Induction of an aging mRNA retinal pigment epithelial cell phenotype by matrix-containing advanced glycation end products in vitro.

PURPOSE: To determine an extensive mRNA phenotype of the established RPE cell line ARPE-19 when grown on a matrix modified by advanced glycation end products (AGEs). METHODS: Growth Factor Reduced Matrigel (Collaborative Biomedical Products, Bedford, MA) was nonenzymatically glycated with glycolaldehyde. ARPE-19 cells were seeded on both AGE-Matrigel and Matrigel and grown to confluence, and serum was withdrawn for 3 days. RNA was extracted, and microarray analysis was performed to characterize the genes, which are altered by a matrix modified by AGEs. Gene expression changes were confirmed by RT-PCR/Southern and Northern blot analysis. Apoptosis was measured by annexin V/propidium iodide labeling. RESULTS: Clusters of genes with altered expression were found related to cell differentiation, growth factors that regulate the RPE cell and basement membrane, and apoptosis. RT-PCR/Southern and Northern blot analysis confirmed the expression patterns of selected genes, and flow cytometry showed increased annexin V/propidium iodide-labeled cells when grown on AGE-Matrigel. CONCLUSIONS: Microarray analysis identified clusters of genes that could promote an aging RPE phenotype in vitro induced by a matrix modified with AGEs.

Ultraviolet B-mediated phosphorylation of the small heat shock protein HSP27 in human keratinocytes.

Exposure of human keratinocytes to environmental stress is known to induce changes in the expression, phosphorylation, and subcellular relocalization of the 27 kDa heat shock protein. This study demonstrates that ultraviolet B (280-320 nM) irradiation with physiologic doses induces a dose-dependent phosphorylation of 27 kDa heat shock protein, generating the more acidic 27 kDa heat shock protein B, C, and D isoforms. Ultraviolet B also induces perinuclear cytoplasmic relocation and nuclear translocation of 27 kDa heat shock protein and caused aggregation of cytoplasmic actin filaments into a broad perinuclear distribution. The ultraviolet B-induced phosphorylation is reversible, returning to baseline levels 4 h after exposure, and this coincides with the reversal of ultraviolet B-induced actin reorganization. The ultraviolet B-induced phosphorylation is not affected by the protein kinase C inhibitor, GF 109203X, is partially inhibited by epidermal growth factor receptor tyrosine kinase inhibitor, PD 153035, and is substantially inhibited by the specific p38 mitogen-activated protein kinase inhibitor, SB 203580. In addition, pretreatment of cells with the anti-oxidant N-acetyl cysteine partially inhibits ultraviolet B-and oxidant-induced 27 kDa heat shock protein phosphorylation. The p38 mitogen-activated protein kinase cascade is thus the major transduction pathway for ultraviolet B-induced 27 kDa heat shock protein phosphorylation, and reactive oxygen species generated in response to ultraviolet B also contribute to this phosphorylation. As 27 kDa heat shock protein phosphorylation and relocalization has been associated with increased cell survival after environmental insult, our data suggest that ultraviolet B, in addition to initiating recognized cytotoxic events in keratinocytes, also initiates a signaling pathway that may provide cellular protection against this ubiquitous environmental insult.

DC electric fields induce rapid directional migration in cultured human corneal epithelial cells.

After an epithelium is wounded, multiple soluble and extracellular matrix-associated signals induce a repair response. An often-overlooked signal is the endogenous electrical field established in the vicinity of the wound immediately upon disruption of epithelial integrity. Previous studies have detected lateral electric fields of approximately 42 mV mm-1 near bovine corneal wounds. In addition, electric fields on the order of 100-200 mV mm-1 have been measured lateral to wounds in mammalian epidermis. Here we report the migratory response of human corneal epithelial cells to DC electric fields of similar, physiologic magnitude. Our findings demonstrate that in a 100 mV mm-1 DC field, corneal epithelial cells demonstrate directed migration towards the cathode. The migratory speed and distances traversed by cultured human corneal epithelial cells is remarkably similar to those of cultured skin-derived keratinocytes under similar conditions; however, corneal epithelial cells demonstrate a more rapid directional response to the field than keratinocytes. These findings suggest that endogenous, wound-induced electric fields present in the cornea play an important role in human corneal wound healing, by orienting the directional response of migratory cells so that they efficiently re-epithelialize the wounded area.

Development of a polyclonal antibody with broad epitope specificity for advanced glycation endproducts and localization of these epitopes in Bruch's membrane of the aging eye.

PURPOSE: To develop an antibody that recognizes a variety of advanced glycation endproduct (AGE) epitopes. METHODS: Glycolaldehyde was used to modify bovine serum albumin and HPLC analysis was used to measure pentosidine formation as an indicator of AGE formation. A polyclonal anti-AGE antibody was synthesized by injecting glycolaldehyde-incubated keyhole limpet hemocyanin into rabbits, affinity purified using AGE modified bovine serum albumin coupled to an affinity resin column, and characterized by immunoblot analysis. RESULTS: HPLC analysis of glycolaldehyde treated bovine serum albumin detected high levels of pentosidine formation, suggesting that glycolaldehyde is a potent precursor for pentosidine. By immunoblot analysis, our antibody recognized carboxymethyllysine and pentosidine, two well-characterized AGEs, as well as other AGE epitopes. Immunohistochemical evaluation showed evidence of AGEs in Bruch's membrane (including basal laminar deposits and drusen), choroidal extracellular matrix, and vessel walls in an 82 year old nondiabetic globe. A similar staining pattern was observed in an age-matched diabetic control. In contrast, no staining was seen with the antibody in a 20 month old nondiabetic globe. CONCLUSIONS: A unique anti-AGE antibody was synthesized that recognizes a variety of AGE epitopes including carboxymethyllysine and pentosidine. Its best use might be in broad surveys of the age-dependent accumulation of a large number of AGE epitopes that might not be revealed by antibodies to pentosidine or CML.

Migration of human keratinocytes in electric fields requires growth factors and extracellular calcium.

Currents that leak out of wounds generate electric fields lateral to the wound. These fields induce directional locomotion of human keratinocytes in vitro and may promote wound healing in vivo. We have examined the effects of growth factors and calcium, normally present in culture medium and the wound fluid, on the directional migration of human keratinocytes in culture. In electric fields of physiologic strength (100 mV per mm), keratinocytes migrated directionally towards the cathode at a rate of about 1 microm per min. This directional migration requires several growth factors. In the absence of these growth factors, the cell migration rate decreased but directionality was maintained. Epidermal growth factor alone restored cell migration rates at concentrations as low as 0.2 ng per ml. Insulin at 5-100 microg per ml or bovine pituitary extract at 0.2%-2% vol/vol also stimulated keratinocyte motility but was not sufficient to fully restore the migration rate. Keratinocyte migration in electric fields requires extracellular calcium. Changes in calcium concentrations from 3 microM to 3.3 mM did not significantly change keratinocyte migration rate nor directionality in electric fields; however, addition of the chelator ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to migration medium reduced, and eventually abolished, keratinocyte motility. Our results show that (i) growth factors and extracellular calcium are required for electric field-induced directional migration of human keratinocytes, and (ii) keratinocytes migrate equally well in low and high calcium media.