Retinal thickness as a biomarker of cognitive impairment in manifest Huntington's disease

Secreted IgM deficiency alters the retinal landscape enhancing neurodegeneration associated with aging

BACKGROUND

Maintenance of the retina, part of the central nervous system, and other structures in the eye is critical for vision preservation. Aging increases the prevalence of vision impairment, including glaucoma, macular degeneration, and diabetic retinopathy. The retina is primarily maintained by glial cells; however, recent literature suggests that lymphocytes may play a role in the homeostasis of central nervous system tissues. Natural antibodies are produced by B cells without infection or immunization and maintain tissue homeostasis. Here, we explored the potential role of natural immunoglobulin M (IgM) produced by B lymphocytes in maintaining retinal health during aging in mice.

RESULTS

Our results indicate that the vitreous humor of both mice and humans contains IgM and IgG, suggesting that these immunoglobulins may play a role in ocular function. Furthermore, we observed that aged mice lacking secreted IgM (µs-/-) exhibited pronounced retinal degeneration, accompanied by reactive gliosis, and a proinflammatory cytokine environment. This contrasts with the aged wild-type counterparts, which retain their ability to secrete IgM and maintain a better retinal structure and anti-inflammatory environment. In addition to these findings, the absence of secreted IgM was associated with significant alterations in the retinal pigment epithelium, including disruptions to its morphology and signs of increased stress. This was further observed in changes to the blood-retinal-barrier, which is critical for regulation of retinal homeostasis.

CONCLUSIONS

These data suggest a previously unrecognized association between a lack of secreted IgM and alterations in the retinal microenvironment, leading to enhanced retinal degeneration during aging. Although the precise mechanism remains unclear, these findings highlight the potential importance of secreted IgM in processes that support retinal health over time. By increasing our understanding of ocular aging, these results show that there is a broader role for the immune system in retinal function and integrity in advanced age, opening new areas for the exploration of immune-related interventions in age-associated retinal conditions.

Characterization of visual cognition in pre-manifest, manifest and reduced penetrance Huntington's disease

Cognitive and visual impairment are common in Huntington's Disease (HD) and may precede motor diagnosis. We investigate the early presence of visual cognitive deficits in 181 participants, including HD carriers (40 pre-manifest, 30 early manifest, 27 manifest, and 6 reduced penetrance) and 78 healthy controls (HC). Significant differences in visual memory were observed between reduced penetrance and pre-manifest groups (p = .003), with pre-manifest showing worse performance. Age, education, CAG repeats, motor status, executive function, and verbal fluency, accounted for up to 72.8% of the variance in general and visual cognitive functions, with motor status having the strongest impact on visual domains in HD carriers. In pre-manifest HD, visual cognitive domains were primarily influenced by executive function, verbal fluency, age, and CAG repeats, while in early and manifest stages motor status and verbal fluency becomes more influential. ROC analyses showed that especially visuospatial abilities, visual memory, and visual attention (AUC = 0.927, 0.878, 0.874, respectively) effectively differentiated HC and pre-manifest from early and manifest HD. Early assessment of visual cognitive domains, particularly visual memory, could be an early marker of cognitive decline in HD. Our findings highlight the different profiles of impairment in visual cognition across HD carriers.

Pleiotropic effects of mutant huntingtin on retinopathy in two mouse models of Huntington's disease

Huntington's disease (HD) is caused by the expansion of a CAG repeat, encoding a string of glutamines (polyQ) in the first exon of the huntingtin gene (HTTex1). This mutant huntingtin protein (mHTT) with extended polyQ forms aggregates in cortical and striatal neurons, causing cell damage and death. The retina is part of the central nervous system (CNS), and visual deficits and structural abnormalities in the retina of HD patients have been observed. Defects in retinal structure and function are also present in the R6/2 and R6/1 HD transgenic mouse models that contain a gene fragment to express mHTTex1. We investigated whether these defects extend to the zQ175KI mouse model which is thought to be more representative of the human condition because it was engineered to contain the extended CAG repeat within the endogenous HTT locus. We found qualitatively similar phenotypes between R6/1 and zQ175KI retinae that include the presence of mHTT aggregates in retinal neurons, cone loss, downregulation of rod signaling proteins and abnormally elongated photoreceptor connecting cilia. In addition, we present novel findings that mHTT disrupts cell polarity in the photoreceptor cell layer and the retinal pigment epithelium (RPE). Furthermore, we show that the RPE cells from R6/1 mice contain mHTT nuclear inclusions, adding to the list of non-neuronal cells with mHTT aggregates and pathology. Thus, the eye may serve as a useful system to track disease progression and to test therapeutic intervention strategies for HD.

Optical Coherence Tomography in Huntington's Disease-A Potential Future Biomarker for Neurodegeneration?

