Aquaporins are proteins in the cell membranes that form a pore, which allows water molecules to be transported into and out of each cell. The main moisture reservoir of the skin is located in the deeper layer of the epidermis (surface of the skin). These layers receive their moisture from blood supply that comes from the deeper layers.
The skin’s ability to self-moisturise efficiently, depends on aquaporins. Your aquaporin level directly correlates with the dryness of your skin.