The aim of this study was to compare the protein profile of vitreous fluid from diabetic patients with proliferative diabetic retinopathy (PDR) with that from non-diabetic patients with idiopathic macular holes (MH). The mRNA of proteins differentially produced was also assessed in the retinas from diabetic and non-diabetic donors.
Materials and methods
Vitreous humour from type 1 diabetic patients with PDR (n = 8) and from non-diabetic patients with MH (n = 10) closely matched in terms of age were studied. The comparative proteomic analysis was performed using fluorescence-based difference gel electrophoresis (DIGE). Differentially produced proteins (abundance ratio >1.4, p < 0.05) were identified by mass spectrometry. Expressions of mRNA were measured by real-time RT-PCR in retinas from ten human eyes obtained at post-mortem (five eyes from diabetic subjects and five eyes from non-diabetic subjects).
Eight proteins were highly produced in PDR patients in comparison with non-diabetic subjects: zinc-α2-glycoprotein (ZAG), apolipoprotein (apo) A1, apoH, fibrinogen A, and the complement factors C3, C4b, C9 and factor B). We found three proteins that were underproduced in PDR subjects: pigment epithelial derived factor (PEDF), interstitial retinol-binding protein (IRBP) and inter-α-trypsin inhibitor heavy chain (ITIH2). There was no overlap in the vitreous levels of the above-mentioned proteins between PDR patients and non-diabetic control subjects. The differential production of ZAG, C3, factor B, PEDF and IRBP was further confirmed by western blot, and was in agreement with mRNA levels detected in the retina.
Proteomic analysis by DIGE, which permits an accurate quantitative comparison, was useful in identifying new potential candidates involved in the pathogenesis of PDR.
Proliferative diabetic retinopathy (PDR) is a leading cause of blindness and visual impairment among adults aged <40 years in the developed world . Investigations into the processes involved in PDR and the testing of new therapies are limited because of the unavailability of human retina samples and the lack of diabetic animal models that faithfully replicate the features of human PDR. In this regard, vitreous fluid obtained from diabetic patients undergoing vitreoretinal surgery is currently used as a surrogate for the retina in clinical research. However, there are two main confounding factors that could lead to misinterpretation of the results. First, vitreous haemorrhage, which often occurs in PDR, can produce a massive influx of serum proteins, thus precluding the usefulness of the vitreous fluid when studying the intraocular production of a particular protein. Second, the disruption of the blood–retina barrier that occurs in diabetic retinopathy produces an increase in proteins in the vitreous body of diabetic patients. Indeed, we have repeatedly detected three- to fourfold higher levels of intravitreal proteins in diabetic patients than in non-diabetic subjects [2–4]. Therefore, an elevated intravitreal level of a particular protein does not necessarily indicate an increase in intraocular production, and might simply reflect a non-specific increase in protein levels due to serum diffusion. In recent years, these problems have been solved by using a simple methodology that has enabled us to rationalise the use of vitreous fluid as a tool for assessing the intraocular production of various angiogenic and anti-angiogenic factors . Nonetheless, the volume of vitreous fluid obtained after vitrectomy is approximately 1 ml and, therefore, only a few peptides can be analysed simultaneously.
The recent development of proteome analysis has made it feasible to analyse protein profiles in various cells, tissues and body fluids with only a small sample . However, few proteome analyses in human vitreous fluid have been performed in the setting of diabetic eye disease [7–11], and no previous quantitative proteomic comparison has been reported. The aim of the present study was to compare the protein profile of human vitreous fluid from diabetic patients with PDR with that of vitreous fluid obtained from non-diabetic patients with idiopathic macular holes (MH), a condition in which, in contrast to PDR, the retina is not affected by neovascularisation. Apart from taking into account the main confounding factors, discussed above (vitreous haemorrhage and intravitreal protein concentration) subjects who had undergone laser photocoagulation in the preceding 6 months were excluded. This is because a significant alteration in the balance of intravitreal growth factors and transcriptional activity in the retina has been shown following this procedure . To carry out this comparative proteomic analysis, we used fluorescence-based difference gel electrophoresis (DIGE) . This technique provides an accurate quantitative comparison of the two groups of samples, allowing the identification of proteins whose levels differ significantly between the two conditions. We also measured the mRNA of proteins differentially produced in retinas from diabetic and non-diabetic donors.
