Lysosomal behavior in the retina and choroid of spontaneously dystrophic rats

Controlled production of active cathepsin D in retinal pigment epithelial cells following adenovirus-mediated gene delivery

The transduction of a low cathepsin D-producing retinal pigment epithelial cell line with a recombinant adenovirus, Ad.proCatD, carrying a viral promoter and the precursor form of the lysosomal enzyme cathepsin D, procathepsin D, led to the upregulation of proCatD expression. However, the resultant aspartic protease activity did not exceed that observed in normal primary human retinal pigment epithelial cells. Following the injection of Ad. proCatD into rat eyes, immunohistochemistry and Western blot analysis localized the expression of procathepsin D to the retinal pigment epithelial cell layer and to the sclera/choroid/retinal epithelial cell layers, respectively. This upregulation of procathepsin D expression was accompanied by a limited increase in aspartic protease activity. The injected eyes did not demonstrate any of the retinal changes that have been associated with the overproduction and secretion of active cathepsin D. Immunoelectronmicroscopy of Ad.proCatD-transduced retinal pigment epithelial cells demonstrated the presence of cathepsin D not only in cytoplasmic vesicles and lysosomes but also in the nucleoli and, less strongly, elsewhere in euchromatic regions of some 10% of cells. In spite of the upregulated expression of procathepsin D, the production of active cathepsin D in Ad.proCatD-transduced retinal pigment epithelial cells was strictly controlled. It is proposed that active cathepsin D production is controlled at the point of posttranslational modification by an intranuclear feedback mechanism initiated by the relative excess of procathepsin D in Ad. proCatD-transduced retinal pigment epithelial cells.

Distribution of cathepsin D in human eyes with or without age-related maculopathy

Cathepsin D is a ubiquitous enzyme which plays an important role in the catabolism of proteins. Enzymatic studies showed that cathepsin D is the most important lysosomal enzyme in the proteolysis of opsin. The importance of cathepsin D in the lysosomal digestion of phagocytosed photoreceptor outer segments by the retinal pigment epithelium suggests that a decrease in cathepsin D activity might contribute to the development of hyalinized drusen and to the development of age-related maculopathy. The aim of this project was to study the immunohistochemical localization of cathepsin D in human eyes and particularly to compare the immunoreactivity of cathepsin D normal retinal pigment epithelial cells and in cells surrounding hyalinized drusen or lesions of age-related maculopathy. Following clinicopathological examinations the eyes were fixed, paraffin embedded and individual sections were subjected to Picro-Mallory staining for histopathological examination. Bleaching was performed then immunohistochemistry was carried out using a monoclonal mouse anti-human cathepsin D antibody. On the basis of the appearance of basal laminar deposit the eyes were divided into five groups corresponding to levels of progression in age-related maculopathy development. Following optimization of bleaching cathepsin D immunostaining was clearly visible in the iris epithelium, ciliary body and the retinal pigment epithelial layer of all eyes with the highest immunoreactivity present in the RPE cells. Within the neural retina the ganglion cells demonstrated a weak signal. Retinal pigment epithelial cathepsin D immunoreactivity was not impaired by age, geographical location or by age-related maculopathy status. There was a small increase in cathepsin D immunoreactivity around hyalinized drusen. The maintenance of cathepsin D immunoreactivity in eyes with hyalinized drusen or in samples with age-related maculopathy suggest that down-regulation of cathepsin D expression in the affected locations does not precede the development of these conditions. However, further studies are required to establish if the immunoreactive cathepsin D represents the fully processed biologically active enzyme.

Gene expression of proteases and protease inhibitors in the human ciliary epithelium and ODM-2 cells

