Stem Cell Round: Improving memory, building up “good” fat, nanomedicine

Stem Cell Photo of the Week

roundup03618In honor of brain awareness week, our featured stem cell photo is of the brain! Scientists at the Massachusetts General Hospital and Harvard Stem Cell Institute identified a genetic switch that could potentially improve memory during aging and symptoms of PTSD. Shown in this picture are dentate gyrus cells (DGC) (green) and CA3 interneurons (red) located in the memory-forming area of the brain known as the hippocampus. By reducing the levels of a protein called abLIM3 in the DGCs of older mice, the researchers were able to boost the connections between DGCs and CA3 cells, which resulted in an improvement in the memories of the mice. The team believes that targeting this protein in aging adults could be a potential strategy for improving memory and treating patients with post-traumatic stress disorder (PTSD). You can read more about this study in The Harvard Gazette.

New target for obesity.
Fat cells typically get a bad rap, but there’s actually a type of fat cell that is considered “healthier” than others. Unlike white fat cells that store calories in the form of energy, brown fat cells are packed with mitochondria that burn energy and produce heat. Babies have brown fat, so they can regulate their body temperature to stay warm. Adults also have some brown fat, but as we get older, our stores are slowly depleted.

In the fight against obesity, scientists are looking for ways to increase the amount of brown fat and decrease the amount of white fat in the body. This week, CIRM-funded researchers from the Salk Institute identified a molecule called ERRg that gives brown fat its ability to burn energy. Their findings, published in Cell Reports, offer a new target for obesity and obesity-related diseases like diabetes and fatty liver disease.

The team discovered that brown fat cells produce the ERRg molecule while white fat cells do not. Additionally, mice that couldn’t make the ERRg weren’t able to regulate their body temperature in cold environments. The team concluded in a news release that ERRg is “involved in protection against the cold and underpins brown fat identity.” In future studies, the researchers plan to activate ERRg in white fat cells to see if this will shift their identity to be more similar to brown fat cells.


Mice that lack ERR aren’t able to regulate their body temperature and are much colder (right) than normal mice (left). (Image credit Salk Institute)

Tale of two nanomedicine stories: making gene therapies more efficient with a bit of caution (Todd Dubnicoff).
This week, the worlds of gene therapy, stem cells and nanomedicine converged for not one, but two published reports in the journal American Chemistry Society NANO.

The first paper described the development of so-called nanospears – tiny splinter-like magnetized structures with a diameter 5000 times smaller than a strand of human hair – that could make gene therapy more efficient and less costly. Gene therapy is an exciting treatment strategy because it tackles genetic diseases at their source by repairing or replacing faulty DNA sequences in cells. In fact, several CIRM-funded clinical trials apply this method in stem cells to treat immune disorders, like severe combined immunodeficiency and sickle cell anemia.

This technique requires getting DNA into diseased cells to make the genetic fix. Current methods have low efficiency and can be very damaging to the cells. The UCLA research team behind the study tested the nanospear-delivery of DNA encoding a gene that causes cells to glow green. They showed that 80 percent of treated cells did indeed glow green, a much higher efficiency than standard methods. And probably due to their miniscule size, the nanospears were gentle with 90 percent of the green glowing cells surviving the procedure.

As Steve Jonas, one of the team leads on the project mentions in a press release, this new method could bode well for future recipients of gene therapies:

“The biggest barrier right now to getting either a gene therapy or an immunotherapy to patients is the processing time. New methods to generate these therapies more quickly, effectively and safely are going to accelerate innovation in this research area and bring these therapies to patients sooner, and that’s the goal we all have.”

While the study above describes an innovative nanomedicine technology, the next paper inserts a note of caution about how experiments in this field should be set up and analyzed. A collaborative team from Brigham and Women’s Hospital, Stanford University, UC Berkeley and McGill University wanted to get to the bottom of why the many advances in nanomedicine had not ultimately led to many new clinical trials. They set out looking for elements within experiments that could affect the uptake of nanoparticles into cells, something that would muck up the interpretation of results.


imaging of female human amniotic stem cells incubated with nanoparticles demonstrated a significant increase in uptake compared to male cells. (Green dots: nanoparticles; red: cell staining; blue: nuclei) Credit: Morteza Mahmoudi, Brigham and Women’s Hospital.

