Host faecal miRNA regulates gut microbiota

Mouse and human faeces contains functional microRNAs (miRNAs), according to a new study published in Cell Host & Microbe. The researchers also showed that host faecal miRNA directly regulates microbial gene expression and growth. “It is known that the commensal bacteria in the gut are important in health and disease. However, little is known about how they are naturally regulated, or strategies to manipulate them,” explains first author Shirong Liu. Previous studies have shown that extracellular miRNAs are present in human faeces, leading Liu et al. to investigate whether faecal extracellular miRNAs are functional, and if they can regulate the gut microbiota by altering bacterial gene expression in the gut. The researchers isolated RNA from human and mouse faeces, finding that samples from both species contained specific miRNAs, such as miR-155 and miR-1224.

Bioinformatic analysis predicted that a number of these miRNAs could bind multiple genomic sites in selected bacterial species. The researchers cultured two bacterial species in the presence of synthetic mimetics of identified miRNAs and found that bacterial growth was markedly affected. After showing that fluorescently labelled miRNA was able to enter bacteria, the authors also demonstrated that bacterial gene expression is directly altered when bacteria were cultured with human or mouse faecal miRNAs. Mice lacking the miRNAgenerating protein Dicer only in intestinal epithelial cells had reduced levels of faecal miRNA, suggesting that intestinal epithelial cells are a major source of miRNA in faeces. Faecal miRNA levels were also reduced in mice in which Dicer was knocked out in intestinal goblet cells and Paneth cells.

Further experiments showed that mice with Dicer knocked out specifically in intestinal epithelial cells had dysbiosis, and were more susceptible to induced colitis than wild-type mice. When these knockout mice received faecal miRNA from wild-type mice via gavage before colitis induction, colonic damage was lessened. “Our findings show that the host can actively affect the microbes through miRNAs, and this provides a unique way to manipulate them,” concludes corresponding author Howard Weiner. “We will investigate whether faecal miRNAs are abnormal in disease, and we plan to explore ways to use exogenously administered miRNAs as therapeutic compounds.

ORIGINAL ARTICLE Liu, S. et al. The host shapes the gut microbiota via fecal microRNA. Cell Host Microbe 19, 32–43 (2016)

Chemicals from gut bacteria maintain vitality in aging animals: Indoles help worms/flies/mice live stronger for longer

A class of chemicals made by intestinal bacteria, known as indoles, help worms, flies and mice maintain mobility and resilience for more of their lifespans, scientists have discovered.

“This is a direct avenue to a drug that could make people live better for longer,” says senior author Daniel Kalman, PhD, professor of pathology and laboratory medicine at Emory University School of Medicine.

Kalman and his colleagues use the term “healthspan” to describe the length of time a human or animal, while aging, can stay active and resist stress. In this research, the focus is on whether the animals live healthier, but not necessarily longer.

“We need a better understanding of healthspan,” he says. “With medical advances, people are living longer; but you might not really want to live longer if it means spending those extra years frail and infirm.” The burden imposed by diseases of aging on the healthcare system is expected to skyrocket in coming decades, he adds.

Interest in the health effects of the microbes that live in our bodies has exploded in recent years. In humans and mice, some studies have shown that the spectra of bacteria in our bodies become narrower with age.

“We don’t always know how various microbiota exert their effects,” Kalman says. “But now we have a big clue to one mechanism.”

Indole, produced by many types of bacteria through breakdown of the amino acid tryptophan, can smell noxious or flowery depending on the concentration. Indole and its chemical relatives can be found in plants, especially vegetables such as broccoli and kale. One such relative is also known as auxin, a growth hormone for plants needed for light-seeking and root development.

Kalman’s lab had previously identified indole and related molecules as compounds released by E. coli bacteria that condition the worm C. elegans and mice to be more resistant to infection and other stresses.

The roundworm C. elegans is one of the premier organisms in which to study aging. Studies in C. elegans led to discovery of a set of genes that control how long the worms can live. Several of the genes are components of the insulin signaling pathway, and they influence lifespan in flies and mice as well.

Worms normally eat bacteria. So researchers fed them E. colibacteria that produce indoles, and compared them with worms fed E. coli that cannot produce indoles.

As they age, older worms spend less time moving around, can’t swallow as well and are more sensitive to stressors. Although indoles didn’t change the maximal lifespan, they markedly increased the amount of time worms were mobile after the age of 15 days, and it increased their swallowing strength and resistance to heat stress, even in young animals.

In addition, worms usually stop reproduction at the age of 5 days, but dietary indole more than doubled their reproductive span, allowing them to remain fertile up to 12 days.

