hematopoetic stem cells

UCLA-led team creates first comprehensive map of human blood stem cell development

/ Esteban Cortez / Leave a comment

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Human blood stem cells emerging from specialized endothelial cells in the wall of an embryonic aorta. UCLA scientists’ confirmation of this process clarifies a longstanding controversy about the stem cells’ cellular origin. Image Credit: Hanna Mikkola Lab/UCLA, Katja Schenke-Layland Lab/University of Tübingen, Nature

California researchers from UCLA and colleagues have created a first-of-its-kind roadmap that traces each step in the development of blood stem cells in the human embryo, providing scientists with a blueprint for producing fully functional blood stem cells in the lab. 

The research, published in the journal Nature, could help expand treatment options for blood cancers like leukemia and inherited blood disorders such as sickle cell disease, said UCLA’s Dr. Hanna Mikkola, who led the study. 

The California Institute for Regenerative Medicine (CIRM) has funded and supported Mikkola’s earlier blood stem cell research through various grants. 

Overcoming Limitations 

Blood stem cells, also called hematopoietic stem cells, can make unlimited copies of themselves and differentiate into every type of blood cell in the human body. For decades, doctors have used blood stem cells from the bone marrow of donors and the umbilical cords of newborns in life-saving transplant treatments for blood and immune diseases.  

However, these treatments are limited by a shortage of matched donors and hampered by the low number of stem cells in cord blood. 

Researchers have long sought to create blood stem cells in the lab from human pluripotent stem cells, which can potentially give rise to any cell type in the body. But success has been elusive, in part because scientists have lacked the instructions to make lab-grown cells become self-renewing blood stem cells rather than short-lived blood progenitor cells, which can only produce limited blood cell types. 

“Nobody has succeeded in making functional blood stem cells from human pluripotent stem cells because we didn’t know enough about the cell we were trying to generate,” said Mikkola. 

A New Roadmap

The new roadmap will help researchers understand the fundamental differences between the two cell types, which is critical for creating cells that are suitable for use in transplantation therapies, said UCLA scientist Vincenzo Calvanese, a co–first author of the research, along with UCLA’s Sandra Capellera-Garcia and Feiyang Ma. 

Researchers Vincenzo Calvanese and Hanna Mikkola. | Credit: Eddy Marcos Panos (left); Reed Hutchinson/UCLA

“We now have a manual of how hematopoietic stem cells are made in the embryo and how they acquire the unique properties that make them useful for patients,” said Calvanese, who is also a group leader at University College London.  

The research team created the resource using new technologies that enable scientists to identify the unique genetic networks and functions of thousands of individual cells and to reveal the location of these cells in the embryo. 

The data make it possible to follow blood stem cells as they emerge and migrate through various locations during their development, starting from the aorta and ultimately arriving in the bone marrow. Importantly, the map unveils specific milestones in their maturation process, including their arrival in the liver, where they acquire the special abilities of blood stem cells. 

The research group also pinpointed the exact precursor in the blood vessel wall that gives rise to blood stem cells. This discovery clarifies a longstanding controversy about the stem cells’ cellular origin and the environment that is needed to make a blood stem cell rather than a blood progenitor cell. 

Through these insights into the different phases of human blood stem cell development, scientists can see how close they are to making a transplantable blood stem cell in the lab. 

A Better Understanding of Blood Cancers

In addition, the map can help scientists understand how blood-forming cells that develop in the embryo contribute to human disease. For example, it provides the foundation for studying why some blood cancers that begin in utero are more aggressive than those that occur after birth. 

“Now that we’ve created an online resource that scientists around the world can use to guide their research, the real work is starting,” Mikkola said. “It’s a really exciting time to be in the field because we’re finally going to be seeing the fruits of our labor.” 

Read the full release here. 

CIRM funded trial for sickle cell disease gives patient a chance for a better future

/ Yimy Villa / 1 Comment
Evie Junior is participating in a CIRM funded clinical trial for sickle cell disease that uses a stem cell gene therapy approach. Image credit: UCLA Broad Stem Cell Research Center

For Evie Junior, personal health and fitness have always been a top priority. During his childhood, he was active and played football, basketball, and baseball in the Bronx, New York. One would never guess that after playing these sports, some nights he experienced pain crises so severe that he was unable to walk. One would also be shocked to hear that he had to have his gallbladder and spleen removed as a child as well.

