Striatal alterations of secretogranin-1, somatostatin, prodynorphin, and cholecystokinin peptides in an experimental mouse model of Parkinson disease

Gut neuropeptide involvement in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting over 10 million people. A key pathological feature of PD is the accumulation of misfolded α-synuclein (aSyn) protein in the substantia nigra pars compacta. Aggregation of aSyn can form Lewy bodies that contribute to dopaminergic neuron degeneration and motor symptoms, such as tremor, rigidity, and bradykinesia. Beyond the central nervous system, aSyn aggregates have been detected in the gastrointestinal (GI) tract, suggesting a link between peripheral aSyn and nonmotor PD symptoms. GI symptoms, often preceding motor symptoms by up to 20 years, highlight the bidirectional communication between the central nervous system and the enteric nervous system (gut-brain axis) in PD. Although microbiome alterations and intestinal inflammation have been associated with PD, functional impacts on gut-brain signaling or aSyn aggregation remain unclear. Intestinal neuropeptides are key modulators of gut-brain communication, alter immune response to pathogens and environmental toxins, and may contribute to the function of the luminal gut barrier. Dysregulation of gut neuropeptide signaling, including vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, ghrelin, cholecystokinin, glucagon-like peptide 1, and substance P, have been associated with pathologic effects of PD in animal models. Despite their potential role in pathogenesis and disease modulation, gut neuropeptide roles in PD are underexplored. This article reviews current knowledge surrounding microbial metabolite and immune influences on gut neuropeptide signaling, aSyn aggregation in the enteric nervous system, and downstream neuroimmune pathway alterations within the context of PD and its mouse models.

The neuroprotective effects of cholecystokinin in the brain: antioxidant, anti-inflammatory, cognition, and synaptic plasticity

Cholecystokinin (CCK) is a major neuropeptide in the brain that functions as a neurotransmitter, hormone, and growth factor. The peptide and its receptors are widely expressed in the brain. CCK signaling modulates synaptic plasticity and can improve or impair memory formation, depending on the brain areas studies and the receptor subtype activated. Studies have shown in a series of animal models of neurodegenerative diseases that CCK receptor agonists show neuroprotective effects and can effectively alleviate oxidative stress, alleviate chronic inflammation of the central nervous system, improve neuronal synaptic plasticity, prevent neuronal loss, and improve cognitive dysfunction in Alzheimer's disease (AD) model mice and motor activity in animal models of Parkinson's disease. In addition, CCK plays important roles in the amygdala to regulate anxiety and depressive states. Activation of interneurons or inhibition of excitatory neurons can improve anxiety levels. This review summarizes the effects on memory formation and synaptic plasticity, the neuroprotective effects of cholecystokinin and its analogs in neurological diseases such as Alzheimer and Parkinson's disease, and the effects on anxiety and neuronal activity in the amygdala.

Cholecystokinin (CCK): a neuromodulator with therapeutic potential in Alzheimer's and Parkinson's disease

Cholecystokinin (CCK) is a neuropeptide modulating digestion, glucose levels, neurotransmitters and memory. Recent studies suggest that CCK exhibits neuroprotective effects in Alzheimer's disease (AD) and Parkinson's disease (PD). Thus, we review the physiological function and therapeutic potential of CCK. The neuropeptide facilitates hippocampal glutamate release and gates GABAergic basket cell activity, which improves declarative memory acquisition, but inhibits consolidation. Cortical CCK alters recognition memory and enhances audio-visual processing. By stimulating CCK-1 receptors (CCK-1Rs), sulphated CCK-8 elicits dopamine release in the substantia nigra and striatum. In the mesolimbic pathway, CCK release is triggered by dopamine and terminates reward responses via CCK-2Rs. Importantly, activation of hippocampal and nigral CCK-2Rs is neuroprotective by evoking AMPK activation, expression of mitochondrial fusion modulators and autophagy. Other benefits include vagus nerve/CCK-1R-mediated expression of brain-derived neurotrophic factor, intestinal protection and suppression of inflammation. We also discuss caveats and the therapeutic combination of CCK with other peptide hormones.

Rare disease research workflow using multilayer networks elucidates the molecular determinants of severity in Congenital Myasthenic Syndromes

Exploring the molecular basis of disease severity in rare disease scenarios is a challenging task provided the limitations on data availability. Causative genes have been described for Congenital Myasthenic Syndromes (CMS), a group of diverse minority neuromuscular junction (NMJ) disorders; yet a molecular explanation for the phenotypic severity differences remains unclear. Here, we present a workflow to explore the functional relationships between CMS causal genes and altered genes from each patient, based on multilayer network community detection analysis of complementary biomedical information provided by relevant data sources, namely protein-protein interactions, pathways and metabolomics. Our results show that CMS severity can be ascribed to the personalized impairment of extracellular matrix components and postsynaptic modulators of acetylcholine receptor (AChR) clustering. This work showcases how coupling multilayer network analysis with personalized -omics information provides molecular explanations to the varying severity of rare diseases; paving the way for sorting out similar cases in other rare diseases.

Possible Signaling Pathways in the Gut Microbiota-Brain Axis for the Development of Parkinson's Disease Caused by Chronic Consumption of Food Additives

It is well-known that consumption of synthetic and natural food additives has both positive and negative effects in the human body. However, it is not clear yet how food additives are related to the development of Parkinson's disease. Therefore, in this review work, the food additive effects related to the gut microbiota-brain axis and the processes that are carried out to develop Parkinson's disease are studied. To this end, a systematic literature analysis is performed with the selected keywords and the food additive effects are studied to draw possible routes of action. This analysis leads to the proposition of a model that explains the pathways that relate the ingestion of food additives to the development of Parkinson's disease. This work motivates further research that ponders the safety of food additives by measuring their impacts over the gut microbiota-brain axis.