Indole had similar effects on mobility and resistance to heat in Drosophila fruit flies, and with mice, a comparable pattern was evident. Researchers treated mice with antibiotics to eliminate the existing flora, and then re-colonized them with either normal E. coli, or, as a control, with bacteria that cannot produce indole. In very old mice (28 months), indoles helped animals maintain their weight, mobility and activity levels. In younger mice, indoles extended survival after exposure to lethal radiation.

The researchers also analyzed the patterns of gene activity affected by indoles — the genes regulated by indoles were distinct from other C. elegans genes previously linked to longevity.

“It’s like the Picture of Dorian Gray, in terms of the genes involved,” Kalman says. “Indoles make old animals look more like the young ones.”

Indoles may be keeping the intestinal barrier intact and/or limiting systemic inflammatory effects. Kalman’s laboratory is now investigating how indoles exert their effects in aging animals, how dysregulation of indoles produced by the microbiota contribute to frailty, and how indoles can be used to reverse these effects.

“Indole is such an ancient messenger,” Kalman says. “It’s how plants steer their growth, how bacteria talk to each other, and it is how plants and bacteria talk with us and ensure proper homeostasis with our immune system. It is perhaps not so surprising that these molecules help maintain our vitality.”

The first author of the paper is postdoctoral fellow Robert Sonowal, PhD. Co-authors include professor of pathology Guy Benian, PhD, assistant professor of pediatrics Rheinallt Jones, PhD, and professor of geriatrics Jonathan Flacker, MD.

The research was supported by the Bio-Merieux Foundation, the National Institute for Diabetes and Digestive and Kidney Diseases (DK074731) and the National Institute on Aging (AG054903).


Journal Reference:

  1. Robert Sonowal, Alyson Swimm, Anusmita Sahoo, Liping Luo, Yohei Matsunaga, Ziqi Wu, Jui A. Bhingarde, Elizabeth A. Ejzak, Ayush Ranawade, Hiroshi Qadota, Domonica N. Powell, Christopher T. Capaldo, Jonathan M. Flacker, Rhienallt M. Jones, Guy M. Benian, and Daniel Kalman. Indoles from commensal bacteria extend healthspanPNAS, August 21, 2017 DOI: 10.1073/pnas.1706464114

Bacteria Use Brainlike Bursts of Electricity to Communicate

Bacteria have an unfortunate — and inaccurate — public image as isolated cells twiddling about on microscope slides. The more that scientists learn about bacteria, however, the more they see that this hermitlike reputation is deeply misleading, like trying to understand human behavior without referring to cities, laws or speech. “People were treating bacteria as … solitary organisms that live by themselves,” said Gürol Süel, a biophysicist at the University of California, San Diego. “In fact, most bacteria in nature appear to reside in very dense communities.”

The preferred form of community for bacteria seems to be the biofilm. On teeth, on pipes, on rocks and in the ocean, microbes glom together by the billions and build sticky organic superstructures around themselves. In these films, bacteria can divide labor: Exterior cells may fend off threats, while interior cells produce food. And like humans, who have succeeded in large part by cooperating with each other, bacteria thrive in communities. Antibiotics that easily dispatch free-swimming cells often prove useless against the same types of cells when they’ve hunkered down in a film.

As in all communities, cohabiting bacteria need ways to exchange messages. Biologists have known for decades that bacteria can use chemical cues to coordinate their behavior. The best-known example, elucidated by Bonnie Bassler of Princeton University and others, is quorum sensing, a process by which bacteria extrude signaling molecules until a high enough concentration triggers cells to form a biofilm or initiate some other collective behavior.

But Süel and other scientists are now finding that bacteria in biofilms can also talk to one another electrically. Biofilms appear to use electrically charged particles to organize and synchronize activities across large expanses. This electrical exchange has proved so powerful that biofilms even use it to recruit new bacteria from their surroundings, and to negotiate with neighboring biofilms for their mutual well-being.

“I think these are arguably the most important developments in microbiology in the last couple years,” said Ned Wingreen, a biophysicist who researches quorum sensing at Princeton. “We’re learning about an entirely new mode of communication.”

Biofilms were already a hot topic when Süel started focusing on them as a young professor recruited to San Diego in 2012. But much about them was still mysterious, including how individual bacteria give up their freedom and settle into large, stationary societies. To gain insight, Süel and his colleagues grew biofilms of Bacillus subtilis, a commonly studied rod-shaped bacterium, and observed them for hours with sophisticated microscopes. In time-lapse movies, they saw biofilms expand outward until cells in the interior consumed the available reserves of the amino acid glutamate, which the bacteria use as a nitrogen source. Then the biofilms would stop expanding until the glutamate was replenished. Süel and his colleagues became curious about how the inner bacteria were telling the outer cells when to divide and when to chill.

