PRMT5 is required for the maintenance of genomic integrity in hematopoietic stem cells

Protein arginine methyltransferase 5 (PRMT5) has been implicated in diverse processes, including spliceosome assembly. PRMT5 was recently reported to be essential for hematopoiesis, and required for splicing in hematopoietic stem/progenitor cells. However, the role of PRMT5, particularly its importance in splicing regulation, in hematopoietic stem cells (HSCs) has not been extensively studied. To do so, we employed a loss-of-function approach, coupled with functional and transcriptome profiling. We report that PRMT5 is essential for HSCs. Mx1-Cre Prmt5fl/fl mice (Prmt5Δ/Δ) exhibited bone marrow (BM) failure; characterized by rapid reduction in BM cellularity, severe pancytopenia and lethality within 17.5 days. Importantly, Prmt5Δ/Δ HSCs failed to reconstitute lethally irradiated wild-type recipients. This was associated with transient expansion of the Prmt5Δ/Δ HSC compartment, followed by significant loss a week after. Correspondingly, apoptosis was increased among Prmt5Δ/Δ HSCs, which was associated with p53 activation and aberrant splicing of MDM4; a negative regulator of p53. We also obtained similar results in vitro with PRMT5 inhibitor (EPZ015666)-treated EML cell line. We also analyzed the splice variant landscape in Prmt5Δ/Δ HSCs, and identified differential splicing events (DSEs) across several splicing classes. Interestingly, DSEs were overrepresented for processes associated with genome integrity; e.g. DNA repair. Notably, we show that splicing of key genes involved in base excision repair, telomere maintenance/repair and Fanconi anemia pathway were dysregulated in Prmt5Δ/Δ HSCs. Thus, suggesting Prmt5Δ/Δ HSCs are potentially deficient in DNA repair. In agreement, Prmt5Δ/Δ HSCs exhibited elevated γH2A.X levels and DNA strand breaks; thus confirming increased DNA damage. Furthermore, Prmt5Δ/Δ HSCs also exhibited increased replicative stress-associated oxidative DNA lesions. Corroborating these observations, Prmt5Δ/Δ HSCs were less quiescent and had higher levels of reactive oxygen species. Thus, loss of PRMT5 renders HSCs vulnerable to DNA damage. Collectively, our study highlights a novel link between PRMT5 and maintenance of genome integrity in HSCs.