A beta2-microglobulin cleavage variant fibrillates at near-physiological pH.

Beta2-microglobulin (beta2m) deposits as amyloid in dialysis-related amyloidosis (DRA), predominantly in joints. The molecular mechanisms underlying the amyloidogenicity of beta2m are still largely unknown. In vitro, acidic conditions, pH < 4.5, induce amyloid fibrillation of native beta2m within several days. Here, we show that amyloid fibrils are generated in less than an hour when a cleavage variant of beta2m--found in the circulation of many dialysis patients--is exposed to pH levels (pH 6.6) occurring in joints during inflammation. Aggregation and fibrillation, including seeding effects with intact, native beta2m were studied by Thioflavin T fluorescence spectroscopy, turbidimetry, capillary electrophoresis, and electron microscopy. We conclude that a biologically relevant variant of beta2m is amyloidogenic at slightly acidic pH. Also, only a very small amount of preformed fibrils of this variant is required to induce fibrillation of native beta2m. This may explain the apparent lack of detectable amounts of the variant beta2m in extracts of amyloid from DRA patients.

Vitreous humor and albumin augment the proliferation of cultured retinal precursor cells.

Intravitreal injection is an important delivery route for studies involving the transplantation of various types of precursor cells to the retina; however, the effect on these cells of exposure to the vitreous microenvironment has not been specifically investigated. Here vitreous humor was evaluated for the potential to influence the proliferation of rat retinal precursor cells in vitro. Cells were isolated at embryonic day 19 and plated in standard proliferation medium in the presence or absence of fluid expressed from porcine vitreous humor. Cellular proliferation at different concentrations of vitreous fluid supplementation was quantified by using a (3)H-thymidine incorporation assay. Active components of vitreous fluid were partially characterized by gel filtration chromatography (GFC) and UV spectral analysis. The effect of each vitreous fraction on proliferation was determined as well. Results showed that addition of 20% vitreous fluid to primary rat retinal cultures significantly increased (3)H-thymidine incorporation compared with growth medium without vitreous supplementation. A vitreous fraction showing growth-promoting activity was localized to a molecular mass range <1000 Da, consistent with ascorbic acid. Ascorbic acid was confirmed in vitreous fluid by UV spectral analysis. Growth-augmenting activity was present in higher molecular mass vitreous fractions, consistent with protein components. Albumin, the major protein in vitreous fluid, was found to augment proliferation. Because vitreous-associated augmentation of retinal precursor proliferation remains an epidermal growth factor-dependent phenomenon, the proliferative status of transplanted cells in the vitreous cavity is likely determined by a combination of factors.

Identification of MHC class I H-2 Kb/Db-restricted immunogenic peptides derived from retinal proteins.

PURPOSE: To identify H-2 Kb/Db-binding immunogenic peptides derived from retinal proteins. METHODS: Computer-based prediction was used to identify potentially H-2 Kb/Db-binding peptides derived from the interphotoreceptor retinol-binding protein (IRBP), soluble retinal antigen (S-antigen), recoverin, phosducin, and pigment epithelium-derived factor (PEDF). The affinity of the peptides was analyzed by their abilities to upregulate the expression of major histocompatibility complex (MHC) class I on TAP-deficient cells (RMA-S cells) with flow cytometry. C57BL/6 mice were immunized subcutaneously, with individual peptides in incomplete Freund's adjuvant (IFA). Eight days after immunization, splenocytes were isolated for cytotoxic T-lymphocyte (CTL) analysis. A 51chromium-release assay was used to detect specific CTL reactivity generated in the cultures. Eyes were enucleated for histopathological analysis on day 21 after immunization with IRBP or IRBP and the immunogenic peptides. RESULTS: All the 21 predicted peptides were found to upregulate expression of H-2 Kb/Db on RMA-S cells. Five peptides, the two IRBP-derived peptides IRBP89-96 and IRBP(101-108), and the three PEDF-derived peptides, PEDF389-397, PEDF139-147, and PEDF272-279, induced specific CTL responses in vivo, whereas the remaining 16 peptides, including 5 IRBP-derived peptides, 5 S-antigen-derived peptides, 1 recoverin-derived peptide, 1 phosducin-derived peptide, and 4 PEDF-derived peptides, did not induce specific CTL reactivity. The immunogenic peptides alone did not induce inflammation in the eyes, but they could enhance severity of uveitis induced by IRBP. CONCLUSIONS: Five of 21 H-2 Kb/Db-binding retinal protein-derived peptides were found to be immunogenic, suggesting that these peptides could function as autoantigenic epitopes in the development of inflammatory eye diseases, such as uveitis.

Aqueous humor enhances the proliferation of rat retinal precursor cells in culture, and this effect is partially reproduced by ascorbic acid.

Aqueous humor has been shown to influence the proliferation of various ocular cell types, but the effect on immature retinal cells is not known. Here, the effect of pig aqueous humor on the proliferation of rat retinal precursor cells (RPCs) was investigated. RPCs were prepared from embryonic day 19 Sprague-Dawley rats and cultured in the presence or absence of aqueous humor from healthy pigs along with a medium consisting of Dulbecco's modified Eagle's medium:Ham's F-12 medium, N2 supplement, and epidermal growth factor. Proliferation was quantified by [(3)H]thymidine incorporation under different treatment conditions, and any associated morphological changes were noted. Potential active components of porcine aqueous humor were partially characterized by gel filtration chromatography, and the effect on RPC proliferation was determined. Results showed that adding 20% aqueous humor increased [(3)H]thymidine incorporation by as much as 317%, as compared with controls. Aqueous supplementation also increased both the number and size of RPC spherical aggregates ("spheres") over the first 4 days, consistent with increased proliferative activity. Using gel filtration and the in vitro proliferation assay, the growth-promoting activity of aqueous humor was localized to two different molecular mass ranges, namely, around 30 kDa and less than 1 kDa. Ascorbic acid was present in the lower molecular mass fraction, and use of this molecule reproduced some, but not all, of the proliferative activity present in aqueous humor. These results highlight the potential role of soluble factors present in the cellular microenvironment with respect to modulation of endogenous progenitor cell activity.