Rab27b promotes lysosomal function and alpha-synuclein clearance in neurons

Alpha-synuclein (αsyn) is the key pathogenic protein implicated in synucleinopathies including Parkinson's Disease (PD) and Dementia with Lewy Bodies (DLB). In these diseases, αsyn is thought to spread between cells where it accumulates and induces pathology; however, mechanisms that drive its propagation or aggregation are poorly understood. We have previously reported that the small GTPase Rab27b is elevated in human PD and DLB and that it can mediate the autophagic clearance and toxicity of αsyn in a paracrine αsyn cell culture neuronal model. Here, we expanded our previous work and further characterized a role for Rab27b in neuronal lysosomal processing and αsyn clearance. We found that Rab27b KD in this αsyn inducible neuronal model resulted in lysosomal dysfunction and increased αsyn levels in lysosomes. Similar lysosomal proteolytic defects and enzymatic dysfunction were observed in both primary neuronal cultures and brain lysates from Rab27b knockout (KO) mice. αSyn aggregation was exacerbated in Rab27b KO neurons upon treatment with αsyn preformed fibrils. We found no changes in lysosomal counts or lysosomal pH in either model, but we did identify defects in acidic vesicle trafficking in Rab27b KO primary neurons which may drive lysosomal dysfunction and promote αsyn aggregation. Rab27b OE enhanced lysosomal activity and reduced insoluble αsyn accumulation. Finally we found elevated Rab27b levels in human postmortem incidental Lewy Body Disease (iLBD) subjects relative to healthy controls. These data suggest a role for Rab27b in neuronal lysosomal activity and identify it as a potential therapeutic target in synucleinopathies.

Advances in the Diagnosis and Management of Psychotic Symptoms in Neurodegenerative Diseases: A Narrative Review

Background: Approximately 15% of older adults may experience psychotic phenomena. Primary psychiatric disorders that manifest with psychosis (delusions, hallucinations, and disorganized thought or behavior) account for less than half. Up to 60% of late-life psychotic symptoms are due to systemic medical or neurological conditions, particularly neurodegenerative diseases. A thorough medical workup including laboratory tests, additional procedures if indicated, and neuroimaging studies is recommended. This narrative review summarizes current evidence regarding the epidemiology and phenomenology of psychotic symptoms encountered as part of the neurodegenerative disease continuum (including prodromal and manifest stages). Results: Prodromes are constellations of symptoms that precede the onset of overt neurodegenerative syndromes. Prodromal psychotic features, particularly delusions, have been associated with an increased likelihood of receiving a neurodegenerative disease diagnosis within several years. Prompt prodrome recognition is crucial for early intervention. The management of psychosis associated with neurodegenerative diseases includes behavioral and somatic strategies, although evidence is scarce and mostly limited to case reports, case series, or expert consensus guidelines, with few randomized controlled trials. Conclusion: The complexity of psychotic manifestations warrants management by interprofessional teams that provide coordinated, integrated care.

Synapses do not facilitate prion-like transfer of alpha-synuclein: a quantitative study in reconstructed unidirectional neural networks

Alpha-synuclein (aSyn) aggregation spreads between cells and underlies the progression of neuronal lesions in the brain of patients with synucleinopathies such as Parkinson's diseases. The mechanisms of cell-to-cell propagation of aggregates, which dictate how aggregation progresses at the network level, remain poorly understood. Notably, while prion and prion-like spreading is often simplistically envisioned as a "domino-like" spreading scenario where connected neurons sequentially propagate protein aggregation to each other, the reality is likely to be more nuanced. Here, we demonstrate that the spreading of preformed aSyn aggregates is a limited process that occurs through molecular sieving of large aSyn seeds. We further show that this process is not facilitated by synaptic connections. This was achieved through the development and characterization of a new microfluidic platform that allows reconstruction of binary fully oriented neuronal networks in vitro with no unwanted backward connections, and through the careful quantification of fluorescent aSyn aggregates spreading between neurons. While this allowed us for the first time to extract quantitative data of protein seeds dissemination along neural pathways, our data suggest that prion-like dissemination of proteinopathic seeding aggregates occurs very progressively and leads to highly compartmentalized pattern of protein seeding in neural networks.

Development, wiring and function of dopamine neuron subtypes

The midbrain dopamine (mDA) system is composed of molecularly and functionally distinct neuron subtypes that mediate specific behaviours and are linked to various brain diseases. Considerable progress has been made in identifying mDA neuron subtypes, and recent work has begun to unveil how these neuronal subtypes develop and organize into functional brain structures. This progress is important for further understanding the disparate physiological functions of mDA neurons and their selective vulnerability in disease, and will ultimately accelerate therapy development. This Review discusses recent advances in our understanding of molecularly defined mDA neuron subtypes and their circuits, ranging from early developmental events, such as neuron migration and axon guidance, to their wiring and function, and future implications for therapeutic strategies.

Phosphorylated α-Synuclein Deposits in Cutaneous Nerves of Early Parkinsonism

BACKGROUND

The role of peripheral phosphorylated-α-Synuclein (p-α-syn) deposition on nerve degeneration in synucleinopathies is still unknown.

