Tick-borne encephalitis as a trigger for anti-N-Methyl-d-aspartate receptor encephalitis.

Tick Borne Encephalitis (TBE) is endemic to an increasing number of countries and is a common cause of meningoencephalitis in Europe and Asia making any potential complications of the disease increasingly relevant to clinicians. We present, what is to our knowledge, the second reported case of N-methyl-d-aspartate receptor (NMDAR) encephalitis following Tick Borne Encephalitis (TBE) in a 47-year-old Lithuanian man. The case provides further evidence of TBE being a possible trigger of NMDAR encephalitis and highlights the importance of being aware of symptoms of autoimmune encephalitis in patients with infectious encephalitis.

Paraneoplastic neurologic syndromes.

Diagnosis of paraneoplastic neurologic syndromes (PNS) requires an understanding of the clinical, immunologic and oncologic heterogeneity. The 2004 PNS criteria were partially outdated due to advances in the field, and updated consensus criteria for PNS have been proposed in 2021, including the PNS-Care score for assessment of PNS probability. Furthermore, knowledge on the limitations of autoantibody testing is crucial to ensure accurate interpretation. This review presents the updated diagnostic criteria for PNS, in a Danish context.

Pathophysiological Effects of Autoantibodies in Autoimmune Encephalitides.

The heterogeneity of autoantibody targets in autoimmune encephalitides presents a challenge for understanding cellular and humoral pathophysiology, and the development of new treatment strategies. Thus, current treatment aims at autoantibody removal and immunosuppression, and is primarily based on data generated from other autoimmune neurological diseases and expert consensus. There are many subtypes of autoimmune encephalitides, which now entails both diseases with autoantibodies targeting extracellular antigens and classical paraneoplastic syndromes with autoantibodies targeting intracellular antigens. Here, we review the current knowledge of molecular and cellular effects of autoantibodies associated with autoimmune encephalitis, and evaluate the evidence behind the proposed pathophysiological mechanisms of autoantibodies in autoimmune encephalitis.

NMDA-receptor encephalitis in Denmark from 2009 to 2019: a national cohort study.

BACKGROUND: To describe the national Danish N-methyl-D-aspartate receptor encephalitis (NMDARE) cohort. METHODS: All NMDAR immunoglobulin G (IgG) positive cases in Denmark from 2009 to 2019 were included. Medical information was assessed retrospectively for clinical phenotype, workup, treatment and outcome. RESULTS: Seventy-seven patients were NMDAR IgG positive in serum/CSF. Fifty-five fulfilled the criteria of NMDARE, 18 did not and 4 had missing data. Incidence was 0.17/100,000 persons per year in 2018, and incidence rates increased since 2009. Of the 55 NMDARE patients (median age 27; 60% female), 9 had post-herpes simplex (HSE) NMDARE and 7 had a tumor (four teratomas). MRI was normal in 51% of patients. Brain FDG PET was performed in 17 patients, and was abnormal in 47% of patients with a normal MRI. First-line therapy was administered to 91%, and 24% required second-line therapy. Maintenance therapy during recovery was given 84% of patients, with no effect on relapse-risk. ICU admission occurred in 29%. Poor outcome (mRS > 2) was reported in 27% and dependent on age and etiology. Patients > 45 years had a poorer outcome (71% vs 8%, p < 0.0001), more frequently post-HSE NMDARE (47% vs 3%, p < 0.0001) and underlying malignancies (18% vs 0%). CONCLUSION: The incidence of NMDARE in Denmark is currently 0.17/100,000 persons per year, and has increased since 2009. NMDARE patients in Denmark display a higher median age, lower female:male ratio, a less frequent tumor association and need for ICU admission. Maintenance therapy did not reduce relapse rate. Poor outcome was seen with higher age, likely related to underlying etiology.

[Autoimmune encephalitis].

Autoimmune encephalitis is an important, treatable subtype of acute encephalitis where autoantibodies target intra- or extracellular neural antigens. Despite research advances, diagnosis is often delayed or incorrect, which affects outcome negatively. We summarise clinical features of the most common autoantibody-mediated autoimmune encephalitis subtypes and focus on classification, current diagnostic challenges using commercially available diagnostic assays, in an attempt to increase awareness.

Identification of bioactive metabolites in human iPSC-derived dopaminergic neurons with PARK2 mutation: Altered mitochondrial and energy metabolism.

