Reducing Myc gene activity extends healthy lifespan in mice

No bones about it Young mice have good bone density whether they have two copies (top row; +/+) or one copy (bottom row; +/-) of the Myc gene. As they age, researchers found, mice with just one copy maintain better bone density and stay healthy longer. Sedivy lab/Brown University

Mice with one rather than the normal two copies of the gene Myc (also found in humans) lived 15 percent longer and had considerably healthier lives than normal mice, according to a new Brown University-led study in Cell.

PROVIDENCE, R.I. [Brown University] — A team of scientists based at Brown University has found that reducing expression of a fundamentally important gene called Myc significantly increased the healthy lifespan of laboratory mice, the first such finding regarding this gene in a mammalian species.

Myc is found in the genomes of all animals, ranging from ancestral single-celled organisms to humans. It is a major topic of biomedical research and has been shown to be a central regulator of cell proliferation, growth, and death. It is of such widespread and fundamental importance that animals cannot live without it. But in humans and mice, too much expression of the protein that Myc encodes has been closely linked to cancer, making it a well-known but elusive target of drug developers.

In a new study in the journal Cell, the scientists report that when they bred laboratory mice to have only one copy of the gene, instead of the normal two, thus reducing the expression of the encoded protein, those mice lived 15 percent longer on average — 20 percent longer for females and 10 percent longer among males — than normal mice. Moreover, the experimental mice showed many signs of better health into old age.

The experimental — “heterozygous” — mice grew to be about 15 percent smaller than the normal mice (a probable disadvantage in the wild) but that was the only discernable downside found to date for lacking a second copy of the gene, said senior author John Sedivy, the Hermon C. Bumpus Professor of Biology and professor of medical science at Brown.

“The animals are definitely aging slower,” he said. “They are maintaining the function of their organs and tissues for longer periods of time.”

Physiological differences

That assessment is based on detailed studies of the physiology — down to the molecular level — of the heterozygous and normal mice. The researchers conducted these experiments to try to understand the longevity difference between the two groups.

John Sedivy “The animals are definitely aging slower [and[ they are maintaining the function of their organs and tissues for longer periods of time.”

Co-lead author Jeffrey Hoffman, a medical and doctoral student, led the studies of the health of the mice, including various bodily systems. In many cases they were just like their normal counterparts. They reproduced just as well, for example.

“These mice are incredibly normal, yet they are really long-lived,” Sedivy said. “The reason why we were struck by that is because in many other longevity models like caloric restriction or treatment with rapamycin, the animals live longer but they also have some health issues.”

Instead the Myc heterozygous mice simply experienced fewer problems of aging. They did not develop osteoporosis, they maintained a healthier balance of immune system T cells, had less cardiac fibrosis, were more active, experienced less age-related slowing of their metabolic rate, produced less cholesterol, and exhibited better coordination.

Graduate student and co-lead author Xiaoai Zhao, meanwhile, led the molecular analysis of several pathways known to be involved in regulating longevity to find out how they might be different. Sure enough, heterozygous mice exhibited changes in IGF-1 signaling and nutrient and energy-sensing pathways, but how Myc engages those mechanisms is still not clear. Of particular interest, heterozygous mice showed less protein synthesis in several tissues. Regulation of this process is known to be under direct Myc control, and its reduction by a variety of means is known to extend lifespan in diverse species from yeast to mammals.

Genome-wide patterns of gene expression showed that Myc heterozygotes had significant differences in pathways related to metabolism and the immune system. Those patterns, however, only overlapped somewhat with patterns seen in other lifespan extending interventions.

Zhao and Hoffman’s studies also argue against a role for Myc in an oft-cited paradigm of greater longevity: upregulation of a variety of stress defense mechanisms. Their experimental mice seemed to suffer from as much stress and consequences of stress as normal mice.

The different benefits of Myc reduction compared to other laboratory longevity extenders shows that just as there are many ways the body can break down with aging, Sedivy said, there may be many ways to forestall that.

“There is more than one way to become long-lived,” Sedivy said.

Help for humans?

In the long term, Sedivy said he is optimistic that the findings about Myc could prove to matter to human health.

Finding the right target for a drug in one of Myc’s key metabolic or immune system pathways may or may not extend human lifespan, he said, but it might help people stay healthier as they age — for example, if it can reduce osteoporosis in people the way it does in mice. In particular, Sedivy said, it emphasizes the importance of the process of protein synthesis as a target of interventions that are likely to have widespread benefits on many organ systems.

