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Stem Cells Remember Tissues’ Past Injuries

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Stem cells, famous for replenishing the body’s stockpile of other cell types throughout life, may have an additional, unforeseen ability to cache memories of past wounds and inflammation. New studies in the skin, gut and airways suggest that stem cells, often in partnership with the immune system, can use these memories to improve the responses of tissues to later injuries and pathogenic assaults.

“What we are starting to realize is that these cells aren’t just there to make tissue. They actually have other behavioral roles,” said Shruti Naik, an immunologist at New York University who has studied this memory effect in skin and other tissues. Stem cells, she said, “have an exquisite ability to sense their environment and respond.”

But when those responses go wrong, they may cause or contribute to a variety of enduring health problems involving chronic inflammation, such as severe allergies and autoinflammatory disorders.

Most tissues in the body contain small reservoirs of long-lived stem cells that can divide and specialize into myriad cell types as required. A stem cell in the skin, for example, can divide and give rise to lineages of cells that produce pigment or keratin, cells that form the sweat glands, or even the flexible barrier cells that allow the skin to stretch when the body moves. Serving as miniature factories for other cell types seemed to be stem cells’ primary function, and because they need to stay versatile, an underlying assumption has been that they have to be “blank slates,” unchanged by their histories. But now a new picture is starting to emerge.

In August, a Nature paper by Boston-area researchers offered fresh evidence for a kind of memory in stem cells, and some of the first for the phenomenon in humans. The team, led by the single-cell sequencing pioneer Alex Shalek and the immunologist José Ordovas-Montañes, both at the Massachusetts Institute of Technology, and the immunologist Nora Barrett at Brigham and Women’s Hospital, had set out to understand why some people suffer from debilitating chronic allergies to airborne dust, pollen and other substances. Most people experience at most a passing bout of coldlike symptoms from these irritants, but about 12 percent of the population has a severe reaction that persists all year and results in uncomfortable polyps or growths.

The work is the first step in the team’s larger quest to understand chronic inflammatory diseases, such as asthma and inflammatory bowel disease, in which the immune system continues to launch unnecessary attacks even after the initial challenge is over. These types of autoinflammatory disorders have long been blamed on the immune system, which is thought to overreact to a perceived threat. But the Boston team suspected there might be a cause in the tissue itself.

They began by taking cells from the inflamed nasal cavities of people with chronic sinusitis and comparing them to cells from healthy control subjects. After collecting about 60,000 cells from 20 different people, they sequenced RNA molecules taken from individual cells to determine which genes were active in them. In the stem cells from the sinusitis patients, they saw that many of the active genes were associated with allergic inflammation — in particular, the genes were targets of two immune mediators called interleukin 4 (IL-4) and interleukin 13 (IL-13). These are small molecules that immune cells like T and B lymphocytes typically use to communicate with one another.

The fact that the targeted genes were active in stem cells meant that the stem cells were apparently in direct communication with the immune system. A hunch that this communication might have an effect on the chronic nature of the disease led the researchers to a further set of experiments.

They removed cells from the airways of allergy patients, grew them in culture for about five weeks, and then profiled their gene activity. They found that the genes involved in allergic inflammation were still active, even though the allergic threat of dust and pollen was long gone. In addition, the researchers described many of the cells as “stuck” in a less-than-fully-mature state.

For Shalek, this result signals “that stem cells may transfer ‘memories’ to future generations of cells and this can cause near-permanent changes in the tissue they replenish.” This process invites comparisons to the immune system: B cells and T cells draw on their experiences with infections they have previously repelled to fight off new ones more effectively. Similarly, stem cells may retain a record of past assaults to sharpen their responses next time. But in the case of the allergy patients, that memory apparently becomes maladaptive. It may keep stem cells perpetually signaling to the immune system that an attacker is there, creating a feedback cycle that promotes inflammation and polyps.

According to Shalek, an understanding of which cells become “bad actors” and how their response propagates throughout a tissue should lead to more effective interventions. In fact, in their paper they were able to test the effects of an antibody that blocks IL-4 and IL-13 on the stem and secretory cells of an individual with nasal polyps. They noted a substantial restoration of gene expression associated with healthy tissue, a promising step toward the development of future therapies.

