Identifying And Targeting Cancer Stem Cells

Here is a paper from several years ago demonstrating further identification of (colon) cancer stem cells, with information on targeting such cells for therapy.  Abstract:

The cancer stem cell (CSC) theory highlights a self-renewing subpopulation of cancer cells that fuels tumour growth. The existence of human CSCs is mainly supported by xeno-transplantation of prospectively isolated cells, but their clonal dynamics and plasticity remain elusive. Here, we demonstrate that human LGR5+ colorectal cancer cells serve as CSCs in growing cancer tissues. Lineage-tracing experiments with a CRISPR-Cas9-mediated LGR5-CreER knock-in allele reveal self-renewal and differentiation capacity of LGR5+ tumour cells. Selective ablation of LGR5+ CSCs in LGR5-iCaspase9 knock-in organoids leads to tumour regression, followed by tumour regrowth driven by re-emerging LGR5+ CSCs. KRT20-CreER marks differentiated cancer cells that constantly diminish in tumour tissues, while reverting to LGR5+ CSCs and contributing to tumour regrowth after LGR5+ CSC ablation. We also show that combined chemotherapy potentiates LGR5+ CSCs targeting. These data provide insights into the plasticity of CSCs and their potential as a therapeutic target in human colorectal cancer.

We'll be following further developments in this field.

Prevent Aging With Stem Cell Rejuvenation?

Discussion of a possible anti-aging approach, abstract:

Characterized by dysfunction of tissues, organs, organ systems and the whole organism, aging results from the reduced function of effective stem cell populations. Recent advances in aging research have demonstrated that old tissue stem cells can be rejuvenated for the purpose of maintaining the old-organ function by youthful re-calibration of the environment where stem cells reside. Biochemical cues regulating tissue stem cell function include molecular signaling pathways that interact between stem cells themselves and their niches. Historically, plasma fractions have been shown to contain factors capable of controlling age phenotypes; subsequently, signaling pathways involved in the aging process have been identified. Consequently, modulation of signaling pathways such as Notch/Delta, Wnt, transforming growth factor-β, JAK/STAT, mammalian target of rapamycin and p38 mitogen-activated protein kinase has demonstrated potential to rejuvenate stem cell function leading to organismic rejuvenation. Several synthetic agents and natural sources, such as phytochemicals and flavonoids, have been proposed to rejuvenate old stem cells by targeting these pathways. However, several concerns still remain to achieve effective organismic rejuvenation in clinical settings, such as possible carcinogenic actions; thus, further research is still required.

Note the point at the end about "possible carcinogenic actions."  Paradox: while the risk of most cancers increases with age, aging itself can be viewed as an anti-cancer mechanism, diminishing cell reproduction and stem cell activity (and elimination of stem cells) to prevent such cells with mutations from multiplying into tumors.  Thus, anti-aging approaches need to be cognizant of the cancer problem and find solutions to this possible problem.

Lessons From Mice And Flies

On Wnt signaling, abstract:

Adult stem cells play critical roles in the basal maintenance of tissue integrity, also known as homeostasis, and in tissue regeneration following damage. The highly conserved Wnt signalling pathway is a key regulator of stem cell fate. In the gastrointestinal tract, Wnt signalling activation drives homeostasis and damage-induced repair. Additionally, deregulated Wnt signalling is a common hallmark of age-associated tissue dysfunction and cancer. Studies using mouse and fruit fly models have greatly improved our understanding of the functional contribution of the Wnt signalling pathway in adult intestinal biology. Here, we summarize the latest knowledge acquired from mouse and Drosophila research regarding canonical Wnt signalling and its key functions during stem cell driven intestinal homeostasis, regeneration, ageing and cancer.

