Stem Cell Stories that Caught Our Eye: GPS for Skin & Different Therapies for Aging vs. Injured Muscles?

Skin stem cells specialize into new skin by sensing neighborhood crowding
When embarking on a road trip, the GPS technology inside our smartphones helps us know where we are and how to get where we’re going. The stem cells buried in the deepest layers of our skin don’t have a GPS and yet, they do just fine determining their location, finding their correct destination and becoming the appropriate type of skin cell. And as a single organ, all the skin covering your body maintains the right density and just the right balance of skin stem cells versus mature skin cells as we grow from a newborn into adult.

crowdinginth

Skin cells growing in a petri dish (green: cytoskeleton, red: cell-cell junction protein).
Credit: MPI for Biology of Aging

This easily overlooked but amazing feat is accomplished as skin cells are continually born and die about every 30 days over your lifetime. How does this happen? It’s an important question to answer considering the skin is our first line of defense against germs, toxins and other harmful substances.

This week, researchers at the Max Planck Institute for Biology of Aging in Cologne, Germany reported a new insight into this poorly understood topic. The team showed that it all comes down to the skin cells sensing the level of crowding in their local environment. As skin stem cells divide, it puts the squeeze on neighboring stem cells. This physical change in tension on these cells “next door” triggers signals that cause them to move upward toward the skin surface and to begin maturing into skin cells.

Lead author Yekaterina Miroshnikova explained in a press release the beauty of this mechanism:

“The fact that cells sense what their neighbors are doing and do the exact opposite provides a very efficient and simple way to maintain tissue size, architecture and function.”

The research was picked up by Phys.Org on Tuesday and was published in Nature Cell Biology.

Stem cells respond differently to aging vs. injured muscle
From aging skin, we now move on to our aging and injured muscles, two topics I know oh too well as a late-to-the-game runner. Researchers at the Sanford Burnham Prebys Medical Discovery Institute (SBP) in La Jolla report a surprising discovery that muscle stem cells respond differently to aging versus injury. This important new insight could help guide future therapeutic strategies for repairing muscle injuries or disorders.

muscle stem cell

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

Muscle stem cells, also called satellite cells, make a small, dormant population of cells in muscle tissue that springs to life when muscle is in need of repair. It turns out that these stem cells are not identical clones of each other but instead are a diverse pool of cells.  To understand how the assortment of muscle stem cells might respond differently to the normal wear and tear of aging, versus damage due to injury or disease, the research team used a technology that tracks the fate of individual muscle stem cells within living mice.

The analysis showed a clear but unexpected result. In aging muscle, the muscle stem cells maintained their diversity but their ability to divide and grow declined. However, the opposite result was observed in injured muscle: the muscle stem cell diversity became limited but the capacity to divide was not affected. In a press release, team leader Alessandra Sacco explains the implications of these findings for therapy development:

sacco

Alessandra Sacco, PhD

“This study has shown clear-cut differences in the dynamics of muscle stem cell pools during the aging process compared to a sudden injury. This means that there probably isn’t a ‘one size fits all’ approach to prevent the decline of muscle stem cells. Therapeutic strategies to maintain muscle mass and strength in seniors will most likely need to differ from those for patients with degenerative diseases.”

This report was picked up yesterday by Eureka Alert and published in Cell Stem Cell.

Advertisements

A new study suggests CRISPR gene editing therapies should be customized for each patient

You know a scientific advance is a big deal when it becomes the main premise and title of a Jennifer Lopez-produced TV drama. That’s the case for CRISPR, a revolutionary gene-editing technology that promises to yield treatments for a wide range of genetic diseases.