Quorum sensing was the obvious suspect. But Süel, who was trained in physics, suspected that something more than the diffusion of chemical messengers was at work in his Bacillus colonies. He focused on ion channels — specialized molecules that nestle into cells’ outer membranes and ferry electrically charged particles in and out. Ion channels are probably most famous for their role in nerve cells, or neurons. Most of the time, neurons pump out sodium ions, which carry a single positive charge, and let in a different number of potassium ions, also with single positive charges. The resulting charge imbalance acts like water piling up behind a dam. When an electrical impulse jolts a neuron’s membrane, specialized channels open to allow the concentrated ions to flood in and out, essentially opening the dam’s floodgates. This exchange propagates along the neuron, creating the electrical “action potentials” that carry information in the brain.

Süel knew that bacteria also pump ions across their membranes, and several recent papers had reported spikes of electrical activity in bacteria that at least loosely resembled those found in the brain. Could bacteria also be using the action-potential mechanism to transmit electrical signals? he wondered.

He and his colleagues treated biofilms in their lab with fluorescent markers that are activated by potassium and sodium ions, and the potassium marker lit up as ions flowed out of starved cells. When the ions reached nearby cells, those cells also released potassium, refreshing the signal. The signal flowed outward in this way until it reached the biofilm’s edge. And in response to the signal, edge cells stopped dividing until the interior cells could get a meal, after which they stopped releasing potassium.

Süel’s team then created mutant bacteria without potassium channels, and they found that the cells did not grow in the same stop-start manner. (The researchers also saw no movement of labeled sodium ions in their experiments.) Like neurons, bacteria apparently use potassium ions to propagate electrical signals, Süel and his colleagues reported in Nature in 2015.

Time-lapse video of two Bacillus subtilis biofilms in a shared environment shows their synchronized growth, which the bacteria coordinate through electrical communication. Green fluorescence reveals waves of released potassium ions that sweep through the biofilms as growth signals. In Süel’s experiment, when a nutrient is plentiful (left), the two biofilms grow at the same time. Their growth signals rise and fall in sync. When the nutrient is in short supply, the two biofilms “time-share” it for more efficient consumption by growing out of phase: each grows while the other is resting.

Time-lapse video of two Bacillus subtilis biofilms in a shared environment shows their synchronized growth, which the bacteria coordinate through electrical communication. Green fluorescence reveals waves of released potassium ions that sweep through the biofilms as growth signals. In Süel’s experiment, when a nutrient is plentiful (left), the two biofilms grow at the same time. Their growth signals rise and fall in sync. When the nutrient is in short supply, the two biofilms “time-share” it for more efficient consumption by growing out of phase: each grows while the other is resting.

Time-lapse video of two Bacillus subtilis biofilms in a shared environment shows their synchronized growth, which the bacteria coordinate through electrical communication. Green fluorescence reveals waves of released potassium ions that sweep through the biofilms as growth signals. In Süel’s experiment, when a nutrient is plentiful (left), the two biofilms grow at the same time. Their growth signals rise and fall in sync. When the nutrient is in short supply, the two biofilms “time-share” it for more efficient consumption by growing out of phase: each grows while the other is resting.

Adapted from Suel Lab at UCSD (Reference: J Liu et al. Science, 2017)

Despite the parallels to neural activity, Süel emphasizes that biofilms are not just like brains. Neural signals, which rely on fast-acting sodium channels in addition to the potassium channels, can zip along at more than 100 meters per second — a speed that is critical for enabling animals to engage in sophisticated, rapid-motion behaviors such as hunting. The potassium waves in Bacillus spread at the comparatively tortoise-like rate of a few millimeters per hour. “Basically, we’re observing a primitive form of action potential in these biofilms,” Süel said. “From a mathematical perspective they’re both exactly the same. It’s just that one is much faster.”

Bacterial Broadcasting

Süel and his colleagues had more questions about that electric signal, however. When the wave of potassium-driven electrical activity reaches the edge of a biofilm, the electrical activity might stop, but the cloud of potassium ions released into the environment keeps going. The researchers therefore decided to look at what happens once the potassium wave leaves a biofilm.

The first answer came earlier this year in Cell paper, in which they showed that Bacillus bacteria seem to use potassium ions to recruit free-swimming cells to the community. Amazingly, the bacteria attracted not only other Bacillus, but also unrelated species. Bacteria, it seems, may have evolved to live not just in monocultures but in diverse communities.

A few months later, in Science, Süel’s team showed that by exchanging potassium signals, two Bacillus biofilms can “time-share” nutrients. In these experiments, two bacterial communities took turns eating glutamate, enabling the biofilms to consume the limited nutrients more efficiently. As a result of this sharing, the biofilms grew more quickly than they could have if the bacteria had eaten as much as they could without interruption. When the researchers used bacteria with ion channels that had been modified to give weaker signals, the biofilms, no longer able to coordinate their feeding, grew more slowly.