Several neuropeptides involved in parkinsonian neuroprotection modulate the firing properties of nigral dopaminergic neurons

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The surviving nigral dopaminergic neurons display altered spontaneous firing activity in Parkinson's disease. The firing rate of nigral dopaminergic neurons decreases long before complete neuronal death and the appearance of parkinsonian symptoms. A mild stimulation could rescue dopaminergic neurons from death and in turn play neuroprotective effects. Several neuropeptides, including cholecystokinin (CCK), ghrelin, neurotensin, orexin, tachykinins and apelin, within the substantia nigra pars compacta play important roles in the modulation of spontaneous firing activity of dopaminergic neurons and therefore involve motor control and motor disorders. Here, we review neuropeptide-induced modulation of the firing properties of nigral dopaminergic neurons. This review may provide a background to guide further investigations into the involvement of neuropeptides in movement control by modulating firing activity of nigral dopaminergic neurons in Parkinson's disease.

Parkinson disease: Protective role and function of neuropeptides

Neuropeptides are bioactive molecules, made up of small chains of amino acids, with many neuromodulatory properties. Several lines of evidence suggest that neuropeptides, mainly expressed in the central nervous system (CNS), play an important role in the onset of Parkinson's Disease (PD) pathology. The wide spread disruption of neuropeptides has been excessively demonstrated to be related to the pathophysiological symptoms in PD where impairment in motor function per example was correlated with neuropeptides dysregulation in the substantia niagra (SN). Moreover, the levels of different neuropeptides have been found modified in the cerebrospinal fluid and blood of PD patients, indicating their potential role in the manifestation of PD symptoms and dysfunctions. In this review, we outlined the neuroprotective effects of neuropeptides on dopaminergic neuronal loss, oxidative stress and neuroinflammation in several models and tissues of PD. Our main focus was to elaborate the role of orexin, pituitary adenylate cyclase activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), opioids, angiotensin, carnosine and many others in the protection and/or involvement in the neurodegeneration of striatal dopaminergic cells. Further studies are required to better assess the mode of action and cellular mechanisms of neuropeptides in order to shift the focus from the in vitro and in vivo testing to applicable clinical testing. This review, allows a support for future use of neuropeptides as therapeutic solution for PA pathophysiology.

Basal ganglia neuropeptides show abnormal processing associated with L-DOPA-induced dyskinesia

L-DOPA administration is the primary treatment for Parkinson’s disease (PD) but long-term administration is usually accompanied by hyperkinetic side-effects called L-DOPA-induced dyskinesia (LID). Signaling neuropeptides of the basal ganglia are affected in LID and changes in the expression of neuropeptide precursors have been described, but the final products formed from these precursors have not been well defined and regionally mapped. We therefore used mass spectrometry imaging to visualize and quantify neuropeptides in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine exposed parkinsonian and LID Macaca mulatta brain samples. We found that dyskinesia severity correlated with the levels of some abnormally processed peptides — notably, des-tyrosine dynorphins, substance P (1-7), and substance P (1-9) — in multiple brain regions. Levels of the active neuropeptides; dynorphin B, dynorphin A (1-8), α-neoendorphin, substance P (1-11), and neurokinin A, in the globus pallidus and substantia nigra correlated with putaminal levels of L-DOPA. Our results demonstrate that the abundance of selected active neuropeptides is associated with L-DOPA concentrations in the putamen, emphasizing their sensitivity to L-DOPA. Additionally, levels of truncated neuropeptides (which generally exhibit reduced or altered receptor affinity) correlate with dyskinesia severity, particularly for peptides associated with the direct pathway (i.e., dynorphins and tachykinins). The increases in tone of the tachykinin, enkephalin, and dynorphin neuropeptides in LID result in abnormal processing of neuropeptides with different biological activity and may constitute a functional compensatory mechanism for balancing the increased L-DOPA levels across the whole basal ganglia.

Cell–Cell Communication Alterations via Intercellular Signaling Pathways in Substantia Nigra of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative movement disorder characterized with dopaminergic neuron (DaN) loss within the substantia nigra (SN). Despite bulk studies focusing on intracellular mechanisms of PD inside DaNs, few studies have explored the pathogeneses outside DaNs, or between DaNs and other cells. Here, we set out to probe the implication of intercellular communication involving DaNs in the pathogeneses of PD at a systemic level with bioinformatics methods. We harvested three online published single-cell/single-nucleus transcriptomic sequencing (sc/snRNA-seq) datasets of human SN (GSE126838, GSE140231, and GSE157783) from the Gene Expression Omnibus (GEO) database, and integrated them with one of the latest integration algorithms called Harmony. We then applied CellChat, the latest cell–cell communication analytic algorithm, to our integrated dataset. We first found that the overall communication quantity was decreased while the overall communication strength was enhanced in PD sample compared with control sample. We then focused on the intercellular communication where DaNs are involved, and found that the communications between DaNs and other cell types via certain signaling pathways were selectively altered in PD, including some growth factors, neurotrophic factors, chemokines, etc. pathways. Our bioinformatics analysis showed that the alteration in intercellular communications involving DaNs might be a previously underestimated aspect of PD pathogeneses with novel translational potential.

Reduced Levels of Intestinal Neuropeptides and Neurotrophins in Neurotoxin-Induced Parkinson Disease Mouse Models

Intestinal neuropeptides and neurotrophins as endocrine messengers play a key role in the bidirectional gut-brain interaction both in health and disease status. Their alterations in several neurological disorders have been reported, but whether a remarkable change occurs in Parkinson disease (PD) remains unexplored. In this study, we aimed to investigate the levels of 13 neuropeptides and 4 neurotrophins in the intestine of neurotoxin-induced PD mice. The PD mice were obtained by chronic injection of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) or MPTP/probenecid (MPTP/p). The levels of mRNA and protein expression in mouse intestines were measured by using real-time reverse transcription polymerase chain reaction and Western blotting, respectively. We found that the mRNA expression of 2 neuropeptides (cholecystokinin [CCK] and dynorphin A [Dyn A]) and 2 neurotrophins (brain-derived neurotrophic factor [BDNF] and neurotrophin-5) was significantly decreased in the colon of MPTP group compared to the vehicle-treated group. The protein levels of CCK, Dyn A, and BDNF were reduced in the colon of MPTP- or MPTP/p-treated mice compared to those of the vehicle-treated group. These data suggest that the intestinal expression of CCK, Dyn A, and BDNF was significantly reduced in PD animal models, and may play a role in the gut-brain axis in PD.

