A robust evaluation of TDP-43, poly GP, cellular pathology and behavior in an AAV-C9ORF72 (GC) mouse model.

The GC hexanucleotide repeat expansion in C9ORF72 is the major genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9-ALS/FTD). Despite considerable efforts, the development of mouse models of C9-ALS/FTD useful for therapeutic development has proven challenging due to the intricate interplay of genetic and molecular factors underlying this neurodegenerative disorder, in addition to species differences. This study presents a robust investigation of the cellular pathophysiology and behavioral outcomes in a previously described AAV mouse model of C9-ALS expressing 66 GC hexanucleotide repeats.

A robust evaluation of TDP-43, poly GP, cellular pathology and behavior in a AAV- C9ORF72 (G 4 C 2) 66 mouse model.

The GC hexanucleotide repeat expansion in the major genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9-ALS/FTD). Despite considerable efforts, the development of mouse models of C9-ALS/FTD useful for therapeutic development has proven challenging due to the intricate interplay of genetic and molecular factors underlying this neurodegenerative disorder, in addition to species differences. This study presents a robust investigation of the cellular pathophysiology and behavioral outcomes in a previously described AAV mouse model of C9-ALS expressing 66 GC hexanucleotide repeats.

A robust evaluation of TDP-43, poly GP, cellular pathology and behavior in a AAV-C9ORF72 (GC) mouse model.

The GC hexanucleotide repeat expansion in is the major genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9-ALS/FTD). Despite considerable efforts, the development of mouse models of C9-ALS/FTD useful for therapeutic development has proven challenging due to the intricate interplay of genetic and molecular factors underlying this neurodegenerative disorder, in addition to species differences. This study presents a robust investigation of the cellular pathophysiology and behavioral outcomes in a previously described AAV mouse model of C9-ALS expressing 66 GC hexanucleotide repeats.

Counter-regulation of RNA stability by UPF1 and TDP43.

RNA quality control is crucial for proper regulation of gene expression. Disruption of nonsense mediated mRNA decay (NMD), the primary RNA decay pathway responsible for the degradation of transcripts containing premature termination codons (PTCs), can disrupt development and lead to multiple diseases in humans and other animals. Similarly, therapies targeting NMD may have applications in hematological, neoplastic and neurological disorders.

Nuclear Pore Dysfunction in Neurodegeneration.

The nuclear pore complex (NPC) is a large multimeric structure that is interspersed throughout the membrane of the nucleus and consists of at least 33 protein components. Individual components cooperate within the nuclear pore to facilitate selective passage of materials between the nucleus and cytoplasm while simultaneously performing pore-independent roles throughout the cell. NPC dysfunction is a hallmark of neurodegenerative disorders including Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis (ALS).

Nuclear RNA binding regulates TDP-43 nuclear localization and passive nuclear export.

Nuclear clearance of the RNA-binding protein TDP-43 is a hallmark of neurodegeneration and an important therapeutic target. Our current understanding of TDP-43 nucleocytoplasmic transport does not fully explain its predominantly nuclear localization or mislocalization in disease. Here, we show that TDP-43 exits nuclei by passive diffusion, independent of facilitated mRNA export.

Polyadenylated RNA and RNA-Binding Proteins Exhibit Unique Response to Hyperosmotic Stress.

Stress granule formation is a complex and rapidly evolving process that significantly disrupts cellular metabolism in response to a variety of cellular stressors. Recently, it has become evident that different chemical stressors lead to the formation of compositionally distinct stress granules. However, it is unclear which proteins are required for the formation of stress granules under different conditions.

RNA Is a Double-Edged Sword in ALS Pathogenesis.

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease that affects upper and lower motor neurons. Familial ALS accounts for a small subset of cases (<10-15%) and is caused by dominant mutations in one of more than 10 known genes. Multiple genes have been causally or pathologically linked to both ALS and frontotemporal dementia (FTD).