Süel’s discoveries about how bacteria communicate electrically have exhilarated bacteria researchers.

“I think it’s some of the most interesting work going on in all of biology right now,” said Moh El-Naggar, a biophysicist at the University of Southern California. El-Naggar studies how bacteria transfer electrons using specialized thin tubes, which he calls nanowires. Even though this transfer could also be considered a form of electrical communication, El-Naggar says that in the past, he would “put the brakes on” if someone suggested that bacteria behave similarly to neurons. Since reading Süel’s 2015 paper, he’s changed his thinking. “A lot of us can’t wait to see what comes out of this,” he said.

For Gemma Reguera, a microbiologist at Michigan State University, the recent revelations bolster an argument she has long been making to her biologist peers: that physical signals such as light, sound and electricity are as important to bacteria as chemical signals. “Perhaps [Süel’s finding] will help the scientific community and [people] outside the scientific community feel more open about other forms of physical communication” among bacteria, Reguera said.

Part of what excites researchers is that electrical signaling among bacteria shows signs of being more powerful than chemically mediated quorum sensing. Chemical signals have proved critical for coordinating certain collective behaviors, but they quickly get diluted and fade out once they’re beyond the immediate vicinity of the bacteria emitting the signal. In contrast, as Süel’s team has found, the potassium signals released from biofilms can travel with constant strength for more than 1,000 times the width of a typical bacterial cell — and even that limit is an artificial upper bound imposed by the microfluidic devices used in the experiments. The difference between quorum sensing and potassium signaling is like the difference between shouting from a mountaintop and making an international phone call.

Moreover, chemicals enable communication only with cells that have specific receptors attuned to them, Wingreen noted. Potassium, however, seems to be part of a universal language shared by animal neurons, plant cells and — scientists are increasingly finding — bacteria.

“I personally have found [positively charged ion channels] in every single-celled organism I’ve ever looked at,” said Steve Lockless, a biologist at Texas A&M University who was Süel’s lab mate in graduate school. Bacteria could thus use potassium to speak not just with one another but with other life-forms, including perhaps humans, as Lockless speculated in a commentary to Süel’s 2015 paper. Research has suggested that bacteria can affect their hosts’ appetite or mood; perhaps potassium channels help provide that inter-kingdom communication channel.The fact that microbes use potassium suggests that this is an ancient adaptation that developed before the eukaryotic cells that make up plants, animals and other life-forms diverged from bacteria, according to Jordi Garcia-Ojalvo, a professor of systems biology at Pompeu Fabra University in Barcelona who provided theoretical modeling to support Süel’s experiments. For the phenomenon of intercellular communications, he said, the bacterial channel “might be a good candidate for the evolutionary ancestor of the whole behavior.”

The findings form “a very interesting piece of work,” said James Shapiro, a bacterial geneticist at the University of Chicago. Shapiro is not afraid of bold hypotheses: He has argued that bacterial colonies might be capable of a form of cognition. But he approaches analogies between neurons and bacteria with caution. The potassium-mediated behaviors Süel has demonstrated so far are simple enough that they don’t require the type of sophisticated circuitry brains have evolved, Shapiro said. “It’s not clear exactly how much information processing is going on.”

Süel agrees. But he’s currently less interested in quantifying the information content of biofilms than in revealing what other feats bacteria are capable of. He’s now trying to see if biofilms of diverse bacterial species time-share the way biofilms of pure Bacillus do.

He also wants to develop what he calls “bacterial biofilm electrophysiology”: techniques for studying electrical activity in bacteria directly, the way neuroscientists have probed the brain for decades. Tools designed for bacteria would be a major boon, said Elisa Masi, a researcher at the University of Florence in Italy who has used electrodes designed for neurons to detect electrical activity in bacteria. “We are talking about cells that are really, really small,” she said. “It’s difficult to observe their metabolic activity, and there is no specific method” for measuring their electrical signals.

Süel and his colleagues are now developing such tools as part of a $1.5 million grant from the Howard Hughes Medical Institute, the Bill and Melinda Gates Foundation, and the Simons Foundation (which publishes Quanta).

The findings could also lead to new kinds of antibiotics or bacteria-inspired technologies, Süel said, but such applications are years away. The more immediate payoff is the excitement of once again revolutionizing our conceptions about bacteria. “It’s amazing how our understanding of bacteria has evolved over the last couple decades,” El-Naggar said. He is curious about how well potassium signaling works in complex, ion-filled natural settings such as the ocean. “Now we’re thinking of [bacteria] as masters of manipulating electrons and ions in their environment. It’s a very, very far cry from the way we thought of them as very simplistic organisms.”

“Step by step we find that all the things we think bacteria don’t do, they actually do,” Wingreen said. “It’s displacing us from our pedestal.”

