Astrogliosis in von Economo's and postencephalitic Parkinson's diseases supports probable viral etiology

Astrocyte inflammatory signaling mediates α-synuclein aggregation and dopaminergic neuronal loss following viral encephalitis

Viral infection of the central nervous system (CNS) can cause lasting neurological decline in surviving patients and can present with symptoms resembling Parkinson's disease (PD). The mechanisms underlying postencephalitic parkinsonism remain unclear but are thought to involve increased innate inflammatory signaling in glial cells, resulting in persistent neuroinflammation. We therefore studied the role of glial cells in regulating neuropathology in postencephalitic parkinsonism by studying the involvement of astrocytes in loss of dopaminergic neurons and aggregation of α-synuclein protein following infection with western equine encephalitis virus (WEEV). Infections were conducted in both wildtype mice and in transgenic mice lacking NFκB inflammatory signaling in astrocytes. For 2 months following WEEV infection, we analyzed glial activation, neuronal loss and protein aggregation across multiple brain regions, including the substantia nigra pars compacta (SNpc). These data revealed that WEEV induces loss of SNpc dopaminergic neurons, persistent activation of microglia and astrocytes that precipitates widespread aggregation of α-synuclein in the brain of C57BL/6 mice. Microgliosis and macrophage infiltration occurred prior to activation of astrocytes and was followed by opsonization of ⍺-synuclein protein aggregates in the cortex, hippocampus and midbrain by the complement protein, C3. Astrocyte-specific NFκB knockout mice had reduced gliosis, α-synuclein aggregate formation and neuronal loss. These data suggest that astrocytes play a critical role in initiating PD-like pathology following encephalitic infection with WEEV through innate immune inflammatory pathways that damage dopaminergic neurons, possibly by hindering clearance of ⍺-synuclein aggregates. Inhibiting glial inflammatory responses could therefore represent a potential therapy strategy for viral parkinsonism.

Manganese exposure in juvenile C57BL/6 mice increases glial inflammatory responses in the substantia nigra following infection with H1N1 influenza virus

Infection with Influenza A virus can lead to the development of encephalitis and subsequent neurological deficits ranging from headaches to neurodegeneration. Post-encephalitic parkinsonism has been reported in surviving patients of H1N1 infections, but not all cases of encephalitic H1N1 infection present with these neurological symptoms, suggesting that interactions with an environmental neurotoxin could promote more severe neurological damage. The heavy metal, manganese (Mn), is a potential interacting factor with H1N1 because excessive exposure early in life can induce long-lasting effects on neurological function through inflammatory activation of glial cells. In the current study, we used a two-hit model of neurotoxin-pathogen exposure to examine whether exposure to Mn during juvenile development would induce a more severe neuropathological response following infection with H1N1 in adulthood. To test this hypothesis, C57BL/6 mice were exposed to MnCl₂ in drinking water (50 mg/kg/day) for 30 days from days 21–51 postnatal, then infected intranasally with H1N1 three weeks later. Analyses of dopaminergic neurons, microglia and astrocytes in basal ganglia indicated that although there was no significant loss of dopaminergic neurons within the substantia nigra pars compacta, there was more pronounced activation of microglia and astrocytes in animals sequentially exposed to Mn and H1N1, as well as altered patterns of histone acetylation. Whole transcriptome Next Generation Sequencing (RNASeq) analysis was performed on the substantia nigra and revealed unique patterns of gene expression in the dual-exposed group, including genes involved in antioxidant activation, mitophagy and neurodegeneration. Taken together, these results suggest that exposure to elevated levels of Mn during juvenile development could sensitize glial cells to more severe neuro-immune responses to influenza infection later in life through persistent epigenetic changes.

Infection with mosquito-borne alphavirus induces selective loss of dopaminergic neurons, neuroinflammation and widespread protein aggregation

Neuroinvasive infections with mosquito-borne alphaviruses such as Western equine encephalitis virus (WEEV) can cause post-encephalitic parkinsonism. To understand the mechanisms underlying these neurological effects, we examined the capacity of WEEV to induce progressive neurodegeneration in outbred CD-1 mice following non-lethal encephalitic infection. Animals were experientally infected with recombinant WEEV expressing firefly luciferase or dsRed (RFP) reporters and the extent of viral replication was controlled using passive immunotherapy. WEEV spread along the neuronal axis from the olfactory bulb to the entorhinal cortex, hippocampus and basal midbrain by 4 days post infection (DPI). Infection caused activation of microglia and astrocytes, selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and neurobehavioral abnormalities. After 8 weeks, surviving mice displayed continued loss of dopamine neurons in the SNpc, lingering glial cell activation and gene expression profiles consistent with a neurodegenerative phenotype. Strikingly, prominent proteinase K-resistant protein aggregates were present in the the entorhinal cortex, hippocampus and basal midbrain that stained positively for phospho-serine129 α-synuclein (SNCA). These results indicate that WEEV may cause lasting neurological deficits through a severe neuroinflammatory response promoting both neuronal injury and protein aggregation in surviving individuals.

