<i>Wwox</i> deletion leads to reduced GABA-ergic inhibitory interneuron numbers and activation of microglia and astrocytes in mouse hippocampus

Abstract

The association of WW domain-containing oxidoreductase <i>WWOX</i> gene loss of function with central nervous system (CNS) related pathologies is well documented. These include spinocerebellar ataxia, epilepsy and mental retardation (SCAR12, OMIM: 614322) and early infantile epileptic encephalopathy (EIEE28, OMIM: 616211) syndromes. However, there is complete lack of understanding of the pathophysiological mechanisms at play. In this study, using a <i>Wwox</i> knockout (<i>Wwox KO</i>) mouse model (2 weeks old, both sexes) and stereological studies we observe that <i>Wwox</i> deletion leads to a significant reduction in the number of hippocampal GABA-ergic (γ-aminobutyric acid) interneurons. <i>Wwox KO</i> mice displayed significantly reduced numbers of calcium-binding protein parvalbumin (PV) and neuropeptide Y (NPY) expressing interneurons in different subfields of the hippocampus in comparison to <i>Wwox</i> wild-type (<i>WT</i>) mice. We also detected decreased levels of Glutamic Acid Decarboxylase protein isoforms GAD65/67 expression in <i>Wwox</i> null hippocampi suggesting lower levels of GABA synthesis. In addition, <i>Wwox</i> deficiency was associated with signs of neuroinflammation such as evidence of activated microglia, astrogliosis, and overexpression of inflammatory cytokines <i>Tnf-a</i> and <i>Il6</i>. We also performed comparative transcriptome-wide expression analyses of neural stem cells grown as neurospheres from hippocampi of <i>Wwox KO</i> and <i>WT</i> mice thus identifying 283 genes significantly dysregulated in their expression. Functional annotation of transcriptome profiling differences identified ‘neurological disease’ and ‘CNS development related functions’ to be significantly enriched. Several epilepsy-related genes were found differentially expressed in <i>Wwox KO</i> neurospheres. This study provides the first genotype-phenotype observations as well as potential mechanistic clues associated with <i>Wwox</i> loss of function in the brain.