The Telomerase Complex Directly Controls Hematopoietic Stem Cell Differentiation and Senescence in an Induced Pluripotent Stem Cell Model of Telomeropathy

Abstract

Telomeropathies are rare disorders associated with impaired telomere length control mechanisms that frequently result from genetic mutations in the telomerase complex. Dyskeratosis congenita is a congenital progressive telomeropathy in which mutation in the telomerase RNA component (TERC) impairs telomere maintenance leading to accelerated cellular senescence and clinical outcomes resembling premature aging. The most severe clinical feature is perturbed hematopoiesis and bone-marrow failure, but the underlying mechanisms are not fully understood. Here, we developed a model of telomerase function imbalance using shRNA to knockdown TERC expression in human induced pluripotent stem cells (iPSCs). We then promoted in vitro hematopoiesis in these cells to analyze the effects of TERC impairment. Reduced TERC expression impaired hematopoietic stem-cell (HSC) differentiation and increased the expression of cellular senescence markers and production of reactive oxygen species. Interestingly, telomere length was unaffected in shTERC knockdown iPSCs, leading to conclusion that the phenotype is controlled by non-telomeric functions of telomerase. We then assessed the effects of TERC-depletion in THP-1 myeloid cells and again observed reduced hematopoietic and myelopoietic differentiative potential. However, these cells exhibited impaired telomerase activity as verified by accelerated telomere shortening. shTERC-depleted iPSC-derived and THP-1-derived myeloid precursors had lower phagocytic capacity and increased ROS production, indicative of senescence. These findings were confirmed using a BIBR1532 TERT inhibitor, suggesting that these phenotypes are dependent on telomerase function but not directly linked to telomere length. These data provide a better understanding of the molecular processes driving the clinical signs of telomeropathies and identify novel roles of the telomerase complex other than regulating telomere length.

Telomerase RNA recruits RNA polymerase II to target gene promoters to enhance myelopoiesis

“…DC patients carrying TERC mutations develop aplastic anemia and cancer more frequently than other DC patients (7), suggesting noncanonical roles for TERC in DC pathogenesis. Recent studies have shown that TERT-TERC complexes bind to ribosomal DNA promoters and stimulate transcription by Pol I during regeneration and in tumorigenesis (29) and that inhibition of TERT and TERC impaired myelopoiesis of human iPS cells independently of telomere length (30). We have found that terc plays an essential role in myelopoiesis in zebrafish by regulating myeloid gene expression but in a manner independent of telomere length and also TERT (19).…”

Regulation of poly(a)-specific ribonuclease activity by reversible lysine acetylation

“…In fact, TERC 2/2 mice have shortened lifespans, signs of pulmonary aging, and induced senescence when compared with TERC 1/1 mice (61,62). Furthermore, knockdown of hTR in human induced pluripotent stem cells results in cellular senescence (63). SIRT1 also regulates cellular senescence, as SIRT1 inhibition has been shown to induce cellular senescence, similar to the effect of hTR ablation (64)(65)(66).…”

Improving Cell Recovery: Freezing and Thawing Optimization of Induced Pluripotent Stem Cells

“…Using the same Matrigel™ coating for these dishes that we also use for the normal plastic dishes, we see a slightly better cell attachment (approximately 10–15% more cells attach to the Nunclon™ Delta surface-treated dishes). These Nunclon™ Delta surface-treated dishes are also used by other laboratories for cultivating iPSC [ 36 , 94 ]. The slightly better attachment may be caused by the hydrophilic surface and/or by the high surface roughness.…”