And the study also offers encouragement to companies seeking to develop cancer drugs that block Myc overexpression. As important as normal Myc expression is to physiology, it appears that at least in mice there were many substantial benefits in reducing it by, say, half. Thus, Sedivy said, any drug that can target Myc directly is likely to find many applications beyond cancer.

In addition to Sedivy, Hoffman, and Zhao, the paper’s other authors are Marco De Cecco, Abigail Peterson, Luca Paglilaroli, Jayameenakshi Manivannan Bin Feng, Thomas Serre, Kevin Bath, Haiyan Xu, and Nicola Neretti of Brown; Gene Hubbard, Wenbo Qi, and Holly Van Remmen of the University of Texas; Yongqing Zhang and Rafael de Cabo of the National Institute on Aging; and Richard Miller of the University of Michigan.

The National Institutes of Health (grants R37AG016694, F30AG035592), the Ellison Medical Foundation, and the Glenn Award for Research on the Biological Mechanism of Aging supported the research. Some experiments were conducted in the Brown University molecular pathology and genomics cores.

Not just a longer life, but a healthier, stronger body “Do you think she might be a Myc hypomorph?” Drawing: Emma Sedivy

Source: Brown University

Shape of things to come in platelet mimicry

By mimicking the shape, size, flexibility and surface chemistry of real platelets, artificial platelets are pushed out of the main blood flow to vessel walls. There, the surface chemistry enables them to anchor on damaged cells and induce faster clotting at the site. Credit: Anirban Sen Gupta

Artificial platelet mimics developed by a research team from Case Western Reserve University and University of California, Santa Barbara, are able to halt bleeding in mouse models 65 percent faster than nature can on its own.

For the first time, the researchers have been able to integratively mimic the shape, size, flexibility and surface chemistry of real blood platelets on albumin-based particle platforms. The researchers believe these four design factors together are important in inducing clots to form faster selectively at vascular injury sites while preventing harmful clots from forming indiscriminately elsewhere in the body.

The new technology, reported in the journal ACS Nano, is aimed at stemming bleeding in patients suffering from traumatic injury, undergoing surgeries or suffering clotting disorders from platelet defects or a lack of platelets. Further, the technology may be used to deliver drugs to target sites in patients suffering atherosclerosis, thrombosis or other platelet-involved pathologic conditions.

Anirban Sen Gupta, an associate professor of biomedical engineering at Case Western Reserve, previously designed peptide-based surface chemistries that mimic the clot-relevant activities of real platelets. Building on this work, Sen Gupta now focuses on incorporating morphological and mechanical cues that are naturally present in platelets to further refine the design.

"Morphological and mechanical factors influence the margination of natural platelets to the blood vessel wall, and only when they are near the wall can the critical clot-promoting chemical interactions take place," he said.

These natural cues motivated Sen Gupta to team up with Samir Mitragotri, a professor of chemical engineering at UC Santa Barbara, whose laboratory has recently developed albumin-based technologies to make particles that mimic the geometry and mechanical properties of red blood cells and platelets.

Together, the team has developed artificial platelet-like nanoparticles (PLNs) that combine morphological, mechanical and surface chemical properties of natural platelets.

The researchers believe this refined design will be able to simulate natural platelet's ability to collide effectively with larger and softer red blood cells in systemic blood flow. The collisions cause margination -- pushing the platelets out of the main flow and closer to the blood vessel wall -- increasing the probability of interacting with an injury site.

The surface coatings enable the artificial platelets to anchor to injury-site-specific proteins, von Willebrand Factor and collagen, while inducing the natural and artificial platelets to aggregate faster at the injury site.

Testing in mouse models showed that intravenous injection of these artificial platelets formed clots at the site of injury three times faster than natural platelets alone in control mice.

The ability to interact selectively with injury site proteins, as well as the ability to remain mechanically flexible like natural platelets, enables these artificial platelets to safely ride through the smallest of blood vessels without causing unwanted clots.

Albumin, a protein found in blood serum and eggs, is already used with cancer drugs and considered a safe material. Artificial platelets that don't become involved in a clot and continue to circulate are metabolized within one to two days.

The researchers believe the new artificial platelet design may be even more effective in larger volume blood flows where margination to the blood vessel wall is more prominent. They expect to soon begin testing those capabilities.

This research was previously funded by American Heart Association and is currently funded by National Institutes of Health.

In addition to stemming bleeding, Sen Gupta believes the technology could also be useful in delivering clot-busting medicines directly to clots, to treat heart attack or stroke without having to systemically suspend the body's coagulation mechanism. The artificial platelets may also be used to deliver cancer medicines to metastatic tumors that have high platelet interactions. Sen Gupta is seeking grants to pursue that work.

