Deficiency of the immunoproteasome subunit ß5i/LMP7 supports the anxiogenic effects of mild stress and facilitates cued fear memory in mice.

Proteolysis as mediated by one of the major cellular protein degradation pathways, the ubiquitin-proteasome system (UPS), plays an essential role in learning and memory formation. However, the functional relevance of immunoproteasomes in the healthy brain and especially their impact on normal brain function including processes of learning and memory has not been investigated so far. In the present study, we analyzed the phenotypic effects of an impaired immunoproteasome formation using a ß5i/LMP7-deficient mouse model in different behavioral paradigms focusing on locomotor activity, exploratory behavior, innate anxiety, startle response, prepulse inhibition, as well as fear and safety conditioning. Overall, our results demonstrate no strong effects of constitutive ß5i/LMP7-deficiency on gross locomotor abilities and anxiety-related behavior in general. However, ß5i/LMP7-deficient mice expressed more anxiety after mild stress and increased cued fear after fear conditioning. These findings indicate that the basal proper formation of immunoproteasomes and/or at least the expression of ß5i/LMP7 in healthy mice seem to be involved in the regulation of anxiety and cued fear levels.