HNRNPU Links RNA Handling, Chromatin Remodeling and DNA Methylation in Developing Neurons

HNRNPU is a multifunctional protein that helps keep chromatin open at active promoters and regulates RNA stability, splicing and transport. Haploinsufficiency of HNRNPU causes a severe neurodevelopmental disorder marked by developmental delay, intellectual disability, autism and epilepsy. Blood DNA methylation studies have found widespread epigenetic differences in affected individuals, but methylation had not been examined in neural cells, and the protein's interaction partners in neural cells were poorly defined.

The team studied human induced pluripotent stem cell-derived neuroepithelial stem cells and differentiating neural cells. They combined three layers of data: protein-protein interaction mapping, identification of RNA targets, and genome-wide DNA methylation profiling after HNRNPU silencing. They then integrated the layers to find genes affected at several molecular levels. They also validated key interactions and examined their effects in an HNRNPU-deficient state.

HNRNPU sat at the center of extensive interaction networks. These included an association with the mammalian SWI/SNF chromatin-remodeling complex and a previously unrecognized connection to translation. HNRNPU also associated with mRNAs encoding proteins important for neuronal development, several of which are themselves linked to neurodevelopmental disorders. Silencing HNRNPU reprogrammed DNA methylation dynamics at regulatory regions, particularly at active and bivalent promoters of neurodevelopmental transcription factors.

Integrating the protein, RNA and methylation datasets identified 19 genes that converged at all three levels. They included the SWI/SNF components SMARCA4 and SMARCC2, which are known neurodevelopmental disorder genes, and RNA-processing machinery such as SYNCRIP. This suggests that HNRNPU loss can disrupt a connected network spanning RNA metabolism, chromatin organization and DNA methylation, rather than a single pathway. The overlap with other neurodevelopmental disorder genes may help explain why mutations in different chromatin and RNA-binding genes produce similar clinical features.

The study is mechanistic and uses cultured human neural cell models, so it does not show that any intervention improves outcomes. Cell models cannot fully capture the timing, cell diversity and circuitry of the developing brain. Interaction and binding data show association, not necessarily causation, and the link between altered promoter methylation and downstream gene expression and neuronal function needs further testing. Even so, the dataset gives a prioritized list of genes and pathways for follow-up in HNRNPU-related disorders and for understanding how RNA-binding proteins shape the neuronal epigenome. Note that only the abstract and introduction of the paper were available for this summary, so finer methodological and quantitative details are not covered.