Biology subjects

Rosser, A. E.

Publications and source records attributed to Rosser, A. E..

9 recordsLinked to original sources

bioRxiv2026

Cell-specific transcription dysregulation in human Huntington's disease-positive developing striatum

Huntingtons disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG-repeat expansion in the HTT gene. Progressive loss of striatal projection neurons leads to cognitive, psychiatric, and motor impairments that typically manifest in midlife, despite the presence of the expansion from conception. Increasing evidence supports a neurodevelopmental component to HD; however, authentic human developing HD striatal tissue has not previously been characterised. We analysed an HD positive human fetal striatal sample alongside an age- and sex-matched control. CAG-repeat length was determined, and single-cell RNA sequencing was used to investigate gene expression. We compared the fetal HD transcriptional signature with publicly available datasets from postmortem adult HD brain tissue. We identified 2,032 differentially expressed genes and defined nine cellular clusters, each exhibiting distinct transcriptional profiles. Gene enrichment analysis revealed disruption of key biological processes across the developing HD striatum, with pathway-level dysregulation varying between clusters. There was overlap in gene expression changes between fetal and adult HD striatal tissues. Together, these findings demonstrate that molecular features of HD pathology are present during early human striatal development, supporting the concept that disease mechanisms are established decades prior to clinical onset.

neuroscience↗

bioRxiv2024

Exploring the Epigenetic Influences on the Differentiation Capacity of Human iPSCs Derived from the Lateral Ganglionic Eminence: Implications for Striatal Medium Spiny Neuron Differentiation and Authenticity

Human pluripotent stem cells (hPSCs) are increasingly used to model human disease and as donor cells for regenerative medicine. However, the fidelity of hPSC-derived cell types remains a major concern, particularly when these cells are intended to replicate complex or region-specific subtypes, such as those required to explore and treat neurological diseases. Medium spiny neurons (MSNs), the principal projection neurons of the striatum, are one such target cell type relevant to disorders such as Huntingtons disease. While protocols for generating hPSC-derived MSNs (hPSC-MSNs) exist, the extent to which these cells faithfully recapitulate their genuine counterparts is unclear. Here, we generated isogenic human induced pluripotent stem cells (hiPSCs) from striatal (LGE) and non-neural (fibroblast) fetal tissues, and differentiated them into MSN-like cells alongside a naive human embryonic stem cell (hESC) line. Using DNA methylation profiling and single-cell RNA sequencing, we systematically compared the epigenetic and transcriptional features of these hPSC-MSNs to authentic fetal MSNs. Our findings reveal persistent epigenetic signatures inherited from the tissue of origin, which influence differentiation outcomes. While LGE-derived hiPSCs retained elements of a striatal-biased methylome and yielded MSN-like cells with enhanced similarity to authentic MSNs, all hPSC-MSNs remained epigenetically and transcriptionally distinct from genuine MSNs and we identified clusters of hPSC-derived cells with aberrant or incomplete phenotypes. These results demonstrate that even isogenic hiPSC lines exhibit variable differentiation potential due to residual epigenetic memory and protocol compatibility. We highlight the need for refined protocols and rigorous benchmarking of hPSC-derived models, particularly for regionally specified neuronal subtypes. Our study underscores the complex relationship between epigenetic status, cell lineage, protocol adaptation, and differentiation outcome. Paper SummaryHuman pluripotent stem cells (hPSCs) are widely used to study otherwise inaccessible human cell phenotypes. However, ensuring the molecular authenticity of hPSC-derived cell types remains critical, as differences between hPSC-derived cells and their native counterparts may impact the validity of these models. Here, medium spiny neurons (MSNs; relevant for studying basal ganglia function and disorders such as Huntingtons disease), serve as a valuable prototype for evaluating the fidelity of hPSC-derived cell types. This study generated human induced pluripotent stem cells (hiPSCs) from developing fetal striatal tissues and fibroblasts, differentiating them into MSN-like cells alongside a human embryonic stem cell (hESC) line. Using single-cell RNA sequencing and DNA methylation analysis, we compared these hPSC-derived MSNs to authentic fetal MSNs. Our findings reveal a significant epigenetic gap between hPSC-derived and authentic MSNs, suggesting that hPSC-MSNs do not acquire a complete and normal striatal epigenome. Additionally, while genetic expression of hPSC-MSNs was striatal-like, it was not equivalent, indicating abberant cells and a failure to reproduce an authentic phoenotype. This study provides insights into the challenges of achieving molecular authenticity in hPSC-derived cells and underscores the need for rigorous evaluation to enhance their utility in research and medicine.