Peptide Profile of Zebrafish Brain in a 6-OHDA-Induced Parkinson Model

Parkinson's disease (PD) is a chronic neurodegenerative disorder mainly attributed to the progressive loss of dopaminergic neurons in the substantia nigra, which leads to uncontrolled voluntary movements causing tremors, postural instability, joint stiffness, and speech and locomotion difficulties, among other symptoms. Previous studies have shown the participation of specific peptides in neurodegenerative diseases. In this context, the present work analyzed changes in the peptide profile in zebrafish brain induced to parkinsonian conditions with 6-hydroxydopamine, using isotopic labeling techniques plus mass spectrometry. These analyses allowed the relative quantitation and identification of 118 peptides. Of these, nine peptides showed significant changes, one peptide was increased and eight decreased. The most altered sequences were fragment of cytosolic and extracellular proteins related to lipid metabolism and dynamic cytoskeleton. These results open new perspectives of study about the function of peptides in PD.

Cerebrospinal fluid proteomics implicates the granin family in Parkinson's disease

Parkinson's disease, the most common age-related movement disorder, is a progressive neurodegenerative disease with unclear etiology. Better understanding of the underlying disease mechanism(s) is an urgent need for the development of disease-modifying therapeutics. Limited studies have been performed in large patient cohorts to identify protein alterations in cerebrospinal fluid (CSF), a proximal site to pathology. We set out to identify disease-relevant protein changes in CSF to gain insights into the etiology of Parkinson's disease and potentially assist in disease biomarker identification. In this study, we used liquid chromatography-tandem mass spectrometry in data-independent acquisition (DIA) mode to identify Parkinson's-relevant biomarkers in cerebrospinal fluid. We quantified 341 protein groups in two independent cohorts (n = 196) and a longitudinal cohort (n = 105 samples, representing 40 patients) consisting of Parkinson's disease and healthy control samples from three different sources. A first cohort of 53 Parkinson's disease and 72 control samples was analyzed, identifying 53 proteins with significant changes (p < 0.05) in Parkinson's disease relative to healthy control. We established a biomarker signature and multiple protein ratios that differentiate Parkinson's disease from healthy controls and validated these results in an independent cohort. The second cohort included 28 Parkinson's disease and 43 control samples. Independent analysis of these samples identified 41 proteins with significant changes. Evaluation of the overlapping changes between the two cohorts identified 13 proteins with consistent and significant changes (p < 0.05). Importantly, we found the extended granin family proteins as reduced in disease, suggesting a potential common mechanism for the biological reduction in monoamine neurotransmission in Parkinson's patients. Our study identifies several novel protein changes in Parkinson's disease cerebrospinal fluid that may be exploited for understanding etiology of disease and for biomarker development.

Protein carbonylation in dopaminergic cells exposed to rotenone

Rotenone is an environmental neurotoxin that induces degeneration of dopaminergic neurons and the most common features of Parkinson's disease in animal models. It acts as a mitochondrial complex I inhibitor that impairs cellular respiration, with consequent increase of reactive oxygen species and oxidative stress. This study evaluates the rotenone-induced oxidative damage in PC12 cells, focusing particularly on protein oxidation. The identification of specific carbonylated proteins highlighted putative alterations of important cellular processes possibly associated with Parkinson's disease. Carbonylation of ATP synthase and of enzymes acting in pyruvate and glucose metabolism suggested a failure of mechanisms ensuring cellular energy supply. Concomitant oxidation of cytoskeletal proteins and of enzymes involved in the synthesis of neuroactive molecules indicated alterations of the neurotransmission system. Carbonylation of chaperon proteins as well as of proteins acting in the autophagy-lysosome pathway and the ubiquitin-proteasome system suggested the possible formation of cytosolic unfolded protein inclusions as result of defective processes assisting recovery/degradation of damaged molecules. In conclusion, this study originally evidences specific protein targets of rotenone-induced oxidative damage, suggesting some possible molecular mechanisms involved in rotenone toxicity.

Toxicity, recovery, and resilience in a 3D dopaminergic neuronal in vitro model exposed to rotenone

To date, most in vitro toxicity testing has focused on acute effects of compounds at high concentrations. This testing strategy does not reflect real-life exposures, which might contribute to long-term disease outcome. We used a 3D-human dopaminergic in vitro LUHMES cell line model to determine whether effects of short-term rotenone exposure (100 nM, 24 h) are permanent or reversible. A decrease in complex I activity, ATP, mitochondrial diameter, and neurite outgrowth were observed acutely. After compound removal, complex I activity was still inhibited; however, ATP levels were increased, cells were electrically active and aggregates restored neurite outgrowth integrity and mitochondrial morphology. We identified significant transcriptomic changes after 24 h which were not present 7 days after wash-out. Our results suggest that testing short-term exposures in vitro may capture many acute effects which cells can overcome, missing adaptive processes, and long-term mechanisms. In addition, to study cellular resilience, cells were re-exposed to rotenone after wash-out and recovery period. Pre-exposed cells maintained higher metabolic activity than controls and presented a different expression pattern in genes previously shown to be altered by rotenone. NEF2L2, ATF4, and EAAC1 were downregulated upon single hit on day 14, but unchanged in pre-exposed aggregates. DAT and CASP3 were only altered after re-exposure to rotenone, while TYMS and MLF1IP were downregulated in both single-exposed and pre-exposed aggregates. In summary, our study shows that a human cell-based 3D model can be used to assess cellular adaptation, resilience, and long-term mechanisms relevant to neurodegenerative research.