This article was reprinted on

Parkinson’s May Begin in Gut and Spread to the Brain Via the Vagus Nerve

A major epidemiological registry-based study from Aarhus University and Aarhus University Hospital indicates that Parkinson’s disease begins in the gastrointestinal tract; the study is the largest in the field so far.

The chronic neurodegenerative Parkinson’s disease affects an increasing number of people. However, scientists still do not know why some people develop Parkinson’s disease. Now researchers from Aarhus University and Aarhus University Hospital have taken an important step towards a better understanding of the disease.

New research indicates that Parkinson’s disease may begin in the gastrointestinal tract and spread through the vagus nerve to the brain.

This image shows the course and distribution of the glossopharyngeal, vagus, and accessory nerves.

“We have conducted a registry study of almost 15,000 patients who have had the vagus nerve in their stomach severed. Between approximately 1970-1995 this procedure was a very common method of ulcer treatment. If it really is correct that Parkinson’s starts in the gut and spreads through the vagus nerve, then these vagotomy patients should naturally be protected against developing Parkinson’s disease,” explains postdoc at Aarhus University Elisabeth Svensson on the hypothesis behind the study.

A hypothesis that turned out to be correct:

“Our study shows that patients who have had the the entire vagus nerve severed were protected against Parkinson’s disease. Their risk was halved after 20 years. However, patients who had only had a small part of the vagus nerve severed where not protected. This also fits the hypothesis that the disease process is strongly dependent on a fully or partially intact vagus nerve to be able to reach and affect the brain,” she says.

The research project has just been published in the internationally recognised journal Annals of Neurology.

The first clinical examination

The research has presented strong evidence that Parkinson’s disease begins in the gastrointestinal tract and spreads via the vagus nerve to the brain. Many patients have also suffered from gastrointestinal symptoms before the Parkinson’s diagnosis is made.

“Patients with Parkinson’s disease are often constipated many years before they receive the diagnosis, which may be an early marker of the link between neurologic and gastroenterologic pathology related to the vagus nerve ,” says Elisabeth Svensson.

Previous hypotheses about the relationship between Parkinson’s and the vagus nerve have led to animal studies and cell studies in the field. However, the current study is the first and largest epidemiological study in humans.

The research project is an important piece of the puzzle in terms of the causes of the disease. In the future the researchers expect to be able to use the new knowledge to identify risk factors for Parkinson’s disease and thus prevent the disease.

“Now that we have found an association between the vagus nerve and the development of Parkinson’s disease, it is important to carry out research into the factors that may trigger this neurological degeneration, so that we can prevent the development of the disease. To be able to do this will naturally be a major breakthrough,” says Elisabeth Svensson.

Original Research: Abstract for “Vagotomy and subsequent risk of Parkinson’s disease” by Elisabeth Svensson PhD, Erzsébet Horváth-Puhó PhD, Reimar W Thomsen PhD, Jens Christian Djurhuus DMSc, Lars Pedersen PhD, Per Borghammer DMSc and Henrik Toft Sørensen DMSc in Annals of Neurology. Published online June 2015 doi:10.1002/ana.24448


Scientists at the Champalimaud Centre for the Unknown and the Instituto de Medicina Molecular, in Lisbon, Portugal, have discovered that neurons located at mucosal tissues can immediately detect an infection in the organism, promptly producing a substance that acts as an “adrenaline rush” for immune cells. Under the effect of this signal, immune cells rapidly become poised to fight the infection and repair the damage caused to surrounding tissues. These totally novel results have been published online in the journal Nature on September 6, 2017.

Most neurons in the body are located in the brain and its vicinity – the central nervous system -, with neurons projecting their axons to every tissue in the organism by way of the spinal cord. In turn, glial cells are neuron satellites ensuring the cohesion of the nervous tissue. Nevertheless, throughout the body there is a very abundant number of peripheral nervous cells. These are so numerous in the gut that they have collectively been dubbed “the second brain”.

What do these peripheral nervous cells do? Experts are just beginning to understand that they are in fact extremely important for the organism to be able to mount adequate immune responses and preserve health.

In 2016, Henrique Veiga-Fernandes and his colleagues (then at the Institute for Molecular Medicine, in Lisbon) published, also in Nature, a study where they showed that glial cells in the gut can stimulate a type of immune cells, called ILC3, to produce substances against bacterial infections.

These immune cells that are being studied by Veiga-Fernandes – collectively called “innate lymphoid cells”, or ILC -, are also very special. We are born with them; they are not produced in response to an immunization, for instance through vaccination. “ILCs were discovered very recently, in 2010, but they are very ancient in evolutionary terms. Even lampreys have them!”, says Veiga-Fernandes. Lampreys belong to a very old animal lineage.

