Neuronal activity regulates Matrin 3 abundance and function in a calcium-dependent manner through calpain-mediated cleavage and calmodulin binding.

RNA-binding protein (RBP) dysfunction is a fundamental hallmark of amyotrophic lateral sclerosis (ALS) and related neuromuscular disorders. Abnormal neuronal excitability is also a conserved feature in ALS patients and disease models, yet little is known about how activity-dependent processes regulate RBP levels and functions. Mutations in the gene encoding the RBP Matrin 3 (MATR3) cause familial disease, and MATR3 pathology has also been observed in sporadic ALS, suggesting a key role for MATR3 in disease pathogenesis. Here, we show that glutamatergic activity drives MATR3 degradation through an NMDA receptor-, Ca2+-, and calpain-dependent mechanism. The most common pathogenic MATR3 mutation renders it resistant to calpain degradation, suggesting a link between activity-dependent MATR3 regulation and disease. We also demonstrate that Ca2+ regulates MATR3 through a nondegradative process involving the binding of Ca2+/calmodulin to MATR3 and inhibition of its RNA-binding ability. These findings indicate that neuronal activity impacts both the abundance and function of MATR3, underscoring the effect of activity on RBPs and providing a foundation for further study of Ca2+-coupled regulation of RBPs implicated in ALS and related neurological diseases.

The Emotional Impact of Novel Coronavirus on Healthcare Workers: A Cross-Sectional Study.

Introduction Healthcare workers (HCWs) are the foundation of the response to a pandemic. Also termed as frontline workers, not only are they at a health risk but also suffer from emotional and psychological stress. Objective The objective of the study was to determine the emotional impact of novel coronavirus on healthcare workers. Methodology An online survey was completed by 239 HCWs from five different countries during the peak of the coronavirus disease 2019 (COVID-19) outbreak amidst the lockdown. Their feelings and concerns as well as the safety measures they adopted were identified. Results The response rate was 100%. Most of the respondents were 20-40 years old (85.36%) and working as doctors (73.22%); 44.77% were working at middle grade. The majority felt confused (19.67%), whereas others felt stressed/overworked (17.15%), unhappy (16.74%), scared (13.81%), nervous (13.39%), motivated (8.79%), and privileged (5.86%). A few felt pressurized to perform their duty (4.6%), and 69.87% felt that it was their moral obligation to continue their duty, whereas 13.39% felt administrative pressure for the same. Of the respondents, 53.97% feared transferring the disease to their family and friends, while others feared the lack of personal protective equipment (PPE) (13.39%). According to the majority of the respondents (25.94%), support from family and friends had them going through the crisis. The most common safety measure adopted by the HCWs was strict hand hygiene (43.51%). The HCWs (28.87%) felt that adequate and easy access to PPE would have helped them better during the pandemic. Conclusion Healthcare institutions are responsible for protecting HCWs or frontline workers during pandemics so they can continue with their duty. From our study, we have concluded that simple protective measures as uninterrupted and easy access to PPE would have helped HCWs deal with their stress and concerns.

Development of a specific live-cell assay for native autophagic flux.

Autophagy is an evolutionarily conserved pathway mediating the breakdown of cellular proteins and organelles. Emphasizing its pivotal nature, autophagy dysfunction contributes to many diseases; nevertheless, development of effective autophagy modulating drugs is hampered by fundamental deficiencies in available methods for measuring autophagic activity or flux. To overcome these limitations, we introduced the photoconvertible protein Dendra2 into the MAP1LC3B locus of human cells via CRISPR/Cas9 genome editing, enabling accurate and sensitive assessments of autophagy in living cells by optical pulse labeling. We used this assay to perform high-throughput drug screens of four chemical libraries comprising over 30,000 diverse compounds, identifying several clinically relevant drugs and novel autophagy modulators. A select series of candidate compounds also modulated autophagy flux in human motor neurons modified by CRISPR/Cas9 to express GFP-labeled LC3. Using automated microscopy, we tested the therapeutic potential of autophagy induction in several distinct neuronal models of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In doing so, we found that autophagy induction exhibited discordant effects, improving survival in disease models involving the RNA binding protein TDP-43, while exacerbating toxicity in neurons expressing mutant forms of UBQLN2 and C9ORF72 associated with familial ALS/FTD. These studies confirm the utility of the Dendra2-LC3 assay, while illustrating the contradictory effects of autophagy induction in different ALS/FTD subtypes.

Matrin 3 in neuromuscular disease: physiology and pathophysiology.