Subjects and methods
Subjects and sample selection
Eight vitreous humours from type 1 diabetic patients with active PDR and ten vitreous humours from non-diabetic patients with macular hole (MH), closely matched in terms of age (48.7 ± 11 vs 48.3 ± 10 years; p = ns) were selected from our vitreous bank. The exclusion criteria were as follows: (1) previous vitreoretinal surgery; (2) photocoagulation in the preceding 6 months; (3) recent vitreous haemorrhage (<3 months before vitrectomy) or intravitreous haemoglobin >5 mg/ml; (4) renal failure (creatinine ≥120 μmol/l); and (5) other chronic diseases apart from diabetes. Details of vitrectomy and sample collection have been described previously elsewhere .
Five eyes were obtained at post-mortem from diabetic donors who were free from fundoscopic abnormalities in ophthalmological examinations performed during the preceding 2 years. Five eyecups obtained from non-diabetic donors matched in terms of age were used as the control group. The time elapsed from death to eye enucleation was less than 6 h. After enucleation, eyes were snap-frozen in liquid nitrogen and stored at −80°C.
The protocol for sample collection was approved by the hospital ethics committee, and informed consent was obtained from the patients. The study was conducted in accordance with the principles of the Declaration of Helsinki.
Vitreous haemoglobin and total protein content
Vitreous haemoglobin and intravitreal protein levels were measured by spectrophotometry and microturbidimetry, respectively. The detailed procedures are described in the Electronic supplementary material.
Sample preparation for two-dimensional gel electrophoresis proteomic analysis
Samples for the proteomic analysis were prepared from four vitreous humours from PDR patients and from six vitreous humours from non-diabetic patients with MH. Samples were concentrated by ultrafiltration. Affinity chromatography was used to remove albumin and IgG from the samples, which were then further purified by acetone precipitation. The detailed procedures are described in the Electronic supplementary material.
Protein concentration was adjusted to 2 mg/ml by the addition of a DIGE labelling buffer (7 mol/l urea, 2 mol/l thiourea, 4% w/v 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate [CHAPS], 30 mmol/l Tris, pH 8.0). A pool consisting of equal amounts of each of the samples analysed in the experiment was prepared as an internal standard for quantitative comparisons . To avoid any possible bias introduced by labelling efficiency, half of the samples from each group were labelled with Cy3 dye and the other half with Cy5 dye. A third fluorescent dye, Cy2, was used to label the internal standard sample. Labelling was carried out by the addition of 400 pmol of the required Cy dye in 1 μl of anhydrous N,N-dimethylformamide per 50 μg of protein. After 30 min of incubation on ice in the dark, the reaction was quenched with 10 mmol/l lysine and the samples incubated for a further 10 min. Samples were combined according to the experimental design, using 50 μg of protein per Cy dye per gel, and diluted twofold with isoelectric focusing (IEF) sample buffer (7 mol/l urea, 2 mol/l thiourea, 4% w/v CHAPS, 2% dithiothreitol [DTT], 2% pharmalytes, pH 3–10). One PDR and one MH sample, together with an aliquot of the internal standard pool, were then separated by two-dimensional electrophoresis (2-DE) in each of the gels (Fig. 1). This experimental design allows the accurate quantification and statistical assessment of the differences in protein abundances observed between the two sample groups .
2-DE was performed using reagents and equipment from GE Healthcare (Fairfield, CT, USA) (for details see the Electronic supplementary material).
Fluorescence images of the gels were obtained on a Typhoon 9400 scanner (GE Healthcare). Cy2, Cy3 and Cy5 images were scanned at excitation/emission wavelengths of 488/520 nm, 532/580 nm and 633/670 nm, respectively, at a resolution of 100 μm. Both image analysis and statistical quantification of relative protein levels were performed using DeCyder v. 5.0 software (GE Healthcare).
