Clinical and Imaging Presentation of a Patient with Beta-Propeller Protein-Associated Neurodegeneration, a Rare and Sporadic form of Neurodegeneration with Brain Iron Accumulation (NBIA)

Pathological characteristics of axons and alterations of proteomic and lipidomic profiles in midbrain dopaminergic neurodegeneration induced by WDR45-deficiency

BACKGROUND

Although WD repeat domain 45 (WDR45) mutations have been linked to β -propeller protein-associated neurodegeneration (BPAN), the precise molecular and cellular mechanisms behind this disease remain elusive. This study aims to shed light on the impacts of WDR45-deficiency on neurodegeneration, specifically axonal degeneration, within the midbrain dopaminergic (DAergic) system. We hope to better understand the disease process by examining pathological and molecular alterations, especially within the DAergic system.

METHODS

To investigate the impacts of WDR45 dysfunction on mouse behaviors and DAergic neurons, we developed a mouse model in which WDR45 was conditionally knocked out in the midbrain DAergic neurons (WDR45cKO). Through a longitudinal study, we assessed alterations in the mouse behaviors using open field, rotarod, Y-maze, and 3-chamber social approach tests. We utilized a combination of immunofluorescence staining and transmission electron microscopy to examine the pathological changes in DAergic neuron soma and axons. Additionally, we performed proteomic and lipidomic analyses of the striatum from young and aged mice to identify the molecules and processes potentially involved in the striatal pathology during aging. Further more, primary midbrain neuronal culture was employed to explore the molecular mechanisms leading to axonal degeneration.

RESULTS

Our study of WDR45cKO mice revealed a range of deficits, including impaired motor function, emotional instability, and memory loss, coinciding with the profound reduction of midbrain DAergic neurons. The neuronal loss, we observed massive axonal enlargements in the dorsal and ventral striatum. These enlargements were characterized by the accumulation of extensively fragmented tubular endoplasmic reticulum (ER), a hallmark of axonal degeneration. Proteomic analysis of the striatum showed that the differentially expressed proteins were enriched in metabolic processes. The carbohydrate metabolic and protein catabolic processes appeared earlier, and amino acid, lipid, and tricarboxylic acid metabolisms were increased during aging. Of note, we observed a tremendous increase in the expression of lysophosphatidylcholine acyltransferase 1 (Lpcat1) that regulates phospholipid metabolism, specifically in the conversion of lysophosphatidylcholine (LPC) to phosphatidylcholine (PC) in the presence of acyl-CoA. The lipidomic results consistently suggested that differential lipids were concentrated on PC and LPC. Axonal degeneration was effectively ameliorated by interfering Lpcat1 expression in primary cultured WDR45-deficient DAergic neurons, proving that Lpcat1 and its regulated lipid metabolism, especially PC and LPC metabolism, participate in controlling the axonal degeneration induced by WDR45 deficits.

CONCLUSIONS

In this study, we uncovered the molecular mechanisms underlying the contribution of WDR45 deficiency to axonal degeneration, which involves complex relationships between phospholipid metabolism, autophagy, and tubular ER. These findings greatly advance our understanding of the fundamental molecular mechanisms driving axonal degeneration and may provide a foundation for developing novel mechanistically based therapeutic interventions for BPAN and other neurodegenerative diseases.

Pathological characteristics of axons and proteome patterns in midbrain dopaminergic neurodegeneration induced by WDR45-deficiency

Background

Although WD repeats domain 45 (WDR45) mutations have been linked to β-propeller protein-associated neurodegeneration (BPAN), the precise molecular and cellular mechanisms behind this disease remain elusive. This study aims to shed light on the effects of WDR45-deficiency on neurodegeneration, specifically axonal degeneration, within the midbrain dopaminergic (DAergic) system. By examining pathological and molecular alterations, we hope to better understand the disease process.

Methods

To investigate the effects of WDR45 dysfunction on mouse behaviors and DAergic neurons, we developed a mouse model in which WDR45 was conditionally knocked out in midbrain DAergic neurons (WDR45cKO). Through a longitudinal study, we assessed alterations in mouse behavior using open field, rotarod, Y-maze, and 3-chamber social approach tests. To examine the pathological changes in DAergic neuron soma and axons, we utilized a combination of immunofluorescence staining and transmission electron microscopy. Additionally, we performed proteomic analyses of the striatum to identify the molecules and processes involved in striatal pathology.

Results

Our study of WDR45cKO mice revealed a range of deficits, including impaired motor function, emotional instability, and memory loss, coinciding with the profound loss of midbrain DAergic neurons. Prior to neuronal loss, we observed massive axonal enlargements in both the dorsal and ventral striatum. These enlargements were characterized by the accumulation of extensively fragmented tubular endoplasmic reticulum (ER), a hallmark of axonal degeneration. Additionally, we found that WDR45cKO mice exhibited disrupted autophagic flux. Proteomic analysis of the striatum in these mice showed that many differentially expressed proteins (DEPs) were enriched in amino acid, lipid, and tricarboxylic acid metabolisms. Of note, we observed significant alterations in the expression of genes encoding DEPs that regulate phospholipids catabolic and biosynthetic processes, such as lysophosphatidylcholine acyltransferase 1, ethanolamine-phosphate phospho-lyase, and abhydrolase domain containing 4, N-acyl phospholipase B. These findings suggest a possible link between phospholipid metabolism and striatal axon degeneration.

