Oligodendrocyte and Extracellular Matrix Contributions to Central Nervous System Motor Function: Implications for Dystonia

AOPEP-related autosomal recessive dystonia: update on Zech-Boesch syndrome

Gene discovery efforts have contributed to a better understanding of the molecular causes of dystonia, but knowledge of the individual monogenic forms remains limited. This review seeks to summarise all available data on the recently identified autosomal recessive subtype of dystonia caused by variants in AOPEP, focusing on the geographical origins of affected families, mutational spectrum, phenotypic expressions and pathophysiology. AOPEP-related dystonia, documented as Zech-Boesch syndrome in the Online Mendelian Inheritance in Man database, has been diagnosed in cohorts around the globe including under-represented populations with increased rates of consanguinity. Predictably leading to loss of protein function, the majority (74%) of disease-associated AOPEP alleles are protein-truncating variants comprising homozygous and compound heterozygous stop-gain, frameshift and splice-site changes. The dystonic disorder shows onset from childhood to the fourth decade and generalises in a significant proportion of cases (60%). Variable expressivity and age-related penetrance are likely to play a role in manifestation of the condition, consistent with occasional occurrence of AOPEP homozygous pathogenic variants in subjects without a diagnosis of dystonia. AOPEP encodes aminopeptidase O, a proteolytic processing enzyme that is preferentially expressed in glia and potentially linked to endosomal-lysosomal pathways. AOPEP-related autosomal recessive Zech-Boesch syndrome is of worldwide relevance for the diagnosis of genetic dystonia. Future research focusing on AOPEP`s role in cellular protein metabolism may provide new insights into dystonia pathogenesis and yet-unidentified therapeutic targets.

A Closer Look at Dystonia with the Glycosylation

Graphical Abstract

The pericellular function of Fibulin-7 in the adhesion of oligodendrocyte lineage cells to neuronal axons during CNS myelination

Myelin is an electrical insulator that enables saltatory nerve conduction and is essential for proper functioning of the central nervous system (CNS). It is formed by oligodendrocytes (OLs) in the CNS, and during OL development various molecules, including extracellular matrix (ECM) proteins, regulate OL differentiation and myelination; however, the role of ECM proteins in these processes is not well understood. Our present work is centered on the analyses of the expression and function of fibulin-7 (Fbln7), an ECM protein of the fibulin family, in OL differentiation. In the expression analysis of Fbln7 in the CNS, we found that it was expressed at early postnatal stage and localized in the processes of OL precursor cells (OPCs), in the inner region of myelin, and in axons. The functional analysis using recombinant Fbln7 protein (rFbln7) revealed that rFbln7 promoted OPC attachment activity via β1 integrin and heparan sulfate receptors. Further, rFbln7 induced the adhesion to neurites and the differentiation of OLs. Altogether, our results show that Fbln7 promotes the adhesion between OLs and axons and OL differentiation.

White matter lesions contribute to motor and non-motor disorders in Parkinson's disease: a critical review

Parkinson's disease (PD) is a prevalent neurodegenerative disease, characterized by movement disorders and non-motor symptoms like cognitive impairment and depression. Degeneration of dopaminergic neurons in the substantia nigra and Lewy bodies have long been considered as main neuropathological changes. However, recent magnetic resonance imaging (MRI) studies have shown that white matter lesions (WMLs) were present in PD patients. WMLs are characterized by loss or impairment of myelin sheath in central nerve fibers, which are closely correlated with motor and cognitive dysfunction in PD. WMLs alterations precede nigrostriatal neuronal losses and can independently affect the clinical severity or characteristics of motor coordination in PD patients. Currently, the exact mechanism of WMLs involvement in the occurrence and development of PD remains unclear. It is speculated that WMLs may participate in the pathogenesis of PD by disrupting important connections in brain or promoting axonal degeneration. In this review, we will discuss the pathological changes and mechanisms of WMLs, elaborate the impact of WMLs on the progression of PD, clarify the importance of WMLs in PD pathogenesis, and thus provide novel targets for PD treatments.

