Nanog Gene Reverses Aging in Adult Stem Cells


Professor Stelios Andreadis from SUNY Buffalo and his colleagues have, in a series of elegant experiments, shown that the gene Nanog can stimulate dormant cellular processes that seem to be vital for preventing weak bones, clogged arteries and other telltale signs of aging. The findings might help counteract premature aging disorders such as Hutchinson-Gilford progeria syndrome.

“Our research into Nanog is helping us to better understand the process of aging and ultimately how to reverse it,” said Andreadis.

In order to delay or even reverse the ravages of aging, the human body holds a reservoir of nonspecialized progenitor cells that can regenerate organs. These cells are collectively called “adult stem cells,” and they are in every tissue of the body. Adult stem cells can rapidly respond to tissue damage to regenerate and heal organs and tissues. Unfortunately, as people age, fewer adult stem cells pare able to properly perform their function. This leads to the clinical scenarios associated with aging. Reversing the effects of aging in adult stem cells – re-booting them if you will – can potentially overcome this problem.

Andreadis and his coworkers have previously shown that the capacity of adult stem cells to form muscle and generate force declines with age. Specifically, Andreadis and others examined smooth muscle cells found in arteries, intestines and other tissues. In this new study, grad student Panagiotis Mistriotis introduced a gene called Nanog into aged stem cells. He found that Nanog activated two key cellular pathways that include Rho-associated protein kinase (ROCK) and Transforming growth factor beta (TGF-β). Activation of these two signaling pathways awakens dormant proteins like actin to build the new cytoskeletal networks that adult stem cells need to form contracting muscle cells. Force generated by these cells ultimately helps restore the regenerative properties that adult stem cells lose due to aging.

“Not only does Nanog have the capacity to delay aging, it has the potential in some cases to reverse it,” said Andreadis, who noted that introduction of the Nanog gene worked in three different models of aging: cells isolated from aged donors, cells aged in culture, and cells isolated from patients with Hutchinson-Gilford progeria syndrome.

Additionally, Andreadis and his group found that Nanog activated the central regulator of muscle formation, a signaling protein called serum response factor (SRF), which suggests that the same results may be applicable for skeletal, cardiac and other muscle types.

Andreadis and others are now examining potential drugs that can replace or mimic the effects of the Nanog gene. This will allow them to study the consequences of aging inside the body can also be reversed. This could have implications in an array of illnesses, everything from atherosclerosis, high blood pressure, and osteoporosis to Alzheimer’s disease.

This fascinating paper was published here: Panagiotis Mistriotis et al., “NANOG Reverses the Myogenic Differentiation Potential of Senescent Stem Cells by Restoring ACTIN Filamentous Organization and SRF-Dependent Gene Expression,” Stem Cells, 2016; DOI: 10.1002/stem.2452.

Stem Cell Behavior in Three-Dimensional Matrices


Scientists from Case Western Reserve in Cleveland, Ohio have used hydrogels (jello-like materials) to make three-dimensional structures that direct stem cell behavior.

Physical and biochemical signals guide stem cell behavior and directs them to differentiate and make tissues like muscle, blood vessels, or bone. The exact recipes to produce each particular tissue remains unknown, but the Case Western Reserve team has provided a way to discover these recipes.

Ultimately, scientists would like to manipulate stem cells in order to repair or replace damaged tissues. They would also like to engineer new tissues and organs.

Eben Alsberg. associate professor of biomedical engineering and orthopedic surgery at Case Western Reserve, who was also the senior author on this research said, “If we can control the spatial preservation of signals, we have be able to have more control over cell behavior and enhance the rate and quality of tissue formation. Many tissues form during development and healing processes at least in part due to gradients of signals: gradients of growth factors, gradients of physical triggers.”

Alsberg and his colleagues have tested their system on mesenchymal stem cells, and in doing so have turned them into bone or cartilage cells. Regulating the presentation of certain signals in three-dimensional space may be a key to engineering complex tissues; such tissues as bone and cartilage. For example, if we want to convert cartilage-making cells into bone-making cells or visa-verse, several different signals are required to induce the stem cells to change into different cell types in order to form the tissues you need.

To test their ideas, Alsberg and coworkers two different growth factors directed the stem cells to differentiate into either bone or cartilage.  One of these growth factors, transforming growth factor-beta (TGF-beta) promotes cartilage formation while a different growth factor, bone morphogen protein-2 (BMP-2).  Alsberg and his crew placed mesenchymal stem cells into an alginate hydrogel with varying concentrations of these growth factors.  Alginate comes from seaweed and when you hit it with ultraviolet light, it crosslinks to form a jello-like material called a hydrogel.   To create gradients of these growth factors, Alsberg developed a very inventive method in which they loaded a syringes with these growth factors and hooked them to a computer controlled pump that released lots of BMP-2 and a little TGF-1beta and tapered the levels of BMP-2 and then gradually increased the levels of TGF-1beta (see panel A below).  