Protein identification by mass spectrometry
Protein spots of interest were excised from the gel using an automated spot picker (GE Healthcare). In-gel trypsin digestion was performed as described previously , using autolysis-stabilised trypsin (Promega, Madison, WI, USA). Tryptic digests were purified using ZipTip microtitre plates (Millipore, Billerica, MA, USA).
Peptide mass fingerprint by matrix-assisted laser desorption ionisation-mass spectrometry (MALDI-MS) was used for protein identification. The detailed procedures are described in the Electronic supplementary material.
Western blot analysis
Aliquots of samples used in the DIGE experiments were analysed by western blotting to investigate five of the proteins shown by DIGE to be differentially produced in vitreous fluid from PDR patients as compared with vitreous fluid from non-diabetic patients with MH (zinc-α2-glycoprotein [ZAG], C3, factor B, pigment epithelial-derived factor [PEDF] and interstitial retinol-l-binding protein [IRBP]). To further evaluate the reproducibility of DIGE, eight additional vitreous samples (four PDR and four MH) were analysed by western blot analysis. For normalisation purposes, an equivalent amount (5 μg) of soluble protein from vitreous fluid was loaded onto the gel. The detailed procedures are described in the Electronic supplementary material. Western blot analysis of ZAG, C3, factor B, PEDF and IRBP was also performed in serum obtained during vitrectomy according to this protocol.
Quantitative real-time RT-PCR
Total RNA was extracted from isolated retinal tissues using the RNeasy Mini Kit with DNAse digestion (Qiagen Distributors, IZASA, Barcelona, Spain) according to the manufacturer’s instructions. A 1 μg sample of total RNA was used directly for reverse transcription, which was carried out using random hexanucleotide primers and TaqMan Reverse Transcription Reagents (Applied Biosystems, Madrid, Spain) in a 50 μl reaction volume, according to the protocol provided by Applied Biosystems.
Quantitative real-time RT-PCR using specific primers (TaqMan pre-made gene expression assay Hs0017267; Applied Biosystems; Gene Bank RefSeq NM 000799.2) was performed, using 2 μl of the reverse transcription reaction as a template in a PCR reaction set up with the TaqMan Universal Mastermix. After 10 min at 95°C, the amplification reaction was carried out through 50 cycles (95°C for 15 s followed by 60°C for 60 s) using Applied Biosystems 7000 equipment. Each sample was assayed in duplicate, and negative controls were included in each experiment. Automatic Relative Quantification data were obtained using ABI Prism 7000 Sequence Detection System software (Applied Biosystems), using the gene for β-actin as an endogenous gene expression control (Hs9999903_m1; Applied Biosystems).
All values are expressed as means±SD. Statistical significance between groups was analysed using the unpaired Student’s t test. A p value of less than 0.05 was considered statistically significant.
The mean protein contents were 4.45 ± 1.4 mg/ml for PDR samples and 1.96 ± 0.5 mg/ml for MH samples. Following depletion of the two most abundant protein types—serum albumin and IgG—by affinity chromatography, approximately 20% of the total protein was recovered, with little variation between the different samples. Identical amounts of the depleted protein mixture were analysed for each group. It can therefore be reasonably assumed that the depletion procedure does not significantly alter the abundance ratios between the two groups of samples.
Approximately 1,400 protein spots were detected. Selecting an abundance ratio of PDR:control of 1.4-fold as the threshold for study, 41 spots were differentially produced (p < 0.05, Student’s t test) in the vitreous samples from PDR patients (28 of them showing an increase and 13 a decrease) compared with those from the MH control group. The corresponding gel spots were excised and digested in-gel with trypsin. Following MALDI-MS time-of-flight/time-of-flight analysis we were able to identify 11 proteins, the levels of eight of which were increased and three were decreased in the vitreous fluid of PDR patients compared with the vitreous fluid of MH patients (Table 1). Most of these proteins were identified in several spots, consistent with the presence of different post-translational modification forms, probably resulting from different glycosylation. Figure 1 shows the positions of the spots corresponding to the proteins with the highest changes in abundance. It should be noted that there was no overlap in vitreal protein levels between the two groups when the range of levels for each group was considered.
