GFAP in health and disease

Glial fibrillary acidic protein (GFAP) is the main intermediate filament protein in mature astrocytes, but also an important component of the cytoskeleton in astrocytes during development. Major recent developments in astrocyte biology and the discovery of novel intermediate filament functions enticed the interest in the function of GFAP. The discovery of various GFAP splice variants gave an additional boost to explore this protein in more detail. The structural role of GFAP in astrocytes has been widely accepted for a long time, but over the years, GFAP has been shown to be involved in astrocyte functions, which are important during regeneration, synaptic plasticity and reactive gliosis. Moreover, different subpopulations of astrocytes have been identified, which are likely to have distinctive tasks in brain physiology and pathology, and which are not only classified by their spatial and temporal appearance, but also by their specific expression of intermediate filaments, including distinct GFAP isoforms. The presence of these isoforms enhances the complexity of the astrocyte cytoskeleton and is likely to underlie subtype specific functions. In this review we discuss the versatility of the GFAP cytoskeletal network from gene to function with a focus on astrocytes during human brain development, aging and disease.     

Eating ourselves to death (and despair): The contribution of adiposity and inflammation to depression

Obesity and related metabolic conditions are of epidemic proportions in most of the world, affecting both adults and children. The accumulation of lipids in the body in the form of white adipose tissue in the abdomen is now known to activate innate immune mechanisms. Lipid accumulation causes adipocytes to directly secrete the cytokines interleukin (IL) 6 and tumor necrosis factor α (TNFα), but also monocyte chemoattractant protein 1 (MCP-1), which results in the accumulation of leukocytes in fat tissue. This sets up a chronic inflammatory state which is known to mediate the association between obesity and conditions such as cardiovascular disease, type 2 diabetes, and cancer. There is also a substantial literature linking inflammation with risk for depression. This includes the observations that: (1) people with inflammatory diseases such as multiple sclerosis, cardiovascular disease, and psoriasis have elevated rates of depression; (2) many people administered inflammatory cytokines such as interferon α develop depression that is indistinguishable from depression in non-medically ill populations; (3) a significant proportion of depressed persons show upregulation of inflammatory factors such as IL-6, C-reactive protein, and TNFα; (4) inflammatory cytokines can interact with virtually every pathophysiologic domain relevant to depression, including neurotransmitter metabolism, neuroendocrine function, and synaptic plasticity. While many factors may contribute to the association between inflammatory mediators and depression, we hypothesize that increased adiposity may be one causal pathway. Mediational analysis suggests a bi-directional association between adiposity and depression, with inflammation possibly playing an intermediary role.     

Neurochemical pathways involved in the protective effects of nicotine and ethanol in preventing the development of Parkinson's disease: potential targets for the development of new therapeutic agents

In this short review, neurochemical targets are identified where nicotine, and possibly ethanol, may interact to prevent the occurrence of Parkinson's disease. These are (a) the nicotinic acetycholine receptors present in the nigrostriatal area or on the surface of microglia, (b) monoamine oxidases and (c) inducible nitric oxide synthase. If such induced changes can be verified in clinical studies, this may help in the design of new therapeutic drugs which may be of relevance to diminish the incidence and perhaps the progression of the debilitating condition of Parkinson's disease.     

The recycling endosome and its role in neurological disorders

The recycling endosome (RE) is an organelle in the endocytic pathway where plasma membranes (proteins and lipids) internalized by endocytosis are processed back to the cell surface for reuse. Endocytic recycling is the primary way for the cell to maintain constituents of the plasma membrane (Griffiths et al., 1989), i.e., to maintain the abundance of receptors and transporters on cell surfaces. Membrane traffic through the RE is crucial for several key cellular processes including cytokinesis and cell migration. In polarized cells, including neurons, the RE is vital for the generation and maintenance of the polarity of the plasma membrane. Many RE dependent cargo molecules are known to be important for neuronal function and there is evidence that improper function of key proteins in RE-associated pathways may contribute to the pathogenesis of neurological disorders, including Huntington's disease. The function of the RE in neurons is poorly understood. Therefore, there is need to understand how membrane dynamics in RE-associated pathways are affected or participate in the development or progression of neurological diseases. This review summarizes advances in understanding endocytic recycling associated with the RE, challenges in elucidating molecular mechanisms underlying RE function, and evidence for RE dysfunction in neurological disorders.     