The health issues that Evie has faced all of his life are related to his diagnosis of sickle cell disease (SCD), a genetic, blood related disorder. SCD causes blood stem cells in the bone marrow, which make blood cells, to produce hard, “sickle” shaped red blood cells. These “sickle” shaped blood cells die early, causing there to be a lack of red blood cells to carry oxygen throughout the body. Due to their “sickle” shape, these cells also get stuck in blood vessels and block blood flow, resulting in excruciating bouts of pain that come on with no warning and can leave patients hospitalized for days.

SCD affects 100,000 people in the United States, the majority of whom are from the Black and Latinx communities, and millions more people around the world,. It can ultimately lead to strokes, organ damage, and early death.

Growing up with SCD inspired Evie to become an emergency medical technician, where he would be able to help patients treat their pain en route to the hospital, in much the same way he has managed his own pain crises for his whole life. Unfortunately as time passed, Evie’s pain crises became harder and harder to manage.

Then in July 2019, Evie decided to enroll in a CIRM funded clinical trial for a stem cell gene therapy to treat SCD. The therapy, developed by Dr. Don Kohn at UCLA, is intended to correct the genetic mutation in a patient’s blood stem cells to allow them to produce healthy red blood cells. Dr. Kohn has already applied the same concept to successfully treat several genetic immune system deficiencies in two other CIRM funded trials, including a cure for a form of Severe Combined Immunodeficiency, also known as bubble baby disease, as well as X-Linked Chronic Granulomatous Disease.

After some delays related to the coronavirus pandemic, Evie finally received an infusion of his own blood stem cells that had been genetically modified to overcome the mutation that causes SCD in July 2020.

Although the results are still very preliminary, so far they look very promising. Three months after his treatment, blood tests indicated that 70% of Evie’s blood stem cells had the new corrected gene. The UCLA team estimates that a 20% correction would be enough to prevent future sickle cell complications. What is also encouraging is that Evie hasn’t had a pain crisis since undergoing the treatment.

In a press release from UCLA, Dr. Kohn discusses that he is cautiously optimistic about these results.

“It’s too early to declare victory, but it’s looking quite promising at this point. Once we’re at six months to a year, if it looks like it does now, I’ll feel very comfortable that he’s likely to have a permanent benefit.”

In the same press release, Evie talks about what a cure would mean for his future and his life going forward.

“I want to be present in my kids’ lives, so I’ve always said I’m not going to have kids unless I can get this cured. But if this works, it means I could start a family one day.”

You can learn more about Evie’s story and the remarkable CIRM funded work at UCLA by watching the video below.

Breakthrough image could lead to better therapies

/ Kevin McCormack / Leave a comment
Image of a blood stem cell in its natural environment: Photo courtesy UC Merced

When it comes to using stem cells for therapy you don’t just need to understand what kinds of cell to use, you also need to understand the environment that is best for them. Trying to get stem cells to grow in the wrong environment would be like trying to breed sheep in a pond. It won’t end well.

But for years scientists struggled to understand how to create the right environment, or niche, for these cells. The niche provides a very specific micro-environment for stem cells, protecting them and enabling them to self-renew over long periods of time, helping repair damaged tissues and organs in the body.

But different stem cells need different niches, and those involve both physical and chemical properties, and getting that mixture right has been challenging. That in turn has slowed down our ability to use those cells to develop new therapies.

UC Merced’s Joel Spencer in the lab: Photo courtesy UC Merced

Now UC Merced’s Professor Joel Spencer and his team have developed a way of capturing an image of hematopoietic or blood stem cells (HSCs), inside their niche in the bone marrow. In an article on UC Merced News, he says this could be a big step forward.

“Everyone knew black holes existed, but it took until last year to directly capture an image of one due to the complexity of their environment. It’s analogous with stem cells in the bone marrow. Until now, our understanding of HSCs has been limited by the inability to directly visualize them in their native environment.