Complementary DNAs (cDNAs), corresponding to the human proteinases cathepsins D and O and proteinase inhibitors alpha2-macroglobulin and PP5/TFPI-2, have recently been isolated and identified from a subtractive human ciliary body library. In the present study we determined: (i) their pattern of expression in the human eye; (ii) the ability of the ciliary body and/or ciliary epithelial cells to synthesize and secrete cathepsin D and alpha1-antitrypsin in vitro; and (iii) whether alpha1-antitrypsin expression in cultured ciliary epithelial cells is modulated by protein kinase C activation. Northern analysis demonstrated that the ciliary body expresses high levels of cathepsins D and O, alpha2-macroglobulin, alpha1-antitrypsin and PP5/TFPI-2 transcripts. Western blot analysis and immunoprecipitation experiments with cathepsin D and alpha1-antitrypsin antibodies indicated that metabolically labeled ciliary body explants and/or ciliary epithelial cells in vitro with 35S-methionine, synthesize and secrete these proteins. Cultured nonpigmented ciliary epithelial ODM-2 cells, in response to phorbol-12-myristate 13-acetate (PMA), but not to the non-protein kinase C binding phorbol ester 4 alpha-phorbol didecanoate (PDBu), elicited up-regulation (up to 5-fold) of transcription, synthesis and secretion of alpha1-antitrypsin. These results provide in vitro evidence that the ciliary epithelium synthesizes and secretes a selective group of proteinases and proteinase inhibitors detected also in aqueous humor. The expression of at least of one of the proteinase inhibitors, alpha1-antitrypsin, can be modulated in response to phorbol ester.

Localization of lysosomal enzymes in the retina and retinal pigment epithelium of RCS rats

Using ultrahistochemical and immunohistochemical techniques, localization of acid phosphatase and cathepsin D was demonstrated in the retina and pigment epithelium of 1 to 42 day old RCS rats and its nonaffected congenic rat strain. Both enzymes are present in the pigment epithelium of the normal and dystrophic rat eye. As early as the age of 1 week, it was found that the lysosomes in the dystrophic rat retina are less stable in releasing acid phosphatase than those of control animals. Infiltration of cathepsin D into the subretinal space could first be detected with certainty in 2-week-old animals. The fragility of the lysosomal membrane and, therefore, the release of both enzymes became more pronounced as the animals aged. The findings of this study indicate that the instability of the lysosomal membrane in the RCS rat pigment epithelium may initiate degeneration of photoreceptors and pigment epithelium. The demonstration of cathepsin D activity has proved very helpful in revealing the physiological or pathophysiological condition of retinal pigment epithelium.

Effect of temperature and pH on release of enzymes from lysosomes of the bovine retinal pigment epithelium in vitro

The effects of buffer concentrations, pH, and temperatures on the release of enzymes from lysosomes of the bovine retinal pigment epithelium were studied in vitro. Cathepsin D, arylsulfatase, and acid phosphatase were used as lysosomal marker enzymes. Elevation of temperature caused a marked increase in the release of cathepsin D and arylsulfatase from lysosomes, but little changes in the release of acid phosphatase. Acidic conditions accelerated the release of arylsulfatase and acid phosphatase. Different buffer concentrations had little effect on the release of these enzymes from lysosomes.

Lysosomal enzymes in ocular tissues and diseases

Lysosomal enzymes are distributed widely in various ocular tissues. Among these tissues, the uvea and retina show the higher enzyme activities of acid phosphates, beta-blucuronidase, alpha-fucosidase, alpha-mannosidase, arylsulfatase, cathepsin D, cathepsin B and others. The particular role of lysosomal enzymes in the pathogenic processes of ocular diseases such as storage disease, uveitis, retinal degeneration, retinal detachment, corneal dystrophy and glaucoma is strongly suggested. The enzymes also have additional importance in ocular physiopathology.

Regional distribution of lysosomal enzymes in the retina and choroid of human eyes

Regional distribution of lysosomal enzymes in the retina and choroid of human eyes was studied biochemically. Specific activities of acid phosphatase, cathepsin D, and arylsulfatase in the retina and choroid varied by area were also studied. The macular area showed the highest activities in comparison to other areas.

Lysosomal enzymes in the serum of patients with with Behçet's disease

Samples of serum from patients with ocular manifestation of Behçet's disease of various types were analyzed using acid phosphatase and beta-glucuronidase as lysosomal marker enzymes, in comparison to those from control patients with myopia, retinal detachment, and uveitis of unknown etiology. The lysosomal enzyme activities in Behçet's disease, especially in the attack phase, were found to be higher than those of the controls. In the sera of two patients with Behçet's disease, the activities in the attack phase were slightly higher than in the remission phase. It was suggested that the ocular symptoms in Behçet's disease might represent exacerbation better than other symptoms, in view of the high lysosomal enzyme activities in the attack phase, as classified by ocular symptoms alone.