OBJECTIVE

To assess the cutaneous neural distribution of p-α-Syn deposits and its correlation with clinical data and with morphology and function of cutaneous sensory and autonomic nerves in early Parkinson's disease (PD) and multiple system atrophy-parkinson type (MSA-p).

METHODS

We recruited 57 PD (F/M = 21/36; age 63.5±9.4 years) and 43 MSA-p (F/M = 16/27; age 62.3±9.0 years) patients within 2 years from motor symptoms. We applied questionnaires and clinical scales, sensory thresholds, and sudomotor testing to assess severity of motor and non-motor involvement and sensory and autonomic dysfunction. We quantified, in skin biopsy from thigh, leg, and fingertip, epidermal, pilomotor, and sudomotor nerve fibers, Meissner corpuscles and intrapapillary myelinated endings and the neural distribution of p-α-syn deposits.

RESULTS

Compared to controls, we found a cutaneous denervation paralleling functional and clinical impairment. Sensory and autonomic denervation was more severe in MSA-p than in PD. Deposits of p-α-syn were found in the majority of patients, with no significant differences among sites in both groups. Higher occurrence of p-α-syn deposits in autonomic nerves differentiated (p < 0.01) PD from MSA-p. p-α-syn deposits correlated positively with sudomotor function, epidermal, pilomotor and sudomotor nerve densities, and inversely with non-motor symptoms and disease progression.

CONCLUSION

Our work demonstrated an early peripheral sensory and autonomic involvement in synucleinopathies, more severe in MSA-p than in PD. Higher p-α-syn deposits in autonomic nerves differentiated PD from MSA-p. p-α-syn deposits were associated with preserved innervation and slower disease progression.

Perspective: cell death mechanisms and early diagnosis as precondition for disease modification in Parkinson's disease: are we on the right track?

INTRODUCTION

Current research paradigms on biomarkers for chronic neurodegenerative diseases, such as Parkinson's disease, focus on identification of reliable, easy-to-apply tools for diagnostic screening and progression assessment.

AREAS COVERED

This perspective discusses possible misconceptions of biomarker research in chronic neurodegeneration from a clinician's view based on a not systematic literature search. Multifactorial disease triggers, heterogeneity of symptom and their progression are main reasons for the still missing availability of biomarkers.

EXPERT OPINION

Onset of chronic neurodegenerative disease entities may probably result from a decompensated endogenous repair machinery in the central nervous system, for example the neogenin receptor associated repulsive guidance molecule pathway. Future clinical research is warranted on these repair structures and aim to identify markers for the imbalance between damage and repair, which hypothetically contributes to generation of disease. An assignment to a specific chronic neurodegenerative disease entity probably appears to be secondary. Decryption of probable molecular signals of an impaired repair potential will enable an earlier diagnosis, better monitoring of disease progress and of treatment response. This concept will hopefully provide better preconditions for prevention, cure or therapeutic beneficial disease modification. These unmet therapeutic needs may be achieved for example via antagonism of repulsive guidance molecule A.

Phosphorylation of endogenous α-synuclein induced by extracellular seeds initiates at the pre-synaptic region and spreads to the cell body

Accumulation of phosphorylated α-synuclein aggregates has been implicated in several diseases, such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and is thought to spread in a prion-like manner. Elucidating the mechanisms of prion-like transmission of α-synuclein is important for the development of therapies for these diseases, but little is known about the details. Here, we injected α-synuclein fibrils into the brains of wild-type mice and examined the early phase of the induction of phosphorylated α-synuclein accumulation. We found that phosphorylated α-synuclein appeared within a few days after the intracerebral injection. It was observed initially in presynaptic regions and subsequently extended its localization to axons and cell bodies.　These results suggest that extracellular α-synuclein fibrils are taken up into the presynaptic region and seed-dependently convert the endogenous normal α-synuclein that is abundant there to an abnormal phosphorylated form, which is then transported through the axon to the cell body.

Adaptive structural changes in the motor cortex and white matter in Parkinson's disease

Parkinson's disease (PD) is a movement disorder characterized by the early loss of nigrostriatal dopaminergic pathways producing significant network changes impacting motor coordination. Recently three motor stages of PD have been proposed (a silent period when nigrostriatal loss begins, a prodromal motor period with subtle focal manifestations, and clinical PD) with evidence that motor cortex abnormalities occur to produce clinical PD[8]. We directly assess structural changes in the primary motor cortex and corticospinal tract using parallel analyses of longitudinal clinical and cross-sectional pathological cohorts thought to represent different stages of PD. 18F-FP-CIT positron emission tomography and subtle motor features identified patients with idiopathic rapid-eye-movement sleep behaviour disorder (n = 8) that developed prodromal motor signs of PD. Longitudinal diffusion tensor imaging before and after the development of prodromal motor PD showed higher fractional anisotropy in motor cortex and corticospinal tract compared to controls, indicating adaptive structural changes in motor networks in concert with nigrostriatal dopamine loss. Histological analyses of the white matter underlying the motor cortex showed progressive disorientation of axons with segmental replacement of neurofilaments with α-synuclein, enlargement of myelinating oligodendrocytes and increased density of their precursors. There was no loss of neurons in the motor cortex in early or late pathologically confirmed motor PD compared to controls, although there were early cortical increases in neuronal neurofilament light chain and myelin proteins in association with α-synuclein accumulation. Our results collectively provide evidence of a direct impact of PD on primary motor cortex and its output pathways that begins in the prodromal motor stage of PD with structural changes confirmed in early PD. These adaptive structural changes become considerable as the disease advances potentially contributing to motor PD.

