Telomere shortening and loss of self-renewal in dyskeratosis congenita induced pluripotent stem cells

Abstract

The differentiation of patient-derived induced pluripotent stem cells (iPSCs) to committed fates such as neurons, muscle and liver is a powerful approach for understanding key parameters of human development and disease1–6. Whether undifferentiated iPSCs themselves can be used to probe disease mechanisms is uncertain. Dyskeratosis congenita (DC) is characterized by defective maintenance of blood, pulmonary tissue, and epidermal tissues and is caused by mutations in genes controlling telomere homeostasis7,8. Short telomeres, a hallmark of DC, impairs tissue stem cell function in mouse models, suggesting that a tissue stem cell defect underlies the pathophysiology of DC9,10. Here, we show that even in the undifferentiated state, iPSCs from DC patients harbor the precise biochemical defects characteristic of each form of the disease and that the magnitude of the telomere maintenance defect in iPSCs correlates with clinical severity. In iPSCs from patients with heterozygous mutations in TERT, the telomerase reverse transcriptase, a 50% reduction in telomerase levels blunts the natural telomere elongation that accompanies reprogramming. In contrast, mutation of dyskerin (DKC1) in X-linked DC severely impairs telomerase activity by blocking telomerase assembly and disrupts telomere elongation during reprogramming. In iPSCs from a form of DC caused by mutations in TCAB1, telomerase catalytic activity is unperturbed, yet the ability of telomerase to lengthen telomeres is abrogated, because telomerase mislocalizes from Cajal bodies to nucleoli within the iPSCs. Extended culture of DKC1-mutant iPSCs leads to progressive telomere shortening and eventual loss of self-renewal, suggesting that a similar process occurs in tissue stem cells in DC patients. These findings in iPSCs from DC patients reveal that undifferentiated iPSCs accurately recapitulate features of a human stem cell disease and may serve as a cell culture-based system for the development of targeted therapeutics.

Telomere dynamics in dyskeratosis congenita: the long and the short of iPS

“…In the past 12 years, elegant studies have revealed mutations in seven genes as a cause of DC, all of which encode telomerase (DKC1, TERT, TERC, NOP10, NHP2, TCAB1) or telomere structural (TINF2) components. Moreover, mutations in some of these genes have been found in familial degenerative disorders without classical DC, including aplastic anemia, myelodysplastic syndrome, and idiopathic pulmonary fibrosis [5] [6,7]. A comparison of the data in these two reports illustrates the advantages and limitations of the iPS approach for modeling human diseases.…”

Brief Report: Impaired Cell Reprogramming in Nonhomologous End Joining Deficient Cells

“…Aiming to discern the biochemical pathways required for the efficient and safe reprogramming of adult somatic cells into iPSCs, recent studies have shown the relevance of telomere homeostasis [2][3][4], signal transducers, and DNA repair proteins [4][5][6][7] in cell reprogramming. These results have shown that a significant DNA stress-reflected by an increased number of DNA double strand breaks (DSBs)-is produced during the reprogramming process.…”

Correlation between telomere maintenance and stemness of mesenchymal stem/stromal cells

“…Based on previous data that demonstrated a crucial role of overexpressed TERT in the generation of iPSCs [9,10] , it is suggested that telomerase has major role in reprogramming, self-renewal and maintenance of iPSCs pluripotency [11] .…”