Gangliosides as a Double-Edged Swordin Neurodegenerative Disease

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Neuroinflammation in Parkinson's Disease and Related Disorders: A Lesson from Genetically Manipulated Mouse Models of α-Synucleinopathies

Neuroinflammation in Parkinson's disease (PD) is a chronic process that is associated with alteration of glial cells, including astrocytes and microglia. However, the precise mechanisms remain obscure. To better understand neuroinflammation in PD, we focused on glial activation in α-synuclein (αS) transgenic and related model mice. In the majority of αS transgenic mice, astrogliosis was observed concomitantly with accumulation of αS during the early stage of neurodegeneration. However, microglia were not extensively activated unless the mice were treated with lipopolysaccharides or through further genetic modification of other molecules, including familial PD risk factors. Thus, the results in αS transgenic mice and related model mice are consistent with the idea that neuroinflammation in PD is a double-edged sword that is protective in the early stage of neurodegeneration but becomes detrimental with disease progression

Distinct mechanisms of axonal globule formation in mice expressing human wild type α-synuclein or dementia with Lewy bodies-linked P123H ß-synuclein

BACKGROUND: Axonopathy is critical in the early pathogenesis of neurodegenerative diseases, including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Axonal swellings such as globules and spheroids are a distinct feature of axonopathy and our recent study showed that transgenic (tg) mice expressing DLB-linked P123H β-synuclein (P123H βS) were characterized by P123H βS-immunoreactive axonal swellings (P123H βS-globules). Therefore, the objectives of this study were to evaluate α-synuclein (αS)-immunoreactive axonal swellings (αS-globules) in the brains of tg mice expressing human wild-type αS and to compare them with the globules in P123H βS tg mice. RESULTS: In αS tg mice, αS-globules were formed in an age-dependent manner in various brain regions, including the thalamus and basal ganglia. These globules were composed of autophagosome-like membranous structures and were reminiscent of P123H βS-globules in P123H βS tg mice. In the αS-globules, frequent clustering and deformation of mitochondria were observed. These changes were associated with oxidative stress, based on staining of nitrated αS and 4-hydroxy-2-nonenal (4-HNE). In accord with the absence of mitochondria in the P123H βS-globules, staining of nitrated αS and 4-HNE in these globules was weaker than that for αS-globules. Leucine-rich repeat kinase 2 (LRRK2), the PARK8 of familial PD, was detected exclusively in αS-globules, suggesting a specific role of this molecule in these globules. CONCLUSIONS: Lysosomal pathology was similarly observed for both αS- and P123H βS-globules, while oxidative stress was associated with the αS-globules, and to a lesser extent with the P123H βS-globules. Other pathologies, such as mitochondrial alteration and LRRK2 accumulation, were exclusively detected for αS-globules. Collectively, both αS- and P123H βS-globules were formed through similar but distinct pathogenic mechanisms. Our findings suggest that synuclein family members might contribute to diverse axonal pathologies

α-Synuclein and DJ-1 as Potential Biological Fluid Biomarkers for Parkinson’s Disease

Parkinson’s disease (PD) is the most common form of movement disorder and affects approximately 4% of the population aged over 80 years old. Currently, PD cannot be prevented or cured, and no single diagnostic biomarkers are available. Notably, recent studies suggest that two familial PD-linked molecules, α-synuclein and DJ-1, are present in cerebrospinal fluid (CSF) and that their levels may be altered during the progression of PD. In this regard, sensitive and accurate methods for evaluation of α-synuclein and DJ-1 levels in the CSF and blood have been developed, and the results suggest that the levels of both molecules are significantly decreased in the CSF in patients with PD compared with age-matched controls. Furthermore, specific detection and quantification of neurotoxic oligometric forms of α-synuclein in the blood using enzyme-linked immunosorbent assays might be expected as potential peripheral biomarkers for PD, although further validation is required. Currently, neither α-synuclein nor DJ-1 is satisfactory as a single biomarker for PD, but combinatory evaluation of these biological fluid molecules with other biomarkers and imaging techniques may provide reliable information for diagnosis of PD

Quantification of excitatory and inhibitory synapseson GABAergic nonpyramidal cell subtypes in the rat cerebral cortex

