Early postnatal treatment with valproate induces gad1 promoter remodeling in the brain and reduces apnea episodes in mecp2-null mice

The deletion of Mecp2, the gene encoding methyl-CpG-binding protein 2, causes severe breathing defects and developmental anomalies in mammals. In Mecp2-null mice, impaired GABAergic neurotransmission is demonstrated at the early stage of life. GABAergic dysfunction in neurons in the rostral ventrolateral medulla (RVLM) is considered as a primary cause of breathing abnormality in Mecp2-null mice, but its molecular mechanism is unclear. Here, we report that mRNA expression levels of Gad1, which encodes glutamate decarboxylase 67 (GAD67), in the RVLM of Mecp2-null (Mecp2^-/y, B6.129P2(C)-Mecp2^tm1.1Bird/J) mice is closely related to the methylation status of its promoter, and valproate (VPA) can upregulate transcription from Gad1 through epigenetic mechanisms. The administration of VPA (300 mg/kg/day) together with L-carnitine (30 mg/kg/day) from day 8 to day 14 after birth increased Gad1 mRNA expression in the RVLM and reduced apnea counts in Mecp2^-/y mice on postnatal day 15. Cytosine methylation levels in the Gad1 promoter were higher in the RVLM of Mecp2^-/y mice compared to wild-type mice born to C57BL/6J females, while VPA treatment decreased the methylation levels in Mecp2^-/y mice. Chromatin immunoprecipitation assay revealed that the VPA treatment reduced the binding of methyl-CpG binding domain protein 1 (MBD1) to the Gad1 promoter in Mecp2^-/y mice. These results suggest that VPA improves breathing of Mecp2^-/y mice by reducing the Gad1 promoter methylation, which potentially leads to the enhancement of GABAergic neurotransmission in the RVLM.