“This work brings an advancement that will open doors to understanding how these cells work which may lead to better therapeutics for hematologic disorders including cancer.”

In the past, studying HSCs involved transplanting them into a mouse or other animal that had undergone radiation to kill off its own bone marrow cells. It enabled researchers to track the HSCs but clearly the new environment was very different than the original, natural one. So, Spencer and his team developed new microscopes and imaging techniques to study cells and tissues in their natural environment.  

In the study, published in the journal Nature, Spencer says all this is only possible because of recent technological breakthroughs.

“My lab is seeking to answer biological questions that were impossible until the advancements in technology we have seen in the past couple decades. You need to be able to peer inside an organ, inside a live animal and see what’s happening as it happens.”

Being able to see how these cells behave in their natural environment may help researchers learn how to recreate that environment in the lab, and help them develop new and more effective ways of using those cells to repair damaged tissues and organs.

Antibody effective in cure for rare blood disorders

/ Yimy Villa / Leave a comment
3D illustration of an antibody binding to a designated target.
Illustration created by Audra Geras.

A variety of diseases can be traced to a simple root cause: problems in the bone marrow. The bone marrow contains specialized stem cells known as hematopoietic stem cells (HSCs) that give rise to different types of blood cells. As mentioned in a previous blog about Sickle Cell Disease (SCD), one problem that can occur is the production of “sickle like” red blood cells. In blood cancers like leukemia, there is an uncontrollable production of abnormal white blood cells. Another condition, known as myelodysplastic syndromes (MDS), are a group of cancers in which immature blood cells in the bone marrow do not mature and therefore do not become healthy blood cells.

For diseases that originate in the bone marrow, one treatment involves introducing healthy HSCs from a donor or gene therapy. However, before this type of treatment can take place, all of the problematic HSCs must be eliminated from the patient’s body. This process, known as pre-treatment, involves a combination of chemotherapy and radiation, which can be extremely toxic and life threatening. There are some patients whose condition has progressed to the point where their bodies are not strong enough to withstand pre-treatment. Additionally, there are long-term side effects that chemotherapy and radiation can have on infant children that are discussed in a previous blog about pediatric brain cancer.

Could there be a targeted, non-toxic approach to eliminating unwanted HSCs that can be used in combination with stem cell therapies? Researchers at Stanford say yes and have very promising results to back up their claim.

Dr. Judith Shizuru and her team at Stanford University have developed an antibody that can eliminate problematic blood forming stem cells safely and efficiently. The antibody is able to identify a protein on HSCs and bind to it. Once it is bound, the protein is unable to function, effectively removing the problematic blood forming stem cells.

Dr. Shizuru is the senior author of a study published online on February 11th, 2019 in Blood that was conducted in mice and focused on MDS. The results were very promising, demonstrating that the antibody successfully depleted human MDS cells and aided transplantation of normal human HSCs in the MDS mouse model.

This proof of concept holds promise for MDS as well as other disease conditions. In a public release from Stanford Medicine, Dr. Shizuru is quoted as saying, “A treatment that specifically targets only blood-forming stem cells would allow us to potentially cure people with diseases as varied as sickle cell disease, thalassemia, autoimmune disorders and other blood disorders…We are very hopeful that this body of research is going to have a positive impact on patients by allowing better depletion of diseased cells and engraftment of healthy cells.”

The research mentioned was partially funded by us at CIRM. Additionally, we recently awarded a $3.7 million dollar grant to use the same antibody in a human clinical trial for the so-called “bubble baby disease”, which is also known as severe combined immunodeficiency (SCID). You can read more about that award on a previous blog post linked here.

Mechanical forces are the key to speedy recovery after blood cancer treatment

/ Pallavi Penumetcha / Leave a comment

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Mesenchymal stem cells grown on a surface with specialized mechanical properties. Image courtesy of Krystyn Van Vliet at MIT.

