Microglial activation induced by neurodegeneration: a proteomic analysis

Neuroprotection of Retinal Ganglion Cells Suppresses Microglia Activation in a Mouse Model of Glaucoma

Purpose

Microglial activation has been implicated in many neurodegenerative eye diseases, but the interrelationship between cell loss and microglia activation remains unclear. In glaucoma, there is no consensus yet whether microglial activation precedes or is a consequence of retinal ganglion cell (RGC) degeneration. We therefore investigated the temporal and spatial appearance of activated microglia in retina and their correspondence to RGC degeneration in glaucoma.

Methods

We used an established microbead occlusion model of glaucoma in mouse whereby intraocular pressure (IOP) was elevated. Specific antibodies were used to immunolabel microglia in resting and activated states. To block retinal gap junction (GJ) communication, which has been shown previously to provide significant neuroprotection of RGCs, the GJ blocker meclofenamic acid was administered or connexin36 (Cx36) GJ subunits were ablated genetically. We then studied microglial activation at different time points after microbead injection in control and neuroprotected retinas.

Results

Histochemical analysis of flatmount retinas revealed major changes in microglia morphology, density, and immunoreactivity in microbead-injected eyes. An early stage of microglial activation followed IOP elevation, as indicated by changes in morphology and cell density, but preceded RGC death. In contrast, the later stage of microglia activation, associated with upregulation of major histocompatibility complex class II expression, corresponded temporally to the initial loss of RGCs. However, we found that protection of RGCs afforded by GJ blockade or genetic ablation largely suppressed microglial changes at all stages of activation in glaucomatous retinas.

Conclusions

Together, our data strongly suggest that microglia activation in glaucoma is a consequence, rather than a cause, of initial RGC degeneration and death.

Mouse models of neurodegenerative disease: preclinical imaging and neurovascular component

Neurodegenerative diseases represent great challenges for basic science and clinical medicine because of their prevalence, pathologies, lack of mechanism-based treatments, and impacts on individuals. Translational research might contribute to the study of neurodegenerative diseases. The mouse has become a key model for studying disease mechanisms that might recapitulate in part some aspects of the corresponding human diseases. Neurodegenerative disorders are very complicated and multifactorial. This has to be taken in account when testing drugs. Most of the drugs screening in mice are very difficult to be interpretated and often useless. Mouse models could be condiderated a 'pathway models', rather than as models for the whole complicated construct that makes a human disease. Non-invasive in vivo imaging in mice has gained increasing interest in preclinical research in the last years thanks to the availability of high-resolution single-photon emission computed tomography (SPECT), positron emission tomography (PET), high field Magnetic resonance, Optical Imaging scanners and of highly specific contrast agents. Behavioral test are useful tool to characterize different animal models of neurodegenerative pathology. Furthermore, many authors have observed vascular pathological features associated to the different neurodegenerative disorders. Aim of this review is to focus on the different existing animal models of neurodegenerative disorders, describe behavioral tests and preclinical imaging techniques used for diagnose and describe the vascular pathological features associated to these diseases.

The Influence of Fluorine on the Disturbances of Homeostasis in the Central Nervous System

Fluorides occur naturally in the environment, the daily exposure of human organism to fluorine mainly depends on the intake of this element with drinking water and it is connected with the geographical region. In some countries, we can observe the endemic fluorosis-the damage of hard and soft tissues caused by the excessive intake of fluorine. Recent studies showed that fluorine is toxic to the central nervous system (CNS). There are several known mechanisms which lead to structural brain damage caused by the excessive intake of fluorine. This element is able to cross the blood-brain barrier, and it accumulates in neurons affecting cytological changes, cell activity and ion transport (e.g. chlorine transport). Additionally, fluorine changes the concentration of non-enzymatic advanced glycation end products (AGEs), the metabolism of neurotransmitters (influencing mainly glutamatergic neurotransmission) and the energy metabolism of neurons by the impaired glucose transporter-GLUT1. It can also change activity and lead to dysfunction of important proteins which are part of the respiratory chain. Fluorine also affects oxidative stress, glial activation and inflammation in the CNS which leads to neurodegeneration. All of those changes lead to abnormal cell differentiation and the activation of apoptosis through the changes in the expression of neural cell adhesion molecules (NCAM), glial fibrillary acidic protein (GFAP), brain-derived neurotrophic factor (BDNF) and MAP kinases. Excessive exposure to this element can cause harmful effects such as permanent damage of all brain structures, impaired learning ability, memory dysfunction and behavioural problems. This paper provides an overview of the fluoride neurotoxicity in juveniles and adults.

Advanced glycation end-products produced systemically and by macrophages: A common contributor to inflammation and degenerative diseases

Advanced glycation end products (AGEs) and their receptor have been implicated in the progressions of many intractable diseases, such as diabetes and atherosclerosis, and are also critical for pathologic changes in chronic degenerative diseases, such as Alzheimer's disease, Parkinson's disease, and alcoholic brain damage. Recently activated macrophages were found to be a source of AGEs, and the most abundant form of AGEs, AGE-albumin excreted by macrophages has been implicated in these diseases and to act through common pathways. AGEs inhibition has been shown to prevent the pathogenesis of AGEs-related diseases in human, and therapeutic advances have resulted in several agents that prevent their adverse effects. Recently, anti-inflammatory molecules that inhibit AGEs have been shown to be good candidates for ameliorating diabetic complications as well as degenerative diseases. This review was undertaken to present, discuss, and clarify current understanding regarding AGEs formation in association with macrophages, different diseases, therapeutic and diagnostic strategy and links with RAGE inhibition.

Clinical implications from proteomic studies in neurodegenerative diseases: lessons from mitochondrial proteins

Mitochondria play a key role in eukaryotic cells, being mediators of energy, biosynthetic and regulatory requirements of these cells. Emerging proteomics techniques have allowed scientists to obtain the differentially expressed proteome or the proteomic redox status in mitochondria. This has unmasked the diversity of proteins with respect to subcellular location, expression and interactions. Mitochondria have become a research 'hot spot' in subcellular proteomics, leading to identification of candidate clinical targets in neurodegenerative diseases in which mitochondria are known to play pathological roles. The extensive efforts to rapidly obtain differentially expressed proteomes and unravel the redox proteomic status in mitochondria have yielded clinical insights into the neuropathological mechanisms of disease, identification of disease early stage and evaluation of disease progression. Although current technical limitations hamper full exploitation of the mitochondrial proteome in neurosciences, future advances are predicted to provide identification of specific therapeutic targets for neurodegenerative disorders.

