Immunology

Rio de Janeiro, Brazil- In the brains of all vertebrates, information is transmitted through synapses, a mechanism that allows an electric or chemical signal to be passed from one brain cell to another. Chemical synapses, which are the most abundant type of synapse, can be either excitatory or inhibitory. Synapse formation is crucial for learning, memory, perception and cognition, and the balance between excitatory and inhibitory synapses critical for brain function. For instance, every time we learn something, the new information is transformed into memory through synaptic plasticity, a process in which synapses are strengthened and become more responsive to different stimuli or environmental cues. Synapses may change their shape or function in a matter of seconds or over an entire lifetime. In humans, a number of disorders are associated with dysfunctional synapses, including autism, epilepsy, substance abuse and depression.

Astrocytes, named for their star-like shape, are ubiquitous brain cells known for regulating excitatory synapse formation through cells. Recent studies have shown that astrocytes also play a role in forming inhibitory synapses, but the key players and underlying mechanisms have remained unknown until now.

A new study just published in the journal Glia and available online on July 11th, details the newly discovered mechanism by which astrocytes are involved in inhibitory synapse formation and presents strong evidence that Transforming Growth Factor Beta 1 (TGF β1), a protein produced by many cell types (including astrocytes) is a key player in this process. The team led by Fl-via Gomes of the Rio de Janeiro Institute of Biomedical Sciences at the Federal University of Rio de Janeiro investigated the process in both mouse and human tissues, first in test tubes, then in living brain cells.

Previous evidence has shown that TGF β1, a molecule associated with essential functions in nervous system development and repair, modulates other components responsible for normal brain function. In this study, the authors were able to show that TGF β1 triggers N-methyl-D-aspartate receptor (NMDA), a molecule controlling memory formation and maintenance through synaptic plasticity. In the study, the group also shows that TGF β1-induction of inhibitory synapses depends on activation of another molecule - Ca2+/calmodulin-dependent protein kinase II (CaMK2)-, which works as a mediator for learning and memory. "Our study is the first to associate this complex pathway of molecules, of which TGF β1 seems to be a key player, to astrocytes' ability to modulate inhibitory synapses", says Fl-via Gomes.

The idea that the balance between excitatory and inhibitory inputs depends on astrocyte signals gains strong support with this new study and suggests a pivotal role for astrocytes in the development of neurological disorders involving impaired inhibitory synapse transmission. Knowing the players and mechanisms underlying inhibitory synapses may improve our understanding of synaptic plasticity and cognitive processes and may help develop new drugs for treating these diseases.

Using spider toxins to study the proteins that let nerve cells send out electrical signals, Johns Hopkins researchers say they have stumbled upon a biological tactic that may offer a new way to protect crops from insect plagues in a safe and environmentally responsible way.

Their finding-that naturally occurring insect toxins can be lethal for one species and harmless for a closely related one-suggests that insecticides can be designed to target specific pests without harming beneficial species like bees. A summary of the research, led by Frank Bosmans, Ph.D., an assistant professor of physiology at the Johns Hopkins University School of Medicine, will be published July 11 in the journal Nature Communications.

"Most insecticides used today take a carpet-bombing approach, killing indiscriminately and sometimes even hurting humans and other animals," says Bosmans. "The more specific a toxin's target, the less dangerous it is for everything else."

Their finding began with the mistaken inclusion of a protein, called Dc1a, in a shipment sent by the team's Australian collaborators. The protein was extracted from the venom of the desert bush spider Diguetia canities, which lives in the deserts of the southwestern United States and Mexico and is harmless to humans.

When Bosmans' Australian collaborators tested the impact of Dc1a on proteins from American cockroaches, the proteins reacted very weakly, so they hadn't planned on sending Dc1a to Bosmans for further study. But it was accidentally included with other spider venom proteins for Bosmans' group to test, says Bosmans, so his laboratory did so.

The Bosmans lab studies proteins called sodium channels, which are found in the outer envelope of nerve cells throughout the body. Stimuli, like the acute pressure of hitting your finger with a hammer, are communicated to the proteins, causing them to open their pores so that sodium flows in. The positive charge of sodium causes an electrical signal to be sent down the nerve, eventually reaching the spinal cord and brain so the body can react.

