Seizure-induced neuronal apoptosis is related to dysregulation of the RNA-edited GluR2 subunit in the developing mouse brain.

Ca2+-permeable AMPA receptors (AMPAR) which crucially modify maturational programs of the developing brain are involved in seizure-induced glutamate excitotoxicity and apoptosis. Regulatory effects on AMPAR subunit composition and RNA-editing in the developing brain and their significance as therapeutic targets are not well understood. Here, we analyzed acute effects of recurrent pilocarpine-induced neonatal seizures on age- and region-specific expression of AMPAR subunits and adenosine deaminases (ADAR) in the developing mouse brain (P10). After recurrent seizure activity and regeneration periods of 6-72 h cerebral mRNA levels of GluR (glutamate receptor subunit) 1, GluR2, GluR3, and GluR4 were unaffected compared to controls. However, ratio of GluR2 and GluR4 to pooled GluR1-4 mRNA concentration significantly decreased in seizure-exposed brains in comparison to controls. After a regeneration period of 24-72 h ADAR1 and ADAR2 mRNA expression was significantly lower in seizure-exposed brains than in those of controls. This was confirmed at the protein level in the hippocampal CA3 region. We observed a regionally increased apoptosis (TUNEL+ and CC3+ cells) in the hippocampus, parietal cortex and subventricular zone of seizure-exposed brains in comparison to controls. Together, present in vivo data demonstrate the maturational age-specific, functional role of RNA-edited GluR2 in seizure-induced excitotoxicity in the developing mouse brain. In response to recurrent seizure activity, we observed reduced expression of GluR2 and the GluR2 mRNA-editing enzymes ADAR1 and ADAR2 accompanied by increased apoptosis in a region-specific manner. Thus, AMPA receptor subtype-specific mRNA editing is assessed as a promising target of novel neuroprotective treatment strategies in consideration of age-related developmental mechanisms.

Activin A regulation under global hypoxia in developing mouse brain.

Activin A is a multifunctional growth and differentiation factor with pronounced neuroprotective properties that is strongly up-regulated in various forms of acute brain disorders and injuries including epilepsy, stroke and trauma. In a pediatric context, activin A has been advanced as a potential marker for the severity of perinatal hypoxic-ischemic brain injury. Here we investigated the regulation of activin A under global hypoxia without ischemia in primary cultures of cortical neurons and in neonatal and adult mice of two strains (C57BL/6 and CD-1). From birth to adulthood, activin ßA subunit, activin receptors, and functional activin antagonists were all expressed at roughly similar mRNA levels in the brain of C57BL/6 mice. Independent of mouse line and age, we found both moderate (11% O2, 2h) and severe hypoxia (8%, 6h) to be consistently associated with normal or even reduced levels of activin ßA (Inhba) mRNA. The surprising unresponsiveness of Inhba expression to hypoxia was confirmed at the protein level. In situ hybridization did not indicate regional, hypoxia-related differences in Inhba expression. Pharmacologic stabilization of hypoxia inducible factors with the prolyl hydroxylase inhibitor FG-4497 did not influence Inhba mRNA levels in neonatal mice. Our data indicate that pure hypoxia differs from other, more complex types of brain damage in that it appears not to recruit activin A as an endogenous neuroprotective agent.