Huntington's disease (HD) is a progressive neurodegenerative disorder for which, until now, only symptomatic treatment has been available. Lately, there have been multiple ongoing clinical trials targeting therapeutic agents for preventing disease onset or slowing disease progression in HD. These studies are in constant need of reliable biomarkers for neurodegeneration in HD. In recent years, retinal biomarkers have attracted significant attention in neurodegenerative disorders. Likewise, optical coherence tomography (OCT) is being evaluated as a potential biomarker in HD. In this article, we review the existing literature on OCT as a biomarker for neurodegeneration in HD.

Serum metabolomic signatures of patients with rare neurogenetic diseases: an insight into potential biomarkers and treatment targets

Introduction

To further advance our understanding of Muscular Dystrophies (MDs) and Spinocerebellar Ataxias (SCAs), it is necessary to identify the biological patterns associated with disease pathology. Although progress has been made in the fields of genetics and transcriptomics, there is a need for proteomics and metabolomics studies. The present study aimed to be the first to document serum metabolic signatures of MDs (DMD, BMD, and LGMD 2A) SCAs (SCA 1-3), from a South Asian perspective.

Methods

A total of 28 patients (SCA 1-10, SCA 2-2, SCA 3-2, DMD-10, BMD-2, LGMD-2) and eight controls (aged 8-65 years) were included. Metabolomic analysis was performed by Ultrahigh Performance Liquid Chromatography-Tandem Mass Spectroscopy (UPLC-MS/MS), with support from the Houston Omics Collaborative.

Results and discussion

Amino acid metabolism was the primary altered super pathway in DMD followed by carbohydrate metabolism and lipid metabolism. In contrast, BMD and LGMD 2A exhibited a more prominent alteration in lipid metabolism followed by amino acid metabolism. In SCAs, primarily lipid, amino acid, peptide, nucleotide, and xenobiotics pathways are affected. Our findings offer new insights into the variance of metabolite levels in MD and SCA, with substantial implications for pathology, drug development, therapeutic targets and clinical management. Intriguingly, this study identified two novel metabolites associated with SCA. This pilot cross-sectional study warrants further research involving larger groups of participants, to validate our findings.

Optical coherence tomography measurements in Huntington's disease: a systematic review and meta-analysis

BACKGROUND

A connection has been established between ocular structural changes and various neurodegenerative diseases. Several studies utilizing optical coherence tomography (OCT) have detected signs of ocular structural alterations among individuals with Huntington's disease (HD). The inconsistent results reported in the literature regarding alterations in the retina and choroid encouraged us to conduct this systematic review and meta-analysis to accumulate the findings.

METHODS

A systematic search was carried out in three electronic databases (PubMed, Embase, Scopus) to find studies reporting OCT measurements in HD cases compared with healthy controls (HC). A fixed-effects or random-effects meta-analysis was conducted according to the detected heterogeneity level. Furthermore, subgroup and sensitivity analyses, meta-regression, and quality assessment were performed.

RESULTS

Eleven studies were included in the systematic review and 9 studies with a total population of 452 participants (241 cases, and 211 HC) underwent meta-analysis. Results of the analysis denoted that subfoveal choroid had a significantly reduced thickness in HD eyes compared to HC (p < 0.0001). Moreover, our analysis indicated that HD cases had a significantly thinner average (p = 0.0130) and temporal peripapillary retinal nerve fiber layer (pRNFL) (p = 0.0012) than HC. However, subjects with pre-HD had insignificant differences in average (p = 0.44) and temporal pRNFL thickness (p = 0.33) with the HC group.

CONCLUSION

Results of the current systematic review and meta-analysis revealed the significant thinning of average and temporal pRNFL and subfoveal choroid in HD compared to HC. However, OCT currently might be considered insensitive to be applied in the pre-HD population at least until further longitudinal investigations considering variables such as the duration between OCT measurement and disease onset validating OCT as a routine diagnostic tool in HD clinics.

Characterizing differences in retinal and choroidal microvasculature and structure in individuals with Huntington's Disease compared to healthy controls: A cross-sectional prospective study

OBJECTIVE

To characterize retinal and choroidal microvascular and structural changes in patients who are gene positive for mutant huntingtin protein (mHtt) with symptoms of Huntington's Disease (HD).