Source: Case Western Reserve University

Platelets modulate clotting behavior by 'feeling' their surroundings

Researchers devised a way to separate the physical stiffness of the material where platelets spread out from its biochemical properties. Credit: Wilbur Lam

Platelets, the tiny cell fragments whose job it is to stop bleeding, are very simple. They don't have a cell nucleus. But they can "feel" the physical environment around them, researchers at Emory and Georgia Tech have discovered.

Platelets respond to surfaces with greater stiffness by increasing their stickiness, the degree to which they "turn on" other platelets and other components of the clotting system, the researchers found.

"Platelets are smarter than we give them credit for, in that they are able to sense the physical characteristics of their environment and respond in a graduated way," says Wilbur Lam, MD, PhD, assistant professor in the Department of Pediatrics at Emory University School of Medicine and in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University.

The results are published in Proceedings of the National Academy of Sciences. The first author of the paper is research associate Yongzhi Qiu. Lam is also a physician in the Aflac 

Cancer and Blood Disorders Center, Children's Healthcare of Atlanta.

The researchers' findings could influence the design of medical devices, because when platelets grab onto the surfaces of catheters and medical implants, they tend to form clots, a major problem for patient care.

Modifying the stiffness of materials used in these devices could reduce clot formation, the authors suggest. The results could also guide the refinement of blood thinning drugs, which are prescribed to millions to reduce the risk of heart attack or stroke.

The team was able to separate physical and biochemical effects on platelet behavior by forming polymer gels with different degrees of stiffness, and then overlaying them each with the same coating of fibrinogen, a sticky protein critical for blood clotting. Fibrinogen is the precursor for fibrin, which forms a mesh of insoluble strands in a blood clot.

With stiffer gels, platelets spread out more and become more activated. This behavior is most pronounced when the concentration of fibrinogen is relatively low, the researchers found.

"This variability helps to explain platelet behavior in the 3D context of a clot in the body, which can be quite heterogenous in makeup," Lam says.

Qiu and colleagues were also able to dissect platelet biochemistry by allowing the platelets to adhere and then spread on the various gels under the influence of drugs that interfere with different biochemical steps.

Proteins called integrins, which engage the fibrinogen, and the protein Rac1 are involved in the initial mechanical sensing during adhesion, while myosin and actin, components of the cytoskeleton, are responsible for platelet spreading.

"We found that the initial adhesion and later spreading are separable, because different biochemical pathways are involved in each step," Lam says. "Our data show that mechanosensing can occur and plays important roles even when the cellular structural building blocks are fairly basic, even when the nucleus is absent."

Source: Emory Health Sciences

Platelet-like particles augment natural blood clotting for treating trauma

Associate Professor Tom Barker and Research Scientist Ashley Brown examine bacteria growing on a plate, part of a technique for evolving antibodies in their work on platelet-like particles.
Credit: Georgia Tech Photo

A new class of synthetic platelet-like particles could augment natural blood clotting for the emergency treatment of traumatic injuries -- and potentially offer doctors a new option for curbing surgical bleeding and addressing certain blood clotting disorders without the need for transfusions of natural platelets.

The clotting particles, which are based on soft and deformable hydrogel materials, are triggered by the same factor that initiates the body's own clotting processes. Testing done in animal models and in a simulated circulatory system suggest that the particles are effective at slowing bleeding and can safely circulate in the bloodstream. The particles have been tested with human blood, but have not undergone clinical trials in humans.

Supported by the National Institutes of Health, the U.S. Department of Defense, and the American Heart Association, the research will be reported September 7, 2014, in the journal Nature Materials. Researchers from the Georgia Institute of Technology, Emory University, Children's Healthcare of Atlanta and Arizona State University collaborated on the research.

"When used by emergency medical technicians in the civilian world or by medics in the military, we expect this technology could reduce the number of deaths from excessive bleeding," said Ashley Brown, a research scientist in the Georgia Tech School of Chemistry and Biochemistry and first author of the paper. "If EMTs and medics had particles like these that could be injected and then go specifically to the site of a serious injury, they could help decrease the number of deaths associated with serious injuries."

The bloodstream contains proteins known as fibrinogen that are the precursors for fibrin, the polymer that provides the basic structure for natural blood clots. When they receive the right signals from a protein known as thrombin, these precursors polymerize at the site of the bleeding. The synthetic platelet-like particles use the same trigger, and so are activated only when the body's natural clotting process is initiated.

To create that trigger, the researchers followed a process known as molecular evolution to develop an antibody that could be attached to the hydrogel particles to change their form when they encounter thrombin-activated fibrin. The resulting antibody has a high affinity for the polymerized form of fibrin and a low affinity for the precursor material.

