The first cells might have used temperature to divide

Cell division illustration

 A simple mechanism could underlie the growth and self-replication of protocells -- putative ancestors of modern living cells -- suggests a study publishing September 3 in Biophysical Journal. Protocells are vesicles bounded by a membrane bilayer and are potentially similar to the first unicellular common ancestor (FUCA). On the basis of relatively simple mathematical principles, the proposed model suggests that the main force driving protocell growth and reproduction is the temperature difference that occurs between the inside and outside of the cylindrical protocell as a result of inner chemical activity.

"The initial motivation of our study was to identify the main forces driving cell division," says the study author Romain Attal of Universcience. "This is important because cancer is characterized by uncontrolled cell division. This is also important to understand the origin of life."

The splitting of a cell to form two daughter cells requires the synchronization of numerous biochemical and mechanical processes involving cytoskeletal structures inside the cell. But in the history of life, such complex structures are a high-tech luxury and must have appeared much later than the ability to split. Protocells must have used a simple splitting mechanism to ensure their reproduction, before the appearance of genes, RNA, enzymes, and all the complex organelles present today, even in the most rudimentary forms of autonomous life.

In the new study, Attal proposed a model based on the idea that the early forms of life were simple vesicles containing a particular network of chemical reactions -- a precursor of modern cellular metabolism. The main hypothesis is that molecules composing the membrane bilayer are synthesized inside the protocell through globally exothermic, or energy-releasing, chemical reactions.

The slow increase of the inner temperature forces the hottest molecules to move from the inner leaflet to the outer leaflet of the bilayer. This asymmetric movement makes the outer leaflet grow faster than the inner leaflet. This differential growth increases the mean curvature and amplifies any local shrinking of the protocell until it splits in two. The cut occurs near the hottest zone, around the middle.

"The scenario described can be viewed as the ancestor of mitosis," Attal says. "Having no biological archives as old as 4 billion years, we don't know exactly what FUCA contained, but it was probably a vesicle bounded by a lipid bilayer encapsulating some exothermic chemical reactions."

Although purely theoretical, the model could be tested experimentally. For example, one could use fluorescent molecules to measure temperature variations inside eukaryotic cells, in which mitochondria are the main source of heat. These fluctuations could be correlated with the onset of mitosis and with the shape of the mitochondrial network.

If borne out by future investigations, the model would have several important implications, Attal says. "An important message is that the forces driving the development of life are fundamentally simple," he explains. "A second lesson is that temperature gradients matter in biochemical processes and cells can function like thermal machines."

Cold planets exist throughout our galaxy, even in the galactic bulge, research suggests

Spiral galaxy

 Although thousands of planets have been discovered in the Milky Way, most reside less than a few thousand light years from Earth. Yet our Galaxy is more than 100,000 light years across, making it difficult to investigate the Galactic distribution of planets. But now, a research team has found a way to overcome this hurdle.

In a study published in The Astrophysical Journal Letters, researchers led by Osaka University and NASA have used a combination of observations and modeling to determine how the planet-hosting probability varies with the distance from the Galactic center.

The observations were based on a phenomenon called gravitational microlensing, whereby objects such as planets act as lenses, bending and magnifying the light from distant stars. This effect can be used to detect cold planets similar to Jupiter and Neptune throughout the Milky Way, from the Galactic disk to the Galactic bulge -- the central region of our Galaxy.

"Gravitational microlensing currently provides the only way to investigate the distribution of planets in the Milky Way," says Daisuke Suzuki, co-author of the study. "But until now, little is known mainly because of the difficulty in measuring the distance to planets that are more than 10,000 light years from the Sun."

To solve this problem, the researchers instead considered the distribution of a quantity that describes the relative motion of the lens and distant light source in planetary microlensing. By comparing the distribution observed in microlensing events with that predicted by a Galactic model, the research team could infer the Galactic distribution of planets.

The results show that the planetary distribution is not strongly dependent on the distance from the Galactic center. Instead, cold planets orbiting far from their stars seem to exist universally in the Milky Way. This includes the Galactic bulge, which has a very different environment to the solar neighborhood, and where the presence of planets has long been uncertain.

"Stars in the bulge region are older and are located much closer to each other than stars in the solar neighborhood," explains lead author of the study Naoki Koshimoto. "Our finding that planets reside in both these stellar environments could lead to an improved understanding of how planets form and the history of planet formation in the Milky Way."

According to the researchers, the next step should be to combine these results with measurements of microlens parallax or lens brightness -- two other important quantities associated with planetary microlensing.

Will it be safe for humans to fly to Mars?