In fact, clinical trials using the CRISPR method are already underway with more on the horizon. And at CIRM, we’re funding several CRISPR projects including a candidate gene and stem cell therapy that applies CRISPR to repair a genetic mutation found in sickle cell anemia patients.

geneeditingclip2

Animation by Todd Dubnicoff/CIRM

While these projects are moving full steam ahead, a study published this week in PNAS suggests a note of caution. They report that the natural genetic variability that is found when comparing  the DNA sequences of individuals has the potential to negatively impact the effectiveness of a CRISPR-based treatment and in some cases, could lead to dangerous side effects. As a result, the research team – a collaboration between Boston Children’s Hospital and the University of Montreal – recommends that therapy products using CRISPR should be customized to take into account the genetic variation between patients.

CRISPR 101
While other gene-editing methods pre-date CRISPR, the gene-editing technique has taken the research community by storm because of its ease of use. Pretty much any lab can incorporate it into their studies. CRISPR protein can cut specific DNA sequence within a person’s cells with the help of an attached piece of RNA. It’s pretty straight-forward to customize this “guide” RNA molecule so that it recognizes a desired DNA sequence that is in need of repair or modification.

https://player.vimeo.com/video/112757040

Because CRISPR activity heavily relies on the guide RNA molecule’s binding to a specific DNA sequence, there have been on-going concerns that a patient’s genetic variability could hamper the effectiveness of a given CRISPR therapy if it didn’t bind well. Even worse, if the genetic variability caused the CRISPR product to bind and inactivate a different region of DNA, say a gene responsible for suppressing cancer growth, it could lead to dangerous, so-called off target effects.

Although, studies have been carried out to measure the frequency of these potential CRISPR mismatches, many of the analyses depend on a reference DNA sequence from one individual. But as senior author Stuart Orkin, of Dana-Farber Boston Children’s Cancer and Blood Disorders Center, points out in a press release, this is not an ideal way to gauge CRISPR effectiveness and safety:

orkin

Stuart Orkin

“Humans vary in their DNA sequences, and what is taken as the ‘normal’ DNA sequence for reference cannot account for all these differences.”

 

 

One DNA sequence is not like the other
So, in this study, the research team analyzed previously published DNA sequence data from 7,444 people. And they focused on 30 disease genes that various researchers were targeting with CRISPR gene-editing. The team also generated 3,000 different guide RNAs with which to target those 30 disease genes.

The analysis showed that, in fact, about 50 percent of the guide RNAs could potentially have mismatches due to genetic variability found in these patients’ DNA sequences. These mismatches could lead to less effective binding of CRISPR to the disease gene target, which would reduce the effectiveness of the gene editing. And, though rare, the team also found cases in which an individual’s genetic variability could cause the CRISPR guide RNA to bind and cut in the wrong spot.

Matthew Canver, an MD-PhD student at Harvard Medical School who is also an author in the study, points out these less-than-ideal activities could also impact other gene editing techniques. Canver gives an overall recommendation how to best move forward with CRISPR-based therapy development:

canver, matthew

Matthew Canver

“The unifying theme is that all these technologies rely on identifying stretches of DNA bases very specifically. As these gene-editing therapies continue to develop and start to approach the clinic, it’s important to make sure each therapy is going to be tailored to the patient that’s going to be treated.”

 

CIRM interviews Lorenz Studer: 2017 recipient of the Ogawa-Yamanaka Stem Cell Prize [Video]

For eight long years, researchers who were trying to develop a stem cell-based therapy for Parkinson’s disease – an incurable movement disorder marked by uncontrollable shaking, body stiffness and difficulty walking – found themselves lost in the proverbial wilderness. In initial studies, rodent stem cells were successfully coaxed to specialize into dopamine-producing nerve cells, the type that are lost in Parkinson’s disease. And further animal studies showed these cells could treat Parkinson’s like symptoms when transplanted into the brain.

