Abstract
RNA engineering has yielded a new class of medicines but faces limitations depending on RNA size and function. Here we demonstrate the synthesis and enzymatic stabilization of telomerase RNA component (TERC), a therapeutically relevant long non-coding RNA (lncRNA) that extends telomere length and replicative lifespan in human stem cells. Compared with therapeutic mRNAs, engineered TERC RNA (eTERC) depends on avoiding nucleoside base modifications and incorporates a distinct trimethylguanosine 5' cap during in vitro transcription. We show that the non-canonical polymerase TENT4B can be repurposed to enzymatically stabilize synthetic RNAs of any size by catalysing self-limited 2'-O-methyladenosine tailing, which is critical for optimal eTERC function in cells. A single transient exposure to eTERC forestalls telomere-induced senescence in telomerase-deficient human cell lines and lengthens telomeres in induced pluripotent stem cells from nine patients carrying different mutations in telomere-maintenance genes, as well as primary CD34+ blood stem/progenitor cells. Our results provide methods and proof of functional reconstitution for a stabilized, synthetic human lncRNA. eTERC may have therapeutic potential to safely extend replicative capacity in human stem cells.