Deletion of ubiquitin ligase Nedd4l exacerbates ischemic brain damage

Ubiquitination by Nedd4 (neuronally expressed developmentally downregulated 4) family of HECT type E3 ligases plays a key role in degrading misfolded and damaged proteins, and its disruption leads to neurodegeneration. Parkinson's disease-causing protein alpha-Synuclein (alpha-Syn) is ubiquitinated by the Nedd4 family and degraded by endosomes. Nedd4l is the only Nedd4 homolog that showed upregulation in post-stroke surviving cortical neurons where it correlated with neuroprotection. We tested the role of Nedd4l after stroke by subjecting the Nedd4l(-/-)mice to transient middle cerebral artery occlusion. Focal ischemia significantly increased Nedd4l expression and poly-ubiquitinated alpha-Syn levels, and knockout of Nedd4l reduced post-ischemic poly-ubiquitinated alpha-Syn that is majorly located in the peri-infarct neurons. Co-immunoprecipitation further shows that focal ischemia enhances the alpha-Syn-Nedd4l interaction resulting in increased ubiquitination of alpha-Syn. Nedd4l knockout mice (n = 7 mice/group) showed exacerbated post-ischemic motor dysfunction manifested by decreased time on the rotarod and increased number of foot faults, and significantly increased ischemic brain damage. This suggests that Nedd4l might be a potential therapeutic target to minimize alpha-Syn-mediated toxicity after cerebral ischemia.