-IMS. Our analysis revealed that the signal intensities of peptides such as m/z 3339.8, 3530.9, 4233.3, 4936.7, and 4963.7 were increased in scCO₂-washed samples. The greatest improvement in the signal-to-noise ratio (S/N) was found at m/z 4963.7, which was identified as thymosin β4, with the S/N reaching almost 190-fold higher than the control. Additionally, all of the improved signals were associated with the morphologic structure. Our method allows us to analyze the distribution of molecules, especially in the region of m/z 3000-5200. For these improvements, the polarity difference between scCO₂ and the matrix solution used was considered as a key. A wider variety of molecules can be analyzed in the future due to this improvement of the detection sensitivity by optimizing the polarity of scCO₂ with various entrainers. Graphical Abstract Mass spectra of m/z 4900-5000 obtained from a scCO₂-washed tissue (upper, blue) and a control tissue (lower, red). Ion distribution of the signals at m/z 4936.7 and m/z 4963.7 specifically ditected from scCO₂-washed samples.

Imaging mass spectrometry in drug development and toxicology

During the last decades, imaging mass spectrometry has gained significant relevance in biomedical research. Recent advances in imaging mass spectrometry have paved the way for in situ studies on drug development, metabolism and toxicology. In contrast to whole-body autoradiography that images the localization of radiolabeled compounds, imaging mass spectrometry provides the possibility to simultaneously determine the discrete tissue distribution of the parent compound and its metabolites. In addition, imaging mass spectrometry features high molecular specificity and allows comprehensive, multiplexed detection and localization of hundreds of proteins, peptides and lipids directly in tissues. Toxicologists traditionally screen for adverse findings by histopathological examination. However, studies of the molecular and cellular processes underpinning toxicological and pathologic findings induced by candidate drugs or toxins are important to reach a mechanistic understanding and an effective risk assessment strategy. One of IMS strengths is the ability to directly overlay the molecular information from the mass spectrometric analysis with the tissue section and allow correlative comparisons of molecular and histologic information. Imaging mass spectrometry could therefore be a powerful tool for omics profiling of pharmacological/toxicological effects of drug candidates and toxicants in discrete tissue regions. The aim of the present review is to provide an overview of imaging mass spectrometry, with particular focus on MALDI imaging mass spectrometry, and its use in drug development and toxicology in general.

Oligodendroglial membrane dynamics in relation to myelin biogenesis

In the central nervous system, oligodendrocytes synthesize a specialized membrane, the myelin membrane, which enwraps the axons in a multilamellar fashion to provide fast action potential conduction and to ensure axonal integrity. When compared to other membranes, the composition of myelin membranes is unique with its relatively high lipid to protein ratio. Their biogenesis is quite complex and requires a tight regulation of sequential events, which are deregulated in demyelinating diseases such as multiple sclerosis. To devise strategies for remedying such defects, it is crucial to understand molecular mechanisms that underlie myelin assembly and dynamics, including the ability of specific lipids to organize proteins and/or mediate protein-protein interactions in healthy versus diseased myelin membranes. The tight regulation of myelin membrane formation has been widely investigated with classical biochemical and cell biological techniques, both in vitro and in vivo. However, our knowledge about myelin membrane dynamics, such as membrane fluidity in conjunction with the movement/diffusion of proteins and lipids in the membrane and the specificity and role of distinct lipid-protein and protein-protein interactions, is limited. Here, we provide an overview of recent findings about the myelin structure in terms of myelin lipids, proteins and membrane microdomains. To give insight into myelin membrane dynamics, we will particularly highlight the application of model membranes and advanced biophysical techniques, i.e., approaches which clearly provide an added value to insight obtained by classical biochemical techniques.

