PlexinA1-deficient mice exhibit decreased cell density and augmented oxidative stress in parvalbumin-expressing interneurons in the medial prefrontal cortex

PlexinA1 (PlxnA1) is a transmembrane receptor for semaphorins (Semas), a large family of axonal guidance cues vital during neural development. PlxnA1 is expressed in embryonic interneurons, and PlxnA1 deletion in mice leads to less interneurons in the developing cortex. In addition, PlxnA1 has been identified as a schizophrenia susceptibility gene. In our previous study, PlxnA1 knockout (KO) mice under a BALB/cAJ genetic background exhibited significantly increased self-grooming and reduced prepulse inhibition, a reliable phenotype for investigating the neurobiology of schizophrenia. However, the mechanism underlying the abnormal behavior of PlxnA1 KO mice remains unclear. We first confirmed PlxnA1 mRNA expression in parvalbumin-expressing interneurons (PV cells) in the medial prefrontal cortex (mPFC) of adult mice. Immunohistochemical analysis (IHC) showed significantly decreased densities of both GABAergic neurons and PV cells in the mPFC of PlxnA1 KO mice compared with wild type mice (WT). PV cells were found to express molecule interacting with CasL 1 (MICAL1), an effector involved in Sema-Plxn signaling for axon guidance, suggesting MICAL1 and PlxnA1 co-expression in PV cells. Furthermore, IHC analysis of 8-oxo-dG, an oxidative stress marker, revealed significantly increased oxidative stress in PlxnA1-deficient PV cells compared with WT. Thus, increased oxidative stress and decreased PV cell density in the mPFC may determine the onset of PlxnA1 KO mice’s abnormal behavior. Accordingly, deficient PlxnA1-mediated signaling may increase oxidative stress in PV cells, thereby disrupting PV-cell networks in the mPFC and causing abnormal behavior related to neuropsychiatric diseases.