Parkinsonsshutterstock_604375424

studer-lorenz

Lorenz Studer, MD
Photo Credit: Sloan Kettering

But when identical recipes were used to make human stem cell-derived dopamine nerve cells the same animal experiments didn’t work. By examining the normal developmental biology of dopamine neurons much more closely, Lorenz Studer cracked the case in 2011. Now seven years later, Dr. Studer, director of the Center for Stem Cell Biology at the Memorial-Sloan Kettering Cancer Center, and his team are on the verge of beginning clinical trials to test their Parkinson’s cell therapy in patients

It’s for these bottleneck-busting contributions to the stem cell field that Dr. Studer was awarded the Gladstone Institutes’ 2017 Ogawa-Yamanaka Stem Cell Prize. Now in its third year, the prize was founded by philanthropists Hiro and Betty Ogawa along with  Shinya Yamanaka, Gladstone researcher and director of the Center for iPS Cell Research and Application at Kyoto University, and is meant to inspire and celebrate discoveries that build upon Yamanaka’s Nobel prize winning discovery of induced pluripotent stem cells (iPSCs).

LorenzStuder_OgawaAward2017-12

(L to R) Shinya Yamanaka, Andrew Ogawa, Deepak Srivastava present Lorenz Studer the 2017 Ogawa-Yamanaka Stem Cell Prize at Gladstone Institutes. Photo Credit: Todd Dubnicoff/CIRM

Studer was honored at the Gladstone in November and presented the Ogawa-Yamanka Stem Cell Prize Lecture. He was kind enough to sit down with me for a brief video interview (watch it below) a few minutes before he took the stage. He touched upon his Parkinson’s disease research as well as newer work related to hirschsprung disease, a dangerous intestinal disorder often diagnosed at birth that is caused by the loss of nerve cells in the gut. Using human embryonic stem cells and iPSCs derived from hirschsprung patients, Studer’s team has worked out the methods for making the gut nerve cells that are lost in the disease. This accomplishment has allowed his lab to better understand the disease and to make solid progress toward a stem cell-based therapy.

His groundbreaking work has also opened up the gates for other Parkinson’s researchers to make important insights in the field. In fact, CIRM is funding several interesting early stage projects aimed at moving therapy development forward:

We posted the 8-minute video with Dr. Studer today on our official YouTube channel, CIRM TV. You can watch the video here:

And for a more detailed description of Studer’s research, watch Gladstone’s webcast recording of his entire lecture:

Comparing two cellular reprogramming methods from one donor’s cells yields good news for iPSCs

In 2012, a mere six years after his discovery of induced pluripotent stem cells (iPSCs), Shinya Yamanaka was awarded the Nobel Prize in Medicine. Many Nobel winners aren’t recognized until decades after their initial groundbreaking studies. That goes to show you the importance of Yamanaka’s technique, which can reprogram a person’s cells, for example skin or blood, into embryonic stem cell-like iPSCs by just adding a small set of reprogramming factors.

These iPSCs are pluripotent, meaning they can be specialized, or differentiated, into virtually any cell type in the body. With these cells in hand, researchers have a powerful tool to study human disease and to develop treatments using human cells directly from patients. And at the same time, this cell source helps avoid the ethical concerns related to embryonic stem cells.

iPSC_Wu

Induced pluripotent stem cell (iPSC) colonies.
Image Credit: Joseph Wu

Still, there has been lingering uneasiness about how well iPSCs match up to embryonic stem cells (ESCs), considered the gold-standard of pluripotent stem cells. One source of those concerns is that the iPSC method doesn’t completely reprogram cells and they retain memory of their original cell source, in the form of chemical – also called epigenetic – modifications of the cells’ DNA structure. So, if a researcher were to make, say, heart muscle cells from iPSCs that have an epigenetic memory of its skin cell origins, any resulting conclusions about a given disease study or cell therapy could be less accurate than ESC-related results. But a report published yesterday in PNAS should help relieve these worries.