"Sodium channels are the fastest ion channels in the human body and are needed to experience nearly every sensation, so mutations in them can lead to severe disorders of the nerves, muscles and heart," Bosmans says. That makes them a critical target for scientific study.

To understand the channels better, Bosmans and his team insert the protein's gene into frog eggs, which are large and easy to study. They can then use electrodes to monitor the flow of sodium into the cells. Adding spider toxins that interfere with the function of the channels sheds light on the channels' activity, since different toxins inhibit different parts of the protein, causing different effects. In addition to testing human sodium channels, the team sometimes works with sodium channels from insects.

Because his laboratory recently acquired the gene for the German cockroach sodium channel, Bosmans' team tested Dc1a on the protein and saw a startling increase in the channels' activity. "Sodium poured into the cells. In a bug, that would cause massive seizures, much like being electrocuted," says Bosmans. "Luckily, the toxin doesn't act on human sodium channels."

Curious about the difference between the two cockroach species' channels, they first identified the region of the channel that the toxin targets, but it turned out to be exactly the same in the two bugs. Digging deeper, they found a region nearby that differed by just two amino acids, the basic building blocks of the proteins. When mutations were made in the German version so that its amino acids were the same as the American version's, the German cockroach sodium channel reacted like the American one.

The team's next step is to test the toxin on other insect species to determine its full range. Now that they know how important this region of sodium channels is, Bosmans says, researchers will know to look for mutations there as they try to find the mechanism for various human disorders. It may also be possible to create drugs that block access to the site in overactive sodium channels.

Amyloid diseases, such as Alzheimer's disease, type 2 diabetes, cataracts, and the spongiform encephalopathies, all share the common trait that proteins aggregate into long fibers which then form plaques. Yet in vitro studies have found that neither the amylin monomer precursors nor the plaques themselves are very toxic. New evidence using two-dimensional infrared (2D IR) spectroscopy has revealed an intermediate structure during the amylin aggregation pathway that may explain toxicity, opening a window for possible interventions, according to a report in the current issue of Biomedical Spectroscopy and Imaging.

"Figuring out how and why amyloid plaques form is exceedingly difficult, because one needs to follow the atomic shapes of the protein molecules as they assemble. Most tools in biology give either shapes or motions, but not both. We have been developing a new spectroscopic tool, called two-dimensional infrared spectroscopy, which can monitor the plaques as they form in a test tube," said lead investigator Martin T. Zanni, PhD, of the Department of Chemistry at the University of Wisconsin-Madison.

The investigators employed this new technology to study the amyloid protein associated with type 2 diabetes. Isotope labeling was used to measure the secondary structure content of individual residues. By following many 2D IR spectra from one particular region (known as the FGAIL region) over several hours, they were able to visualize the amylin as it progressed from monomers to fibers.

"We learned that, prior to making the plaques, the proteins first assemble into an unexpected and intriguing intermediate and organized structure," commented Dr. Zanni. The proteins undergo a transition from disordered coil (in the monomer), to ordered β-sheet (in the oligomer) to disordered structure again (in the fiber).

These results help to elucidate the physics of the aggregation process, the chemistry of amyloid inhibitors, and the biology of type 2 diabetes, as well as clarify previously contradictory data.

The authors suggest that differences between species in their capacity to develop type 2 diabetes may be related to the capacity to form these intermediate amylin structures. That may be why humans develop the disease while dogs and rats do not. "I am not encouraging us to begin engineering our DNA to match that of rats, but our findings may help to develop plaque inhibitors or hormone replacement therapies for people suffering from type 2 diabetes, because we know the structure we want to avoid," says Dr. Zanni. He adds that mutations in the FGAIL region may inhibit fiber formation by interfering with the formation of these intermediates.

Childhood obesity is one of the top public health concerns in the United States, with 32 percent of youths aged 2-19 classified as obese as of 2012. As health problems such as childhood obesity grow, individuals and organizations have taken to Twitter to discuss the problem.

A new study, led by Jenine K. Harris, PhD, assistant professor at the Brown School at Washington University in St. Louis, examined the use of the hashtag #childhoodobesity in tweets to track Twitter conversations about the issue of overweight kids.