Cellular phenotypes as inflammatory mediators in Parkinson's disease: Interventional targets and role of natural products

Pathogenesis of Parkinson's disease (PD) is undoubtedly a multifactorial phenomenon, with diverse etiological agents. Pro-inflammatory mediators act as a skew that directs disease progression during neurodegenerative diseases. Understanding the dynamics of inflammation and inflammatory mediators in preventing or reducing disease progression has recently gained much attention. Inflammatory neuro-degeneration is regulated via cytokines, chemokines, lipid mediators and immune cell subsets; however, individual cellular phenotypes in the Central Nervous System (CNS) acts in diverse ways whose persistent activation leads to unresolving inflammation often causing unfavorable outcomes in neurodegenerative disease like PD. Specifically, activation of cellular phenotypes like astrocytes, microglia, activation of peripheral immune cells requires different activation signals and agents like (cytokines, misfolded protein aggregates, infectious agents, pesticides like organophosphates, etc.,). However, what is unknown is how the different cellular phenotypes respond uniquely and the role of the factors they secrete alters the signal cascades in the complex neuron-microglial connections in the CNS. Hence, understanding the role of cellular phenotypes and the inflammatory mediators, the cross talk among the signals and their receptors can help us to identify the potential therapeutic target using natural products. In this review we have tried to put together the role of cellular phenotypes as a skew that favors PD progression and we have also discussed how the lack of experimental approaches and challenges that affects understanding the cellular targets that can be used against natural derivatives in alleviating PD pathophysiology. Together, this review will provide the better insights into the role of cellular phenotypes of neuroinflammation, inflammatory mediators and the orchestrating factors of inflammation and how they can be targeted in a more specific way that can be used in the clinical management of PD.

Medical and molecular perspectives into a forgotten epidemic: encephalitis lethargica, viruses, and high-throughput sequencing

The emergence of encephalitis lethargica (EL), an acute-onset polioencephalitis of unknown etiology as an epidemic in the years 1917-1925 is still unexplainable today. Questioned by the first descriptor of EL himself, Constantin von Economo, there has been much debate shrouding a possible role of the "Spanish" H1N1 influenza A pandemic virus in the development of EL. Previous molecular studies employing conventional PCR for the detection of influenza A virus RNA in archived human brain samples from patients who died of acute EL were negative. However, the clinical and laboratory characteristics of EL and its epidemiology are consistent with an infectious disease, and recently a possible enterovirus cause was investigated. With the rapid development of high-throughput sequencing, new information about a possible viral etiology can be obtained if sufficient specimens for analysis were still available today. Here, we discuss the implications of these technologies for the investigation of a possible infectious cause of EL from archived material, as well as a prospectus for future work for acquiring viral nucleic acids from these sources.

Glial-mediated inflammation underlying parkinsonism

The interest in studying neuroimmune interactions is increasing in the scientific community, and for many researchers, immunity is becoming a crucial factor in the understanding of the physiology of the normal brain as well as the biology underlying neurodegenerative diseases. Mounting data over the last two decades point toward immune and inflammatory alterations as important mediators of the progressive dopaminergic degeneration in Parkinson's disease. The purpose of this review is to address, under a historical perspective, as well as in the light of recent reports, the glial-mediated inflammatory and immune responses that occur in Parkinsonism. In line with this, this review also evaluates and highlights available anti-inflammatory drugs and putative targets for Parkinson's disease therapy for the near future.

Gene-environment interactions: key to unraveling the mystery of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. The gradual, irreversible loss of dopamine neurons in the substantia nigra is the signature lesion of PD. Clinical symptoms of PD become apparent when 50-60% of nigral dopamine neurons are lost. PD progresses insidiously for 5-7 years (preclinical period) and then continues to worsen even under the symptomatic treatment. To determine what triggers the disease onset and what drives the chronic, self-propelling neurodegenerative process becomes critical and urgent, since lack of such knowledge impedes the discovery of effective treatments to retard PD progression. At present, available therapeutics only temporarily relieve PD symptoms. While the identification of causative gene defects in familial PD uncovers important genetic influences in this disease, the majority of PD cases are sporadic and idiopathic. The current consensus suggests that PD develops from multiple risk factors including aging, genetic predisposition, and environmental exposure. Here, we briefly review research on the genetic and environmental causes of PD. We also summarize very recent genome-wide association studies on risk gene polymorphisms in the emergence of PD. We highlight the new converging evidence on gene-environment interplay in the development of PD with an emphasis on newly developed multiple-hit PD models involving both genetic lesions and environmental triggers.