Among the proteins with decreased abundance, we identified PEDF, a protein with anti-angiogenic properties, which has previously been reported to be decreased in the vitreous fluid of PDR patients [15, 16]. The identification of this protein as decreased in abundance, as would be expected, provides an internal control for this comparative proteomic analysis. The other two proteins displaying decreases in abundance were IRBP and inter-α-trypsin inhibitor heavy chain-2 (ITIH2).
The proteins showing increases in abundance included fibrinogen A, ZAG, apolipoprotein (apo) A1, apoH and several members of the complement system (factor B, C3, C9 and C4-B). Complement C3 was identified at two different groups of spots with molecular masses of about 42 kDa and 75 kDa (average ratio PDR/MH 1.64 and 1.30, respectively), consistent with two of the bands observed by western blot analysis (see below). Regarding C4, a fragment of about 42 kDa was observed, which, according to the mass values of the peptides matching the sequence, can be assigned to fragment C4d-B (amino acids 957–1325).
Western blot analysis
To validate the results obtained in the proteomic study we selected five candidate proteins differentially produced in PDR patients to be directly assessed by western blotting. These proteins were ZAG, C3, factor B (which were overproduced in the vitreous fluid of PDR patients), PEDF and IRBP (which were underproduced in the vitreous fluid of PDR patients) (Figs. 2 and 3). These proteins were analysed in the samples used in DIGE and an additional set of four PDR and four MH vitreous samples.
ZAG, C3 (42 kDa fraction) and factor B (93 kDa fraction) were significantly higher in PDR patient samples than control group samples (9.57 ± 0.12 vs 6.99 ± 0.73, p = 0.003; 14.12 ± 0.21 vs 7.49 ± 0.29, p = 0.018; and 15.11 ± 3.12 vs 6.98 ± 1.34, p = 0.005; Fig. 2). Both C3 and factor B presented additional fragments, thus indicating the presence of their activation products. The patterns observed in our vitreous samples were consistent with the native α and β chains of C3 (115 and 75 kDa) and the presence of other smaller bands, with the 42 kDa fragment (corresponding to the breakdown of C3b ) being the most apparent. Factor B patterns showed a major band of 93 kDa and two fragments consistent with breakdown fragments of 63 kDa (Bb) and 30 kDa (Ba) .
By contrast, the intravitreous amounts of PEDF and IRBP were significantly lower in the PDR group than the control group (6.76 ± 0.97 vs 18.25 ± 8.9, p = 0.03; and 6.48 ± 0.79 vs 13.22 ± 4.98, p = 0.04; Fig. 3).
The average ratios of abundance determined for all the proteins assayed by western blot analysis were in very good agreement with those observed by DIGE proteomic analysis, as shown by plotting the changes observed by the two methodologies against each other (Fig. 4). This is particularly relevant given that one set of samples used for western blot analysis were different from those used for proteomic analysis. Additionally, this consistency supports the assumption that affinity depletion treatment does not significantly alter the quantitative comparison of the samples by DIGE analysis.
There were no differences between PDR patients and control subjects in serum amounts of the proteins analysed (Figs. 2 and 3). Since IRBP is only intra-ocularly produced, it was not detected in any serum samples.
Quantitative real-time RT-PCR
Comparative mRNA expression between diabetic and non-diabetic retinas corresponding to AZGP1, C3, CFB, SERPINF1 and RBP3 (the genes encoding the proteins ZAG, C3, factor B, PEDF and IRBP, respectively) is shown in Fig. 5. At the retinal level, the mRNA expression of the proteins that were more abundant in the vitreous fluid of PDR patients was also higher in diabetic donors than non-diabetic donors. However, the difference was only statistically significant for CFB. Regarding proteins underproduced in the vitreous fluid of PDR, both SERPINF1 and RBP3 mRNA expression were lower in the retinas from diabetic donors than in the retinas from non-diabetic donors, and the difference was significant for PEDF.