The enigma and implications of brain hemispheric asymmetry in neurodegenerative diseases

The lateralization of the human brain may provide clues into the pathogenesis and progression of neurodegenerative diseases. Though differing in their presentation and underlying pathologies, neurodegenerative diseases are all devastating and share an intriguing theme of asymmetrical pathology and clinical symptoms. Parkinson’s disease, with its distinctive onset of motor symptoms on one side of the body, stands out in this regard, but a review of the literature reveals asymmetries in several other neurodegenerative diseases. Here, we review the lateralization of the structure and function of the healthy human brain and the common genetic and epigenetic patterns contributing to the development of asymmetry in health and disease. We specifically examine the role of asymmetry in Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, and multiple sclerosis, and interrogate whether these imbalances may reveal meaningful clues about the origins of these diseases. We also propose several hypotheses for how lateralization may contribute to the distinctive and enigmatic features of asymmetry in neurodegenerative diseases, suggesting a role for asymmetry in the choroid plexus, neurochemistry, protein distribution, brain connectivity and the vagus nerve. Finally, we suggest how future studies may reveal novel insights into these diseases through the lens of asymmetry.

An autopsy case of corticobasal syndrome with pure diffuse Lewy Body Disease

Corticobasal syndrome (CBS) is associated with diverse pathological substrates such as tau, prion protein, transactive response and, rarely, alpha synuclein. We report the case of a54-year-old man, who presented with asymmetric levodopa-poor-responsive parkinsonism, frontal lobe signs and behavioral changes. He was diagnosed with CBS, and postmortem analyses revealed Lewy body disease Braak stage VI without comorbid pathologies. Retrospectively, the clinical course of our patient and previous reports indicate that CBS plus mood changes and autonomic dysfunction, including reduced uptake of metaiodobenzylguanidine, are predictive factors of Lewy body pathology, even if the clinical picture is atypical.

Progressive supranuclear palsy: Neuropathology of patients with a short disease duration due to unexpected death

Progressive supranuclear palsy (PSP) presents with a wide variety of signs/symptoms, making early initial diagnosis difficult. We investigated the clinical and neuropathological features of five patients with autopsy-proven PSP of short duration, ranging from 11 to 41 months (average, 26.2 months) due to unexpected death, focusing particularly on the distribution and severity of neuronal loss as well as neuronal and glial tau pathology in the affected brain. Clinical features were studied retrospectively through careful review of the medical records, and neuropathological examinations were carried out, along with tau immunohistochemistry using a monoclonal antibody AT8. These patients were diagnosed as having probable PSP (n = 4) and suggestive PSP (n = 1), respectively. In all cases, neuronal loss was evident in the substantia nigra, subthalamic nucleus, globus pallidus, and locus ceruleus. AT8-identified tau lesions, that is, pretangles/neurofibrillary tangles (PTs/NFTs), tufted astrocytes (TAs), and coiled bodies/neuropil threads (CBs/NTs), were distributed widely in the brain regions, especially in patients with longer disease duration. All cases showed variation in the regional tau burden among PTs/NFTs, TAs, and CBs/NTs. There was also a tendency for tau deposition to be more predominant in neuronal cells in the brainstem and cerebellum and in glial cells in the cerebral cortex and subcortical gray matter. These findings suggest that in PSP, the initial signs/symptoms are associated with degeneration and subsequent death of neurons with pathological tau deposition, and that the tau deposition in neuronal cells is independent of that in glial cells.

Environmental exposure to phthalates and dementia with Lewy bodies: contribution of metabolomics

BACKGROUND

In neurodegenerative diseases, alongside genetic factors, the possible intervention of environmental factors in the pathogenesis is increasingly being considered. In particular, recent evidence suggests the intervention of a pesticide-like xenobiotic in the initiation of disease with Lewy bodies (DLB).

OBJECTIVES

To test for the presence of pesticides or other xenobiotics in the cerebrospinal fluid (CSF) of patients with DLB.

METHODS

A total of 45 patients were included in this study: 16 patients with DLB at the prodromal stage, 8 patients with DLB at the demented stage, 8 patients with Alzheimer's disease (AD) at the prodromal stage and 13 patients with AD at the demented stage. CSF was obtained by lumbar puncture and analysed by liquid chromatography-mass spectrometry.