“This opens a new paradigm where we don’t only focus on the self-renewal potential of these cells but on their potential interaction with their surroundings,” said Semir Beyaz, an immunologist at Cold Spring Harbor Laboratory. Beyaz was not involved in the study by the Boston group but has made similar findings in the gut: In a paper published in Nature in 2016 he demonstrated that the intestines of mice on a high-fat diet produced a greater number of stemlike cells than did those of mice eating less fat. When dividing, the intestinal stem cells also seemed to add to their own numbers more frequently rather than producing more differentiated cells, a change that has been linked to diseases like cancer.

“Functionally, we are realizing that cells can be tuned,” Naik said. “Immunologists are starting to understand that immune reactions take place in tissues, and the way tissues respond to this is at the level of the stem cell.”

A few years ago, in collaboration with stem cell biologists, Naik looked at the effects of prior injury and inflammation on wound healing in mice, in the hope of understanding whether experience with inflammation affects stem cells. As described in their 2017 paper in Nature, she and her colleagues discovered that if patches of skin on mice were inflamed and allowed to heal, subsequent wounds to that same spot would heal 2.5 times as quickly, an effect that could last as long as six months.

In that experiment, Naik explained, the memory retained in the stem cells was beneficial because it was “tuning cells to be more powerful at healing wounds and regeneration.” But the flip side of this finding, as Shalek, Barrett and Ordovas-Montañes had observed, is that “if you teach [the cells] bad behaviors … they are going to remember those bad behaviors as well,” she said.

How the stem cells are storing these memories is unknown; in both the allergy and the wound healing studies, the mechanism appears to involve some modification of the DNA that makes certain genes more or less accessible to activation. Naik found that the DNA in the skin stem cells of the twice-wounded mice contained many regions that were less tightly packed, which usually indicates gene activity, and some of those open regions were retained long after the inflammation was over.

As Naik and her colleagues discussed recently in a review paper for Cell, stem cells in a wide range of tissues engage in a chemical “dialogue” with the immune system, with both sides — and potentially many other cell types — pooling their information to cope most effectively with changing conditions. Whatever the details of those conversations might be, all the evidence points to stem cells playing a central role in helping to make tissues more adaptable by preserving some record of their history.

“It makes more sense that a tissue would just learn from its experience,” Naik said. “That way it doesn’t have to reinvent the wheel every single time.”

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tbjohnston
28 days ago
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It ended in 1767, yet this experiment is still linked to higher incomes and education levels today

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tbjohnston
31 days ago
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Mastering Disctraction Through Practice | Friday Forward (#146)

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I can say with confidence that I am probably the least popular person in my household this week. While there are likely a few reasons that I would be up for this distinction in any given week, I know for sure that it was my decision to turn on Apple’s new Screen Time function for myself and my kids that earned me the honor this time.

Part of iOS 12, this new Screen Time feature is designed to provide users with detailed information on how long they are on their phone in a given day and for what.

When a company creates a feature that is designed to make you use their product less, it should raise an eyebrow. Apple clearly is aware that our distraction with technology is becoming a serious health issue. In fact, several other technology giants are also starting to acknowledge that technology and social media has both harmful and addictive properties.

There are two main aspects of the Screen Time function: awareness and control. In terms of awareness, it allows you to see your detailed usage stats for the day, including the number of “pickups” – the times when you pick up your phone from the resting position.

In terms of control, you can both limit access to apps and enable “downtime,” which disables the phone overnight except for critical/emergency functions. Screen Time also allows parents to set usage limits and see how kids are using their phones.

I implemented several of the Screen Time features on my phone, including time limits on apps where I know the little red buttons distract me from both the task at hand and conversations in which I should be fully present. I also enabled downtime an hour before bedtime.

When I did the same for my kids, it did not go over as well. They let me know in no uncertain terms how it would impact their life and one of them stated, “Dad, literally no one else does this.” To which I responded, “Great, I don’t want to be like everyone else, nor do I want you to be.”

Here’s the reality. We get better at what we practice. If you practice 100 free throws, chances are that you will get better at free throws. The same goes for driving and studying a subject.

Sadly, what many of us are spending our time practicing these days is being distracted. And we are all getting really good at it. In fact, many of us are probably on our way to becoming distraction masters.

Recent studies have shown that you are actually significantly more distracted just from having your cell phone in the room, even if it’s not turned on. And the distraction gets worse when it’s sitting on a table next to you.