Low Oxygen And Osteogenic Differentiation

Low oxygen conditions can affect the differentiation of bone precursor cells.  Abstract:

This study examined the effects of low oxygen tension on the osteogenic differentiation of embryonic stem cells (ESCs) in a three-dimensional culture system. The high expression levels of hypoxia-related proteins hypoxia-inducible factor-1α and vascular endothelial growth factor were first validated in ESCs subjected to hypoxic conditions compared with normoxic controls. The osteogenic differentiation of hypoxic ESCs with either osteogenic or osteogenic factor-free media was subsequently evaluated by measuring alkaline phosphatase activity, intracellular calcium levels, matrix mineralization, and the protein levels of osteogenic markers Runt-related transcription factor 2 and osterix. We confirmed that hypoxia significantly stimulated ESC osteogenic activity; the strongest stimulation of ESC osteogenesis was exerted when cells were grown in osteogenic media. To identify differentially expressed genes associated with hypoxia-induced ESC differentiation, we performed microarray analysis of ESCs cultured in osteogenic media under normoxic and hypoxic conditions. This study demonstrated that differences in oxygen tension induced the differential expression of genes known to play roles in such processes as skeletal system development and signaling pathways for bone morphogenetic protein, Wnt, Notch, mitogen-activated protein kinase, and integrin. These findings reveal the effects of low oxygen tension on osteogenic progression in ESCs and provide insight into the molecular pathways that regulate ESC differentiation following exposure to hypoxia.

Another Useful Phytochemical

A phytochemical can suppress dangerous cancer stem cell qualities in liver cancer by inhibiting Wnt signaling; abstract:

The hierarchical tumor propagation or cancer stem cells (CSCs) model of carcinogenesis postulates that like physiologic adult stem cell (ASC), the CSCs positioned at the apex of any tumor population form the crux of tumor evolution with a constitutive regenerative capacity and differentiation potential. The propagation and recurrence of the characteristically heterogeneous and therapy-resistant hepatocellular carcinoma (HCC), adds to accumulating evidence to support this CSCs model. Based on the multi-etiologic basis of HCC formation which among others, focuses on the disruption of the canonical Wnt signaling pathway, this study evaluated the role of cembrane-type phytochemical, Ovatodiolide, in the modulation of the Wnt/[Formula: see text]-catenin pathway, and its subsequent effect on liver CSCs' activities. Our fluorescence-activated cell sorting (FACS) and quantitative RT-PCR analyses of side population (SP) indicated that CD133+ cells were [Formula: see text]-catenin-overexpressing, more aggressive, and resistant to the conventional anticancer agents, Cisplatin and Doxorubicin, when compared to [Formula: see text]-catenin-downregulated group. We demonstrated that marked upregulation of [Formula: see text]-catenin and its downstream targets effectively enhanced hepatosphere formation, with an associated induction of CD133, OCT4 and Sox2 expression and also caused an significant enhancement of HCC proliferation. However, treatment with Ovatodiolide induced downregulation of [Formula: see text]-catenin and its downstream effector genes, abolished hepatosphere formation and reversed the [Formula: see text]-catenin-associated enhancement of HCC growth. In summary, we demonstrated for the first time that Ovatodiolide suppressed the canonical Wnt signaling pathway, and inhibited the generation of liver CSCs; Thus, projecting Ovatodiolide as a putatively effective therapeutic agent for anti-HCC target therapy.

Cancer Stem Cells And Lipid Metabolism

Cancer stem cells seem to have an increased reliance on lipid metabolism, which can be a target for anti-cancer therapy.  I wonder if this has any implications for a ketogenic (high-fat) diet for cancer?  On the one hand, most cancer cells seem “glucose-addicted” so a low-carb, high-fat diet may be preferable.  On the other hand, if cancer stem cells rely more on fat, then will increased dietary fat be a problem?  This question needs to be investigated.  Abstract:

BACKGROUND:

Cancer stem cells (CSCs) or tumor-initiating cells (TICs) represent a small population of cancer cells with self-renewal and tumor-initiating properties. Unlike the bulk of tumor cells, CSCs or TICs are refractory to traditional therapy and are responsible for relapse or disease recurrence in cancer patients. Stem cells have distinct metabolic properties compared to differentiated cells, and metabolic rewiring contributes to self-renewal and stemness maintenance in CSCs.

MAIN BODY:

Recent advances in metabolomic detection, particularly in hyperspectral-stimulated raman scattering microscopy, have expanded our knowledge of the contribution of lipid metabolism to the generation and maintenance of CSCs. Alterations in lipid uptake, de novo lipogenesis, lipid droplets, lipid desaturation, and fatty acid oxidation are all clearly implicated in CSCs regulation. Alterations on lipid metabolism not only satisfies the energy demands and biomass production of CSCs, but also contributes to the activation of several important oncogenic signaling pathways, including Wnt/β-catenin and Hippo/YAP signaling. In this review, we summarize the current progress in this attractive field and describe some recent therapeutic agents specifically targeting CSCs based on their modulation of lipid metabolism.