Gender-Specific Associations between CHGB Genetic Variants and Schizophrenia in a Korean Population

PURPOSE

Schizophrenia is a devastating mental disorder and is known to be affected by genetic factors. The chromogranin B (CHGB), a member of the chromogranin gene family, has been proposed as a candidate gene associated with the risk of schizophrenia. The secretory pathway for peptide hormones and neuropeptides in the brain is regulated by chromogranin proteins. The aim of this study was to investigate the potential associations between genetic variants of CHGB and schizophrenia susceptibility.

MATERIALS AND METHODS

In the current study, 15 single nucleotide polymorphisms of CHGB were genotyped in 310 schizophrenia patients and 604 healthy controls.

RESULTS

Statistical analysis revealed that two genetic variants (non-synonymous rs910122; rs2821 in 3'-untranslated region) were associated with schizophrenia [minimum p=0.002; odds ratio (OR)=0.72], even after correction for multiple testing (p(corr)=0.02). Since schizophrenia is known to be differentially expressed between sexes, additional analysis for sex was performed. As a result, these two genetic variants (rs910122 and rs2821) and a haplotype (ht3) showed significant associations with schizophrenia in male subjects (p(corr)=0.02; OR=0.64), whereas the significance disappeared in female subjects (p>0.05).

CONCLUSION

Although this study has limitations including a small number of samples and lack of functional study, our results suggest that genetic variants of CHGB may have sex-specific effects on the risk of schizophrenia and provide useful preliminary information for further study.

Proteomic studies associated with Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is an insidious disorder affecting more than 1-2% of the population over the age of 65. Understanding the etiology of PD may create opportunities for developing new treatments. Genomic and transcriptomic studies are useful, but do not provide evidence for the actual status of the disease. Conversely, proteomic studies deal with proteins, which are real time players, and can hence provide information on the dynamic nature of the affected cells. The number of publications relating to the proteomics of PD is vast. Therefore, there is a need to evaluate the current proteomics literature and establish the connections between the past and the present to foresee the future. Areas covered: PubMed and Web of Science were used to retrieve the literature associated with PD proteomics. Studies using human samples, model organisms and cell lines were selected and reviewed to highlight their contributions to PD. Expert commentary: The proteomic studies associated with PD achieved only limited success in facilitating disease diagnosis, monitoring and progression. A global system biology approach using new models is needed. Future research should integrate the findings of proteomics with other omics data to facilitate both early diagnosis and the treatment of PD.

Dissociation between dopaminergic response and motor behavior following intrastriatal, but not intravenous, transplant of bone marrow mononuclear stem cells in a mouse model of Parkinson's disease

Parkinson's disease is characterized by the progressive loss of dopaminergic neurons from the substantia nigra, a process that leads to a dopamine deficiency in the striatum. This deficiency is responsible for the development of motor symptoms, including resting tremor, bradykinesia, rigidity and postural instability. Based on the observation of substantial neuronal death, alternatives to Parkinson's disease treatment have been studied, including cell-based therapies. The present study aimed to assess the therapeutic potential of intravenous and intrastriatal transplant of bone marrow mononuclear cells in a mouse model of Parkinson's disease. Animals underwent stereotaxic surgery and received an injection of 6-hydroxydopamine into their medial forebrain bundle. Three weeks later, mice were injected with bone marrow mononuclear cells or saline through the caudal vein or directly into their right striatum. Motor function was assessed using the rotarod and apomorphine-induced rotation tests. Our results showed that intrastriatal bone marrow mononuclear cells, but not intravenous, have a short-term therapeutic effect on dopaminergic response in this mice model of parkinsonism assessed by the apomorphine-induced rotation test. This phenomenon was not identified on the rotarod test, showing dissociation between dopaminergic response and motor behavior. Further experiments are needed to elucidate the precise mechanisms involved in these effects.

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.

Glaucoma related Proteomic Alterations in Human Retina Samples

Glaucoma related proteomic changes have been documented in cell and animal models. However, proteomic studies investigating on human retina samples are still rare. In the present work, retina samples of glaucoma and non-glaucoma control donors have been examined by a state-of-the-art mass spectrometry (MS) workflow to uncover glaucoma related proteomic changes. More than 600 proteins could be identified with high confidence (FDR < 1%) in human retina samples. Distinct proteomic changes have been observed in 10% of proteins encircling mitochondrial and nucleus species. Numerous proteins showed a significant glaucoma related level change (p < 0.05) or distinct tendency of alteration (p < 0.1). Candidates were documented to be involved in cellular development, stress and cell death. Increase of stress related proteins and decrease of new glaucoma related candidates, ADP/ATP translocase 3 (ANT3), PC4 and SRFS1-interacting protein 1 (DFS70) and methyl-CpG-binding protein 2 (MeCp2) could be documented by MS. Moreover, candidates could be validated by Accurate Inclusion Mass Screening (AIMS) and immunostaining and supported for the retinal ganglion cell layer (GCL) by laser capture microdissection (LCM) in porcine and human eye cryosections. The workflow allowed a detailed view into the human retina proteome highlighting new molecular players ANT3, DFS70 and MeCp2 associated to glaucoma.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Novel protein-protein interactions of TPPII, p53, and SIRT7