Blood cancers, such as leukemia and lymphoma, are projected to be responsible for 10% of all new cancer diagnoses this year. These types of cancers are often treated by killing the patient’s bone marrow (the site of blood cell manufacturing), with a treatment called irradiation. While effective for ridding the body of cancerous cells, this treatment also kills healthy blood cells. Therefore, for a time after the treatment, patients are particularly vulnerable to infections, because the cellular components of the immune system are down for the count.

Now scientists at MIT have devised a method to make blood cells regenerate faster and  minimize the window for opportunistic infections.

Using multipotent stem cells (stem cells that are able to become multiple cell types) grown on a new and specialized surface that mimics bone marrow, the investigators changed the stem cells into different types of blood cells. When transplanted into mice that had undergone irradiation, they found that the mice recovered much more quickly compared to mice given stem cells grown on a more traditional plastic surface that does not resemble bone marrow as well.

This finding, published in the journal Stem Cell Research and Therapy, is particularly revolutionary, because it is the first time researchers have observed that mechanical properties can affect how the cells differentiate and behave.

The lead author of the study attributes the decreased recovery time to the type of stem cell that was given to mice compared to what humans are normally given after irradiation. Humans are given a stem cell that is only able to become different types of blood cells. The mice in this study, however, were give a stem cell that can become many different types of cells such as muscle, bone and cartilage, suggesting that these cells somehow changed the bone marrow environment to promote a more efficient recovery. They attributed a large part of this phenomenon to a secreted protein call ostepontin, which has previously been describe in activating the cells of the immune system.

In a press release, Dr. Viola Vogel, a scientist not related to study, puts the significance of these findings in a larger context:

“Illustrating how mechanopriming of mesenchymal stem cells can be exploited to improve on hematopoietic recovery is of huge medical significance. It also sheds light onto how to utilize their approach to perhaps take advantage of other cell subpopulations for therapeutic applications in the future.”

Dr. Krystyn Van Vliet, explains the potential to expand these findings beyond the scope of just blood cancer treatment:

“You could imagine that by changing their culture environment, including their mechanical environment, MSCs could be used for administration to target several other diseases such as Parkinson’s disease, rheumatoid arthritis, and others.”

 

Support cells have different roles in blood stem cell maintenance before and after stress

/ Pallavi Penumetcha / Leave a comment

How-Stem-Cells-Act-When-Stressed-Versus-When-At-Rest

Expression of pleiotrophin (green) in bone marrow blood vessels (red) and stromal cells (white) in normal mice (left), and in mice 24 hours after irradiation (right). UCLA Broad Stem Cell Research Center/Cell Stem Cell

A new study published in the journal Cell Stem Cell, reveals how different types of cells in the bone marrow are responsible for supporting blood stem cell maintenance before and after injury.

It was already well known in the field that two different cell types, namely endothelial cells (which line blood vessels) and stromal cells (which make up connective tissue, or tissue that provides structural support for any organ), are responsible for maintaining the population of blood stem cells in the bone marrow. However, how these cells and the molecules they secrete impact blood stem cell development and maintenance is not well understood.

Hematopoietic stem cells are responsible for generating the multiple different types of cells found in blood, from our oxygen carrying red blood cells to the many different types of white blood cells that make up our immune system.

Dr. John Chute’s group at UCLA had previously discovered that a molecule called pleiotrophin, or PTN, is important for promoting self-renewal of the blood stem cell population. They did not, however, understand which cells secrete this molecule and when.

To answer this question, the scientists developed mouse models that did not produce PTN in different types of bone marrow cells, such as endothelial cells and stromal cells. Surprisingly, they saw that the inability of stromal cells to produce PTN decreased the blood stem cell population, but deletion of PTN in endothelial cells did not affect the blood stem cell niche.

Even more interestingly, the researchers found that in animals that were subjected to an environmental stressor, in this case, radiation, the result was reversed: endothelial cell PTN was necessary for blood stem cell renewal, whereas stromal cell PTN was not. While an important part of the knowledge base for blood stem cell biology, the reason for this switch in PTN secretion at times of homeostasis and disease is still unknown.