Nuclear accumulation of CHMP7 initiates nuclear pore complex injury and subsequent TDP-43 dysfunction in sporadic and familial ALS.

Alterations in the components [nucleoporins (Nups)] and function of the nuclear pore complex (NPC) have been implicated as contributors to the pathogenesis of genetic forms of neurodegeneration including amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD). We hypothesized that Nup alterations and the consequential loss of NPC function may lie upstream of TDP-43 dysfunction and mislocalization widely observed in ALS, FTD, and related neurodegenerative diseases. Here, we provide evidence that CHMP7, a critical mediator of NPC quality control, is increased in nuclei of and sporadic ALS induced pluripotent stem cell (iPSC)-derived spinal neurons (iPSNs) and postmortem human motor cortex before the emergence of Nup alterations.

UPF1 reduces C9orf72 HRE-induced neurotoxicity in the absence of nonsense-mediated decay dysfunction.

Multiple cellular pathways have been suggested to be altered by the C9orf72 GGGGCC (GC) hexanucleotide repeat expansion (HRE), including aspects of RNA regulation such as nonsense-mediated decay (NMD). Here, we investigate the role that overexpression of UPF1, a protein involved in NMD, plays in mitigating neurotoxicity in multiple models of C9orf72 ALS/FTD. First, we show that NMD is not altered in our endogenous induced pluripotent stem cell (iPSC)-derived spinal neuron (iPSN) model of C9orf72 ALS (C9-ALS) or postmortem motor cortex tissue from C9-ALS patients.

GC Repeat RNA Initiates a POM121-Mediated Reduction in Specific Nucleoporins in C9orf72 ALS/FTD.

Through mechanisms that remain poorly defined, defects in nucleocytoplasmic transport and accumulations of specific nuclear-pore-complex-associated proteins have been reported in multiple neurodegenerative diseases, including C9orf72 Amyotrophic Lateral Sclerosis and Frontotemporal Dementia (ALS/FTD). Using super-resolution structured illumination microscopy, we have explored the mechanism by which nucleoporins are altered in nuclei isolated from C9orf72 induced pluripotent stem-cell-derived neurons (iPSNs). Of the 23 nucleoporins evaluated, we observed a reduction in a subset of 8, including key components of the nuclear pore complex scaffold and the transmembrane nucleoporin POM121.

Post-transcriptional Inhibition of Hsc70-4/HSPA8 Expression Leads to Synaptic Vesicle Cycling Defects in Multiple Models of ALS.

Amyotrophic lateral sclerosis (ALS) is a synaptopathy accompanied by the presence of cytoplasmic aggregates containing TDP-43, an RNA-binding protein linked to ∼97% of ALS cases. Using a Drosophila model of ALS, we show that TDP-43 overexpression (OE) in motor neurons results in decreased expression of the Hsc70-4 chaperone at the neuromuscular junction (NMJ). Mechanistically, mutant TDP-43 sequesters hsc70-4 mRNA and impairs its translation.

Failure to Deliver and Translate-New Insights into RNA Dysregulation in ALS.

Amyotrophic Lateral Sclerosis (ALS) is a progressive and fatal neurodegenerative disease affecting both upper and lower motor neurons. The molecular mechanisms underlying disease pathogenesis remain largely unknown. Multiple genetic loci including genes involved in proteostasis and ribostasis have been linked to ALS providing key insights into the molecular mechanisms underlying disease.

Fragile X protein mitigates TDP-43 toxicity by remodeling RNA granules and restoring translation.

RNA dysregulation is a newly recognized disease mechanism in amyotrophic lateral sclerosis (ALS). Here we identify Drosophila fragile X mental retardation protein (dFMRP) as a robust genetic modifier of TDP-43-dependent toxicity in a Drosophila model of ALS. We find that dFMRP overexpression (dFMRP OE) mitigates TDP-43 dependent locomotor defects and reduced lifespan in Drosophila.