CONCLUSION:

Increased reliance on lipid metabolism makes it a promising therapeutic strategy to eliminate CSCs. Targeting key players of fatty acids metabolism shows promising to anti-CSCs and tumor prevention effects.

Blood Stem Cell Hierarchy

Blood stem cells seem to have preferences to what they will differentiate into, including the “multipotent” stem cells that typically have the potential to become many cell types.  There seems to be a “hierarchy” of such stem cells, which may have implications for stem cell therapies.  Abstract:

Rare multipotent hematopoietic stem cells (HSCs) in adult bone marrow (BM) with extensive self-renewal potential possess the ability to efficiently replenish all myeloid and lymphoid blood cells, securing long-term multilineage reconstitution following physiological and clinical challenges, including chemotherapy and hematopoietic transplantations. HSC transplantation remains the only curative treatment for many hematological malignancies, but inefficient blood-lineage replenishment remains a major cause of morbidity and mortality. Single cell transplantation has uncovered considerable heterogeneity among reconstituting HSCs, supported by findings in unperturbed hematopoiesis and suggested to reflect different propensities for lineage-fate decisions by distinct myeloid-, lymphoid- and platelet-biased HSCs. Other studies suggested that such lineage bias might reflect generation within the phenotypic HSC compartment of unipotent or oligopotent self-renewing progenitors, and implicated uncoupling of the defining HSC properties of self-renewal and multipotency. Here, highly sensitive tracking of progenitors and mature cells of the megakaryocyte/platelet, erythroid, myeloid, B and T cell lineages produced from singly transplanted HSCs revealed a highly organized, predictable and stable framework for lineage-restricted fates of long-term self-renewing HSCs. Most notably, a distinct class of HSCs adopts a fate towards effective and stable replenishment of a megakaryocyte/platelet-lineage tree but not other blood cell lineages, despite sustained multipotency, whereas no HSCs contribute exclusively to any other single blood-cell lineage. Single multipotent HSCs can also fully restrict towards simultaneous replenishment of megakaryocyte, erythroid and myeloid lineages without executing their sustained lymphoid lineage potential. Genetic lineage tracing supports an important role of platelet-biased HSCs also in unperturbed adult hematopoiesis. These findings uncover a limited repertoire of distinct HSC subsets, defined by a predictable and hierarchical propensity to adopt a fate towards replenishment of a restricted set of blood lineages, prior to loss of self-renewal and multipotency.

CRISPR Editing In Blood Stem Cells

CRISPR editing in blood stem cells; abstract:

Genome editing via homologous recombination (HR) (gene targeting) in human hematopoietic stem cells (HSCs) has the power to reveal gene-function relationships and potentially transform curative hematological gene and cell therapies. However, there are no comprehensive and reproducible protocols for targeting HSCs for HR. Herein, we provide a detailed protocol for the production, enrichment, and in vitro and in vivo analyses of HR-targeted HSCs by combining CRISPR/Cas9 technology with the use of rAAV6 and flow cytometry. Using this protocol, researchers can introduce single-nucleotide changes into the genome or longer gene cassettes with the precision of genome editing. Along with our troubleshooting and optimization guidelines, researchers can use this protocol to streamline HSC genome editing at any locus of interest. The in vitro HSC-targeting protocol and analyses can be completed in 3 weeks, and the long-term in vivo HSC engraftment analyses in immunodeficient mice can be achieved in 16 weeks. This protocol enables manipulation of genes for investigation of gene functions during hematopoiesis, as well as for the correction of genetic mutations in HSC transplantation-based therapies for diseases such as sickle cell disease, β-thalassemia, and primary immunodeficiencies.