The vitreous provides a means of indirectly exploring the events that are taking place in the retina. However, there is little information on the proteomic analysis of the intravitreal proteins differentially produced in PDR patients in comparison with non-diabetic subjects. In the present study we have optimised the proteomic analysis of vitreous fluid in PDR patients in several ways. First, we facilitated the identification of potential candidates by depleting the two most abundant proteins (albumin and IgG) prior to electrophoresis. It has been reported that albumin and IgG account for more than 80% of whole-vitreous protein, and the large spots of these proteins overlap other small spots, corresponding to less abundant proteins, so precluding their identification. Second, DIGE, which permits an accurate quantitative comparison, was used for the first time to analyse vitreous samples. Third, the results were validated by western blotting on a different set of samples. Fourth, blood contamination was ruled out by selecting vitreous samples with haemoglobin levels <5 mg/ml. Fifth, the difference in vitreal protein levels between the PDR patients and control subjects was determined by loading the same amounts of total protein onto a gel. Sixth, vitreous samples from PDR patients were carefully selected so as to minimise biological variation, which could be erroneously interpreted as being disease-specific. Using this new approach, 11 proteins were identified as differentially produced in the vitreous fluid of PDR patients in comparison with vitreous samples from non-diabetic subjects; eight were overproduced (ZAG, apoA1, apoH, fibrinogen A and several components of the complement system, namely, C4b, factor B, C3 and C9) and three were significantly underproduced (PEDF, IRBP and ITIH2). The differences observed in five of these 11 proteins (ZAG, C3, factor B, PEDF and IRBP) were analysed and confirmed by western blotting.
Although no differences were observed between the two groups in terms of serum levels of the five proteins, determined by western blotting, and in spite of the above-mentioned optimisation, it might be claimed that increased leakage of plasma components through the blood–retina barrier could account for increased concentrations of certain proteins in the vitreous. However, we have found that mRNA expression in retinas from diabetic donors without clinically detectable retinopathy is consistent with the results of both DIGE and western blot analyses. Therefore, eye production rather than serum diffusion seems to be the main factor accounting for the different protein abundances detected in diabetic patients. In addition, this result suggests that the differential production of the five candidates identified by DIGE is an early event in the development of diabetic retinopathy. The potential relevance of these proteins in the pathogenesis of PDR is discussed below.
ZAG is a 41-kDa soluble protein, identified by Sanchez et al.  as a fat-depleting factor, which is related to MHC class I molecules. Although its biological functions are incompletely understood, it seems to be a novel adipokine that may be involved in the local regulation of adipose tissue function [20–23]. ZAG has been recently identified by proteomic analysis in vitreous fluid from PDR patients [8, 9]. In the present study we have confirmed this finding. In addition, both DIGE proteomic analysis and western blotting indicated that ZAG production was significantly higher in the vitreous fluid from PDR patients compared with that from non-diabetic patients. We do not why ZAG levels are increased in the vitreous of diabetic patients with PDR, but it should be noted that hyperglycaemia has been involved in ZAG production , and gene expression of ZAG has been found to be upregulated in mice with diabetic nephropathy . In addition, ZAG hinders cell proliferation and reduces Cdc2 expression (a rate-limiting step in cell cycle)  and may therefore be a reactive limiting factor for PDR progression. Obviously, the mechanisms involved in the intraocular production of ZAG and its role in the pathogenesis of diabetic retinopathy require further investigation.
In recent years evidence has accumulated indicating that inflammation is an important event in the pathogenesis of diabetic retinopathy [26–28]. In the present study, vitreous levels of several components of the complement system (C4b, factor B, C3 and C9) have been found, for the first time, to be simultaneously increased in PDR patients relative to control subjects. In addition, C3 and factor B, as well as their activation products, have been confirmed as increased by western blot analysis. Although complement activation could be secondary to the inflammatory process, in recent studies on human and experimental non-proliferative diabetic retinopathy, Zhang et al.  have demonstrated an early complement activation associated with a prominent and selective decrease in the levels of CD55 and CD59, two glycosylphosphatidylinositol-anchored complement inhibitors. In addition, these authors have shown that C1q and C4, the complement components unique to the classical pathway, were not detected in diabetic retinas, thus suggesting that the alternative pathway is the main mechanism of complement activation in the early stages of diabetic retinopathy. In our study, apart from factor B, which is a specific component of the alternative activation pathway, higher intravitreal levels of C4 were detected in PDR subjects. Therefore, classical pathway activation also seems to be involved in the advanced stages of diabetic retinopathy. In fact, intravitreal C4 has been found to be increased in patients with non-diabetic proliferative vitreoretinopathy . Activation of the complement cascade can both compound and initiate thrombosis, leucostasis and apoptosis, all of which are processes involved in vascular lesions of diabetic retinopathy. Interestingly, it has been reported that the inhibition of aldose reductase prevents the activation of complement in the wall of retinal vessels and decreased levels of complement inhibitors in diabetic rats . Therefore, since several ways of specifically manipulating the complement system already exist, they could represent a possible therapeutic approach in diabetic retinopathy.