PARK2 (parkin) mutations cause early-onset Parkinson's disease (PD). Parkin is an ubiquitin E3 ligase that participates in several cellular functions, including mitochondrial homeostasis. However, the specific metabolomic changes caused by parkin depletion remain unknown. Here, we used isogenic human induced pluripotent stem cells (iPSCs) with and without PARK2 knockout (KO) to investigate the effect of parkin loss of function by comparative metabolomics supplemented with ultrastructural and functional analyses. PARK2 KO neurons displayed increased tricarboxylic acid (TCA) cycle activity, perturbed mitochondrial ultrastructure, ATP depletion, and dysregulation of glycolysis and carnitine metabolism. These perturbations were combined with increased oxidative stress and a decreased anti-oxidative response. Key findings for PARK2 KO cells were confirmed using patient-specific iPSC-derived neurons. Overall, our data describe a unique metabolomic profile associated with parkin dysfunction and show that combining metabolomics with an iPSC-derived dopaminergic neuronal model of PD is a valuable approach to obtain novel insight into the disease pathogenesis.

Neurodegeneration Induced by Anti-IgLON5 Antibodies Studied in Induced Pluripotent Stem Cell-Derived Human Neurons.

Anti-IgLON5 disease is a progressive neurological disorder associated with autoantibodies against a neuronal cell adhesion molecule, IgLON5. In human postmortem brain tissue, the neurodegeneration and accumulation of hyperphosphorylated tau (p-tau) are found. Whether IgLON5 antibodies induce neurodegeneration or neurodegeneration provokes an immune response causing inflammation and antibody formation remains to be elucidated. We investigated the effects of anti-IgLON5 antibodies on human neurons. Human neural stem cells were differentiated for 14-48 days and exposed from Days 9 to 14 (short-term) or Days 13 to 48 (long-term) to either (i) IgG from a patient with confirmed anti-IgLON5 antibodies or (ii) IgG from healthy controls. The electrical activity of neurons was quantified using multielectrode array assays. Cultures were immunostained for ß-tubulin III and p-tau and counterstained with 4',6-Diamidine-2'-phenylindole dihydrochloride (DAPI). To study the impact on synapses, cultures were also immunostained for the synaptic proteins postsynaptic density protein 95 (PSD95) and synaptophysin. A lactate dehydrogenase release assay and nuclei morphology analysis were used to assess cell viability. Cultures exposed to anti-IgLON5 antibodies showed reduced neuronal spike rate and synaptic protein content, and the proportion of neurons with degenerative appearance including p-tau (T205)-positive neurons was higher when compared to cultures exposed to control IgG. In addition, cell death was increased in cultures exposed to anti-IgLON5 IgG for 21 days. In conclusion, pathological anti-IgLON5 antibodies induce neurodegenerative changes and cell death in human neurons. This supports the hypothesis that autoantibodies may induce the neurodegenerative changes found in patients with anti-IgLON5-mediated disease. Furthermore, this study highlights the potential use of stem cell-based in vitro models for investigations of antibody-mediated diseases. As anti-IgLON5 disease is heterogeneous, more studies with different IgLON5 antibody samples tested on human neurons are needed.

Role of RhoA-ROCK signaling in Parkinson's disease.

Parkinson's disease (PD) is a complex and widespread neurodegenerative disease characterized by depletion of midbrain dopaminergic (DA) neurons. Key issues are the development of therapies that can stop or reverse the disease progression, identification of dependable biomarkers, and better understanding of the pathophysiological mechanisms of PD. RhoA-ROCK signals appear to have an important role in PD symptoms, making it a possible approach for PD treatment strategies. Activation of RhoA-ROCK (Rho-associated coiled-coil containing protein kinase) appears to stimulate various PD risk factors including aggregation of alpha-synuclein (αSyn), dysregulation of autophagy, and activation of apoptosis. This manuscript reviews current updates about the biology and function of the RhoA-ROCK pathway and discusses the possible role of this signaling pathway in causing the pathogenesis of PD. We conclude that inhibition of the RhoA-ROCK signaling pathway may have high translational potential and could be a promising therapeutic target in PD.

CSF-Neurofilament Light Chain Levels in NMDAR and LGI1 Encephalitis: A National Cohort Study.