In this study, they report that the sex of cells has a surprising, noticeable impact on nanoparticle uptake. Nanoparticles were incubated with human amniotic stem cells derived from either males or females. The team showed that the female cells took up the nanoparticles much more readily than the male cells.  Morteza Mahmoudi, PhD, one of the authors on the paper, explained the implications of these results in a press release:

“These differences could have a critical impact on the administration of nanoparticles. If nanoparticles are carrying a drug to deliver [including gene therapies], different uptake could mean different therapeutic efficacy and other important differences, such as safety, in clinical data.”


UCSD scientists devise tiny sensors that detect forces at cellular level

A big focus of stem cell research is trying to figure how to make a stem cell specialize, or differentiate, into a desired cell type like muscle, liver or bone. When we write about these efforts in the Stem Cellar, it’s usually in terms of researchers identifying proteins that bind to a stem cell’s surface and trigger changes in gene activity inside the cell that ultimately leads to a specific cell fate.

But, that’s not the only game in town. As incredible as it sounds, affecting a cell’s shape through mechanical forces also plays a profound role in gene activity and determining a cell’s fate. In one study, mesenchymal stem cells would specialize into fat cells or bone-forming cells depending on how much the MSCs were stretched out on a petri dish.

An artist’s illustration of nano optical fibers detecting the minuscule forces produced by swimming bacteria. Credit: Rhett S. Miller/UC Regents

Since we’re talking about individual cells, the strength of these mechanical forces is tiny, making measurements nearly impossible. But now, a research team at UC San Diego has engineered a device 100 times thinner than a human hair that can detect these miniscule forces. The study, funded in part by CIRM, was reported yesterday in Nature Photonics.

The device is made of a very thin optical fiber that’s coated with a resin which contains gold particles. The fiber is placed directly into the liquid that cells are grown in and then hit with a beam of light. The light is scattered by the gold particles and measured with a conventional light microscope. Forces and even sound waves caused by cells in the petri dish change the intensity of the light scattering which is detected by the microscope.

Donald Sirbuly,
team lead

In this study, the researchers measured astonishingly small forces (0.0000000000001 pound of force, to be exact!) in a culture of gut bacteria which swim around in the solution with the help of their whip-like flagella. The team also detected the sound of beating heart muscle cells at a level that’s a thousand times below the range of human hearing.

Dr. Donald Sirbuly, the team lead and a professor at UCSD’s Jacobs School of Engineering is excited about the research possibilities with this device:

“This work could open up new doors to track small interactions and changes that couldn’t be tracked before,” he said in a press release.

Bradley Fikes, the biotechnology reporter for the San Diego Union Tribune, reached out to others in the field to get their take on potential applications of this nanofiber device. Dr. John Marohn at Columbia University told Fikes in a news article (subscription is needed to access) that it could help stem cell scientists’ fully understand all of the intricacies of cell fate:

“So one of the cues that cells get, and they listen to these cues to decide how to change how to evolve, are just outside forces. This would give a way to kind of feel the outside forces that the cells feel, in a noninvasive way.”

And Eli Rothenberg at NYU School of Medicine, also not part of the study, summed up the device’s novelty, power and ease of use in an interview with Fikes:

“One of the main challenges in measuring things in biology is forces. We have no idea what’s going on in terms of forces in cells, in term of motion of molecules, the forces they interact with. But these sensors, you can put anywhere. They’re tiny, you can place them on the cells. If a cancer cell’s surface is moving, you can measure the forces…The fabrication of this device is quite straightforward. So, the simplicity of having this device and what you can measure with it, that’s kind of striking.”



Speak Friend and Enter: How Cells Let the Right Travelers through their Doors

For decades, it’s been a molecular mystery that scientists were seemingly unable to solve: how do large molecules pass through the cell and into the nucleus, while others half their size remain stranded outside?

These are nuclear pores imaged by atomic force microscopy, appearing as a craterlike landscape in which each crater corresponds to a pore of ~100 nm diameter. [Credit: UCL]

Nuclear pores imaged by atomic force microscopy, appearing as a crater-like landscape in which each crater corresponds to a pore of ~100 nm diameter. [Credit: UCL]

But as reported in the latest issue of Nature Nanotechnology, researchers now believe they may have cracked the case. By shedding light on this strange anomaly, University College London (UCL) scientists have opened the door for one day delivering gene therapies directly into the nucleus. With numerous research teams working on ways to merge stem cell therapy and gene therapy, this could be extremely valuable to our field.

Scientists already knew that the membrane that surrounds the cell’s nucleus is ‘punctured’ with millions of tiny holes, known as nuclear pores. Co-lead author Bart Hoogenboom likened the pores to a strange kind of sieve:

“The pores have been to known to act like a sieve that could hold back sugar while letting grains of rice fall through at the same time, but it was not clear how they were able to do that.”