Conclusions

In this study, we have uncovered the molecular mechanisms underlying the contribution of WDR45-deficiency to axonal degeneration, revealing intricate relationships between tubular ER dysfunction, phospholipid metabolism, BPAN and other neurodegenerative diseases. These findings significantly advance our understanding of the fundamental molecular mechanisms driving neurodegeneration and may provide a foundation for developing novel, mechanistically-based therapeutic interventions.

Seizure in Neurodegeneration with Brain Iron Accumulation: A Systematic Review

BACKGROUND

Neurodegeneration with brain iron accumulation (NBIA) is a rare genetic disorder. Its clinical manifestations comprise a wide spectrum mainly movement disorders. Seizure as a clinical manifestation is known to occur in some NBIAs, but the exact prevalence of epilepsy in each individual disorder is not well elucidated. The aim of this review was to investigate the frequency of seizures in NBIA disorders as well as to determine the associated features of patients with seizures.

METHOD

The electronic bibliographic databases PubMed, Scopus, Embase, and Google Scholar were systematically searched for all cases in any type of article from inception to December 16, 2019. All the reported cases of NBIA (with or without genetic confirmation) were identified. Case reports with an explicit diagnosis of any types of NBIA, which have reported occurrence (or absence) of any type of seizure or epilepsy, in the English language, were included. Seizure incidence rate, type, and age of onset were reported as frequencies and percentages.

RESULT

1698 articles were identified and 51 were included in this review. Of 305 reported cases, 150 (49.2%) had seizures (phospholipase A2-associated neurodegeneration (PLAN) = 64 (50.8%), beta-propeller protein-associated neurodegeneration (BPAN) = 57 (72.1%), pantothenate kinase-associated neurodegeneration (PKAN) = 11 (23.4%), and others = 18 (very variable proportions)). The most frequent seizure type in NBIA patients was generalized tonic-clonic seizure with the mean age of seizure onset between 2 and 36 years. However, most of these papers had been published before the new classification of epilepsy became accessible. Affected patients were more likely to be females.

CONCLUSION

Seizures are common in NBIA, particularly in PLAN and BPAN. In PKAN, the most common type of NBIA, around 10% of patients are affected by seizures. BPAN is the most possible NBIA accompanying seizure. Most of the findings regarding the seizure characteristics in the NBIAs are biased due to the huge missing data. Therefore, any conclusions should be made with caution and need further investigations.

Neuroimaging Pearls from the MDS Congress Video Challenge. Part 1: Genetic Disorders

We selected several "imaging pearls" presented during the Movement Disorder Society (MDS) Video Challenge for this review. While the event, as implicated by its name, was video-centered, we would like to emphasize the important role of imaging in making the correct diagnosis. We divided this anthology into two parts: genetic and acquired disorders. Genetic cases described herein were organized by the inheritance pattern and the focus was put on the imaging findings and differential diagnoses. Despite the overlapping phenotypes, certain described disorders have pathognomonic MRI brain findings that would provide either the "spot" diagnosis or result in further investigations leading to the diagnosis. Despite this, the diagnosis is often challenging with a broad differential diagnosis, and hallmark findings may be present for only a limited time.

Neurodegeneration with brain iron accumulation: Characterization of clinical, radiological, and genetic features of pediatric patients from Southern India

BACKGROUND

Neurodegeneration with brain iron accumulation (NBIA) is a group of rare inherited neurodegenerative disorders. Ten types of NBIA are known. Studies reporting various NBIA subtypes together are few. This study was aimed at describing clinical features, neuroimaging findings, and genetic mutations of different NBIA group disorders.

METHODS

Clinical, radiological, and genetic data of patients diagnosed with NBIA in a tertiary care centre in Southern India from 2014 to 2020 was retrospectively collected and analysed.

RESULTS

In our cohort of 27 cases, PLA2G6-associated neurodegeneration (PLAN) was most common (n = 13) followed by Pantothenate kinase-associated neurodegeneration (PKAN) (n = 9). We had 2 cases each of Mitochondrial membrane-associated neurodegeneration (MPAN) and Beta-propeller protein- associated neurodegeneration (BPAN) and 1 case of Kufor-Rakeb Syndrome (KRS). Walking difficulty was the presenting complaint in all PKAN cases, whereas the presentation in PLAN was that of development regression with onset at a mean age of 2 years. Overall, 50% patients of them presented with development regression and one-third had epilepsy. Presence of pyramidal signs was most common examination feature (89%) followed by one or more eye findings (81%) and movement disorders (50%). Neuroimaging was abnormal in 24/27 cases and cerebellar atrophy was the commonest finding (52%) followed by globus pallidus hypointensities (44%).

