A behavioral screen for mediators of age-dependent TDP-43 neurodegeneration identifies SF2/SRSF1 among a group of potent suppressors in both neurons and glia

Abstract

Cytoplasmic aggregation of Tar-DNA/RNA binding protein 43 (TDP-43) occurs in 97 percent of amyotrophic lateral sclerosis (ALS), about 40 percent of frontotemporal dementia (FTD) and in many cases of Alzheimers disease (AD). Cytoplasmic TDP-43 inclusions are seen in both sporadic and familial forms of these disorders, including those cases that are caused by repeat expansion mutations in the C9orf72 gene. To identify downstream mediators of TDP-43 toxicity, we expressed human TDP-43 in a subset of Drosophila motor neurons. Such expression causes age-dependent deficits in negative geotaxis behavior. Using this behavioral readout of locomotion, we conducted an shRNA suppressor screen and identified 32 transcripts whose knockdown was sufficient to ameliorate the neurological phenotype. The majority of these suppressors also substantially suppressed the negative effects on lifespan seen with glial TDP-43 expression. In addition to identification of a number of genes whose roles in neurodegeneration were not previously known, our screen also yielded genes involved in chromatin regulation and nuclear import-export pathways that were previously identified in the context of cell based or neurodevelopmental suppressor screens. A notable example is SF2, a conserved orthologue of mammalian SRSF1, an RNA binding protein with roles in splicing and nuclear export. Our identification SF2/SRSF1 as a potent suppressor of both neuronal and glial TDP-43 toxicity also provides a convergence with C9orf72 expansion repeat mediated neurodegeneration, where this gene also acts as a downstream mediator.

Identification of potential pathways and biomarkers linked to progression in ALS

“…Two hits were recently identified in an independent genome‐wide screen in TDP‐43‐expressing flies and correspond to fly homologues of ARIDB1 and WAPL, 38 confirming their specificity. MED23 is relevant because subunits of the Mediator complex suppressed TDP‐43 toxicity in another screen 39 and interact with WAPL, 40 suggesting its importance in disease pathogenesis. TUBB2A transcripts were dysregulated in the axonal compartment of TDP‐43‐depleted motor neurons 41 .…”

Peptides that Mimic RS repeats modulate phase separation of SRSF1, revealing a reliance on combined stacking and electrostatic interactions

“…The protein SRSF1 (Serine/Arginine-Rich Splicing Factor 1, also known as ASF/SF2) is essential for the early-stage assembly of the spliceosome (15,16). Several in vivo studies have shown that SRSF1 is found in condensates (5,(17)(18)(19)(20)(21)(22). Aberrant condensation behaviors have also been observed in disease states (20)(21)(22).…”

“…Several in vivo studies have shown that SRSF1 is found in condensates (5,(17)(18)(19)(20)(21)(22). Aberrant condensation behaviors have also been observed in disease states (20)(21)(22). SRSF1 belongs to the Ser/Arg-rich protein family (SR proteins), which contains 12 members possessing one to two structured RNA-recognition motifs (RRMs) and a repetitive Arg/Ser repeat region (RS domain) (23)(24)(25).…”

Modelling dementia inDrosophilauncovers shared and specific targets of TDP-43 proteinopathy across ALS and FTD relevant circuits

“…Models of TDP-43 proteinopathy in Drosophila have recapitulated the locomotor phenotypes, motor neuron dysfunction, and shortened lifespan (Estes et al, 2011;Li et al, 2010;Romano et al, 2012) observed in ALS and highlighted degeneration in central brain structures (Li et al, 2010) reminiscent of FTD. Beyond simply simulating disease states, these fly models have identified translational targets (Coyne et al, 2017;Coyne et al, 2014;Lehmkuhl et al, 2021) and genetic modifiers of TDP-43 proteinopathy (Azpurua et al, 2021;Coyne et al, 2015;Sreedharan et al, 2015;Zhan et al, 2013), and exposed systemic effects on metabolic pathways (Loganathan et al, 2022;Manzo et al, 2019).…”