"Fibrin production is on the back end of the clotting process, so we feel that it is a safer place to try to interact with it," said Tom Barker, an associate professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, and one of the paper's co-corresponding authors. "The specificity of this material provides a very important advantage in triggering clotting at just the right time."

The effectiveness of the platelet-like particles has been tested in an animal model and in a microfluidic chamber designed to simulate conditions within the body's circulatory system. In the chamber, tubes about the thickness of a human hair were lined with endothelial cells as in natural blood vessels.

The chamber was used to study normal human blood, as well as human blood that had been depleted of its natural platelets. In platelet-rich blood, clots formed as expected, and blood without platelets did not form clots. When the platelet-like particles were added to the platelet-depleted blood, it was able to clot.

The researchers also tested blood from infants that had undergone open heart surgery, which requires that their blood be diluted, reducing its clotting ability. When platelet-like particles were added to the dilute neonate blood, it was able to form clots.

Finally, safety testing was done on blood from hemophiliac patients. Because that blood lacks the triggers needed to cause fibrin formation, the particles had no effect. Before they can be used in humans, the particles will have to undergo human trials and receive clearance from the U.S. Food & Drug Administration (FDA).

About one micron in diameter, the particles were originally developed to be used on the battlefield by wounded soldiers, who might self-administer them using a device about the size of a smartphone. But the researchers believe the particles could also reduce the need for platelet transfusions in patients undergoing chemotherapy or bypass surgery, and in those with certain blood disorders.

"For a patient with insufficient platelets due to bleeding or an inherited disorder, physicians often have to resort to platelet transfusions, which can be difficult to obtain," said Dr. Wilbur Lam, another of the paper's co-authors and a physician in the Aflac Cancer and 
Blood Disorders Center at Children's Healthcare of Atlanta and the Department of Pediatrics at the Emory University School of Medicine. "These particles could potentially be a way to obviate the need for a transfusion. Though they don't have all the assets of natural platelets, a number of intriguing experiments have shown that the particles help augment the clotting process."

In addition to providing new treatment options, the particles could also cut costs by reducing costly natural transfusions, said Lam, who is also an assistant professor in the Coulter Department of Biomedical Engineering at Georgia Tech and Emory University.

What ultimately happens to the hydrogel particles circulating in the bloodstream will be the topic of future research, noted Brown. Particles of similar size and composition are normally eliminated from the body.

While the platelet-like particles lack many features of natural platelets, the researchers were surprised to find one property in common. Clots formed by natural platelets begin to contract over a period of hours, beginning the body's repair process. Clots formed from the synthetic particles also contract, but over a longer period of time, Brown noted.

Source: Georgia Institute of Technology

Computer model predicts red blood cell flow

Rendering of stream of blood cells. Credit: © Witold Krasowski / Fotolia

Adjacent to the walls of our arterioles, capillaries, and venules -- the blood vessels that make up our microcirculation -- there exists a peculiar thin layer of clear plasma, devoid of red blood cells. Although it is just a few millionths of a meter thick, that layer is vital. It controls, for example, the speed with which platelets can reach the site of a cut and start the clotting process.

"If you destroy this layer, your bleeding time can go way up, by 60 percent or more, which is a real issue in trauma," said Eric Shaqfeh, the Lester Levi Carter Professor and a professor of chemical engineering and mechanical engineering at Stanford University. Along with his colleagues, Shaqfeh has now created the first simplified computer model of the process that forms that layer -- a model that could help to improve the design of artificial platelets and medical treatments for trauma injuries and for blood disorders such as sickle cell anemia and malaria.

The model is described in a paper appearing in the journal Physics of Fluids.

The thin plasma layer, known as the Fåhræus-Lindqvist layer, is created naturally when blood flows through small vessels. In the microcirculation, the layer forms because red blood cells tend to naturally deform and lift away from the vessel walls. "The reason they don't just continually move away from the wall and go far away is because, as they move away, then also collide with other red blood cells, which force them back," Shaqfeh explained. "So the Fåhræus-Lindqvist layer represents a balance between this lift force and collisional forces that exist in the blood."

Because the deformation of red blood cells is a key factor in the Fåhræus-Lindqvist layer, its properties are altered in diseases, such as sickle cell anemia, that affect the shape and rigidity of those cells. The new model, which is a scaled-down version of an earlier numerical model by Shaqfeh and colleagues that provided the first large-scale, quantitative explanation of the formation of the layer, can predict how blood cells with varying shapes, sizes, and properties -- including the crescent-shaped cells that are the hallmark of sickle cell anemia -- will influence blood flow.