Early involvement of the cerebral cortex in Parkinson's disease: Convergence of multiple metabolic defects

Parkinson's disease (PD) has been considered a paradigm of degenerative diseases of the nervous system characterized by motor impairment (parkinsonism) due to malfunction and loss of dopaminergic neurons of the substantia nigra pars compacta. However, PD is a systemic disease of the nervous system with variegated clinical symptoms appearing before parkinsonism and due to the involvement of selected nuclei of the medulla oblongata, pons, autonomic nervous system and olfactory structures, among others. Furthermore, recent clinical data have shown modifications in behavior, personality changes and cognitive impairment leading to dementia. Lewy pathology, hallmark of PD, in the cerebral cortex does not correlate with cognitive impairment. However, recent studies have shown abnormal mitochondria content and function, and increased oxidative stress and oxidative responses in the cerebral cortex in PD. Furthermore, several key PD-related proteins are oxidatively damaged, including α-synuclein, β-synuclein, superoxide dismutases, parkin, DJ1, UCHL1 and enzymes involved in glycolysis and energy metabolism. DNA and RNA are also targets of oxidative damage. Furthermore, abnormal phosphorylation of α-synuclein and tau occurs at the cortical synapses. Finally, abnormal cortical metabolism has been revealed with neuroimaging methods. These data demonstrate early involvement of the cerebral cortex in PD due to the convergence of multiple metabolic defects. Lewy pathology is a relative late event, geared to isolate unremoved damaged protein, with little significance on cortical neurological deficits.     

Calcium dysregulation in Alzheimer's disease: From mechanisms to therapeutic opportunities

Calcium is involved in many facets of neuronal physiology, including activity, growth and differentiation, synaptic plasticity, and learning and memory, as well as pathophysiology, including necrosis, apoptosis, and degeneration. Though disturbances in calcium homeostasis in cells from Alzheimer's disease (AD) patients have been observed for many years, much more attention was focused on amyloid-β (Aβ) and tau as key causative factors for the disease. Nevertheless, increasing lines of evidence have recently reported that calcium dysregulation plays a central role in AD pathogenesis. Systemic calcium changes accompany almost the whole brain pathology process that is observed in AD, including synaptic dysfunction, mitochondrial dysfunction, presenilins mutation, Aβ production and Tau phosphorylation. Given the early and ubiquitous involvement of calcium dysregulation in AD pathogenesis, it logically presents a variety of potential therapeutic targets for AD prevention and treatment, such as calcium channels in the plasma membrane, calcium channels in the endoplasmic reticulum membrane, Aβ-formed calcium channels, calcium-related proteins. The review aims to provide an overview of the current understanding of the molecular mechanisms involved in calcium dysregulation in AD, and an insight on how to exploit calcium regulation as therapeutic opportunities in AD.     

Cell death and proliferation in acute slices and organotypic cultures of mammalian CNS

Analysis of the interplay between cell proliferation and death has been greatly advantaged by the development of CNS slice preparations. In slices, interactions between neurons and neurons and the glial cells are fundamentally preserved in a fashion close to the in vivo situation. In parallel, these preparations offer the possibility of an easy experimental manipulation. Two main types of slices are currently in use: the acute slices, which are short living preparations where the major functions of the intact brain (including neurogenesis) are maintained, and the organotypic cultures, where the maturation and plasticity of neuronal circuitries in relation to naturally occurring neuronal death and/or experimental insults can be followed over several weeks in vitro.     

Parkinson's disease: Insights from non-traditional model organisms

Parkinson's disease (PD) was one of the first neurological disorders to have aspects of the disease modeled faithfully in non-human animal species. A key feature of the disease is a diminished control over voluntary movement and progressive depletion of brain dopamine (DA) levels that stems from the large-scale loss of DA-producing neurons. Despite their inherent limitations, rodent and non-human primate models of PD have helped unravel several aspects of PD pathogenesis. Thus, we now have neurotransmitter replacement therapy for PD, and a number of neuroprotective compounds that can be assessed in clinical trials. However, no treatment is currently available that can halt or retard the progressive loss of DA neurons, which underlies PD pathology. Moreover, no therapies can permanently alleviate the clinical features of the disease. The lack of a cure or long-term effective treatment is paralled by our incomplete understanding of the underlying pathomechanisms of the disease. A range of robust, flexible, and complementary animal models will be an invaluable tool with which to unravel the pathogenesis of PD. Here we review the most important contributions made by non-mammalian model organisms. These include zebrafish (Danio rerio), flies (Drosophila melanogaster), anurans (frogs and toads) and nematodes (Caenorhabditis elegans). While it is not anticipated that they will replace rodent and primate-based ones, they offer convenient systems with which to explore the relative contribution made by genetic and environmental factors to PD pathology. In addition, they offer an economic and rapid alternative for testing compounds that target PD. Most importantly, the combined use of these models allow for ongoing research to uncover the basic mechanisms underlying PD pathogenesis.     

