Alterations of ubiquitin related proteins in the pathology and development of schizophrenia: Evidence from human and animal studies

Gene expression analyses in post-mortem schizophrenia brains suggest that a number of ubiquitin proteasome system (UPS) genes are associated with schizophrenia; however the status of UPS proteins in the schizophrenia brain is largely unknown. Ubiquitin related proteins are inherently involved in memory, neuronal survival and morphology, which are processes implicated in neurodevelopmental disorders such as schizophrenia. We examined levels of five UPS proteins (Protein Inhibitor of Activated STAT2 [PIAS2], F-Box and Leucine rich repeat protein 21 [FBXL21], Mouse Double Minute 2 homolog [MDM2], Ubiquitin Carboxyl-Terminal Hydrolase-L1 [UCHL1] and Ubiquitin Conjugating Enzyme E2D1 [UBE2D1]) involved in these neuronal processes, within the dorsolateral prefrontal cortex of post-mortem schizophrenia subjects and matched controls (n = 30/group), in addition to across neurodevelopmental time-points (juvenile, adolescent and adult stages of life), utilizing a well-established neurodevelopmental phencyclidine (PCP) animal model of schizophrenia. We observed significant reductions in PIAS2, FBXL21 and MDM2 in schizophrenia subjects compared to controls (p-values ranging from 0.002 to 0.004). In our developmental PCP model, MDM2 protein was significantly reduced in adult PCP-treated rats compared to controls (p = 0.034). Additionally, FBXL21 (p = 0.022) and UCHL1 (p = 0.022) were significantly decreased, whilst UBE2D1 was increased (p = 0.022), in juvenile phencyclidine-treated rats compared to controls. This is the first study reporting alterations of UPS proteins in post-mortem human schizophrenia subjects and in a neurodevelopmental model of schizophrenia. The findings from this study provide strong support for a role of these UPS proteins in the pathology and development of schizophrenia.