RNA-binding proteins (RBPs) are essential factors required for the physiological function of neurons, muscle, and other tissue types. In keeping with this, a growing body of genetic, clinical, and pathological evidence indicates that RBP dysfunction and/or gene mutation leads to neurodegeneration and myopathy. Here, we summarize the current understanding of matrin 3 (MATR3), a poorly understood RBP implicated not only in ALS and frontotemporal dementia but also in distal myopathy. We begin by reviewing MATR3's functions, its regulation, and how it may be involved in both sporadic and familial neuromuscular disease. We also discuss insights gleaned from cellular and animal models of MATR3 pathogenesis, the links between MATR3 and other disease-associated RBPs, and the mechanisms underlying RBP-mediated disorders.

TDP-43 Nuclear Bodies: A NEAT Response to Stress?

In this issue of Molecular Cell, Wang et al. (2020) investigate stress-induced nuclear condensates of the RNA-binding protein TDP-43, uncovering a protective function for these granules as well as an RNA-dependent mechanism for scaffolding them.

DDX3X and specific initiation factors modulate FMR1 repeat-associated non-AUG-initiated translation.

A CGG trinucleotide repeat expansion in the 5' UTR of FMR1 causes the neurodegenerative disorder Fragile X-associated tremor/ataxia syndrome (FXTAS). This repeat supports a non-canonical mode of protein synthesis known as repeat-associated, non-AUG (RAN) translation. The mechanism underlying RAN translation at CGG repeats remains unclear. To identify modifiers of RAN translation and potential therapeutic targets, we performed a candidate-based screen of eukaryotic initiation factors and RNA helicases in cell-based assays and a Drosophila melanogaster model of FXTAS. We identified multiple modifiers of toxicity and RAN translation from an expanded CGG repeat in the context of the FMR1 5'UTR. These include the DEAD-box RNA helicase belle/DDX3X, the helicase accessory factors EIF4B/4H, and the start codon selectivity factors EIF1 and EIF5. Disrupting belle/DDX3X selectively inhibited FMR1 RAN translation in Drosophila in vivo and cultured human cells, and mitigated repeat-induced toxicity in Drosophila and primary rodent neurons. These findings implicate RNA secondary structure and start codon fidelity as critical elements mediating FMR1 RAN translation and identify potential targets for treating repeat-associated neurodegeneration.

An Intramolecular Salt Bridge Linking TDP43 RNA Binding, Protein Stability, and TDP43-Dependent Neurodegeneration.

The majority of individuals with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) exhibit neuronal cytoplasmic inclusions rich in the RNA binding protein TDP43. Even so, the relation between the RNA binding properties of TDP43 and neurodegeneration remains obscure. Here, we show that engineered mutations disrupting a salt bridge between the RNA recognition motifs of TDP43 interfere with RNA binding and eliminate the recognition of native TDP43 substrates. The same mutations dramatically destabilize TDP43, alter its subcellular localization, and abrogate TDP43-dependent neurodegeneration. Worms harboring homologous TDP-1 mutations phenocopy knockout strains, confirming the necessity of salt bridge residues for TDP43 function. Moreover, the accumulation of functional TDP43, but not RNA binding-deficient variants, disproportionately affects transcripts encoding ribosome and oxidative phosphorylation components. These studies demonstrate the significance of the salt bridge in sustaining TDP43 stability and RNA binding properties, factors that are crucial for neurodegeneration arising from TDP43 deposition in ALS and FTD.

Matrin 3-dependent neurotoxicity is modified by nucleic acid binding and nucleocytoplasmic localization.

Abnormalities in nucleic acid processing are associated with the development of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Mutations in Matrin 3 (MATR3), a poorly understood DNA- and RNA-binding protein, cause familial ALS/FTD, and MATR3 pathology is a feature of sporadic disease, suggesting that MATR3 dysfunction is integrally linked to ALS pathogenesis. Using a rat primary neuron model to assess MATR3-mediated toxicity, we noted that neurons were bidirectionally vulnerable to MATR3 levels, with pathogenic MATR3 mutants displaying enhanced toxicity. MATR3's zinc finger domains partially modulated toxicity, but elimination of its RNA recognition motifs had no effect on survival, instead facilitating its self-assembly into liquid-like droplets. In contrast to other RNA-binding proteins associated with ALS, cytoplasmic MATR3 redistribution mitigated neurodegeneration, suggesting that nuclear MATR3 mediates toxicity. Our findings offer a foundation for understanding MATR3-related neurodegeneration and how nucleic acid binding functions, localization, and pathogenic mutations drive sporadic and familial disease.