We are training our brains to be distracted in the same way that meditation trains our brains to be focused. And that has a toll. It changes the way our brain develops, hurts our concentration, impacts our relationships and strips us of the ability to be with our own thoughts or appreciate silence and quiet.

We begin to crave technology stimulation like a drug; the dopamine in our brain responds in a similar manner.

A week into our new experiment, I have adjusted to the changes. Even though I can override the controls I set (my kids can’t), it serves as an important reminder for when I am engaged with my phone. This awareness has noticeably reduced my phone use.

While I can’t say that my kids are happy, they too have adjusted. There are no more fights about shutting down at night, they understand the limits and are learning to manage them better and request more time if they really need it.

Hopefully, with less practice at distraction, we will all become worse at it.

Should you need more evidence for why you should use your phone less, watch this incredibly powerful video titled “Look Up.”

Quote of The Week

Daniel Goleman, author of Focus: The Hidden Driver of Excellence

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tbjohnston
52 days ago
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ALPHA experiment takes antimatter to a new level

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In a paper published today in the journal Nature, the ALPHA collaboration reports that it has literally taken antimatter to a new level. The researchers have observed the Lyman-alpha electronic transition in the antihydrogen atom, the antimatter counterpart of hydrogen, for the first time. The finding comes hot on the heels of recent measurements by the collaboration of another electronic transition, and demonstrates that ALPHA is quickly and steadily paving the way for precision experiments that could uncover as yet unseen differences between the behaviour of matter and antimatter.

The Lyman-alpha (or 1S-2P) transition is one of several in the Lyman series of electronic transitions that were discovered in atomic hydrogen just over a century ago by physicist Theodore Lyman. The transition occurs when an electron jumps from the lowest-energy (1S) level to a higher-energy (2P) level and then falls back to the 1S level by emitting a photon at a wavelength of 121.6 nanometres.

It is a special transition. In astronomy, it allows researchers to probe the state of the medium that lies between galaxies and test models of the cosmos. In antimatter studies, it could enable precision measurements of how antihydrogen responds to light and gravity. Finding any slight difference between the behaviour of antimatter and matter would rock the foundations of the Standard Model of particle physics and perhaps cast light on why the universe is made up almost entirely of matter, even though equal amounts of antimatter should have been produced in the Big Bang.

The ALPHA team makes antihydrogen atoms by taking antiprotons from CERN’s Antiproton Decelerator (AD) and binding them with positrons from a sodium-22 source. It then confines the resulting antihydrogen atoms in a magnetic trap, which prevents them from coming into contact with matter and annihilating. Laser light is then shone onto the trapped atoms to measure their spectral response. The measurement involves using a range of laser frequencies and counting the number of atoms that drop out of the trap as a result of interactions between the laser and the trapped atoms.

The ALPHA collaboration has previously employed this technique to measure the so-called 1S-2S transition. Using the same approach and a series of laser wavelengths around 121.6 nanometres, ALPHA has now detected the Lyman-alpha transition in antihydrogen and measured its frequency with a precision of a few parts in a hundred million, obtaining good agreement with the equivalent transition in hydrogen.

This precision is not as high as that achieved in hydrogen, but the finding represents a pivotal technological step towards using the Lyman-alpha transition to chill large samples of antihydrogen using a technique known as laser cooling. Such samples would allow researchers to bring the precision of this and other measurements of antihydrogen to a level at which any differences between the behaviour of antihydrogen and hydrogen might emerge.

“We are really excited about this result,” says Jeffrey Hangst, spokesperson for the ALPHA experiment. “The Lyman-alpha transition is notoriously difficult to probe – even in ‘normal’ hydrogen. But by exploiting our ability to trap and hold large numbers of antihydrogen atoms for several hours, and using a pulsed source of Lyman-alpha laser light, we were able to observe this transition. Next up is laser cooling, which will be a game-changer for precision spectroscopy and gravitational measurements.”

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tbjohnston
108 days ago
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Ancient Quasars Provide Incredible Evidence for Quantum Entanglement

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Using two ancient galactic cores called quasars, researchers have taken a massive step forward toward confirming quantum entanglement — a concept that says that the properties of particles can be linked no matter how far apart in the universe they may be.

