Toward a stem cell model of human nervous system development Human cells could one day show us more about why neural tube birth defects occur and how to prevent them.

Human embryonic stem cells can be guided to become the precursor tissue of the central nervous system, research led by the University of Michigan has demonstrated. The new study also reveals the important role of mechanical signals in the development of the human nervous system.

While studying embryonic development using animal embryos can provide useful insights about what happens during human development, human embryos grow differently even at this early stage.

“There is a critical need to establish embryonic developmental models using human cells. Not only could they advance our fundamental understanding of human development, they are also essential for regenerative medicine and for testing the safety of drugs and chemicals that pregnant women may need or encounter,” said Jianping Fu, an associate professor of mechanical engineering, who has been supervising this research.

“For the first time, we are able to use human embryonic stem cells to develop a synthetic model of neuroectoderm patterning, the embryonic event that begins the formation of the brain and spinal cord in the human embryo.”

There is a critical need to establish embryonic developmental models using human cells.Jianping Fu, associate professor of mechanical engineering.

In humans, the cells that will later differentiate into the central nervous system (including the brain and spinal cord) are known as the neural plate, while those that stand between the neural plate and future skin cells are called the neural plate border. The neural plate folds in on itself about 28 days after conception, becoming the neural tube, and the border on either side of it fuses together along its length. When the neural tube fails to close properly, it typically results in paralysis or death.

“The exact causes of neural tube defects are not clear, and there is currently no cure for them. Environmental factors, such as certain drugs pregnant women take, may play roles in causing neural tube defects,” said Fu.

In the new study, Fu’s research team arranged human embryonic stem cells into circular cell colonies with defined shapes and sizes. The cells were then exposed to chemicals known to coax them to differentiate into neural cells. During the differentiation process, cells in circular colonies organized themselves with neural plate cells in the middle and neural plate border cells in a ring around the outside.

“Since all of the cells in a micropatterned colony are in the same chemical environment, it’s amazing to see the cells autonomously differentiate into different cells and organize themselves into a multicellular pattern that mimics human development,” said Xufeng Xue, a PhD student in mechanical engineering working in Fu’s research group.  Xue is a co-first author of the paper.

Disc-shaped colonies shown with phase contrast (top) and fluorescence (bottom) microscopy. Between day 3 and day 9, cells in the center of the colony grow faster and become much more densely packed. Confined space drives the cells in the center of the colony to become neural plate cells, whereas those cells at the colony border (experiencing less confinement) differentiate into neural plate border cells. Image: Xufeng Xue, Integrated Biosystems and Biomechanics Laboratory, University of Michigan.

 

Fu’s team observed that cells in the circular colony became more densely packed in the middle of the colony, where they became neural plate cells, versus the colony border, where they became neural plate border cells. Suspecting mechanical signals might affect their differentiation, they placed single human embryonic stem cells onto adhesive spots of different sizes.

In the same chemical environment, single human embryonic stem cells grown on larger spots began signaling events within the cells that drove them toward becoming neural plate border cells. These signaling events were inhibited in stem cells confined on smaller spots. The team also developed a system to stretch cells in the middle of a colony. Responding to this mechanical signal, the cells in the middle of a colony differentiated into neural plate border cells, rather than the neural plate cells at the center of an ordinary colony.

“While many current models attribute patterning of embryonic tissues to chemical gradients or cell migration, our results show that these factors may not be the only drivers,” said Yubing Sun (ME PhD ’15), a former doctoral student in Fu’s lab and now an assistant professor of mechanical and industrial engineering at the University of Massachusetts, Amherst. Sun is a co-first author of the paper.

The study, titled, “Mechanics-guided embryonic patterning of neuroectoderm tissue from human pluripotent stem cells,” is published in Nature Materials.

This work was supported by the National Science Foundation (grant numbers CMMI 1129611, CBET 1149401and CMMI 1662835), the American Heart Association (grant number 12SDG12180025) and the U-M Department of Mechanical Engineering.

Fu is also an associate professor of biomedical engineering, cell and developmental biology, and is an associate director of the Michigan Center for Integrative Research in Critical Care.

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‘Nightmare bacteria:’ Michigan Engineers discuss how to combat antibiotic resistance Drug-resistant bugs are on the rise and new approaches are needed.

Health officials at the U.S. Centers for Disease Control and Prevention earlier this month said they are seeing rising cases of “nightmare bacteria” that show strong resistance to antibiotics. More than 200 cases were reported in the last year alone, and across every state in the U.S.

“Unusual resistance germs—which are resistant to all or most antibiotics tested and are uncommon or carry special resistance genes—are constantly developing and spreading,” the CDC said.

A particular concern is the number of cases that crop up in hospitals and nursing homes where IVs, catheters and medical implants—all particularly susceptible to infection—are common.