The model can also help predict the outcome of -- and perfect -- treatments for trauma-related injuries. One common thing to do during treatment for trauma injuries is to inject saline, which among other things reduces the hematocrit, the blood fraction of red blood cells. With our model, Shaqfeh said, "we can predict how thick the Fåhræus-Lindqvist layer will be with a given hematocrit, and therefore how close the platelets will be to the periphery of the blood vessels -- and how quickly clotting will occur.

Source: American Institute of Physics (AIP)

Hormone that controls supply of iron in red blood cell production discovered by researchers

This is a microscopic image of erythroblasts, which are the bone marrow cells that secrete erythroferrone. Credit: Leon Kautz/UCLA

A UCLA research team has discovered a new hormone called erythroferrone, which regulates the iron supply needed for red blood-cell production.

Iron is an essential functional component of hemoglobin, the molecule that transports oxygen throughout the body. Using a mouse model, researchers found that erythroferrone is made by red blood-cell progenitors in the bone marrow in order to match iron supply with the demands of red blood-cell production. Erythroferrone is greatly increased when red blood-cell production is stimulated, such as after bleeding or in response to anemia.

The erythroferrone hormone acts by regulating the main iron hormone, hepcidin, which controls the absorption of iron from food and the distribution of iron in the body. Increased erythroferrone suppresses hepcidin and allows more iron to be made available for red blood-cell production.

"If there is too little iron, it causes anemia. If there is too much iron, the iron overload accumulates in the liver and organs, where it is toxic and causes damage," said senior author Dr. Tomas Ganz, a professor of medicine and pathology at the David Geffen School of Medicine at UCLA. "Modulating the activity of erythroferrone could be a viable strategy for the treatment of iron disorders of both overabundance and scarcity."

The early findings were reported online June 1 in the journal Nature Genetics.

"Our previous work anticipated that a regulator of hepcidin could be secreted by the bone marrow," said the study's first author, Leon Kautz, a postdoctoral fellow at UCLA. "In this research, we searched for new substances that were made in bone marrow that could fill that role."

Researchers first focused on what happens in the bone marrow after hemorrhage. From there, they focused on a specific protein that was secreted into the blood. This protein attracted their attention because it belonged to a family of proteins involved in cell-to-cell communication. Using recombinant DNA technology, they showed that the hormone suppressed the production of hepcidin and demonstrated the effect it had on iron metabolism.

The team foresees that the discovery could help people with a common congenital blood disorder called Cooley's anemia, also known as thalassemia, which causes excessive destruction of red blood cells and of their progenitors in the bone marrow. Many of these patients require regular blood transfusions throughout their lives. Most iron overload is attributed to the iron content of transfused blood. However, even patients who are rarely, or never, transfused can also develop iron overload.

"Overproduction of erythroferrone may be a major cause of iron overload in untransfused patients and may contribute to iron overload in transfused patients," said study author Elizabeta Nemeth, a professor of medicine at the David Geffen School of Medicine at UCLA and co-director of the UCLA Center for Iron Disorders. "The identification of erythroferrone can potentially allow researchers and drug developers to target the hormone for specific treatment to prevent iron overload in Cooley's anemia."

The discovery could also lead to treatments for other common anemia-related conditions associated with chronic kidney disease, rheumatologic disorders and other inflammatory diseases. In these conditions, iron is "locked up" by the effect of the hormone hepcidin, whose levels are increased by inflammation. Erythroferrone, or drugs acting like it, could suppress hepcidin and make more iron available for red blood-cell production.

The next stage of research is to understand the role of the new hormone in various blood diseases and study the molecular mechanisms through which erythroferrone regulates hepcidin.

Additional study authors included Grace Jung and Erika Valore of UCLA and Stefano Rivella of Weill Cornell Medical College in New York.

The study was supported by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases and the National Heart, Lung and Blood Institute.

The Board of Regents of the University of California is the owner of patent applications and uses directed at erythroferrone, which are managed by UCLA's Office of Intellectual Property and Industry Sponsored Research. This intellectual property is the subject of license negotiations with a company for which authors Ganz and Nemeth are scientific advisors and equity holders. Other disclosures are available in the manuscript.

Source: University of California, Los Angeles (UCLA), Health Sciences

Mechanics of cells' long-range communication modeled by researchers

As fibrosis progresses, "bridges" of extracellular matrix appear between cells. Credit: Image courtesy of University of Pennsylvania

Interdisciplinary research at the University of Pennsylvania is showing how cells interact over long distances within fibrous tissue, like that associated with many diseases of the liver, lungs and other organs.

