Reduced C9orf72 expression exacerbates polyGR toxicity in patient iPSC-derived motor neurons and a Type I protein arginine methyltransferase inhibitor reduces that toxicity

Introduction

Intronic repeat expansions in the C9orf72 gene are the most frequent known single genetic causes of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). These repeat expansions are believed to result in both loss-of-function and toxic gain-of-function. Gain-of-function results in the production of toxic arginine-rich dipeptide repeat proteins (DPRs), namely polyGR and polyPR. Small-molecule inhibition of Type I protein arginine methyltransferases (PRMTs) has been shown to protect against toxicity resulting from polyGR and polyPR challenge in NSC-34 cells and primary mouse-derived spinal neurons, but the effect in human motor neurons (MNs) has not yet been explored.

Methods

To study this, we generated a panel of C9orf72 homozygous and hemizygous knockout iPSCs to examine the contribution of C9orf72 loss-of-function toward disease pathogenesis. We differentiated these iPSCs into spinal motor neurons (sMNs).

Results

We found that reduced levels of C9orf72 exacerbate polyGR15 toxicity in a dose-dependent manner. Type I PRMT inhibition was able to partially rescue polyGR15 toxicity in both wild-type and C9orf72-expanded sMNs.

Discussion

This study explores the interplay of loss-of-function and gain-of-function toxicity in C9orf72 ALS. It also implicates type I PRMT inhibitors as a possible modulator of polyGR toxicity.

Hypothesis and Theory: Roles of Arginine Methylation in C9orf72-Mediated ALS and FTD

Hexanucleotide repeat expansion (G4C2_n) mutations in the gene C9ORF72 account for approximately 30% of familial cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), as well as approximately 7% of sporadic cases of ALS. G4C2_n mutations are known to result in the production of five species of dipeptide repeat proteins (DRPs) through non-canonical translation processes. Arginine-enriched dipeptide repeat proteins, glycine-arginine (polyGR), and proline-arginine (polyPR) have been demonstrated to be cytotoxic and deleterious in multiple experimental systems. Recently, we and others have implicated methylation of polyGR/polyPR arginine residues in disease processes related to G4C2_n mutation-mediated neurodegeneration. We previously reported that inhibition of asymmetric dimethylation (ADMe) of arginine residues is protective in cell-based models of polyGR/polyPR cytotoxicity. These results are consistent with the idea that PRMT-mediated arginine methylation in the context of polyGR/polyPR exposure is harmful. However, it remains unclear why. Here we discuss the influence of arginine methylation on diverse cellular processes including liquid-liquid phase separation, chromatin remodeling, transcription, RNA processing, and RNA-binding protein localization, and we consider how methylation of polyGR/polyPR may disrupt processes essential for normal cellular function and survival.

Type I PRMT Inhibition Protects Against C9ORF72 Arginine-Rich Dipeptide Repeat Toxicity

Repeat expansion mutations in the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Repeat-associated non-AUG translation of this expansion produces dipeptide repeat proteins (DRPs). The arginine containing DRPs, polyGR and polyPR, are consistently reported to be the most toxic. Here we demonstrated that small molecule inhibition of type I protein arginine methyltransferases (PRMT) protects against polyGR and polyPR toxicity. Furthermore, our findings suggest that asymmetric dimethylation of polyGR and polyPR by Type I PRMTs plays important roles in their cytotoxicity.

Association between Oral Candida and Bacteriome in Children with Severe ECC

Candida albicans is an opportunistic fungal organism frequently detected in the oral cavity of children with severe early childhood caries (S-ECC). Previous studies suggested the cariogenic potential of C. albicans, in vitro and in vivo, and further demonstrated its synergistic interactions with Streptococcus mutans. In combination, the 2 organisms are associated with higher caries severity in a rodent model. However, it remains unknown whether C. albicans influences the composition and diversity of the entire oral bacterial community to promote S-ECC onset. With 16s rRNA amplicon sequencing, this study analyzed the microbiota of saliva and supragingival plaque from 39 children (21 S-ECC and 18 caries-free [CF]) and 33 mothers (17 S-ECC and 16 CF). The results revealed that the presence of oral C. albicans is associated with a highly acidogenic and acid-tolerant bacterial community in S-ECC, with an increased abundance of plaque Streptococcus (particularly S. mutans) and certain Lactobacillus/Scardovia species and salivary/plaque Veillonella and Prevotella, as well as decreased levels of salivary/plaque Actinomyces. Concurrent with this microbial community assembly, the activity of glucosyltransferases (cariogenic virulence factors secreted by S. mutans) in plaque was significantly elevated when C. albicans was present. Moreover, the oral microbial community composition and diversity differed significantly by disease group (CF vs. S-ECC) and sample source (saliva vs. plaque). Children and mothers within the CF and S-ECC groups shared microbiota composition and diversity, suggesting a strong maternal influence on children's oral microbiota. Altogether, this study underscores the importance of C. albicans in association with the oral bacteriome in the context of S-ECC etiopathogenesis. Further longitudinal studies are warranted to examine how fungal-bacterial interactions modulate the onset and severity of S-ECC, potentially leading to novel anticaries treatments that address fungal contributions.