PEDF is mainly secreted by retinal pigment epithelial cells in the eye, as well as by other body tissues . Apart from its neurotrophic and neuroprotective properties, there is growing evidence to suggest that PEDF is among the most important natural inhibitors of angiogenesis, and that it is the main factor accounting for the anti-angiogenic activity of the vitreous fluid, where it is found in abundant quantities [32, 33]. The relevance of PEDF to human neovascular disease is supported by studies showing that decreased levels of PEDF in the vitreous are associated with PDR [15, 16]. We have confirmed a PEDF deficit in the vitreous fluid of diabetic patients with PDR by both proteomic analysis and western blotting. In addition, it should be noted that the upregulation of PEDF in proliferating retinal pigment epithelial cells may, in part, account for the success of pan-retinal photocoagulation in reducing neovascularisation . Therefore, there are good reasons for proposing PEDF as a serious candidate for diabetic retinopathy treatment.
IRBP is a large glycoprotein (molecular mass ∼140 kDa) that constitutes approximately 70% of the protein component of the interphotoreceptor matrix, in which it has a highly restricted tissue-specific expression . IRBP plays a major role in the visual cycle [36, 37] and, therefore, the lower levels detected in PDR patients could be involved in the impairment of vision detected in these patients. Further studies investigating the precise role of IRBP in diabetic retinopathy are needed.
There are two main limitations to the present study. The first involves the intrinsic limitations of 2-DE in the analysis of complex protein mixtures. Proteins of very high or low molecular mass are frequently precluded from the analysis by the electrophoresis procedure itself. Conversely, even after depletion of the very abundant proteins, both detection in 2DE and identification by MS are limited by the abundance of the proteins of the mixture, in that minor components will always escape analysis. Therefore, potential candidates involved in the pathogenesis of diabetic retinopathy at picogram levels, such as vascular endothelial growth factor (VEGF), cannot be identified. The second limitation pertains to the rigorous selection of vitreous samples, which precludes the inclusion of an ample set of samples and may consequently impede the consideration of other potential candidate proteins that exist in the vitreous fluid of PDR patients. However, although the number of samples included in this study was relatively low, the selection process enabled us to minimise the dispersion of the measurements in each group. The observed differences by DIGE were further validated by western blot analysis of samples from different patients, which confirmed the observed differences with good quantitative agreement. Therefore, although additional differentially expressed proteins could probably be identified by the analysis of a larger set of samples, those reported here would probably also be found.
In summary, we have shown that two-dimensional DIGE, by providing an accurate quantitative comparison, could facilitate the identification of new potential candidate proteins involved in the development of PDR. Further studies are needed to address the precise role of these candidates in the pathogenesis of PDR and their potential as therapeutic targets.