Novel protein-protein interactions of TPPII, SIRT7, and p53 were detected by co-immunoprecipitation using both HeLa cell lysates and the cytoplasmic fraction prepared by fractionation of mouse liver tissue. The interactions were further verified in vivo by in situ proximity ligation assay (PLA) within control HEK293 cells transformed with empty vector, highactTPPII HEK293 cells over-expressing murine TPPII displaying high specific enzymatic activity and in lowactTPPII HEK293 cells over-expressing human TPPII having low specific activity of the enzyme. Besides an abundant cytoplasmic localization of TPPII-p53 interaction signal, the nuclear interactions were also demonstrated. The cytoplasmic interactions were likewise detected between TPPII and SIRT7 in control HEK293 and lowactTPPII HEK293 cells. The interactions of SIRT7 with p53 were confirmed in three HEK293 cell transformants as well. The cytoplasmic occurrence of SIRT7 protein was demonstrated by immunofluorescence, when both nucleolar and cytoplasmic signals were identified within HEK293 cells and primary human fibroblasts. The unique cytoplasmic localization of SIRT7 protein was discussed based on an epitope specificity of N-terminus specific SIRT7 antibodies utilized in the present study compared with C-terminus specific antibodies previously used for nuclear detection of SIRT7 by other authors. The epitope sequence of N-terminal antibodies is occurring in all three splicing variants of SIRT7 compared to the epitope of C-terminal antibody, which is specific exclusively to the splicing variant 1. The cytoplasmic localization of p53 detected by immunofluorescence supported the results from its interactions with TPPII and SIRT7 observed by in situ PLA within model cells. Novel interactions of TPPII, p53, and SIRT7 presented in this study might contribute to the knowledge of the regulatory effects of these proteins on apoptotic pathways and to the understanding mechanisms of aging and lifespan regulation.

NeuroPep: a comprehensive resource of neuropeptides

Neuropeptides play a variety of roles in many physiological processes and serve as potential therapeutic targets for the treatment of some nervous-system disorders. In recent years, there has been a tremendous increase in the number of identified neuropeptides. Therefore, we have developed NeuroPep, a comprehensive resource of neuropeptides, which holds 5949 non-redundant neuropeptide entries originating from 493 organisms belonging to 65 neuropeptide families. In NeuroPep, the number of neuropeptides in invertebrates and vertebrates is 3455 and 2406, respectively. It is currently the most complete neuropeptide database. We extracted entries deposited in UniProt, the database (www.neuropeptides.nl) and NeuroPedia, and used text mining methods to retrieve entries from the MEDLINE abstracts and full text articles. All the entries in NeuroPep have been manually checked. 2069 of the 5949 (35%) neuropeptide sequences were collected from the scientific literature. Moreover, NeuroPep contains detailed annotations for each entry, including source organisms, tissue specificity, families, names, post-translational modifications, 3D structures (if available) and literature references. Information derived from these peptide sequences such as amino acid compositions, isoelectric points, molecular weight and other physicochemical properties of peptides are also provided. A quick search feature allows users to search the database with keywords such as sequence, name, family, etc., and an advanced search page helps users to combine queries with logical operators like AND/OR. In addition, user-friendly web tools like browsing, sequence alignment and mapping are also integrated into the NeuroPep database. Database URL: http://isyslab.info/NeuroPep

Quantitative proteomics of delirium cerebrospinal fluid

Delirium is a common cause and complication of hospitalization in older people, being associated with higher risk of future dementia and progression of existing dementia. However relatively little data are available on which biochemical pathways are dysregulated in the brain during delirium episodes, whether there are protein expression changes common among delirium subjects and whether there are any changes which correlate with the severity of delirium. We now present the first proteomic analysis of delirium cerebrospinal fluid (CSF), and one of few studies exploring protein expression changes in delirium. More than 270 proteins were identified in two delirium cohorts, 16 of which were dysregulated in at least 8 of 17 delirium subjects compared with a mild Alzheimer's disease neurological control group, and 31 proteins were significantly correlated with cognitive scores (mini-mental state exam and acute physiology and chronic health evaluation III). Bioinformatics analyses revealed expression changes in several protein family groups, including apolipoproteins, secretogranins/chromogranins, clotting/fibrinolysis factors, serine protease inhibitors and acute-phase response elements. These data not only provide confirmatory evidence that the inflammatory response is a component of delirium, but also reveal dysregulation of protein expression in a number of novel and unexpected clusters of proteins, in particular the granins. Another surprising outcome of this work is the level of similarity of CSF protein profiles in delirium patients, given the diversity of causes of this syndrome. These data provide additional elements for consideration in the pathophysiology of delirium as well as potential biomarker candidates for delirium diagnosis.

Recent advances in quantitative neuroproteomics

The field of proteomics is undergoing rapid development in a number of different areas including improvements in mass spectrometric platforms, peptide identification algorithms and bioinformatics. In particular, new and/or improved approaches have established robust methods that not only allow for in-depth and accurate peptide and protein identification and modification, but also allow for sensitive measurement of relative or absolute quantitation. These methods are beginning to be applied to the area of neuroproteomics, but the central nervous system poses many specific challenges in terms of quantitative proteomics, given the large number of different neuronal cell types that are intermixed and that exhibit distinct patterns of gene and protein expression. This review highlights the recent advances that have been made in quantitative neuroproteomics, with a focus on work published over the last five years that applies emerging methods to normal brain function as well as to various neuropsychiatric disorders including schizophrenia and drug addiction as well as of neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. While older methods such as two-dimensional polyacrylamide electrophoresis continued to be used, a variety of more in-depth MS-based approaches including both label (ICAT, iTRAQ, TMT, SILAC, SILAM), label-free (label-free, MRM, SWATH) and absolute quantification methods, are rapidly being applied to neurobiological investigations of normal and diseased brain tissue as well as of cerebrospinal fluid (CSF). While the biological implications of many of these studies remain to be clearly established, that there is a clear need for standardization of experimental design and data analysis, and that the analysis of protein changes in specific neuronal cell types in the central nervous system remains a serious challenge, it appears that the quality and depth of the more recent quantitative proteomics studies is beginning to shed light on a number of aspects of neuroscience that relates to normal brain function as well as of the changes in protein expression and regulation that occurs in neuropsychiatric and neurodegenerative disorders.