Methylmercury can induce Parkinson's-like neurotoxicity similar to 1-methyl-4- phenylpyridinium: a genomic and proteomic analysis on MN9D dopaminergic neuron cells

Exposure to environmental chemicals has been implicated as a possible risk factor for the development of neurodegenerative diseases. Our previous study showed that methylmercury (MeHg) exposure can disrupt synthesis, uptake and metabolism of dopamine similar to 1-methyl-4-phenylpyridinium (MPP(+)). The objective of this study was to investigate the effects of MeHg exposure on gene and protein profiles in a dopaminergic MN9D cell line. MN9D cells were treated with MeHg (1-5 μM) and MPP(+) (10-40 μM) for 48 hr. Real-time PCR Parkinson's disease (PD) arrays and high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) were performed for the analysis. PD PCR array results showed that 19% genes were significantly changed in the 2.5 μM MeHg treated cells, and 39% genes were changed in the 5 μM MeHg treated cells. In comparison, MPP(+) treatment (40 µM) resulted in significant changes in 25% genes. A total of 15 common genes were altered by both MeHg and MPP(+), and dopaminergic signaling transduction was the most affected pathway. Proteomic analysis identified a total of 2496 proteins, of which 188, 233 and 395 proteins were differentially changed by 1 μM and 2.5 μM MeHg, and MPP(+) respectively. A total of 61 common proteins were changed by both MeHg and MPP(+) treatment. The changed proteins were mainly involved in energetic generation-related metabolism pathway (propanoate metabolism, pyruvate metabolism and fatty acid metabolism), oxidative phosphorylation, proteasome, PD and other neurodegenerative disorders. A total of 7 genes/proteins including Ube2l3 (Ubiquitin-conjugating enzyme E2 L3) and Th (Tyrosine 3-monooxygenase) were changed in both genomic and proteomic analysis. These results suggest that MeHg and MPP(+) share many similar signaling pathways leading to the pathogenesis of PD and other neurodegenerative diseases.

Approaches for targeted proteomics and its potential applications in neuroscience

An extensive guide on practicable and significant quantitative proteomic approaches in neuroscience research is important not only because of the existing overwhelming limitations but also for gaining valuable understanding into brain function and deciphering proteomics from the workbench to the bedside. Early methodologies to understand the functioning of biological systems are now improving with high-throughput technologies, which allow analysis of various samples concurrently, or of thousand of analytes in a particular sample. Quantitative proteomic approaches include both gel-based and non-gel-based methods that can be further divided into different labelling approaches. This review will emphasize the role of existing technologies, their advantages and disadvantages, as well as their applications in neuroscience. This review will also discuss advanced approaches for targeted proteomics using isotope-coded affinity tag (ICAT) coupled with laser capture microdissection (LCM) followed by liquid chromatography tandem mass spectrometric (LC-MS/MS) analysis. This technology can further be extended to single cell proteomics in other areas of biological sciences and can be combined with other 'omics' approaches to reveal the mechanism of a cellular alterations. This approach may lead to further investigation in basic biology, disease analysis and surveillance, as well as drug discovery. Although numerous challenges still exist, we are confident that this approach will increase the understanding of pathological mechanisms involved in neuroendocrinology, neuropsychiatric and neurodegenerative disorders by delivering protein biomarker signatures for brain dysfunction.

Proteomics in Traditional Chinese Medicine with an Emphasis on Alzheimer's Disease

In recent years, there has been an increasing worldwide interest in traditional Chinese medicine (TCM). This increasing demand for TCM needs to be accompanied by a deeper understanding of the mechanisms of action of TCM-based therapy. However, TCM is often described as a concept of Chinese philosophy, which is incomprehensible for Western medical society, thereby creating a gap between TCM and Western medicine (WM). In order to meet this challenge, TCM research has applied proteomics technologies for exploring the mechanisms of action of TCM treatment. Proteomics enables TCM researchers to oversee various pathways that are affected by treatment, as well as the dynamics of their interactions with one another. This review discusses the utility of comparative proteomics to better understand how TCM treatment may be used as a complementary therapy for Alzheimer's disease (AD). Additionally, we review the data from comparative AD-related TCM proteomics studies and establish the relevance of the data with available AD hypotheses, most notably regarding the ubiquitin proteasome system (UPS).

Acrylamide induces mitochondrial dysfunction and apoptosis in BV-2 microglial cells

Acrylamide (ACR), a potent neurotoxin, can be produced during food processing at high temperature. This study examined the redox-dependent apoptotic and inflammatory responses of ACR in an immortalized mouse microglia cell line BV2. The exposure of BV2 cells to ACR reduced cell viability and induced apoptosis in a concentration-dependent manner. ACR impaired cell energy metabolism by decreasing mitochondrial respiration, anaerobic glycolysis, and lowering expression of the complex I, III, and IV subunits. Mitochondrial dysfunction was associated with a decrease of the mitochondrial membrane potential and the Bcl-2/Bax ratio, thus resulting in activation of the mitochondrion-driven apoptotic signaling. This was accompanied by (a) the modulation of redox-sensitive signaling, suppressed Akt activation and increased JNK and p38 activation, and (b) increased expression of NFκB and downstream inducible nitric oxide synthase (iNOS) and nitric oxide generation, thus supporting indirectly a proinflammatory effect of ACR. Nrf2 expression was also increased but not its translocation to the nucleus. Expectedly, the electrophilic attack of ACR on GSH resulted in substantial loss of GSH with a minor GSSG formation. These changes in the cell׳s redox status elicited by ACR resulted in increased H2O2 formation. The changes in mitochondrial functionality and complex subunit expression caused by ACR were reversed by N-acetyl-L-cysteine (NAC). Likewise, NAC restored the cell׳s redox status by increasing GSH levels with concomitant attenuation of H2O2 generation; these effects resulted in decreased apoptotic cell death and inflammatory responses. ACR-mediated mitochondrial dysfunction along with a more oxidized redox status seems to be critical events leading to activation of the intrinsic apoptotic pathway and inflammatory responses.

