Correlation between C9ORF72 mutation and neurodegenerative diseases: A comprehensive review of the literature

Genetic Screening of Patients with Sporadic Alzheimer's Disease and Frontotemporal Lobar Degeneration in the Chinese Population

Background

Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) account for the vast majority of neurodegenerative dementias. AD and FTLD have different clinical phenotypes with a genetic overlap between them and other dementias.

Objective

This study aimed to identify the genetic spectrum of sporadic AD and FTLD in the Chinese population.

Methods

A total of 74 sporadic AD and 29 sporadic FTLD participants were recruited. All participants underwent whole-exome sequencing (WES) and testing for a hexanucleotide expansion in C9orf72 was additionally performed for participants with negative WES results.

Results

Four known pathogenic or likely pathogenic variants, including PSEN1 (p.G206D), MAPT (p.R5H), LRRK2 (p.W1434*), and CFAP43 (p.C934*), were identified in AD participants, and 1 novel pathogenic variant of ANXA11 (p.D40G) and two known likely pathogenic variants of MAPT (p.D177V) and TARDBP (p.I383V) were identified in FTLD participants. Twenty-four variants of uncertain significance as well as rare variants in risk genes for dementia, such as ABCA7, SORL1, TRPM7, NOS3, MPO, and DCTN1, were also found. Interestingly, several variants in participants with semantic variant primary progressive aphasia were detected. However, no participants with C9orf72 gene variants were found in the FTLD cohort.

Conclusions

There was a high frequency of genetic variants in Chinese participants with sporadic AD and FTLD and a complex genetic overlap between these two types of dementia and other neurodegenerative diseases.

Cdk5 phosphorylation-dependent C9orf72 degradation promotes neuronal death in Parkinson's disease models

AIMS

Chromosome 9 open reading frame 72 (C9orf72) is one of the most dazzling molecules in neurodegenerative diseases, albeit that its role in Parkinson's disease (PD) remains unknown. This article aimed to explore the potential mechanism of C9orf72 involved in the pathogenesis of PD.

METHODS

The expression and phosphorylation levels of C9orf72 were examined by Western blotting, RT-PCR, and immunoprecipitation using PD models. Multiple bioinformatics software was used to predict the potential phosphorylation sites of C9orf72 by Cdk5, followed by verification of whether Cdk5-inhibitor ROSCOVITINE could reverse the degradation of C9orf72 in PD. By constructing the sh-C9orf72-knockdown adenovirus and overexpressing the FLAG-C9orf72 plasmid, the effects of C9orf72 knockdown and overexpression, respectively, were determined. A short peptide termed Myr-C9orf72 was used to verify whether interfering with Cdk5 phosphorylation at the Ser9 site of the C9orf72 protein could alleviate autophagy disorder, neuronal death, and movement disorder in PD models.

RESULTS

The expression level of the C9orf72 protein was significantly reduced, albeit the mRNA expression was not changed in the PD models. Moreover, the phosphorylation level was enhanced, and its reduction was mainly degraded by the ubiquitin-proteasome pathway. The key nervous system kinase Cdk5 directly phosphorylated the S9 site of the C9orf72 protein, which promoted the degradation of the C9orf72 protein. The knockdown of C9orf72 aggravated autophagy dysfunction and increased neuronal loss and motor dysfunction in substantia nigra neurons of PD mice. The overexpression of C9orf72 alleviated autophagy dysfunction in PD neurons. Specifically, interference with Cdk5 phosphorylation at the S9 site of C9orf72 alleviated autophagy dysfunction, neuronal death, and motor dysfunction mediated by C9orf72 protein degradation during PD.

CONCLUSIONS

Cumulatively, our findings illustrate the importance of the role of C9orf72 in the regulation of neuronal death during PD progression via the Cdk5-dependent degradation.

C9orf72 ALS mutation carriers show extensive cortical and subcortical damage compared to matched wild-type ALS patients

OBJECTIVE

C9orf72 mutation carriers with different neurological phenotypes show cortical and subcortical atrophy in multiple different brain regions, even in pre-symptomatic phases. Despite there is a substantial amount of knowledge, small sample sizes, clinical heterogeneity, as well as different choices of image analysis may hide anatomical abnormalities that are unique to amyotrophic lateral sclerosis (ALS) patients with this genotype or that are indicative of the C9orf72-specific trait overlain in fronto-temporal dementia patients.

