Biology subjects

Mojsilovic-Petrovic, J.

Publications and source records attributed to Mojsilovic-Petrovic, J..

4 recordsLinked to original sources

bioRxiv2025

The molecular mechanism of uptake and cell-to-cell transmission of arginine-containing dipeptide repeat proteins.

Micro-satellite repeat expansion of the 5 GGGGCC 3 sequence in the C9orf72 gene is the most common monogenic form of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Dipeptide repeat proteins (DPRs) translated from the mutant allele can be detected in postmortem brains of afflicted individuals. The arginine containing peptides, poly-PR and poly-GR, are particularly noxious to cells. Both have been shown to undergo cell-cell transmission, but the underlying mechanisms are not understood. We found rapid internalization and nucleolar localization of bath-applied hemagglutinin (HA) tagged poly-PR with twenty repeats (HA-PR20) in cell lines and neurons. Small molecule and RNAi approaches implicated a temperature-dependent, fluid phase endocytosis mechanism in HA-PR20 uptake. We sought to identify DPR-related cell surface uptake factors using a high-resolution proximity labeling technique developed in the MacMillan group, termed {micro}Map. DPR-iridium conjugates identified candidate cell-surface proteins which were interrogated in an RNAi screen. Focusing on our strongest candidate, chondroitin sulfate proteoglycan 4 (CSPG4), we showed that cellular uptake of HA-PR20 is blocked by inhibition of glycosaminoglycan chain synthesis (using drugs or RNAi) and knockdown or ablation of CSPG4 (using RNAi or CRISPR editing). Reduction of CSPG4 protected PR20-induced neuronal toxicity. We used a dual reporter system to interrogate in vitro neuron-to-neuron transmission of PR50 and found that PR50 synthesized by one neuron readily spread to neighboring neurons. Transmission was significantly reduced when CSPG4 was knocked down. These results suggest CSPG4 is an important factor in poly-PR internalization and transmission and therefore may be a therapeutic target to slow DPR transmission and disease progression. Significance StatementA GGGGCC hexanucleotide repeat expansion in the C9orf72 gene is the most common monogenic form of ALS/FTD. This expansion leads to dipeptide repeat protein (DPR) production through non-canonical translation of repeat-containing RNA. DPRs have been shown to transmit between cells, but how this occurs is not well understood. We identified the cell surface protein chondroitin sulfate proteoglycan 4 (CSPG4) as a mediator of the uptake and intercellular spread of toxic arginine-rich DPRs. Targeting CSPG4 may provide a strategy to block DPR transmission and slow disease progression.

neuroscience↗

bioRxiv2025

Ubiquitin Proteasome System Components, RAD23A and USP13, Modulate TDP-43 Solubility and Neuronal Toxicity

At autopsy, >95% of ALS cases display a redistribution of the essential RNA binding protein TDP-43 from the nucleus into cytoplasmic aggregates. The mislocalization and aggregation of TDP-43 is believed to be a key pathological driver in ALS. Due to its vital role in basic cellular mechanisms, direct depletion of TDP-43 is unlikely to lead to a promising therapy. Therefore, we have explored the utility of identifying modifier genes that modify its mislocalization or aggregation. We have previously shown that loss of rad-23 improves locomotor deficits in TDP-43 C. elegans models of disease and increases the degradation rate of TDP-43 in cellular models. To understand the mechanism through which these protective effects occur, we generated an inducible mutant TDP-43 HEK293 cell line. We find that knockdown of RAD23A reduces insoluble TDP-43 levels in this model and primary rat cortical neurons expressing human TDP-43A315T. Utilizing a discovery-based proteomics approach, we then explored how loss of RAD23A remodels the proteome. Through this proteomic screen, we identified USP13, a deubiquitinase, as a new potent modifier of TDP-43 induced aggregation and cytotoxicity. We find that knockdown of USP13 reduces the abundance of sarkosyl insoluble mTDP-43 in both our HEK293 model and primary rat neurons, reduces cell death in primary rat motor neurons, and improves locomotor deficits in C. elegans ALS models. Significance StatementAmyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease (NDD) with no effective therapies. The mislocalization and aggregation of TAR DNA binding protein 43 (TDP-43) is a key pathological marker of ALS and other NDDs. Due to its vital functions, targeted therapeutic reduction of TDP-43 could be problematic. Here, we have explored the utility of targeting modifier genes. We find that knockdown of two members of the ubiquitin proteasome system, RAD23A and USP13, enhance TDP-43 solubility and decrease TDP-43 induced neurotoxicity.

