553. Dual Lipopolysaccharide injection induces prolonged activation of the kynurenine pathway and alters schizophrenia-associated proteins in vivo

Abstract

Abstract Background Schizophrenia is a severe chronic psychiatric disease that affects approximately 0.3% of the population and imposes a substantial emotional and economic burden on families and society worldwide1,2. It is characterized by positive, negative and cognitive symptoms1. Current treatments address the positive symptoms, but there are no effective therapies for the long-term cognitive deficits observed in patients. Therefore, a deeper understanding of the schizophrenia pathology is crucial for the development of disease-modifying treatments. In this context, the dual injection lipopolysaccharide (LPS) model has been shown to activate the kynurenine pathway and increase kynurenic acid (KYNA) in mice, a feature also observed in patients with schizophrenia3,4. Repeated LPS injections additionally induce memory deficits in mice, mimicking behavioral features of this disorder5. Although the effects of LPS on the kynurenine pathway have been characterized up to 120 hours after the first injection, little is known about the longer-term impact of this endotoxin on the kynurenine pathway. Regarding the molecular pathology, it remains unclear whether LPS affects schizophrenia-associated proteins in brain regions involved with cognitive processes. Aims & Objectives The present study aimed to investigate if the kynurenine pathway remains activated seven days after LPS injections and whether LPS alters the levels of schizophrenia-associated proteins in mice. Method Three- to four-month-old C57Bl/6N male and female mice received two injections of LPS (0.5mg/kg) or saline, with 16h between injections. Brains were collected either 24 hours or seven days after the first LPS injection. Samples from the prefrontal cortex, striatum, hippocampus and cerebellum were analysed by UPLC-MS to assess the kynurenine pathway. In addition, protein levels of DISC1, NPAS3, Dysbindin, TRIOBP and CRMP1 from the hippocampus and prefrontal cortex were evaluated by Western Blot. Results LPS activated the kynurenine pathway 24 hours after first LPS injection in male and female mice across all brain regions. In males, tryptophan, kynurenine, 3-hydroxykynurenine (3-HK) and KYNA were significantly increased in all brain regions. In females, kynurenine pathway activation was more region dependent. Tryptophan was increased in the striatum and cerebellum, kynurenine and 3-HK were elevated in all brain regions and KYNA was increased only in the hippocampus and cerebellum. Notably, all male brain regions showed elevated kynurenine levels seven days after LPS. The kynurenine:tryptophan ratio was increased in all brain regions and in both sexes at 24 hours and seven days after LPS injections, suggesting a sustained activation effect on the kynurenine pathway. LPS also induced significant changes in several of the examined proteins. In the male prefrontal cortex, NPAS3, CRMP1, Dysbindin and DISC1 were altered 24 hours after LPS, with DISC1 remaining decreased at seven days. In females, NPAS3 in the prefrontal cortex was changed seven days after LPS injections. The female hippocampus showed alterations in CRMP1, TRIOBP and DISC1 levels 24 hours after LPS injections. Discussion & Conclusions Together, these data suggests that repeated LPS administration induces prolonged activation of the kynurenine pathway and modifies schizophrenia-related proteins in a region and sex-dependent matter. Future studies should address if sustained activation of this pathway is followed by memory impairment and whether LPS impacts the proteostasis network.