Downregulation of ubiquitin-specific protease 15 (USP15) does not provide therapeutic benefit in experimental mesial temporal lobe epilepsy

Abstract

AbstractStructural epilepsies display complex immune activation signatures; however, it is unclear which neuroinflammatory pathways drive disease pathobiology. Transcriptome studies of brain resections from mesial temporal lobe epilepsy (mTLE) patients revealed a dysregulation of transforming growth factor β, interferon α/β and nuclear factor erythroid 2-related factor 2 pathways among other neuroinflammatory mechanisms. Since these pathways are regulated by ubiquitin-specific proteases (USP), in particular USP15, we hypothesized that USP15 blockade may provide therapeutic relief in treatment-resistant epilepsies. For validation, transgenic mice which either constitutively or inducibly lack USP15 underwent intrahippocampal kainate injections to induce mTLE and to investigate the impact of USP15 downregulation at the molecular and phenotypic levels. We show that the severity ofstatus epilepticusis unaltered in mice constitutively lacking Usp15 compared to wildtype littermates. Cell death, reactive gliosis and changes in the inflammatory transcriptome were pronounced at 4 days after kainate injection. However, the lack of USP15 did not alter brain inflammation signatures. Likewise, induced deletion of Usp15 in chronic epilepsy neither affected seizure generation, nor cell death, gliosis or the transcriptome. Concordantly, siRNA-mediated knockdown of Usp15 in a microglial cell line did not impact inflammatory responses in form of cytokine release. Our data show that a lack of USP15 is insufficient to modulate the expression of relevant neuroinflammatory pathways in mTLE and has no impact on epileptic activity in a mouse model. Although previous reports implicated a checkpoint function for USP15 in inflammation, our results do not support targeting USP15 as a therapeutic approach for pharmacoresistant epilepsy.