RESULTS

Among the compounds detected in greater abundance in the CSF of patients with DLB compared with patients with AD, only one had a xenobiotic profile potentially related to the pathophysiology of DLB. After normalisation and scaling, bis(2-ethylhexyl) phthalate was more abundant in the CSF of patients with DLB (whole cohort: 2.7-fold abundant in DLB, p=0.031; patients with dementia: 3.8-fold abundant in DLB, p=0.001).

CONCLUSIONS

This study is the first reported presence of a phthalate in the CSF of patients with DLB. This molecule, which is widely distributed in the environment and enters the body orally, nasally and transdermally, was first introduced in the 1920s as a plasticizer. Thereafter, the first cases of DLB were described in the 1960s and 1970s. These observations suggest that phthalates may be involved in the pathophysiology of DLB.

Trans-synaptic and retrograde axonal spread of Lewy pathology following pre-formed fibril injection in an in vivo A53T alpha-synuclein mouse model of synucleinopathy

It is necessary to develop an understanding of the specific mechanisms involved in alpha-synuclein aggregation and propagation to develop disease modifying therapies for age-related synucleinopathies, including Parkinson's disease and Dementia with Lewy Bodies. To adequately address this question, we developed a new transgenic mouse model of synucleinopathy that expresses human A53T SynGFP under control of the mouse prion protein promoter. Our characterization of this mouse line demonstrates that it exhibits several distinct advantages over other, currently available, mouse models. This new model allows rigorous study of the initial location of Lewy pathology formation and propagation in the living brain, and strongly suggests that aggregation begins in axonal structures with retrograde propagation to the cell body. This model also shows expeditious development of alpha-synuclein pathology following induction with small, in vitro-generated alpha-synuclein pre-formed fibrils (PFFs), as well as accelerated cell death of inclusion-bearing cells. Using this model, we found that aggregated alpha-synuclein somatic inclusions developed first in neurons, but later showed a second wave of inclusion formation in astrocytes. Interestingly, astrocytes appear to survive much longer after inclusion formation than their neuronal counterparts. This model also allowed careful study of peripheral-to-central spread of Lewy pathology after PFF injection into the hind limb musculature. Our results clearly show evidence of progressive, retrograde trans-synaptic spread of Lewy pathology through known neuroanatomically connected pathways in the motor system. As such, we have developed a promising tool to understand the biology of neurodegeneration associated with alpha-synuclein aggregation and to discover new treatments capable of altering the neurodegenerative disease course of synucleinopathies.

Where and how alpha-synuclein pathology spreads in Parkinson's disease

In Parkinson's disease (PD), neuronal alpha-synuclein aggregates are distributed throughout the nervous system, including the brain, spinal cord, sympathetic ganglia, submandibular gland, enteric nervous system, cardiac and pelvic plexuses, adrenal medulla, and skin. Thus, PD is a progressive multiorgan disease clinically associated with various motor and nonmotor symptoms. The earliest PD-related lesions appear to develop in the olfactory bulb, dorsal vagal nucleus, and possibly also the peripheral autonomic nervous system. The brain is closely connected with the enteric nervous system via axons of the efferent fibers of the dorsal nucleus of vagal nerve. Anatomical connections also exist between the olfactory bulb and brainstem. Accumulating evidence from experimental studies indicates that transneuronal propagation of misfolded alpha-synuclein is involved in the progression of PD. However, it cannot be ruled out that alpha-synuclein pathology in PD is multicentric in origin. Based on pathological findings from studies on human materials, the present review will update the progression pattern of alpha-synuclein pathology in PD.

The Evolution-Driven Signature of Parkinson's Disease

In this review, we approach Parkinson's disease (PD) in the context of an evolutionary mismatch of central nervous system functions. The neurons at risk have hyperbranched axons, extensive transmitter release sites, display spontaneous spiking, and elevated mitochondrial stress. They function in networks largely unchanged throughout vertebrate evolution, but now connecting to the expanded human cortex. Their breakdown is favoured by longevity. At the cellular level, mitochondrial dysfunction starts at the synapses, then involves axons and cell bodies. At the behavioural level, network dysfunctions provoke the core motor syndrome of parkinsonism including freezing and failed gait automatization, and non-motor deficits including inactive blindsight and autonomic dysregulation. The proposed evolutionary re-interpretation of PD-prone cellular phenotypes and of prototypical clinical symptoms allows a new conceptual framework for future research.

Anxiety symptoms are quantitatively and qualitatively different in dementia with Lewy bodies than in Alzheimer's disease in the years preceding clinical diagnosis

AIM

Dementia with Lewy bodies (DLB) is a common but underdiagnosed type of cognitive impairment and dementia. The current diagnostic criteria for research purposes have a high specificity but lack sensitivity. Moreover, patients who live alone are not always aware that they have core clinical features such as cognitive fluctuations, visual hallucinations, and parasomnia. Anxiety is a common and early manifestation in DLB.

METHODS

We matched 41 DLB patients with 41 patients with Alzheimer's disease (AD) according to gender, age, and cognitive status and retrospectively analyzed their files for the presence of anxiety, depression, constipation, and the core clinical features of DLB in the documented period before diagnosis.

