Brg1/PRMT5 nuclear complex epigenetically regulates FOXO1 in IPF mesenchymal progenitor cells.

We have discovered intrinsically fibrogenic mesenchymal progenitor cells (MPCs) in the human idiopathic pulmonary fibrosis (IPF) lung. IPF MPCs display a durably distinct transcriptome, suggesting that they have undergone epigenetic modifications. Prior studies indicate that the chromatin remodeler Brg1 associates with the arginine methyltransferase PRMT5 to epigenetically regulate transcription factors. We hypothesize that a Brg1/PRMT5 nuclear complex epigenetically regulates critical nodes in IPF MPC self-renewal signaling networks. IPF and control MPCs were isolated from primary mesenchymal cell lines established from IPF and control patients. RNA-sequencing identified increased expression of the FOXO1 transcription factor in IPF MPCs compared with controls, a result we confirmed by Q-PCR and Western blot analysis. Immunoprecipitation identified a CD44/Brg1/PRMT5 nuclear complex in IPF MPCs. Chromatin immunoprecipitation assays showed that PRMT5 and its methylation mark H3R2me2 are enriched on the promoter. We show that loss of Brg1 and PRMT5 function decreases FOXO1 expression and impairs IPF MPC self-renewal, and that loss of FOXO1 function decreases IPF MPC self-renewal and expression of the SOX2 and OCT4 stemness markers. Our findings indicate that the gene is overexpressed in IPF MPCs in a CD44/Brg1/PRMT5 nuclear complex-dependent manner. Our data suggest that Brg1 alters chromatin accessibility, enriching PRMT5 occupancy on the promoter, and PRMT5 methylates histone H3 arginine 2 (H3R2) on the promoter, increasing its expression. Our data are in accord with the concept that this coordinated interplay is responsible for promoting IPF MPC self-renewal and maintaining a critical pool of fibrogenic MPCs that drive IPF progression. Our research offers valuable understanding regarding the epigenetic control of IPF MPC. The data we obtained strongly support the idea that the coordination between chromatin remodeling and histone methylation plays a key role in regulating transcription factors. Specifically, our findings indicate that FOXO1, an essential transcription factor, likely governs the self-renewal of IPF MPC, which is crucial for maintaining a critical pool of fibrogenic MPCs. This interplay could be an important therapeutic target.