In the blog entry The stem cell supply chain – closing the loop for very long lives, I have suggested that it might be possible to re-introduce fully pluripotent stem cells into the body so as to close the loop in the stem cell supply chain and enable much longer lives. This post reports progress towards that point, again a topic related to Vitamin C suggested by reader jeg3.
Recapitulating the essence of the stem cell supply chain concept: “Stem Cell Supply Chain Breakdown is the newest theory of aging described in my treatise and the one I am currently most excited about. According to a simplified model of this theory a newly-conceived human embryo consists of pluripotent stem cells (Type A), ones that can potentially divide into any body cells. With growth, these proliferate and, in a remarkably articulated manner, progressively differentiate into multipotent stem cells (Type B), progenitor cells (Type C), mature body somatic cells (Type D), and many eventually become senescent cells (Type E).” — ‘According to the best current understanding of stem cells this is an open-loop once-through process. The above list is in order of increasing cell-type specificity and decreasing cell-type potency to differentiate into other cell types. Starting at conception and throughout life, all cells on this list except the senescent ones will selectively reproduce and possibly differentiate into cells of types further down in the list. The state of the body in terms of makeup of cell types continues to change through life and the process goes inexplicably from start (conception) leading to end (death’). The stem cells themselves are subject to replicative senescence. Early in life, Type A cells tend to vanish. With aging, pools of type B and type C cells become exhausted and are less capable of differentiation to renew the supply of Type D cells. The stem cell supply chain slows down and ceases to function well. There are fewer healthy Type D cells and more Type E cells, and disease and death soon follow.
The blog entry The stem cell supply chain – closing the loop for very long lives suggests an approach that could conceivably transform the stem cell supply chain from being a once-through process to being a continuous open-loop process. “There is a possibility of keeping the stem cell supply chain active indefinitely. The key idea is to use induced Pluripotent Stem cells (iPSCs) which are fully pluripotent and equivalent to embryonic stem cells(ref)(ref)(ref) as feedstock Type A cells in adults to make the stem cell supply chain as a continuous loop process instead of a once-through process.”
I assume the reader is generally familiar with iPSCs and the general approaches to reprogramming cells to iPSC status. See, for example, the blog posts Rebooting cells and longevity, Update on induced pluripotent stem cells and “Footprint-free” iPSCs – and a crazy wager offer.
This blog post reports research progress on creating iPSCs which may eventually lead to closing the loop. An old dear friend seems to be involved, Vitamin C. The study Vitamin C Enhances the Generation of Mouse and Human Induced Pluripotent Stem Cells was timed as a Christmas present and published December 24 2009. Some of the points related to the new study are:
1. The approaches to reverting cells to iPSC status have been remarkably inefficient. “Soon after the exciting discovery of a method to transform human skin cells into stem cells in 2007 came the frustration of actually trying to make a sufficient amount of these induced pluripotent stem (iPSC) cells. The process is so inefficient that scientists typically only get 0.01 percent of a sample of human skin, or fibroblast, cells to form iPS cell colonies after they infect fibroblasts with the retroviruses used to induce pluripotency(ref).” The new study report indicates “However, the low efficiency of iPSC generation is a significant handicap for mechanistic studies and high throughput screening, and also makes bona fide colony isolation time consuming and costly. The efficiency of alkaline phosphatase-positive (AP+) colony formation with the four Yamanaka’s factors (Sox2, Klf4, Oct4, c-Myc; SKOM) in mouse fibroblasts is about 1% of the starting population, but only around 1 in 10 of those colonies is sufficiently reprogrammed to be chimera competent – -. ” This iPSC reprogramming inefficiency has been noted by others as well(ref)(ref).
2. It is hard to revert old or near-senescent cells to iPSC status given age-related upregulation of tumor suppressor genes. “While our work was in progress, six independent laboratories identified cell senescence as a roadblock for reprogramming (Hong et al. 2009) — “Functional analyses of these genes demonstrate that the p53-p21 pathway serves as a barrier not only in tumorigenicity, but also in iPS cell generation,” Kawamura et al., 2009, Li et al. 2009 “In murine cells, Arf, rather than Ink4a, is the main barrier to reprogramming by activation of p53 (encoded by Trp53) and p21 (encoded by Cdkn1a); whereas, in human fibroblasts, INK4a is more important than ARF. Furthermore, organismal ageing upregulates the Ink4/Arf locus and, accordingly, reprogramming is less efficient in cells from old organisms,” MariÃ³n et al. 2009 “These observations indicate that during reprogramming cells increase their intolerance to different types of DNA damage and that p53 is critical in preventing the generation of human and mouse pluripotent cells from suboptimal parental cells,” Utikal et al., 2009, Zhao et al., 2008).” This has led to significant interest in finding compounds that “alleviate cell senescence without increasing the risk of mutations.” The researchers set out testing antioxidants for this purpose. The one that worked was vitamin C.
3. The main finding of the study is that vitamin C can markedly improve the efficiency of the reprogramming process for both mouse and human cells. “We show here that vitamin C, a common nutrient vital to human health, enhances the reprogramming of somatic cells to pluripotent stem cells. By adding Vc to the culture medium, we can now obtain high-quality iPSCs from mouse and human cells routinely.” Exactly how vitamin C works to achieve this end is not clear. Other tested antioxidants appeared not to have an effect. It is highly possible that epigenetic factors are involved. “Besides reducing p53, Vc accelerates transcriptome changes during reprogramming and allows the conversion of pre-iPSCs to iPSCs. The extent to which these observations relate to cell senescence is unclear, and it is possible that Vc is acting in other ways as well. For example, it could accelerate stochastic events during reprogramming, perhaps by promoting epigenetic modifications that allow further changes to proceed. In this regard, Vc is a cofactor in reactions driven by dioxygenases including collagen prolyl hydroxylases, HIF (hypoxia-inducible factor) prolyl hydroxylases, and histone demethylases (Shi, 2007), and it is interesting to consider that Vc might influence reprogramming by increasing the activity of these enzymes. Histone demethylases are important for development and modulate the expression of the ESC master transcription factor Nanog (Cloos et al., 2008), so it is possible that Vc allows the reprogramming to run more smoothly by facilitating histone demethylation.”
The new finding can result in increased productivity in creating iPSCs. However, there is still a way to go before the “closing the stem cell supply chain loop” hypothesis can be tested. If iPSCs are created outside the body from a person’s tissue, safe ways must be found to introduce them back into the body so they will go about replenishing stocks of Type B and Type C stem cells without creating problems such as tumors or teratomas.
Oh Spirit of Linus Pauling Great Father of Vitamin C, are you listening? A few days ago I wrote a blog entry Surprise! Just when we thought we knew everything about vitamin C, pointing to new research indicating that vitamin C could be a cure for Werner’s Syndrome. It looks like regularly taking vitamin C does a myriad of other things besides serving as a good antioxidant, things like preventing DNA damage induced by renovascular hypertension, and helping to control obesity. This week’s new finding relates to the usefulness of Vitamin C in creating iPSCs, possibly an important finding for regenerative medicine.
We have new powerful frameworks for looking at old familiar substances like vitamin C, frameworks like epigenetics, proteomics, telomere science and cell cycle molecular biology, and these frameworks are telling us things about vitamin C that Linus may have intuited but could not have put into words. Because most of the needed words did not exist in his time.
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