Aquaporin-9 gene is mapped on chromosome 15q containing 6 exons that mediates passage of non-charged solutes including carbamides, polyols, pyrimidines and purines which plays a vital role in highly differentiated keratinocytes and exhibits glycerol permeability. It is also involved in urea elimination from hepatocytes and has been regulated by testosterone and estrogen.
Aquaporin-9 is highly restricted to the stratum granulosum in the epidermis where occludin is also expressed at the tight junctions. It is expressed in various types of tissues including leukocytes, brain, liver and lung. Its presence in the epidermis functions as conduit for inside to outside movement of glycerol and urea. It is also found in male reproductive tract where it localizes to the efferent ductile epithelium, vas deferens and epididymis that involved in sperm maturation, storage and concentration.
Aquaporin-9 is implicated as an important for hepatic glycerol metabolism and functions in glycerol and glucose metabolism in diabetes mellitus where it potentially contributes to the elevated hepatic glucose production.
Gene name: AQP9
Protein name: Aquaporin-9