ABSTRACT: Posttranslational modifications with ubiquitin alter protein function and stability, thereby regulating cell homeostasis and viability, particularly under stress. Ischemic stroke induces protein ubiquitination at the periphery of the ischemic territory, wherein cells remain viable. Revealing the identity of ubiquitinated proteins, their cellular location, and the functional consequences of ubiquitin modification may shed light on the role of ubiquitination in ischemic injury. Here, we employed a proteomics approach to identify proteins ubiquitinated following ischemic stroke, induced by transient middle cerebral artery occlusion (tMCAO) in mice. We detected increased ubiquitination of 198 proteins, many of which localize to the postsynaptic density (PSD) of glutamatergic neurons. Among these were proteins essential for maintaining PSD architecture, such as PSD93, PSD95 and Shank3, as well as NMDA and AMPA receptor subunits. The largest enzymatic group at the PSD with high post-ischemic ubiquitination levels were kinases, such as CaMKII, PKC, Cdk5, and Pyk2, the aberrant activity of which contributes to post-ischemic neuronal death. Concurrent phospho-proteomics revealed altered phosphorylation patterns associated with the PSD, indicative of modified PSD kinase activity following stroke. CaMKII, PKC, and Cdk5 activity was decreased while Pyk2 activity was increased at the PSD after stroke, accompanied by the hypo- and hyper-phosphorylation of downstream targets, respectively. Removal of ubiquitin restored kinases’ activity to pre-stroke levels, identifying ubiquitination as the responsible molecular mechanism for post-ischemic kinase regulation. These findings unveil a previously unrecognized role of post-ischemic ubiquitination in the regulation of essential kinases involved in ischemic injury, and presents targeting ubiquitination as a potential new avenue for the treatment of ischemic stroke.
Qin Fu 