Oxysterol 7alpha-hydroxylase (CYP39A1) in the ciliary nonpigmented epithelium of bovine eye.

The CYP39A1 oxysterol 7alpha-hydroxylase preferentially catalyzes the 7alpha-hydroxylation of 24-hydroxycholesterol and has been suggested to play a role in the alternative bile acid synthesis pathway in the liver. The presence of CYP39A1 oxysterol 7alpha-hydroxylase has been reported only in the liver. To investigate the physiologic characteristics of the ciliary processes in bovine ocular tissues, we raised a mAb, 42C, against nonpigmented epithelial (NPE) cells, which have tight junctions that act as a blood-aqueous barrier and are involved in producing aqueous humor and maintaining ocular homeostasis. Immunohistochemical analysis showed that 42C antibody reacted intensely with an antigen in the NPE cells of the ciliary processes but not with other ocular tissues. The SDS-PAGE profile of immunoaffinity-purified antigens from bovine ciliary processes showed a predominant protein of molecular mass of 44.0 kDa. The amino acid sequence of this antigenic protein was identical to human CYP39A1 oxysterol 7alpha-hydroxylase. Immunoreactivity with 42C antibody was found only in hepatocytes and ocular tissues. These data suggest a new physiologic function for the CYP39A1 oxysterol 7alpha-hydroxylase in addition to the production of bile acids and provide new insight into the physiologic role of the ciliary NPE cells concerning the metabolism of sterols in the eye.