 

Spaceship on Mars illustration

Sending human travelers to Mars would require scientists and engineers to overcome a range of technological and safety obstacles. One of them is the grave risk posed by particle radiation from the sun, distant stars and galaxies.

Answering two key questions would go a long way toward overcoming that hurdle: Would particle radiation pose too grave a threat to human life throughout a round trip to the red planet? And, could the very timing of a mission to Mars help shield astronauts and the spacecraft from the radiation?

In a new article published in the peer-reviewed journal Space Weather, an international team of space scientists, including researchers from UCLA, answers those two questions with a "no" and a "yes."

That is, humans should be able to safely travel to and from Mars, provided that the spacecraft has sufficient shielding and the round trip is shorter than approximately four years. And the timing of a human mission to Mars would indeed make a difference: The scientists determined that the best time for a flight to leave Earth would be when solar activity is at its peak, known as the solar maximum.

The scientists' calculations demonstrate that it would be possible to shield a Mars-bound spacecraft from energetic particles from the sun because, during solar maximum, the most dangerous and energetic particles from distant galaxies are deflected by the enhanced solar activity.

A trip of that length would be conceivable. The average flight to Mars takes about nine months, so depending on the timing of launch and available fuel, it is plausible that a human mission could reach the planet and return to Earth in less than two years, according to Yuri Shprits, a UCLA research geophysicist and co-author of the paper.

"This study shows that while space radiation imposes strict limitations on how heavy the spacecraft can be and the time of launch, and it presents technological difficulties for human missions to Mars, such a mission is viable," said Shprits, who also is head of space physics and space weather at GFZ Research Centre for Geosciences in Potsdam, Germany.

The researchers recommend a mission not longer than four years because a longer journey would expose astronauts to a dangerously high amount of radiation during the round trip -- even assuming they went when it was relatively safer than at other times. They also report that the main danger to such a flight would be particles from outside of our solar system.

Shprits and colleagues from UCLA, MIT, Moscow's Skolkovo Institute of Science and Technology and GFZ Potsdam combined geophysical models of particle radiation for a solar cycle with models for how radiation would affect both human passengers -- including its varying effects on different bodily organs -- and a spacecraft. The modeling determined that having a spacecraft's shell built out of a relatively thick material could help protect astronauts from radiation, but that if the shielding is too thick, it could actually increase the amount of secondary radiation to which they are exposed.

The two main types of hazardous radiation in space are solar energetic particles and galactic cosmic rays; the intensity of each depends on solar activity. Galactic cosmic ray activity is lowest within the six to 12 months after the peak of solar activity, while solar energetic particles' intensity is greatest during solar maximum, Shprits said.

Brain refreshing: Why the dreaming phase matters

Dreaming concep

 Scientists have long wondered why almost all animals sleep, despite the disadvantages to survival of being unconscious. Now, researchers led by a team from the University of Tsukuba have found new evidence of brain refreshing that takes place during a specific phase of sleep: rapid eye movement (REM) sleep, which is when you tend to dream a lot.

Previous studies have measured differences in blood flow in the brain between REM sleep, non-REM sleep, and wakefulness using various methods, with conflicting results. In their latest work, the Tsukuba-led team used a technique to directly visualize the movement of red blood cells in the brain capillaries (where nutrients and waste products are exchanged between brain cells and blood) of mice during awake and asleep states.

"We used a dye to make the brain blood vessels visible under fluorescent light, using a technique known as two-photon microscopy," says senior author of the study Professor Yu Hayashi. "In this way, we could directly observe the red blood cells in capillaries of the neocortex in non-anesthetized mice."

The researchers also measured electrical activity in the brain to identify REM sleep, non-REM sleep, and wakefulness, and looked for differences in blood flow between these phases.

"We were surprised by the results," explains Professor Hayashi. "There was a massive flow of red blood cells through the brain capillaries during REM sleep, but no difference between non-REM sleep and the awake state, showing that REM sleep is a unique state"

The research team then disrupted the mice's sleep, resulting in "rebound" REM sleep -- a stronger form of REM sleep to compensate for the earlier disruption. Blood flow in the brain was further increased during rebound REM sleep, suggesting an association between blood flow and REM sleep strength. However, when the researchers repeated the same experiments in mice without adenosine A2a receptors (the receptors whose blockade makes you feel more awake after drinking coffee), there was less of an increase in blood flow during REM sleep, even during rebound REM sleep.

"These results suggest that adenosine A2a receptors may be responsible for at least some of the changes in blood flow in the brain during REM sleep," says Professor Hayashi.