As Dr. Chute states in a press release, this result could have important implications for cancer treatments such as radiation:

“It may be possible to administer modified, recombinant versions of pleiotrophin to patients to accelerate blood cell regeneration. This strategy also may apply to patients undergoing bone marrow transplants.”

Another important consideration to take away from this work is that animal models developed in the laboratory should take into account the possibility that blood stem cell maintenance and regeneration is distinctly controlled under healthy and disease state. In other words, cellular function in one state is not always indicative of its role in another state.

This work was partially funded by a CIRM Leadership Award.

 

 

CIRM weekly stem cell roundup: stomach bacteria & cancer; vitamin C may block leukemia; stem cells bring down a 6’2″ 246lb football player

/ Kevin McCormack / Leave a comment

gastric

This is what your stomach glands looks like from the inside:  Credit: MPI for Infection Biology”

Stomach bacteria crank up stem cell renewal, may be link to gastric cancer (Todd Dubnicoff)

The Centers for Disease Control and Prevention estimate that two-thirds of the world’s population is infected with H. pylori, a type of bacteria that thrives in the harsh acidic conditions of the stomach. Data accumulated over the past few decades shows strong evidence that H. pylori infection increases the risk of stomach cancers. The underlying mechanisms of this link have remained unclear. But research published this week in Nature suggests that the bacteria cause stem cells located in the stomach lining to divide more frequently leading to an increased potential for cancerous growth.

Tumors need to make an initial foothold in a tissue in order to grow and spread. But the cells of our stomach lining are replaced every four days. So, how would H. pylori bacterial infection have time to induce a cancer? The research team – a collaboration between scientists at the Max Planck Institute in Berlin and Stanford University – asked that question and found that the bacteria are also able to penetrate down into the stomach glands and infect stem cells whose job it is to continually replenish the stomach lining.

Further analysis in mice revealed that two groups of stem cells exist in the stomach glands – one slowly dividing and one rapidly dividing population. Both stem cell populations respond similarly to an important signaling protein, called Wnt, that sustains stem cell renewal. But the team also discovered a second key stem cell signaling protein called R-spondin that is released by connective tissue underneath the stomach glands. H. pylori infection of these cells causes an increase in R-spondin which shuts down the slowly dividing stem cell population but cranks up the cell division of the rapidly dividing stem cells. First author, Dr. Michal Sigal, summed up in a press release how these results may point to stem cells as the link between bacterial infection and increased risk of stomach cancer:

“Since H. pylori causes life-long infections, the constant increase in stem cell divisions may be enough to explain the increased risk of carcinogenesis observed.”

vitamin-c-1200x630

Vitamin C may have anti-blood cancer properties

Vitamin C is known to have a number of health benefits, from preventing scurvy to limiting the buildup of fatty plaque in your arteries. Now a new study says we might soon be able to add another benefit: it may be able to block the progression of leukemia and other blood cancers.

Researchers at the NYU School of Medicine focused their work on an enzyme called TET2. This is found in hematopoietic stem cells (HSCs), the kind of stem cell typically found in bone marrow. The absence of TET2 is known to keep these HSCs in a pre-leukemic state; in effect priming the body to develop leukemia. The researchers showed that high doses of vitamin C can prevent, or even reverse that, by increasing the activity level of TET2.

In the study, in the journal Cell, they showed how they developed mice that could have their levels of TET2 increased or decreased. They then transplanted bone marrow with low levels of TET2 from those mice into healthy, normal mice. The healthy mice started to develop leukemia-like symptoms. However, when the researchers used high doses of vitamin C to restore the activity levels of TET2, they were able to halt the progression of the leukemia.

Now this doesn’t mean you should run out and get as much vitamin C as you can to help protect you against leukemia. In an article in The Scientist, Benjamin Neel, senior author of the study, says while vitamin C does have health benefits,  consuming large doses won’t do you much good:

“They’re unlikely to be a general anti-cancer therapy, and they really should be understood based on the molecular understanding of the many actions vitamin C has in cells.”

However, Neel says these findings do give scientists a new tool to help them target cells before they become leukemic.