RESULTS

Anxiety, but not depression, occurred significantly more frequently in DLB than in AD (63.4% vs 26.8%). It appears up to 4-5 years before the diagnosis of DLB and is associated with depression and living at home. Anxiety in DLB was often described as intermittent panic attacks without reason or during states of delirium; it was also severe enough to require medical treatment and inpatient or outpatient psychiatric care. It was often mistaken for a psychiatric illness or a manifestation of other common forms of dementia. Anxiety in AD seemed much milder, was often related to the patient's coping with cognitive dysfunction, and was never cited as a specific reason for medical help. The concomitant presence of anxiety with at least one core clinical criterion of DLB enabled us to differentiate it from AD in our study, with a sensitivity of 63.4% but a specificity of 100%.

CONCLUSIONS

In all patients over 50 who present with cognitive problems and anxiety, DLB should be considered. Patients and informants should be carefully questioned regarding the presence of other typical signs and symptoms of DLB.

Nuclear Factor-κB Dysregulation and α-Synuclein Pathology: Critical Interplay in the Pathogenesis of Parkinson's Disease

The loss of dopaminergic neurons of the nigrostriatal system underlies the onset of the typical motor symptoms of Parkinson's disease (PD). Lewy bodies (LB) and Lewy neurites (LN), proteinaceous inclusions mainly composed of insoluble α-synuclein (α-syn) fibrils are key neuropathological hallmarks of the brain of affected patients. Compelling evidence supports that in the early prodromal phases of PD, synaptic terminal and axonal alterations initiate and drive a retrograde degeneration process culminating with the loss of nigral dopaminergic neurons. This notwithstanding, the molecular triggers remain to be fully elucidated. Although it has been shown that α-syn fibrillary aggregation can induce early synaptic and axonal impairment and cause nigrostriatal degeneration, we still ignore how and why α-syn fibrillation begins. Nuclear factor-κB (NF-κB) transcription factors, key regulators of inflammation and apoptosis, are involved in the brain programming of systemic aging as well as in the pathogenesis of several neurodegenerative diseases. The NF-κB family of factors consists of five different subunits (c-Rel, p65/RelA, p50, RelB, and p52), which combine to form transcriptionally active dimers. Different findings point out a role of RelA in PD. Interestingly, the nuclear content of RelA is abnormally increased in nigral dopamine (DA) neurons and glial cells of PD patients. Inhibition of RelA exert neuroprotection against (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) MPTP and 1-methyl-4-phenylpyridinium (MPP+) toxicity, suggesting that this factor decreases neuronal resilience. Conversely, the c-Rel subunit can exert neuroprotective actions. We recently described that mice deficient for c-Rel develop a PD-like motor and non-motor phenotype characterized by progressive brain α-syn accumulation and early synaptic changes preceding the frank loss of nigrostriatal neurons. This evidence supports that dysregulations in this transcription factors may be involved in the onset of PD. This review highlights observations supporting a possible interplay between NF-κB dysregulation and α-syn pathology in PD, with the aim to disclose novel potential mechanisms involved in the pathogenesis of this disorder.

The expression level of alpha-synuclein in different neuronal populations is the primary determinant of its prion-like seeding

Alpha-synuclein (aSyn)-rich aggregates propagate in neuronal networks and compromise cellular homeostasis leading to synucleinopathies such as Parkinson's disease. Aggregated aSyn spread follows a conserved spatio-temporal pattern that is not solely dependent on connectivity. Hence, the differential tropism of aSyn-rich aggregates to distinct brain regions, or their ability to amplify within those regions, must contribute to this process. To better understand what underlies aSyn-rich aggregates distribution within the brain, we generated primary neuronal cultures from various brain regions of wild-type mice and mice expressing a reduced level of aSyn, and exposed them to fibrillar aSyn. We then assessed exogenous fibrillar aSyn uptake, endogenous aSyn seeding, and endogenous aSyn physiological expression levels. Despite a similar uptake of exogenous fibrils by neuronal cells from distinct brain regions, the seeded aggregation of endogenous aSyn differed greatly from one neuronal population to another. The different susceptibility of neuronal populations was linked to their aSyn expression level. Our data establish that endogenous aSyn expression level plays a key role in fibrillar aSyn prion-like seeding, supporting that endogenous aSyn expression level participates in selective regional brain vulnerability.