The CIRM-funded study – a collaboration between the labs of Joseph Wu and Michael Synder at Stanford University and Shoukhrat Mitalipov at Oregon Health & Science University – carried out an exhaustive series of experiments that carefully compared the gene activity and cell functions of iPSC-derived cells with cells derived from embryonic stem cells. The teams sought to compare cells generated from the same person to be sure any differences were not the result of genetics. To make this “apples-to-apples” comparison, they generated embryonic stem cells using another reprogramming technique called somatic cell nuclear transfer (SCNT).

With SCNT, a nucleus from an adult cell is transferred to an egg which has its own nucleus removed. The resulting cell becomes reprogrammed back into an embryo from which embryonic stem cells are generated – the researchers call them NT-ESCs for short. In this study, the skin cell sample used for making the iPSCs and the cell nucleus used for making the NT-ESCs came from the same person. In scientific lingo, the iPSCs and SCNT stem cells are considered isogenic.

Now, it turns out the NT-ESC reprogramming process is more complete and eliminates epigenetic memory of the original cell source. So why even bother with iPSCs if you have NT-ESCs? There are big disadvantages with SCNT: it’s a complex technique – only a limited number of labs pull it off – and it requires donated human eggs which carries ethical issues. So, if a direct comparison iPSCs and SNCT stem cells shows little difference then it would be fair to argue that iPSCs can replace NT-ESCs for deriving patient-specific stem cells.

And that’s exactly what the teams found, as Dr. Wu summarized it to me in an interview:

“Direct comparison between differentiated cells derived from iPSCs and SCNT had never been performed because it had been difficult to generate patient-specific ESCs by the SCNT method. Collaborating with Dr. Shoukhrat Mitalipov at Oregon Health & Science University and Dr. Michael Snyder at Stanford University, we compared patient-specific cardiomocytes (heart muscle cells) and endothelial (blood vessel) cells derived by these two reprogramming methods (SCNT and iPSCs) and found they were relatively equivalent regarding molecular and functional features.”

PSC-ECs2 copy

Blood vessel cells derived by iPSC (left) and SCNT (right) reprogramming methods.
Image credit: Joseph Wu

Because the heart muscle and blood vessel cells were similar regardless of reprogramming method, it suggests that the epigenetic memory that remained in the iPSCs is less of a worry. Dr. Wu explained to me this way:

joewu

Joseph Wu

“If iPSCs carry substantial epigenetic memory of the cell-of-origin, it is unlikely these iPSCs can differentiate to a functional cardiac cell or blood vessel cell. Only the stem cells free of significant epigenetic memory can differentiate into functional cells.”

 

Hopefully these results hold up over time because it will bode well for the countless iPSC-related disease studies as well as the growing number of iPSC-related projects that are nearing clinical trials.

Second “Don’t Eat Me” Signal Identified in Cancer Cells, Points to New Immunotherapies

When the immune system comes up as a topic in everyday conversation, it’s usually related to fighting off a cold or flu. While our immune cells certainly do detect and neutralize invading bacteria and viruses, they also play a critical role in killing abnormal, cancerous cells from within our bodies.

“Don’t Eat Me” Signal 101
A white blood cell called a macrophage (macro = “big”; phage = “eater”) is part of the so-called innate immune system and acts as a first line of defense by patrolling our organs and gobbling up infected as well as cancerous cells (see macrophages in action in the cool video below).

Unfortunately, cancer cells possess the ability to cloak themselves and escape a macrophage’s engulfing grasp. Nearly all cancer cells carry a protein called CD47 on their surface. When CD47 binds to a protein called SIRPalpha on the surface of macrophages, a “don’t eat me” signal is triggered and the macrophage ignores the cancer cell.