Jordan reed

Bad toe forces Jordan Reed to take a knee: Photo courtesy FanRag Sports

Toeing the line: how unapproved stem cell treatment made matters worse for an NFL player  

American football players are tough. They have to be to withstand pounding tackles by 300lb men wearing pads and a helmet. But it wasn’t a crunching hit that took Washington Redskins player Jordan Reed out of the game; all it took to put the 6’2” 246 lb player on the PUP (Physically Unable to Perform) list was a little stem cell injection.

Reed has had a lingering injury problem with the big toe on his left foot. So, during the off-season, he thought he would take care of the issue, and got a stem cell injection in the toe. It didn’t quite work the way he hoped.

In an interview with the Richmond Times Dispatch he said:

“That kind of flared it up a bit on me. Now I’m just letting it calm down before I get out there. I’ve just gotta take my time, let it heal and strengthen up, then get back out there.”

It’s not clear what kind of stem cells Reed got, if they were his own or from a donor. What is clear is that he is just the latest in a long line of athletes who have turned to stem cells to help repair or speed up recovery from an injury. These are treatments that have not been approved by the Food and Drug Administration (FDA) and that have not been tested in a clinical trial to make sure they are both safe and effective.

In Reed’s case the problem seems to be a relatively minor one; his toe is expected to heal and he should be back in action before too long.

Stem cell researcher and avid blogger Dr. Paul Knoepfler wrote he is lucky, others who take a similar approach may not be:

“Fortunately, it sounds like Reed will be fine, but some people have much worse reactions to unproven stem cells than a sore toe, including blindness and tumors. Be careful out there!”

Engineered bone tissue improves stem cell transplants

/ Karen Ring / Leave a comment

Bone marrow transplants are currently the only approved stem cell-based therapy in the United States. They involve replacing the hematopoietic, or blood-forming stem cells, found in the bone marrow with healthy stem cells to treat patients with cancers, immune diseases and blood disorders.

For bone marrow transplants to succeed, patients must undergo radiation therapy to wipe out their diseased bone marrow, which creates space for the donor stem cells to repopulate the blood system. Radiation can lead to complications including hair loss, nausea, fatigue and infertility.

Scientists at UC San Diego have a potential solution that could make current bone marrow transplants safer for patients. Their research, which was funded in part by a CIRM grant, was published yesterday in the journal PNAS.

Engineered bone with functional bone marrow in the center. (Varghese Lab)

Led by bioengineering professor Dr. Shyni Varghese, the team engineered artificial bone tissue that contains healthy donor blood stem cells. They implanted the engineered bone under the skin of normal mice and watched as the “accessory bone marrow” functioned like the real thing by creating new blood cells.

The implant lasted more than six months. During that time, the scientists observed that the cells within the engineered bone structure matured into bone tissue that housed the donor bone marrow stem cells and resembled how bones are structured in the human body. The artificial bones also formed connections with the mouse circulatory system, which allowed the host blood cells to populate the implanted bone tissue and the donor blood cells to expand into the host’s bloodstream.

Normal bone structure (left) and engineered bone (middle) are very similar. Bone tissue shown on top right and bone marrow cells on bottom right. (Varghese lab)

The team also implanted these artificial bones into mice that received radiation to mimic the procedures that patients typically undergo before bone marrow transplants. The engineered bone successfully repopulated the blood systems of the irradiated mice, similar to how blood stem cell functions in normal bone.

In a UC San Diego news release, Dr. Varghese explained how their technology could be translated into the clinic,

“We’ve made an accessory bone that can separately accommodate donor cells. This way, we can keep the host cells and bypass irradiation. We’re working on making this a platform to generate more bone marrow stem cells. That would have useful applications for cell transplantations in the clinic.”

The authors concluded that engineered bone tissue would specifically benefit patients who needed bone marrow transplants for non-cancerous bone marrow-related diseases such as sickle cell anemia or thalassemia where there isn’t a need to destroy cancer-causing cells.