“Antibiotic resistance is one of the most important public health problems of the 21st century,” said Angela Violi, professor of mechanical engineering and chemical engineering at U-M.

Violi is one of many researchers at Michigan Engineering who are are tackling this issue from a variety of angles. Some are exploring new ways to combine antibiotics to stay one step ahead of the bugs. Others are looking beyond antibiotics—to nanoparticles.

Nicholas Kotov, the Joseph B. and Florence V. Celka professor of chemical engineering, is part of a team researching the use of nanoparticles as a new form of antibiotics. Nanoparticles can be shaped specifically to get past a bacterium’s defenses and shut down processes essential to its survival. Nanoparticles can also be used to coat medical implants in order to prevent infection from drug resistant bacteria.

“New methods of suppressing or otherwise diminishing the health impact of antibiotic resistant bacteria are needed,” Kotov said. “Molecular and nanoscale engineering of inorganic nanoparticles offers this opportunity by utilizing the latest experimental and computational tools targeting the bacteria where it does not expect.”

Violi helps identify the best pathways for utilizing nanoparticles to attack antibiotic resistant bacteria.

“Potentially, all it takes is a single mutated bacterium to render an antibiotic useless for that infection,” she said. “When that mutant cell replicates, it will pass on its resistant phenotype to its daughter cells, and so on.

“At that point part of the replicating bacteria will be drug resistant: the drug will kill only those cells that do not have the newly evolved drug-resistance capacity. Eventually, the entire bacterial population will become resistant to the prescribed antibiotic.

“It is only when antibiotics are used that drug-resistant phenotypes have a selective advantage and survive.

“Nano and chemical engineering approaches provide unparalleled flexibility to control the composition, size, shape, surface chemistry, and functionality of nanostructures that can be used to develop a new generation of modified materials or to coat existing solid surfaces to fight bacteria.”

Professor working on a computer in the lab
Sriram Chandrasekaran, an assistant professor of biomedical engineering, uses computer simulations to develop strategies for using current antibiotics in combination as well as roadmaps for creating new classes of antibiotics. Photo by Joseph Xu

Sriram Chandrasekaran, an assistant professor of biomedical engineering, approaches drug resistant bacteria from a different angle. He and his team study proteins and analyze their behaviors via computer simulations to develop strategies for using current antibiotics in combination as well as roadmaps for creating new classes of antibiotics.

“In addition to better stewardship of antibiotics, we also need to come up with smarter treatment strategies that can reduce the rise of resistance,” Chandrasekaran said.

“For example, our lab and others are designing combinations of antibiotics that are more effective in retarding the evolution of drug resistance compared to using drugs individually. Such combinations of FDA approved drugs can also reach the clinic faster than developing new drugs from scratch.

“We are also developing computer algorithms that can identify the most optimal combination of drugs for a specific strain of pathogen. Overall, what we can learn from this crisis is that we cannot take antibiotics for granted. We have to keep investing on new treatments as bacteria will always eventually evolve resistance to whatever new drug we throw at it.”

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No sponge left behind: tags for surgical equipment A simple, easy-to-implement technology could prevent the debilitating injuries that can occur when organs are damaged by surgical tools left in the body.

Items left behind in patients after surgery can have an enormous personal cost when organs and tissues are damaged. Surgical sponges are among the worst offenders – difficult to see in post-surgical X-rays and yet capable of causing holes when the intestines grow around them, for example. These rare cases, estimated around one in 3,000 surgeries that carry a risk, add up to around $1.5 billion in costs per year.

X-ray image showing scissors inside a cadaver
Marentis took about 2,800 X-ray images of the tag to train and test the software.

The current method of accounting for surgical tools involves counting them before and after surgery and performing an X-ray if there’s a mismatch. Without the metal bands inside them, the gauze sponges wouldn’t appear at all, but they are still difficult to see. A new, unmistakeable tag could change that – and its signature is so clear that computers can also detect it.

The tag, which is about the same size and shape as an acetaminophen tablet, contains four metal spheres, arranged at the points of a tetrahedron. This simple shape can be recognized by the computer no matter how it is turned. With human radiologists having a first look at the X-rays and then comparing their findings with a computer, over 98 percent of the tags can be seen. In contrast, as many as half of surgical sponges are missed in X-rays today.

The research team has formed the company Kalyspo, and they are building partnerships with surgical sponge manufacturers and hospitals in an effort to make the tag and software a standard part of surgical procedures, keeping patients safer.

Nikolaos Chronis, an associate professor of mechanical engineering at U-M, led the development of the tag. Theodore Marentis, then a radiology resident at U-M, identified the need for such a tag and worked with Chronis to develop and test it. Lubomir Hadjiyski, a professor of radiology at U-M, led the development of the software that locates the tags.

Chronis is also an associate professor of biomedical engineering and macromolecular science and engineering. Marentis is now a radiologist at the Mercy Medical Center in Mt. Shasta, CA.

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