　　The neocortex is composed of excitatory (pyramidal) and inhibitory (GABAergic nonpyramidal) neurons. Pyramidal neurons receive excitatory synaptic input from their own recurrent collaterals as well as thalamic fibers. Pyramidal neurons also receive inhibitory synaptic input from local GABAergic nonpyramidal cells. This mixture of synaptic input maintains the excitatory and inhibitory balance in the cortex. Neocortical GABAergic cells are morphologically and physiologically heterogeneous, but specific subtypes can be identified based on differential expression of specific peptides and proteins. Individual GABAergic cell subtypes tend to innervate specific surface domains of other cortical cells. Somatostatin-expressing Martinotti cells mostly innervate thin dendritic shafts and spines, whereas parvalbumin fast-spiking (FS) basket cells also make synapses on somata. Thus, cortical inhibition is differentially exerted onto specific cellular domains based on the innervation patterns of different interneuron subtypes. Therefore, to understand the mechanisms that maintain the excitatory and inhibitory activity balance in the cortex, it is necessary to reveal the specific excitatory and inhibitory input patterns onto individual GABAergic cell subtypes.　　GABAergic neuron subtypes show differential dendritic spatial extension, branching patterns, and spine densities. The local input impedance influences local postsynaptic potentials induced by active synaptic conductances, and is in turn dependent on the postsynaptic dendritic geometry. Local synaptic current amplitudes are related to the postsynaptic synapse density and junctional area related to the receptor number. The total excitatory depolarization would be determined by interaction between the activated excitatory and inhibitory synapses. However, it remains to be investigated how local postsynaptic morphologies, important for the local synaptic integration and current transfer to the soma, are related to synaptic density. Furthermore, it is not known if these relationships are different between excitatory and inhibitory terminals onto the various GABAergic neuron subtypes. The cell body integrates all excitatory currents from the dendrite and generates depolarization for spike induction. The differences in excitatory and inhibitory balances would affect the firing regulation a lot.　　The majority of GABAergic neurons can be identified by chemical expression of parvalbumin, calretinin and somatostatin. These chemical classes are further divided into subtypes, such as a somatostatin subpopulation expressing nitric oxide synthase (NOS). Here they have investigated the relationships between postsynaptic density of GABA-positive and GABA-negative terminals onto different GABAergic neuron subtypes.　　First they confirmed that substance P receptors (SPR) were selectively expressed in NOS cells, a subpopulation of somatostatin cells (13% of somatostatin cells in layer II/III, 20% in layer V and 25% in layer VI) by double immunofluorescence. Parvalbumin and calretinin cells were not positive for SPR. Next they labeled the somata and dendrites of 4 chemically defined nonpyramidal neuron subtypes positive for somatostatin, SPR, parvalbumin, or calretinin by pre-embedding immunohistochemistry using Ni-DAB reaction. These sections were embedded in Epon for electron microscopic observations. Some immunostained somata and dendrites were reconstructed 3-dimensionally at the light microscopic level using the Neurolucida system. Immunopositive tissues were serially sectioned in 90 nm thicknesses. To identify GABAergic terminals, they applied GABA postembedding immunohistochemistry to ultrathin sections, detected by colloidal gold particles. Synaptic boutons were quantitatively divided into two classes on the basis of gold particle densities for GABA immunohistochemistry. The particle density differences between GABA-negative and -positive terminals were similar among the materials immunostained for the above 4 chemical markers.　　The labeled somata and dendrites and associated structures were reconstructed from serial electron microscopic images by a 3D reconstruction system using the software package ‘Reconstruct’. From the reconstructed dendrites, they measured the length and surface area, followed by a calculation of the averaged cross-sectional area. In individual reconstructed dendritic segments, they counted GABA-positive and -negative synapses, followed by evaluation of their density per surface area. 　　Cell bodies of 4 chemical types were partially reconstructed, and somatic synaptic input patterns were compared between them. GABA-positive synapse densities on the soma were similar between the subtypes, but GABA-negative densities were significantly different. Parvalbumin cells had higher densities of GABA-negative synapses than did calretinin and somatostatin cells. Therefore, the proportion of GABA-positive synapses on the soma was significantly different between the 4 classes. Somatostatin somata had a higher proportion of GABA-positive synapses than did SPR and parvalbumin somata. Calretinin-positive somata had a higher proportion of GABA-positive synapses than those of parvalbumin cells. These indicate that nonpyramidal neuron subtype influences the ratio of inhibitory to excitatory somatic input.　　Dendritic spines were found in somatostatin cells, but not in those of parvalbumin and calretinin cells. Although SPR cells were a subpopulation of somatostatin cells, spines were not identified in SPR dendritic segments.　　The dendritic synaptic densities and cross-sectional areas were well correlated in GABA-negative synapses. Larger dendrites were lower in GABA-negative synapse density, and smaller dendrites had higher synaptic densities. The density dependency on the postsynaptic dendritic dimension was most prominent in SPR cells and least in calretinin cells. On the other hand the correlation between GABA-positive synapse densities and dendritic dimensions was weaker than that of GABA-negative synapses. These data show that GABA synapse density is relatively constant between dendritic locations, but excitatory input density changes according to the postsynaptic dendritic dimension and location.　　They next compared dendritic synaptic densities as a whole. GABA-positive synapse densities on dendrites were similar between the neuronal subtypes, but GABA-negative synaptic densities were significantly different. Calretinin dendrites had lower GABA-negative densities than did parvalbumin and SPR cells. Somatostatin dendrites were lower in GABA-negative densities than were parvalbumin-positive neurons.　　These observations revealed that the GABAergic inhibitory synaptic density is similar between the subtypes, the somata and dendrites, the dendritic surface locations, or the dendritic dimensions. On the other hand, the excitatory density varies between the subtypes. It is higher in dendrites than in somata, and also higher in distal thinner dendrites.<br /