There are several types of these innate lymphocytes (white cells). In their 2016 study, the team had analyzed the behavior of ILC3s in the gut – and their “dialog” with their glial cell neighbours. In the new study, also led by Veiga-Fernandes, they focused on another type of innate lymphoid cells: ILC2s.

ILC2s produce substances that are essential to immune responses against parasites, such as worms. “These cells are normally abundant at barrier sites, such as the gut, lungs and skin”, which serve as physical forteresses to the body”, Veiga-Fernandes explains.

Now, the team showed that these immune cells would not be able to develop their protective actions against infections without establishing a “dialog” with neurons residing at those sites.

The study brings “two big novelties”, says Veiga-Fernandes. The first, he explains, “is that neurons define the immune cells’ function. Nobody could have imagined that the nervous system coordinates, commands and controls the immune response throughout the whole organism.” Second, he adds, “it’s one of the fastest and most powerful immune reactions we have ever seen”. Comparatively, the newly discovered neuronal stimulus induces an immune response in a few minutes, while the immune response following vaccination typically takes several weeks to mount.

How did the scientists discover this neuro-immune “tandem”? “What happened was that we observed, in high-resolution microphotographs of the lungs and gut of mice, that ILC2s were placed along the axons of neurons residing in these mucosa, a bit like pearls on a string”, replies Veiga-Fernandes. “So we asked ourselves if these two distinct tissues could productively ‘talk’ to each other.”

To test this hypothesis, the team started by analyzing the whole genome of a series of immune cells – ILC1s, ILC2s, ILC3s, T-cells, etc. -, “searching for genes that code molecules that may act as receivers of neuronal signals”, says Veiga-Fernandes. They found that only ILC2s possessed a defined “receptor” (membrane molecules that act as antennae) for nervous signals.

Notably, the authors discovered that ILC2s have receptors to a neuronal messenger called neuromedin U (NMU). Since neurons are the only cells that produce abundant levels of NMU, this indicated that only neurons could be sending this signal to ILC2s.

Later, they used a rodent parasite, Nippostrongylus brasiliensis (a sort of hookworm) to infect “normal” control mice and mutant mice whose ILC2s had been stripped of their NMU receptors. In the first group of animals, the innate immune cells immediately triggered a response to neutralize the parasite and repair damaged tissue. In the second group, the mice were unable to fight the infection and the damage caused by the parasite – including the internal bleeding of the lungs due to N. brasiliensis.

The researchers also showed that neurons are able to detect the products secreted by parasites that infect the organism – and that, when this happens, they rapidly produce NMU. In turn, NMU acts vigorously on ILC2s, thus generating a protective response in a few minutes.

Could these results be extrapolated to humans? “Maybe. In humans, ILC2s also have NMU receptors”, replies Veiga-Fernandes. “But we are still very far from understanding how we could safely use this neuro-immunological ‘bomb’; for now, we are at the fundamental research level”, he adds.

Source: Maria João Soares – Champalimaud Centre for the Unknown
Original Research: Abstract for “Neuronal regulation of type 2 innate lymphoid cells via neuromedin U” by Vânia Cardoso, Julie Chesné, Hélder Ribeiro, Bethania García-Cassani, Tânia Carvalho, Tiffany Bouchery, Kathleen Shah, Nuno L. Barbosa-Morais, Nicola Harris & Henrique Veiga-Fernandes in Nature. Published online September 6 2017 doi:10.1038/nature23469

Image shows lymphocytes in the gut.

Gut Microbes May Talk to the Brain Through Cortisol

Gut microbes have been in the news a lot lately. Recent studies show they can influence human health, behavior, and certain neurological disorders, such as autism. But just how do they communicate with the brain? Results from a new University of Illinois study suggest a pathway of communication between certain gut bacteria and brain metabolites, by way of a compound in the blood known as cortisol. And unexpectedly, the finding provides a potential mechanism to explain the characteristics of autism.

“Changes in neurometabolites during infancy can have profound effects on brain development, and it is possible that the microbiome — or collection of bacteria, fungi, and viruses inhabiting our gut — plays a role in this process,” says Austin Mudd, a doctoral student in the Neuroscience Program at U of I. “However, it is unclear which specific gut bacteria are most influential during brain development and what factors, if any, might influence the relationship between the gut and the brain.”

The researchers studied 1-month-old piglets, which are remarkably similar to human infants in terms of their gut and brain development. They first identified the relative abundances of bacteria in the feces and ascending colon contents of the piglets, then quantified concentrations of certain compounds in the blood and in the brain.

“Using the piglet as a translatable animal model for human infants provides a unique opportunity for studying aspects of development which are sometimes more difficult or ethically challenging to collect data on in human infants,” Mudd says. “For example, in this study we wanted to see if we could find bacteria in the feces of pigletsthat might predict concentrations of compounds in the blood and brain, both of which are more difficult to characterize in infants.”

