The autocrine derivation of the opioid growth factor, [Met5]-enkephalin, in ocular surface epithelium

Endogenous opioid peptides serve as growth factors in developing, renewing, healing, and neoplastic cells and tissues. A native opioid peptide, [Met5]-enkephalin, termed opioid growth factor (OGF), has been discovered to regulate DNA synthesis in the epithelium of the ocular surface. OGF and its receptor zeta have been localized in both the basal and suprabasal cells of the epithelium. This study examined the hypothesis that OGF is an autocrine growth factor. Using probe for preproenkephalin (PPE) mRNA that encodes OGF, and in situ hybridization techniques, silver grains related to PPE mRNA were detected in both basal and suprabasal cells of the central and peripheral cornea, limbus, and conjunctiva. No distinct regional differences in the presence or location of message, as reflected by the density and distribution of PPE mRNA signal, were noted. These results demonstrate that a growth factor known to serve as a tonic, inhibitory, and receptor-mediated influence on the epithelium of the ocular surface is derived in an autocrine manner, thereby permitting local control of homeostatic cellular replication.