Molecular Histochemistry Identifies Peptidomic Organization and Reorganization Along Striatal Projection Units

Matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) (MALDI-IMS) provides a technical means for simultaneous analysis of precise anatomic localization and regulation of peptides. We explored the technical capability of matrix-assisted laser desorption ionization mass spectrometry for characterization of peptidomic regulation by an addictive substance along two distinct projection systems in the mouse striatum. The spatial expression patterns of substance P and proenkephalin, marker neuropeptides of two distinct striatal projection neurons, were negatively correlated at baseline. We detected 768 mass/charge (m/z) peaks whose expression levels were mostly negatively and positively correlated with expression levels of substance P and proenkephalin A (amino acids 218-228), respectively, within the dorsal striatum. After nicotine administration, there was a positive shift in correlation of mass/charge peak expression levels with substance P and proenkephalin A (218-228). Our exploratory analyses demonstrate the technical capacity of MALDI-IMS for comprehensive identification of peptidomic regulation patterns along histochemically distinguishable striatal projection pathways.

Proteomics of the Synapse--A Quantitative Approach to Neuronal Plasticity

The advances in mass spectrometry based proteomics in the past 15 years have contributed to a deeper appreciation of protein networks and the composition of functional synaptic protein complexes. However, research on protein dynamics underlying core mechanisms of synaptic plasticity in brain lag far behind. In this review, we provide a synopsis on proteomic research addressing various aspects of synaptic function. We discuss the major topics in the study of protein dynamics of the chemical synapse and the limitations of current methodology. We highlight recent developments and the future importance of multidimensional proteomics and metabolic labeling. Finally, emphasis is given on the conceptual framework of modern proteomics and its current shortcomings in the quest to gain a deeper understanding of synaptic plasticity.

Correlating microscopy techniques and ToF-SIMS analysis of fully grown mammalian oocytes

An innovative protocol for the 2D-molecular thin film analysis applying ToF-SIMS, SEM, AFM and optical microscopy imaging of fully grown mice oocytes is described.

Peptidomics and Secretomics of the Mammalian Peripheral Sensory-Motor System

The dorsal root ganglion (DRG) and its anatomically and functionally associated spinal nerve and ventral and dorsal roots are important components of the peripheral sensory-motor system in mammals. The cells within these structures use a number of peptides as intercellular signaling molecules. We performed a variety of mass spectrometry (MS)-based characterizations of peptides contained within and secreted from these structures, and from isolated and cultured DRG cells. Liquid chromatography-Fourier transform MS was utilized in DRG and nerve peptidome analysis. In total, 2724 peptides from 296 proteins were identified in tissue extracts. Neuropeptides are among those detected, including calcitonin gene-related peptide I, little SAAS, and known hemoglobin-derived peptides. Solid phase extraction combined with direct matrix-assisted laser desorption/ionization time-of-flight MS was employed to investigate the secretome of these structures. A number of peptides were detected in the releasate from semi-intact preparations of DRGs and associated nerves, including neurofilament- and myelin basic protein-related peptides. A smaller set of analytes was observed in releasates from cultured DRG neurons. The peptide signals observed in the releasates have been mass-matched to those characterized and identified in homogenates of entire DRGs and associated nerves. This data aids our understanding of the chemical composition of the mammalian peripheral sensory-motor system, which is involved in key physiological functions such as nociception, thermoreception, itch sensation, and proprioception.

Closing the gap between brain banks and proteomics to advance the study of neurodegenerative diseases

Neurodegenerative diseases (NDs), such as Alzheimer's disease and Parkinson's disease, are among the most debilitating neurological disorders, and as life expectancy rises quickly around the world, the scientific and clinical challenges of dealing with them will also increase dramatically, putting increased pressure on the biomedical community to come up with innovative solutions for the understanding, diagnosis, and treatment of these conditions. Despite several decades of intensive research, there is still little that can be done to prevent, cure, or even slow down the progression of NDs in most patients. There is an urgent need to develop new lines of basic and applied research that can be quickly translated into clinical application. One way to do this is to apply the tools of proteomics to well-characterized samples of human brain tissue, but a closer partnership must still be forged between proteomic scientists, brain banks, and clinicians to explore the maximum potential of this approach. Here, we analyze the challenges and potential benefits of using human brain tissue for proteomics research toward NDs.

MALDI mass spectrometric imaging meets “omics”: recent advances in the fruitful marriage

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI MSI) is a method that allows the investigation of the molecular content of surfaces, in particular, tissues, within its morphological context.