Role of α- and β-Synucleins in the Axonal Pathology of Parkinson’s Disease and Related Synucleinopathies

Axonal swellings are histological hallmarks of axonopathies in various types of disorders in the central nervous system, including neurodegenerative diseases. Given the pivotal role of axonopathies during the early phase of neurodegenerative process, axonal swellings may be good models which may provide some clues for early pathogenesis of α-synucleinopathies, including Parkinson’s disease and dementia with Lewy bodies (DLB). In this mini-review, such a possibility is discussed based on our recent studies as well as other accumulating studies. Consistent with the current view that dysfunction in the autophagy-lysosomal system may play a major role in the formation of axonal swellings, our studies showed globule, small axonal swellings, derived from transgenic mice expressing either human wild-type α-synuclein (αS-globule) or DLB-linked P123H β-synuclein (βS-globule), contained autophagosome-like membranes. However, other pathological features, such as abnormal mitochondria, enhanced oxidative stress and LRRK2 accumulation, were observed in the αS-globules, but not in the βS-globules. Collectively, it is predicted that αS and βS may be involved in axonopathies through similar but distinct mechanisms, and thus, contribute to diverse axonal pathologies. Further studies of the axonal swellings may lead to elucidating the pathogenic mechanism of early α-synucleinopathies and illuminating a strategy for a disease-modifying therapy against these devastating disorders

Possible Alterations in β-Synuclein, the Non-Amyloidogenic Homologue of α-Synuclein, during Progression of Sporadic α-Synucleinopathies

α-Synucleinopathies are neurodegenerative disorders that are characterized by progressive decline of motor and non-motor dysfunctions. α-Synuclein (αS) has been shown to play a causative role in neurodegeneration, but the pathogenic mechanisms are still unclear. Thus, there are no radical therapies that can halt or reverse the disease’s progression. β-Synuclein (βS), the non-amyloidogenic homologue of αS, ameliorates the neurodegeneration phenotype of αS in transgenic (tg) mouse models, as well as in cell free and cell culture systems, which suggests that βS might be a negative regulator of neurodegeneration caused by αS, and that “loss of function” of βS might be involved in progression of α-synucleinopathies. Alternatively, it is possible that “toxic gain of function” of wild type βS occurs during the pathogenesis of sporadic α-synucleinopathies, since tg mice expressing dementia with Lewy bodies-linked P123H βS develop progressive neurodegeneration phenotypes, such as axonal pathology and dementia. In this short review, we emphasize the aspects of “toxic gain of function” of wild type βS during the pathogenesis of sporadic α-synucleinopathies