CONCLUSIONS

One should have a high index of clinical suspicion for the diagnosis of NBIA in children presenting with neuroregression and vision abnormalities in presence of pyramidal signs or movement disorders. Neuroimaging and ophthalmological evaluation provide important clues to diagnosis in NBIA syndromes.

MRI of neurodegeneration with brain iron accumulation

PURPOSE OF REVIEW

The diagnosis of neurodegeneration with brain iron accumulation (NBIA) typically associates various extrapyramidal and pyramidal features, cognitive and psychiatric symptoms with bilateral hypointensities in the globus pallidus on iron-sensitive magnetic resonance images, reflecting the alteration of iron homeostasis in this area. This article details the contribution of MRI in the diagnosis by summarizing and comparing MRI patterns of the various NBIA subtypes.

RECENT FINDINGS

MRI almost always shows characteristic changes combining iron accumulation and additional neuroimaging abnormalities. Iron-sensitive MRI shows iron deposition in the basal ganglia, particularly in bilateral globus pallidus and substantia nigra. Other regions may be affected depending on the NBIA subtypes including the cerebellum and dentate nucleus, the midbrain, the striatum, the thalamus, and the cortex. Atrophy of the cerebellum, brainstem, corpus callosum and cortex, and white matter changes may be associated and worsen with disease duration. Iron deposition can be quantified using R2 or quantitative susceptibility mapping.

SUMMARY

Recent MRI advances allow depicting differences between the various subtypes of NBIA, providing a useful analytical framework for clinicians. Standardization of protocols for image acquisition and analysis may help improving the detection of imaging changes associated with NBIA and the quantification of iron deposition.

Beta-propeller protein-associated neurodegeneration (BPAN) as a genetically simple model of multifaceted neuropathology resulting from defects in autophagy

Autophagy is an essential and conserved cellular homeostatic process. Defects in the core and accessory components of the autophagic machinery would most severely impact terminally differentiated cells, such as neurons. The neurodevelopmental/neurodegenerative disorder β-propeller protein-associated neurodegeneration (BPAN) resulted from heterozygous or hemizygous germline mutations/pathogenic variant of the X chromosome geneWDR45, encoding WD40 repeat protein interacting with phosphoinositides 4 (WIPI4). This most recently identified subtype of the spectrum of neurodegeneration with brain iron accumulation diseases is characterized by a biphasic mode of disease manifestation and progression. The first phase involves early-onset of epileptic seizures, global developmental delay, intellectual disability and autistic syndrome. Subsequently, Parkinsonism and dystonia, as well as dementia, emerge in a subacute manner in adolescence or early adulthood. BPAN disease phenotypes are thus complex and linked to a wide range of other neuropathological disorders. WIPI4/WDR45 has an essential role in autophagy, acting as a phosphatidylinositol 3-phosphate binding effector that participates in autophagosome biogenesis and size control. Here, we discuss recent updates on WIPI4’s mechanistic role in autophagy and link the neuropathological manifestations of BPAN’s biphasic infantile onset (epilepsy, autism) and adolescent onset (dystonic, Parkinsonism, dementia) phenotypes to neurological consequences of autophagy impairment that are now known or emerging in many other neurodevelopmental and neurodegenerative disorders. As monogenicWDR45mutations in BPAN result in a large spectrum of disease phenotypes that stem from autophagic dysfunctions, it could potentially serve as a simple and unique genetic model to investigate disease pathology and therapeutics for a wider range of neuropathological conditions with autophagy defects.

Substantia Nigra Swelling and Dentate Nucleus T2 Hyperintensity May Be Early Magnetic Resonance Imaging Signs of β-Propeller Protein-Associated Neurodegeneration

Background and Methods

Mutations in WDR45 cause β-propeller protein-associated neurodegeneration (BPAN), a type of neurodegeneration with brain iron accumulation (NBIA). We reviewed clinical and MRI findings in 4 patients with de novo WDR45 mutations.

Results

Psychomotor delay and movement disorders were present in all cases; early-onset epileptic encephalopathy was present in 3. In all cases, first MRI showed: prominent bilateral SN enlargement, bilateral dentate nuclei T2-hyperintensity, and corpus callosum thinning. Iron deposition in the SN and globus pallidus (GP) only became evident later. Diffuse cerebral atrophy was present in 3 cases.

Conclusions

In this series, SN swelling and dentate nucleus T2 hyperintensity were early signs of BPAN, later followed by progressive iron deposition in the SN and GP. When clinical suspicion is raised, MRI is crucial for identifying early features suggesting this type of NBIA.

Beta-propeller protein-associated neurodegeneration: a case report and review of the literature

Beta‐propeller protein‐associated neurodegeneration (BPAN) is a rare disorder, which is increasingly recognized thanks to next‐generation sequencing. Due to a highly variable phenotype, patients may present to pediatrics, neurology, psychiatry, or internal medicine. It is therefore essential that physicians of different specialties are familiar with this severe and debilitating condition.