The CUL3 adaptor protein SPOP plays a role in tauopathy mechanisms

Abstract

AbstractBackgroundThe pathological accumulation of the microtubule binding protein tau drives age‐related neurodegeneration in a variety of disorders, collectively called tauopathies. In the most common tauopathy, Alzheimer’s disease (AD), the accumulation of pathological tau strongly correlates with cognitive decline. The underlying molecular mechanisms that drive neurodegeneration in tauopathies remain unknown and no effective disease modifying pharmacological interventions for tauopathy currently exist.MethodsWe employed classical forward genetic approaches and identified multiple loss of function alleles in the C. elegans spop‐1 gene that ameliorate tauopathy, suggesting SPOP is required for tau mediated neurodegeneration. CRISPR based genome editing methodology enabled the generation of customized SPOP‐1 loss of function and null alleles. Molecular genetics, behavioral, neuronal reporter assays, and biochemical analyses were also employed to characterize the consequences of spop‐1 loss of function on tauopathy related phenotypes in model systems.ResultsKnockout of SPOP‐1 rescues tau mediated behavioral deficits caused by neuronal dysfunction in tau transgenic C. elegans. Biochemical analysis revealed that SPOP‐1 loss of function promotes clearance of phosphorylated and total tau species from C. elegans neurons, but no change in tau transgene mRNA levels. Tau transgenic animals exhibit obvious neurodegeneration of GABAergic neurons, but loss of spop‐1 rescues neurodegeneration. While SPOP functions as an CUL3 E3 ligase adaptor protein, CUL3 function is not required for SPOP loss of function rescue of tauopathy. Genetic epistasis analysis suggests the nuclear speckle resident poly(A) RNA binding protein sut‐2 and spop‐1 function in a parallel molecular pathway.ConclusionsSPOP is a novel modifier of tauopathy phenotypes. Combined with previous findings investigating ALYREF, PARN/TOE1, SUT‐1 and SUT‐2/MSUT2, this work suggests phase‐separated nuclear speckles are an important cellular site controlling susceptibility to pathological tau. Recent work showing SPOP modification of PR dipeptides derived from C9orf72 expansion suggests common pathways may be at work in the neurodegenerative molecular mechanisms of tauopathy and repeat dipeptides.