By developing mathematical models of how the collagen matrix that connects cells in tissue stiffens, the researchers are providing insights into the pathology of fibrosis, cirrhosis of the liver and certain cancers.

Tissue stiffness has long been know to be clinically relevant in these diseases, but the underlying changes that alter the mechanics of tissues are poorly understood. Consisting of a complex network of fibers, tissues have proven difficult to simulate and model beyond local, neighbor-to-neighbor interactions.

Developing a better understanding of the large-scale mechanical changes that occur over longer distances, specifically the process by which the extracellular matrix is pulled into compact, highly-aligned "bridges," could eventually form the basis of treatments for related diseases.

Vivek Shenoy, professor in the Department of Materials Science and Engineering in Penn's School of Engineering and Applied Science, has led an interdisciplinary research team to tackle this problem, authoring a pair of papers that were published in Biophysical Journal.

One, "Remodeling of Fibrous Extracellular Matrices by Contractile Cells: Predictions from Discrete Fiber Network Simulations" involved developing simulations that extrapolated the overall remodeling of the extracellular matrix based on the behavior of neighboring pairs of cells. The other, "Long Range Force Transmission in Fibrous Matrices Enabled by Tension-Driven Alignment of Fibers," took a more mathematical approach, producing a coarse-grained model of this remodeling that could be more broadly applied to fibrotic tissue.

"We're trying to understand how force is transmitted in tissues," Shenoy said. "Cells are the ones that generate force, and it has to be transmitted through what surrounds the cell, the extracellular matrix, or ECM. But imagine trying to model the ECM by trying to keep track of each collagen fibril in your liver; there are tens of millions of those. So we're taking what we learn from simulating those networks to turn it into a model that captures the main features with only a few parameters.

"The key here is the mechanics," he said. "In particular, how does ECM, as a fibrous material, differ from solids, gels and other materials that are better studied."

Rebecca Wells, an associate professor in Penn's Perelman School of Medicine and a co-author on the latter paper, provided insight into the clinical relevance of the mechanics that characterize ECM-related disorders.

"Fibrosis occurs when you have an injury and the tissue responds by depositing ECM, forming scar tissue," Wells said. "In liver fibrosis, the liver can stiffen by up to an order of magnitude, so measuring stiffness is a common diagnostic test for the disease. Increased stiffness also occurs in cancer, where tumors are typically stiffer than the surrounding tissue."

Existing experimental evidence showed that mechanical forces were at play in the changes in both fibrosis and cancer and that these forces were important to their development and progression but could not explain the long-ranging changes cells were able to produce to change their environments. When put in tissue-simulating gels, cells can deform their immediate surroundings but are unable to pull on more distant cells. In real, ECM-linked tissue, however, cells' range of influence can be up to 20 times their own diameter.

"If you look at a normal tissue," Shenoy said, "you see the cells are more rounded, and the network of ECM fibers is more random. But as cancer progresses, you see more elliptical cells, more ECM, and you see that the ECM fibers are more aligned. The cells are the ones generating force, so they're contracting and pulling the fibers, stretching them out into bridges."

"That's also the pathology of cirrhosis," Wells said. "My group had been looking at the early mechanical changes associated with liver fibrosis, which progresses to cirrhosis, but then, by collaborating with Vivek, we started to wonder if these large scale changes in the architecture of the liver could have a mechanical basis and if something similar to what is seen in gels might be occurring in the liver. This is a new way of approaching the problem, which has largely been thought of as biochemical in origin. And there are other tissues where it is probably the same thing, the lung, for example."

The researchers found that the critical difference between the existing models and ECM's long-range behavior was rooted in its elastic properties. Materials with linear elasticity cannot transmit force over the distances observed, but the team's simulations showed that nonlinear elasticity could arise from the ECM's fibrous structure.

"In our model, every component is linearly elastic," Shenoy said, "but the collective behavior is nonlinear; it emerges because of the connectivity. When you deform the network, it's easy to bend the 'sticks' that represent collagen fibers but hard to stretch them. When you deform it to a small extent, it's all the bending of the fibers, but, as you deform further, it can't accommodate bending any more and moves over to stretching, forming the bridges we see in the tissue."

Such simulations can't predict which fibers will end up in which bridge, necessitating the coarser-grained model the researchers described in their second paper. By showing the point at which linear elasticity gives way to its nonlinear counterpart, the team produced a more complete picture of how the alignment of collagen bridges under tension transmit force between distant cells.

Further studies are needed to elucidate the feedback loops between ECM stiffening and cell contraction strength. The team is conducting physical experiments to confirm and refine their in silico findings.

