Tumor suppressor key in maintaining stem cell status in muscle

A gene known to suppress tumor formation in a broad range of tissues plays a key role in keeping stem cells in muscles dormant until needed, a finding that may have implications for both human health and animal production, according to a Purdue University study.

Shihuan Kuang, professor of animal sciences, and Feng Yue, a postdoctoral researcher in Kuang's lab, reported their findings in two papers published in the journals Cell Reports and Nature Communications. The results suggest modifying expression of the PTEN gene could one day play a role in increasing muscle mass in agricultural animals and improve therapies for muscle injuries in humans.
Muscle stem cells, called satellite cells, normally sit in a quiescent, or dormant, state until called upon to build muscle or repair a damaged muscle. Inability to maintain the quiescence would lead to a loss of satellite cells. As humans age, the number of satellite cells gradually declines and the remaining cells become less effective in regenerating muscles, resulting in muscle loss – a condition called sarcopenia.
Kuang and Yue, in the Nature Communications paper, explored the role tumor-suppressor gene PTEN plays in satellite cells. The PTEN gene encodes a protein that suppresses the growth signaling, thereby, limiting the growth of fast-growing tumor cells. Mutation of the PTEN gene is associated with many types of cancers, but how the gene functions in muscle stem cells is unknown.
To understand the function of a gene, the authors first wanted to know how the gene is expressed.
"This gene is highly expressed in the satellite cells when the cells are in the quiescent state. When they become differentiated, the PTEN level reduces," Yue said.
By knocking out the PTEN gene in resting satellite cells, the researchers found that satellite cells quickly differentiate and become muscle cells. So PTEN plays an essential role in keeping satellite cells in their quiescent state.
"You no longer have the stem cells once you knock out the gene," Kuang said.
In their Cell Reports paper, Kuang and Yue took a step further to examine PTEN function in proliferating stem cells. This time, they knocked out PTEN in embryonic progenitor cells, those that will later become muscle in the mouse. They found that as the mouse grew, muscle mass increased significantly—by as much as 40 percent in some muscles—over that of a normal mouse.
"That would be significant in an animal production point of view," Kuang said.
The increased muscle came with a cost, however. Besides creating muscle, those progenitor cells create satellite cells. Without PTEN, not only fewer satellite cells were created, but the resulting satellite cells cannot maintain dormancy, leading to an accelerated rate of depletion during aging.
The faster depletion of satellite cells during aging wouldn't matter much in an animal production scenario, Kuang said. Beef cattle, for example, are harvested before they age. The increase in muscle mass, however, would be a significant advantage in production efficiency.
The findings may lead to improvement in human health, the authors said. The ability to control the expression of PTEN could lead to therapies for quicker healing of muscle injuries.
"If you want to quickly boost up the stem cells to repair something, you need to suppress PTEN," Kuang said. "After that, you'd need to increase PTEN to return the cells back to quiescent state. If we could do that, you would suspect that the muscle would repair more quickly."
Knowing that PTEN also suppresses tumors in many types of tissues, the authors noted that the elimination of the gene did not cause tumor formation in the muscle cells they studied. That suggests regulation of PTEN could be a feasible method for improving human health and animal agriculture.

Credit : Brian Wallheimer

The strength of real hair inspires new materials for body armor

Researchers at the University of California San Diego investigate why hair is incredibly strong and resistant to breaking. Credit: iStock.com/natevplas

In a new study, researchers at the University of California San Diego investigate why hair is incredibly strong and resistant to breaking. The findings could lead to the development of new materials for body armor and help cosmetic manufacturers create better hair care products.

