The authors of the study say their new understanding of how epidermal cells form a barrier may explain the paradox of how we can shed them without compromising our skin’s integrity. It could also help us to understand what happens when it forms incorrectly, which could lead to conditions like psoriasis and eczema.

Humans lose 200,000,000 skin cells every hour. During a 24-hour period, a person loses almost five thousand million skin cells. It has been a challenge for scientists to explain how this colossal shedding process can occur without there being a break in the skin barrier.

Scientists have previously known the epidermis consists of a thick outer barrier of dead epidermal cells, which are constantly shedding. What they’ve known less about is a secondary barrier deeper below the surface in the epidermis that is made up of only a single layer of cells, which forms a much thinner, though no less important, protective barrier.

Now, a team from Keio University in Japan, working with a researcher at Imperial College London, have discovered that the shape of the epidermal cells combined with their ability to temporarily glue together, may explain how they form this strong barrier.

The researchers suggest that a shape of an epidermal cell is actually a flattened version of a tetrakaidecahedron — a 14-sided 3D solid made out of six rectangular and eight hexagonal sides. The authors came to their conclusion after studying skin cells in mouse models using a confocal and two-photon microscopes, and developing mathematical models.

The tetrakaidecahedron shape was first proposed in 1887 by William Thomson (Lord Kelvin), a Scotch-Irish mathematical physicist and engineer. He claimed that the tetrakaidecahedron was the best shape for packing equal-sized objects together to fill space with minimal surface area.

The team in today’s study say the epidermal cells’ unique tetrakaidecahedron-like geometry means that it can always form a very tight, cohesive bond with the epidermal cells surrounding it. This is because the mix of rectangular and hexagonal sides enables the cell to always be tightly connected to the cells surrounding it.

The team also discovered that these cells manufacture proteins, which act as a temporary glue that binds the cells together in what are called ‘tight junctions’. The combination of the cells’ geometry and tight junction formation means that the skin barrier can maintain its integrity even though it is very thin.

When new cells underneath form the new tight junctions, this pushes the older cells upwards towards the surface of the skin, and the older cells lose their tight junctions. In this way, the tight junction barrier in the cell sheet is always maintained.

The team suggest that ‘malfunctions’ in the production of the tight junctions may be a contributing factor that explains why some people have conditions such as eczema, where the skin barrier is weakened, which leads to bacterial infiltration, inflammation, scratching and further infection. In other cases, fails in the interlocking barrier between cells — the tight junctions — may partly explain why in psoriasis there is an overproduction of epidermal cells, causing thick patches of skin on the surface.

Dr Reiko Tanaka, one of the study’s authors from the Department of Bioengineering at Imperial College London, said: “It is amazing to think that an abstract concept for a shape devised by the mathematician Lord Kelvin over a century ago may be an important shape in nature, helping our skin to maintain its effectiveness as barrier.

“Our study is also helping us to see how the cells that make up our skin can switch on a mechanism to make a kind of glue, which binds the cells together, ensuring that our skin maintains its integrity.

“Our skin is the largest organ in our body and it is vital that we completely understand how it works, so when it doesn’t work as it should, such as in eczema or psoriasis, we can understand the mechanisms that might be causing the problems.”

The study is published in the journal eLIFE.

The next steps will see the team analysing how skin thickness is determined and how the balance between cell growth and cell shedding is maintained. Faults in this process can lead to a thickening of the skin, leading to conditions like psoriasis. The team will also determine why skin thins as we get older, providing new insights into aging, or when it thins because special treatments like steroids are administered to treat eczema.

Story Source:

Materials provided by Imperial College London. Original written by Colin Smith. Note: Content may be edited for style and length.

Journal Reference:

1. Mariko Yokouchi, Toru Atsugi, Mark van Logtestijn, Reiko J Tanaka, Mayumi Kajimura, Makoto Suematsu, Mikio Furuse, Masayuki Amagai, Akiharu Kubo. Epidermal cell turnover across tight junctions based on Kelvin’s tetrakaidecahedron cell shape. eLife, 2016; 5 DOI: 10.7554/eLife.19593

The finding represents a major benchmark in our knowledge of how water conducts a positive electrical charge, which is a fundamental mechanism found in biology and chemistry. The researchers, led by Yale chemistry professor Mark Johnson, report their discovery in the Dec. 1 edition of the journal Science.

For more than 200 years, scientists have speculated about the specific forces at work when electricity passes through water — a process known as the Grotthuss mechanism. It occurs in vision, for example, when light hits the eye’s retina. It also turns up in the way fuel cells operate.

But the details have remained murky. In particular, scientists have sought an experimental way to follow the structural changes in the web of interconnected water molecules when an extra proton is transferred from one oxygen atom to another.