Neurotoxin-induced neuropeptide perturbations in striatum of neonatal rats

The cyanobacterial toxin β-N-methylamino-l-alanine (BMAA) is suggested to play a role in neurodegenerative disease. We have previously shown that although the selective uptake of BMAA in the rodent neonatal striatum does not cause neuronal cell death, exposure during the neonatal development leads to cognitive impairments in adult rats. The aim of the present study was to characterize the changes in the striatal neuropeptide systems of male and female rat pups treated neonatally (postnatal days 9-10) with BMAA (40-460 mg/kg). The label-free quantification of the relative levels of endogenous neuropeptides using mass spectrometry revealed that 25 peptides from 13 neuropeptide precursors were significantly changed in the rat neonatal striatum. The exposure to noncytotoxic doses of BMAA induced a dose-dependent increase of neurosecretory protein VGF-derived peptides, and changes in the relative levels of cholecystokinin, chromogranin, secretogranin, MCH, somatostatin and cortistatin-derived peptides were observed at the highest dose. In addition, the results revealed a sex-dependent increase in the relative level of peptides derived from the proenkephalin-A and protachykinin-1 precursors, including substance P and neurokinin A, in female pups. Because several of these peptides play a critical role in the development and survival of neurons, the observed neuropeptide changes might be possible mediators of BMAA-induced behavioral changes. Moreover, some neuropeptide changes suggest potential sex-related differences in susceptibility toward this neurotoxin. The present study also suggests that neuropeptide profiling might provide a sensitive characterization of the BMAA-induced noncytotoxic effects on the developing brain.

Evaluation of database search programs for accurate detection of neuropeptides in tandem mass spectrometry experiments

Neuropeptide identification in mass spectrometry experiments using database search programs developed for proteins is challenging. Unlike proteins, the detection of the complete sequence using a single spectrum is required to identify neuropeptides or prohormone peptides. This study compared the performance of three open-source programs used to identify proteins, OMSSA, X!Tandem and Crux, to identify prohormone peptides. From a target database of 7850 prohormone peptides, 23550 query spectra were simulated across different scenarios. Crux was the only program that correctly matched all peptides regardless of p-value and at p-value < 1 × 10^–2, 33%, 64%, and >75%, of the 5, 6, and ≥7 amino acid-peptides were detected. Crux also had the best performance in the identification of peptides from chimera spectra and in a variety of missing ion scenarios. OMSSA, X!Tandem and Crux correctly detected 98.9% (99.9%), 93.9% (97.4%) and 88.7% (98.3%) of the peptides at E- or p-value < 1 × 10^–6 (< 1 × 10^–2), respectively. OMSSA and X!Tandem outperformed the other programs in significance level and computational speed, respectively. A consensus approach is not recommended because some prohormone peptides were only identified by one program.

Dysregulated expression of secretogranin III is involved in neurotoxin-induced dopaminergic neuron apoptosis

The neurotoxins paraquat (PQ) and dopamine (DA or 6-OHDA) cause apoptosis of dopaminergic neurons in the substantia nigra pars compacta (SNpc), reproducing an important pathological feature of Parkinson's disease (PD). Secretogranin III (SCG3), a member of the multifunctional granin family, plays a key role in neurotransmitter storage and transport and in secretory granule biogenesis, which involves the uptake of exogenous toxins and endogenous "toxins" in neuroendocrine cells. However, the molecular mechanisms of neurotoxin-induced apoptosis in dopaminergic neurons and the role of SCG3-associated signaling pathways in neuroendocrine regulation are unclear. To address this, we used PQ- and DA-induced apoptosis in SH-SY5Y human dopaminergic cells as an in vitro model to investigate the association between SCG3 expression level and apoptosis. SCG3 was highly expressed in SH-SY5Y cells, and SCG3 mRNA and protein levels were dramatically decreased after PQ treatment. Apoptosis induced by PQ is associated with caspase activation and decreased SCG3 expression, and restoration of SCG3 expression is observed after treatment with caspase inhibitors. Overexpressed SCG3 in nonneuronal cells and endogenous SCG3 in SH-SY5Y cells are cleaved into specific fragments by recombinant caspase-3 and -7, but the fragments were not detected in PQ-treated SH-SY5Y cells. Therefore, SCG3 may be involved in apoptosis signal transduction as a caspase substrate, leading to loss of its original biological functions. In addition, SCG3 may be a pivotal component of the neuroendocrine pathway and play an important role in neuronal communication and neurotransmitter release, possibly representing a new potential target in the course of PD pathogenesis.

Modulation of acetylcholine release by cholecystokinin in striatum: receptor specificity; role of dopaminergic neuronal activity