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Evidence of inflammatory system involvement in Parkinson's disease

Parkinson's disease (PD) is a chronic neurodegenerative disease underpinned by both genetic and environmental etiologic factors. Recent findings suggest that inflammation may be a pathogenic factor in the onset and progression of both familial and sporadic PD. Understanding the precise role of inflammatory factors in PD will likely lead to understanding of how the disease arises. In vivo evidence for inflammation in PD includes dysregulated molecular mediators such as cytokines, complement system and its receptors, resident microglial activation, peripheral immune cells invasion, and altered composition and phenotype of peripheral immune cells. The growing awareness of these factors has prompted novel approaches to modulate the immune system, although it remains whether these approaches can be used in humans. Influences of ageing and differential exposure to environmental agents suggest potential host-pathogen specific pathophysiologic factors. There is a clear need for research to further unravel the pathophysiologic role of immunity in PD, with the potential of developing new therapeutic targets for this debilitating condition.

Proteome of brain glia: the molecular basis of diverse glial phenotypes

Several different types of nonneuronal glial cells with diverse phenotypes are present in the CNS, and all have distinct indispensible functions. Although glial cells primarily provide neurons with metabolic and structural support in the healthy brain, they may switch phenotype from a "resting" to a "reactive" state in response to pathological insults. Furthermore, this reactive gliosis is an invariant feature of the pathogeneses of CNS maladies. The glial proteome serves as a signature of glial phenotype, and not only executes physiological functions, but also acts as a molecular mediator of the reactive glial phenotype. The glial proteome is also involved in intra- and intercellular communications as exemplified by glia-glia and neuron-glia interactions. The utilization of authoritative proteomic tools and the bioinformatic analyses have helped to profile the brain glial proteome and explore the molecular mechanisms of diverse glial phenotypes. Furthermore, technologic innovations have equipped the field of "glioproteomics" with refined tools for studies of the expression, interaction, and function of glial proteins in the healthy and in the diseased CNS. Glioproteomics is expected to contribute to the elucidation of the molecular mechanisms of CNS pathophysiology and to the discovery of biomarkers and theragnostic targets in CNS disorders.

Suppressed pro-inflammatory response of microglia in CX3CR1 knockout mice

Neuronal fractalkine acts via its receptor, CX3CR1, on microglia to regulate neuroinflammation. Conflicting results have been reported in studies employing CX3CR1 deficient (Cx3cr1(-/-)) mice. Here, compared to wild-type, endotoxin-treated neuron-glial Cx3cr1(-/-)cultures produced less TNF-α, nitric oxide and superoxide; however, fractalkine treatment inhibited the release of pro-inflammatory factors in wild-type and BV-2 cell cultures. Furthermore, endotoxin-treated BV-2 cells expressing siRNA against CX3CR1 increased nitric oxide and TNF-α production. We hypothesize that CX3CL1-CX3CR1 signaling is neuroprotective and propose that the reduced production of pro-inflammatory signals in Cx3cr1(-/-)microglia may result from compensatory mechanisms and not be the direct result of CX3CR1 deficiency.

Concussive injury before or after controlled cortical impact exacerbates histopathology and functional outcome in a mixed traumatic brain injury model in mice

Traumatic brain injury (TBI) may involve diverse injury mechanisms (e.g., focal impact vs. diffuse impact loading). Putative therapies developed in TBI models featuring a single injury mechanism may fail in clinical trials if the model does not fully replicate multiple injury subtypes, which may occur concomitantly in a given patient. We report development and characterization of a mixed contusion/concussion TBI model in mice using controlled cortical impact (CCI; 0.6 mm depth, 6 m/sec) and a closed head injury (CHI) model at one of two levels of injury (53 vs. 83 g weight drop from 66 in). Compared with CCI or CHI alone, sequential CCI-CHI produced additive effects on loss of consciousness (p<0.001), acute cell death (p<0.05), and 12-day lesion size (p<0.05) but not brain edema or 48-h contusion volume. Additive effects of CHI and CCI on post-injury motor (p<0.05) and cognitive (p<0.005) impairment were observed with sequential CCI-CHI (83 g). The data suggest that concussive forces, which in isolation do not induce histopathological damage, exacerbate histopathology and functional outcome after cerebral contusion. Sequential CHI-CCI may model complex injury mechanisms that occur in some patients with TBI and may prove useful for testing putative therapies.

Pesticides, microglial NOX2, and Parkinson's disease

Accumulating evidence indicates that pesticide exposure is associated with an increased risk for developing Parkinson's disease (PD). Several pesticides known to damage dopaminergic (DA) neurons, such as paraquat, rotenone, lindane, and dieldrin also demonstrate the ability to activate microglia, the resident innate immune cell in the brain. While each of these environmental toxicants may impact microglia through unique mechanisms, they all appear to converge on a common final pathway of microglial activation: NADPH oxidase 2 (NOX2) activation. This review will detail the role of microglia in selective DA neurotoxicity, highlight what is currently known about the mechanism of microglial NOX2 activation in these key pesticides, and describe the importance for DA neuron survival and PD etiology.

Comprehensive profiling of metastasis-related proteins in paired hepatocellular carcinoma cells with different metastasis potentials

Precise and comprehensive identifications of the proteins associated with metastasis are critical for early diagnosis and therapeutic intervention of hepatocellular carcinoma (HCC). Therefore, we investigated the proteomic differences between a pair of HCC cell lines, originating from the same progenitor, with different metastasis potential using amino acid-coded mass tagging-based LC-MS/MS quantitative proteomic approach. Totally the relative abundance of 336 proteins in these cell lines were quantified, in which 121 proteins were upregulated by >30%, and 64 proteins were downregulated by >23% in the cells with high metastasis potential. Further validation studies by Western blotting in a series of HCC cell types with progressively increasing trend of metastasis showed that peroxiredoxin 4, HSP90β and HSP27 were positively correlated with increasing metastasis while prohibitin was negatively correlated with metastasis potential. These validation results were also consistent with that obtained from comparative analysis of clinic tissues samples. Function annotations of differentially expressed HCC proteome suggested that the emergence and development of high metastasis involved the dysregulation of cell migration, cell cycle and membrane traffics. Together our results revealed a much more comprehensive profile than that from 2-DE-based method and provided more global insights into the mechanisms of HCC metastasis and potential markers for clinical diagnosis.