p53 Inhibits CRISPR-Cas9 Engineering In Human Pluripotent Stem Cells

Human pluripotent stem cells are difficult to engineer with the CRSPR system compared to other cell types, which is unfortunate given the great potential in being able to modify human stem cells.  The p53 gene protects against cancer and it seems that p53 function interferes with CRISPR modification of these human stem cell types by making the genetic alterations induced by CRISPR relatively toxic to the cells.  Human stem cells can acquire p53 mutations – which can lead to cancer – and it would seem that human stem cells that have been successfully engineered with CRISPR may be at higher risk for having p53 mutations since the presence of such mutations, inactivating toxicity to CRISPR, may have been the reason the cells were successfully engineered in the first place.  This is an important finding suggesting caution in using CRISPR in such cells and also suggests the need to find novel approaches that can increase CRISPR efficiency in these cells while still maintaining p53 and its anti-cancer functions.  Abstract:

CRISPR/Cas9 has revolutionized our ability to engineer genomes and conduct genome-wide screens in human cells1-3. Whereas some cell types are amenable to genome engineering, genomes of human pluripotent stem cells (hPSCs) have been difficult to engineer, with reduced efficiencies relative to tumour cell lines or mouse embryonic stem cells3-13. Here, using hPSC lines with stable integration of Cas9 or transient delivery of Cas9-ribonucleoproteins (RNPs), we achieved an average insertion or deletion (indel) efficiency greater than 80%. This high efficiency of indel generation revealed that double-strand breaks (DSBs) induced by Cas9 are toxic and kill most hPSCs. In previous studies, the toxicity of Cas9 in hPSCs was less apparent because of low transfection efficiency and subsequently low DSB induction 3 . The toxic response to DSBs was P53/TP53-dependent, such that the efficiency of precise genome engineering in hPSCs with a wild-type P53 gene was severely reduced. Our results indicate that Cas9 toxicity creates an obstacle to the high-throughput use of CRISPR/Cas9 for genome engineering and screening in hPSCs. Moreover, as hPSCs can acquire P53 mutations 14 , cell replacement therapies using CRISPR/Cas9-enginereed hPSCs should proceed with caution, and such engineered hPSCs should be monitored for P53 function.

Fasting And Stem Cell Function

In mice, a 24 hour fast improves the function of intestinal stem cells through effects on fatty acid oxidation (FAO).  Genetic knockout experiments emphasize the importance of FAO in the fasting effects and suggest possibilities for boosting intestinal stem cell regeneration.  Abstract:

Diet has a profound effect on tissue regeneration in diverse organisms, and low caloric states such as intermittent fasting have beneficial effects on organismal health and age-associated loss of tissue function. The role of adult stem and progenitor cells in responding to short-term fasting and whether such responses improve regeneration are not well studied. Here we show that a 24 hr fast augments intestinal stem cell (ISC) function in young and aged mice by inducing a fatty acid oxidation (FAO) program and that pharmacological activation of this program mimics many effects of fasting. Acute genetic disruption of Cpt1a, the rate-limiting enzyme in FAO, abrogates ISC-enhancing effects of fasting, but long-term Cpt1a deletion decreases ISC numbers and function, implicating a role for FAO in ISC maintenance. These findings highlight a role for FAO in mediating pro-regenerative effects of fasting in intestinal biology, and they may represent a viable strategy for enhancing intestinal regeneration.

Chemotherapy Conundrum

Chemotherapy is usually effective against cancer, but recurrence/resistance can occur.  Senescence – stopping of cell cycle and cell growth – is typically considered good for malignant cancer cells, stop them from dividing as a therapy.  But here we see that chemotherapy-induced senescence changes cancer cells so that if they are released from senescence and re-enter cell cycle growth, they are more dangerous than before – with more stem cell like properties and more aggressive growth.  This needs to be addressed.  Abstract:

Cellular senescence is a stress-responsive cell-cycle arrest program that terminates the further expansion of (pre-)malignant cells. Key signalling components of the senescence machinery, such as p16INK4a, p21CIP1 and p53, as well as trimethylation of lysine 9 at histone H3 (H3K9me3), also operate as critical regulators of stem-cell functions (which are collectively termed 'stemness'). In cancer cells, a gain of stemness may have profound implications for tumour aggressiveness and clinical outcome. Here we investigated whether chemotherapy-induced senescence could change stem-cell-related properties of malignant cells. Gene expression and functional analyses comparing senescent and non-senescent B-cell lymphomas from Eμ-Myc transgenic mice revealed substantial upregulation of an adult tissue stem-cell signature, activated Wnt signalling, and distinct stem-cell markers in senescence. Using genetically switchable models of senescence targeting H3K9me3 or p53 to mimic spontaneous escape from the arrested condition, we found that cells released from senescence re-entered the cell cycle with strongly enhanced and Wnt-dependent clonogenic growth potential compared to virtually identical populations that had been equally exposed to chemotherapy but had never been senescent. In vivo, these previously senescent cells presented with a much higher tumour initiation potential. Notably, the temporary enforcement of senescence in p53-regulatable models of acute lymphoblastic leukaemia and acute myeloid leukaemia was found to reprogram non-stem bulk leukaemia cells into self-renewing, leukaemia-initiating stem cells. Our data, which are further supported by consistent results in human cancer cell lines and primary samples of human haematological malignancies, reveal that senescence-associated stemness is an unexpected, cell-autonomous feature that exerts its detrimental, highly aggressive growth potential upon escape from cell-cycle blockade, and is enriched in relapse tumours. These findings have profound implications for cancer therapy, and provide new mechanistic insights into the plasticity of cancer cells

Human Colon Reconstruction In A Mouse Model

This is an exciting paper, in which human colon stem cells were used to reconstruct human colon epithelium – a step toward colon reconstruction – in a mouse model.  The transplanted human material was stable in the mouse once the original mouse tissues were removed.  This new model allows for further experimental analysis of this system, which is not only useful for basic science, but also for regenerative medicine approaches (e.g., replacing human colon that had to be removed for medical reasons).  Abstract:

Genetic lineage tracing has revealed that Lgr5+ murine colon stem cells (CoSCs) rapidly proliferate at the crypt bottom. However, the spatiotemporal dynamics of human CoSCs in vivo have remained experimentally intractable. Here we established an orthotopic xenograft system for normal human colon organoids, enabling stable reconstruction of the human colon epithelium in vivo. Xenografted organoids were prone to displacement by the remaining murine crypts, and this could be overcome by complete removal of the mouse epithelium. Xenografted organoids formed crypt structures distinctively different from surrounding mouse crypts, reflecting their human origin. Lineage tracing using CRISPR-Cas9 to engineer an LGR5-CreER knockin allele demonstrated self-renewal and multipotency of LGR5+ CoSCs. In contrast to the rapidly cycling properties of mouse Lgr5+ CoSCs, human LGR5+ CoSCs were slow-cycling in vivo. This organoid-based orthotopic xenograft model enables investigation of the functional behaviors of human CoSCs in vivo, with potential therapeutic applications in regenerative medicine.

Cancer Stem Cells And Lipid Metabolism

Cancer stem cells are highly dependent upon lipid metabolism; abstract:

Cancer stem cells (CSCs) are an uncommon subset of tumor cells capable of self-renewal, differentiating, and recreating the parental tumor when transplanted into the murine background. Over the past two decades, efforts toward understanding CSC biology culminated into identifying a set of signaling pathways sustaining "stemness". Nevertheless, while metabolic rewiring is nowadays considered a hallmark of cancer, no consensus has been reached on the metabolic features underlying the plastic nature of CSCs, which are capable of residing in a dormant state, and able to rapidly proliferate when the need to repopulate the tumor mass arises. An emerging concept in the field of CSC metabolism is that these cells are extremely reliant on the activity of enzymes involved in lipid metabolism, such as stearoyl-CoA desaturase 1 (SCD1) and 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR). Indeed, SCD1 and HMG-CoAR have been described as key factors for the correct function of a number of concatenated pathways involved in CSC fate decision, such as Hippo and Wnt. In the present review, we describe metabolic futures of CSCs with a special focus on lipid metabolism, which until now represents an underappreciated force in maintaining CSCs and an attractive therapeutic target.

Besides being a potential therapeutic target one can speculate if this is involved – even if indirectly – in the link between obesity and cancer.

