Associations of mitochondrial genomic variation with corticobasal degeneration, progressive supranuclear palsy, and neuropathological tau measures

Associations of mitochondrial genomic variation with successful neurological aging

Mitochondrial health is an integral factor in aging, with mitochondrial dysfunction known to increase with age and contribute to the development of age-related neurodegenerative disorders. Additionally, the mitochondrial genome (mtDNA) has been shown to acquire potentially damaging somatic variation as part of the aging process, while mtDNA single nucleotide polymorphism (SNPs) have been shown to be both protective and detrimental for various neurodegenerative diseases. Yet, little is known about the involvement of mtDNA variation in longevity and successful neurological aging. In this study, we examined the association of mtDNA SNPs, in the form of mitochondrial haplogroups, with successful neurological aging in 1,405 unrelated neurologically healthy subjects. Although not quite significant after correcting for multiple testing (P < 0.0017 considered as significant), we detected a nominally significant association between the I haplogroup (N = 45, 3.2 %) and a younger age (β: -5.00, P = 0.006), indicating that this haplogroup is observed less frequently in older neurologically healthy individuals and may be associated with decreased survival. Replication of this finding in independent neurologically healthy cohorts will be imperative for shaping our understanding of the biological processes underlying healthy neurological aging.

Neuronal Vulnerability to Degeneration in Parkinson's Disease and Therapeutic Approaches

Parkinson's disease is the second most common neurodegenerative disease affecting millions of people worldwide. Despite the crucial threat it poses, currently, no specific therapy exists that can completely reverse or halt the progression of the disease. Parkinson's disease pathology is driven by neurodegeneration caused by the intraneuronal accumulation of alpha-synuclein (α-syn) aggregates in Lewy bodies in the substantia nigra region of the brain. Parkinson's disease is a multiorgan disease affecting the central nervous system (CNS) as well as the autonomic nervous system. A bidirectional route of spreading α-syn from the gut to CNS through the vagus nerve and vice versa has also been reported. Despite our understanding of the molecular and pathophysiological aspects of Parkinson's disease, many questions remain unanswered regarding the selective vulnerability of neuronal populations, the neuromodulatory role of the locus coeruleus, and alpha-synuclein aggregation. This review article aims to describe the probable factors that contribute to selective neuronal vulnerability in Parkinson's disease, such as genetic predisposition, bioenergetics, and the physiology of neurons, as well as the interplay of environmental and exogenous modulators. This review also highlights various therapeutic strategies with cell transplants, through viral gene delivery, by targeting α-synuclein and aquaporin protein or epidermal growth factor receptors for the treatment of Parkinson's disease. The application of regenerative medicine and patient-specific personalized approaches have also been explored as promising strategies in the treatment of Parkinson's disease.

Mitochondrial genomic variation in dementia with Lewy bodies: association with disease risk and neuropathological measures

Dementia with Lewy bodies (DLB) is clinically diagnosed when patients develop dementia less than a year after parkinsonism onset. Age is the primary risk factor for DLB and mitochondrial health influences ageing through effective oxidative phosphorylation (OXPHOS). Patterns of stable polymorphisms in the mitochondrial genome (mtDNA) alter OXPHOS efficiency and define individuals to specific mtDNA haplogroups. This study investigates if mtDNA haplogroup background affects clinical DLB risk and neuropathological disease severity. 360 clinical DLB cases, 446 neuropathologically confirmed Lewy body disease (LBD) cases with a high likelihood of having DLB (LBD-hDLB), and 910 neurologically normal controls had European mtDNA haplogroups defined using Agena Biosciences MassARRAY iPlex technology. 39 unique mtDNA variants were genotyped and mtDNA haplogroups were assigned to mitochondrial phylogeny. Striatal dopaminergic degeneration, neuronal loss, and Lewy body counts were also assessed in different brain regions in LBD-hDLB cases. Logistic regression models adjusted for age and sex were used to assess associations between mtDNA haplogroups and risk of DLB or LBD-hDLB versus controls in a case-control analysis. Additional appropriate regression models, adjusted for age at death and sex, assessed associations of haplogroups with each different neuropathological outcome measure. No mtDNA haplogroups were significantly associated with DLB or LBD-hDLB risk after Bonferroni correction.Haplogroup H suggests a nominally significant reduced risk of DLB (OR=0.61, P=0.006) but no association of LBD-hDLB (OR=0.87, P=0.34). The haplogroup H observation in DLB was consistent after additionally adjusting for the number of APOE ε4 alleles (OR=0.59, P=0.004). Haplogroup H also showed a suggestive association with reduced ventrolateral substantia nigra neuronal loss (OR=0.44, P=0.033). Mitochondrial haplogroup H may be protective against DLB risk and neuronal loss in substantia nigra regions in LBD-hDLB cases but further validation is warranted.