METHODS

Brain structural and resting state functional magnetic imaging was obtained in 24 C9orf72 positive (ALSC9+) ALS patients paired for burden disease with 24 C9orf72 negative (ALSC9-) ALS patients. A comprehensive structural evaluation of cortical thickness and subcortical volumes between ALSC9+ and ALSC9- patients was performed while a region of interest (ROI)-ROI analysis of functional connectivity was implemented to assess functional alterations among abnormal cortical and subcortical regions. Results were corrected for multiple comparisons.

RESULTS

Compared to ALSC9- patients, ALSC9+ patients exhibited extensive disease-specific patterns of thalamo-cortico-striatal atrophy, supported by functional alterations of the identified abnormal regions. Cortical thinning was most pronounced in posterior areas and extended to frontal regions. Bilateral atrophy of the mediodorsal and pulvinar nuclei was observed, emphasizing a focal rather than global thalamus atrophy. Volume loss in a large portion of bilateral caudate and left putamen was reported. The marked reduction of functional connectivity observed between the left posterior thalamus and almost all the atrophic cortical regions support the central role of the thalamus in the pathogenic mechanism of C9orf72-mediated disease.

CONCLUSIONS

These findings constitute a coherent and robust picture of ALS patients with C9orf72-mediated disease, unveiling a specific structural and functional characterization of thalamo-cortico-striatal circuit alteration. Our study introduces new evidence in the characterization of the pathogenic mechanisms of C9orf72 mutation.

Inhibition of the TLR/NF-κB Signaling Pathway and Improvement of Autophagy Mediates Neuroprotective Effects of Plumbagin in Parkinson's Disease

A naphthoquinone molecule known as plumbagin (PL), which has a wide range of pharmacological properties including antitumor, antioxidation, anti-inflammation, and neuroprotective effects, is extracted from the roots of the medicinal herb Plumbago zeylanica L. Plumbagin has been studied for its potential to treat Parkinson's disease (PD). However, its effectiveness and mechanism are still unknown. This study intends to evaluate plumbagin's effectiveness against PD in vitro and in vivo. Plumbagin partially repaired the loss of dopaminergic neurons in the nigral substantia nigra and the resulting behavioural impairment caused by MPTP or MPTP/probenecid in mice. Furthermore, plumbagin treatment significantly inhibited the TLR/NF-κB pathways. It reduced the TNF-α, IL-6, and IL-1β mRNA expression in PD mice induced by MPTP or MPTP/probenecid, which was consistent with the findings in the inflammatory model of BV2 cells induced by MPP+ or LPS. In addition, plumbagin treatment enhanced the microtubule-associated protein 1 light chain 3 beta (LC3) LC3-II/LC3-I levels while decreasing the p-mTOR and p62 protein accumulation in PD mice induced by MPTP or MPTP/probenecid, which was similar to the results obtained from the experiments in SH-SY5Y and PC12 cells induced by MPP+. Consequently, our results support the hypothesis that plumbagin, by promoting autophagy and inhibiting the activation of the TLR/NF-κB signaling pathway, is a promising treatment agent for treating Parkinson's disease (PD). However, to confirm plumbagin's anti-PD action more thoroughly, other animal and cell PD models must be used in future studies.

Involvement of striatal motoric subregions in familial frontotemporal dementia with parkinsonism harboring the C9orf72 repeat expansions

