Chromatin reorganization drives overexpression of a Btaf1 variant underpinning hematopoietic aging.

Age-associated hematopoietic stem cell (HSC) dysfunction is accompanied by dramatic transcription changes, but it remains unclear whether specific transcripts could orchestrate these HSC aging phenotypes. Here, we perform epigenetic profiling in male mice to investigate the regulatory mechanisms underlying the HSC aging transcriptome and screen for potential aging driver genes. We identify a looping structure formed between part of the Btaf1 gene and the whole Ide gene in old HSCs which is accompanied by overexpression of a shorter variant of Btaf1 (nBtaf1). Mechanistically, elevated expression of nBtaf1 drives the aging-associated overexpression of HSC and megakaryocyte progenitor (MkP) signature genes via regulating TBP binding at their promoters, which contributes to HSC expansion and elevated MkP production in aged mice. ShRNA-mediated knockdown of nBtaf1 restores a younger HSC transcriptome and specifically represses aging-associated HSC expansion and elevated MkP production. In summary, our data provide high resolution analysis of a dysregulated HSC aging epigenome and reveal a Btaf1 variant that drives HSC aging phenotypes in mice.