Increasing evidence suggests that phosphorylation may play an important role in the oligomerization, fibrillogenesis, Lewy body (LB) formation, and neurotoxicity of ␣-synuclein (␣-syn) in Parkinson disease. Herein we demonstrate that ␣-syn is phosphorylated at S87 in vivo and within LBs. The levels of S87-P are increased in brains of transgenic (TG) models of synucleinopathies and human brains from Alzheimer disease (AD), LB disease (LBD), and multiple system atrophy (MSA) patients. Using antibodies against phosphorylated ␣-syn (S129-P and S87-P), a significant amount of immunoreactivity was detected in the membrane in the LBD, MSA, and AD cases but not in normal controls. In brain homogenates from diseased human brains and TG animals, the majority of S87-P ␣-syn was detected in the membrane fractions. A battery of biophysical methods were used to dissect the effect of S87 phosphorylation on the structure, aggregation, and membranebinding properties of monomeric ␣-syn. These studies demonstrated that phosphorylation at S87 expands the structure of ␣-syn, increases its conformational flexibility, and blocks its fibrillization in vitro. Furthermore, phosphorylation at S87, but not S129, results in significant reduction of ␣-syn binding to membranes. Together, our findings provide novel mechanistic insight into the role of phosphorylation at S87 and S129 in the pathogenesis of synucleinopathies and potential roles of phosphorylation in ␣-syn normal biology.

The aggregation of α-synuclein (aSyn) leading to the formation of Lewy bodies is the defining pathological hallmark of Parkinson's disease (PD). Rare familial PD-associated mutations in aSyn render it aggregation-prone; however, PD patients carrying wild type (WT) aSyn also have aggregated aSyn in Lewy bodies. The mechanisms by which WT aSyn aggregates are unclear. Here, we report that inflammation can play a role in causing the aggregation of WT aSyn. We show that activation of the inflammasome with known stimuli results in the aggregation of aSyn in a neuronal cell model of PD. The insoluble aggregates are enriched with truncated aSyn as found in Lewy bodies of the PD brain. Inhibition of the inflammasome enzyme caspase-1 by chemical inhibition or genetic knockdown with shRNA abated aSyn truncation. In vitro characterization confirmed that caspase-1 directly cleaves aSyn, generating a highly aggregation-prone species. The truncation-induced aggregation of aSyn is toxic to neuronal culture, and inhibition of caspase-1 by shRNA or a specific chemical inhibitor improved the survival of a neuronal PD cell model. This study provides a molecular link for the role of inflammation in aSyn aggregation, and perhaps in the pathogenesis of sporadic PD as well.ver the past two decades, studies stimulated by the discovery of genetic mutations occurring in familial Parkinson's disease (PD) have generated a number of hypotheses concerning potential mechanisms of PD pathogenesis. Nonetheless, the causes and mechanism of sporadic PD, which constitutes the majority of cases, remain unknown.Before the genetic discoveries, epidemiologic evidence suggested environmental toxins, traumatic brain injury, and viral infection as potential causes of idiopathic PD (1-7). All of these insults could cause neural inflammation, a common feature of PD brains; however, whether neural inflammation contributes to the etiology of the disease or is part of its effect remained unclear. Suggestive evidence indicating the involvement of inflammation in the pathogenesis of PD emerged after an outbreak of encephalitis lethargica following the 1918 influenza pandemic, which killed approximately 1 million people and left many survivors with postencephalitic Parkinsonism (PEP). Affected persons presented with cardinal symptoms of typical Parkinson's disease, including stooped posture, masklike faces, muscular rigidity, and tremorous extremities. Contemporary cases of viral infection-associated Parkinsonism are rare, but both epidemiology and patient case studies indicate that infection-associated PD still occurs today (8-10).The role of viral infection in the pathogenesis of PD has been a controversial subject for more than 50 years. Proponents have pointed out the known close temporal association between infection and PEP, whereas opponents have cited studies that failed to find any viral remnants in the brains of affected patients. Moreover, there were no known routes for peripheral viral migration into the central nervous system (CNS). Recently, R. Smey...

