Regulation and manipulation of the telomerase RNA component in hematopoiesis

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PROJECT SUMMARY/ABSTRACT Telomerase is critical for health and longevity, but there is a fundamental lack of understanding of how it is regulated in human cells. This knowledge gap impedes the ability to develop therapies for a growing spectrum of disorders in which telomerase dysfunction is implicated. The long-term goal of this project is to be able to manipulate telomerase in human cells for therapeutic benefit, with a key target being the hematopoietic system. The level of the noncoding telomerase RNA component TERC is a critical determinant of telomerase function in cells. Low TERC levels resulting from genetic mutations cause a wide spectrum of degenerative disorders, including dyskeratosis congenita (DC), aplastic anemia, MDS/leukemia, cardiovascular disease, pulmonary fibrosis, and cirrhosis. Recent work identifies the non-canonical polymerase PAPD5 as a key negative regulator of TERC. PAPD5 is thus a novel target for small molecule inhibitors to restore TERC and telomeres in human diseases. What is not known is the basis of selective regulation of non-coding RNAs (ncRNAs) by PAPD5, nor whether inhibiting PAPD5 will be therapeutically effective. The overall objectives of this proposal are (1) to understand how PAPD5 selectively regulates ncRNAs, and (2) to determine the in vivo efficacy of PAPD5 inhibitors in restoring hematopoietic stem cell (HSC) function. The central hypothesis is that PAPD5 selectively regulates TERC and a small number of ncRNAs, providing a therapeutic window for systemic PAPD5 inhibition to restore telomeres and self-renewal capacity in stem cells. The rationale for our work is that understanding mechanisms of selectivity and demonstrating therapeutic efficacy of small molecule PAPD5 inhibitors will provide a strong scientific framework for their development as treatments for bone marrow failure and a range of diseases. The central hypothesis will be tested by pursuing two Specific Aims: (1) Identify the mechanisms of selective regulation of ncRNAs by PAPD5, and (2) Determine the therapeutic efficacy of PAPD5 inhibitors in vivo. Under the first aim, biochemical and genetic approaches will be used to rigorously identify bona fide PAPD5 targets, and to decipher the regulatory logic of the PAPD5-dependent transcriptome in human cells, emphasizing HSCs. Tools and techniques that have been developed and demonstrated to be feasible in the applicants’ hands will be used. Under the second aim, the therapeutic efficacy of small molecule PAPD5 inhibitors to restore telomere maintenance and HSC function in vivo will be determined. New approaches to overcome interspecies differences in telomere biology and model human HSC failure will be applied. The approach is innovative because PAPD5 is a long-sought, novel and tractable target regulating TERC, the inhibition of which may enable a systemic telomerase-modulating therapy that selectively impacts stem cells. The proposed research is significant, because it is expected to yield new strategies to manipulate telomerase in a growing number of hematopoietic and degenerative disorders including aplastic anemia, MDS/leukemia, pulmonary and cardiovascular disease, in which telomerase dysfunction is implicated but for which there are few if any curative therapies.