In this study—which used cells taken from frog eggs—Hoogenboom, along with co-lead author Ariberto Fassati, harnessed atomic force microscopy (AFM) to give them a new understanding of how these pores work. Like a blind person moving their fingers to read braille, AFM uses a tiny needle to pass over the nuclear pores in order to measure their shape and structure.

“AFM can reveal far smaller structures than optical microscopes,” said Hoogenboom, “but it’s feeling more than seeing. The trick is to press hard enough to feel the shape and the hardness of the sample, but not so hard that you break it. [In this study], we used it to successfully probe the membrane…to reveal the structure of the pores.”

And what they found, adds Fassati, offered an explanation for how these pores worked:

“We found that the proteins in the center of the pores tangle together just tightly enough to form a barrier—like a clump of spaghetti. Large molecules can only pass through [the pores] when accompanied by chaperone molecules. These chaperones, called nuclear transport receptors, have the property of lubricating the [spaghetti] strands and relaxing the barrier, letting the larger molecules through.”

Astoundingly, Fassati said that this process happens upwards of several thousand times per second.

These results are exciting not only for solving a long-standing mystery, but also for pointing to new ways of delivering gene therapies.

As evidenced by recent clinical advances in conditions such as sickle cell disease and SCID (‘bubble baby’ disease), gene therapy represents a promising way to treat—and even cure—patients. Hoogenboom and Fassati are optimistic that their team’s discovery could lead further refinements to gene therapy techniques.

Said Fassati, “It may be possible to improve the design of current mechanisms for delivering gene therapy to better cross the nuclear pores and deliver their therapeutic genes into the nucleus.”

A Tumor’s Trojan Horse: CIRM Researchers Build Nanoparticles to Infiltrate Hard-to-Reach Tumors

Some tumors are hard to find, while others are hard to destroy. Fortunately, a new research study from the University of California, Davis, has developed a new type of nanoparticle that could one day do both.

UC Davis scientists have developed a new type of nanoparticle to target tumor cells.

UC Davis scientists have developed a new type of nanoparticle to target tumor cells.

Reporting in the latest issue of Nature Communications, researchers in the laboratory of UC Davis’ Dr. Kit Lam describe a type of ‘dynamic nanoparticle’ that they created, which not only lights up tumors during an MRI or PET scan, but which may also serve as a microscopic transport vehicle, carrying chemotherapy drugs through the blood stream—and releasing them upon reaching the tumor.

This is not the first time scientists have attempted to develop nanoparticles for medicinal purposes, but is perhaps one of the more successful. As Yuanpei Li, one of the study’s co-first authors stated in a news release:

“These are amazingly useful particles. As a contrast agent, they make tumors easier to see on MRI and other scans. We can also use them as vehicles to deliver chemotherapy directly to tumors.”

Nanoparticles can be constructed out of virtually any material—but the material used often determines for what purpose they can be used. Nanoparticles made of gold-based materials, for example, may be strong for diagnostic purposes, but have been shown to have issues with safety and toxicity. On the flip side, nanoparticles made from biological materials are safer, but inherently lack imaging ability. What would be great, the team reasoned, was a new type of nanoparticle that had the best qualities of both.

In this study, which was funded in part by CIRM, Lam and the UC Davis team devised a new type of nanoparticle that was ‘just right,’—simple to make, safe and able to perform the desired task, in this case: attack tumors.

Built of organic porphyrin and cholic acid polymers and coated with the amino acid cysteine, the 32 nanometer-wide particles developed in this study offer a number of advantages over other models. They are small enough to pass into tumors, can be filled with a chemo agent and with a specially designed cysteine coating, and don’t accidentally release their payload before reaching their destination.

And this is where the truly ingenious part kicks in. With a simple flash of light, the researchers could direct the particles to drop their payload—at just the right time, offering some intriguing possibilities for new ways to deliver chemotherapy drugs.

But wait, there’s more. The fact that these new particles, which the team are calling cysteine nanoparticles, or CNP’s, appear to congregate inside tumors means that they also end up being easy to spot on an MRI.

Continued Li in the same release:

“These particles can combine imaging and therapeutics. We could potentially use them to simultaneously deliver treatment and monitor treatment efficacy. This is the first nanoparticle to perform so many different jobs. From delivering chemo, photodynamic and photothermal therapies to enhancing diagnostic imaging. It’s the complete package.”

And while the team cautions that these results are preliminary, they open the door to an entirely new and far more exact method of drug delivery to tumors—no matter how well-hidden in the body they may be.