cell biology↗

bioRxiv2023

Differences in white matter detected by ex vivo 9.4T MRI are associated with axonal changes in the R6/1 model of Huntington's Disease

White matter (WM) volume loss has been reported in people with Huntingtons disease (HD), but the cellular basis of this deficit remains to be elucidated. To address this, we assessed ex vivo WM microstructure in the transgenic R6/1 mouse model of HD with magnetic resonance imaging (MRI) and studied the neurobiological basis of the MRI brain signals with histological and electron microscopy analyses in a separate cohort of age- and sex-matched mice. Differences in the macromolecular proton fraction (MPF) from quantitative magnetization transfer (qMT) as a proxy myelin measure, and the intra-axonal signal fraction (FR) from the composite hindered and restricted model of diffusion (CHARMED) as a proxy marker of axon density, were assessed alongside diffusion tensor imaging (DTI) parameters. A tractometry approach was employed to inspect region-specific differences across the corpus callosum (CC). Furthermore, voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) were used to explore brain-wise WM macro- and microstructure abnormalities. To gain insight into disease-associated impairments in attentional and visuospatial processing, a third cohort of age-matched mice was assessed with the 5-choice serial reaction time task (5-CSRTT). We report cognitive impairments in R6/1 mice and, by evaluating MRI and light and electron microscopy results, we show that this HD mouse model presents disruptions in axonal morphology (i.e. less complex, thinner axons) and organization (i.e. more densely packed axons). Furthermore, we show that, at least early in disease progression, R6/1 mice present a reduction in the expression or content of myelin-associated proteins without significant alterations in the structure of myelin sheaths. Finally, our findings indicate that neuroinflammation-driven glial and axonal swelling might also affect this mouse model early in disease progression. Crucially, we demonstrate the potential of FR, an in vivo estimate of axon density, as a novel MRI biomarker of HD-associated changes in WM microstructure.

neuroscience↗

bioRxiv2022

Huntington's disease phenocopy syndromes revisited: a clinical comparison and next-generation sequencing exploration

When the genetic test for the Huntingtons disease (HD) HTT expansion first became available almost 30 years ago, only 1% of patients tested negative. Since then, the test has become more accessible and the HD phenotype has expanded. More patients are being tested overall, and more negative tests are being received. These patients are deemed "HD phenocopy syndromes" (HDPC). In this study we established a current estimate for the prevalence of these patients. We also surveyed HD clinician experts on what would make them consider an HD test and compared both HD and HDPC patients to these expectations to decide whether they could be distinguished clinically; this proved impossible even when comparing symptom patterns. We re-analysed existing gene panel data for likely and potentially deleterious variants. Furthermore, we determined principles to prioritise patients for whole-genome sequencing (WGS). It was used to probe a 50 patient strong subcohort of HD phenocopy syndromes for known causes of HD-like and other neurodegenerative disease, identifying one ATXN1 expansion using ExpansionHunter(R). This was a small genetic substudy and therefore unsurprisingly no other known deleterious variants could be identified as in these cryptic understudied syndromes. Novel variants in known genes and variants in genes not yet linked to neurodegeneration may play an outsized role.