Hair has a strength to weight ratio comparable to steel. It can be stretched up to one and a half times its original length before breaking. "We wanted to understand the mechanism behind this extraordinary property," said Yang (Daniel) Yu, a nano-engineering Ph.D. student at UC San Diego and the first author of the study.
"Nature creates a variety of interesting materials and architectures in very ingenious ways. We're interested in understanding the correlation between the structure and the properties of biological materials to develop synthetic materials and designs—based on nature—that have better performance than existing ones," said Marc Meyers, a professor of mechanical engineering at the UC San Diego Jacobs School of Engineering and the lead author of the study.
In a study published online in Dec. in the journal Materials Science and Engineering C, researchers examined at the nano-scale level how a strand of human hair behaves when it is deformed, or stretched. The team found that hair behaves differently depending on how fast or slow it is stretched. The faster hair is stretched, the stronger it is. "Think of a highly viscous substance like honey," Meyers explained. "If you deform it fast it becomes stiff, but if you deform it slowly it readily pours."
Hair consists of two main parts—the cortex, which is made up of parallel fibrils, and the matrix, which has an amorphous (random) structure. The matrix is sensitive to the speed at which hair is deformed, while the cortex is not. The combination of these two components, Yu explained, is what gives hair the ability to withstand high stress and strain.
And as hair is stretched, its structure changes in a particular way. At the nano-scale, the cortex fibrils in hair are each made up of thousands of coiled spiral-shaped chains of molecules called alpha helix chains. As hair is deformed, the alpha helix chains uncoil and become pleated sheet structures known as beta sheets. This structural change allows hair to handle up a large amount deformation without breaking.
This structural transformation is partially reversible. When hair is stretched under a small amount of strain, it can recover its original shape. Stretch it further, the structural transformation becomes irreversible. "This is the first time evidence for this transformation has been discovered," Yu said.
"Hair is such a common material with many fascinating properties," said Bin Wang, a UC San Diego PhD alumna and co-author on the paper. Wang is now at the Shenzhen Institutes of Advanced Technology in China continuing research on hair.
The team also conducted stretching tests on hair at different humidity levels and temperatures. At higher humidity levels, hair can withstand up to 70 to 80 percent deformation before breaking. Water essentially "softens" hair—it enters the matrix and breaks the sulfur bonds connecting the filaments inside a strand of hair. Researchers also found that hair starts to undergo permanent damage at 60 degrees Celsius (140 degrees Fahrenheit). Beyond this temperature, hair breaks faster at lower stress and strain.
"Since I was a child I always wondered why hair is so strong. Now I know why," said Wen Yang, a former postdoctoral researcher in Meyers' research group and co-author on the paper.
The team is currently conducting further studies on the effects of water on the properties of human hair. Moving forward, the team is investigating the detailed mechanism of how washing hair causes it to return to its original shape.

In highly lethal type of leukemia, cancer gene predicts treatment response

New research led by Washington University School of Medicine in St. Louis shows that patients with acute myeloid leukemia (AML) whose cancer cells carry TP53 mutations -- a feature that correlates with an extremely poor prognosis -- may live longer if they are treated with decitabine, a less intensive chemotherapy drug. The study's first author, John Welch, M.D., PhD, is pictured with Phillip Houghton, who is being treated for AML. Credit: Washington University

Patients with the most lethal form of acute myeloid leukemia (AML) - based on genetic profiles of their cancers - typically survive for only four to six months after diagnosis, even with aggressive chemotherapy. But new research indicates that such patients, paradoxically, may live longer if they receive a milder chemotherapy drug.