Given that reduced blood flow in the brain and decreased REM sleep are correlated with the development of Alzheimer's disease, which involves the buildup of waste products in the brain, it may be interesting to address whether increased blood flow in the brain capillaries during REM sleep is important for waste removal from the brain. This study lays preliminary groundwork for future investigations into the role of adenosine A2a receptors in this process, which could ultimately lead to the development of new treatments for conditions such as Alzheimer's disease.

Reducing sugar in packaged foods can prevent disease in millions

Grocery shopping

Cutting 20% of sugar from packaged foods and 40% from beverages could prevent 2.48 million cardiovascular disease events (such as strokes, heart attacks, cardiac arrests), 490,000 cardiovascular deaths, and 750,000 diabetes cases in the U.S. over the lifetime of the adult population, according to micro-simulation study published in Circulation.

A team of researchers from Massachusetts General Hospital (MGH), the Friedman School of Nutrition Science & Policy at Tufts University, Harvard T.H. Chan School of Public Health and New York City Department of Health and Mental Hygiene (NYC DOH) created a model to simulate and quantify the health, economic, and equity impacts of a pragmatic sugar-reduction policy proposed by the U.S. National Salt and Sugar Reduction Initiative (NSSRI). A partnership of more than 100 local, state and national health organizations convened by the NYC DOH, the NSSRI released draft sugar-reduction targets for packaged foods and beverages in 15 categories in 2018. This February, NSSRI finalized the policy with the goal of industry voluntarily committing to gradually reformulate their sugary products.

Implementing a national policy, however, will require government support to monitor companies as they work toward the targets and to publicly report on their progress. The researchers hope their model will build consensus on the need for a national-sugar reformulation policy in the US. "We hope that this study will help push the reformulation initiative forward in the next few years," says Siyi Shangguan, MD, MPH, lead author and attending physician at MGH. "Reducing the sugar content of commercially prepared foods and beverages will have a larger impact on the health of Americans than other initiatives to cut sugar, such as imposing a sugar tax, labeling added sugar content, or banning sugary drinks in schools."

Ten years after the NSSRI policy goes into effect, the U.S. could expect to save $4.28 billion in total net healthcare costs, and $118.04 billion over the lifetime of the current adult population (ages 35 to 79), according to the model. Adding the societal costs of lost productivity of Americans developing diseases from excessive sugar consumption, the total cost savings of the NSSRI policy rises to $160.88 billion over the adult population's lifetime. These benefits are likely to be an underestimation since the calculations were conservative. The study also demonstrated that even partial industry compliance with the policy could generate significant health and economic gains.

The researchers found that the NSSRI policy became cost-effective at six years and cost-saving at nine years. The policy could also reduce disparities, with the greatest estimated health gains among Black and Hispanic adults, and Americans with lower income and less education -- populations that consume the most sugar as a historical consequence of inequitable systems.

Product reformulation efforts have been shown to be successful in reducing other harmful nutrients, such as trans fats and sodium. The U.S., however, lags other countries in implementing strong sugar-reduction policies, with countries such as the UK, Norway, and Singapore taking the lead on sugar-reformulation efforts. The US may yet become a leader in protecting its people from the dangers of excessive sugar consumption if the NSSRI's proposed sugar-reduction targets are achieved. "The NSSRI policy is by far the most carefully designed and comprehensive, yet achievable, sugar-reformulation initiative in the world," says Shangguan.

Consuming sugary foods and beverages is strongly linked to obesity and diseases such as type 2 diabetes and cardiovascular disease, the leading cause of mortality in the U.S. More than two in five American adults are obese, one in two have diabetes or prediabetes, and nearly one in two have cardiovascular disease, with those from lower-income groups being disproportionately burdened.

"Sugar is one of the most obvious additives in the food supply to reduce to reasonable amounts," says Dariush Mozaffarian, MD, DrPH, co-senior author and dean of the Friedman School of Nutrition Science and Policy at Tufts University. "Our findings suggest it's time to implement a national program with voluntary sugar reduction targets, which can generate major improvements in health, health disparities, and healthcare spending in less than a decade."

Major funding for this study provided by the National Institutes of Health.

Shangguan is an attending at MGH and an instructor of Medicine at Harvard Medical School. Mozaffarian is dean of the Friedman School of Nutrition Science and Policy at Tufts University. Thomas Gaziano, MD, MSc, is associate professor at Brigham and Women's Hospital and assistant professor of Medicine at HMS. Renata Micha, PhD, is research associate professor at the Friedman School of Nutrition Science and Policy at Tufts University and associate professor at the University of Thessaly in Greece.