fluorescence-based difference gel electrophoresis
interstitial retinol-binding protein
inter-α-trypsin inhibitor heavy chain
matrix-assisted laser desorption ionisation-mass spectrometry
pigment epithelial-derived factor
proliferative diabetic retinopathy
Congdon N, Friedman DS, Lietman T (2003) Important causes of visual impairment in the world today. JAMA 290:2057–2060
Burgos R, Mateo C, Canton R, Hernandez C, Mesa J, Simo R (2000) Vitreous levels of IGF-1, IGF binding protein 1, and IGF binding protein 3 in proliferative diabetic retinopathy. A case–control study. Diabetes Care 23:80–83
Simo R, Lecube A, Segura RM, Garcia-Arumi J, Hernandez C (2002) Free insulin growth factor-I and vascular endothelial growth factor in the vitreous fluid of patients with proliferative diabetic retinopathy. Am J Ophthalmol 134:376–382
Simo R, Lecube A, Sararols L, Garcia-Arumi J, Segura RM, Hernandez C (2002) Deficit of somatostatin-like immunoreactivity in the vitreous fluid of diabetic patients. Diabetes Care 25:2282–2286
Simo R, Carrasco E, Garcia-Ramirez M, Hernandez C (2006) Angiogenic and antiangiogenic factors in proliferative diabetic retinopathy. Curr Diab Rev 2:71–98
Gorg A, Weiss W, Dunn MJ (2004) Current two-dimensional electrophoresis technology for proteomics. Proteomics 4:3666–3685
Nakanishi T, Koyama R, Ikeda T, Shimizu A (2002) Catalogue of soluble proteins in the human vitreous humor: comparison between diabetic retinopathy and macular hole. J Chromatogr B Analyt Technol Biomed Life Sci 776:89–100
Koyama R, Nakanishi T, Ikeda T, Shizimu A (2003) Catalogue of soluble proteins in human vitreous humor by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray ionization mass spectrometry including seven angiogenesis-regulating factors. J Chromatogr B Analyt Technol Biomed Life Sci 792:5–21
Yamane K, Minamoto A, Yamashita H et al (2003) Proteome analysis of human vitreous proteins. Mol Cell Proteomics 2:1177–1187
Wu CH, Sauter JL, Johnson PK, Chen CD, Olsen TW (2004) Identification and localization of major soluble vitreous proteins in human ocular tissue. Am J Ophthalmol 137:655–661
Ouchi M, West K, Crabb JW, Kinoshita S, Kamei M (2005) Proteomic analysis of vitreous from diabetic macular edema. Exp Eye Res 81:176–182
Wilson AS, Hobbs BG, Shen WY et al (2003) Argon laser photocoagulation-induced modification of gene expression in the retina. Invest Ophthalmol Vis Sci 44:1426–1434
Alban A, David SO, Bjorkesten L et al (2003) A novel experimental design for comparative two-dimensional gel analysis: two-dimensional difference gel electrophoresis incorporating a pooled internal standard. Proteomics 3:36–44
Shevchenko A, Wilm M, Vorm O, Mann M (1996) Mass spectrometric sequencing of proteins from silver-stained polyacrylamide gels. Anal Chem 68:850–858
Spranger J, Osterhoff M, Reimann M et al (2001) Loss of the antiangiogenic pigment epithelium-derived factor in patients with angiogenic eye disease. Diabetes 50:2641–2645
Ogata N, Tombran-Tink J, Nishikawa M et al (2001) Pigment epithelium-derived factor in the vitreous is low in diabetic retinopathy and high in rhegmatogenous retinal detachment. Am J Ophthalmol 132:378–382
Cunnion KM, Hair PS, Buescher ES (2004) Cleavage of complement C3b to iC3b on the surface of Staphylococus aureus is mediated by serum complement factor I. Infect Immun 72:2858–2863
Thomas A, Gasque P, Vaudry D, Gonzalez B, Fontaine M (2000) Expression of a complete and functional complement system by human neuronal cells in vitro. Int Immunol 12:1015–1023
Sanchez LM, Lopez-Otin C, Bjorkman PJ (1997) Biochemical characterization and crystalization of human Zn-alpha2-glycoprotein, a soluble class I major histocompatibility complex homolog. Proc Natl Acad Sci USA 94:4626–4630