Neuropathology of Lewy body disease: Clinicopathological crosstalk between typical and atypical cases

Lewy body disease (LBD) is characterized by the presence of Lewy bodies (LBs) and Lewy neurites and comprises a diagnostic spectrum that includes Parkinson's disease (PD), PD with dementia, and dementia with LBs. LBs and Lewy neurites are insoluble aggregates composed mainly of phosphorylated α-synuclein and can be widely distributed throughout the central and peripheral nervous systems. The distribution of LBs may determine the LBD phenotype. Braak hypothesized that Lewy pathology progresses ascendingly from the peripheral nervous system to the olfactory bulbs and brainstem and then to other brain regions. Braak's PD staging suggests that LBD is a prion-like disease. Most typical PD cases fit with Braak's PD staging, but the scheme fails in some cases. Alzheimer's disease, progressive supranuclear palsy, corticobasal syndrome, multiple system atrophy, frontotemporal lobar degeneration, Creutzfeldt-Jakob disease, cerebrovascular diseases, and essential tremor are common misdiagnoses for pathologically confirmed LBD. LBD exhibits considerable heterogeneity in both clinical and pathological settings, which makes clinical diagnosis challenging.

The Impact of Photorefractive Keratectomy and Mitomycin C on Corneal Nerves and Their Regeneration

PURPOSE

To determine how photorefractive keratectomy (PRK) and mitomycin C (MMC) affect corneal nerves and their regeneration over time after surgery.

METHODS

Twenty-eight New Zealand rabbits had corneal epithelial scraping with (n = 3) and without (n = 3) MMC 0.02% or -9.00 diopter PRK with (n = 6) and without (n = 16) MMC 0.02%. Corneas were removed after death and corneal nerve morphology was evaluated using acetylcholinesterase immunohistochemistry and beta-III tubulin staining after 1 day for all groups, after 1 month for PRK with and without MMC, and 2, 3, and 6 months after PRK without MMC. Image-Pro software (Media Cybernetics, Rockville, MD) was used to quantitate the area of nerve loss after the procedures and, consequently, regeneration of the nerves over time. Opposite eyes were used as controls.

RESULTS

Epithelial scraping with MMC treatment did not show a statistically significant difference in nerve loss compared to epithelial scraping without MMC (P = .40). PRK with MMC was significantly different from PRK without MMC at 1 day after surgery (P = .0009) but not different at 1 month after surgery (P = .90). In the PRK without MMC group, nerves regenerated at 2 months (P < .0001) but did not return to the normal preoperative level of innervation until 3 months after surgery (P = .05). However, the morphology of the regenerating nerves was abnormal-with more tortuosity and aberrant innervation compared to the preoperative controls-even at 6 months after surgery.

CONCLUSIONS

PRK negatively impacts the corneal nerves, but they are partially regenerated by 3 months after surgery in rabbits. Nerve loss after PRK extended peripherally to the excimer laser ablated zone, indicating that there was retrograde degeneration of nerves after PRK. MMC had a small additive toxic effect on the corneal nerves when combined with PRK that was only significant prior to 1 month after surgery. [J Refract Surg. 2018;34(12):790-798.].

Behavioral symptomatology and psychopharmacology of Lewy body dementia

Lewy body dementia (LBD) is an umbrella term for major neurocognitive disorders caused by Lewy body pathology. Parkinson's disease dementia (PDD) and Dementia with Lewy bodies (DLB) are the two main syndromes in LBD. LBDs typically present with cognitive impairment, cholinergic deficiency, neuropsychiatric symptoms such as visual hallucinations and paranoid delusions, as well as parkinsonian symptoms. Due to the urgency in diagnosing LBD early in the disease course to provide the most optimal management of these syndromes, it is important that clinicians elicit the most clinically significant symptoms during patient encounters. The focus of this chapter is to discuss current LBD classification systems and assessments, neuropathology of LBDs, behavioral symptomatology, contemporary management options, and possible future targets of treatment. PubMed was searched to obtain reviews and studies that pertain to classification, behavioral symptomatology, neurobiology, neuroimaging, and treatment of LBDs. Articles were chosen with a predilection to more recent clinical trials and systematic reviews or meta-analyses. Updates to diagnostic criteria have increased clinical diagnostic sensitivity and specificity. Current therapeutic modalities are limited as there is no current disease-modifying drug available. Cholinesterase inhibitors have been reported to be effective in decreasing neuropsychiatric and cognitive symptoms. Neuroleptics should be avoided unless clinically indicated. There is a paucity of studies investigating treatment options for mood symptoms. Current novel targets of treatment focus on decreasing α-synuclein burden. LBDs are a group of dementia syndromes that affect a significant portion of the elderly population. Early diagnosis and treatment is necessary to improve patient quality of life with current treatment options more focused on alleviating severe symptomatology rather than modifying disease pathology.

Enteric Neurodegeneration is Mediated Through Independent Neuritic and Somal Mechanisms in Rotenone and MPP+ Toxicity