White Matter Microstructural Changes Using Ultra-Strong Diffusion Gradient MRI in Adult-Onset Idiopathic Focal Cervical Dystonia

BACKGROUND AND OBJECTIVES

Adult-onset idiopathic focal cervical dystonia (AOIFCD) involves abnormal posturing of the cervical musculature and, in some individuals, an associated head tremor. Existing neuroimaging studies have implicated key motor networks. However, measures used to date lack specificity toward underlying pathophysiologic differences. We aim to assess white matter motor pathways for localized, microstructural differences, which may aid in understanding underlying mechanisms.

METHODS

Individuals diagnosed with AOIFCD and an age- and sex-matched control group were prospectively recruited through the Welsh Movement Disorders Research Network. All participants underwent in-depth clinical phenotyping and MRI (structural and diffusion sequences) using ultra-strong diffusion gradients. Tractography (whole-tract median values) and tractometry (along tract profiling) were performed for key white matter motor pathways assessing diffusion kurtosis imaging (DKI), neurite orientation dispersion and density imaging (NODDI), and standard model parameters. Groups were compared using linear model analysis with Bonferroni multiple comparison correction.

RESULTS

Fifty participants with AOIFCD and 30 healthy control participants were recruited, with 46 with AOIFCD and 30 healthy controls included for analysis (33 without head tremor, 13 with head tremor). Significant differences were observed in the anterior thalamic radiations (lower mid-tract fractional anisotropy [estimate = -0.046, p = 3.07 × 10-3], radial kurtosis [estimate = -0.165, p = 1.42 × 10-4], f-intra-axonal signal fraction [estimate = -0.044, p = 2.78 × 10-3], p2 orientation coherence [estimate = -0.043, p = 1.64 × 10-3], higher Orientation Dispersion Index [ODI, estimate = 0.023, p = 2.22 × 10-3]) and thalamopremotor tracts (higher mid-tract mean kurtosis [estimate = 0.064, p = 7.56 × 10-4], lower Neurite Density Index [estimate = 0.062, p = 2.1 × 10-3], higher distal tract ODI [estimate = 0.062, p = 3.1 × 10-3], lower f [estimate = -0.1, p = 2.3 × 10-3], and striatopremotor tracts [proximal lower f: estimate = -0.075, p = 1.06 × 10-3]). These measures correlated with clinical measures: dystonia duration (right thalamopremotor distal ODI: r = -0.9, p = 1.29 × 10-14), psychiatric symptoms (obsessive compulsive symptoms: left anterior thalamic radiation p2 r = 0.92, p = 2.797 × 10-11), sleep quality (Sleep Disorders Questionnaire Score: left anterior thalamic radiation ODI: r = -0.84, p = 4.84 × 10-11), pain (left anterior thalamic radiation ODI: r = -0.89, p = 1.4 × 10-13), and cognitive functioning (paired associated learning task p2, r = 0.94, p = 6.68 × 10-20).

DISCUSSION

Overall, localized microstructural differences were identified within tracts linking the prefrontal and premotor cortices with thalamic and basal ganglia regions, suggesting pathophysiologic processes involve microstructural aberrances of motor system modulatory pathways, particularly involving intra-axonal and fiber orientation dispersion measures.

Fibulin-2 is an extracellular matrix inhibitor of oligodendrocytes relevant to multiple sclerosis

Impairment of oligodendrocytes and myelin contributes to neurological disorders including multiple sclerosis (MS), stroke, and Alzheimer's disease. Regeneration of myelin (remyelination) decreases the vulnerability of demyelinated axons, but this repair process commonly fails with disease progression. A contributor to inefficient remyelination is the altered extracellular matrix (ECM) in lesions, which remains to be better defined. We have identified fibulin-2 (FBLN2) as a highly upregulated ECM component in lesions of MS and stroke and in proteome databases of Alzheimer's disease and traumatic brain injury. Focusing on MS, the inhibitory role of FBLN2 was suggested in the experimental autoimmune encephalomyelitis (EAE) model, in which genetic FBLN2 deficiency improved behavioral recovery by promoting the maturation of oligodendrocytes and enhancing remyelination. Mechanistically, when oligodendrocyte progenitors were cultured in differentiation medium, FBLN2 impeded their maturation into oligodendrocytes by engaging the Notch pathway, leading to cell death. Adeno-associated virus deletion of FBLN2 in astrocytes improved oligodendrocyte numbers and functional recovery in EAE and generated new myelin profiles after lysolecithin-induced demyelination. Collectively, our findings implicate FBLN2 as a hitherto unrecognized injury-elevated ECM, and a therapeutic target, that impairs oligodendrocyte maturation and myelin repair.