genetics↗

bioRxiv2021

Mutation-related apparent myelin, not axon density, drives white matter differences in premanifest Huntington's disease: Evidence from in vivo ultra-strong gradient MRI

White matter (WM) alterations have been observed early in Huntingtons disease (HD) progression but their role in the disease-pathophysiology remains unknown. We exploited ultra-strong-gradient MRI to tease apart contributions of myelin (with the magnetization transfer ratio), and axon density (with the restricted volume fraction from the Composite Hindered and Restricted Model of Diffusion) to WM differences between premanifest HD patients and age- and sex-matched controls. Diffusion tensor MRI (DT-MRI) measures were also assessed. We used tractometry to investigate region-specific changes across callosal segments with well-characterized early- and late-myelinating axonal populations, while brain-wise alterations were explored with tract-based cluster analysis (TBCA). Behavioural measures were included to explore disease-associated brain-function relationships. We detected lower myelin in the rostrum of patients (tractometry: p = 0.0343; TBCA: p = 0.030), but higher myelin in their splenium (p = 0.016). Importantly, patients myelin and mutation size were positively associated (all p-values < 0.01), indicating that increased myelination might be a direct result of the mutation. Finally, myelin was higher than controls in younger patients but lower in older patients (p = 0.003), suggesting detrimental effects of increased myelination later in the course of the disease. Higher FR in patients left cortico-spinal tract (CST) (p = 0.03) was detected, and was found to be positively associated with MTR in the posterior callosum (p = 0.033), possibly suggesting compensation to myelin alterations. This comprehensive, ultra-strong gradient MRI investigation provides novel evidence of CAG-driven myelin alterations in premanifest HD which may reflect neurodevelopmental, rather than neurodegenerative disease-associated changes.

neuroscience↗

bioRxiv2021

Huntington's disease age at motor onset is modified by the tandem hexamer repeat in TCERG1

BackgroundHuntingtons disease is caused by an expanded CAG tract in HTT. The length of the CAG tract accounts for over half the variance in age at onset of disease, and is influenced by other genetic factors, mostly implicating the DNA maintenance machinery. We examined a single nucleotide variant, rs79727797, on chromosome 5 in the TCERG1 gene, previously reported to be associated with Huntingtons disease and a quasi-tandem repeat (QTR) hexamer in exon 4 of TCERG1 with a central pure repeat. MethodsWe developed a novel method for calling perfect and imperfect repeats from exome sequencing data, and tested association between the QTR in TCERG1 and residual age at motor onset (after correcting for the effects of CAG length in the HTT gene) in 610 individuals with Huntingtons disease via regression analysis. ResultsWe found a significant association between age at onset and the sum of the repeat lengths from both alleles of the QTR (p = 2.1x10-9), with each added repeat hexamer reducing age at onset by one year (95% confidence interval [0.7, 1.4]). This association explained that previously observed with rs79727797. ConclusionsThe association with age at onset in the genome-wide association study is due to a QTR hexamer in TCERG1, translated to a glutamine/alanine tract in the protein. We could not distinguish whether this was due to cis-effects of the hexamer repeat on gene expression or of the encoded glutamine/alanine tract in the protein. These results motivate further study of the mechanisms by which TCERG1 modifies onset of HD.

genetics↗

bioRxiv2021

FAN1 nuclease activity affects CAG expansion and age at onset of Huntington's disease

The age at onset of motor symptoms in Huntingtons disease (HD) is driven by HTT CAG repeat length but modified by other genes. We used exome sequencing of 683 HD patients with extremes of onset or phenotype relative to CAG length to identify rare variants associated with clinical effect. We identified damaging coding variants in candidate modifier genes from prior genome-wide association studies associated with altered HD onset or severity. Variants in FAN1 clustered in its DNA-binding and nuclease domains and were associated predominantly with earlier onset HD. Nuclease activities of these variants correlated with residual age at motor onset of HD. Mutating endogenous FAN1 to a nuclease-inactive form in an induced pluripotent stem cell model of HD led to rates of CAG expansion comparable to those observed with complete FAN1 knock out. Together, these data implicate FAN1 nuclease activity in slowing somatic repeat expansion and hence onset of HD.