Gut motility malfunction and pathological changes in the enteric nervous system (ENS) are observed in the early stages of Parkinson's disease (PD). In many cases disturbances in the autonomous functions such as gut motility precedes the observed loss of central motor functions in PD. However, the mechanism by which ENS degeneration occurs in PD is unknown. We show that parkinsonian mimetics rotenone and MPP+ induce neurite degeneration that precedes cell death in primary enteric neurons cultured in vitro. If the neuronal death signals originate from degenerating neurites, neuronal death should be prevented by inhibiting neurite degeneration. Our data demonstrate that overexpression of cytNmnat1, an axon protector, maintains healthy neurites in enteric neurons treated with either of the parkinsonian mimetics, but cannot protect the soma. We also demonstrate that neurite protection via cytNmnat1 is independent of mitochondrial dynamics or ATP levels. Overexpression of Bcl-xl, an anti-apoptotic factor, protects both the neuronal cell body and the neurites in both rotenone and MPP+ treated enteric neurons. Our data reveals that Bcl-xl and cytNmnat1 act through separate mechanisms to protect enteric neurites. Our findings suggest that neurite protection alone is not sufficient to inhibit enteric neuronal degeneration in rotenone or MPP+ toxicity, and enteric neurodegeneration in PD may be occurring through independent somatic and neuritic mechanisms. Thus, therapies targeting both axonal and somal protection can be important in finding interventions for enteric symptoms in PD.

Dynactin is involved in Lewy body pathology

Dynactin forms a protein complex with dynein that retrogradely transports cargo along microtubules. Dysfunction of this dynein-dynactin complex causes several neurodegenerative diseases such as Perry syndrome, motor neuron diseases and progressive supranuclear palsy. Recently, we reported colocalization of phosphorylated α-synuclein (p-SNCA) and the largest subunit of dynactin (DCTN1) in Lewy body (LB)-like structures in Perry syndrome. Previous reports have not focused on the relationship between dynactin and synucleinopathies. Thus, we examined autopsied human brains from patients with Parkinson's disease, dementia with LBs, and multiple system atrophy using immunohistochemistry for p-SNCA, DCTN1, dynactin 2 (DCTN2, dynamitin) and dynein cytoplasmic 1 intermediate chain 1 (DYNC1I1). We also examined microtubule affinity-regulating kinases (MARKs), which phosphorylate microtubule-associated proteins and trigger microtubule disruption. Both brainstem-type and cortical LBs were immunopositive for DCTN1, DCTN2, DYNC1I1 and p-MARK and their staining often overlapped with p-SNCA. Lewy neurites were also immunopositive for DCTN1, DCTN2 and DYNC1I1. However, p-SNCA-positive inclusions of multiple system atrophy, which included both glial and neuronal cytoplasmic inclusions, were immunonegative for DCTN1, DCTN2, DYNC1I1 and p-MARK. Thus, immunohistochemistry for dynein-dynactin complex molecules, especially DCTN1, can clearly distinguish LBs from neuronal cytoplasmic inclusions. Our results suggest that dynactin is closely associated with LB pathology.

Is Braak staging valid for all types of Parkinson's disease?

Braak et al. proposed that cases with Lewy pathology in the peripheral nervous sytem, spinal cord and brain stem are prodromal Parkinson's disease (PD), suggesting a hypothesized progression of PD pathology. However, the putative potential of peripheral α-synuclein to promote brain pathology has been questioned recently. The Braak staging is a matter of vigorous debate, since < 100% of cases with Lewy pathology fitting the proposed PD staging scheme; however, most studies assessing typical PD cases show that the vast majority (80-100%) fit the Braak staging scheme. Incidental Lewy body disease and PD can show Lewy pathology in substantia nigra or other brain areas without involvement of dorsal motor nucleus of the vagus nerve. The Braak staging system is valid for PD patients with young onset, long duration with motor symptoms, but not for others, e.g., late onset and rapid course PD. The validity of Braak staging and its relationship to various subtypes of PD warrants further studies.

Are dementia with Lewy bodies and Parkinson's disease dementia the same disease?

BACKGROUND

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), which share many clinical, neurochemical, and morphological features, have been incorporated into DSM-5 as two separate entities of major neurocognitive disorders with Lewy bodies. Despite clinical overlap, their diagnosis is based on an arbitrary distinction concerning the time of onset of motor and cognitive symptoms, namely as early cognitive impairment in DLB and later onset following that of motor symptoms in PDD. Their morphological hallmarks - cortical and subcortical α-synuclein/Lewy body plus β-amyloid and tau pathologies - are similar, but clinical differences at onset suggest some dissimilar profiles. Based on recent publications, including the fourth consensus report of the DLB Consortium, a critical overview is provided herein.

DISCUSSION

The clinical constellations of DLB and PDD include cognitive impairment, parkinsonism, visual hallucinations, and fluctuating attention. Intravitam PET and postmortem studies have revealed a more pronounced cortical atrophy, elevated cortical and limbic Lewy body pathologies, higher Aβ and tau loads in cortex and striatum in DLB compared to PDD, and earlier cognitive defects in DLB. Conversely, multitracer PET studies have shown no differences in cortical and striatal cholinergic and dopaminergic deficits. Clinical management of both DLB and PDD includes cholinesterase inhibitors and other pharmacologic and non-drug strategies, yet with only mild symptomatic effects. Currently, no disease-modifying therapies are available.