Stanford researcher Irv Weissman and his team discovered this “don’t eat me” signal several years ago and showed that adding an antibody protein that binds tightly to CD47 interferes with the CD47/SIRPalpha signal. As a result, the anti-CD47 antibody deactivates the cancer cell’s “don’t eat me” signal and restores the macrophage’s ability to detect and kill the cancer cells.

cd47-gene3

CD47 protein on surface of cancer cells triggers “don’t eat me signal” which can be blocked with anti-CD47 antibody. Image: Acrobiosystems

Because CD47 is found on the surface of most cancer cells, this anti-CD47 antibody represents an exciting new strategy for targeting cancer stem cells – the cells thought to maintain cancer growth and cause tumor relapse – in a wide variety of cancers. In fact, CIRM has provided funding for three clinical trials, one sponsored by Stanford University and two by Forty-Seven Inc. (a company that was spun out of Stanford), that are testing anti-CD47 therapy for the treatment of the blood cancer acute myeloid leukemia (AML), as well as colon cancer and other solid tumors.

“Reaching Clinical Trials” does not equal “The Research is Done”
Although these clinical trials are underway, the Weissman team continues to seek new insights related to blocking the CD47 “don’t eat me” signal. They observed that although anti-CD47 led to increased macrophage-induced killing of most cancer cell samples tested, some were resistant to anti-CD47 and remained cloaked from macrophages. And even the cancer cells that did respond to the antibody varied widely in the amount of increased killing by macrophages.

These results suggested that alternate processes may exist that allow some cancers to evade macrophages even when the CD47 “don’t eat me” signal is blocked. In a report published this week in Nature Immunology, the researchers report the identification of a second, independent “don’t eat me” signal, which may lead to more precise methods to disarm a cancer’s evasiveness.

To track down this alternate “don’t eat me” signal, they looked for, but didn’t find, correlations between specific types of cancer cells and the cancer’s resistance to anti-CD47 treatment.  So instead they analyzed surface proteins found on the various cancer cell samples and found that cancer cells that had high levels of MHC (Major Histocompatibility Complex) class I proteins were more likely to be resistant to anti-CD47 antibodies.

A Second “Don’t Eat Me” Signal
MHC class I proteins help another arm of the immune system, the adaptive immune response, detect what’s going inside a cell. They are found on nearly all cells and display, at the cell surface, bits of proteins sampled from inside the cell. If cells of the adaptive immune response, such as T or B cells, recognize one of those protein bits as abnormal or foreign, efficient killing mechanisms are kicked into high gear to destroy those cells.

But in the case of cancers cells, the MHC class I protein are harnessed as a “don’t eat me” signal by binding to a protein called LILRB1 on macrophages. When either the MHC class I proteins or LILRB1 were blocked, the “don’t eat me” signal was lifted and restored the macrophages’ ability to kill the cancer cells both in petri dish samples as well as in mice that carried human cancers.

Graduate student and co-lead author Amira Barkal described in a press release the impact of blocking both “don’t eat me” signals at the same time:

barkalSm

Amira Barkal

“Simultaneously blocking both these pathways in mice resulted in the infiltration of the tumor with many types of immune cells and significantly promoted tumor clearance, resulting in smaller tumors overall. We are excited about the possibility of a double- or perhaps even triple-pronged therapy in humans in which we combine multiple blockades to cancer growth.”

The Big Picture for Cancer Immunotherapies
Because MHC protein class I proteins play an important role in stimulating immune cells called T cells to kill cancer cells as part of the adaptive immune response, the level of MHC protein on an individual patient’s cancer cells could serve as an indicator, or “biomarker”, for what type of cancer therapy to pursue.  The big picture implications of this idea are captured in the press release:

“Understanding the balance between adaptive and innate immunity is important in cancer immunotherapy. For example, it’s not uncommon for human cancer cells to reduce the levels of MHC class 1 on their surfaces to escape destruction by T cells. People with these types of tumors may be poor candidates for cancer immunotherapies meant to stimulate T cell activity against the cancer. But these cells may then be particularly vulnerable to anti-CD47 treatment, the researchers believe. Conversely, cancer cells with robust MHC class 1 on their surfaces may be less susceptible to anti-CD47.”

