Posttranscriptional modulation of TERC by PAPD5 inhibition rescues hematopoietic development in dyskeratosis congenita

Abstract

Reduced levels of <i>TERC</i>, the telomerase RNA component, cause dyskeratosis congenita (DC) in patients harboring mutations in TERC, PARN, NOP10, NHP2, NAF1, or DKC1. Inhibition of the noncanonical poly(A) polymerase <i>PAPD5</i>, or the exosome RNA degradation complex, partially restores <i>TERC</i> levels in immortalized DKC1 mutant cells, but it remains unknown if modulation of posttranscriptional processing of <i>TERC</i> could improve hematopoietic output in DC. We used human embryonic stem cells (hESCs) with a common dyskerin mutation (DKC1_A353V), which have defective telomere maintenance and reduced definitive hematopoietic potential, to understand the effects of reducing EXOSC3 activity, or silencing PAPD5-mediated oligoadenylation, on hematopoietic progenitor specification and function in DC. Reduction of <i>EXOSC3</i> or <i>PAPD5</i> levels in DKC1 mutant hESCs led to functional improvements in <i>TERC</i> levels and telomerase activity, with concomitant telomere elongation and reduced levels of DNA damage signaling. Interestingly, the silencing of <i>PAPD5</i>, but not <i>EXOSC3</i>, significantly restored definitive hematopoietic potential in DKC1 mutant cells. Mechanistically, we show that <i>PAPD5</i> inhibition is sustained in differentiated CD34⁺ cells, with a concomitant increase in mature, functional, forms of <i>TERC</i>, indicating that regulation of <i>PAPD5</i> is a potential strategy to reverse hematologic dysfunction in DC patients.