Astrocyte activation: a key step in rotenone induced cytotoxicity and DNA damage

Astrocytes are the most abundant glial cells, which provide metabolic support for neurons. Rotenone is a botanical pesticide of natural origin, known to exhibit neurotoxic potential via inhibition of mitochondrial complex-I. This study was carried out to explore the effect of rotenone on C6 cells. The cell line C6 derived from rat glioma cells represents astrocyte-like cell. C6 cells were treated with rotenone (0.1, 1 and 10 μM) for 4 h. The effect of rotenone was studied on cell survival (MTT reduction and PI uptake); free radicals (ROS and RNS) and DNA damage (comet assay and Hoechst staining). The glial cell activation and apoptotic cell death was evaluated by expression of Glial fibrillary acidic protein (GFAP) and caspase-3 respectively. The treatment with rotenone resulted in decreased cell survival and increased free radical generation. Altered nuclear morphology and DNA damage were evident following rotenone treatment in Hoechst staining and Comet assay. Rotenone elevated expression of GFAP and caspase-3 that indicates glial cell activation and apoptosis, respectively. We further studied the effect of melatonin, an antioxidant, on the observed toxic effects. Co-incubation of antioxidant, melatonin (300 μM), significantly suppressed rotenone induced above-mentioned effects in C6 cells. Inhibitory effects of melatonin suggest that free radicals play a major role in rotenone induced astrocyte activation and cellular toxicity leading to apoptosis of astroglial cells.

The changing phenotype of microglia from homeostasis to disease

It has been nearly a century since the early description of microglia by Rio-Hortega; since then many more biological and pathological features of microglia have been recognized. Today, microglia are generally considered to be beneficial to homeostasis at the resting state through their abilities to survey the environment and phagocytose debris. However, when activated microglia assume diverse phenotypes ranging from fully inflamed, which involves the release of many pro-inflammatory cytokines, to alternatively activated, releasing anti-inflammatory cytokines or neurotrophins, the consequences to neurons can range from detrimental to supportive. Due to the different experimental sets and conditions, contradictory results have been obtained regarding the controversial question of whether microglia are “good” or “bad.” While it is well understood that the dual roles of activated microglia depend on specific situations, the underlying mechanisms have remained largely unclear, and the interpretation of certain findings related to diverse microglial phenotypes continues to be problematic. In this review we discuss the functions of microglia in neuronal survival and neurogenesis, the crosstalk between microglia and surrounding cells, and the potential factors that could influence the eventual manifestation of microglia.

Nitric oxide in neurodegeneration: potential benefits of non-steroidal anti-inflammatories

The cellular messenger nitric oxide (NO) has been linked to neurodegenerative disorders due to the increased expression of the enzymes that catalyze its synthesis in postmortem tissues derived from sufferers of these diseases. Nitrated proteins have also been detected in these samples, revealing that NO is biologically active in regions damaged during neurodegeneration. Modulation of NO levels has been reported not only in the neurons of the central nervous system, but also in the glial cells (microglia and astroglia) activated during the neuroinflammatory response. Neuroinflammation has been found in some neurodegenerative conditions, and inhibition of these neuroinflammatory signals has been shown to delay the progress of such disorders. Thus NO and the pathways triggering its release are emerging as an important research focus in the search for strategies to prevent, halt or cure neurodegenerative diseases.

Microglia and neuroprotection: from in vitro studies to therapeutic applications

Microglia are the main immune cells in the brain, playing a role in both physiological and pathological conditions. Microglial involvement in neurodegenerative diseases is well-established, being microglial activation and neuroinflammation common features of these neuropathologies. Microglial activation has been considered harmful for neurons, but inflammatory state is not only associated with neurotoxic consequences, but also with neuroprotective effects, such as phagocytosis of dead neurons and clearance of debris. This brought to the idea of protective autoimmunity in the brain and to devise immunomodulatory therapies, aimed to specifically increase neuroprotective aspects of microglia. During the last years, several data supported the intrinsic neuroprotective function of microglia through the release of neuroprotective molecules. These data led to change the traditional view of microglia in neurodegenerative diseases: from the idea that these cells play an detrimental role for neurons due to a gain of their inflammatory function, to the proposal of a loss of microglial neuroprotective function as a causing factor in neuropathologies. This "microglial dysfunction hypothesis" points at the importance of understanding the mechanisms of microglial-mediated neuroprotection to develop new therapies for neurodegenerative diseases. In vitro models are very important to clarify the basic mechanisms of microglial-mediated neuroprotection, mainly for the identification of potentially effective neuroprotective molecules, and to design new approaches in a gene therapy set-up. Microglia could act as both a target and a vehicle for CNS gene delivery of neuroprotective factors, endogenously produced by microglia in physiological conditions, thus strengthening the microglial neuroprotective phenotype, even in a pathological situation.

Neuroproteomics approaches to decipher neuronal regeneration and degeneration

Given the complexity of brain and nerve tissues, systematic approaches are essential to understand normal physiological conditions and functional alterations in neurological diseases. Mass spectrometry-based proteomics is increasingly used in neurosciences to determine both basic and clinical differential protein expression, protein-protein interactions, and post-translational modifications. Proteomics approaches are especially useful to understand the mechanisms of nerve regeneration and degeneration because changes in axons following injury or in disease states often occur without the contribution of transcriptional events in the cell body. Indeed, the current understanding of axonal function in health and disease emphasizes the role of proteolysis, local axonal protein synthesis, and a broad range of post-translational modifications. Deciphering how axons regenerate and degenerate has thus become a postgenomics problem, which depends in part on proteomics approaches. This review focuses on recent proteomics approaches designed to uncover the mechanisms and molecules involved in neuronal regeneration and degeneration. It emerges that the principal degenerative mechanisms converge to oxidative stress, dysfunctions of axonal transport, mitochondria, chaperones, and the ubiquitin-proteasome systems. The mechanisms regulating nerve regeneration also impinge on axonal transport, cytoskeleton, and chaperones in addition to changes in signaling pathways. We also discuss the major challenges to proteomics work in the nervous system given the complex organization of the brain and nerve tissue at the anatomical, cellular, and subcellular levels.

Effects of early and delayed treatment with an mGluR5 antagonist on motor impairment, nigrostriatal damage and neuroinflammation in a rodent model of Parkinson's disease

The loss of nigrostriatal dopaminergic neurons that characterizes Parkinson's disease (PD) causes complex functional alterations in the basal ganglia circuit. Increased glutamatergic activity at crucial points of the circuit may be central to these alterations, thereby contributing to the onset of PD motor symptoms. Signs of neuroinflammation accompanying the neuronal loss have also been observed; also in this case, glutamate-mediated mechanisms may be involved. Glutamate may therefore intervene at multiple levels in PD pathophysiology, possibly through the modulation of metabotropic receptors. To address this issue, we evaluated the effects of systemic treatment with MPEP (2-methyl-6-(phenylethynyl)-pyridine), an antagonist of metabotropic receptor mGluR5, in a rodent model of progressive nigrostriatal degeneration based on the intrastriatal injection of 6-hydroxydopamine (6-OHDA). Following 6-OHDA injection, Sprague-Dawley rats underwent a 4-week, daily treatment with MPEP (1.5mg/kg, i.p.). To investigate whether the effects varied with the progression of the lesion, subgroups of lesioned animals started the treatment at different time-points: (1) immediately, (2) 1 week, or (3) 4 weeks after the neurotoxin injection. Akinesia, dopaminergic nigrostriatal damage and neuroinflammatory response (microglial and astroglial activation) were investigated. MPEP prompted immediate amelioration of 6-OHDA-induced akinesia, as measured by the Adjusting step test, in all subgroups, regardless of the degree of nigrostriatal damage. Conversely, MPEP did not modify neuronal survival or neuroinflammatory response in the nigrostriatal pathway. In conclusion, chronic treatment with MPEP exerted a pure symptomatic effect, further supporting that mGluR5 modulation may be a viable strategy to counteract the basal ganglia functional modifications underlying PD motor symptoms.