Cholecystokinin, a neuroactive peptide functioning as a neurotransmitter and neuromodulator in the central nervous system, mediates a number of processes and is implicated in neurological and psychiatric disorders such as Parkinson's disease, anxiety and schizophrenia. Striatum is one of the brain structures with the highest concentrations of CCK in the brain, rich in CCK receptors as well. The physiological effect of CCK on cholinergic interneurons, which are the major interneurons in striatum and the modulatory interactions which exist between dopamine, acetylcholine and cholecystokinin in this brain structure are still unclear. We studied the effect of cholecystokinin octapeptide (CCK-8) on the release of acetylcholine (ACh) from striatal slices of the rat brain. CCK-8 (0.01-0.1μM) showed no statistically significant effect on the basal but enhanced dose-dependently the electrically (2Hz)-evoked release of [(3)H]ACh. When slices were preperfused with 100μM sulpiride, a selective dopamine D(2) receptor antagonist, the CCK-8 (0.01μM) effect on electrically stimulated ACh release was increased nearly 2-fold. A similar increase was observed after depletion of endogenous dopamine (DA) from nigro-striatal dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (2× 250μg/animal, i.c.v.). Furthermore in the presence of dopamine (100μM) or apomorphine (10μM), the prototypical DA receptor agonist, CCK-8 (0.01μM) failed to enhance the stimulation-evoked release of [(3)H]ACh. The D(2) receptor agonist quinpirol (1μM) abolished the CCK-8 effect on electrically stimulated ACh release as well. The increase in electrically induced [(3)H]ACh release produced by 0.01μM CCK-8 was antagonized by d,l loxiglumide (CR 1505), 10μM, a non-peptide CCK-A receptor antagonist and by Suc-Tyr-(OSO3)-Met-Gly-Trp-Met-Asp-β-phenethyl-amide (GE-410), 1μM, a peptide CCK-A receptor antagonist. The antagonistic effect of GE-410 on the CCK-8-potentiated, electrically induced release of [(3)H]ACh was studied in striatum for the first time. CAM 1028 (10μM), a CCK-B receptor antagonist, also prevented the potentiating effect of CCK-8 (0.01μM) on electrically stimulated release of [(3)H]ACh. The presented results indicate that (i) CCK-8 is capable of increasing ACh elicited by field electrical stimulation in striatum; (ii) CCK-8 is more effective in its ACh-stimulating effect when dopaminergic activity in striatum is blocked i.e. CCK-8-facilitated release of electrically induced ACh from cholinergic interneurons in the striatum is under the inhibitory control of the tonic activity of dopamine from the nigrostriatal pathway; (iii) the enhancing effect of CCK-8 on electrically evoked ACh release is mediated through both CCK-A and CCK-B cholecystokinin receptors located most likely on the cell bodies of cholinergic interneurons in striatum.

Presynaptic modulation by somatostatin in the rat neostriatum is altered in a model of parkinsonism

Somatostatin (SST) is a peptide synthesized and released by a class of neostriatal local GABAergic interneurons, which, to some extent, are in charge of the feedforward inhibitory circuit. Spiny projection neurons (SPNs) make synapses with each other via their local axon collaterals, shaping the feedback inhibitory circuit. Both inhibitory circuits, feedforward and feedback, are related through SST, which, being released by interneurons, presynaptically inhibits connections among SPNs. Here, we studied SST presynaptic modulation of synapses among SPNs in the 6-hydroxydopamine (6-OHDA) rodent model of parkinsonism. We performed antidromic field stimulation from the external globus pallidus and whole cell voltage-clamp recordings of antidromically evoked inhibitory postsynaptic currents (IPSCs) among SPNs. SST presynaptically reduced IPSCs by ∼34% in all control synapses tested. However, after striatal dopamine deprivation, three changes became evident. First, it was harder to evoke feedback inhibition. Second, presynaptic inhibition of some SPNs connections was larger than in controls: 57% reduction in ∼53% of evoked IPSCs. Presynaptic inhibition was recorded from direct pathway neurons (direct SPNs). Finally, SST also induced presynaptic facilitation in some SPNs connections, with 82% enhancement in ∼43% of evoked IPSCs. Presynaptic facilitation was recorded from indirect pathway neurons (indirect SPNs). Both inhibition and facilitation were accompanied by corresponding changes in the paired pulse ratio. It was demonstrated that after dopamine deprivation, SST modulation is altered in surviving feedback inhibitory synapses. It may underlie a homeostatic mechanism trying to compensate for the excitability imbalance between direct and indirect basal ganglia pathways found during parkinsonism.

Somatostatinergic systems: an update on brain functions in normal and pathological aging

Somatostatin is highly expressed in mammalian brain and is involved in many brain functions such as motor activity, sleep, sensory, and cognitive processes. Five somatostatin receptors have been described: sst(1), sst(2) (A and B), sst(3), sst(4), and sst(5), all belonging to the G-protein-coupled receptor family. During the recent years, numerous studies contributed to clarify the role of somatostatin systems, especially long-range somatostatinergic interneurons, in several functions they have been previously involved in. New advances have also been made on the alterations of somatostatinergic systems in several brain diseases and on the potential therapeutic target they represent in these pathologies.

Extensive characterization of Tupaia belangeri neuropeptidome using an integrated mass spectrometric approach

Neuropeptidomics is used to characterize endogenous peptides in the brain of tree shrews (Tupaia belangeri). Tree shrews are small animals similar to rodents in size but close relatives of primates, and are excellent models for brain research. Currently, tree shrews have no complete proteome information available on which direct database search can be allowed for neuropeptide identification. To increase the capability in the identification of neuropeptides in tree shrews, we developed an integrated mass spectrometry (MS)-based approach that combines methods including data-dependent, directed, and targeted liquid chromatography (LC)-Fourier transform (FT)-tandem MS (MS/MS) analysis, database construction, de novo sequencing, precursor protein search, and homology analysis. Using this integrated approach, we identified 107 endogenous peptides that have sequences identical or similar to those from other mammalian species. High accuracy MS and tandem MS information, with BLAST analysis and chromatographic characteristics were used to confirm the sequences of all the identified peptides. Interestingly, further sequence homology analysis demonstrated that tree shrew peptides have a significantly higher degree of homology to equivalent sequences in humans than those in mice or rats, consistent with the close phylogenetic relationship between tree shrews and primates. Our results provide the first extensive characterization of the peptidome in tree shrews, which now permits characterization of their function in nervous and endocrine system. As the approach developed fully used the conservative properties of neuropeptides in evolution and the advantage of high accuracy MS, it can be portable for identification of neuropeptides in other species for which the fully sequenced genomes or proteomes are not available.

