Neurotoxic mechanisms by which the USP14 inhibitor IU1 depletes ubiquitinated proteins and Tau in rat cerebral cortical neurons: Relevance to Alzheimer's disease

Magdalena J Kiprowska, Anna Stepanova, Dustin R Todaro, Alexander Galkin, Arthur Haas, Scott M Wilson, Maria E Figueiredo-Pereira

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

In Alzheimer's disease proteasome activity is reportedly downregulated, thus increasing it could be therapeutically beneficial. The proteasome-associated deubiquitinase USP14 disassembles polyubiquitin-chains, potentially delaying proteasome-dependent protein degradation. We assessed the protective efficacy of inhibiting or downregulating USP14 in rat and mouse (Usp14(axJ)) neuronal cultures treated with prostaglandin J2 (PGJ2). IU1 concentrations (HIU1>25μM) reported by others to inhibit USP14 and be protective in non-neuronal cells, reduced PGJ2-induced Ub-protein accumulation in neurons. However, HIU1 alone or with PGJ2 is neurotoxic, induces calpain-dependent Tau cleavage, and decreases E1~Ub thioester levels and 26S proteasome assembly, which are energy-dependent processes. We attribute the two latter HIU1 effects to ATP-deficits and mitochondrial Complex I inhibition, as shown herein. These HIU1 effects mimic those of mitochondrial inhibitors in general, thus supporting that ATP-depletion is a major mediator of HIU1-actions. In contrast, low IU1 concentrations (LIU1≤25μM) or USP14 knockdown by siRNA in rat cortical cultures or loss of USP14 in cortical cultures from ataxia (Usp14(axJ)) mice, failed to prevent PGJ2-induced Ub-protein accumulation. PGJ2 alone induces Ub-protein accumulation and decreases E1~Ub thioester levels. This seemingly paradoxical result may be attributed to PGJ2 inhibiting some deubiquitinases (such as UCH-L1 but not USP14), thus triggering Ub-protein stabilization. Overall, IU1-concentrations that reduce PGJ2-induced accumulation of Ub-proteins are neurotoxic, trigger calpain-mediated Tau cleavage, lower ATP, E1~Ub thioester and E1 protein levels, and reduce proteasome activity. In conclusion, pharmacologically inhibiting (with low or high IU1 concentrations) or genetically down-regulating USP14 fail to enhance proteasomal degradation of Ub-proteins or Tau in neurons.

Original languageEnglish
Pages (from-to)1157-1170
Number of pages14
JournalBiochimica et biophysica acta
Volume1863
Issue number6
Early online date01 Apr 2017
DOIs
Publication statusPublished - 01 Jun 2017

Keywords

  • Journal Article

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