Mesenchymal stem cell transplantation attenuates blood brain barrier damage and neuroinflammation and protects dopaminergic neurons against MPTP toxicity in the substantia nigra in a model of Parkinson's disease

Immunomodulatory effects of transplanted mesenchymal stem cells (MSCs) in the treatment of Parkinson's disease were studied in the MPTP-induced mouse model. MPTP treatment induced a significant loss of dopaminergic neurons, decreased expressions of claudin 1, claudin 5 and occludin in the substantia nigra compacta (SNc), and functional damage of the blood brain barrier (BBB). Our study further discovered that infiltration of MBLs into the brain to bind with microglia was detected in the SNc of MPTP-treated mice, suggesting that the BBB compromise and MBL infiltration might be involved in the pathogenesis of MPTP-induced PD. In addition, MPTP treatment also increased the expression of mannose-binding lectins (MBLs) in the liver tissue. Intravenous transplantation of MSCs into MPTP-treated mice led to recovery of BBB integrity, suppression of MBL infiltration at SNc and MBL expression in the liver, suppression of microglial activation and prevention of dopaminergic neuron death. No transplanted MSCs were observed to differentiate into dopaminergic neurons, while the MSCs migrated into the SNc and released TGF-beta1 there. Therefore, intravenous transplantation of MSCs which protect dopaminergic neurons from MPTP toxicity may be engaged in anyone or a combination of these mechanisms: repair of the BBB, reduction of MBL in the brain, inhibition of microglial cytotoxicity, and direct protection of dopaminergic neurons.

Proteomic studies of nitrated alpha-synuclein microglia regulation by CD4+CD25+ T cells

Microglial inflammatory responses affect Parkinson's disease (PD) associated nigrostriatal degeneration. This is triggered, in measure, by misfolded, nitrated alpha-synuclein (N-alpha-syn) contained within Lewy bodies that are released from dying or dead dopaminergic neurons into the extravascular space. N-alpha-syn-stimulated microglial immunity is regulated by CD4+ T cell subset. Indeed, CD4+CD25+ regulatory T cells (Treg) induce neuroprotective immune responses. This is seen in rodent models of stroke, amyotrophic lateral sclerosis, human immunodeficiency virus associated neurocognitive disorders, and PD. To elucidate the mechanism for Treg-mediated microglial neuroregulatory responses, we used a proteomic platform integrating difference gel electrophoresis and tandem mass spectrometry peptide sequencing. These tests served to determine consequences of Treg on the N-alpha-syn stimulated microglia. The data demonstrated that Treg substantially alter the microglial proteome in response to N-alpha-syn. This is seen through Treg abilities to suppress microglial proteins linked to cell metabolism, migration, protein transport and degradation, redox biology, cytoskeletal, and bioenergetic activities. We conclude that Treg modulate the N-alpha-syn microglial proteome and, in this way, can slow the tempo and course of PD.

Macrophage antigen complex-1 mediates reactive microgliosis and progressive dopaminergic neurodegeneration in the MPTP model of Parkinson's disease

Neuronal death is known to trigger reactive microgliosis. However, little is known regarding the manner by which microglia are activated by injured neurons and how microgliosis participates in neurodegeneration. In this study we delineate the critical role of macrophage Ag complex-1 (MAC1), a member of the beta(2) integrin family, in mediating reactive microgliosis and promoting dopaminergic (DAergic) neurodegeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. MAC1 deficiency greatly attenuated the DAergic neurodegeneration induced by MPTP or 1-methyl-4-phenyl-pyridium iodide (MPP(+)) exposure both in vivo and in vitro, respectively. Reconstituted experiments created by adding microglia from MAC1(-/-) or MAC1(+/+) mice back to MAC1(+/+) neuron-enriched cultures showed that microglia with functional MAC1 expression was mandatory for microglia-enhanced neurotoxicity. Both in vivo and in vitro morphological and Western blot studies demonstrated that MPTP/MPP(+) produced less microglia activation in MAC1(-/-) mice than MAC1(+/+) mice. Further mechanistic studies revealed that a MPP(+)-mediated increase in superoxide production was reduced in MAC1(-/-) neuron-glia cultures compared with MAC1(+/+) cultures. The stunted production of superoxide in MAC1(-/-) microglia is likely linked to the lack of translocation of the cytosolic NADPH oxidase (PHOX) subunit (p47(phox)) to the membrane. In addition, the production of PGE(2) markedly decreased in neuron plus MAC1(-/-) microglia cocultures vs neuron plus MAC1(+/+) microglia cocultures. Taken together, these results demonstrate that MAC1 plays a critical role in MPTP/MPP(+)-induced reactive microgliosis and further support the hypothesis that reactive microgliosis is an essential step in the self-perpetuating cycle leading to progressive DAergic neurodegeneration observed in Parkinson's disease.

HDAC inhibitor increases histone H3 acetylation and reduces microglia inflammatory response following traumatic brain injury in rats

Traumatic brain injury (TBI) produces a rapid and robust inflammatory response in the brain characterized in part by activation of microglia. A novel histone deacetylase (HDAC) inhibitor, 4-dimethylamino-N-[5-(2-mercaptoacetylamino)pentyl]benzamide (DMA-PB), was administered (0, 0.25, 2.5, 25 mg/kg) systemically immediately after lateral fluid percussion TBI in rats. Hippocampal CA2/3 tissue was processed for acetyl-histone H3 immunolocalization, OX-42 immunolocalization (for microglia), and Fluoro-Jade B histofluorescence (for degenerating neurons) at 24 h after injury. Vehicle-treated TBI rats exhibited a significant reduction in acetyl-histone H3 immunostaining in the ipsilateral CA2/3 hippocampus compared to the sham TBI group (p<0.05). The reduction in acetyl-histone H3 immunostaining was attenuated by each of the DMA-PB dosage treatment groups. Vehicle-treated TBI rats exhibited a high density of phagocytic microglia in the ipsilateral CA2/3 hippocampus compared to sham TBI in which none were observed. All doses of DMA-PB significantly reduced the density of phagocytic microglia (p<0.05). There was a trend for DMA-PB to reduce the number of degenerating neurons in the ipsilateral CA2/3 hippocampus (p=0.076). We conclude that the HDAC inhibitor DMA-PB is a potential novel therapeutic for inhibiting neuroinflammation associated with TBI.

