Altered Expression of GABAergic Markers in the Forebrain of Young and Adult Engrailed-2 Knockout Mice

Abstract

Impaired function of GABAergic interneurons, and the subsequent alteration of excitation/inhibition balance, is thought to contribute to autism spectrum disorders (ASD). Altered numbers of GABAergic interneurons and reduced expression of GABA receptors has been detected in the brain of ASD subjects and mouse models of ASD. We previously showed a reduced expression of GABAergic interneuron markers parvalbumin (PV) and somatostatin (SST) in the forebrain of adult mice lacking the Engrailed2 gene (En2-/- mice). Here, we extended this analysis to postnatal day (P) 30 by using in situ hybridization, immunohistochemistry, and quantitative RT-PCR to study the expression of GABAergic interneuron markers in the hippocampus and somatosensory cortex of En2-/- and wild type (WT) mice. In addition, GABA receptor subunit mRNA expression was investigated by quantitative RT-PCR in the same brain regions of P30 and adult En2-/- and WT mice. As observed in adult animals, PV and SST expression was decreased in En2-/- forebrain of P30 mice. The expression of GABA receptor subunits (including the ASD-relevant Gabrb3) was also altered in young and adult En2-/- forebrain. Our results suggest that GABAergic neurotransmission deficits are already evident at P30, confirming that neurodevelopmental defects of GABAergic interneurons occur in the En2 mouse model of ASD.

GABAergic System Dysfunction in Autism Spectrum Disorders

“…Protein EN2 is mainly present in postnatal GABAergic neurons of the mouse hippocampus and cerebral cortex, and it was found that persistant high expression of EN2 during the prenatal and early postnatal period contributes to autism by affecting the maturation of Purkinje cell (PCs) in the cerebellum (James et al, 2013(James et al, , 2014. EN2 expression levels alter the number of GABAergic interneurons (Sgadò et al, 2013;Provenzano et al, 2020). Evidence from an in vitro study found that En2 increases the complexity of the dendritic tree of GABAergic neurons and reduced the number of mature synapses as well as the area of postsynaptic densities (Soltani et al, 2017).…”

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

“…Indeed, rare mutations, including de novo and intrinsic variants, have been found in the chromosome 15q11–q13 region, a site containing coding regions of specific subunits of GABA receptors, including GABRB3, GABRA5, and GABRG3 [ 289 , 290 , 291 , 292 ]. Finally, direct evidence of GABAergic dysfunction has been obtained from molecular and cellular studies in several genetic and pharmacological animal models of ASD [ 293 , 294 , 295 , 296 , 297 , 298 , 299 , 300 , 301 , 302 , 303 , 304 , 305 , 306 ]. Overall, the dysfunctions shown in both glutamatergic and GABAergic neurotransmission suggest a pathological switch in the E/I balance underlying, at least partly, the failure of compensatory mechanisms, such as adaptation of synaptic efficacy, plasticity, membrane excitability, and/or synapse numbers, physiologically implemented to prevent over-excitation [ 307 ].…”

The Parvalbumin Hypothesis of Autism Spectrum Disorder

“…TRN (Provenzano et al, 2020) Reduction of Pvalb mRNA (P30) Reduction in the number of PV + cells (6 weeks) VISUAL CORTEX (L2/3 and L5/6) (Pirone et al, 2020) Increase in the number of PV + cells (P30 and adult)…”