Mapping of neuronal redox conditions in a mouse model of Rett syndrome.

Rett syndrome (RTT) is associated with a systemic redox imbalance, potentially provoking cellular dysfunction and contributing to some of the disease symptoms. While previous studies have reported these redox alterations also in brain, the exact cerebral redox pattern remains unclear. We therefore generated MeCP2-deficient mice expressing the cytosolic redox sensor roGFPc in excitatory projection neurons. Taking advantage of the earlier developed excitation ratiometric 2-photon imaging, we mapped the redox conditions of individual hippocampal and cortical neurons in acute brain tissue slices of female mice. These quantitative redox analyses revealed clear brain-regional differences in the degree of roGFPc oxidation, with dentate gyrus and CA3 being most oxidized, CA1 being least oxidized and cortical areas presenting intermediate oxidation levels. On postnatal day p50, hardly any RTT-related differences were evident. With maturation (>p100), redox conditions became more reducing in WT females. This was, however, not the case in MeCP2-deficient females, whose hippocampal and especially cortical neurons now appeared clearly more oxidized. By correlative redox microscopy, we succeeded to relate cellular redox-conditions to cellular MeCP2 expression. Validation in CA1 and somatosensory cortex revealed that, based on improved discrimination sensitivity, a more oxidized redox balance became detectable in MeCP2-deficient cortical neurons already on p50. Expression of a mitochondrial catalase efficiently abolished the more oxidizing redox milieu in MeCP2-deficient cortical neurons. This confirms a widespread oxidative burden in forebrain neurons, which manifests already in pre-symptomatic MeCP2-deficient female mice and intensifies with disease progression. Stabilizing mitochondrial function by targeted catalase expression proved potentially protective.