Augmentation of trypsin resistance of retinal pigment epithelium adhesion in vitro by near ultraviolet.

In the process of subculturing near-ultraviolet (NUV)-irradiated retinal pigment epithelial (RPE) monolayers by trypsinization, we surprisingly found that the adhesion capacity of these cells was significantly enhanced. The nature of the enhanced cell adhesion induced by NUV was then studied. To quantitate this capacity, RPE monolayers were exposed to 0.05% trypsin in the presence of 0.53 mM EDTA for 10 min at 37 degrees C. The ratio of RPE cells remaining on the culture surface over total cells was measured and termed as trypsin resistance. (TR). TR of RPE cells without NUV irradiation was null (TR = 0). With NUV energy at 3.24 or 12.96 J/cm2, the RPE-TR was increased to 56.8 +/- 8.5 or 82.3 +/- 8.8%, respectively. With NUV irradiation above 12.96 J/cm2, TR reached a plateau, suggesting a maximal inducible adhesion capacity. When RPE cells were irradiated in an oxygen-free environment, TR was 33.5 +/- 1.6% lower than that in an oxygen-saturated condition, suggesting that it is an oxygen-related process. NUV-enhanced TR was inversely correlated with the concentration of trypsin or the trypsin digestion time. Moreover, NUV-induced TR was gradually diminished with elapsed time. The pre-exposed NUV energy inversely determined the degree of TR recovery. Cycloheximide, a protein synthesis inhibitor, prevented the recovery of TR. These results suggest that NUV-induced TR is a NUV-energy-dependent process. The new protein(s) which is required for TR recovery needs to be further identified.