Thomas Rando

The life of a sleeping muscle stem cell is very busy

/ Todd Dubnicoff / Leave a comment

For biological processes, knowing when to slow down is as important as knowing when to step on the accelerator. Take for example muscle stem cells. In a healthy state, these cells mostly lay quiet and rarely divide but upon injury, they bolt into action by dividing and specializing into new muscle cells to help repair damaged muscle tissue. Once that mission is accomplished, the small pool of muscle stem cells is replenished through self-renewal before going back into a dormant, or quiescent, state.

muscle stem cell

Muscle stem cell (pink with green outline) sits along a muscle fiber. Image: Michael Rudnicki/OIRM

“Dormant” may not be the best way to describe it because a lot of activity is going on within the cells to maintain its sleepy state. And a better understanding of the processes at play in a dormant state could reveal insights about treating aging or diseased muscles which often suffer from a depletion of muscle stem cells. One way to analyze cellular activity is by examining RNA transcripts which are created when a gene is turned “on”. These transcripts are the messenger molecules that provide a gene’s instructions for making a particular protein.

By observing something, you change it
In order to carry out the RNA transcript analyses in animal studies, researchers must isolate and purify the stem cells from muscle tissue. The worry here is that all of the necessary poking of prodding of the cells during the isolation method will alter the RNA transcripts leading to a misinterpretation of what is actually happening in the native muscle tissue. To overcome this challenge, Dr. Thomas Rando and his team at Stanford University applied a recently developed technique that allowed them to tag and track the RNA transcripts within living mice.

The CIRM-funded study reported today in Cell Reports found that there are indeed significant differences in results when comparing the standard in vitro lab method to the newer in vivo method. As science writer Krista Conger summarized in a Stanford Medical School press release, those differences led to some unexpected results that hadn’t been observed previously:

“The researchers were particularly surprised to learn that many of the RNAs made by the muscle stem cells in vivo are either degraded before they are made into proteins, or they are made into proteins that are then rapidly destroyed — a seemingly shocking waste of energy for cells that spend most of their lives just cooling their heels along the muscle fiber.”

It takes a lot of energy to stay ready
Dr. Rando thinks that these curious observations do not point to an inefficient use of a cell’s resources but instead, “it’s possible that this is one way the cells stay ready to undergo a rapid transformation, either by blocking degradation of RNA or proteins or by swiftly initiating translation of already existing RNA transcripts.”

The new method provides Rando’s team a whole new perceptive on understanding what’s happening behind the scenes during a muscle stem cell’s “dormant” state. And Rando thinks the technique has applications well beyond this study:

Rando

Thomas Rando

“It’s so important to know what we are and are not modeling about the state of these cells in vivo. This study will have a big impact on how researchers in the field think about understanding the characteristics of stem cells as they exist in their native state in the tissue.”

 

 

Could revving up stem cells help senior citizens heal as fast as high school seniors?

/ Todd Dubnicoff / Leave a comment

All physicians, especially surgeons, sport medicine doctors, and military medical corps share a similar wish: to able to speed up the healing process for their patients’ incisions and injuries. Data published this week in Cell Reports may one day fulfill that wish. The study – reported by a Stanford University research team – pinpoints a single protein that revs up stem cells in the body, enabling them to repair tissue at a quicker rate.

Screen Shot 2017-04-19 at 5.37.38 PM

Muscle fibers (dark areas surrounding by green circles) are larger in mice injected with HGFA protein (right panel) compared to untreated mice (left panel), an indication of faster healing after muscle injury.
(Image: Cell Reports 19 (3) p. 479-486, fig 3C)

Most of the time, adult stem cells in the body keep to themselves and rarely divide. This calmness helps preserve this important, small pool of cells and avoids unnecessary mutations that may happen whenever DNA is copied during cell division.

To respond to injury, stem cells must be primed by dividing one time, which is a very slow process and can take several days. Once in this “alert” state, the stem cells are poised to start dividing much faster and help repair damaged tissue. The Stanford team, led by Dr. Thomas Rando, aimed to track down the signals that are responsible for this priming process with the hope of developing drugs that could help jump-start the healing process.

Super healing serum: it’s not just in video games
The team collected blood serum from mice two days after the animals had been subjected to a muscle injury (the mice were placed under anesthesia during the procedure and given pain medication afterwards). When that “injured” blood was injected into a different set of mice, their muscle stem cells became primed much faster than mice injected with “uninjured” blood.

“Clearly, blood from the injured animal contains a factor that alerts the stem cells,” said Rando in a press release. “We wanted to know, what is it in the blood that is doing this?”

 

A deeper examination of the priming process zeroed in on a muscle stem cell signal that is turned on by a protein in the blood called hepatocyte growth factor (HGF). So, it seemed likely that HGF was the protein that they had been looking for. But, to their surprise, there were no differences in the amount of HGF found in blood from injured and uninjured mice.

HGFA: the holy grail of healing?
It turns out, though, that HGF must first be chopped in two by an enzyme called HGFA to become active. When the team went back and examined the injured and uninjured blood, they found that it was HGFA which showed a difference: it was more active in the injured blood.

