α-Synuclein Pathology in PRKN-Linked Parkinson's Disease: New Insights from a Blood-Based Seed Amplification Assay.

Pathogenic variants in PRKN cause early-onset Parkinson's disease (PD), while the role of alpha-synuclein in PRKN-PD remains uncertain. One study performed a blood-based alpha-synuclein seed amplification assay (SAA) in PRKN-PD, not detecting seed amplification in 17 PRKN-PD patients. By applying a methodologically different SAA focusing on neuron-derived extracellular vesicles, we demonstrated alpha-synuclein seed amplification in 8 of 13 PRKN-PD patients, challenging the view of PRKN-PD as a non-synucleinopathy. Moreover, we performed blinded replication of the neuron-derived extracellular vesicles-dependent SAA in idiopathic PD patients and healthy controls. In conclusion, blood-based neuron-derived extracellular vesicles-dependent SAA represents a promising biomarker to elucidate the underpinnings of (monogenic) PD. ANN NEUROL 2024;95:1173-1177.

Multiomics analysis identifies novel facilitators of human dopaminergic neuron differentiation.

Midbrain dopaminergic neurons (mDANs) control voluntary movement, cognition, and reward behavior under physiological conditions and are implicated in human diseases such as Parkinson's disease (PD). Many transcription factors (TFs) controlling human mDAN differentiation during development have been described, but much of the regulatory landscape remains undefined. Using a tyrosine hydroxylase (TH) human iPSC reporter line, we here generate time series transcriptomic and epigenomic profiles of purified mDANs during differentiation. Integrative analysis predicts novel regulators of mDAN differentiation and super-enhancers are used to identify key TFs. We find LBX1, NHLH1 and NR2F1/2 to promote mDAN differentiation and show that overexpression of either LBX1 or NHLH1 can also improve mDAN specification. A more detailed investigation of TF targets reveals that NHLH1 promotes the induction of neuronal miR-124, LBX1 regulates cholesterol biosynthesis, and NR2F1/2 controls neuronal activity.

DJ-1 regulates mitochondrial gene expression during ischemia and reperfusion.

The early-onset Parkinson's disease protein DJ-1 is a multifunctional protein that plays a protective role against ischemia and reperfusion (I/R) injury and oxidative stress. Despite lacking a canonical RNA-binding domain DJ-1 exhibits RNA-binding activity and multiple transcripts have been identified. However, no functional characterization has been provided to date. Here, we have investigated the DJ-1-interacting transcripts, as well as the role of DJ-1 RNA-binding activity during ischemia and reperfusion. Among the identified DJ-1-interacting transcripts, we have distinguished a significant enrichment of mRNAs encoding mitochondrial proteins. The effects of DJ-1 depletion on mitochondrial protein expression and mitochondrial morphology were investigated using a CRISPR/Cas9 generated DJ-1 knockout (DJ-1KO) cell model. DJ-1 depletion resulted in increased MTND2 protein expression in resting cells; however, after exposure to I/R, MTND2 levels were significantly reduced with respect to wild type cells. Increased mitochondrial fission was consistently found in DJ-1KO cells after I/R exposure. MTND2 transcript binding to DJ-1 was increased during ischemia. Our results indicate that the RNA-binding activity of DJ-1 shield mitochondrial transcripts from oxidative damage.

Mutant WDR45 Leads to Altered Ferritinophagy and Ferroptosis in ß-Propeller Protein-Associated Neurodegeneration.

Beta-propeller protein-associated neurodegeneration (BPAN) is a subtype of neurodegeneration with brain iron accumulation (NBIA) caused by loss-of-function variants in WDR45. The underlying mechanism of iron accumulation in WDR45 deficiency remains elusive. We established a primary skin fibroblast culture of a new BPAN patient with a missense variant p.(Asn61Lys) in WDR45 (NM_007075.3: c.183C>A). The female patient has generalized dystonia, anarthria, parkinsonism, spasticity, stereotypies, and a distinctive cranial MRI with generalized brain atrophy, predominantly of the cerebellum. For the functional characterization of this variant and to provide a molecular link of WDR45 and iron accumulation, we looked for disease- and variant-related changes in the patient's fibroblasts by qPCR, immunoblotting and immunofluorescence comparing to three controls and a previously reported WDR45 patient. We demonstrated molecular changes in mutant cells comprising an impaired mitochondrial network, decreased levels of lysosomal proteins and enzymes, and altered autophagy, confirming the pathogenicity of the variant. Compared to increased levels of the ferritinophagy marker Nuclear Coactivator 4 (NCOA4) in control cells upon iron treatment, patients' cells revealed unchanged NCOA4 protein levels, indicating disturbed ferritinophagy. Additionally, we observed abnormal protein levels of markers of the iron-dependent cell death ferroptosis in patients' cells. Altogether, our data suggests that WDR45 deficiency affects ferritinophagy and ferroptosis, consequentially disturbing iron recycling.

