Dnmt3a Controls Hematopoietic Stem Cells via DNA Methylation-Independent Regulation of Telomeres
Dnmt3a is the most recurrently mutated gene in clonal hematopoiesis (CH) and it is a critical regulator of hematopoietic stem cells (HSCs). Conditional deletion of Dnmt3a in mouse HSC results in enhanced self-renewal but impaired differnetiation. Dnmt3a encodes for a de novo DNA methyltransferase enzyme but both mouse and human cells with loss of Dnmt3a show minimal change in DNA methylation levels which do not correlate with gene expression differences. To understand if these changes are due to non-canonical function of Dnmt3a, we generated varying levels of DNA methyaltion-impared Dnmt3a mouse models. Our data depicts that DNA methyaltion-impaired Dnmt3a phenocopy wild-type in serial transplant. And Dnmt3a methyltransferase-deficient HSCs showed differntially methylated regions (DMRs) and gene expression  pattern that overlapped with Dnmt3a-null HScs. Suggesting that Dnmt3a has important non-canonical function that partially regulates HSC fate. Dnmt3a-null HSC increased HSC self-renwal and can be transplanted indefinitely and increase longevity with no erosion of telomere length. Dnmt3a-null HSCs showed increased telomere at baseline and maintained overa serial transplant and increased telomerase activity. The role of Dnmt3a in telomere maintenance was not strictly linked to elongated telomere length but in regulation of DNA damage response that occurs at stressed telomeres. These data show a unidentified role of Dnmt3a in HSC telomere maintenance that is note related to DNA methylation function. Overall design: To investigate the diffential DNA methylation and gene expression patterns in hematopoietic cells expressing Dnmt3a-variants with varying DNA methyltransferase activity, we established Cre-mediated knockin mouse models. Competitive HSC transplantation was performed.  Post-transplant cells were isolated 18-weeks post transplant for analysis of gene expression patterns by RNA sequencing and DNA methylation patterns by whole genome bisulfite sequencing.