Aberrant downregulation of Y-box binding protein 1 expression impairs the cell cycle in an m5C-dependent manner in human granulosa cells from patients with primary ovarian insufficiency.

Y-box binding protein 1 (YBX1) has been reported to play a role in human granulosa cell (GC) dysfunction by binding with long noncoding RNAs in patients with primary ovarian insufficiency (POI). 5-Methylcytosine (m⁵C) methylation is an abundant RNA epigenetic modification that is widely present in eukaryotic RNAs. However, whether YBX1, an important m⁵C reader, whether YBX1 participates in POI in an m⁵C- dependent manner remains unknown. Here, we demonstrated that the expression levels of YBX1 were decreased in GCs from patients with biochemical POI. YBX1 knockdown in a human granulosa cell line (KGN) impaired cell proliferation by preventing the G1 to S transition in the cell cycle. Conversely, YBX1 overexpression promoted the KGN cell proliferation. Integrated analysis of the transcriptome and m⁵C methylome profiles revealed that in human GCs, knockdown of YBX1 expression destabilized cell cycle-associated transcripts in an m⁵C-dependent manner, resulting in cell cycle arrest. Our results provide new insights of the pathogenesis of POI, revealing an alternative molecular mechanism in which YBX1 participates in human GC dysfunction by affecting the stability of cell cycle-associated genes in an m⁵C-dependent manner and thereby modulating GC proliferation.