Background and Objectives: The two most common autoimmune encephalitides (AE), N-methyl-D-Aspartate receptor (NMDAR) and Leucine-rich Glioma-Inactivated 1 (LGI1) encephalitis, have been known for more than a decade. Nevertheless, no well-established biomarkers to guide treatment or estimate prognosis exist. Neurofilament light chain (NfL) has become an unspecific screening marker of axonal damage in CNS diseases, and has proven useful as a diagnostic and disease activity marker in neuroinflammatory diseases. Only limited reports on NfL in AE exist. We investigated NfL levels at diagnosis and follow-up in NMDAR and LGI1-AE patients, and evaluated the utility of CSF-NfL as a biomarker in AE. Methods: Patients were included from the National Danish AE cohort (2009-present) and diagnosed based upon autoantibody positivity and diagnostic consensus criteria. CSF-NfL was analyzed by single molecule array technology. Clinical and diagnostic information was retrospectively evaluated and related to NfL levels at baseline and follow-up. NMDAR-AE patients were subdivided into: idiopathic/teratoma associated or secondary NMDAR-AE (post-viral or concomitant with malignancies/demyelinating disease). Results: A total of 74 CSF samples from 53 AE patients (37 NMDAR and 16 LGI1 positive) were included in the study. Longitudinal CSF-NfL levels was measured in 21 patients. Median follow-up time was 23.8 and 43.9 months for NMDAR and LGI1-AE respectively. Major findings of this study are: i) CSF-NfL levels were higher in LGI1-AE than in idiopathic/teratoma associated NMDAR-AE at diagnosis; ii) CSF-NfL levels in NMDAR-AE patients distinguished idiopathic/teratoma cases from cases with other underlying etiologies (post-viral or malignancies/demyelinating diseases) and iii) Elevated CSF-NfL at diagnosis seems to be associated with worse long-term disease outcomes in both NMDAR and LGI1-AE. Discussion: CSF-NfL measurement may be beneficial as a prognostic biomarker in NMDAR and LGI1-AE, and high CSF-NfL could foster search for underlying etiologies in NMDAR-AE. Further studies on larger cohorts, using standardized methods, are warranted.

Autoimmune Encephalitis: Current Knowledge on Subtypes, Disease Mechanisms and Treatment.

Autoimmune Encephalitides (AE) comprises a group of diseases with antibodies against neuronal synaptic and cell surface antigens. Since the discovery of the most common subtype, NMethyl- D-Aspartate (NMDA) receptor encephalitis, an astonishing number of novel disease-causing antibodies have been described. This includes other glutamatergic and GABAergic receptor antibodies and antibodies against various other surface proteins. Many of these novel conditions present as limbic encephalitis with memory impairment, psychiatric features and epileptic seizures, often alongside subtype specific clinical features. Others present with a clinical disease course specific to the antibody. In contrast to the well-known paraneoplastic syndromes with antibodies directed against intracellular antigens (e.g. limbic encephalitis with Hu antibodies), autoimmune encephalitides are often highly responsive to immunotherapy, with a good outcome if diagnosed and treated early. Prognosis depends on aggressive immunotherapy, often with a combination of corticosteroids, intravenous immunoglobulin, plasma exchange or in some cases anti-CD20 therapy and cyclophosphamide. Other treatment regimens exist, and prognosis varies between disease subtypes and occurrence of underlying cancer. We review current knowledge on subtype-specific clinical presentation, disease mechanisms, diagnosis including pitfalls, treatment paradigms and outcome in autoimmune encephalitides, and provide suggestions for future research.

Lysosomal perturbations in human dopaminergic neurons derived from induced pluripotent stem cells with PARK2 mutation.

Mutations in the PARK2 gene encoding parkin, an E3 ubiquitin ligase, are associated with autosomal recessive early-onset Parkinson's disease (PD). While parkin has been implicated in the regulation of mitophagy and proteasomal degradation, the precise mechanism leading to neurodegeneration in both sporadic and familial PD upon parkin loss-of-function remains unknown. Cultures of isogenic induced pluripotent stem cell (iPSC) lines with and without PARK2 knockout (KO) enable mechanistic studies of the effect of parkin deficiency in human dopaminergic neurons. We used such cells to investigate the impact of PARK2 KO on the lysosomal compartment and found a clear link between parkin deficiency and lysosomal alterations. PARK2 KO neurons exhibited a perturbed lysosomal morphology with enlarged electron-lucent lysosomes and an increased lysosomal content, which was exacerbated by mitochondrial stress and could be ameliorated by antioxidant treatment. We also found decreased lysosomal enzyme activity and autophagic perturbations, suggesting an impairment of the autophagy-lysosomal pathway in parkin-deficient cells. Interestingly, activity of the GBA-encoded enzyme, ß-glucocerebrosidase, was increased, suggesting the existence of a compensatory mechanism. In conclusion, our data provide a unique characterization of the morphology, content, and function of lysosomes in PARK2 KO neurons and reveal an important new connection between mitochondrial dysfunction and lysosomal dysregulation in PD pathogenesis.