The researchers took a stepwise approach, first identifying predictive relationships between fecal bacteria and brain metabolites. They found that the bacterial genera Bacteroides and Clostridium predicted higher concentrations of myo-inositol, Butyricimonas positively predicted n-acetylaspartate (NAA), and Bacteroides also predicted higher levels of total creatine in the brain. However, when bacteria in the genus Ruminococcus were more abundant in the feces of the piglets, NAA concentrations in the brain were lower.

“These brain metabolites have been found in altered states in individuals diagnosed with autism spectrum disorder (ASD), yet no previous studies have identified specific links between bacterial genera and these particular metabolites,” Mudd notes.

The next step was to determine if these four bacterial genera could predict compounds in the blood. “Blood biomarkers are something we can actually collect from an infant, so it’s a clinically relevant sample. It would be nice to study an infant’s brain directly, but imaging infants is logistically and ethically difficult. We can, however, obtain feces and blood from infants,” says Ryan Dilger, associate professor in the Department of Animal Sciences, Division of Nutritional Sciences, and Neuroscience Program at U of I.

The researchers found predictive relationships between the fecal microbiota and serotonin and cortisol, two compounds in the blood known to be influenced by gut microbiota. Specifically, Bacteroides was associated with higher serotonin levels, while Ruminococcus predicted lower concentrations of both serotonin and cortisol. Clostridium and Butyricimonas were not associated strongly with either compound.

Again, Mudd says, the results supported previous findings related to ASD. “Alterations in serum serotonin and cortisol, as well as fecal Bacteroides and Ruminococcus levels, have been described in ASD individuals.”

Based on their initial analyses, the researchers wanted to know if there was a three-way relationship between Ruminococcus, cortisol, and NAA. To investigate this further, they used a statistical approach known as “mediation analysis,” and found that serum cortisol mediated the relationship between fecal Ruminococcus abundance and brain NAA concentration. In other words, it appears that Ruminococcus communicates with and makes changes to the brain indirectly through cortisol. “This mediation finding is interesting, in that it gives us insight into one way that the gut microbiota may be communicating with the brain. It can be used as a framework for developing future intervention studies which further support this proposed mechanism,” Dilger adds.

Image shows a gut.

“Initially, we set out to characterize relationships between the gut microbiota, blood biomarkers, and brain metabolites. But once we looked at the relationships identified in our study, they kept leading us to independently reported findings in the autism literature. We remain cautious and do not want to overstate our findings without support from clinical intervention trials, but we hypothesize that this could be a contributing factor to autism’s heterogenous symptoms,” Mudd says. Interestingly, in the time since the researchers wrote the paper, other publications have also reported relationships between Ruminococcus and measures of brain development, supporting that this might be a promising area for future research.

Dilger adds, “We admit this approach is limited by only using predictive models. Therefore, the next step is to generate empirical evidence in a clinical setting. So it’s important to state that we’ve only generated a hypothesis here, but it’s exciting to consider the progress that may be made in the future based on our evidence in the pre-clinical pig model.”

Austin T. Mudd, Kirsten Berding, Mei Wang, Sharon M. Donovan & Ryan N. Dilger. (2017). Serum cortisol mediates the relationship between fecal Ruminococcus and brain N-acetylaspartate in the young pig. Gut Microbes. doi:10.1080/19490976.2017.1353849

Neurosecretory protein GL stimulates food intake, de novo lipogenesis, and onset of obesity

Throughout history, our ancestors needed to accumulate fat to survive during times when food sources were scarce. However, for most people in the modern age, food is
abundant and eating too much is a major cause of weight gain, obesity and diseases affecting the metabolism. Obesity in particular, can lead to diseases such as diabetes and heart disease.
Hunger and appetite are regulated by proteins and other chemicals that act as messengers, for example insulin, and a region of the brain called the hypothalamus. However, the full mechanisms that regulate these sensations remain unclear. Only recently, a protein called NPGL was discovered in a part of the hypothalamus of birds and mammals. However, it was not known if NPGL plays a role in regulating eating habits and weight gain.
Iwakoshi-Ukena et al. have now discovered that NPGL is found in the hypothalamus of rats and is regulated by diet and insulin. When the gene for NPGL was manipulated to produce too much of the protein, rats fed a high calorie diet started to eat more, and gained more weight and body fat. Adding additional NPGL to their brains had the same effect.

