Possible role of sialylation of retinal protein glycans in the regulation of electroretinogram response in mice.

AIM: To evaluate if the nature, degree and extent of Siaα2-3-/Siaα2-6-sialylation of retinal protein glycans plays a possible role in the development and regulation of electroretinogram response (ERG) in mice. METHODS: Proteins extracted, from retinae of postnatal day 2 (PN2), PN7, and PN14 wild type (wt) and retinal degeneration 1 (rd1) mice were quantified, labeled and used for lectin-microarray profiling with immobilized lectins which recognize a wide range of N-/O-glycans. Net fluorescence intensities of lectin-ligand complexes were measured and images of fluorescent lectin-microarrays were acquired. From the binding curves between each lectin and protein extracts from PN14 wt and PN14 rd1 mice retinae, the protein concentration was selected to determine optimum signal intensity for lectin-ligand binding. Mean±SEM values of proteins and fluorescence-intensities of lectin-ligand-complexes between 45 lectins and 36 protein extracts from wt and rd1 mice retinae were compared for significance of differences. RESULTS: Comparison of the progressive relative changes in the sialylated glycans of retinal proteins from wt and rd1 mice showed that Siaα2-3Galß1-4GlcNAc-glycans (but not Siaα2-6-glycans) were detectable and quantifiable from the retinal-proteins of PN7 and PN14 wt and rd1 mice. Siaα2-3-sialylation of retinal-protein Gal/α-linked-Gal-glycans was significantly increased with age in PN7 and PN14 wt and less so in PN14 rd1 mice. Siaα2-3-/Siaα2-6-sialylation of retinal-protein Gal/α-linked-Gal-glycans was absent in PN2 wt and rd1 mice. Comparison of published ERG responses of wt and rd1 mice retinae with degree of Siaα2-3-sialylation of retinal-protein-glycans showed that PN2 wt and rd1 mice lack both the ERG response and Siaα2-3-/Siaα2-6-sialylation of retinal-protein Gal/α-linked-Gal-glycans; rd1 mice with relatively lower Siaα2-3-sialylation of retinal-protein Gal/α-linked-Gal-glycans showed aberrant ERG response; and wt mice with significantly higher Siaα2-3-sialylation of retinal-protein Gal/α-linked-Gal-glycans showed normal ERG response. CONCLUSION: Degree of Siaα2-3-sialylation of glycans possibly regulates ERG function in mice.

Lectin microarray profiling and relative quantification of glycome associated with proteins of neonatal wt and rd1 mice retinae.

PURPOSE: Progressive dynamic, relative quantitative changes were compared in glycans associated with retinal proteins of wild type (wt) and retinal degeneration 1 (rd1) mice during neonatal development and degeneration of retinae. METHODS: Proteins extracted from retinae of postnatal days 2 (PN2), PN7, and PN14 wt and rd1 mice were labeled with Cy3-fluorescent dye. Glycome of these proteins was quantified relatively by lectin microarray technique. Net fluorescence emitted by individual complexes formed between 45 lectins and Cy3-labeled proteins was measured by evanescent-field fluorescence-assisted microarray reader. RESULTS: GlcNAcß1-oligomer and high-mannose/Manα1-6Man were major glycans associated with the proteins of PN2, PN7, and PN14 wt and rd1 mice retinae. Gal/GalNAc/Man3-core-bi-/tri-antennary-complex, Sia2-3Galß1-4GlcNAc, and high-mannose glycans were conjugated mainly to proteins from PN7 rd1 and PN14 wt retinae, respectively. With increasing neonatal age, mannosylated, GlcNAcß, and sialylated (minor component) glycans were increased, and fucosylated GlcNAc/Galß glycans were decreased significantly in wt retinal proteins. This trend was less evident in PN14 rd1 retinal proteins. Mouse retina was almost devoid of Siaα2-6 (except WGA bound Sia), Fucα1-2, and Gal/GalNAc-containing glycans. STL reacting GlcNAc oligomers were high in PN2 rd1 retinae. CONCLUSIONS: Quantitative dynamic, relative variation in high-mannose and GlcNAc glycans, Siaα2-3Galß1-4GlcNAc associated with proteins from PN2, PN7, and PN14 wt and rd1 mice retinae suggested that these glycans participate in retinal development and degeneration, and may be used as markers for retinal electrophysiologic integrity during transplantation/therapy studies; Siaα2-3Galß1-4GlcNAc-specific Agrocybe cylindracea lectin and other lectins may be used to enrich/purify retinal ribbon synapse glycoproteins and other glycoproteins including rhodopsin. Further investigations are required.