Peroxiredoxin 6 is an antioxidant enzyme and is the 1-cys member of the peroxiredoxin family. Using two-dimensional electrophoresis and Western blotting, we have shown for the first time that, in human control and brain tissue of patient’s with Alzheimer’s disease (AD), this enzyme exists as three major and five minor forms with pIs from 5.3 to 6.1. Using specific cellular markers, we have shown that peroxiredoxin 6 is present in astrocytes with very low levels in neurons, but not detectable in microglia or oligodendrocytes. In control brains, there was a very low level of peroxiredoxin 6 staining in astrocytes that was confined to a “halo” around the nucleus. In AD, there were marked increases in the number and staining intensity of peroxiredoxin 6 positive astrocytes in both gray and white matter in the midfrontal cortex, cingulate, hippocampus and amygdala. Confocal microscopy using antibodies to Aβ peptide, tau and peroxiredoxin 6 showed that peroxiredoxin 6 positive astrocytes are closely involved with diffuse plaques and to a lesser extent with neuritic plaques, suggesting that plaques are producing reactive oxygen species. There appeared to be little astrocytic response to tau containing neurons. Although peroxiredoxin 6 positive astrocytes were seen to make multiple contacts with tau positive neurons, there was no intraneuronal colocalization. In brain tissue of patients with AD, many blood vessels exhibited peroxiredoxin 6 staining that appeared to be due to the astrocytic foot processes. These results suggest that oxidative stress conditions exist in AD and that peroxiredoxin 6 is an important antioxidant enzyme in human brain defenses.

Neuronal loss in specific brain regions and neurons with intracellular inclusions termed Lewy bodies are the pathologic hallmark in both Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Lewy bodies comprise of aggregated intracellular vesicles and proteins and α-synuclein is reported to be a major protein component. Using human brain tissue from control, PD and DLB and light and confocal immunohistochemistry with antibodies to superoxide dismutase 2 as a marker for mitochondria, α-synuclein for Lewy bodies and βIII Tubulin for microtubules we have examined the relationship between Lewy bodies and mitochondrial loss. We have shown microtubule regression and mitochondrial and nuclear degradation in neurons with developing Lewy bodies. In PD, multiple Lewy bodies were often observed with α-synuclein interacting with DNA to cause marked nuclear degradation. In DLB, the mitochondria are drawn into the Lewy body and the mitochondrial integrity is lost. This work suggests that Lewy bodies are cytotoxic. In DLB, we suggest that microtubule regression and mitochondrial loss results in decreased cellular energy and axonal transport that leads to cell death. In PD, α-synuclein aggregations are associated with intact mitochondria but interacts with and causes nuclear degradation which may be the major cause of cell death.

Multiple system atrophy (MSA) is characterized by the formation of oligodendroglial cytoplasmic inclusions (GCIs) consisting of alpha-synuclein filaments. AlphaB-crystallin, a small chaperone protein that binds to unfolded proteins and inhibits aggregation, has been documented in GCIs. We investigated the relative abundance and speciation of alphaB-crystallin in GCIs in MSA brains. We also examined the influence of alphaB-crystallin on the formation of cytoplasmic inclusions in cultured glial cells. Immunohistochemistry and confocal microscopy revealed alphaB-crystallin is a prominent component of GCIs, more abundant than in Lewy bodies in Lewy body dementia. One- and two-dimensional gel electrophoresis and mass spectrometric analysis of GCIs immunopurified from MSA brains indicated that alphaB-crystallin is a major protein component with multiple post-translationally modified species. In cultured C6 glioma cells treated with the proteasomal inhibitor, lactacystin, to induce accumulation of ubiquitinated proteins, a subset of cells showed increased cytoplasmic staining for alphaB-crystallin. Proteasome-inhibited cells transfected with GFP-tagged alpha-synuclein resulted in ubiquitin- and alphaB-crystallin-positive aggregates resembling GCIs in MSA brains. Our results indicate that alphaB-crystallin is a major chaperone in MSA, and suggest a role of the protein in the formation of inclusion bodies in glial cells.