Repeat-Associated Non-AUG Translation of AGAGGG Repeats that Cause X-Linked Dystonia-Parkinsonism.

BACKGROUND: X-linked dystonia-parkinsonism (XDP) is a neurodegenerative disorder caused by the intronic insertion of a SINE-VNTR-Alu (SVA) retrotransposon carrying an (AGAGGG)n repeat expansion in the TAF1 gene. The molecular mechanisms by which this mutation causes neurodegeneration remain elusive. OBJECTIVES: We investigated whether (AGAGGG)n repeats undergo repeat-associated non-AUG (RAN) translation, a pathogenic mechanism common among repeat expansion diseases. METHODS: XDP-specific RAN translation reporter plasmids were generated, transfected in HEK293 cells, and putative dipeptide repeat proteins (DPRs) were detected by Western blotting. Immunocytochemistry was performed in COS-7 cells to determine the subcellular localization of one DPR. RESULTS: We detected putative DPRs from two reading frames, supporting the translation of poly-(Glu-Gly) and poly-(Arg-Glu) species. XDP RAN translation initiates within the (AGAGGG)n sequence and poly-(Glu-Gly) DPRs formed nuclear inclusions in transfected cells. CONCLUSIONS: In summary, our work provides the first in-vitro proof of principle that the XDP-linked (AGAGGG)n repeat expansions can undergo RAN translation. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Electrophysiological Properties of Induced Pluripotent Stem Cell-Derived Midbrain Dopaminergic Neurons Correlate With Expression of Tyrosine Hydroxylase.

Induced pluripotent stem cell (iPSC)-based generation of tyrosine hydroxylase-positive (TH+) dopaminergic neurons (DNs) is a powerful method for creating patient-specific in vitro models to elucidate mechanisms underlying Parkinson's disease (PD) at the cellular and molecular level and to perform drug screening. However, currently available differentiation paradigms result in highly heterogeneous cell populations, often yielding a disappointing fraction (<50%) of the PD-relevant TH+ DNs. To facilitate the targeted analysis of this cell population and to characterize their electrophysiological properties, we employed CRISPR/Cas9 technology and generated an mCherry-based human TH reporter iPSC line. Subsequently, reporter iPSCs were subjected to dopaminergic differentiation using either a "floor plate protocol" generating DNs directly from iPSCs or an alternative method involving iPSC-derived neuronal precursors (NPC-derived DNs). To identify the strategy with the highest conversion efficiency to mature neurons, both cultures were examined for a period of 8 weeks after triggering neuronal differentiation by means of immunochemistry and single-cell electrophysiology. We confirmed that mCherry expression correlated with the expression of endogenous TH and that genetic editing did neither affect the differentiation process nor the endogenous TH expression in iPSC- and NPC-derived DNs. Although both cultures yielded identical proportions of TH+ cells (≈30%), whole-cell patch-clamp experiments revealed that iPSC-derived DNs gave rise to larger currents mediated by voltage-gated sodium and potassium channels, showed a higher degree of synaptic activity, and fired trains of mature spontaneous action potentials more frequently compared to NPC-derived DNs already after 2 weeks in differentiation. Moreover, spontaneous action potential firing was more frequently detected in TH+ neurons compared to the TH- cells, providing direct evidence that these two neuronal subpopulations exhibit different intrinsic electrophysiological properties. In summary, the data reveal substantial differences in the electrophysiological properties of iPSC-derived TH+ and TH- neuronal cell populations and that the "floor plate protocol" is particularly efficient in generating electrophysiologically mature TH+ DNs, which are the most vulnerable neuronal subtype in PD.

Parkin Deficiency Impairs Mitochondrial DNA Dynamics and Propagates Inflammation.