Treatment with the less intensive drug, decitabine, is not a cure. But surprisingly, AML patients whose leukemia cells carried mutations in a nefarious cancer gene called TP53 consistently achieved remission after treatment with decitabine. Their median survival was just over a year.
The study, by a team of scientists at Washington University School of Medicine in St. Louis, is published Nov. 24 in The New England Journal of Medicine.
In AML, treatment involves intensive chemotherapy to try to kill the patient's leukemia cells and put the cancer into remission. If successful, a follow-up bone-marrow transplant can offer a possible cure, but this course of treatment is recommended only for patients with a high risk of relapse because the procedure can cause severe complications, even death.
"What's really unique here is that all the patients in the study with TP53 mutations had a response to decitabine and achieved an initial remission," said the study's senior author, Timothy J. Ley, MD, the Lewis T. and Rosalind B. Apple Professor of Medicine, noting that in AML, TP53 mutations have been correlated with an extremely poor prognosis. "With standard aggressive chemotherapy, we only see about 20 to 30 percent of these patients achieving remission, which is the critical first step to have a chance to cure patients with additional therapies.
"The findings need to be validated in a larger trial," Ley added, "but they do suggest that TP53 mutations can reliably predict responses to decitabine, potentially prolonging survival in this ultra high-risk group of patients and providing a bridge to transplantation in some patients who might not otherwise be candidates."
In an accompanying editorial, Elihu Estey, MD, an AML expert at the University of Washington Medical Center and Fred Hutchinson Cancer Research Center in Seattle, noted that AML is not one disease but many, each driven by different genetic mutations. The results of the current trial, he said, point to the inevitable need to replace large cancer clinical trials evaluating homogeneous drug treatments with smaller trials that involve subgroups of patients, with treatments targeted to their specific mutations.

The current study involved 116 patients treated with decitabine at the Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital, and at the University of Chicago. The patients either had AML - a cancer of the bone marrow - or myelodysplastic syndrome (MDS), a group of blood cancers that often progresses to AML. This year, an estimated 20,000 people living in the U.S. will be diagnosed with AML, and at least 11,000 deaths will be attributed to the disease.
Decitabine often is given to older patients with AML or MDS because it is less toxic than standard chemotherapies. But fewer than half of patients who get the drug achieve an initial remission, so the researchers wanted to determine whether specific mutations in the patients' cancer cells could predict their responses to treatment.
To find out, they sequenced all the genes in patients' cancer cells or analyzed select cancer genes. They also conducted standard tests to look for broken, missing or rearranged chromosomes. Then, the researchers correlated these molecular markers with treatment response to identify subgroups of patients likely to benefit from decitabine.
Among the patients in the study, 46 percent achieved a remission with decitabine. But, remarkably, all 21 patients whose leukemia cells carried TP53 mutations went into remission.
Patients also were likely to respond to decitabine if they were deemed to have an "unfavorable risk" prognosis based on extensive chromosomal rearrangements in their cancer cells; many of these patients also had TP53 mutations. Indeed, 66 percent of patients with an unfavorable risk achieved remission, compared with 34 percent of patients who had more favorable prognoses.
"The challenge with using decitabine has been knowing which patients are most likely to respond," said co-author Amanda Cashen, MD, an associate professor of medicine who led an earlier clinical trial of decitabine in older patients with AML. "The value of this study is the comprehensive mutational analysis that helps us figure out which patients are likely to benefit. This information opens the door to using decitabine in a more targeted fashion to treat not just older patients, but also younger patients who carry TP53 mutations."
First author John Welch, MD, PhD, an assistant professor of medicine, added: "It's important to note that patients with an extremely poor prognosis in this relatively small study had the same survival outcomes as patients facing a better prognosis, which is encouraging. We don't yet understand why patients with TP53 mutations consistently respond to decitabine, and more work is needed to understand that phenomenon."
Responses to decitabine are usually short-lived, however, with remissions typically lasting for about a year. Decitabine does not completely clear all the leukemia cells that carry TP53 mutations, and these cells invariably become resistant to the drug, leading to relapse.
"Remissions with decitabine typically don't last long, and no one was cured with this drug," Ley explained. "But patients who responded to decitabine live longer than what you would expect with aggressive chemotherapy, and that can mean something. Some people live a year or two and with a good quality of life, because the chemotherapy is not too toxic."
Roughly 10 percent of AML patients carry TP53 mutations in their leukemia cells. Among patients in the study with such mutations, median survival was 12.7 months - which is not significantly different from the 15.4 months' survival seen in patients without the mutations - and is longer than the typical four- to six-month survival observed in such patients treated with more aggressive therapies.
Decitabine was approved by the FDA in 2006 as a treatment for MDS, but oncologists often prescribe it off-label as a treatment for AML, particularly in older patients. AML typically strikes in a person's mid-60s; the average age of people in the current study was 74.
"We're now planning a larger trial to evaluate decitabine in AML patients of all ages who carry TP53 mutations," Welch said. "It's exciting to think we may have a therapy that has the potential to improve response rates in this group of high-risk patients."