The kinetic characterization and X-ray structure of a putative benzoylformate decarboxylase from M. smegmatis highlights the difficulties in the functional annotation of ThDP-dependent enzymes.

Benzoylformate decarboxylase (BFDC) is a thiamin diphosphate (ThDP)-dependent enzyme that catalyzes the nonoxidative decarboxylation of benzoylformate. It is the penultimate enzyme in both the mandelate pathway and the d-phenylglycine degradation pathway. The ThDP-dependent Enzyme Engineering Database (TEED) now lists more than 800 sequences annotated as BFDCs, including one from Mycobacterium smegmatis (MsBFDC). However, there is no evidence that either pathway for benzoylformate formation exists in the M. smegmatis genome. Further, sequence alignments of MsBFDC with the well characterized enzyme isolated from Pseudomonas putida (PpBFDC) indicate that there will be active site substitutions in MsBFDC likely to reduce activity with benzoylformate. Taken together these data would suggest that the annotation is unlikely to be correct. To test this hypothesis the putative MsBFDC was cloned, expressed, purified, and the X-ray structure was solved to a resolution of 2.2Å. While showing no evidence for ThDP in the active site, the structure was very similar to that of PpBFDC. A number of 2-oxo acids were tested as substrates. For MsBFDC the K(m) value for benzoylformate was ~23 mM, nearly 100-fold greater than that of PpBFDC while the k(cat) value was reduced 60-fold. These values would suggest that benzoylformate is not the physiological substrate for this enzyme, and that annotation as a 2-oxo acid decarboxylase may be more appropriate.

Abnormal mineralization of the Ts65Dn Down syndrome mouse appendicular skeleton begins during embryonic development in a Dyrk1a-independent manner.

The relationship between gene dosage imbalance and phenotypes associated with Trisomy 21, including the etiology of abnormal bone phenotypes linked to Down syndrome (DS), is not well understood. The Ts65Dn mouse model for DS exhibits appendicular skeletal defects during adolescence and adulthood but the developmental and genetic origin of these phenotypes remains unclear. It is hypothesized that the postnatal Ts65Dn skeletal phenotype originates during embryonic development and results from an increased Dyrk1a gene copy number, a gene hypothesized to play a critical role in many DS phenotypes. Ts65Dn embryos exhibit a lower percent bone volume in the E17.5 femur when compared to euploid embryos. Concomitant with gene copy number, qPCR analysis revealed a ~1.5 fold increase in Dyrk1a transcript levels in the Ts65Dn E17.5 embryonic femur as compared to euploid. Returning Dyrk1a copy number to euploid levels in Ts65Dn, Dyrk1a(+/-) embryos did not correct the trisomic skeletal phenotype but did return Dyrk1a gene transcript levels to normal. The size and protein expression patterns of the cartilage template during embryonic bone development appear to be unaffected at E14.5 and E17.5 in trisomic embryos. Taken together, these data suggest that the dosage imbalance of genes other than Dyrk1a is involved in the development of the prenatal bone phenotype in Ts65Dn embryos.

Prospective randomized study of N-acetylcysteine, fenoldopam, and saline for prevention of radiocontrast-induced nephropathy.

The objective of this study was to compare the efficacy of N-acetylcysteine (NAC), fenoldopam, and saline in preventing radiocontrast-induced nephropathy (RCIN) in high-risk patients undergoing cardiovascular procedures. We prospectively enrolled 123 patients who were scheduled for cardiovascular procedures and had a baseline creatinine > 1.6 mg/dl or creatinine clearance of < 60 ml/min. Patients were randomly assigned to receive either saline (0.45% normal saline at 1 cc/kg) for 12 hr before and 12 hr after the procedure, or fenoldopam (0.1 microg/kg/min) plus saline for 4 hr prior and 4 hr after the procedure, or NAC orally (600 mg) plus saline every 12 hr for 24 hr prior and 24 hr after the procedure. All the patients received low-osmolality nonionic contrast. RCIN was defined as an increase in creatinine level > 0.5 mg/dl after 48 hr. The incidence of RCIN was 17.7% in the NAC group, 15.3% in the saline group, and 15.7% in the fenoldopam group (P = 0.919). Of the 20 patients who developed RCIN, 2 required dialysis. Serum creatinine decreased after 48 hr (vs. baseline) in 38% patients in the NAC group, 18% in the fenoldopam group, and 15% in the saline group. In patients with chronic renal insufficiency, NAC or fenoldopam offered no additional benefit over hydration with saline in preventing RCIN.