If quantum entanglement is valid, then a pair of entangled particles can exist billions of light-years apart from one another and actions affecting the properties of one particle will affect the properties of the other particle. Albert Einstein described this correlation between particles as "spooky action at a distance." Last year, physicists from MIT, the University of Vienna and other institutions provided strong evidence for quantum entanglement, and now, this same team of scientists has gone even further to confirm quantum entanglement.

Scientists looking to prove quantum entanglement have to show that measured correlations between particles cannot be explained by classical physics, according to a statement from MIT describing the new work. In the 1960s, physicist John Bell calculated a theoretical limit, past which correlations between particles must have a quantum, not a classical, explanation. [Time Crystals to Tetraquarks: Quantum Physics in 2017]

The distant quasar B1608+656 is smeared into bright arcs by two closer galaxies in the foreground. Researchers have used two ancient quasars, which emitted their light billions of years ago, to provide evidence for quantum entanglement.

Credit: ESA/Hubble, NASA, Suyu et al.

But there are loopholes in this theoretical limit, in which observations of what seem to be correlated particles have a hidden, classical explanation, the MIT researchers said. One of these loopholes that scientists are working to close is known as the "freedom-of-choice" loophole, or the possibility that an unknown classical influence is affecting a measurement of an entangled particle. With this loophole, researchers observe a quantum correlation when there is none.

Last year, this team of scientists demonstrated, using 600-year-old starlight, that if the correlations they observed between particles could be explained by classical physics, this classical origin would have to stem from more than 600 years ago — before the star's light ever shone.

To close this loophole even further, these researchers have now used distant, ancient quasars — luminous, energetic galactic nuclei — to see if the correlation between particles can be explained by classical mechanics stemming from earlier than 600 years ago. In other words, they're taking the success of their study from last year and scaling it up to provide further evidence for quantum entanglement.

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To do this, they chose to use two quasars that emitted light 7.8 billion years ago and 12.2 billion years ago. The researchers used light from these two quasars to determine the angle at which to tilt a polarizer, which measures the orientation of each photon's electric field.

They used telescopes located at detectors to measure the wavelength of the entangled photons (light particles) in the light coming from the quasars. If the light was redder than a reference wavelength — a measurement used for comparison that is taken at a different wavelength than those being studied — the polarizer tilted to measure the incoming photon. If the light was bluer than the reference wavelength, the polarizer would tilt to a different angle to measure the photon.

In the study performed last year, researchers used small telescopes that only allowed them to measure light from stars 600 light-years away, but by using larger, more powerful telescopes, the researchers have now managed to measure the light from much older, more distant quasars.

In studying entangled photons with these ancient quasars, the team found correlations in over 30,000 pairs of photons. These correlations went well beyond the limit set by Bell, showing that, if there were any classical explanation for the correlated particles, it would have to come from before these ancient quasars emitted light — many billions of years ago.

"If some conspiracy is happening to simulate quantum mechanics by a mechanism that is actually classical, that mechanism would have had to begin its operations — somehow knowing exactly when, where, and how this experiment was going to be done — at least 7.8 billion years ago," Alan Guth, a physicist at MIT and a co-author of the new work, said in the statement. "That seems incredibly implausible, so we have very strong evidence that quantum mechanics is the right explanation."

So, with these findings, it is "implausible" that the measured correlations have a classical explanation, the researchers said. This is strong evidence that quantum mechanics caused this correlation and that quantum entanglement is valid, they said.

"The Earth is about 4.5 billion years old, so any alternative mechanism — different from quantum mechanics — that might have produced our results by exploiting this loophole would've had to be in place long before even there was a planet Earth, let alone an MIT," David Kaiser, also a physicist at MIT and a co-author of the study, added in the statement. "So we've pushed any alternative explanations back to very early in cosmic history."

The work was published Aug. 20 in the journal Physical Review Letters.

Email Chelsea Gohd at cgohd@space.com or follow her @chelsea_gohd. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com

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tbjohnston
109 days ago
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Any Weight Loss Can Be Healthful, but More Can Be Much Better

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Overweight people who lost 5 to 10 percent of their weight lowered their risk for metabolic syndrome by 22 percent. Those who lost 20 percent cut their risk by over 50 percent.
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tbjohnston
116 days ago
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