Motopsin deficiency imparts partial insensitivity to doxorubicin-induced hippocampal impairments in adult mice.

Motopsin is a serine protease that plays a crucial role in synaptic functions. Loss of motopsin function causes severe intellectual disability in humans. In this study, we evaluated the role of motopsin in the neuropathological development of cognitive impairments following chemotherapy, also known as chemobrain. Motopsin knockout (KO) and wild-type (WT) mice were intravenously injected with doxorubicin (Dox) or saline four times every 8 days and were evaluated for open field, novel object recognition, and passive avoidance tests. Parvalbumin-positive neurons in the hippocampus were immunohistochemically analyzed. Dox administration significantly decreased the total distance in the open field test in both WT and motopsin KO mice without affecting the duration spent in the center square. A significant interaction between the genotype and drug treatment was detected in the recognition index (the rate to investigate a novel object) in the novel object recognition test, although Dox treatment did not affect the total investigation time. Additionally, Dox treatment significantly decreased the recognition index in WT mice, whereas it tended to increase the recognition index in motopsin KO mice. Dox treatment did not affect the latency to enter a dark compartment in either WT or motopsin KO mice in the passive avoidance test. Interestingly, Dox treatment increased the parvalbumin-positive neurons in the stratum oriens of the hippocampus CA1 region of only WT mice, not motopsin KO mice. Our data suggest that motopsin deficiency imparted partial insensitivity to Dox-induced hippocampal impairments. Alternatively, motopsin may contribute to the neuropathology of chemobrain.