The percipient observations of Constantin von Economo on encephalitis lethargica and sleep disruption and their lasting impact on contemporary sleep research

The study, and the preceding companion article, reviews the pioneering contributions of Constantin von Economo (1876-1931) to Neuroscience in a modern context. The neurological studies of von Economo include the discovery of a new nosological entity, encephalitis lethargica, with which his name is forever linked ('von Economo disease'). Based on a percipient analysis of pathoanatomical material from patients with encephalitis lethargica who manifested with either insomnia or somnolence, von Economo deduced the existence of distinct centres in the brain for the regulation of sleep and wakefulness. He presented a synthesis of his ideas in a series of lectures in New York in 1929 and at the First International Neurological Congress held in Berne in 1931. Constantin von Economo was nominated three times for the Nobel Prize in Physiology or Medicine for the discovery of encephalitis lethargica. As those studies have exerted and continue to exert the highest impact among von Economo's publications, the present article examines the spectrum of his observations on encephalitis lethargica and the cerebral control of sleep, documented in 63 published works--including post-humous translations into French and English of original German texts; complete bibliographic information is given. His remaining 76 works of an annotated total of 139 scientific publications deal with brain structure, evolution and intelligence, as well as general works on nervous and mental pathology and form the focus of the preceding article.

Parkinson's disease and exposure to infectious agents and pesticides and the occurrence of brain injuries: role of neuroinflammation

Idiopathic Parkinson's disease (PD) is a devastating movement disorder characterized by selective degeneration of the nigrostriatal dopaminergic pathway. Neurodegeneration usually starts in the fifth decade of life and progresses over 5-10 years before reaching the fully symptomatic disease state. Despite decades of intense research, the etiology of sporadic PD and the mechanism underlying the selective neuronal loss remain unknown. However, the late onset and slow-progressing nature of the disease has prompted the consideration of environmental exposure to agrochemicals, including pesticides, as a risk factor. Moreover, increasing evidence suggests that early-life occurrence of inflammation in the brain, as a consequence of either brain injury or exposure to infectious agents, may play a role in the pathogenesis of PD. Most important, there may be a self-propelling cycle of inflammatory process involving brain immune cells (microglia and astrocytes) that drives the slow yet progressive neurodegenerative process. Deciphering the molecular and cellular mechanisms governing those intricate interactions would significantly advance our understanding of the etiology and pathogenesis of PD and aid the development of therapeutic strategies for the treatment of the disease.

Influenza RNA not detected in archival brain tissues from acute encephalitis lethargica cases or in postencephalitic Parkinson cases

Encephalitis lethargica (EL) was a mysterious epidemic. temporally associated with the 1918 Spanish influenza pandemic. Numerous symptoms characterized this disease, including headache, diplopia, fever, fatal coma, delirium, oculogyric crisis, lethargy, catatonia, and psychiatric symptoms. Many patients who initially recovered subsequently developed profound, chronic parkinsonism. The etiologic association of influenza with EL is controversial. Five acute EL autopsies and more than 70 postencephalitic parkinsonian autopsies were available in the Armed Forces Institute of Pathology (AFIP) tissue repository. Two of these 5 acute EL cases had histopathologic changes consistent with that diagnosis. The remaining 3 cases were classified as possible acute EL cases as the autopsy material was insufficient for detailed histopathologic examination. RNA lysates were prepared from 29 CNS autopsy tissue blocks from the 5 acute cases and 9 lysates from blocks containing substantia nigra from 2 postencephalitic cases. RNA recovery was assessed by amplification of beta-2-microglobulin mRNA and 65% of the tissue blocks contained amplifiable RNA. Reverse transcription-polymerase chain reaction (RT-PCR) for influenza matrix and nucleoprotein genes was negative in all cases. Thus, it is unlikely that the 1918 influenza virus was neurotropic and directly responsible for the outbreak of EL.