“The oxygen atoms don’t need to move much at all,” Johnson said. “It is kind of like Newton’s cradle, the child’s toy with a line of steel balls, each one suspended by a string. If you lift one ball so that it strikes the line, only the end ball moves away, leaving the others unperturbed.”

Johnson’s lab has spent years exploring the chemistry of water at the molecular level. Often, this is done with specially designed instruments built at Yale. Among the lab’s many discoveries are innovative uses of electrospray ionization, which was developed by the late Yale Nobel laureate John Fenn.

Johnson and his team have developed ways to fast-freeze the chemical process so that transient structures can be isolated, revealing the contorted arrangements of atoms during a reaction. The practical uses for these methods range from the optimization of alternative energy technologies to the development of pharmaceuticals.

In the case of the proton relay race, previous attempts to capture the process hinged on using infrared color changes to see it. But the result always came out looking like a blurry photograph.

“In fact, it appeared that this blurring would be too severe to ever allow a compelling connection between color and structure,” Johnson said.

The answer, he found, was to work with only a few molecules of “heavy water” — water made of the deuterium isotope of hydrogen — and chill them to almost absolute zero. Suddenly, the images of the proton in motion were dramatically sharper.

“In essence, we uncovered a kind of Rosetta Stone that reveals the structural information encoded in color,” Johnson said. “We were able to reveal a sequence of concerted deformations, like the frames of a movie.” Johnson’s lab was assisted by the experimental group of Knut Asmis at the University of Leipzig and the theory groups of Ken Jordan of the University of Pittsburgh and Anne McCoy of the University of Washington.

One area where this information will be useful is in understanding chemical processes that occur at the surface of water, Johnson noted. There is active debate among scientists regarding whether the surface of water is more or less acidic than the bulk of water. At present, there is no way to measure the surface pH of water.

The paper’s first author is Conrad Wolke, a former Yale doctoral student in Johnson’s lab. Co-authors of the paper are from the University of Chicago, Ohio State University, the University of Pittsburgh, the University of Washington, the University of Leipzig, and the Fritz Haber Institute of the Max Planck Society.

Financial support for the research came from the U.S. Department of Energy, the National Science Foundation, the Ohio Supercomputing Center, and the Collaborative Research Center of the German Research Foundation DFG.

Story Source:

Materials provided by Yale University. Original written by Jim Shelton. Note: Content may be edited for style and length.

Robert Korty, associate professor in the Department of Atmospheric Sciences, along with colleague William Boos of Yale University, have had their work published in the current issue of Nature Geoscience.

The two researchers have looked into precipitation patterns of the Holocene era nd compared them with present-day movements of the intertropical convergence zone, a large region of intense tropical rainfall. Using computer models and other data, the researchers found links to rainfall patterns thousands of years ago.

“The framework we developed helps us understand why the heaviest tropical rain belts set up where they do,” Korty explains.

“Tropical rain belts are tied to what happens elsewhere in the world through the Hadley circulation, but it won’t predict changes elsewhere directly, as the chain of events is very complex. But it is a step toward that goal.”

The Hadley circulation is a tropical atmospheric circulation that rises near the equator. It is linked to the subtropical trade winds, tropical rainbelts, and affects the position of severe storms, hurricanes, and the jet stream. Where it descends in the subtropics, it can create desert-like conditions. The majority of Earth’s arid regions are located in areas beneath the descending parts of the Hadley circulation.

“We know that 6,000 years ago, what is now the Sahara Desert was a rainy place,” Korty adds.

“It has been something of a mystery to understand how the tropical rain belt moved so far north of the equator. Our findings show that that large migrations in rainfall can occur in one part of the globe even while the belt doesn’t move much elsewhere.

“This framework may also be useful in predicting the details of how tropical rain bands tend to shift during modern-day El Niño and La Niña events (the cooling or warming of waters in the central Pacific Ocean which tend to influence weather patterns around the world).”

The findings could lead to better ways to predict future rainfall patterns in parts of the world, Korty believes.

“One of the implications of this is that we can deduce how the position of the rainfall will change in response to individual forces,” he says. “We were able to conclude that the variations in Earth’s orbit that shifted rainfall north in Africa 6,000 years ago were by themselves insufficient to sustain the amount of rain that geologic evidence shows fell over what is now the Sahara Desert. Feedbacks between the shifts in rain and the vegetation that could exist with it are needed to get heavy rains into the Sahara.”

Story Source:

Materials provided by Texas A&M University. Note: Content may be edited for style and length.

Journal Reference:

1. William R. Boos, Robert L. Korty. Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall. Nature Geoscience, 2016; 9 (12): 892 DOI: 10.1038/ngeo2833