09. Skin

Our skin has an outer layer, called the epidermis, and a lower, thicker layer called the dermis. Between the epidermis and the dermis there’s a thin layer called the basement membrane that is made from proteins like collagen and laminin and glues the epidermis and dermis together. When the proteins of the basement membrane don’t work properly, the two layers are not held together strongly and the skin is easily damaged causing symptoms of EB.

The outermost layer of our skin (epidermis) is made out of keratin protein and the cells, called keratinocytes, that make keratin. New keratinocytes are made when cells near the basement membrane divide and they push the older keratinocytes up towards the surface of the skin. These cells make more and more keratin until they are full of it and die. Normal skin has a layer of dead cells and keratin as its surface and this flakes off to be replaced by more growing up from beneath. The protein keratin is made from lots of protein subunits, joined and twisted together in long chains, each one encoded by a different gene. Changes to genes involved in making keratin can cause epidermolysis bullosa simplex.

Beneath the epidermis is the dermis. This is made mostly out of collagen protein and contains cells like macrophages that protect against germs and fibroblasts that produce collagen. Like keratin, collagen protein is made from lots of collagen subunits, each encoded by a different gene. Changes to the COL7A1 gene cause dystrophic epidermolysis bullosa.

Other proteins that can be broken in EB include laminin which is used to make the basement membrane between the epidermis and the dermis as well as forming the ‘glue’ in between skin cells (the extracellular matrix) and integrin which fixes skin cells into position in the extracellular matrix. 

 

Anatomy and physiology of the skin

Image credit: 3D medical animation skin layer, by https://www.scientificanimations.com/. Licensed under the Creative Commons Attribution-Share Alike 4.0 International license.