Year 4 (NCE)

In the final year of this grant, we developed means to introduce patient mutations into human ES cells. These patient mutations derive from from individuals with a genetic stem cell disease. Dyskeratosis congenita is a rare disease affecting stem cells in multiple tissues. Patients with dyskeratosis congenita develop life-threatening bone marrow failure and pulmonary fibrosis, and are highly prone to cancers. In addition, they develop defects in skin, nails and many other organs. Dyskeratosis congenita is caused by mutations in an enzyme – telomerase – that is particularly important in stem cells. Telomerase elongates telomeres, caps that protect chromosome ends. If telomerase is defective, telomeres shorten and loss of the protective cap at telomeres can cause serious problems in stem cells. It has been very difficult to study this disease because isolating stem cells from dyskeratosis congenita patients is challenging. To overcome this problem, we engineered induced pluripotent stem (iPS) cells from dyskeratosis congenita patients. This is a way to change skin cells into cells that closely resemble embryonic stem cells – stem cells that can give rise to all tissues within the body. We studied these iPS cells from dyskeratosis congenita patients and found that the type of effects on telomerase were very specific and depended on the specific gene that is mutated in the patient. Normal cells from healthy people show significant elongation of telomeres during the making of iPSCs, because telomerase is reactivated during this process. In iPS cells from patients with dyskeratosis congenita by contrast, telomere elongation during reprogramming is compromised. Introducing mutations from patients directly into human ES cells bypasses the iPS-generation step and has major advantages over the use of iPS cells. These findings create new opportunities to study stem cell diseases in cell culture and to develop therapies that could specifically reverse the disease defect.