BACKGROUND: Mutations in the E3 ubiquitin ligase parkin cause autosomal recessive Parkinson's disease (PD). Together with PTEN-induced kinase 1 (PINK1), parkin regulates the clearance of dysfunctional mitochondria. New mitochondria are generated through an interplay of nuclear- and mitochondrial-encoded proteins, and recent studies suggest that parkin influences this process at both levels. In addition, parkin was shown to prevent mitochondrial membrane permeability, impeding mitochondrial DNA (mtDNA) escape and subsequent neuroinflammation. However, parkin's regulatory roles independent of mitophagy are not well described in patient-derived neurons. OBJECTIVES: We sought to investigate parkin's role in preventing neuronal mtDNA dyshomeostasis, release, and glial activation at the endogenous level. METHODS: We generated induced pluripotent stem cell (iPSC)-derived midbrain neurons from PD patients with parkin (PRKN) mutations and healthy controls. Live-cell imaging, proteomic, mtDNA integrity, and gene expression analyses were employed to investigate mitochondrial biogenesis and genome maintenance. To assess neuroinflammation, we performed single-nuclei RNA sequencing in postmortem tissue and quantified interleukin expression in mtDNA/lipopolysaccharides (LPS)-treated iPSC-derived neuron-microglia co-cultures. RESULTS: Neurons from patients with PRKN mutations revealed deficits in the mitochondrial biogenesis pathway, resulting in mtDNA dyshomeostasis. Moreover, the energy sensor sirtuin 1, which controls mitochondrial biogenesis and clearance, was downregulated in parkin-deficient cells. Linking mtDNA disintegration to neuroinflammation, in postmortem midbrain with PRKN mutations, we confirmed mtDNA dyshomeostasis and detected an upregulation of microglia overexpressing proinflammatory cytokines. Finally, parkin-deficient neuron-microglia co-cultures elicited an enhanced immune response when exposed to mtDNA/LPS. CONCLUSIONS: Our findings suggest that parkin coregulates mitophagy, mitochondrial biogenesis, and mtDNA maintenance pathways, thereby protecting midbrain neurons from neuroinflammation and degeneration. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

H-ABC- and dystonia-causing TUBB4A mutations show distinct pathogenic effects.

Mutations in the brain-specific ß-tubulin 4A (TUBB4A) gene cause a broad spectrum of diseases, ranging from dystonia (DYT-TUBB4A) to hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Currently, the mechanisms of how TUBB4A variants lead to this pleiotropic manifestation remain elusive. Here, we investigated whether TUBB4A mutations causing either DYT-TUBB4A (p.R2G and p.Q424H) or H-ABC (p.R2W and p.D249N) exhibit differential effects at the molecular and cellular levels. Using live-cell imaging of disease-relevant oligodendrocytes and total internal reflection fluorescence microscopy of whole-cell lysates, we observed divergent impact on microtubule polymerization and microtubule integration, partially reflecting the observed pleiotropy. Moreover, in silico simulations demonstrated that the mutants rarely adopted a straight heterodimer conformation in contrast to wild type. In conclusion, for most of the examined variants, we deciphered potential molecular disease mechanisms that may lead to the diverse clinical manifestations and phenotype severity across and within each TUBB4A-related disease.

Transcriptional Alterations in X-Linked Dystonia-Parkinsonism Caused by the SVA Retrotransposon.

X-linked dystonia-parkinsonism (XDP) is a severe neurodegenerative disorder that manifests as adult-onset dystonia combined with parkinsonism. A SINE-VNTR-Alu (SVA) retrotransposon inserted in an intron of the TAF1 gene reduces its expression and alters splicing in XDP patient-derived cells. As a consequence, increased levels of the TAF1 intron retention transcript TAF1-32i can be found in XDP cells as compared to healthy controls. Here, we investigate the sequence of the deep intronic region included in this transcript and show that it is also present in cells from healthy individuals, albeit in lower amounts than in XDP cells, and that it undergoes degradation by nonsense-mediated mRNA decay. Furthermore, we investigate epigenetic marks (e.g., DNA methylation and histone modifications) present in this intronic region and the spanning sequence. Finally, we show that the SVA evinces regulatory potential, as demonstrated by its ability to repress the TAF1 promoter in vitro. Our results enable a better understanding of the disease mechanisms underlying XDP and transcriptional alterations caused by SVA retrotransposons.

Parkinson's Disease Phenotypes in Patient Neuronal Cultures and Brain Organoids Improved by 2-Hydroxypropyl-ß-Cyclodextrin Treatment.