Giving thanks to Caleb and all of our stem cell pioneers [Video]

For our last blog before the Thanksgiving holiday, we give thanks to the patients and their caregivers who are forging a path toward a new era of regenerative medicine therapies through their participation in CIRM-funded clinical trials.

Some of our trials are in the early stages which means they are mainly focused on safety. Participants go into these trials knowing that the cell therapy dose they receive will probably be too low to get any benefit for themselves. And in later trials, some patients will receive a placebo, or blank therapy, for comparison purposes. Even if a patient gets an effective dose, it may not work for them. So the decision to enroll in an experimental clinical trial is often a selfless act. Yet final approval of a therapy by the U.S. Food and Drug Administration (and other regulatory agencies around the world) depends on these brave souls and for that we are truly grateful.

So, with this Thanksgiving Day spirit in mind, we leave you with our latest video featuring Caleb Sizemore, a charming young man who epitomizes the courage of our clinical trial pioneers. At just 7 years old, Caleb was diagnosed with Duchenne Muscular Dystrophy (DMD), a degenerative muscle disease which makes it difficult for him to walk and climb stairs, has led to dangerous scarring of his heart muscle and carries a shortened life expectancy with most DMD patients not living past their 20s or 30s.

In a sit-down interview with us and in clips from his June 2017 presentation to the CIRM governing Board, Caleb talked about the impact of DMD on his life and his experience enrolling in Capricor Therapeutics’ CIRM-funded clinical trial. The trial is testing a stem cell therapy designed to repair the heart scarring that occurs with DMD. By the end of the three-minute video, I can assure you that you’ll be as captivated as we were by Caleb’s delightful, sincere and full-of-faith personality.

The life of a sleeping muscle stem cell is very busy

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.”

 

 

Stem cell-derived mini-intestines reveal bacteria’s key role in building up a newborn’s gut

The following factoid may induce an identity crisis for some people but it is true that our bodies carry more microbes than human cells. Some studies in 1970’s estimated the ratio at 10:1 though more recent calculations suggest we’re merely half microbe, half human.

Because microbes are much smaller than human cells they make up only about 1 or 2 percent of our total body mass. But that still amounts to trillions of micro-organisms, mostly bacteria, that live on and inside our bodies. The gut is one part of our body that is teeming with bacteria. Though that may sound gross, you’re very life depends on them. For example, these bacteria allow us to digest foods and take up nutrients that we wouldn’t be able to otherwise.

Intestines

E. coli bacteria, visible in this enhanced microscope image as tiny green rods, were injected into the center of a germ-free hollow ball of cells called a human intestinal organoid (inset image, top right). Within 48 hours, the cells formed much tighter connections with one another, visible as red in this image. Image courtesy of University of Michigan.

When we’re first born our intestines are germ-free but overtime helpful bacteria gain access to our gut and help it function, protecting it from infection by the continual exposure to harmful bacteria and viruses. New research out of the University of Michigan Medical School reported in eLife now shows that the initial bacterial infiltration is even more important than scientists previously thought. It appears to play a key role in stimulating human gut cells to shore up the intestine in preparation for the full wave of both micro-organisms and pathogens that are present throughout a person’s lifetime. The finding could help researchers discover methods to protect the gut from diseases like necrotizing enterocolitis, a rare but dangerous infection that strikes newborns.

To reach these conclusions, the research team grew human embryonic stem cells into miniature intestines in the lab. These so-called human intestinal organoids, or HIOs, are structures made up of a few thousand cells that form hollow tubes with many of the hallmarks of a bona fide intestine. The HIOs were first kept in a germ-free environment to mimic a newborn’s intestine. Then a form of helpful E. Coli bacteria, the same that’s often found in an infant’s diaper, was injected into the HIO and allowed to colonize the inside of the intestine.