The putative neurodegenerative links between depression and Alzheimer's disease

Alzheimer's disease (AD) is the leading neurodegenerative cause of dementia in the elderly. Thus far, there is no curative treatment for this devastating condition, thereby creating significant social and medical burdens. AD is characterized by progressive cognitive decline along with various neuropsychiatric symptoms, including depression and psychosis.     

Biomarkers of Parkinson's disease and Dementia with Lewy bodies

Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are progressive and disabling neurodegenerative disorders, in which signs and symptoms overlap with each other and with other neurodegenerative conditions. Currently, diagnosis, measurement of progression, and response to therapeutic intervention rely upon clinical observation. However, there remains a critical need for validated biomarkers in each of these areas. A definitive diagnostic test would improve clinical management and enrollment into clinical trials. An objective measure of progression is vitally important in identifying neuroprotective interventions. Biomarkers may also provide insight into pathogenesis, and might therefore suggest possible novel targets for therapeutic intervention. In addition, certain biomarkers might be of use in monitoring the biochemical and physiological effects of therapeutic interventions. Development of diagnostic biomarkers has focused until recently upon imaging techniques based upon measuring loss of dopamine neurons. Additionally, advances in understanding the genetic contribution to neurodegenerative disorders, in particular in PD, have identified multiple causative genes and risk factors that in some cases may help estimate PD risk. However, recent availability of increasingly sophisticated bioinformatics technology has rendered development of fluid biomarkers feasible, opening the possibility of generally accessible blood or cerebrospinal fluid (CSF) tests that could impact upon diagnosis, management, and research in PD, PDD, and DLB.     

Apoptosis-inducing factor: a matter of neuron life and death

The mitochondrial flavoprotein apoptosis-inducing factor (AIF) is the main mediator of caspase-independent apoptosis-like programmed cell death. Upon pathological permeabilization of the outer mitochondrial membrane, AIF is translocated to the nucleus, where it participates in chromatin condensation and is associated to large-scale DNA fragmentation. Heavy down-regulation of AIF expression in mutant mice or reduced AIF expression achieved with small interfering RNA (siRNA) provides neuroprotection against acute neurodegenerative insults. Paradoxically, in addition to its pro-apoptotic function, AIF likely plays an anti-apoptotic role by regulating the production of reactive oxygen species (ROS) via its putative oxidoreductase and peroxide scavenging activities. In this review, we discuss accumulating evidence linking AIF to both acute and chronic neurodegenerative processes by emphasising mechanisms underlying the dual roles apparently played by AIF in these processes.     

The influence of microglia on the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is characterised by degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Inflammation may be associated with the neuropathology of PD due to the following accumulating evidence: excessive microglial activation and increased levels of the pro-inflammatory cytokines tumour necrosis factor-α and interleukin-1β in the SNpc of patients with PD; the emergence of PD-like symptoms following influenza infection; the increased susceptibility to PD associated with bacterial vaginosis; the presence of inflammatory mediators and activators in animal models of PD; the ability of anti-inflammatory drugs to decrease susceptibility to PD; and the emerging possibility of the use of microglial activation inhibitors as a therapy in PD. In this review, we will discuss the role of inflammation in PD. We will focus on the influence of microglia in the pathogenesis of PD and discuss potential therapeutic interventions for PD, that target microglia.     

RACK1 has the nerve to act: structure meets function in the nervous system

The receptor for activated protein kinase C 1 (RACK1) is an intracellular adaptor protein. Accumulating evidence attributes to this member of the tryptophan-aspartate (WD) repeat family the role of regulating several major nervous system pathways. Structurally, RACK1 is a seven-bladed-beta-propeller, interacting with diverse proteins having distinct structural folds. When bound to the IP3 receptor, RACK1 regulates intracellular Ca2+ levels, potentially contributing to processes such as learning, memory and synaptic plasticity. By binding to the NMDA receptor, it dictates neuronal excitation and sensitivity to ethanol. When bound to the stress-induced acetylcholinesterase variant AChE-R, RACK1 is implicated in stress responses and behavior, compatible with reports of RACK1 modulations in brain ageing and in various neurodegenerative diseases. This review sheds new light on both the virtues and the variety of neuronal RACK1 interactions and their physiological consequences.     