Tauopathies: new perspectives and challenges

BACKGROUND

Tauopathies are a class of neurodegenerative disorders characterized by neuronal and/or glial tau-positive inclusions.

MAIN BODY

Clinically, tauopathies can present with a range of phenotypes that include cognitive/behavioral-disorders, movement disorders, language disorders and non-specific amnestic symptoms in advanced age. Pathologically, tauopathies can be classified based on the predominant tau isoforms that are present in the inclusion bodies (i.e., 3R, 4R or equal 3R:4R ratio). Imaging, cerebrospinal fluid (CSF) and blood-based tau biomarkers have the potential to be used as a routine diagnostic strategy and in the evaluation of patients with tauopathies. As tauopathies are strongly linked neuropathologically and genetically to tau protein abnormalities, there is a growing interest in pursuing of tau-directed therapeutics for the disorders. Here we synthesize emerging lessons on tauopathies from clinical, pathological, genetic, and experimental studies toward a unified concept of these disorders that may accelerate the therapeutics.

CONCLUSIONS

Since tauopathies are still untreatable diseases, efforts have been made to depict clinical and pathological characteristics, identify biomarkers, elucidate underlying pathogenesis to achieve early diagnosis and develop disease-modifying therapies.

Deep learning-based model for diagnosing Alzheimer's disease and tauopathies

AIMS

This study aimed to develop a deep learning-based model for differentiating tauopathies, including Alzheimer's disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Pick's disease (PiD), based on tau-immunostained digital slide images.

METHODS

We trained the YOLOv3 object detection algorithm to detect five tau lesion types: neuronal inclusions, neuritic plaques, tufted astrocytes, astrocytic plaques and coiled bodies. We used 2522 digital slide images of CP13-immunostained slides of the motor cortex from 10 cases each of AD, PSP and CBD for training. Data augmentation was performed to increase the size of the training dataset. We next constructed random forest classifiers using the quantitative burdens of each tau lesion from motor cortex, caudate nucleus and superior frontal gyrus, ascertained from the object detection model. We split 120 cases (32 AD, 36 PSP, 31 CBD and 21 PiD) into training (90 cases) and test (30 cases) sets to train random forest classifiers.

RESULTS

The resultant random forest classifier achieved an average test score of 0.97, indicating that 29 out of 30 cases were correctly diagnosed. A validation study using hold-out datasets of CP13- and AT8-stained slides from 50 cases (10 AD, 17 PSP, 13 CBD and 10 PiD) showed >92% (without data augmentation) and >95% (with data augmentation) diagnostic accuracy in both CP13- and AT8-stained slides.

CONCLUSION

Our diagnostic model trained with CP13 also works for AT8; therefore, our diagnostic tool can be potentially used by other investigators and may assist medical decision-making in neuropathological diagnoses of tauopathies.

Association of Mitochondrial DNA Genomic Variation With Risk of Pick Disease

OBJECTIVE

To determine whether stable polymorphisms that define mitochondrial haplogroups in mitochondrial DNA (mtDNA) are associated with Pick disease risk, we genotyped 52 pathologically confirmed cases of Pick disease and 910 neurologically healthy controls and performed case-control association analysis.

METHODS

Fifty-two pathologically confirmed cases of Pick disease from Mayo Clinic Florida (n = 38) and the University of Pennsylvania (n = 14) and 910 neurologically healthy controls collected from Mayo Clinic Florida were genotyped for unique mtDNA haplogroup-defining variants. Mitochondrial haplogroups were determined, and in a case-control analysis, associations of mtDNA haplogroups with risk of Pick disease were evaluated with logistic regression models that were adjusted for age and sex.

