Absent, Small, or Homeotic 2-Like-Mediated H3K4 Methylation and Nephrogenesis.

KEY POINTS: Deficits in nephron numbers are associated with higher risk of adult-onset kidney disease seen in congenital anomalies of the kidney and urinary tract. Mouse model experiments suggested that absent, small, or homeotic 2-like was vital for kidney development by activating cell cycle genes through histone methylation. Our findings identified absent, small, or homeotic 2-like–regulated genes as a potential target for treating congenital anomalies of the kidney and urinary tract. BACKGROUND: Many congenital anomalies of the kidney and urinary tract involve deficits in the number of nephrons, which are associated with a higher risk of hypertension and CKD later in life. Prior work has implicated histone modifications in regulating kidney lineage–specific gene transcription and nephron endowment. Our earlier study suggested that absent, small, or homeotic 2-like (ASH2L), a core subunit of the H3K4 methyltransferase complex, plays a role in ureteric bud morphogenesis during mammalian kidney development. However, the potential involvement of ASH2L in nephron formation remains an open question. METHODS: To investigate the role of ASH2L in nephron development, we inactivated Ash2l specifically in nephron progenitor cells by crossing Six2-e(Kozak-GFPCre-Wpre-polyA)1 mice with Ash2l(fl/fl) mice. We used RNA sequencing combined with Cleavage Under Targets and Tagmentation sequencing to screen for gene and epigenomic changes, which were further verified by rescue experiments conducted on ex vivo culture explants. RESULTS: Inactivating ASH2L in nephron progenitor cells disrupted H3K4 trimethylation establishment at promoters of genes controlling nephron progenitor cell stemness, differentiation, and cell cycle, inhibiting their progression through the cell cycle and differentiation into epithelial cell types needed to form nephrons. Inhibition of the TGF-β/suppressor of mothers against decapentaplegic signaling pathway partially rescued the dysplastic phenotype of the mutants. CONCLUSIONS: ASH2L-mediated H3K4 methylation was identified as a novel epigenetic regulator of kidney development. Downregulation of ASH2L expression or H3K4 trimethylation may be linked to congenital anomalies of the kidney and urinary tract.