Skin Cell Geometry Maintains Healthy Barrier

New research into how epidermal cells form a barrier may explain the paradox of how we can shed skin cells without compromising our skin's integrity. It has been an ongoing challenge for scientists to understand how this colossal shedding process—approximately 200,000 skin cells every hour—can occur without causing a break in the skin. A team from Keio University in Japan, working with a researcher at Imperial College London, studied mouse models using confocal and two-photon microscopes and through mathematical modeling. They 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 3-D structure made out of six rectangular and eight hexagonal sides. William Thomson, a Scotch-Irish mathematical physicist and engineer, first proposed the tetrakaidecahedron shape in 1887, claiming it was ideal for packing equal-sized objects together to fill space with minimal surface area, like the skin. The epidermal cells' unique rectangular and hexagonal sides mean that they can always form a very tight, cohesive bond with the surrounding cells. That’s not all‑the team also discovered the cells manufacture proteins, or a temporary glue, that bind the cells together in what’s known as tight junctions. The combination of the cells' geometry and adhesive action means that the skin barrier can maintain its integrity, even though it is very thin. The team suggest that malfunctions in the production of the tight junctions may be a contributing factor in conditions such as eczema, where the skin barrier is weakened leading to bacterial infiltration, inflammation, scratching, and further infection. In other cases, problems with the tight junctions may partly explain why in psoriasis there is an overproduction of epidermal cells, causing thick patches of skin on the surface. Says Reika Tanaka, Ph.D., TK title at the Department of Bioengineering at Imperial College London, "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."