Neuropeptidomics of mouse hypothalamus after imipramine treatment reveal somatostatin as a potential mediator of antidepressant effects

Excessive activation of the hypothalamic-pituitary-adrenal (HPA) axis has been associated with numerous diseases, including depression, and the tricyclic antidepressant imipramine has been shown to suppress activity of the HPA axis. Central hypothalamic control of the HPA axis is complex and involves a number of neuropeptides released from multiple hypothalamic subnuclei. The present study was therefore designed to determine the effects of imipramine administration on the mouse hypothalamus using a peptidomics approach. Among the factors found to be downregulated after acute (one day) or chronic (21 days) imipramine administration were peptides derived from secretogranin 1 (chromogranin B) as well as peptides derived from cerebellin precursors. In contrast, peptides SRIF-14 and SRIF-28 (1-11) derived from somatostatin (SRIF, somatotropin release inhibiting factor) were significantly upregulated by imipramine in the hypothalamus. Because diminished SRIF levels have long been known to occur in depression, a second part of the study investigated the roles of individual SRIF receptors in mediating potential antidepressant effects. SRA880, an antagonist of the somatostatin-1 autoreceptor (sst1) which positively modulates release of endogenous SRIF, was found to synergize with imipramine in causing antidepressant-like effects in the tail suspension test. Furthermore, chronic co-administration of SRA880 and imipramine synergistically increased BDNF mRNA expression in the cerebral cortex. Application of SRIF or L054264, an sst2 receptor agonist, but not L803807, an sst4 receptor agonist, increased phosphorylation of CaMKII and GluR1 in cerebrocortical slices. Our present experiments thus provide evidence for antidepressant-induced upregulation of SRIF in the brain, and strengthen the notion that augmented SRIF expression and signaling may counter depressive-like symptoms. This article is part of a Special Issue entitled 'Anxiety and Depression'.

L-DOPA-induced dyskinesia is associated with regional increase of striatal dynorphin peptides as elucidated by imaging mass spectrometry

Opioid peptides are involved in various pathophysiological processes, including algesia, epilepsy, and drug dependence. A strong association between L-DOPA-induced dyskinesia (LID) and elevated prodynorphin mRNA levels has been established in both patients and in animal models of Parkinson's disease, but to date the endogenous prodynorphin peptide products have not been determined. Here, matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) was used for characterization, localization, and relative quantification of striatal neuropeptides in a rat model of LID in Parkinson's disease. MALDI IMS has the unique advantage of high sensitivity and high molecular specificity, allowing comprehensive detection of multiple molecular species in a single tissue section. Indeed, several dynorphins and enkephalins could be detected in the present study, including dynorphin A(1-8), dynorphin B, α-neoendorphin, MetEnkRF, MetEnkRGL, PEnk (198-209, 219-229). IMS analysis revealed elevated levels of dynorphin B, α-neoendorphin, substance P, and PEnk (220-229) in the dorsolateral striatum of high-dyskinetic animals compared with low-dyskinetic and lesion-only control rats. Furthermore, the peak-intensities of the prodynorphin derived peptides, dynorphin B and α-neoendorphin, were strongly and positively correlated with LID severity. Interestingly, these LID associated dynorphin peptides are not those with high affinity to κ opioid receptors, but are known to bind and activate also μ- and Δ-opioid receptors. In addition, the peak intensities of a novel endogenous metabolite of α-neoendorphin lacking the N-terminal tyrosine correlated positively with dyskinesia severity. MALDI IMS of striatal sections from Pdyn knockout mice verified the identity of fully processed dynorphin peptides and the presence of endogenous des-tyrosine α-neoendorphin. Des-tyrosine dynorphins display reduced opioid receptor binding and this points to possible novel nonopioid receptor mediated changes in the striatum of dyskinetic rats. Because des-tyrosine dynorphins can only be detected by mass spectrometry, as no antibodies are available, these findings highlight the importance of MALDI IMS analysis for the study of molecular dynamics in neurological diseases.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Proteomics in human Parkinson's disease research

During the last decades, considerable advances in the understanding of specific mechanisms underlying neurodegeneration in Parkinson's disease have been achieved, yet neither definite etiology nor unifying sequence of molecular events has been formally established. Current unmet needs in Parkinson's disease research include exploring new hypotheses regarding disease susceptibility, occurrence and progression, identifying reliable diagnostic, prognostic and therapeutic biomarkers, and translating basic research into appropriate disease-modifying strategies. The most popular view proposes that Parkinson's disease results from the complex interplay between genetic and environmental factors and mechanisms believed to be at work include oxidative stress, mitochondrial dysfunction, excitotoxicity, iron deposition and inflammation. More recently, a plethora of data has accumulated pinpointing an abnormal processing of the neuronal protein alpha-synuclein as a pivotal mechanism leading to aggregation, inclusions formation and degeneration. This protein-oriented scenario logically opens the door to the application of proteomic strategies to this field of research. We here review the current literature on proteomics applied to Parkinson's disease research, with particular emphasis on pathogenesis of sporadic Parkinson's disease in humans. We propose the view that Parkinson's disease may be an acquired or genetically-determined brain proteinopathy involving an abnormal processing of several, rather than individual neuronal proteins, and discuss some pre-analytical and analytical developments in proteomics that may help in verifying this concept.

Development and evaluation of normalization methods for label-free relative quantification of endogenous peptides

The performances of 10 different normalization methods on data of endogenous brain peptides produced with label-free nano-LC-MS were evaluated. Data sets originating from three different species (mouse, rat, and Japanese quail), each consisting of 35-45 individual LC-MS analyses, were used in the study. Each sample set contained both technical and biological replicates, and the LC-MS analyses were performed in a randomized block fashion. Peptides in all three data sets were found to display LC-MS analysis order-dependent bias. Global normalization methods will only to some extent correct this type of bias. Only the novel normalization procedure RegrRun (linear regression followed by analysis order normalization) corrected for this type of bias. The RegrRun procedure performed the best of the normalization methods tested and decreased the median S.D. by 43% on average compared with raw data. This method also produced the smallest fraction of peptides with interblock differences while producing the largest fraction of differentially expressed peaks between treatment groups in all three data sets. Linear regression normalization (Regr) performed second best and decreased median S.D. by 38% on average compared with raw data. All other examined methods reduced median S.D. by 20-30% on average compared with raw data.