CONCLUSION

DLB and PDD are important dementia syndromes that overlap in many clinical features, genetics, neuropathology, and management. They are currently considered as subtypes of an α-synuclein-associated disease spectrum (Lewy body diseases), from incidental Lewy body disease and non-demented Parkinson's disease to PDD, DLB, and DLB with Alzheimer's disease at the most severe end. Cognitive impairment in these disorders is induced not only by α-synuclein-related neurodegeneration but by multiple regional pathological scores. Both DLB and PDD show heterogeneous pathology and neurochemistry, suggesting that they share important common underlying molecular pathogenesis with Alzheimer's disease and other proteinopathies. While we prefer to view DLB and PDD as extremes on a continuum, there remains a pressing need to more clearly differentiate these syndromes and to understand the synucleinopathy processes leading to either one.

Dementia with Lewy bodies and Parkinson's disease-dementia: current concepts and controversies

Dementia with Lewy bodies (DLB) and Parkinson's disease-dementia (PDD), although sharing many clinical, neurochemical and morphological features, according to DSM-5, are two entities of major neurocognitive disorders with Lewy bodies of unknown etiology. Despite considerable clinical overlap, their diagnosis is based on an arbitrary distinction between the time of onset of motor and cognitive symptoms: dementia often preceding parkinsonism in DLB and onset of cognitive impairment after onset of motor symptoms in PDD. Both are characterized morphologically by widespread cortical and subcortical α-synuclein/Lewy body plus β-amyloid and tau pathologies. Based on recent publications, including the fourth consensus report of the DLB Consortium, a critical overview is given. The clinical features of DLB and PDD include cognitive impairment, parkinsonism, visual hallucinations, and fluctuating attention. Intravitam PET and post-mortem studies revealed more pronounced cortical atrophy, elevated cortical and limbic Lewy pathologies (with APOE ε4), apart from higher prevalence of Alzheimer pathology in DLB than PDD. These changes may account for earlier onset and greater severity of cognitive defects in DLB, while multitracer PET studies showed no differences in cholinergic and dopaminergic deficits. DLB and PDD sharing genetic, neurochemical, and morphologic factors are likely to represent two subtypes of an α-synuclein-associated disease spectrum (Lewy body diseases), beginning with incidental Lewy body disease-PD-nondemented-PDD-DLB (no parkinsonism)-DLB with Alzheimer's disease (DLB-AD) at the most severe end, although DLB does not begin with PD/PDD and does not always progress to DLB-AD, while others consider them as the same disease. Both DLB and PDD show heterogeneous pathology and neurochemistry, suggesting that they share important common underlying molecular pathogenesis with AD and other proteinopathies. Cognitive impairment is not only induced by α-synuclein-caused neurodegeneration but by multiple regional pathological scores. Recent animal models and human post-mortem studies have provided important insights into the pathophysiology of DLB/PDD showing some differences, e.g., different spreading patterns of α-synuclein pathology, but the basic pathogenic mechanisms leading to the heterogeneity between both disorders deserve further elucidation. In view of the controversies about the nosology and pathogenesis of both syndromes, there remains a pressing need to differentiate them more clearly and to understand the processes leading these synucleinopathies to cause one disorder or the other. Clinical management of both disorders includes cholinesterase inhibitors, other pharmacologic and nonpharmacologic strategies, but these have only a mild symptomatic effect. Currently, no disease-modifying therapies are available.

Altered neurofilament protein expression in the lateral vestibular nucleus in Parkinson's disease

A major cause of morbidity in Parkinson's disease (PD) is postural instability. The neuropathology underlying postural instability is unknown. Postural control is mediated by Deiters' neurons of the lateral vestibular nucleus (LVN), which are the brainstem origin of descending vestibulospinal reflexes. Deiters' neurons express the cytostructural protein, non-phosphorylated neurofilament protein (NPNFP). In PD, reduced expression of NPNFP in substantia nigra (SN) neurons is believed to contribute to dysfunction. It was the aim of this study to determine if there is altered expression of NPNFP in the LVN in PD. We immunolabeled NPNFP in brainstem sections of six aged controls (mean age 92 yo) and six PD donors (mean age 83 yo). Our results show there was a ~ 50% reduction in NPNFP-positive Deiters' neurons compared to controls (13 ± 2.0/section vs 25.7 ± 3.0/section; p < 0.01, repeated measures ANOVA). In contrast, there was no difference in NPNFP-positive counts in the facial nucleus between control and PD. The normalized intensity of NPNFP labeling in LVN was also reduced in PD (0.87 ± 0.05 vs 1.09 ± 0.03; p < 0.01). There was a 35% concurrent reduction in NPNFP-positive neuropil in PD relative to controls (p < 0.01). We also show there was an 84% increase (p < 0.05) in somatic lipofuscin in PD patients compared to control. Lipofuscin aggregation has been shown to increase not only with age but also with neurodegeneration. Furthermore, decreased NPNFP intensity was strongly correlated with increasing lipofuscin autofluorescence across all cases (R ² = 0.81, p < 0.01). These results show two alterations in cellular content with PD, reduced expression and intensity of NPNFP and increased lipofuscin aggregation in Deiter's neurons. These changes may contribute to degeneration of postural reflexes observed in PD.