155308_web

A single human intestinal organoid, or HIO — a hollow ball of cells grown from human embryonic stem cells and coaxed to become gut-lining cells. Scientists can use it to study basic gut development, and the effect of microbes on the cells, in a way that mimics the guts of newborn babies. Image courtesy of University of Michigan

The team observed several changes in gene activity shortly after the bacteria was introduced. Within a day or two, genes involved in producing proteins that fight off harmful microbes increased as well as genes that encode mucus production, a key part of protecting the cells that face the inside of the intestine. Other key features of a maturing intestine, such as tighter cell-to-cell connections and lowered oxygen levels were also stimulated by the presence of the bacteria. As co-senior author Vincent Young, M.D., Ph.D. explained in a press release, these results put the team in a position to uncover new insights about intestinal biology and disease:

VBY

Vincent Young

“We have developed a system that faithfully reproduces the physiology of the immature human intestine, and will now make it possible to study a range of host-microbe interactions in the intestine to understand their functional role in health and disease.”

 

The particular mix of microbes found in one person versus another can differ a lot. And the impact of these differences on an individual’s health has been a trending topic in the media. Lead author David Hill, Ph.D., a postdoctoral fellow in the lab of Jason Spence, Ph.D., thinks that’s one specific research path that they aim to investigate with their HIO system:

HillD_spence_website

David Hill

“We hope to examine whether different bacteria produce different types of responses in the gut. This type of work might help to explain why different types of gut bacteria seem to be associated with positive or negative health outcomes.”

 

Stem cell stories that caught our eye: the tale of a tail that grows back and Zika’s devious Trojan Horse

The tale of a tail that grows back (Kevin McCormack)

Ask people what they know about geckos and the odds are they’ll tell you geckos have English accents and sell car insurance. Which tells you a lot more about the power of advertising than it does about the level of knowledge about lizards. Which is a shame, because the gecko has some amazing qualities, not the least of which is its ability to re-grow its tail. Now some researchers have discovered how it regenerates its tail, and what they’ve learned could one day help people with spinal cord injuries.

Geckos often detach a bit of their tail when being pursued by a predator, then grow a new one over the course of 30 days. Researchers at the University of Guelph in Canada found that the lizards use a combination of stem cells and proteins to do that.

They found that geckos have stem cells in their tail called radial glias. Normally these cells are dormant but that changes when the lizard loses its tail. As Matthew Vickaryous, lead author of the study, said in a news release:

“But when the tail comes off everything temporarily changes. The cells make different proteins and begin proliferating more in response to the injury. Ultimately, they make a brand new spinal cord. Once the injury is healed and the spinal cord is restored, the cells return to a resting state.”

Vickaryous hopes that understanding how the gecko can repair what is essentially an injury to its spinal cord, we’ll be better able to develop ways to help people with the same kind of injury.

The study is published in the Journal of Comparative Neurology.

Zika virus uses Trojan Horse strategy to infect developing brain
In April 2015, the World Health Organization declared that infection by Zika virus and its connection to severe birth defects was an international public health emergency. The main concern has been the virus’ link to microcephaly, a condition in which abnormal brain development causes a smaller than normal head size at birth. Microcephaly leads to number of problems in these infants including developmental delays, seizures, hearing loss and difficulty swallowing.

A false color micrograph shows microglia cells (green) infected by the Zika virus (blue). Image Muotri lab/UCSD

Since that time, researchers have been racing to better understand how Zika infection affects brain development with the hope of finding treatment strategies. Now, a CIRM-funded study in Human Molecular Genetics reports important new insights about how Zika virus may be transmitted from infected pregnant women to their unborn babies.

The UCSD researchers behind the study chose to focus on microglia cells. In a press release, team leader Alysson Muotri explained their rationale for targeting these cells:

“During embryogenesis — the early stages of prenatal development — cells called microglia form in the yolk sac and then disperse throughout the central nervous system (CNS) of the developing child. Considering the timing of [Zika] transmission, we hypothesized that microglia might be serving as a Trojan horse to transport the virus during invasion of the CNS.”