neuroscience↗

bioRxiv2021

Multi-compartment analysis of the complex gradient-echo signal quantifies myelin breakdown in premanifest Huntington's disease

White matter (WM) alterations have been identified as a relevant pathological feature of Huntingtons disease (HD). Increasing evidence suggests that WM changes in this disorder are due to alterations in myelin-associated biological processes. Multi-compartmental analysis of the complex gradient-echo MRI signal evolution in WM has been shown to quantify myelin in vivo, therefore pointing to the potential of this technique for the study of WM myelin changes in health and disease. This study first characterized the reproducibility of metrics derived from the complex multi-echo gradient-recalled echo (mGRE) signal across the corpus callosum in healthy participants, finding highest reproducibility in the posterior callosal segment. Subsequently, the same analysis pipeline was applied in this callosal region in a sample of premanifest HD patients (n = 19) and age, sex and education matched healthy controls (n = 21). In particular, we focused on two myelin-associated derivatives: i. the myelin water signal fraction (fm), a parameter dependent on myelin content; and ii. the difference in frequency between myelin and intra-axonal water pools ({Delta}{omega}), a parameter dependent on the ratio between the inner and the outer axonal radii. fm was found to be lower in HD patients ({beta} = -0.13, p = 0.03), while {Delta}{omega} did not show a group effect. Performance in tests of working memory, executive function, social cognition and movement was also assessed, and a greater age-related decline in executive function was detected in HD patients ({beta} = -0.06, p = 0.006), replicating previous evidence of executive dysfunction in HD. Finally, the correlation between fm, executive function, and proximity to disease onset was explored in patients, and a positive correlation between executive function and fm was detected (r = 0.542; p = 0.02). This study emphasises the potential of complex mGRE signal analysis for aiding understanding of HD pathogenesis and progression. Moreover, expanding on evidence from pathology and animal studies, it provides novel in vivo evidence supporting myelin breakdown as an early feature of HD.

neuroscience↗

bioRxiv2020

The onset and prevalence of motor and psychiatric symptoms in Huntingtons disease

ObjectiveTo assess the prevalence, timing and functional impact of psychiatric, cognitive and motor abnormalities in Huntingtons disease (HD) gene carriers, we analysed retrospective clinical data from individuals with manifest HD. MethodsClinical features of HD patients were analysed for 6316 individuals in the European REGISTRY study from 161 sites across 17 countries. Data came from clinical history and the patient-completed Clinical Characteristics Questionnaire that assessed eight symptoms: motor, cognitive, apathy, depression, perseverative/obsessive behavior, irritability, violent/aggressive behavior, and psychosis. Multiple logistic regression was used to analyse relationships between symptoms and functional outcomes. ResultsThe initial manifestation of HD is increasingly likely to be motor, and less likely to be psychiatric, as age at presentation increases, and is independent of pathogenic CAG repeat length. The Clinical Characteristics Questionnaire captures data on non-motor symptom prevalence that correlate specifically with validated clinical measures. Psychiatric and cognitive symptoms are common in HD gene carriers, with earlier onsets associated with longer CAG repeats. 42.4% of HD patients reported at least one psychiatric or cognitive symptom before motor symptoms, with depression most common. Each non-motor symptom was associated with significantly reduced total functional capacity scores. ConclusionsPsychiatric and cognitive symptoms are common and functionally debilitating in HD gene carriers. They require recognition and targeting with clinical outcome measures and treatments. However, as it is impossible to distinguish confidently between non-motor symptoms arising from HD and primary psychiatric disorders, particularly in younger pre-manifest patients, non-motor symptoms should not be used to make a clinical diagnosis of HD.

neuroscience↗