BACKGROUND: The etiology of Parkinson's disease (PD) is only partially understood despite the fact that environmental causes, risk factors, and specific gene mutations are contributors to the disease. Biallelic mutations in the phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) gene involved in mitochondrial homeostasis, vesicle trafficking, and autophagy are sufficient to cause PD. OBJECTIVES: We sought to evaluate the difference between controls' and PINK1 patients' derived neurons in their transition from neuroepithelial stem cells to neurons, allowing us to identify potential pathways to target with repurposed compounds. METHODS: Using two-dimensional and three-dimensional models of patients' derived neurons we recapitulated PD-related phenotypes. We introduced the usage of midbrain organoids for testing compounds. Using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), we corrected the point mutations of three patients' derived cells. We evaluated the effect of the selected compound in a mouse model. RESULTS: PD patient-derived cells presented differences in their energetic profile, imbalanced proliferation, apoptosis, mitophagy, and a reduced differentiation efficiency to tyrosine hydroxylase positive (TH+) neurons compared to controls' cells. Correction of a patient's point mutation ameliorated the metabolic properties and neuronal firing rates as well as reversing the differentiation phenotype, and reducing the increased astrocytic levels. Treatment with 2-hydroxypropyl-ß-cyclodextrin increased the autophagy and mitophagy capacity of neurons concomitant with an improved dopaminergic differentiation of patient-specific neurons in midbrain organoids and ameliorated neurotoxicity in a mouse model. CONCLUSION: We show that treatment with a repurposed compound is sufficient for restoring the impaired dopaminergic differentiation of PD patient-derived cells. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Patient-derived cells - an irreplaceable tool for research of reduced penetrance in movement disorders.

Movement disorders comprise a clinically, pathologically, and genetically heterogeneous group of diseases associated with the phenomenon of reduced penetrance. Penetrance refers to the likelihood that a clinical condition will occur when a particular genotype is present. Elucidating the cause of reduced penetrance may contribute to more personalized medicine by identifying genetic factors that may prevent individuals from developing disease. Therefore, patient material becomes an irreplaceable resource in this approach. It is needed to identify genetic modifiers of the disease in the first place and to subsequently elucidate underlying mechanisms in endogenous human cell models that provide the entire genetic background.

Brain Regional Differences in Hexanucleotide Repeat Length in X-Linked Dystonia-Parkinsonism Using Nanopore Sequencing.

OBJECTIVE: Our study investigated the presence of regional differences in hexanucleotide repeat number in postmortem brain tissues of 2 patients with X-linked dystonia-parkinsonism (XDP), a combined dystonia-parkinsonism syndrome modified by a (CCCTCT)n repeat within the causal SINE-VNTR-Alu retrotransposon insertion in the TAF1 gene. METHODS: Genomic DNA was extracted from blood and postmortem brain samples, including the basal ganglia and cortex from both patients and from the cerebellum, midbrain, and pituitary gland from 1 patient. Repeat sizing was performed using fragment analysis, small-pool PCR-based Southern blotting, and Oxford nanopore sequencing. RESULTS: The basal ganglia (p < 0.001) and cerebellum (p < 0.001) showed higher median repeat numbers and higher degrees of repeat instability compared with blood. CONCLUSIONS: Somatic repeat instability may predominate in brain regions selectively affected in XDP, thereby hinting at its potential role in disease manifestation and modification.

sGC Activity and Regulation of Blood Flow in a Zebrafish Model System.

Soluble guanylyl cyclase (sGC) protein is a heterodimer formed by two subunits encoded by GUCY1A1 and GUCY1B1 genes. The chromosomal locus 4q32.1 harbors both of these genes, which has been previously significantly associated with coronary artery disease, myocardial infarction, and high blood pressure. Blood pressure is influenced by both the environment and genetics and is complemented by several biological pathways. The underlying mechanisms associated with this locus and its genes still need to be investigated. In the current study, we aimed to establish the zebrafish as a model organism to investigate the mechanisms surrounding sGC activity and blood pressure. A zebrafish mutant gucy1a1 line was generated using the CRISPR-Cas9 system by inducing a 4-bp deletion frameshift mutation. This mutation resulted in a reduction of gucy1a1 expression in both heterozygote and homozygote zebrafish. Blood flow parameters (blood flow, arterial pulse, linear velocity, and vessel diameter) investigated in the gucy1a1 mutants showed a significant increase in blood flow and linear velocity, which was augmented in the homozygotes. No significant differences were observed for the blood flow parameters measured from larvae with individual morpholino downregulation of gucy1a1 and gucy1b1, but an increase in blood flow and linear velocity was observed after co-morpholino downregulation of both genes. In addition, the pharmacological sGC stimulator BAY41-2272 rescued the impaired cGMP production in the zebrafish gucy1a1 ± mutant larvae. Downregulation of cct7 gene did not show any significant difference on the blood flow parameters in both wild-type and gucy1a1 ± background larvae. In summary, we successfully established a zebrafish platform for investigating sGC-associated pathways and underlying mechanisms in depth. This model system will have further applications, including for potential drug screening experiments.

Mild dopa-responsive dystonia in heterozygous tyrosine hydroxylase mutation carrier: Evidence of symptomatic enzyme deficiency?

We present a case of mild, adult-onset dopa-responsive dystonia (DRD) with a heterozygous mutation in the tyrosine hydroxylase (TH) gene. We propose that this genetic state may have led to partial enzyme deficiency. Future studies should attempt to identify and characterize the phenotype of other patients with single TH variants.