The integrated stress response pathway and neuromodulator signaling in the brain: lessons learned from dystonia

The integrated stress response (ISR) is a highly conserved biochemical pathway involved in maintaining proteostasis and cell health in the face of diverse stressors. In this Review, we discuss a relatively noncanonical role for the ISR in neuromodulatory neurons and its implications for synaptic plasticity, learning, and memory. Beyond its roles in stress response, the ISR has been extensively studied in the brain, where it potently influences learning and memory, and in the process of synaptic plasticity, which is a substrate for adaptive behavior. Recent findings demonstrate that some neuromodulatory neuron types engage the ISR in an "always-on" mode, rather than the more canonical "on-demand" response to transient perturbations. Atypical demand for the ISR in neuromodulatory neurons introduces an additional mechanism to consider when investigating ISR effects on synaptic plasticity, learning, and memory. This basic science discovery emerged from a consideration of how the ISR might be contributing to human disease. To highlight how, in scientific discovery, the route from starting point to outcomes can often be circuitous and full of surprise, we begin by describing our group's initial introduction to the ISR, which arose from a desire to understand causes for a rare movement disorder, dystonia. Ultimately, the unexpected connection led to a deeper understanding of its fundamental role in the biology of neuromodulatory neurons, learning, and memory.

Brain Region Size Differences Associated With Dystonia in People With Cerebral Palsy Born Premature

BACKGROUND

Dystonia in cerebral palsy (CP) is classically associated with deep gray matter injury at term gestation, but the patterns of injury associated with dystonia following premature birth are unclear. We examined whether there were brain regional size differences associated with dystonia in people with CP born premature.

METHODS

In this retrospective cohort study, we identified subjects with CP born premature (<37 weeks gestational age) seen at a tertiary care CP center between February 1, 2017, to February 1, 2021, who had T1-weighted brain magnetic resonance imaging (MRI) done between ages one and five years available in the clinical record. We measured the following on these brain MRI images per the 2013 Kidokoro criteria: interhemispheric distance, biparietal width, lateral ventricle diameter, transcerebellar diameter, deep gray matter area, and corpus callosum thickness. We then compared the sizes of these structures between those with and without dystonia correcting for gestational age at birth and gross motor functional ability (univariate general linear models).

RESULTS

Fifty-five subjects met the inclusion and exclusion criteria. Interhemispheric distance was significantly greater in those with dystonia, suggesting decreased cortical volume (P = 0.005). There was no significant difference in the other measured structures between those with and without dystonia, including deep gray matter area.

CONCLUSIONS

Increased interhemispheric distance, not measures of deep gray matter size, correlate with the presence of dystonia in people with CP born premature.

Transcriptional regulatory network for neuron-glia interactions and its implication for DYT6 dystonia

Advances in sequencing technologies have identified novel genes associated with inherited forms of dystonia, providing valuable insights into its genetic basis and revealing diverse genetic pathways and mechanisms involved in its pathophysiology. Since identifying genetic variation in the transcription factor coding THAP1 gene linked to isolated dystonia, numerous investigations have employed transcriptomic studies in DYT-THAP1 models to uncover pathogenic molecular mechanisms underlying dystonia. This review examines key findings from transcriptomic studies conducted on in vivo and in vitro DYT-THAP1 models, which demonstrate that the THAP1-regulated transcriptome is diverse and cell-specific, yet it is bound and co-regulated by a common set of proteins. Prominent among its functions, THAP1 and its co-regulatory network target molecular pathways critical for generating myelinating oligodendrocytes that ensheath axons and generate white matter in the central nervous system. Several lines of investigation have demonstrated the importance of myelination and oligodendrogenesis in motor function during development and in adults, emphasizing the non-cell autonomous contributions of glial cells to neural circuits involved in motor function. Further research on the role of myelin abnormalities in motor deficits in DYT6 models will enhance our understanding of axon-glia interactions in dystonia pathophysiology and provide potential therapeutic interventions targeting these pathways.