To show that HGFA was directly involved in stimulating tissue repair, the team injected mice with the enzyme two days before the muscle injury procedure. Twenty days post injury, the mice injected with HGFA had regenerated larger muscle fibers compared to untreated mice. Even more telling, nine days after the HGFA treatment, the mice had better recovery in terms of their wheel running activity compared to untreated mice.

To mimic tissue repair after a surgery incision, the team also looked at the impact of HGFA on skin wound healing. Like the muscle injury results, injecting animals with HGFA two days before creating a skin injury led to better wound healing compared to untreated mice. Even the hair that had been shaved at the surgical site grew back faster. First author Dr. Joseph Rodgers, now at USC, summed up the clinical implications of these results :

“Our research shows that by priming the body before an injury you can speed the process of tissue repair and recovery, similar to how a vaccine prepares the body to fight infection. We believe this could be a therapeutic approach to improve recovery in situations where injuries can be anticipated, such as surgery, combat or sports.”

Could we help senior citizens heal as fast as high school seniors?
Another application for this therapeutic approach may be for the elderly. Lots of things slow down when you get older including your body’s ability to heal itself. This observation sparks an intriguing question for Rando:

“Stem cell activity diminishes with advancing age, and older people heal more slowly and less effectively than younger people. Might it be possible to restore youthful healing by activating this [HGFA] pathway? We’d love to find out.”

I bet a lot of people would love for you to find out, too.

Helping stem cells sleep can boost their power to heal

/ Kevin McCormack / Leave a comment

Mouse muscle

Mighty mouse muscle cells

We are often told that sleep is one of the most important elements of a healthy lifestyle, that it helps in the healing and repair of our heart and blood vessels – among other things.

It turns out that sleep, or something very similar, is equally important for stem cells, helping them retain their power or potency, which is a measure of their effectiveness and efficiency in generating the mature adult cells that are needed to repair damage. Now researchers from Stanford, with a little help from CIRM, have found a way to help stem cells get the necessary rest before kicking in to action. This could pave the way for a whole new approach to treating a variety of genetic disorders such as muscular dystrophy.

Inside out

One problem that has slowed down the development of stem cell therapies has been the inability to manipulate stem cells outside of the body, without reducing their potency. In the body these cells can remain quiescent or dormant for years until called in to action to repair an injury. That’s because they are found in a specialized environment or niche, one that has very particular physical, chemical and biological properties. However, once the stem cells are removed from that niche and placed in a dish in the lab they become active and start proliferating and changing into other kinds of cells.

You might think that’s good, because we want those stem cells to change and mature, but in this case we don’t, at least not yet. We want them to wait till we return them to the body to do their magic. Changing too soon means they have less power to do that.

Researchers at Stanford may have found a way to stop that happening, by creating an environment in the lab that more closely resembles that in the body, so the stem cells remain dormant longer.

As senior author, Thomas Rando, said in a Stanford news release, they have found a way to keep the stem cells dormant longer:

Dr. Thomas Rando, Stanford

Dr. Thomas Rando, Stanford

“Normally these stem cells like to cuddle right up against their native muscle fibers. When we disrupt that interaction, the cells are activated and begin to divide and become less stemlike. But now we’ve designed an artificial substrate that, to the cells, looks, smells and feels like a real muscle fiber. When we also bathe these fibers in the appropriate factors, we find that the stem cells maintain high-potency and regenerative capacity.”

Creating an artificial home

When mouse muscle stem cells (MuSCs) are removed from the mouse they lose their potency after just two days. So the Stanford team set out to identify what elements in the mouse niche helped the cells remain dormant. They identified the molecular signature of the quiescent MuSCs and used that to help screen different compounds to see which ones could help keep those cells dormant, even after they were removed from the mouse and collected in a lab dish.

They whittled down the number of potential compounds involved in this process from 50 to 10, and then tested these in different combinations until they found a formulation that kept the stem cells quiescent for at least 2 days outside of the mouse.

But that was just the start. Next they experimented with different kinds of engineered muscle fibers, to simulate the physical environment inside the mouse niche. After testing various materials, they found that the one with the greatest elasticity was the most effective and used that to create a kind of scaffold for the stem cells.

The big test

The artificial niche they created clearly worked in helping keep the MuSCs in a dormant state outside of the mouse. But would they work when transplanted back into the mouse? To answer this question they tested these stem cells to see if they retained their ability to self-renew and to change into other kinds of cells in the mouse. The good news is they did, and were far more effective at both than MuSCs that had not been stored in the artificial niche.

So, great news for mice but what about people, would this same approach work with human muscle stem cells (hMuSCs)? They next tested this approach using hMuSCs and found that the hMuSCs cultured on the artificial niche were more effective at both self-renewal and retaining their potency than hMuSCs kept in more conventional conditions, at least in the lab.

In the study, published in the journal Nature Biotechnology, the researchers say this finding could help overcome some of the challenges that have slowed down the development of effective therapies:

“Research on MuSCs, hematopoietic stem cells and neural stem cells has shown that very small numbers of quiescent stem cells, even single cells, can replace vast amounts of tissue; culture systems that that maintain stem cell quiescence may allow these findings to be translated to clinical practice. In addition, the possibility of culturing hMuSCs for longer time periods without loss of potency in order to correct mutations associated with genetic disorders, such as muscular dystrophy, followed by transplantation of the corrected cells to replace the pathogenic tissue may enable improved stem cell therapeutics for muscle disorders.”