Proteomics in the study of hippocampal plasticity

Synaptic plasticity is the dynamic regulation of the strength of synaptic communication between nerve cells. It is central to neuronal development as well as experience-dependent remodeling of the adult nervous system as occurs during memory formation. Aberrant forms of synaptic plasticity also accompany a variety of neurological and psychiatric diseases, and unraveling the biological basis of synaptic plasticity has been a major goal in neurobiology research. The biochemical and structural mechanisms underlying different forms of synaptic plasticity are complex, involving multiple signaling cascades, reconfigurations of structural proteins and the trafficking of synaptic proteins. As such, proteomics should be a valuable tool in dissecting the molecular events underlying normal and disease-related forms of plasticity. In fact, progress in this area has been disappointingly slow. We discuss the particular challenges associated with proteomic interrogation of synaptic plasticity processes and outline ways in which we believe proteomics may advance the field over the next few years. We pay particular attention to technical advances being made in small sample proteomics and the advent of proteomic imaging in studying brain plasticity.

Immunological features of alpha-synuclein in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized pathologically by the presence, in the brain, of intra-cellular protein inclusions highly enriched in aggregated α-synuclein (αSyn), known as Lewy bodies. The onset of PD is accompanied by a local immune reaction in regions of the brain affected by the inclusions, although the mechanism that leads to pathogenesis is far from clear. It is, however, established that disease onset and progression are characterized by sustained activation of microglia, which is linked to significant dopaminergic neuron loss in the substantia nigra. A recent body of evidence indicates that aggregated or modified αSyn can indeed trigger the activation of microglia, inducing a lethal cascade of neuroinflammation and eventually, neuronal loss, pointing at aggregated and modified forms of αSyn as a primary cause of PD pathogenesis. By releasing toxic factors, or by phagocy-tosing neighbouring cells, activated microglia and astrocytes may form a self-perpetuating cycle for neuronal degeneration. Additional findings suggest a link between αSyn and humoural-mediated mechanisms in PD. In this review, we attempt to recapitulate our current understanding of PD physiopathology focused on αSyn and its links with the immune system, as well as of novel and promising therapeutic avenues for the treatment of PD and of other synucleinopathies.

Predominant release of lysosomal enzymes by newborn rat microglia after LPS treatment revealed by proteomic studies

Growing evidence suggest that microglia may play an important role in the pathogenesis of neurodegenerative disease including Parkinson's disease, Alzheimer's disease, and so forth. The activation of microglia may cause neuronal damage through the release of reactive oxygen species and proinflammatory cytokines. However, the early response of microglial cells remains unclear before cells can secrete the proinflammatory cytokines. Here, a time course analysis showed the earliest expression of inducible nitric oxide synthase and cyclooxygenase-2 at 3 and 24 h following lipopolysaccharide (LPS) treatment. To further define initial response proteins of microglia after LPS treatment, we utilized a novel mass spectrometry-based quantitative proteomic technique termed SILAC (for stable isotope labeling by amino acids in cell culture) to compare the protein profiles of the cell culture-conditioned media of 1 h LPS-treated microglia as compared with controls. The proteomic analysis identified 77 secreted proteins using SignalP; of these, 28 proteins were associated with lysosome of cells and 13 lysosome-related proteins displayed significant changes in the relative abundance after 1 h LPS treatment. Four proteins were further evaluated with Western blot, demonstrating good agreement with quantitative proteomic data. These results suggested that microglia first released some lysosomal enzymes which may be involved in neuronal damage process. Furthermore, ammonium chloride, which inhibits microglia lysosomal enzyme activity, could prevent microglia from causing neuronal injury. Hence, in addition to the numerous novel proteins that are potentially important in microglial activation-mediated neurodegeneration revealed by the search, the study has indicated that the early release of lysosomal enzymes in microglial cells would contribute to LPS-activated inflammatory response.

Neuroinflammation in the pathophysiology of Parkinson's disease: evidence from animal models to human in vivo studies with [11C]-PK11195 PET

Increasing evidence suggests that neuroinflammation is an active process in Parkinson's disease (PD) that contributes to ongoing neurodegeneration. PD brains and experimental PD models show elevated cytokine levels and up-regulation of inflammatory-associated factors as cyclo-oxygenase-2 and inducible nitric oxide oxidase. Antiinflammatory treatment reduced neuronal degeneration in experimental models. In this review, we summarize the place of neuroinflammation in the pathophysiology of PD. In vivo PET studies are discussed. These methods provide a means to monitor in vivo potential clinical relevance of antiinflammatory treatment strategies in PD.

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

Neurodegeneration and peroxidases

Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that affect different parts of the central nervous system. However, a review of the literature indicates that certain biochemical reactions involved in neurodegeneration in these three diseases are quite similar and could be partly identical. This article critically examines the similarities and, based on data from our own and other laboratories, proposes a novel explanation for neurodegeneration in these three diseases. We identified about 20 commonalities that exist in the neurodegenerative process of each disease. We hypothesize that there are two enzyme-catalyzed pathways that operate in affected neurons: an oxidative pathway leading to destruction of various neuronal proteins and lipids, and an apoptotic pathway which the body normally uses to remove unwanted and dysfunctional cells. Data from many laboratories indicate that oxidative reactions are primarily responsible for neurodegeneration, whereas apoptosis may well be a secondary response to the presence of neurons that have already been severely damaged by oxidative reactions. Attempts to inhibit apoptosis for the purpose of attenuating progression of these diseases may therefore be only of marginal benefit. Specific oxidative reactions within affected neurons led us to propose that one or more heme peroxidases may be the catalyst(s) involved in oxidation of proteins and lipids. Support for this proposal is provided by the recent finding that amyloi-beta peptide may act as a peroxidase in AD. Possible participation of the peroxidase activity of cytochrome c, herein designated as cytochrome c(px) to distinguish it from yeast cytochrome c peroxidase, is discussed. Of special interest is our recent finding that many compounds that cause attenuation of neurodegeneration are inhibitors of the peroxidase activity of cytochrome c. Several inhibitors were subsequently identified as suicide substrates. Such inhibitors could be ideally suited for targeted clinical approaches aimed at arresting progression of neurodegeneration. Finally, it is possible that immobilized yet still active peroxidase(s) may be present in protein aggregates in AD, PD, and ALS. This activity could be the catalyst for the slow, self-perpetuating and irreversible degeneration of affected neurons that occurs over long periods of time in these neurodegenerative diseases.

