The novel role of GADD45A in the etiology of autism: modulating neuronal excitability via TET1/R-loop dependent regulation of KCNQ5

The etiology of autism currently includes prenatal exposure factors and genetic variants, but it remains unclear how these factors converge on a common pathway. Through multiple autism transcriptome analyses of public data, we discovered that the disruption of Gadd45a may explain the pathogenesis of various types of autism, including the most established valproic acid (VPA) prenatal exposure and MECP2 gene-related autism. Subsequently, we generated Gadd45a knockout mice and found that these mice exhibit significant deficits in social ability, as well as autistic-like phenotypes such as increased digging behaviors. We demonstrated the preferential expression of Gadd45a in cortical excitatory neurons. Through in vivo electrophysiological recordings, we found that the firing frequency of excitatory neurons in the medial prefrontal cortex of knockout mice is abnormal in both resting and task states, which may explain the autistic-like phenotypes exhibited by these mice. Remarkably, we revealed that abnormal neuron firing may be due to the failure of TET1, a GADD45A-interacting protein, to be recruited to the promoter region of Kcnq5, thereby preventing normal DNA demethylation and transcription initiation in the absence of GADD45A. We also demonstrated that GADD45A can recognize R-loop structure to recruit TET1 to the CpG islands of KCNQ5 and regulate the transcription level of KCNQ5. This process also involved nearby antisense lncRNA in the formation of R-loops. Our study revealed a hub gene, GADD45A, and its epigenetic regulation of ion channels (GADD45A/TET1-KCNQ5 axis), which plays a critical role in the pathogenesis of autism.