Familial transmission of leprosy in post-war Britain--discrimination and dissent

A Polish immigrant, who was resident in the United Kingdom (UK), presented with lepromatous leprosy and was detained in two hospitals against his wishes in the late 1940s. The public reaction to his diagnosis was remarkable, with street riots and questions in the Houses of Parliament about 'this leper'. His wife was persecuted and had to change her name. The index patient died of tuberculosis during enforced isolation in hospital, and several years later his daughter (who had never left the UK) presented with a left median nerve palsy and probable lepromatous dactylitis of the left third finger, eventually requiring amputation and prolonged dapsone treatment. Her disease resolved slowly but completely. We believe these two familial cases represent the first documented episode of autochthonous leprosy transmission in the UK since the early 1920s. They also demonstrate the ability of this disease to engender fear, dissent and discrimination amongst the public. Parallels are drawn with reactions to the cholera epidemics in nineteenth century Britain, and to HIV/AIDS, SARS and multi-drug resistant tuberculosis in more recent times.

Leprosy in Britain: 50 years experience in Liverpool

BACKGROUND

Leprosy is a chronic infection that presents with varying dermal and neurological symptoms, and which can lead to extensive disability and morbidity, often with accompanying social stigma.

AIM

To review the patients presenting to the Liverpool School of Tropical Medicine (LSTM) between 1946 and 2003, looking specifically at country of birth and of infection, details of clinical presentation, diagnosis, management and reactions.

DESIGN

Retrospective record review.

METHODS

We retrieved all available clinical records for patients seen between 1946 and 2003 (n = 50), consisting of letters, hospital and LSTM casenotes, and some radiographs and photographs. Any history of tuberculosis or diabetes was recorded.

RESULTS

Most patients (64%) were born in the Indian subcontinent, and most were thought to have contracted the disease there (62%). Features at presentation included anaesthetic skin lesions in 19 (36%), hypopigmentation in 15 (30%), and peripheral nerve enlargement in 25 (50%). Diagnoses were made by a combination of clinical data and biopsy (60%), and slit skin smears were positive for acid-fast bacilli in 61% of multibacillary patients. Initial presentation was with a leprosy reaction in five cases (10%), and reactions were documented in 42% of all patients. Treatments were varied, progressing from traditional Eastern medicine to the WHO-approved multidrug therapy in use today, with prophylaxis for children and close contacts.

DISCUSSION

Leprosy remains an important diagnosis to consider in patients with a history of work or travel in the tropics, and is a diagnosis with far-reaching medical, social and emotional consequences.

High-pressure treatment of milk: effects on casein micelle structure and on enzymic coagulation

High isostatic pressures up to 600 MPa were applied to samples of skim milk before addition of rennet and preparation of cheese curds. Electron microscopy revealed the structure of rennet gels produced from pressure-treated milks. These contained dense networks of fine strands, which were continuous over much bigger distances than in gels produced from untreated milk, where the strands were coarser with large interstitial spaces. Alterations in gel network structure gave rise to differences in rheology with much higher values for the storage moduli in the pressure-treated milk gels. The rate of gel formation and the water retention within the gel matrix were also affected by the processing of the milk. Casein micelles were disrupted by pressure and disruption appeared to be complete at treatments of 400 MPa and above. Whey proteins, particularly beta-lactoglobulin, were progressively denatured as increasing pressure was applied, and the denatured beta-lactoglobulin was incorporated into the rennet gels. Pressure-treated micelles were coagulated rapidly by rennet, but the presence of denatured beta-lactoglobulin interfered with the secondary aggregation phase and reduced the overall rate of coagulation. Syneresis from the curds was significantly reduced following treatment of the milk at 600 MPa, probably owing to the effects of a finer gel network and increased inclusion of whey protein. Levels of syneresis were more similar to control samples when the milk was treated at 400 MPa or less.