Nitrated alpha-synuclein-activated microglial profiling for Parkinson's disease

Microglial neuroinflammatory processes play a primary role in dopaminergic neurodegeneration for Parkinson's disease (PD). This can occur, in part, by modulation of glial function following activation by soluble or insoluble modified alpha-synuclein (alpha-syn), a chief component of Lewy bodies that is released from affected dopaminergic neurons. alpha-Syn is nitrated during oxidative stress responses and in its aggregated form, induces inflammatory microglial functions. Elucidation of these microglial function changes in PD could lead to new insights into disease mechanisms. To this end, PD-associated inflammation was modeled by stimulation of microglia with aggregated and nitrated alpha-syn. These activated microglia were ameboid in morphology and elicited dopaminergic neurotoxicity. A profile of nitrated, aggregated alpha-syn-stimulated microglia was generated using combinations of genomic (microarrays) and proteomic (liquid chromatography-tandem mass spectrometry, differential gel electrophoresis, and protein array) assays. Genomic studies revealed a substantive role for nuclear factor-kappa B transcriptional activation. Qualitative changes in the microglial proteome showed robust increases in inflammatory, redox, enzyme, and cytoskeletal proteins supporting the genomic tests. Autopsy brain tissue acquired from substantia nigra and basal ganglia of PD patients demonstrated that parallel nuclear factor-kappa B-related inflammatory processes were, in part, active during human disease. Taken together, the transcriptome and proteome of nitrated alpha-syn activated microglia, shown herein, provide new potential insights into disease mechanisms.

Chronic microglial activation and progressive dopaminergic neurotoxicity

PD (Parkinson's disease) is characterized by the selective and progressive loss of DA neurons (dopaminergic neurons) in the substantia nigra. Inflammation and activation of microglia, the resident innate immune cell in the brain, have been strongly linked to neurodegenerative diseases, such as PD. Microglia can respond to immunological stimuli and neuronal death to produce a host of toxic factors, including cytokines and ROS (reactive oxygen species). Microglia can also become persistently activated after a single stimulus and maintain the elevated production of both cytokines and ROS, long after the instigating stimulus is gone. Current reports suggest that this chronic microglial activation may be fuelled by either dying/damaged neurons or autocrine and paracrine signals from local glial cells, such as cytokines. Here, we review proposed mechanisms responsible for chronic neuroinflammation and explain the interconnected relationship between deleterious microglial activation, DA neuron damage and neurodegenerative disease.

Clinical proteomics in neurodegenerative diseases

Investigation of the human specimens is an essential element for understanding the pathogenesis of neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. The studies hold promise for identifying biomarkers for diagnosis and prognosis, elucidating disease mechanisms, and accelerating the development of new strategies for therapeutic intervention. Here, we review proteomics studies of human brain samples in light of recent advances of mass spectrometry, focusing on the general strategies for experimental design and analysis (e.g., sample pooling and replication, selection of proteomics platforms, and false discovery rate in data processing), because quantitative analysis of clinical samples is confounded by a number of variables, including genetic differences, antemortem and postmortem factors, and experimental errors. Diverse proteomics platforms are also discussed with respect to sensitivity, throughput, and accuracy. Regarding the enormous complexity of the human brain and the limitation of current proteomics technologies, it may be more practical to analyze a subset of proteome in a functional context, in order to facilitate the identification of important disease-related proteins in the substantial noise reflecting biological and technical variances.

Microglial PHOX and Mac-1 are essential to the enhanced dopaminergic neurodegeneration elicited by A30P and A53T mutant alpha-synuclein

alpha-Synuclein, a gene whose mutations, duplication, and triplication has been linked to autosomal dominant familial Parkinson's disease (fPD), appears to play a central role in the pathogenesis of sporadic PD (sPD) as well. Enhancement of neurodegeneration induced by mutant alpha-synuclein has been attributed to date largely to faster formation of alpha-synuclein aggregates in neurons. Recently, we reported that microglial activation enhances wild type (WT) alpha-synuclein-elicited dopaminergic neurodegeneration. In the present study, using a primary mesencephalic culture system, we tested whether mutated alpha-synuclein could activate microglia more powerfully than WT alpha-synuclein, thereby contributing to the accelerated neurodegeneration observed in fPD. The results showed that alpha-synuclein with the A30P or A53T mutations caused greater microglial activation than WT alpha-synuclein. Furthermore, the extent of microglial activation paralleled the degree of dopaminergic neurotoxicity induced by WT and mutant alpha-synuclein. Mutant alpha-synuclein also induced greater production of reactive oxygen species than WT alpha-synuclein by NADPH oxidase (PHOX), and PHOX activation was linked to direct activation of macrophage antigen-1 (Mac-1) receptor, rather than alpha-synuclein internalization via scavenger receptors. These results have, for the first time, demonstrated that microglia are also critical in enhanced neurotoxicity induced by mutant alpha-synuclein.

Identification of novel proteins affected by rotenone in mitochondria of dopaminergic cells

Background

Many studies have shown that mitochondrial dysfunction, complex I inhibition in particular, is involved in the pathogenesis of Parkinson's disease (PD). Rotenone, a specific inhibitor of mitochondrial complex I, has been shown to produce neurodegeneration in rats as well as in many cellular models that closely resemble PD. However, the mechanisms through which complex I dysfunction might produce neurotoxicity are as yet unknown. A comprehensive analysis of the mitochondrial protein expression profile affected by rotenone can provide important insight into the role of mitochondrial dysfunction in PD.