neuroscience↗

bioRxiv2021

Neurons undergo pathogenic metabolic reprograming in models of familial ALS

Normal cellular function requires a rate of ATP production sufficient to meet demand. In most neurodegenerative diseases (including Amyotrophic Lateral Sclerosis, ALS), mitochondrial dysfunction is postulated raising the possibility of impaired ATP production and a need for compensatory maneuvers to sustain the ATP production/demand balance. We find in our rodent models of familial ALS (fALS), impairment in neuronal glycolytic flux with maintained or enhanced activity of the citric acid cycle. This rewiring of metabolism is associated with normal ATP levels and redox status, supporting the notion that mitochondrial function is not compromised in neurons expressing fALS genes. Genetic loss-of-function manipulation of individual steps in the glycolysis and the pentose phosphate pathway blunt the negative phenotypes seen in various fALS models. We propose that neurons adjust fuel utilization in the setting of neurodegenerative disease-associated mitochondrial dysfunction in a baleful manner and targeting this process can be healthful.

neuroscience↗

bioRxiv2021

The nuclear ubiquitin ligase adaptor SPOP is a conserved regulator of C9orf72 dipeptide toxicity

A hexanucleotide repeat expansion in the C9orf72 gene is the most common cause of inherited amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Unconventional translation of the C9orf72 repeat produces dipeptide repeat proteins (DPRs). Previously, we showed that the DPRs (PR)50 and (GR)50 are highly toxic when expressed in C. elegans and this toxicity depends on nuclear localization of the DPR. In an unbiased genome-wide RNAi screen for suppressors of (PR)50 toxicity, we identified 12 genes that consistently suppressed either the developmental arrest and/or paralysis phenotype evoked by (PR)50 expression. All of these genes have vertebrate homologs and 7/12 contain predicted nuclear localization signals. One of these genes was spop-1, the C. elegans homolog of SPOP, a nuclear localized E3 ubiquitin ligase adaptor only found in metazoans. SPOP is also required for (GR)50 toxicity and functions in a genetic pathway that includes cul-3, which is the canonical E3 ligase partner for SPOP. Genetic or pharmacological inhibition of SPOP in mammalian primary spinal cord motor neurons suppressed DPR toxicity without affecting DPR expression levels. Finally, we find that genetic inhibition of bet-1, the C. elegans homolog of the known SPOP ubiquitination targets BRD2/3/4, suppresses the protective effect of SPOP mutations. Together, these data suggest a model in which SPOP promotes the DPR-dependent ubiquitination and degradation of BRD proteins. We speculate the pharmacological manipulation of this pathway, which is currently underway for multiple cancer subtypes, could also represent a novel entry point for therapeutic intervention to treat C9 FTD/ALS. Significance statementThe G4C2 repeat expansion in the C9orf72 gene is a major cause of Fronto-Temporal Dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS). Unusual translation of the repeat sequence produces two highly toxic dipeptide repeat proteins, PRX and GRX, which accumulate in the brain tissue of individuals with these diseases. Here, we show that PR and GR toxicity in both C. elegans and mammalian neurons depends on the E3 ubiquitin ligase adaptor SPOP. SPOP acts through the bromodomain protein BET-1 to mediate dipeptide toxicity. SPOP inhibitors, which are currently being developed to treat SPOP-dependent renal cancer, also protect neurons against DPR toxicity. Our findings identify a highly conserved and druggable pathway that may represent a new strategy for treating these currently incurable diseases.

neuroscience↗