Accuracy of the clinical diagnosis of postencephalitic parkinsonism: a clinicopathologic study

The accuracy of the clinical diagnosis of postencephalitic parkinsonism (PEP) is unknown. We determined the validity of the clinical diagnosis of PEP by presenting 105 records with neuropathologic diagnoses of PEP (n = 7), progressive supranuclear palsy (n = 24), Parkinson's disease (n = 15), dementia with Lewy bodies (n = 14), multiple system atrophy (n = 16), corticobasal degeneration (n = 10), Creutzfeldt-Jakob disease (n = 4), and other dementia disorders (n = 15), as clinical vignettes to six neurologists unaware of the autopsy findings. The neurologists' own clinical diagnoses were compared with neuropathologic diagnoses for measures of diagnostic accuracy, including reliability (kappa statistics), sensitivity and positive predictive values for the first and last visits. The group reliability for the diagnosis of PEP was almost perfect (kappa = 0.91, 0.9). The mean sensitivity at the first visit was 86% (range, 71-100%) with minimal change at the last visit (83%; range, 71-100%). Positive predictive values remained unchanged (100%). The high reliability, sensitivity and positive predictive values of the clinical diagnosis of PEP indicate that neurologists identify this disorder even when they report that they have never evaluated a case. In our data set, the best predictors for the diagnosis of PEP included onset below middle age; symptom duration lasting more than 10 years, and the presence of oculogyric crisis. History of encephalitis lethargica, present in most PEP cases, was an important individual diagnostic predictor. Copyright 1998 Lippincott Williams & Wilkins

Supranuclear gaze palsy and eyelid apraxia in postencephalitic parkinsonism

We describe six patients with clinicopathologically confirmed post-encephalitic parkinsonism (PEP) in whom oculomotor abnormalities developed several years after suffering the initial episode of encephalitis lethargica. Four of the cases had vertical supranuclear gaze palsy and two eyelid apraxia, features typically associated with progressive supranuclear palsy (PSP). Our findings indicate that the presence of gaze palsy alone may not be a reliable clinical discriminator between PEP and PSP. Involvement of the dorsal central gray nucleus, nucleus centralis pontis oralis, nucleus dorsal raphe interpositus, rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), nucleus interstitialis of Cajal, nucleus of the posterior commissure, pedunculopontine nuclei and frontal cortex was observed in several of our PEP cases and may contribute to the oculomotor abnormalities in this disorder. Whether the dorsal tegmental nucleus, caudal to the supratrochlear nucleus, severely affected in all our PEP cases, has a role in vertical gaze needs to be further studied.

Viruses, neurosis and fatigue

The evidence for viral infections as a cause of anxiety, depression and fatigue is reviewed. It is argued that in order to fully understand any proposed relationship the effects of psychosocial factors on immunity, convalescence and illness behaviour must be acknowledged.

Two neurotropic viruses, herpes simplex virus type 1 and mouse hepatitis virus, spread along different neural pathways from the main olfactory bulb

Several neurotropic viruses enter the brain after peripheral inoculation and spread transneuronally along pathways known to be connected to the initial site of entry. In this study, the pathways utilized by two such viruses, herpes simplex virus type 1 and mouse hepatitis virus strain JHM, were compared using in situ hybridization following inoculation into either the nasal cavity or the main olfactory bulb of the mouse. The results indicate that both viruses spread to infect a unique and only partially overlapping set of connections of the main olfactory bulb. Both quantitative and qualitative differences were observed in the patterns of infection of known primary and secondary main olfactory bulb connections. Using immunohistochemistry for tyrosine hydroxylase combined with in situ hybridization, it was shown that only herpes simplex virus infected noradrenergic neurons in the locus coeruleus. In contrast, both viruses infected dopaminergic neurons in the ventral tegmental area, although mouse hepatitis virus produced a more widespread infection in the A10 group, as well as infecting A8 and A9. The results suggest that differential virus uptake in specific neurotransmitter systems contributes to the pattern of viral spread, although other factors, such as differences in access to particular synapses on infected cells and differences in the distribution of the cellular receptor for the two viruses, are also likely to be important. The data show that neural tracing with different viruses may define unique neural pathways from a site of inoculation. The data also demonstrate that two viruses can enter the brain via the olfactory system and localize to different structures, suggesting that neurological diseases involving disparate regions of the brain could be caused by different viruses, even if entry occurred at a common site.

Distribution of neurofibrillary tangles and senile plaques in the cerebral cortex in postencephalitic parkinsonism

Postencephalitic parkinsonism is characterized neuropathologically by severe loss of pigmented neurons in the substantia nigra and the presence of high densities of neurofibrillary tangles in several brainstem structures. In 5 cases of postencephalitic parkinsonism, we observed that the neurofibrillary tangle distribution in the cerebral cortex predominated in the hippocampus and entorhinal cortex. In the prefrontal and inferior temporal cortex, neurofibrillary tangles were preferentially localized in layers II and III. This pattern contrasts with the neurofibrillary tangle distribution observed in neocortical areas of Alzheimer's disease cases, where neurofibrillary tangles are denser in layer V than in layer III. These results suggest that specific elements of the cortical circuitry might be differentially affected in postencephalitic parkinsonism as compared to Alzheimer's disease, and that cortical involvement is likely to be a common feature of this condition.