Antioxidants rescue photoreceptors in rd1 mice: Relationship with thiol metabolism.

We have previously shown that the use of a combination of antioxidants delayed the degeneration process in rd1 mouse retina. In an effort to understand the mechanism of action of these substances (zeaxanthin, lutein, alpha-lipoic acid, glutathione, and Lycium barbarum extract) the changes in the levels of several proteins and oxidative stress markers in the rd1 retina have been studied. The treatment increased glutathione peroxidase activity and glutathione levels and decreased cystine concentrations in rd1 retinas. Considering all the results obtained from treated and untreated animals, a high correlation was present between glutathione concentration and glutathione peroxidase activity, and there was a negative correlation between glutathione retinal concentration and number of TUNEL-positive cells. No difference was observed between the numbers of nNOS- and NADPH-diaphorase-positive cells in treated and untreated rd1 mice. Thiol contents and thiol-dependent peroxide metabolism seem to be directly related to the survival of photoreceptors in rd1 mouse retina.

rd1 Mouse retina shows an imbalance in the activity of cysteine protease cathepsins and their endogenous inhibitor cystatin C.

PURPOSE: To compare in vivo levels, spatial localization, and in vitro secretion of cysteine protease cathepsins and cystatin C (cysC) in the retinal degeneration 1 (rd1) mouse model of retinitis pigmentosa and control (wt) mouse retinas. METHODS: The spatial localization, protein contents, cysC levels and cathepsin-B, -S, and -L activities in wt and rd1 retinas at postnatal (PN) days 2, 7, 14, 21, and 28 were analyzed by immunostaining, spectrophotometry, ELISA, and fluorescence spectrophotometry. The in vitro secretion of cysC and cysteine proteases by PN7 retinal explants into the conditioned medium (RCM) was quantified. RESULTS: The pigment epithelium, photoreceptors, and inner retinal and ganglion cell layers of both wt and rd1 retinas showed cysC and cathepsin-B labeling. CysC immunostaining was extensive in the optic nerve head fibers. The rd1 explants secreted higher amounts of cysteine protease into the RCM. The protein content in wt and rd1 retinal extracts increased up to PN14, then decreased in rd1 but not in wt. In rd1 extracts at PN14 to -28, cathepsin activity was higher and increased with age, but the cysC level was higher and constant. The ratios of cathepsin activity to cysC (cathepsin-L at PN2 and total, -B, and -L at PN14 to -28) were higher in rd1 extracts. CONCLUSIONS: Similar localization of both cathepsin-B and cysC in wt and rd1 retinas along with lower proteins and higher cathepsin activity in rd1 retinal extracts and RCM are consistent with their localization in extracellular matrix and a role in physiopathologic remodeling in wt and rd1 retinas.

Low glutathione peroxidase in rd1 mouse retina increases oxidative stress and proteases.

Malondialdehyde, reduced glutathione, glutathione peroxidase, glutathione reductase and cysteine protease cathepsins at postnatal (PN) days 2, 7, 14, 21 and 28 in controls (wt) and the retinal degeneration 1 (rd1) mouse model for retinitis pigmentosa retinas were measured to determine oxidative stress. In PN28 wt and PN2 rd1 retinas, elevated malondialdehyde and low glutathione peroxidase activity indicate higher oxidative load, despite higher reduced glutathione in PN2 rd1 retinas. This is due to physiological exposure to light and retinal vascular/neural restructuring, respectively. Compared with wt retinas, relatively high malondialdehyde at PN2 and cathepsin levels at PN14, 21 and 28 in rd1 retinas indicate that cells of the residual inner retina also contribute to the oxidative stress and retinal degeneration.