Regenerating Human Skin

Stem cell therapy is an exciting approach for many human disorders; here we see an example of an entire epidermis (skin) being regenerated on a child suffering from a life-threatening case of a skin disorder, junctional epidermolysis bullosa. Abstract:

Junctional epidermolysis bullosa (JEB) is a severe and often lethal genetic disease caused by mutations in genes encoding the basement membrane component laminin-332. Surviving patients with JEB develop chronic wounds to the skin and mucosa, which impair their quality of life and lead to skin cancer. Here we show that autologous transgenic keratinocyte cultures regenerated an entire, fully functional epidermis on a seven-year-old child suffering from a devastating, life-threatening form of JEB. The proviral integration pattern was maintained in vivo and epidermal renewal did not cause any clonal selection. Clonal tracing showed that the human epidermis is sustained not by equipotent progenitors, but by a limited number of long-lived stem cells, detected as holoclones, that can extensively self-renew in vitro and in vivo and produce progenitors that replenish terminally differentiated keratinocytes. This study provides a blueprint that can be applied to other stem cell-mediated combined ex vivo cell and gene therapies.

Blue Light Activation Of Gene Expression

Here is an interesting study in which human cells are modified so that they react to blue light exposure with altered gene expression.  This has many implications for gene therapy, as well as for stem cell therapy; for the latter, blue light exposure could be used to make stem cells given to the patient differentiate (i.e., transform into) the type of mature cell needed for the relevant therapy.  Abstract:

Our improved CRISPR-Cas9-based photoactivatable transcription systems, CPTS2.0 and Split-CPTS2.0, enable high blue-light-inducible activation of endogenous target genes in various human cell lines. We achieved reversible activation of target genes with CPTS2.0 and induced neuronal differentiation in induced pluripotent stem cells (iPSCs) by upregulating NEUROD1 with Split-CPTS2.0

Potential Stem Cell Therapeutic Engineering

This paper discusses some advances in genetic engineering of cells, which may be of use “to develop innovative stem cell-based therapeutics.”  The link between basic science and therapeutic advances remains strong.  Abstract:

Precise and efficient manipulation of genes is crucial for understanding the molecular mechanisms that govern human hematopoiesis and for developing novel therapies for diseases of the blood and immune system. Current methods do not enable precise engineering of complex genotypes that can be easily tracked in a mixed population of cells. We describe a method to multiplex homologous recombination (HR) in human hematopoietic stem and progenitor cells and primary human T cells by combining rAAV6 donor delivery and the CRISPR/Cas9 system delivered as ribonucleoproteins (RNPs). In addition, the use of reporter genes allows FACS-purification and tracking of cells that have had multiple alleles or loci modified by HR. We believe this method will enable broad applications not only to the study of human hematopoietic gene function and networks, but also to perform sophisticated synthetic biology to develop innovative engineered stem cell-based therapeutics.

Cancer Stem Cell Switch

By Philippe Hupé - Emmanuel Barillot, Laurence Calzone, Philippe Hupé, Jean-Philippe Vert, Andrei Zinovyev, Computational Systems Biology of Cancer Chapman & Hall/CRC Mathematical & Computational Biology , 2012, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18530796

The cancer stem cell hypothesis postulates that at least some cancers are driven by carcinogenic stem cells, that are resistant to treatment.  Forcing those cancer stem cells to stop proliferating (stopping self-renewal) and differentiate (become a more specialized cell type with decreased or no ability to reproduce) is a possible therapeutic approach.  A small RNA that affects gene expression (micro-RNA) called miR-600 can promote a “switch” between self-renewal and proliferation of these cancer stem cells; an example of basic science discoveries that one day can be used for cancer therapy.  Abstract:

Tumors are organized in a cellular hierarchy with a population of cancer stem cell (CSC) driving cancer progression and resistance to treatment. Recently, we identified miR-600 as a bimodal switcher that balances breast CSC-fate from a self-renewing to a differentiation state, with a direct impact on tumor progression.

iPS Cells Against Parkinson's Disease

By Y tambe - Y_tambe's file, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3210604

Induced pluripotent stem (iPS) cells have the potential to help with many human disorders, and bypass the ethical problems of embyronic stem cells, since the iPS cells are derived from adult cells. A study has shown promise in using iPS cells against Parkinson's disease in a macaque primate model of the disease.  Abstract:

Induced pluripotent stem cells (iPS cells) are a promising source for a cell-based therapy to treat Parkinson's disease (PD), in which midbrain dopaminergic neurons progressively degenerate. However, long-term analysis of human iPS cell-derived dopaminergic neurons in primate PD models has never been performed to our knowledge. Here we show that human iPS cell-derived dopaminergic progenitor cells survived and functioned as midbrain dopaminergic neurons in a primate model of PD (Macaca fascicularis) treated with the neurotoxin MPTP. Score-based and video-recording analyses revealed an increase in spontaneous movement of the monkeys after transplantation. Histological studies showed that the mature dopaminergic neurons extended dense neurites into the host striatum; this effect was consistent regardless of whether the cells were derived from patients with PD or from healthy individuals. Cells sorted by the floor plate marker CORIN did not form any tumours in the brains for at least two years. Finally, magnetic resonance imaging and positron emission tomography were used to monitor the survival, expansion and function of the grafted cells as well as the immune response in the host brain. Thus, this preclinical study using a primate model indicates that human iPS cell-derived dopaminergic progenitors are clinically applicable for the treatment of patients with PD.

Forever young versus the self-destruction of the body

The Daily Beast named 2015 "The Year We Decided to Live Forever". Why? Because the rich people (e.g., Peter Thiel, Sergey Brin, Mark Zuckerberg, etc.) would like to live if not forever, for a very, very long time, and therefore, are ready to fund research on extending human life with millions of dollars.

However, increasing the quality of the years, rather than the number of years, we live might be a better goal. For example, can we increase dramatically the quality of life beyond age of 50? To achieve this, we need to know exactly what causes aging and the associated conditions.


Artistic representation of human age
 
A 2015 study based upon 1554 individuals (including centenarians), established that among all physiological markers, the inflammation score was the best predictor of successful aging at extreme old age (Arai Y, et al. Inflammation, But Not Telomere Length, Predicts Successful Ageing at Extreme Old Age: A Longitudinal Study of Semi-supercentenarians. EBioMedicine. 2(10):1549-58; 2015.) This study confirmed the already established consensus that chronic inflammation is a defining feature of aging, and that inflammation is present in many, if not all age-associated diseases and conditions: Alzheimer’s disease, dementia, cardiovascular disease, multiple sclerosis, diabetes, etc. The increase in pro-inflammatory factors with age has been well documented. Plasma levels of the complement protein C1q were shown to increase with age and to promote age-related MuSC decline by activation of the Wnt signaling pathway (A. S. Brack et al., Science 317, 807–810 (2007) A. T. Naito et al., Cell 149, 1298–1313, 2012). Similarly, beta 2-microglobulin, a component of the major histocompatibility complex, was found to be elevated in the blood of aged mice and to contribute to the age-related decline of the organism (L. K. Smith et al., Nat. Med. 21, 932–937, 2015).

There are many hypotheses about the association between age and inflammation. However, scientists are still unsure whether inflammation causes aging, or vice versa, aging causes inflammation.

One of the best explanations (with most logic in it) is that inflammation does cause aging, and inflammation is the result of the immune response to the mutations that we accumulate with age. The more we live, the more mutations we accumulate. Some of these mutations could  contribute to cancer development, but some do not. However, all mutations that change our proteins sufficiently to induce immune response may contribute to the increasing levels of inflammation in the body. As a result, our own immune system starts attacking and damaging our own body.

To slow down, but not eliminate entirely, the accumulation of mutations (and therefore, the ensuing inflammation and aging) one needs to live a life free of mutagens (as a part of a healthy lifestyle). Of course, we cannot be entirely free of mutagens, but we can eliminate the most obvious ones (e.g., smoking, alcohol, processed meat, etc.).   

Another complimentary approach of evading fast aging is this of slowing down the division of the adult stem cells in our bodies. This is important, since most mutations accumulate during stem cell divisions (by the way, the attrition of telomeres also happens during cell division), and these stem cells can give rise to many other cells (stem cells, progenitor and differentiated cells of the body). 

Drosophila (fruit fly)

The only way that we might be able to slow down stem cell divisions in our body is through periodic fasting and calorie restriction. The more we eat, the faster the adult stem cells divide, and the faster we age. There is a direct evidence that well-fed state results in more stem cell divisions at least in studies of fruit flies.