Cell-autonomous and non-cell-autonomous toxicity in polyglutamine diseases

Polyglutamine diseases are neurodegenerative disorders caused by expansion of polyglutamine tracts in the coding regions of specific genes. One of the most important features of polyglutamine diseases is that, despite the widespread and in some cases ubiquitous expression of the polyglutamine proteins, specific populations of neurons degenerate in each disease. This finding has led to the idea that polyglutamine diseases are cell-autonomous diseases, in which selective neuronal dysfunction and death result from damage caused by the mutant protein within the targeted neuronal population itself. Development of animal models for conditional expression of polyglutamine proteins, along with new pharmacologic manipulation of polyglutamine protein expression and toxicity, has led to a remarkable change of the current view of polyglutamine diseases as cell-autonomous disorders. It is becoming evident that toxicity in the neighboring non-neuronal cells contributes to selective neuronal damage. This observation implies non-cell-autonomous mechanisms of neurodegeneration in polyglutamine diseases. Here, we describe cell-autonomous and non-cell-autonomous mechanisms of polyglutamine disease pathogenesis, including toxicity in neurons, skeletal muscle, glia, germinal cells, and other cell types.     

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.     

The serotonergic system in ageing and Alzheimer's disease

Alzheimer's disease (AD) is one of the major neurodegenerative diseases that deteriorates cognitive functions and primarily affects associated brain regions involved in learning and memory, such as the neocortex and the hippocampus. Following the discovery and establishment of its role as a neurotransmitter, serotonin (5-HT), was found to be involved in a multitude of neurophysiological processes including mnesic function, through its dedicated pathways and interaction with cholinergic, glutamatergic, GABAergic and dopaminergic transmission systems. Abnormal 5-HT neurotransmission contributes to the deterioration of cognitive processes in ageing, AD and other neuropathologies, including schizophrenia, stress, mood disorders and depression. Numerous studies have confirmed the pathophysiological role of the 5-HT system in AD and that several drugs enhancing 5-HT neurotransmission are effective in treating the AD-related cognitive and behavioural deficits. Here we present a comprehensive overview of the role of serotonergic neurotransmission in brain development, maturation and ageing, discuss its role in higher brain function and provide an in depth account of pathological modifications of serotonergic transmission in neurological diseases and AD.     

Dysfunction of constitutive and inducible ubiquitin-proteasome system in amyotrophic lateral sclerosis: implication for protein aggregation and immune response

The ubiquitin-proteasome system (UPS) is the major intracellular proteolytic mechanism controlling the degradation of misfolded/abnormal proteins. A common hallmark in amyotrophic lateral sclerosis (ALS) and in other neurodegenerative disorders is the accumulation of misfolded/abnormal proteins into the damaged neurons, leading to the formation of cellular inclusions that are mostly ubiquitin-positive. Although proteolysis is a complex mechanism requiring the participation of different pathways, the abundant accumulation of ubiquitinated proteins strongly suggests an important contribution of UPS to these neuropathological features. The use of cellular and animal models of ALS, particularly those expressing mutant SOD1, the gene mutation most represented in familiar ALS, has provided significant evidence for a role of UPS in protein inclusions formation and motor neuron death. This review will specifically discuss this piece of evidence and provide suggestions of potential strategies for therapeutic intervention. We will also discuss the finding that, unlike the constitutive proteasome subunits, the inducible subunits are overexpressed early during disease progression in SOD1 mice models of ALS. These subunits form the immunoproteasome and generate peptides for the major histocompatibility complex class I molecules, suggesting a role of this system in the immune responses associated with the pathological features of ALS. Since recent discoveries indicate that innate and adaptive immunity may influence the disease process, in this review we will also provide evidence of a possible connection between immune-inflammatory reactions and UPS function, in the attempt to better understand the etiopathology of ALS and to identify appropriate targets for novel treatment strategies of this devastating disease.     

Wnt signaling in neuroprotection and stem cell differentiation

In the past several years, we postulated that the loss of Wnt signaling was implicated in the pathology of Alzheimer's disease (AD). Since then, our lab and other groups have confirmed the involvement of the Wnt signaling in some aspects of AD. So far, we have demonstrated that activation of Wnt signaling protects neurons against neurotoxic injuries, including both amyloid-beta (Abeta) fibrils and Abeta oligomers by using either lithium, an inhibitor of the glycogen-synthase-kinase-3beta (GSK-3beta), or different Wnt ligands. Also, we have found that several molecules which activate well known neurotransmitter systems and other signaling system, are able by crosstalk to activate Wnt/beta-catenin signaling in order to protect neurons against both Abeta fibrils or Abeta oligomers. In particular, the activation of non-canonical Wnt signaling was able to protect postsynaptic regions and dendritic spines against Abeta oligomers. Furthermore Wnt signaling ligands also affect stem cells, and they are also involved in cell fate decision during neurogenesis and embryonic development as well as in adult stem cells differentiation in the nervous system. The Wnt signaling plays a key role modulating their cell differentiation or proliferation states. Altogether, these findings in both stem cell biology and neuroprotection, may introduce new approaches in the treatment of neurodegenerative diseases, including drug screening and therapies against neurodegenerative diseases which activates the Wnt signaling pathway.