The chromosome 9 open reading frame 72 (C9ORF72) has been proposed as the causative gene of frontotemporal dementia with parkinsonism (FTDP), but its pathophysiological mechanism of parkinsonism is poorly understood. To explore the roles of striatal motor subdivisions in the pathogenesis of parkinsonism resulting from C9ORF72 repeat expansions in the FTDP, two patients with FTDP from one pedigree and seventeen healthy controls were enrolled. The participants received clinical interviews, physical examinations, genetic testing, [¹⁸F]-fluorodeoxyglucose PET/MRI, and [¹⁸F]-dihydrotetrabenazine PET/CT. Voxel-wise and region of interest analysis were conducted with respect to gray matter volume, metabolism, and dopamine transport function between patients and controls, focusing on the motor part of the striatum according to the Oxford-GSK-Imanova Striatal Connectivity Atlas. Patient 1 presented with parkinsonism as the initial symptom, while patient 2 exhibited behavior disturbance as the first symptom, followed by parkinsonism within one year. Both patients had the hexanucleotide expansion detected in C9ORF72(>52 repeats). Gray matter volume atrophy, hypometabolism and dopamine dysfunction were observed in the motor areas of the striatum. Of the two patients, marked glucose hypometabolism within the striatal motor subregion was observed in patient 1, with corresponding gray matter atrophy. In addition, presynaptic dopaminergic integrity of patient 2 was deteriorated in the motor subregions which was consistent with gray matter atrophy. These findings imply that parkinsonism in FTDP may be associated with the degeneration and dopaminergic dysfunction of the striatal motor subregion, which might be attributed to C9orf72 repeat expansions.

Does epilepsy contribute to the clinical phenotype of C9orf72 mutation in fronto-temporal dementia?

C9orf72 mutation is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) worldwide. Recently, several reports of patients with FTD who carried the C9orf72 mutation and also manifested epilepsy have been published, since seizures occur in FTD at a higher rate than in the general population, the possible association between epilepsy and C9orf72 mutation remains to be clarified. In the attempt to understand whether epilepsy contributes to the phenotype of the C9orf72 mutation, we compared epilepsy occurrence in patients with FTD who carried the C9orf72 mutation and those who did not. In our sample of 84 patients with FTD, 7.1% of cases reported epilepsy, with no significant differences between subsamples of patients with FTD stratified according to the presence of the C9orf72 mutation or to family history of FTD/parkinsonism/motor neuron disease. Our findings did not support to the possibility that epilepsy represents a characteristic feature of the C9orf72 mutation, as suggested by recent case reports published in the English literature.

Genotype-Phenotype Correlation in Progressive Supranuclear Palsy Syndromes: Clinical and Radiological Similarities and Specificities

The progressive supranuclear palsy (PSP) syndrome encompasses different entities. PSP disease of sporadic origin is the most frequent presentation, but different genetic mutations can lead either to monogenic variants of PSP disease, or to other conditions with a different pathophysiology that eventually may result in PSP phenotype. PSP syndrome of monogenic origin is poorly understood due to the low prevalence and variable expressivity of some mutations. Through this review, we describe how early age of onset, family history of early dementia, parkinsonism, dystonia, or motor neuron disease among other clinical features, as well as some neuroimaging signatures, may be the important clues to suspect PSP syndrome of monogenic origin. In addition, a diagnostic algorithm is proposed that may be useful to guide the genetic diagnosis once there is clinical suspicion of a monogenic PSP syndrome.

Parkin beyond Parkinson’s Disease—A Functional Meaning of Parkin Downregulation in TDP-43 Proteinopathies

Parkin and PINK1 are key regulators of mitophagy, an autophagic pathway for selective elimination of dysfunctional mitochondria. To this date, parkin depletion has been associated with recessive early onset Parkinson’s disease (PD) caused by loss-of-function mutations in the PARK2 gene, while, in sporadic PD, the activity and abundance of this protein can be compromised by stress-related modifications. Intriguingly, research in recent years has shown that parkin depletion is not limited to PD but is also observed in other neurodegenerative diseases—especially those characterized by TDP-43 proteinopathies, such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Here, we discuss the evidence of parkin downregulation in these disease phenotypes, its emerging connections with TDP-43, and its possible functional implications.

Aberrant Stress Granule Dynamics and Aggrephagy in ALS Pathogenesis

Stress granules are conserved cytosolic ribonucleoprotein (RNP) compartments that undergo dynamic assembly and disassembly by phase separation in response to stressful conditions. Gene mutations may lead to aberrant phase separation of stress granules eliciting irreversible protein aggregations. A selective autophagy pathway called aggrephagy may partially alleviate the cytotoxicity mediated by these protein aggregates. Cells must perceive when and where the stress granules are transformed into toxic protein aggregates to initiate autophagosomal engulfment for subsequent autolysosomal degradation, therefore, maintaining cellular homeostasis. Indeed, defective aggrephagy has been causally linked to various neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). In this review, we discuss stress granules at the intersection of autophagy and ALS pathogenesis.