"Right now," Wells said," we're hypothesizing that the mechanical interactions modeled by the Shenoy lab explain aspects of cancer and fibrosis, and we're developing the experimental systems to confirm it with real cells."

Source: University of Pennsylvania

Hunter-gatherer past shows our fragile bones result from inactivity since invention of farming

Hunter-gatherer bone mass compared to agriculturalist bone mass. Credit: Timothy Ryan

New research across thousands of years of human evolution shows that our skeletons have become much lighter and more fragile since the invention of agriculture -- a result of our increasingly sedentary lifestyles as we shifted from foraging to farming.

The new study, published today in the journal PNAS, shows that, while human hunter-gatherers from around 7,000 years ago had bones comparable in strength to modern orangutans, farmers from the same area over 6,000 years later had significantly lighter and weaker bones that would have been more susceptible to breaking.

Bone mass was around 20% higher in the foragers -- the equivalent to what an average person would lose after three months of weightlessness in space.

After ruling out diet differences and changes in body size as possible causes, researchers have concluded that reductions in physical activity are the root cause of degradation in human bone strength across millennia. It is a trend that is reaching dangerous levels, they say, as people do less with their bodies today than ever before.

Researchers believe the findings support the idea that exercise rather than diet is the key to preventing heightened fracture risk and conditions such as osteoporosis in later life: more exercise in early life results in a higher peak of bone strength around the age of 30, meaning the inevitable weakening of bones with age is less detrimental.

There is, in fact, no anatomical reason why a person born today could not achieve the bone strength of an orangutan or early human forager, say researchers; but even the most physically active people alive are unlikely to be loading bones with enough frequent and intense stress to allow for the increased bone strength seen in the 'peak point' of traditional hunter-gatherers and non-human primate bones.

"Contemporary humans live in a cultural and technological milieu incompatible with our evolutionary adaptations. There's seven million years of hominid evolution geared towards action and physical activity for survival, but it's only in the last say 50 to 100 years that we've been so sedentary -- dangerously so," said co-author Dr Colin Shaw from the University of Cambridge's Phenotypic Adaptability, Variation and Evolution (PAVE) Research Group.

"Sitting in a car or in front of a desk is not what we have evolved to do."

The researchers x-rayed samples of human femur bones from the archaeological record, along with femora from other primate species, focusing on the inside of the femoral head: the ball at the top of the femur which fits into the pelvis to form the hip joint, one of the most load-bearing bone connections in the body.

Two types of tissue form bone: the cortical or 'hard' bone shell coating the outside, and the trabecular or 'spongy' bone: the honeycomb-like mesh encased within cortical shell that allows flexibility but is also vulnerable to fracture.

The researchers analysed the trabecular bone from the femoral head of four distinct archaeological human populations representing mobile hunter-gatherers and sedentary agriculturalists, all found in the same area of the US state of Illinois (and likely to be genetically similar as a consequence).

The trabecular structure is very similar in all populations, with one notable exception: within the mesh, hunter-gatherers have a much higher amount of actual bone relative to air.

"Trabecular bone has much greater plasticity than other bone, changing shape and direction depending on the loads imposed on it; it can change structure from being pin or rod-like to much thicker, almost plate-like. In the hunter-gatherer bones, everything was thickened," said Shaw.

This thickening is the result of constant loading on the bone from physical activity as hunter-gatherers roamed the landscape seeking sustenance. This fierce exertion would result in minor damage that caused the bone mesh to grow back ever stronger and thicker throughout life -- building to a 'peak point' of bone strength which counter-balanced the deterioration of bones with age.

Shaw believes there are valuable lessons to be learnt from the skeletons of our prehistoric predecessors. "You can absolutely morph even your bones so that they deal with stress and strain more effectively. Hip fractures, for example, don't have to happen simply because you get older if you build your bone strength up earlier in life, so that as you age it never drops below that level where fractures can easily occur."

Other theories for humans evolving a lighter, more fragile skeleton include changes in diet or selection for a more efficient, lighter skeleton, which was never reversed.

While the initial switch to farming did cause a dip in human health due to monoculture diets that lacked variety, the populations tested were unaffected by this window in history. "Of course we need a level of calcium to maintain bone heath, but beyond that level excess calcium isn't necessary," said Shaw.

The research also counters the theory that, at some point in human evolution, our bones just became lighter -- perhaps because there wasn't enough food to support a denser skeleton. "If that was true, human skeletons would be entirely distinct from other living primates. We've shown that hunter-gatherers fall right in line with primates of a similar body size. Modern human skeletons are not systemically fragile; we are not constrained by our anatomy."