Prediction of solubility on recombinant expression of Plasmodium falciparum erythrocyte membrane protein 1 domains in Escherichia coli.

BACKGROUND: Cellular interactions elicited by Plasmodium falciparum erythrocyte membrane protein antigen 1 (PfEMP1) are brought about by multiple DBL (Duffy binding like), CIDR (cysteine-rich interdomain region) and C2 domain types. Elucidation of the functional and structural characteristics of these domains is contingent on the abundant availability of recombinant protein in a soluble form. A priori prediction of PfEMP1 domains of the 3D7 genome strain, most likely to be expressed in the soluble form in Escherichia coli was computed and proven experimentally. METHODS: A computational analysis correlating sequence-dependent features to likelihood for expression in soluble form was computed and predictions were validated by the colony filtration blot method for rapid identification of soluble protein expression in E. coli. RESULTS: Solubility predictions for all constituent PfEMP1 domains in the decreasing order of their probability to be expressed in a soluble form (% mean solubility) are as follows: ATS (56.7%) > CIDR1alpha (46.8%) > CIDR2beta (42.9%) > DBL2-4gamma (31.7%) > DBL2beta + C2 (30.6%) > DBL1alpha (24.9%) > DBL2-7epsilon (23.1%) > DBL2-5delta (14.8%). The length of the domains does not correlate to their probability for successful expression in the soluble form. Immunoblot analysis probing for soluble protein confirmed the differential in solubility predictions. CONCLUSION: The acidic terminal segment (ATS) and CIDR alpha/beta domain types are suitable for recombinant expression in E. coli while all DBL subtypes (alpha, beta, gamma, delta, epsilon) are a poor choice for obtaining soluble protein on recombinant expression in E. coli. This study has relevance for researchers pursuing functional and structural studies on PfEMP1 domains.

rd1 mouse retina shows imbalance in cellular distribution and levels of TIMP-1/MMP-9, TIMP-2/MMP-2 and sulfated glycosaminoglycans.

BACKGROUND: The rd1 mouse retina displays fast degeneration of photoreceptors resulting in a depletion of almost all rod photoreceptors by postnatal day 21 (PN21). To evaluate the role of proteinases in the pathophysiology of this animal model of retinitis pigmentosa, C3H rd1 and congenic wild-type (wt) mice retinas were analyzed. MATERIAL AND METHODS: The cellular localization and levels of proteins, matrix metalloproteinases (MMPs), their endogenous inhibitors (TIMPs), total sulfated glycosaminoglycans (sGAG) and nature of saccharides in rd1 and wt retinal extracts were compared. RESULTS: MMP-2/TIMP-2 and MMP-9/TIMP-1 were predominantly localized in the interphotoreceptor matrix (IPM) of both genotypes, but MMP-2/TIMP-2 also appeared in the Muller cell fibers of rd1 retina. In rd1 retinal extracts the levels of total proteins were lower and those of active MMP-9, MMP-2, TIMP-1 and total sGAG were higher than those of wt extracts. Despite an increase in TIMP-1, active MMP-9/MMP-2 were disproportionately elevated in rd1 compared to wt retina. With increasing age, MMPs in wt retinas were decreased but were increased in rd1. The sialylation of proteoglycans in PN2 and PN7 rd1 retinas was lower, and galactosylation was higher than that in wt retinas. CONCLUSIONS: MMP-9/MMP-2 and TIMP-1/TIMP-2 are associated with IPM, possibly after secretion by retinal pigmented epithelial cells. In degenerating rd1 retina, MMP-2/TIMP-2 are associated with the Muller cell fibers, which apparently play a central role in modifying the balance between MMPs and TIMPs. Elevated sGAG and proteolysis due to an imbalance in the levels of TIMPs and active MMP-9/MMP-2 in rd1 retina possibly contribute to retinal degeneration in the rd1 mouse.