 Fabrication of microparticle-based gradient alginate hydrogels. (A) Photograph of gradient making system. (B) Flow rates of two syringes to pump a linear gradient for a 5 cm length × 2 mm diameter alginate hydrogel. After linear gradient pumping for 3 min, an additional 50 μL of alginate solution, which is the volume from the Y point to the beginning of quartz tube, was further pumped into a spiral mixer for 1 min. (C) Photomicrographs of microparticles in cross-sections of gradient alginate hydrogel segments. Segments 1-10 represent sequential segments of the gel. (D) Quantification of microparticles in each segment of gradient alginate hydrogels.
Fabrication of microparticle-based gradient alginate hydrogels. (A) Photograph of gradient making system. (B) Flow rates of two syringes to pump a linear gradient for a 5 cm length × 2 mm diameter alginate hydrogel. After linear gradient pumping for 3 min, an additional 50 μL of alginate solution, which is the volume from the Y point to the beginning of quartz tube, was further pumped into a spiral mixer for 1 min. (C) Photomicrographs of microparticles in cross-sections of gradient alginate hydrogel segments. Segments 1-10 represent sequential segments of the gel. (D) Quantification of microparticles in each segment of gradient alginate hydrogels.

The result has an alginate hydrogen with mesenchymal stem cell embedded in it that had a high concentration of BMP-2 at one end and a high concentration of TGF-1beta at the other end.  Alsberg also modified the hydrogel by attached RGD peptides to it so that the stem cells would bind the hydrogel.  The peptide RGD (arginine-glycine-aspartic acid) binds to the integrin receptors, which happen to be one of the main cell adhesion protein on the surfaces of these cells.  This modification increases the exposure of the mesenchymal stem cells to the growth factors.  After culturing mesenchymal stem cells in the hydrogel, they discovered that the majority of the cells were in the areas of the hydrogel that had the highest concentration of RDG peptides.  

In another other experiment Alsberg and others varied the crosslinks in the hydrogel.  They used hydrogels with few crosslinks that were more flexible and hydrogels that have quite a few crosslinks and were stiffer.  The stem cells clearly preferred the more flexible hydrogels.  Alsberg thinks that the more flexible hydrogels might show better diffusion of the growth factors and better waste removal.  

“This is exciting,” gushed Alsberg.  “We can look at this work as a proof of principle.  Using this approach, you can use any growth factor or any adhesion ligand that influences cell behavior and study the role of gradient presentation.  We can also examine multiple different parameters in one system to investigate the role of these gradients in combination on cell behavior.”  

This technology might also be a platform for testing different recipes that would direct stem cells to become fat, cartilage, bone, or other tissues.  Also, since this hydrogel is also biodegradable, stem cells grown in the hydrogel could be implanted into patients.  Since the cells would be in the process of forming the desired tissue, their implantation might restore function and promote healing.  Clearly Alsberg is on to something.  

Making New Neurons When You Need Them


Western societies are aging societies, and the incidence of dementias, Alzheimer’s disease, and other diseases of the aged are on the rise. Treatments for these conditions are largely supportive, but being able to make new neurons to replace the ones that have died is almost certainly where it’s at.

At INSERM and CEA in Marseille, France, researchers have shown that chemicals that block the activity of a growth factor called TGF-beta improves the generation of new neurons in aged mice. These findings have spurred new investigations into compounds that can enable new neuron production in order to mitigate the symptoms of neurodegenerative diseases. Such treatments could also restore the cognitive abilities of those who have suffered neuron loss as a result of radiation therapy or a stroke.

The brain forms new neurons regularly to maintain our cognitive abilities, but aging or radiation therapy to treat tumors can greatly perturb this function. Radiation therapy is the adjunctive therapy of choice for brain tumors in children and adults.

Various studies suggest that the reduction in our cache of neurons contributes to cognitive decline. For example, exposure of mice to 15 Grays of radiation is accompanied by disruption to the olfactory memory and reduction in neuron production. A similar event occurs as a result of aging, but in human patients undergoing radiation treatment, cognitive decline is accelerated and seems to result from the death of neurons.

How then, can we preserve the cache of neurons in our brains? The first step is to determine the factors responsible for the decline is neuron production. In contrast to contemporary theory, neither heavy doses of radiation nor aging causes completely destruction of the neural stem cells that can replenish neurons. Even after doses of radiation and aging, neuron stem cell activity remains highly localized in the subventricular zone (a paired brain structure located in the outer walls of the lateral ventricles), but they do not work properly.

Subventricular Zone
Subventricular Zone

Experiments at the INSERM and CEA strongly suggest that in response to aging and high doses of radiation, the brain makes high levels of a signaling molecule called TGF-beta, and this signaling molecule pushes neural stem cell populations into dormancy. This dormancy also increases the susceptibility of neural stem cells into apoptosis.

Marc-Andre Mouthon, one of the main authors of this research, explained his results in this manner: “Our study concluded that although neurogenesis is reduced in aging and after a high dose of radiation, many stem cells survive for several months, retaining their ‘stem’ characteristics.”

Part two of this project showed that blocking TGFbeta with drugs restored the production of new neurons in aging or irradiated mice.

Thus targeted therapies that block TGFbeta in the brains of older patients or cancer patients who have undergone high dose radiation for a brain tumor might reduce the impact of brain lesions caused by such events in elderly patients who show distinct signs of cognitive decline.