| Telomeres play key roles in maintaining chromosome stability and cell replicative capacity. Progressive telomere shortening due to absent or insufficient telomerase activity plays important roles in driving degenerative pathologies in humans. Somatic cell reprogramming holds great promise in future clinical applications, especially in the treatment of degeneration disorders. Somatic cell nuclear transfer (SCNT) and induced pluripotent stem cells (iPSCs) represent two major approaches for cell reprogramming. However, little is known regarding the ability of these two strategies to rejuvenate cells from donors with telomere dysfunction-related syndromes.Telomere re-elongation is of great importance for the acquisition of pluripotency during reprogramming. Telomere lengthening during iPSCs induction mainly relies on telomerase, the action of which is a very time consuming process, and iPSCs telomeres need postreprogramming to reach the length resembling that of ESCs. Recently, oocyte-derived factor Zscan4has been shown to dramatically elongates telomeres during iPSCs induction and thus improves the reprogramming efficiency and the quality of iPSCs. Therefore, we speculate that SCNT utilizing factors in occytes to reprogramming somatic cells may rejuvenate cells with dysfuntioncal telomeres in a manner superior to that of iPSCs technology with only a few reprogramming factors. Here, we utilized late generation telomerase-deficient(Terc-/-) mice as a model to probe this question. In the third generation Terc-/-mice, disease states associated with short telomeres become evident, with a reduced body size, a decreased life span and atrophy of multiple tissues such as small intestine, spleen and testicles. SCNT-derived embryonic stem cells (ntESCs) and iPSCs were successfully derived from second generation (G2) and third generation (G3) Terc-/-mice, and ntESCs showed better differentiation potential and self-renewal ability. Telomeres lengthened extensively in cloned embryos while remained or slightly increased in the process of iPSCs induction. Furthermore, G3Terc-/-ntESCs exhibited improvement of telomere capping function as evidenced by decreased signal free ends and chromosome end-to-end fusion events. In contrast, there was a further decline of telomere capping function in G3Terc-/-iPSCs. In addition to telomere dysfunction, mitochondria function was severely impaired in G3Terc-/-iPSCs as evidenced by oxygen consumption rate (OCR) decline, reactive oxygen species (ROS) accumulation and dramatically increased mitochondria genome mutations while these deficiencies were greatly mitigated in G3Terc-/-ntESCs. Interestingly, PGC-la expression appeared to be irrelevant to the mitochondrial dysfunction in G3Terc-/-iPSCs. However, impaired mitochondrial maturation in differentiating G3Tern-/-iPSCs was associated with a failure of PGC-1α reactivation, which was mitigated in G3Terc-/-ntESCs.In summary, this study demonstrates that SCNT is superior to transcription factors mediated reprogramming in rejuvenating somatic cells with telomere and mitochondria defects. The breakthrough recently achieved in human SCNT studies further suggests that the identification of novel reprogramming factors might greatly improve the current iPSCs technology and enhance the quality of human iPSCs derived particularly from patients with telomere and mitochondria defects. |