METHODS

This study is a cross-sectional comparison of patients who are gene positive for mHtt and exhibit symptoms of HD, either motor manifest or prodromal (HD group), and cognitively normal individuals without a family history of HD (control group). HD patients were diagnosed by Duke movement disorder neurologists based on the Unified Huntington's Disease Rating Scale (UHDRS). Fovea and optic nerve centered OCT and OCTA images were captured using Zeiss Cirrus HD-5000 with AngioPlex. Outcome metrics included central subfield thickness (CST), peripapillary retinal nerve fiber layer (pRNFL) thickness, ganglion cell-inner plexiform layer (GCIPL) thickness, and choroidal vascularity index (CVI) on OCT, and foveal avascular zone (FAZ) area, vessel density (VD), perfusion density (PD), capillary perfusion density (CPD), and capillary flux index (CFI) on OCTA. Generalized estimating equation (GEE) models were used to account for inter-eye correlation.

RESULTS

Forty-four eyes of 23 patients in the HD group and 77 eyes of 39 patients in the control group were analyzed. Average GCIPL thickness and FAZ area were decreased in the HD group compared to controls (p = 0.001, p < 0.001). No other imaging metrics were significantly different between groups.

CONCLUSIONS

Patients in the HD group had decreased GCIPL thickness and smaller FAZ area, highlighting the potential use of retinal biomarkers in detecting neurodegenerative changes in HD.

Metabolomics: An Emerging "Omics" Platform for Systems Biology and Its Implications for Huntington Disease Research

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The precise mechanisms of HD progression are poorly understood; however, it is known that there is an expansion of the trinucleotide cytosine-adenine-guanine (CAG) repeat in the Huntingtin gene. Important new strategies are of paramount importance to identify early biomarkers with predictive value for intervening in disease progression at a stage when cellular dysfunction has not progressed irreversibly. Metabolomics is the study of global metabolite profiles in a system (cell, tissue, or organism) under certain conditions and is becoming an essential tool for the systemic characterization of metabolites to provide a snapshot of the functional and pathophysiological states of an organism and support disease diagnosis and biomarker discovery. This review briefly highlights the historical progress of metabolomic methodologies, followed by a more detailed review of the use of metabolomics in HD research to enable a greater understanding of the pathogenesis, its early prediction, and finally the main technical platforms in the field of metabolomics.

Retina Oculomics in Neurodegenerative Disease

Ophthalmic biomarkers have long played a critical role in diagnosing and managing ocular diseases. Oculomics has emerged as a field that utilizes ocular imaging biomarkers to provide insights into systemic diseases. Advances in diagnostic and imaging technologies including electroretinography, optical coherence tomography (OCT), confocal scanning laser ophthalmoscopy, fluorescence lifetime imaging ophthalmoscopy, and OCT angiography have revolutionized the ability to understand systemic diseases and even detect them earlier than clinical manifestations for earlier intervention. With the advent of increasingly large ophthalmic imaging datasets, machine learning models can be integrated into these ocular imaging biomarkers to provide further insights and prognostic predictions of neurodegenerative disease. In this manuscript, we review the use of ophthalmic imaging to provide insights into neurodegenerative diseases including Alzheimer Disease, Parkinson Disease, Amyotrophic Lateral Sclerosis, and Huntington Disease. We discuss recent advances in ophthalmic technology including eye-tracking technology and integration of artificial intelligence techniques to further provide insights into these neurodegenerative diseases. Ultimately, oculomics opens the opportunity to detect and monitor systemic diseases at a higher acuity. Thus, earlier detection of systemic diseases may allow for timely intervention for improving the quality of life in patients with neurodegenerative disease.

HSF1 protects cells from cadmium toxicity by governing proteome integrity

BACKGROUND

Cadmium toxicity has been associated with disruption of protein homeostasis by interfering with protein folding processes. Heat shock factor 1 (HSF1) coordinates the rapid and extensive cellular response to maintain proteomic balance facing the challenges from many environmental stressors. Thus, we suspect that HSF1 may shield cells from cadmium toxicity by conserving proteome integrity.

RESULTS

Here, we demonstrate that cadmium, a highly poisonous metal, induces aggregation of cytosolic proteins in human cells, which disrupts protein homeostasis and activates HSF1. Cadmium exposure increases HSF1's phosphorylation, nuclear translocation and DNA bindings. Aside from this, HSF1 goes through liquid-liquid phase separation to form small nuclear condensates upon cadmium exposure. A specific regulatory domain of HSF1 is critical for HSF1's phase separation capability. Most importantly, human cells with impaired HSF1 are sensitized to cadmium, however, cells with overexpressed HSF1 are protected from cadmium toxicity. Overexpression of HSF1 in human cells reduces protein aggregates, amyloid fibrils and DNA damages to antagonize cadmium toxicity.

CONCLUSIONS

HSF1 protects cells from cadmium toxicity by governing the integrity of both proteome and genome. Similar mechanisms may enable HSF1 to alleviate cellular toxicity caused by other heavy metals. HSF1's role in cadmium exposure may provide important insights into the toxic effects of heavy metals on human cells and body organs, allowing us to better manage heavy metal poisoning.