A single protein can boost blood stem cell regeneration

/ Karen Ring / 1 Comment

Today, CIRM-funded scientists from the UCLA Broad Stem Cell Research Center reported  in Nature Medicine that hematopoietic stem cells (HSCs) – blood stem cells that generate the cell in your blood and immune system – get a helping hand after injury from cells in the bone marrow called bone progenitor cells. By secreting a protein called dickkopf-1 (Dkk1), bone progenitor cells improve the recovery and survival of blood stem cells in a culture dish and in mice whose immune systems are suppressed by irradiation.

These findings build upon a related study published by the same UCLA team last month showing that deleting a single gene in HSCs boosts blood stem cell regeneration. We covered this initial story previously on the Stem Cellar, and you can refer to it for background on the importance of stimulating the regenerative capacity of HSCs in patients that need bone marrow transplants or have undergone radiation therapy for cancer.

Dkk1 boost blood stem cell regeneration

Senior author on the study, UCLA Professor Dr. John Chute, wanted to understand how the different cell types in the bone marrow environment, or niche, interact with HSCs to enhance their ability to recover from injury and regenerate the immune system. As mentioned earlier, he and his team found that bone progenitor cells secrete Dkk1 protein in response to injury caused by exposing mice to full body irradiation. Dkk1 promoted blood stem cell regeneration in the mice and increased their survival rates.

I inquired with Dr. Chute about this seemingly beneficial relationship between HSCs and cells in the bone marrow niche.

Dr. John Chute, UCLA

Dr. John Chute, UCLA

“The precise functions of bone cells, stromal cells and endothelial cells in regulating blood stem cell fate are not completely understood,” said Dr. Chute. “Our prior studies demonstrated that endothelial cells are necessary for blood stem cell regeneration after irradiation.  The current study suggests that bone progenitor cells are also necessary for normal blood stem cell regeneration after irradiation, and that this activity is mediated by secretion of Dkk1 by the bone progenitor cells.”

He further commented in a UCLA press release:

“The cellular niche is like the soil that surrounds the stem cell ‘seed’ and helps it grow and proliferate. Our hypothesis was that the bone progenitor cell in the niche may promote hematopoietic stem cell regeneration after injury.”

Not only did Dkk1 improve HSC regeneration in irradiated mice, it also boosted the regeneration of HSCs that were irradiated in a culture dish. On the other hand, when Dkk1 was deleted from HSCs in irradiated mice, the HSCs did not recover and regenerate. Diving in deeper, the team found that Dkk1 promotes blood stem cell regeneration by direct action on the stem cells and by indirectly increasing the secretion of the stem cell growth factor EGF by bone marrow blood vessels. Taken together, the team concluded that Dkk1 is necessary for blood stem cell recovery following injury/irradiation.

After radiation, blood cells (purple) regenerated in bone marrow when mice were given DKK1 intravenously (left), but not in those that received saline solution (right). (UCLA/Nature Medicine)

After radiation, blood cells (purple) regenerated in bone marrow when mice were given DKK1 (left), but not in those that received saline solution (right). (UCLA/Nature Medicine)

Future applications for blood stem cell regeneration

When I asked Dr. Chute how his current study on Dkk1 and HSCs relates to his previous study on boosting HSC regeneration by deleting a gene called Grb10, he explained:

“In this paper we discovered the role of a niche cell-derived protein, Dkk1, and how it promotes blood stem cell regeneration after myelosuppression in mice.  In the Cell Reports paper, we described our discovery of an adaptor protein, Grb10, which is expressed by blood stem cells and the inhibition of which also promotes blood stem cell regeneration after myelosuppression. So, these are two novel molecular mechanisms that regulate blood stem cell regeneration that could be therapeutically targeted.”

Both studies offer new strategies for promoting blood stem cell regeneration in patients who need to replenish their blood and immune systems following radiation treatments or bone marrow transplants.

Dr. Chute concluded:

“We are very interested in translating our observations into the clinic for the purpose of accelerating hematologic recovery in patients receiving chemotherapy or undergoing hematopoietic stem cell transplantation.”

Related Links:

Deleting a single gene can boost blood stem cell regeneration

/ Karen Ring / Leave a comment

A serious side effect that cancer patients undergoing chemotherapy experience is myelosuppression. That’s a big word for a process that involves the decreased production of the body’s immune cells from hematopoietic stem cells (HSCs) or blood stem cells in the bone marrow. Without these important cells that make up the immune system, patients are at risk for major infections and even death.

