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Deletion of ubiquitin ligase Nedd4l exacerbates ischemic brain damage.

ABSTRACT: 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 α-Synuclein (α-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 α-Syn levels, and knockout of Nedd4l reduced post-ischemic poly-ubiquitinated α-Syn that is majorly located in the peri-infarct neurons. Co-immunoprecipitation further shows that focal ischemia enhances the α-Syn-Nedd4l interaction resulting in increased ubiquitination of α-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 α-Syn-mediated toxicity after cerebral ischemia.

SUBMITTER: Kim T

PROVIDER: S-EPMC8054722 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Stroke is one of the leading causes of morbidity and mortality worldwide. Inflammation, oxidative stress, apoptosis, and excitotoxicity contribute to neuronal death during ischemic stroke; however, the mechanisms underlying these complicated pathophysiological processes remain to be fully elucidated. Here, we found that the expression of tumor necrosis factor receptor-associated factor 6 (TRAF6) was markedly increased after cerebral ischemia/reperfusion (I/R) in mice. TRAF6 ablation in male mice decreased the infarct volume and neurological deficit scores and decreased proinflammatory signaling, oxidative stress, and neuronal death after cerebral I/R, whereas transgenic overexpression of TRAF6 in male mice exhibited the opposite effects. Mechanistically, we demonstrated that TRAF6 induced Rac1 activation and consequently promoted I/R injury by directly binding and ubiquitinating Rac1. Either functionally mutating the TRAF6 ubiquitination site on Rac1 or inactivating Rac1 with a specific inhibitor reversed the deleterious effects of TRAF6 overexpression during I/R injury. In conclusion, our study demonstrated that TRAF6 is a key promoter of ischemic signaling cascades and neuronal death after cerebral I/R injury. Therefore, the TRAF6/Rac1 pathway might be a promising target to attenuate cerebral I/R injury.SIGNIFICANCE STATEMENT Stroke is one of the most severe and devastating neurological diseases globally. The complicated pathophysiological processes restrict the translation of potential therapeutic targets into medicine. Further elucidating the molecular mechanisms underlying cerebral ischemia/reperfusion injury may open a new window for pharmacological interventions to promote recovery from stroke. Our study revealed that ischemia-induced tumor necrosis factor receptor-associated factor 6 (TRAF6) upregulation binds and ubiquitinates Rac1 directly, which promotes neuron death through neuroinflammation and neuro-oxidative signals. Therefore, precisely targeting the TRAF6-Rac1 axis may provide a novel therapeutic strategy for stroke recovery.

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Deletion of ubiquitin ligase Nedd4l exacerbates ischemic brain damage.

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