Evaluation of a precision medicine approach for hnRNP U-related developmental epileptic encephalopathy using a mouse model of disease

Mutations in genes that cause transcriptional dysregulation, such as genes that encode DNA and RNA-binding proteins (RNABPs), are a well-described cause of neurodevelopmental syndromes such as autism and epilepsy. Heterozygous de novo mutations involving the gene HNRNPU, which encodes the heterogeneous nuclear ribonuclear protein U, have been implicated in a neurodevelopmental syndrome most commonly characterized by epileptic encephalopathy. Although hnRNP U is a highly-abundant and ubiquitously-expressed DNA- and RNA-binding protein involved in a variety of important nuclear processes—most notably gene expression regulation—the role it plays in neurological disease is unclear and has yet to be studied. The work presented here examines a precision medicine approach for epilepsies thought to have a transcriptomic basis, starting with a thorough neurophysiological characterization of a heterozygous loss-of-function Hnrnpu mouse model (Hnrnpu+/113DEL), followed by a comprehensive and region-specific single-cell transcriptomic study, and finally the validation of implicated brain regions. Characterization of the Hnrnpu+/113DEL mouse line revealed an increased susceptibility to seizures in Hnrnpu+/113DEL mice, along with an increased perinatal mortality, global developmental delay and gait abnormalities. Gene expression profiling, including bulk RNA-sequencing of neocortex and single cell RNA-sequencing of both neocortex and hippocampus, revealed widespread, yet modest, dysregulation of gene expression that was largely inversely correlated to gene-length, and involved important, neurodevelopmental disease genes. In particular, pyramidal neurons of the subiculum displayed greater transcriptional burden upon heterozygous loss of Hnrnpu, with the known epilepsy gene Mef2c as a clear outlier showing greater than 50% reduction in expression. Follow-up investigation into whether this region- and cell-type specific gene dysregulation correlated to differences in neuronal function using c-Fos immunostaining, revealed an overall decrease in neuronal activity within the ventral subiculum in Hnrnpu+/113DEL mice. In summary, our data validates the presence of neurodevelopmental defects upon heterozygous loss of Hnrnpu and supports the notion of transcriptional dysregulation as a likely contributing factor to hnRNP U-related disease, possibly through the dysfunction of subiculum-derived excitatory neurons. Future studies evaluating the relationship between reduced activity within the ventral subiculum and hnRNP U disease phenotypes are an important next step, and may serve as the basis for targeted therapeutic discovery.