In the developing brain, microglia continually travel throughout the brain and clear away dead or infected cells. Smuggling itself aboard microglia would give Zika a devious way to slip through the body’s defenses and infect other brain cells. And that’s exactly what Dr. Muotri’s team found.

Using human induced pluripotent stem cells (iPSCs), they generated brain stem cells – the kind found in the developing brain – and in lab dish infected them with Zika virus. When iPSC-derived microglia were added to the infected neural stem cells, the microglia gobbled them up and destroyed them, just as they would do in the brain. But when those microglia were placed next to uninfected brain stem cells, the Zika virus was easily transmitted to those cells. Muotri summed up the results this way:

“Our findings show that the Zika virus can infect these early microglia, sneaking into the brain where they transmit the virus to other brain cells, resulting in the devastating neurological damage we see in some newborns.”

The team went on to show that an FDA-approved drug to treat hepatitis – a liver disease often caused by viral infection – was effective at decreasing the infection of brain stem cells by Zika-carrying microglia. Since these studies were done in petri dishes, more research will be required to confirm that the microglia are a true drug target for stopping the devastating impact of Zika on newborns.

Clever technique uncovers role of stem cells in cartilage repair

Over 50 million adults in the U.S. are estimated to be affected by some form of arthritis, a very painful, debilitating condition in which the cartilage that provides cushioning within bone joints gradually degrades. Health care costs of treating arthritis in California alone has been estimated at over $12 billion and that figure is already over a decade old. Unfortunately, the body doesn’t do a good job at healing cartilage in the joint so doctors rely mostly on masking symptoms with pain management therapy and, in severe cases, resorting to surgery.

Illustration of damaged cartilage within an osteoarthritic hip joint Image: Wikipedia/Open Stax

Mesenchymal stem cells (MSCs) – found in bone marrow, fat and blood – give rise to several cell types including cartilage-producing cells called chondrocytes. For that reason, they hold a lot of promise to restore healthy joints for arthritis sufferers. While there is growing evidence that injection of MSCs into joint cartilage is effective, it is still not clear how exactly the stem cells work. Do they take up residence in the cartilage, and give rise to new cartilage production in the joint? Or do they simply release proteins and molecules that stimulate other cells within the joint to restore cartilage? These are important questions to ask when it comes to understanding what tweaks you can make to your cell therapy to optimize its safety and effectiveness. Using some clever genetic engineering techniques in animal models, a research team at the University of Veterinary Medicine in Vienna, Austria report this week in JCI Insights that they’ve uncovered an answer.

Tracking the fate of a stem cell treatment after they’ve been injected into an animal, requires the attachment of some sort of “beacon” to the cells. A number of methods exist to accomplish this feat and they all rely on creating transgenic animals engineered to carry a gene that produces a protein label on the cells. For instance, cells from mice or rats engineered to carry the luciferase gene from fireflies, will glow and can be tracked in live animals. So, in this scenario, MSCs from a genetically-engineered donor animal are injected into the joints of a recipient animal which lacks this protein marker. This technique allows the researchers to observe what happens to the labeled cells.

There’s a catch, though. The protein marker carried along with the injected cells is seen as foreign to the immune system of the animal that receives the cells. As a result, the cells will be rejected and destroyed. To get around that problem, the current practice is to use recipient animals bred to have a limited immune response so that the injected cells survive. But solving this problem adds yet another: the immune system plays a key role in the mechanisms of arthritis so removing the effects of it in this experiment will likely lead to misinterpretations of the results.

So, the research team did something clever. They genetically engineered both the donor and recipient mice to carry the same protein marker but with an ever-so-slight difference in their genetic code. The genetic difference in the protein marker was large enough to allow the team to track the donor stem cells in the recipient animals, but similar enough to avoid rejection from the immune system. With all these components of the experiment in place, the researchers were able to show that the MSCs release protein factors to help the body repair its own cartilage damage and not by directly replacing the cartilage-producing cells.