A TNR Frameshift Variant in Weimaraner Dogs with an Exercise-Induced Paroxysmal Movement Disorder

BACKGROUND

Some paroxysmal movement disorders remain without an identified genetic cause.

OBJECTIVES

The aim was to identify the causal genetic variant for a paroxysmal dystonia-ataxia syndrome in Weimaraner dogs.

METHODS

Clinical and diagnostic investigations were performed. Whole genome sequencing of one affected dog was used to identify private homozygous variants against 921 control genomes.

RESULTS

Four Weimaraners were presented for episodes of abnormal gait. Results of examinations and diagnostic investigations were unremarkable. Whole genome sequencing revealed a private frameshift variant in the TNR (tenascin-R) gene in an affected dog, XM_038542431.1:c.831dupC, which is predicted to truncate more than 75% of the open read frame. Genotypes in a cohort of 4 affected and 70 unaffected Weimaraners showed perfect association with the disease phenotype.

CONCLUSIONS

We report the association of a TNR variant with a paroxysmal dystonia-ataxia syndrome in Weimaraners. It might be relevant to include sequencing of this gene in diagnosing humans with unexplained paroxysmal movement disorders. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

What have we learned about the biology of dystonia from deep brain stimulation?

Deep brain stimulation has dramatically changed the management of patients with dystonia, therapeutic approach of dystonia with marked improvement of dystonia and functional disability. However, despite decades of experience and identification of good prognosis factors, prediction of beneficial effect at the individual level is still a challenge. There is inter-individual variability in therapeutic outcome. Genetic factors are identified but subgroups of patients still have relapse or worsening of dystonia in short or long term. Possible "biological factors" underlying such a difference among patients are discussed, including structural or functional differences including altered plasticity.

Mutation Screening of MED27 in a Large Dystonia Cohort

Objectives. Recently, biallelic variants in MED27 have been identified to correlate with complex dystonia. However, no replicative study has been conducted in larger dystonia cohorts. In this study, we aimed to systematically evaluate the genetic associations of MED27 with dystonia in a large dystonia cohort. Materials and Methods. We analyzed rare variants (minor allele $\text{frequency}<0.01$ ) of MED27 in a large Chinese dystonia cohort with whole exome sequencing. The overrepresentation of rare variants in patients was examined with Fisher’s exact test at allele and gene levels. Results. A total of 688 patients with dystonia were included in the study, including 483 isolated dystonia, 133 combined dystonia, and 72 complex dystonia. The average age at onset (SD) was 34.3 (19.1) years old. After applying filtering criteria, five rare variants, namely, p.R247H, p.P174A, p.P123A, p.L120F, and p.F56C, were identified in six individuals. All of them carried the variant in the heterozygous form, and no patients with compound heterozygous or homozygous alleles were identified. At allele level, no variant was associated with risk of dystonia. Gene-based burden analysis did not detect enrichment of rare variants of MED27 in dystonia either. Conclusion. Variants of MED27 were rare in Chinese dystonia patients, probably because that mutations in MED27 are more associated with more complex neurodevelopmental disorders that can also include dystonia among the various neurological features. Further studies are needed to confirm the role of MED27 in dystonia and other neurological disorders.

The Mechanism and Function of Glia in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disease that primarily affects elderly people. The mechanism on onset and progression of PD is unknown. Currently, there are no effective treatment strategies for PD. PD is thought to be the loss of midbrain dopaminergic neurons, but it has recently been discovered that glia also affects brain tissue homeostasis, defense, and repair in PD. The neurodegenerative process is linked to both losses of glial supportive-defensive functions and toxic gain of glial functions. In this article, we reviewed the roles of microglia, astrocytes, and oligodendrocytes in the development of PD, as well as the potential use of glia-related medications in PD treatment.