Perturbations in RhoA signalling cause altered migration and impaired neuritogenesis in human iPSC-derived neural cells with PARK2 mutation.

Mutations in parkin, encoded by the PARK2 gene, causes early-onset familial Parkinson's disease (PD), but dysfunctional parkin has also been implicated in sporadic PD. By combining human isogenic induced pluripotent stem cells (iPSCs) with and without PARK2 knockout (KO) and a novel large-scale mass spectrometry based proteomics and post-translational modification (PTM)-omics approach, we have mapped changes in protein profiles and PTMs caused by parkin deficiency in neurons. Our study identifies changes to several proteins previously shown to be dysregulated in brains of sporadic PD patients. Pathway analysis and subsequent in vitro assays reveal perturbations in migration and neurite outgrowth in the PARK2 KO neurons. We confirm the neurite defects using long-term engraftment of neurons in the striatum of immunosuppressed hemiparkinsonian adult rats. The GTP-binding protein RhoA was identified as a key upstream regulator, and RhoA activity was significantly increased in PARK2 KO neurons. By inhibiting RhoA signalling the migration and neurite outgrowth phenotypes could be rescued. Our study provides new insight into the pathogenesis of PD and demonstrates the broadly applicable potential of proteomics and PTMomics for elucidating the role of disease-causing mutations.

PARK2 Mutation Causes Metabolic Disturbances and Impaired Survival of Human iPSC-Derived Neurons.

The protein parkin, encoded by the PARK2 gene, is vital for mitochondrial homeostasis, and although it has been implicated in Parkinson's disease (PD), the disease mechanisms remain unclear. We have applied mass spectrometry-based proteomics to investigate the effects of parkin dysfunction on the mitochondrial proteome in human isogenic induced pluripotent stem cell-derived neurons with and without PARK2 knockout (KO). The proteomic analysis quantified nearly 60% of all mitochondrial proteins, 119 of which were dysregulated in neurons with PARK2 KO. The protein changes indicated disturbances in oxidative stress defense, mitochondrial respiration and morphology, cell cycle control, and cell viability. Structural and functional analyses revealed an increase in mitochondrial area and the presence of elongated mitochondria as well as impaired glycolysis and lactate-supported respiration, leading to an impaired cell survival in PARK2 KO neurons. This adds valuable insight into the effect of parkin dysfunction in human neurons and provides knowledge of disease-related pathways that can potentially be targeted for therapeutic intervention.

Nonhypoxic pharmacological stabilization of Hypoxia Inducible Factor 1α: Effects on dopaminergic differentiation of human neural stem cells.

Parkinson's disease is a neurodegenerative disease resulting in degeneration of midbrain dopaminergic neurons. Exploratory studies using human foetal tissue or predifferentiated stem cells have suggested that intracerebral transplantation of dopaminergic precursor cells may become an effective treatment for patients with Parkinson's disease. However, strategies for dopaminergic stem cell differentiation vary widely in efficiency, and better methods still need to be developed. Hypoxia Inducible Factor 1 (HIF-1) is a transcription factor involved in the regulation of genes important for cellular adaption to hypoxia and low glucose supply. HIF-1 is to a large degree regulated by the availability of oxygen as in its presence, the subunit HIF-1α is degraded by HIF prolyl hydroxylase enzymes (HPHs). Stabilization of HIF-1α through inhibition of HPHs has been shown to increase dopaminergic differentiation of stem cells and to protect dopaminergic neurons against neurotoxins. This study investigated the effects of noncompetitive (FG-0041) and competitive (Compound A and JNJ-42041935) HIF-1α stabilizing compounds on the dopaminergic differentiation of human neural stem cells. Treatment with all HPH inhibitors at high oxygen tension (20%) resulted in HIF-1α stabilization as assessed by immunocytochemistry for HIF-1α and detection of increased levels of vascular endothelial growth factor in the conditioned culture medium. Following 10 days of HIF-1α stabilization, the cultures displayed a slightly reduced proliferative activity and significantly increased relative levels of tyrosine hydroxylase-positive dopaminergic neurons. In conclusion, HIF-1α stabilization may represent a promising strategy for the generation of dopaminergic neurons intended for use in experimental in vitro studies and cell replacement therapies.