Mutations in RHOT1 Disrupt Endoplasmic Reticulum-Mitochondria Contact Sites Interfering with Calcium Homeostasis and Mitochondrial Dynamics in Parkinson's Disease.

Aims: The outer mitochondrial membrane protein Miro1 is a crucial player in mitochondrial dynamics and calcium homeostasis. Recent evidence indicated that Miro1 mediates calcium-induced mitochondrial shape transition, which is a prerequisite for the initiation of mitophagy. Moreover, altered Miro1 protein levels have emerged as a shared feature of monogenic and sporadic Parkinson's disease (PD), but, so far, no disease-associated variants in RHOT1 have been identified. Here, we aim to explore the genetic and functional contribution of RHOT1 mutations to PD in patient-derived cellular models. Results: For the first time, we describe heterozygous RHOT1 mutations in two PD patients (het c.815G>A; het c.1348C>T) and identified mitochondrial phenotypes with reduced mitochondrial mass in patient fibroblasts. Both mutations led to decreased endoplasmic reticulum-mitochondrial contact sites and calcium dyshomeostasis. As a consequence, energy metabolism was impaired, which in turn caused increased mitophagy. Innovation and Conclusion: Our study provides functional evidence that ROTH1 is a genetic risk factor for PD, further implicating Miro1 in calcium homeostasis and mitochondrial quality control.

A hexanucleotide repeat modifies expressivity of X-linked dystonia parkinsonism.

OBJECTIVE: X-linked dystonia parkinsonism (XDP) is a neurodegenerative movement disorder caused by a single mutation: SINE-VNTR-Alu (SVA) retrotransposon insertion in TAF1. Recently, a (CCCTCT)n repeat within the SVA insertion has been reported as an age-at-onset (AAO) modifier in XDP. Here we investigate the role of this hexanucleotide repeat in modifying expressivity of XDP. METHODS: We genotyped the hexanucleotide repeat in 355 XDP patients and correlated the repeat number (RN) with AAO (n = 295), initial clinical manifestation (n = 294), site of dystonia onset (n = 238), disease severity (n = 28), and cognitive function (n = 15). Furthermore, we investigated i) repeat instability by segregation analysis and Southern blotting using postmortem brain samples from two affected individuals and ii) relative TAF1 expression in blood RNA from 31 XDP patients. RESULTS: RN showed significant inverse correlations with AAO and with TAF1 expression and a positive correlation with disease severity and cognitive dysfunction. Importantly, AAO (and not RN) was directly associated with whether dystonia or parkinsonism will manifest at onset. RN was lower in patients affected by mouth/tongue dystonia compared with blepharospasm. RN was unstable across germline transmissions with an overall tendency to increase in length and exhibited somatic mosaicism in brain. INTERPRETATION: The hexanucleotide repeat within the SVA insertion acts as a genetic modifier of disease expressivity in XDP. RN-dependent TAF1 repression and subsequent differences in TAF1 mRNA levels in patients may be potentiated in the brain through somatic variability leading to the neurological phenotype. ANN NEUROL 2019;85:812-822.

Parkin Interacts with Apoptosis-Inducing Factor and Interferes with Its Translocation to the Nucleus in Neuronal Cells.

Mutations in the PRKN gene (encoding parkin) have been linked to the most frequent known cause of recessive Parkinson's disease (PD), and parkin dysfunction represents a risk factor for sporadic PD. Parkin is widely neuroprotective through different cellular pathways, as it protects dopaminergic neurons from apoptosis in a series of cellular and animal models of PD. The mitochondrial protein apoptosis-inducing factor (AIF) is an important cell death effector, which, upon cellular stress in many paradigms, is redistributed from the mitochondria to the nucleus to function as a proapoptotic factor, mostly independent of caspase activity, while in normal mitochondria it functions as an antiapoptotic factor. AIF is known to participate in dopaminergic neuron loss in experimental PD models and in patients with PD. We, therefore, investigated possible crosstalk between parkin and AIF. By using immunoprecipitation and proximity ligation assays, we demonstrated a physical interaction between the two proteins. Nuclear AIF translocation was significantly reduced by parkin expression in neuroblastoma SH-SY5Y cells after exposure to an apoptogenic stimulus. These results were confirmed in primary murine cortical neurons, which showed a higher nuclear translocation of AIF in parkin-deficient neurons upon an excitotoxic stimulus. Our results indicate that the interaction of parkin with AIF interferes with the nuclear translocation of AIF, which might contribute to the neuroprotective activity of parkin.