Characterization and localization of CD38 in the vertebrate eye

CD38 is a 42-kDa type II transmembrane glycoprotein that has been shown to catalyze the synthesis and hydrolysis of cyclic ADP-ribose, a metabolite with well-known calcium mobilizing properties independent of IP3. In this report, characterization and localization of CD38 in the porcine and rat eyes were carried out. Western blot analysis of a purified microsomal eye extract detected a single 42-kDa protein band characteristic of CD38. Subcellular fractionation studies indicate the presence of ADP-ribosyl cyclase and NADase activities in the nuclear, membrane and microsomal fractions. Immunohistochemical staining of the rat retina showed the expression of CD38 in three distinct layers: the ganglion cell layer, inner nuclear layer and the pigmented epithelium. In the lens, the lenticular epithelium and lens cells were also immunoreactive for CD38 while in the ciliary body, both the pigmented and non-pigmented epithelium also showed the presence of CD38. For the first time, the presence of CD38/ADP-ribosyl cyclase was detected in the vertebrate eye.