The study published this month in the American Journal of Public Health, noted that conversations involving childhood obesity on Twitter don't often include comments from representatives of government and public health organizations that likely have evidence relating to how best to approach this issue.

"Childhood obesity is of great concern to the public health community," Harris said. "People are really talking about it on Twitter, and we saw an opportunity to better understand perceptions of the problem."

Twitter use is growing nationwide. In its 2014 Twitter update, the Pew Research Center found that Twitter is used more by those in lower-income groups, which traditionally are more difficult to reach with health information.

While younger Americans also are more likely to use Twitter, it is used equally across education groups and is used more by non-white Americans than whites.

This, Harris said, is one of the reasons Twitter is an avenue that the academic and government sources with accurate health information should consider taking advantage of in order to reach a wide variety of people.

"I think public health so far doesn't have a great game plan for using social media, we're still laying the foundation for that," she said. "We're still learning what works.

"Public health communities, politicians, and government sources - people who really know what works - should join in the conversation. Then we might be able to make an impact," she said.

For decades, health-conscious people around the globe have taken antioxidant supplements and eaten foods rich in antioxidants, figuring this was one of the paths to good health and a long life.

Yet clinical trials of antioxidant supplements have repeatedly dashed the hopes of consumers who take them hoping to reduce their cancer risk. Virtually all such trials have failed to show any protective effect against cancer. In fact, in several trials antioxidant supplementation has been linked with increased rates of certain cancers. In one trial, smokers taking extra beta carotene had higher, not lower, rates of lung cancer.

In a brief paper appearing today in The New England Journal of Medicine, David Tuveson, M.D. Ph.D., Cold Spring Harbor Laboratory Professor and Director of Research for the Lustgarten Foundation, and Navdeep S. Chandel, Ph.D., of the Feinberg School of Medicine at Northwestern University, propose why antioxidant supplements might not be working to reduce cancer development, and why they may actually do more harm than good.

Their insights are based on recent advances in the understanding of the system in our cells that establishes a natural balance between oxidizing and anti-oxidizing compounds. These compounds are involved in so-called redox (reduction and oxidation) reactions essential to cellular chemistry.

Oxidants like hydrogen peroxide are essential in small quantities and are manufactured within cells. There is no dispute that oxidants are toxic in large amounts, and cells naturally generate their own anti-oxidants to neutralize them. It has seemed logical to many, therefore, to boost intake of antioxidants to counter the effects of hydrogen peroxide and other similarly toxic "reactive oxygen species," or ROS, as they are called by scientists. All the more because it is known that cancer cells generate higher levels of ROS to help feed their abnormal growth.

Drs. Tuveson and Chandel propose that taking antioxidant pills or eating vast quantities of foods rich in antioxidants may be failing to show a beneficial effect against cancer because they do not act at the critical site in cells where tumor-promoting ROS are produced - at cellular energy factories called mitochondria. Rather, supplements and dietary antioxidants tend to accumulate at scattered distant sites in the cell, "leaving tumor-promoting ROS relatively unperturbed," the researchers say.

Quantities of both ROS and natural antioxidants are higher in cancer cells - the paradoxically higher levels of antioxidants being a natural defense by cancer cells to keep their higher levels of oxidants in check, so growth can continue. In fact, say Tuveson and Chandel, therapies that raise the levels of oxidants in cells may be beneficial, whereas those that act as antioxidants may further stimulate the cancer cells. Interestingly, radiation therapy kills cancer cells by dramatically raising levels of oxidants. The same is true of chemotherapeutic drugs - they kill tumor cells via oxidation.

Paradoxically, then, the authors suggest that "genetic or pharmacologic inhibition of antioxidant proteins" - a concept tested successfully in rodent models of lung and pancreatic cancers -- may be a useful therapeutic approach in humans. The key challenge, they say, is to identify antioxidant proteins and pathways in cells that are used only by cancer cells and not by healthy cells. Impeding antioxidant production in healthy cells will upset the delicate redox balance upon which normal cellular function depends.

The authors propose new research to profile antioxidant pathways in tumor and adjacent normal cells, to identify possible therapeutic targets.