Human blood (red) and immune cells (green) are made from hematopoietic/blood stem cells. Photo credit: ZEISS Microscopy.

Human blood (red) and immune cells (green) are made from hematopoietic/blood stem cells. Photo credit: ZEISS Microscopy.

Scientists are trying to find ways to treat cancer patients that have undergone myelosuppressive therapies, as well as patients that need bone marrow transplants to replace their own bone marrow that’s been damaged or removed. One possible solution is boosting the regenerative capacity of HSCs. Transplanting HSCs that are specially primed to reproduce rapidly into cells of the immune system could improve the outcome of bone marrow transplants in patients.

Deleting Grb10 boost blood stem cell regeneration

A CIRM-funded team from the UCLA Broad Stem Cell Research Center and the Jonsson Comprehensive Cancer Center has identified a single gene that can be manipulated to boost HSC regeneration in mice. The study, which was published in Cell Reports, found that deleting or turning off expression of an imprinted gene called Grb10 in HSCs caused these blood stem cells to reproduce more robustly after being transplanted into mice that had their bone marrow removed.

I just used another big word in that last paragraph, so let me explain. An imprinted gene is a gene that is expressed or activated based on which parent it was inherited from. Typically, you receive one copy of a gene from your mother and one from your father and both are expressed – a process called Mendelian inheritance. But imprinted genes are different – they are marked with specific epigenetic tags that silence their expression in the sperm or egg cells of the parents. Thus if you inherited an imprinted gene from your mother, the other copy of that gene from your father would be expressed and vice versa.

Scientists have discovered that imprinted genes are important for human development and also for directing what cell types adult stem cells like HSCs develop into. The team from UCLA led by senior author Dr. John Chute, was interested in answering a different question: are imprinted genes involved in determining the function of HSCs? They compared two different populations of HSCs derived from mouse bone marrow: a normal, healthy population and HSCs exposed to total body irradiation (TBI), which destroys the immune system. They discovered that the expression of an imprinted gene called Grb10 was dramatically higher in HSCs exposed to TBI compared to healthy HSCs.

Cell Reports

Deleting Grb10  increases blood stem cell regeneration in the bone marrow of irradiated mice (bottom) compared to normal mice (top). Cell Reports

Because Grb10 is an imprinted gene, the scientists deleted either the paternal or maternal copy of that gene in mice. While deleting the paternal Grb10 gene had no effect on the function of HSCs, maternal deletion dramatically boosted the capacity of HSCs to divide and make more copies of themselves. Without the maternal copy of Grb10, HSCs were able to regenerate at a much faster scale than normal HSCs.

To further prove their point, the team transplanted normal HSCs and HSCs that lacked Grb10 into TBI or fully irradiated mice. HSCs that lacked Grb10 were able to regenerate themselves and produce other immune cells more robustly 20 weeks after transplantation compared to normal HSCs.

Potential applications and future studies

This study offers two important findings. First, they discovered that Grb10 plays an important role “in regulating HSC self-renewal following transplantation and HSC regeneration in response to injury.” Second, they found that inhibiting Grb10 function in HSCs could have potential therapeutic applications for boosting “hematopoietic regeneration in the setting of HSC transplantation or following myelosuppressive injury.” Patients in need of bone marrow transplants could potentially receive more benefit from transplants of HSCs that don’t express the Grb10 gene.

In my opinion, further studies should be done to further understand the role of Grb10 in regulating HSC self-renewal and regeneration. What is the benefit of having this gene expressed in HSCs if inhibiting its expression leads to an increased regenerative capacity? Is it to prevent cancer from forming? Additionally, the authors will need to address the potential long-term side effects of inhibiting Grb10 expression in HSCs. They did report that mice that lacked the Grb10 gene did not develop blood cancers at one year of age which is good news. They also suggested that instead of deleting Grb10, new drugs could be identified that inhibit Grb10 function in HSCs.