When the animals were fed a normal diet, NPGL only moderately affected how much they ate, but it substantially increased how much fat they produced. Iwakoshi-Ukena et al. also observed that when animals were starved and insulin levels were low, the rats started to produce more NPGL. These results suggest that NPGL plays a role in fat storage when energy sources are limited, and can contribute to obesity when too much NPGL is produced in animals on a high calorie diet.
These findings indicate that NPGL could be an additional brain chemical that regulates hunger and fat storage in mammals. A next step will be to reveal the specific echanisms by which NPGL regulates overeating and fat accumulation. These findings will further advance the study and treatment of obesity and obesity-related diseases.
DOI: 10.7554/eLife.28527.002

HIV Vaccine Draws Renewed Interest

Almost 7 years after the first evidence that an HIV vaccine is possible, researchers are launching a new trial hoping to improve on the 2009 results.

The vaccine used in the so-called RV-144 trial, conducted in Thailand, yielded modest protection — a reduction in the risk of HIV of about 31%. But it was enough to suggest that tweaking the vaccine might get a better outcome.

“We’re looking for ways — not just of repeating the trial — but of doing better,” commented Carl Dieffenbach, PhD, director of the Division of AIDS at the National Institute of Allergy and Infectious Diseases.

Dieffenbach, whose institute is deeply involved in HIV vaccine research, moderated a press briefing at the International AIDS Conference here where details of the new studies were given.

The RV-144 trial actually used two vaccines — a canarypox virus called ALVAC, engineered so it could not cause disease, and carrying the gag, env, and pro IUV genes. Volunteers were given four injections of ALVAC over 6 months or a matching placebo.

And at the last two injections, volunteers also got a shot of AIDSVAX B/E (which targets the HIV gp120 protein) or placebo — a vaccine candidate that had been tested on its own and found to be safe, but without benefit.

For the current studies, researchers first had to adjust vaccines to target proteins from clade C HIV, which is the type of virus that circulates in Africa, according to Linda-Gail Bekker, MBChB, PhD, of the Desmond Tutu HIV Centre in Cape Town, South Africa. The RV-144 vaccine was aimed at clades B and E, seen in Southeast Asia and elsewhere.

But they also added a new adjuvant to increase its immunogenicity and an extra booster shot at 12 months to the 6-month series of vaccinations used in Thailand, said Bekker, who is also president-elect of the International AIDS Society.

The tweaked vaccine has now been tested for safety and immunogenicity and been given the go-ahead for a full-scale efficacy trial in South Africa, Bekker told reporters.

To get the go-ahead, it had to pass four immunological criteria to show it would work better than RV-144, she said. In a phase II study dubbed HVTN 100 with 250 HIV-negative volunteers, she said, the vaccine candidate showed:

  • A high antibody response rate to the HIV env protein.
  • An env antibody response whose magnitude was at least as good as that seen in the RV-144 trial.
  • A powerful CD4-positive T cell response to env.
  • And an antibody response to the conserved region between the env V1 and V2 loops.

The vaccine candidate beat pre-specified levels for the go-ahead and also did markedly better than the RV-144 vaccine on all four, Bekker said.

The efficacy trial, HVTN 702, is set to start enrolling 5,400 people across South Africa, with the hope of showing at least a 50% vaccine efficacy, according to Glenda Gray, MBChB, president of the South African Medical Research Council, who will lead the trial.

Results should be available in 2020, she told MedPage Today.

While a 50% efficacy might seem small, Gray said, it’s likely enough to have an important effect on the HIV pandemic in places where there is a high burden of HIV. And it would only be the first step in an “iterative process” that she and others hope would lead eventually to even better vaccines.

And 50% is better than some versions of the annual influenza virus, commented Larry Corey, MD, of the Fred Hutchinson Cancer Research Center in Seattle, and principal investigator of the HIV Vaccine Trials Network, which is sponsoring the new studies.

An HIV vaccine had long been a mirage, Corey noted. At the 2000 AIDS conference here, “there was no mention of it,” he said.

Since then, the emphasis has been on improving treatment, spurred by the realization that HIV therapy is a powerful prevention tool as well as a life-saving intervention. But Corey said the world needs prevention tools “that are so generalizable that can be given to everyone.”

“The best way to do that is a vaccine,” he said.

Gray noted that a vaccine would also fill another need — prevention methods that can be controlled by women, who are often unable to insist their partners use such things as condoms.

“A vaccine is the ultimate female prevention tool,” she said. “You put it in your arm and it works in your vagina.”

While South Africa is gearing up for a trial of a fairly traditional vaccine, investigators are also looking a novel approach — using monoclonal antibodies against HIV to see if they can prevent transmission.

Corey said a study of the “broadly neutralizing antibody” VRC01 started in March in the U.S., South America, and Europe, aiming to see if it reduces the risk of HIV among a cohort of 2,700 men who have sex with men and transgendered women.

And a parallel study began in June in South Africa, aiming at enrolling 1,500 heterosexual women in seven sub-Saharan countries.

The so-called AMP trials, Corey said, are expected to have results by 2018.

The study had support from the NIH.