Results

Here, we present our findings using a recently developed proteomic technology called SILAC (stable isotope labeling by amino acids in cell culture) combined with polyacrylamide gel electrophoresis and liquid chromatography-tandem mass spectrometry to compare the mitochondrial protein profiles of MES cells (a dopaminergic cell line) exposed to rotenone versus control. We identified 1722 proteins, 950 of which are already designated as mitochondrial proteins based on database search. Among these 950 mitochondrial proteins, 110 displayed significant changes in relative abundance after rotenone treatment. Five of these selected proteins were further validated for their cellular location and/or treatment effect of rotenone. Among them, two were confirmed by confocal microscopy for mitochondrial localization and three were confirmed by Western blotting (WB) for their regulation by rotenone.

Conclusion

Our findings represent the first report of these mitochondrial proteins affected by rotenone; further characterization of these proteins may shed more light on PD pathogenesis.

Identification of proteins involved in microglial endocytosis of alpha-synuclein

Aggregated alpha-synuclein, a protein playing pivotal roles in the pathogenesis of Parkinson disease (PD) and related synucleinopathy, has been shown to activate microglia, the key cells in neuroinflammation. However, the mechanisms by which aggregated alpha-synuclein enters microglia remain uncharacterized. In this study, we first replicated our previous results with a modified protocol that generated aggregated alpha-synuclein more efficiently. Next, using two recently developed proteomic techniques, SILAC (Stable Isotope Labeling of Amino acid in Cell cultures) and PROCEED (PROteome of Cell Exposed Extracellular Domains), we studied the plasma membrane proteins of primary cultured microglia that might be interacting with aggregated alpha-synuclein and mediating its internalization. The results demonstrated that 250 nM alpha-synuclein, aged for 6 h with a magnetic stir bar, was just as potent in activating microglia as the aggregated alpha-synuclein produced by aging without constant agitation for 7 days. The proteomic analysis identified 111 membrane proteins; of these, 46 proteins were altered in relative abundance in the membrane compartment after treatment with aggregated alpha-synuclein for 3 h. Two of these proteins, clathrin and calnexin, were further evaluated with Western blotting, demonstrating good agreement with quantitative proteomics. Finally, immunocytochemical as well as co-immunoprecipitation studies indicated that clathrin was indeed co-localized with internalized alpha-synuclein in microglia. These results suggest for the first time that microglial activation secondary to internalization of aggregated alpha-synuclein likely requires participation of clathrin, which is an essential protein of the polyhedral coat of coated pits and vesicles that play major roles in endocytosis and vesicular trafficking.

14-3-3 Expression in Denervated Hippocampus after Entorhinal Cortex Lesion Assessed by Culture-Derived Isotope Tags in Quantitative Proteomics

Activation of astrocytes accompanies many brain pathologies. Reactive astrocytes have a beneficial role in acute neurotrauma but later on might inhibit regeneration. 2D-gel electrophoresis and mass spectrometry were applied to study the proteome difference in denervated hippocampus in wildtype mice and mice lacking intermediate filament proteins glial fibrillary acidic protein (GFAP) and vimentin (GFAP-/-Vim-/-) that show attenuated reactive gliosis and enhanced posttraumatic regeneration. Proteomic data and immunohistochemical analyses showed upregulation of the adapter protein 14-3-3 four days postlesion and suggested that 14-3-3 upregulation after injury is triggered by reactive gliosis. Culture-derived isotope tags (CDIT) and mass spectrometry demonstrated that 14-3-3 epsilon was the major isoform upregulated in denervated hippocampus and that its upregulation was attenuated in GFAP-/-Vim-/- mice and thus most likely connected to reactive gliosis.

Identification of Novel Proteins Associated with Both α-Synuclein and DJ-1

The molecular mechanisms leading to neurodegeneration in Parkinson disease (PD) remain elusive, although many lines of evidence have indicated that alpha-synuclein and DJ-1, two critical proteins in PD pathogenesis, interact with each other functionally. The investigation on whether alpha-synuclein directly interacts with DJ-1 has been controversial. In the current study, we analyzed proteins associated with alpha-synuclein and/or DJ-1 with a robust proteomics technique called stable isotope labeling by amino acids in cell culture (SILAC) in dopaminergic MES cells exposed to rotenone versus controls. We identified 324 and 306 proteins in the alpha-synuclein- and DJ-1-associated protein complexes, respectively. Among alpha-synuclein-associated proteins, 141 proteins displayed significant changes in the relative abundance (increase or decrease) after rotenone treatment; among DJ-1-associated proteins, 119 proteins displayed significant changes in the relative abundance after rotenone treatment. Although no direct interaction was observed between alpha-synuclein and DJ-1, whether analyzed by affinity purification followed by mass spectrometry or subsequent direct co-immunoprecipitation, 144 proteins were seen in association with both alpha-synuclein and DJ-1. Of those, 114 proteins displayed significant changes in the relative abundance in the complexes associated with alpha-synuclein, DJ-1, or both after rotenone treatment. A subset of these proteins (mortalin, nucleolin, grp94, calnexin, and clathrin) was further validated for their association with both alpha-synuclein and DJ-1 using confocal microscopy, Western blot, and/or immunoprecipitation. Thus, we not only confirmed that there was no direct interaction between alpha-synuclein and DJ-1 but also, for the first time, report these five novel proteins to be associating with both alpha-synuclein and DJ-1. Further characterization of these docking proteins will likely shed more light on the mechanisms by which DJ-1 modulates the function of alpha-synuclein, and vice versa, in the setting of PD.

Proteomic identification of novel proteins in cortical lewy bodies

Lewy body (LB) inclusions are one of the pathological hallmarks of Parkinson's disease (PD) and dementia with Lewy bodies (DLB). One way to better understand the process leading to LB formation and associated pathogenesis responsible for neurodegeneration in PD and DLB is to examine the content of LB inclusions. Here, we performed a proteomic investigation of cortical LBs, obtained by laser capture microdissection from neurons in the temporal cortex of dementia patients with cortical LB disease. Analysis of over 2500 cortical LBs discovered 296 proteins; of those, 17 had been associated previously with brainstem and/or cortical LBs. We validated several proteins with immunohistochemical staining followed by confocal microscopy. The results demonstrated that heat shock cognate 71 kDa protein (also known as HSC70, HSP73, or HSPA10) was indeed not only colocalized with the majority of LBs in the temporal cortex but also colocalized to LBs in the frontal cortex of patients with diffuse LB disease. Our investigation represents the first extensive proteomic investigation of cortical LBs, and it is expected that characterization of the proteins in the cortical LBs may reveal novel mechanisms by which LB forms and pathways leading to neurodegeneration in DLB and/or advanced PD. Further investigation of these novel candidates is also necessary to ensure that the potential proteins in cortical LBs are not identified incorrectly because of incomplete current human protein database.