"The fact is, we're human, we can be as strong as an orangutan -- we're just not, because we are not challenging our bones with enough loading, predisposing us to have weaker bones so that, as we age, situations arise where bones are breaking when, previously, they would not have" Shaw said.

While the 7,000-year-old foragers had vastly stronger bones than the 700-year-old farmers, Shaw says that neither competes with even earlier hominids from around 150,000 years ago. 

"Something is going on in the distant past to create bone strength that outguns anything in the last 10,000 years."

The next step for Shaw's research team will be to look at how different types of loading and mobility shape bodies and bones by cross-referencing archaeological records with testing on modern ultra-marathon runners, who cover punishing distances over a range of terrains -- from the Himalayas to the Namibian desert. He hopes this future work will provide insight into the kind of mobility that gave our ancient ancestors such powerful physical strength.

Source: University of Cambridge

Promising compound rapidly eliminates malaria parasite

A new report says that the rapid action of (+)-SJ733 will likely slow malaria drug resistance. Credit: Peter Barta, St. Jude Children's Research Hospital

An international research collaborative has determined that a promising anti-malarial compound tricks the immune system to rapidly destroy red blood cells infected with the malaria parasite but leave healthy cells unharmed. St. Jude Children's Research Hospital scientists led the study, which appears in the current online early edition of the Proceedings of the National Academy of Sciences (PNAS).

The compound, (+)-SJ733, was developed from a molecule identified in a previous St. Jude-led study that helped to jumpstart worldwide anti-malarial drug development efforts. Malaria is caused by a parasite spread through the bite of an infected mosquito. The disease remains a major health threat to more than half the world's population, particularly children. The World Health Organization estimates that in Africa a child dies of malaria every minute.

In this study, researchers determined that (+)-SJ733 uses a novel mechanism to kill the parasite by recruiting the immune system to eliminate malaria-infected red blood cells. In a mouse model of malaria, a single dose of (+)-SJ733 killed 80 percent of malaria parasites within 24 hours. After 48 hours the parasite was undetectable.

Planning has begun for safety trials of the compound in healthy adults.

Laboratory evidence suggests that the compound's speed and mode of action work together to slow and suppress development of drug-resistant parasites. Drug resistance has long undermined efforts to treat and block malaria transmission.

"Our goal is to develop an affordable, fast-acting combination therapy that cures malaria with a single dose," said corresponding author R. Kiplin Guy, Ph.D., chair of the St. Jude Department of Chemical Biology and Therapeutics. "These results indicate that SJ733 and other compounds that act in a similar fashion are highly attractive additions to the global malaria eradication campaign, which would mean so much for the world's children, who are central to the mission of St. Jude."

Whole genome sequencing of the Plasmodium falciparum, the deadliest of the malaria parasites, revealed that (+)-SJ733 disrupted activity of the ATP4 protein in the parasites. The protein functions as a pump that the parasites depend on to maintain the proper sodium balance by removing excess sodium.

The sequencing effort was led by co-author Joseph DeRisi, Ph.D., a Howard Hughes Medical Institute investigator and chair of the University of California, San Francisco Department of Biochemistry and Biophysics. Investigators used the laboratory technique to determine the makeup of the DNA molecule in different strains of the malaria parasite.

Researchers showed that inhibiting ATP4 triggered a series of changes in malaria-infected red blood cells that marked them for destruction by the immune system. The infected cells changed shape and shrank in size. They also became more rigid and exhibited other alterations typical of aging red blood cells. The immune system responded using the same mechanism the body relies on to rid itself of aging red blood cells.

Another promising class of antimalarial compounds triggered the same changes in red blood cells infected with the malaria parasite, researchers reported. The drugs, called spiroindolones, also target the ATP4 protein. The drugs include NITD246, which is already in clinical trials for treatment of malaria. Those trials involve investigators at other institutions.

"The data suggest that compounds targeting ATP4 induce physical changes in the infected red blood cells that allow the immune system or erythrocyte quality control mechanisms to recognize and rapidly eliminate infected cells," DeRisi said. "This rapid clearance response depends on the presence of both the parasite and the investigational drug. That is important because it leaves uninfected red blood cells, also known as erythrocytes, unharmed."

Laboratory evidence also suggests that the mechanism will slow and suppress development of drug-resistant strains of the parasite, researchers said.

Planning has begun to move (+)-SJ733 from the laboratory into the clinic beginning with a safety study of the drug in healthy adults. The drug development effort is being led by a consortium that includes scientists at St. Jude, the Swiss-based non-profit Medicines for Malaria Venture and Eisai Co., a Japanese pharmaceutical company.

Source: St. Jude Children's Research Hospital