Embryonic gene reverses old age in adult stem cells, in the lab

Getting old is an inevitable fact of life but what exactly causes it? One major hallmark of the aging process is cell senescence, in which cells gradually lose the ability to divide, leading to a breakdown in proper organ function. Adult stem cells that reside in our tissues usually spring into action to replenish cells lost to senescence (as well as injury and disease). But, unfortunately, senescence also affects stem cells, causing their natural regenerative capacity to diminish as we age.

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During the aging process, our stem cells gradually lose their regenerative potential (image source)

But what if we could tinker with senescence in these elderly stem cells? Could we slow down the aging process? A recent study by University of Buffalo scientists says yes, at least in a petri dish. Reporting in Stem Cells, the team shows that artificially activating the NANOG gene alone can reverse aging in adult mesenchymal stem cells (MSCs) and restore their full potential to form functional muscle tissue.

If you’re up on your induced pluripotent stem (iPS) cell knowledge, then you probably know that NANOG is a member of the “famous four”: the group of genes that can reprogram, say, a skin or blood cell, back into an embryonic stem cell-like state.  In this study, the research team derived human MSCs and mimicked senescence by allowing the cells to divide 12 to 16 times (Late Passage, or LP) in petri dishes and compared them to cells allowed to divide only a few times (Early Passage, or EP). The cells were genetically engineered to produce high levels of NANOG when the drug tetracycline was added to the cell culture.

First, the team looked at the impact of NANOG activation on various genes. They found that the activation level of several genes that had been suppressed in the senescent LP cells was restored to the levels seen in the pre-senescent EP cells. A closer look at the identity of those genes showed they were genes important for the capacity of a cell to develop into muscle and blood vessel which corresponds well with the MSCs potential to specialize into muscle and vascular tissue. Based on that genetic analysis, follow up experiments showed that NANOG indeed restored the senescent LP cells’ potential to develop into muscle and restore the muscle tissue’s contractile function.

Premature senescence is observed in diseases such as Hutchinson–Gilford Progeria Syndrome (HGPS), a fatal genetic disorder that causes rapid aging in childhood. NANOG was artificially activated in human MSCs, derived from a HGPS patient in this study, and also showed a restoration of the MSCs’ potential, as seen in the other donor cells.

In a university press release, lead author Stelios Andreadis, summarized the findings this way:

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

 

This work is very early days for this research especially given that these studies were performed in lab dishes and not animals. And because NANOG is a powerful gene that promotes embryonic and stem cell identity, the scientists will need to look into potential negative long term side effects for activating NANOG in adult stem cells. Ultimately, this path of research could uncover methods to treat aging-related diseases.

Bringing down the gatekeeper for a stem cell-based Parkinson’s cure

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University of Buffalo researchers converted these dopamine neurons directly from human skin cells. Image shows a protein found only in neurons (red) and an enzyme that synthesizes dopamine (green). Cell DNA is labeled in blue.

On the surface, a stem cell-based cure for Parkinson’s disease seems pretty straight-forward. This age-related neurodegenerative disorder, which leads to progressively worsening tremors, slowness of movement and muscle rigidity, is caused by the death of a specific type of nerve cell, or neuron, that produces the chemical dopamine in a specific region of the brain. So it would seem that simply transplanting stem cell-derived dopamine-producing neurons (DA neurons) in the brains of Parkinson’s patients to replace the lost cells would restore dopamine levels and alleviate Parkinson’s symptoms.

Easier said than done
Well, it hasn’t turned out to be that easy. After initial promising results using fetal brain stem cell transplants in the 80’s and 90’s, larger clinical trials showed no significant benefit and even led to a worsening of symptoms in some patients. One potential issue with those early trials could have been variable cell composition of the fetal cell-based therapy. On top of that, the availability of fetal tissue is limited and the quantities of transplantable cells obtained from these samples are very low.

More recently, researchers have been busy at generating more pure populations of DA neurons from human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). Great progress has been made so far, but the field is still hampered by not being able to make enough DA neurons from hESCs and iPSCs in a timely manner.

Cutting out the pluripotent “middle man”
This week a research team at the University of Buffalo reported in Nature Communications about a much more efficient method for producing DA neurons. It’s a finding that could provide a strong push towards stem cell-based therapy development for Parkinson’s disease.

The team bypassed the need to start with hESCs or iPSCs and instead converted skin cells directly into DA neurons. A thorough analysis of the cells confirmed that they were functional and matched that characteristics of the specific dopamine neurons that are lost in Parkinson’s.

This direct reprogramming of skin cells into DA neurons as well as other cells is a technique pioneered by several independent researchers including some of our own grantees. This method is thought to have a few advantages over the specialization of immature hESCs or iPSCs into tissue-specific cells. Not only is the direct reprogramming process faster it also doesn’t require cell division so there’s less concern about the introduction of DNA mutations and the potential of tumor formation. Another plus for direct reprogramming is the possibility of inducing the direct conversion of one cell type into another inside the body rather than relying on the manipulation of hESCs and iPSCs in the lab. Still, despite these advantages the efficiency of direct reprogramming is still very low. That’s where the University of Buffalo team comes into the picture.

Bringing down the gatekeeper
The researchers led by physiology and biophysics professor Jian Feng, made a few key modifications to increase the efficiency of the current skin cell to DA neuron direct reprogramming methods. They first reduced the level of a protein call p53. This protein has several nicknames like “guardian of our genes” and “tumor suppressor” because it plays critical roles in controlling cell division and DNA repair and, in turn, helps keep a clamp on cell growth.

Reducing the presence of p53 during the direct reprogramming process led to a much more efficient conversion of skin cells to DA neurons. And because the conversion from a skin cell to a neuron happens quickly – just a couple days – timing the introduction of cell nutrients specific to neurons had to be carefully watched. Together, these tweaks improved upon previous studies as Feng mentioned in a University of Buffalo press release:

“The best previous method could take two weeks to produce 5 percent dopamine neurons. With ours, we got 60 percent dopamine neurons in ten days.”

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Jian Feng, PhD, professor of physiology and biophysics, Jacobs School of Medicine and Biomedical Sciences, University of Buffalo

IMHO (In my humble opinion)
I imagine there’s a lot more work ahead to get this method of deriving DA neurons from skin ready for the clinic. This reprogramming technique relied on the introduction of neuron-specific genes into the skin cells using a deactivated virus as the means of delivery. Even though the virus is inactive, its viral DNA randomly inserts into the cells’ chromosomes which can turn on genes that cause cancer. Therefore, a non-viral version of this method would need to be developed for clinical use.

Also, as mentioned earlier, since p53 inhibits tumors by suppressing uncontrolled cell division, it would be important to make sure that a reduction of p53 didn’t lead to any long-term negative consequences, like the transplantation of potentially cancerous cells into the patient.

Still, this dramatic increase in efficiency for making functional DA neurons and the identification of p53 as a key control point for direct reprogramming are very exciting developments for a disease field that is committed to finding cures for its patients.

Related links:

From the Stem Cellar archives: blogs about direct reprogramming
Video: CIRM Grantee Marius Wernig discusses direct reprogramming
Video: Thirty second elevator pitch describing direct reprogramming