A suit-X trio designed to support workers: Meet MAX

(Tech Xplore)—Not all of us park our bodies in a chair in the morning and cross our legs to do our work. In fact, just think of vast numbers of workers doing physically demanding or just physically repetitive tasks including bending and lifting.

Workers on construction sites, factories and warehouses might cope with aches and pains brought on by their work. Hopefully, the future will provide an easy answer for workers to suit up in a suitable way for them to avoid these aches and pain.
There is a new kid on the block aiming to address such a solution, and a number of tech watchers have put them in the news this month. A California-based group aptly called suit-X announced its MAX, which stands for Modular Agile Exoskeleton. The company designs and makes exoskeletons.
"MAX is designed to support workers during the repetitive tasks that most frequently cause injury," said a company release.
Will Knight in MIT Technology Review said that this essentially is " a trio of devices that use robotic technologies to enhance the abilities of able-bodied workers and prevent common workplace injuries."
Target users, for example, could include those who carry out ceiling inspections, welding, installations and repairs. "It's not only lifting 75 pounds that can hurt your back; it is also lifting 20 pounds repeatedly throughout the day that will lead to injury," said Dr. Homayoon Kazerooni, founder and CEO, suitX."The MAX solution is designed for unstructured workplaces where no robot can work as efficiently as a human worker. Our goal is to augment and support workers who perform demanding and repetitive tasks in unstructured workplaces in order to prevent and reduce injuries."
Seeker referred to the MAX system as an exoskeleton device that could potentially change the way millions of people work.

Seeker noted its advantages as workplace exoskeletons in several ways, being lightweight such that the user can walk around unimpeded. "The exoskeleton units kick in only when you need them, and they don't require any external power source."
MAX is a product with three modules. You use them independently or in combination, depending on work needs. The three modules are backX, shoulderX, and legX.

According to the company, "All modules intelligently engage when you need them, and don't impede you otherwise."
The backX (lower back) reduces forces and torques.
The shoulderX reduces forces; it "enables the wearer to perform chest-to-ceiling level tasks for longer periods of time." In a video the company defines shoulderX as "an industrial arm exoskeleton that augments its wearer by reducing gravity-induced forces at the shoulder complex."
The legX was designed to support knee joint and quadriceps. It incorporates microcomputers in each leg. They communicate with each other to determine if the person is walking, bending, or taking the stairs." Seeker said these communicate via Bluetooth, monitoring spacing and position.

Credit: suitx

Kazerooni spoke about his company and its mission, in Seeker. "My job is easy. I sit in front of a computer. But these guys work all day long, put their bodies through abuse. We can use bionics to help them." He also said he and his team did not create this "because of science fiction movies. We were responding to numbers from the Department of Labor, which said that back, knee and shoulder injuries are the most common form of injuries among workers."
Will Knight meanwhile has reflected on the bigger picture in exoskeleton developments. Can they help in preventing injury on the job and help prolong workers' careers? "New materials, novel mechanical designs, and cheaper actuators and motors have enabled a new generation of cheaper, more lightweight exoskeletons to emerge in recent years," he wrote. "For instance, research groups at Harvard and SRI are developing systems that are passive and use soft, lightweight materials."
Some companies, such as BMW, said Knight, have been experimenting with exoskeletons. "The MAX is another (bionic) step toward an augmented future of work."

credit;   Nancy Owano