RESULTS

No individual mtDNA haplogroups or superhaplogroups were significantly associated with risk of Pick disease after adjustment for multiple testing (p < 0.0021, considered significant). However, nominally significant (p < 0.05) associations toward an increased risk of Pick disease were observed for mtDNA haplogroup W (5.8% cases vs 1.6% controls, odds ratio [OR] 4.78, p = 0.020) and subhaplogroup H4 (5.8% cases vs 1.2% controls, OR 4.82, p = 0.021).

CONCLUSION

Our findings indicate that mtDNA variation is not a disease driver but may influence disease susceptibility. Ongoing genetic assessments in larger cohorts of Pick disease are currently underway.

MAPT subhaplotypes in corticobasal degeneration: assessing associations with disease risk, severity of tau pathology, and clinical features

The microtubule-associated protein tau (MAPT) H1 haplotype is the strongest genetic risk factor for corticobasal degeneration (CBD). However, the specific H1 subhaplotype association is not well defined, and it is not clear whether any MAPT haplotypes influence severity of tau pathology or clinical presentation in CBD. Therefore, in the current study we examined 230 neuropathologically confirmed CBD cases and 1312 controls in order to assess associations of MAPT haplotypes with risk of CBD, severity of tau pathology (measured as semi-quantitative scores for coiled bodies, neurofibrillary tangles, astrocytic plaques, and neuropil threads), age of CBD onset, and disease duration. After correcting for multiple testing (P < 0.0026 considered as significant), we confirmed the strong association between the MAPT H2 haplotype and decreased risk of CBD (Odds ratio = 0.26, P = 2 × 10-12), and also observed a novel association between the H1d subhaplotype and an increased CBD risk (Odds ratio = 1.76, P = 0.002). Additionally, although not statistically significant after correcting for multiple testing, the H1c haplotype was associated with a higher risk of CBD (Odds ratio = 1.49, P = 0.009). No MAPT haplotypes were significantly associated with any tau pathology measures, age of CBD onset, or disease duration. Though replication will be important and there is potential that population stratification could have influenced our findings, these results suggest that several MAPT H1 subhaplotypes are primarily responsible for the strong association between MAPT H1 and risk of CBD, but that H1 subhaplotypes are unlikely to play a major role in driving tau pathology or clinical features. Our findings also indicate that similarities in MAPT haplotype risk-factor profile exist between CBD and the related tauopathy progressive supranuclear palsy, with H2, H1d, and H1c displaying associations with both diseases.

Association of mitochondrial genomic background with risk of Multiple System Atrophy

INTRODUCTION

Multiple system atrophy (MSA) is a rare, sporadic, and progressive neurodegenerative disease which is characterized neuropathologically by alpha-synuclein aggregates in oligodendroglia, and clinically by parkinsonism, ataxia, and autonomic dysfunction. Mitochondrial health influences neurodegeneration and defects in mitochondria, particularly in oxidative phosphorylation, are reported in MSA. Mitochondrial DNA (mtDNA) codes for 13 critical OXPHOS proteins, however no study has investigated if mtDNA variation, in the form of mitochondrial haplogroups, influences MSA risk. Therefore, in this study we investigated the association of mtDNA haplogroups with MSA risk in a case-control manner.

METHODS

176 pathologically confirmed MSA cases and 910 neurologically healthy controls from Mayo Clinic Jacksonville were genotyped for 39 unique mtDNA variants using Agena Biosciences MassARRAY iPlex technology. Mitochondrial haplogroups were assigned to mitochondrial phylogeny, and logistic regression models that were adjusted for age and sex were used to assess associations between mitochondrial haplogroups and risk of MSA.

RESULTS

After adjusting for multiple testing (P<0.0019 considered significant), no mitochondrial haplogroups were significantly associated with MSA risk. However, several nominally significant (P<0.05) associations were observed; haplogroup I was associated with a decreased risk of MSA (OR=0.09, P=0.021), while an increased risk of MSA was observed for haplogroups H3 (OR=2.43, P=0.017) and T1 and T2 (OR=2.04, P=0.007).

CONCLUSION

This study investigated whether population-specific mtDNA variation is associated with risk of MSA, and our nominally significant findings suggest mitochondrial haplogroup background may influence MSA risk. Validation of these findings and additional meta-analytic studies will be important.