Bao Y, Bing C, Hunter L, Jenkins JR, Wabitsh M, Trayhurn P (2005) Zinc-alpha2-glycoprotein, a lipid mobilizing factor, is expressed and secreted by human (SGBS) adipocytes. FEBS Lett 579:41–47
Bing C, Bao Y, Jenkins J et al (2004) Zinc-alpha2-glycoprotein, a lipid mobilizing factor, is expressed in adipocytes and is up-regulated in mice with cancer cachexia. Proc Natl Acad Sci USA 101:2500–2505
Russell ST, Zimmerman TP, Domin BA, Tisdale MJ (2003) Induction of lipolysis in vitro and loss of body fat in vivo by zinc-alpha2-glycoprotein. Biochim Biophys Acta 1636:59–68
Gohda T, Makita Y, Shike T et al (2003) Identification of epistatic interaction involved in obesity using the KK/Ta mouse as a type 2 diabetes model: is Zn-alpha2 glycoprotein-1 a candidate gene for obesity? Diabetes 52:2175–2181
Gohda T, Tanimoto M, Shiina K et al (2004) Altered mouse cholinephosphotransferase gene expression in kidneys of type 2 diabetic KK/TA mouse. Metabolism 53:842–846
He N, Brysk H, Tyring SK, Ohkubo I, Brysk MM (2001) Zinc-alpha2-glycoprotein hinders cell proliferation and reduces Cdc2 expression. J Cell Biochem 81:162–169
Joussen AM, Poulaki V, Le ML et al (2004) A central role of inflammation in the pathogenesis of diabetic retinopathy. FASEB J 18:1450–1452
Meleth AD, Agron E, Chan CC et al (2005) Serum inflammatory markers in diabetic retinopathy. Invest Opthalmol Vis Sci 46:4295–4301
Hernandez C, Segura RM, Fonollosa A, Carrasco E, Francisco G, Simo R (2005) Interleukin-8, monocyte chemoattractant protein-1 and IL-10 in the vitreous fluid of patients with proliferative diabetic retinopathy. Diabet Med 22:710–722
Zhang J, Gerhardinger C, Lorenzi M (2002) Early complement activation and decreased levels of glycosylphosphatidylinositol-anchored complement inhibitors in human and experimental diabetic retinopathy. Diabetes 51:3499–3504
Grisanti S, Wiedemann P, Weller M, Heimann K, Zilles K (1991) The significance of complement in proliferative vitreoretinopathy. Invest Ophthalmol Vis Sci 32:2711–2717
Dagher Z, Park YS, Asnaghi V, Hoehn T, Gerhardinger C, Lorenzi M (2004) Studies of rat and human retinas predict a role for the polyol pathway in human diabetic retinopathy. Diabetes 53:2404–2411
Barnstable CJ, Tombran-Tink J (2004) Neuroprotective and antiangiogenic actions of PEDF in the eye: molecular targets and therapeutic potential. Prog Retin Eye Res 23:561–577
Dawson DW, Volpert OV, Gilis P et al (1999) Pigment epithelium-derived factor: a potent inhibitor of angiogenesis. Science 285:245–248
Ogata N, Tombran-Tink J, Jo N, Mrazek D, Matsumura M (2001) Upregulation of pigment epithelium-derived factor after laser photocoagulation. Am J Ophthalmol 132:427–429
Chader GJ (1989) Interphotoreceptor retinoid-binding protein (IRBP): a model protein for molecular biological and clinically relevant studies. Friedenwald lecture. Invest Ophthalmol Vis Sci 30:7–22
Liou GI, Bridges CD, Fong SL, Alvarez RA, Gónzalez-Fernandez F (1982) Vitamin A transport between retina and pigment epithelium—an interstitial protein carrying endogenous retinol (interstitial retinol-binding protein). Vision Res 22:1457–1467
Pepperberg DR, Okajima TL, Wiggert B, Ripps H, Crouch RK, Chader GJ (1993) Interphotoreceptor retinoid-binding protein (IRBP). Molecular biology and physiological role in the visual cycle of rhodopsin. Mol Neurobiol 7:61–85
This study was supported by grants from Novo Nordisk Pharma SA (01/0066), the Ministerio de Sanidad y Consumo. Instituto de Salud Carlos III (RED DIABETES- REDIMET), and the Ministerio de Ciencia y Tecnología (SAF2003-00550 and SAF2006-05284). The proteomics laboratory at the IR-HUVH belongs to the Spanish National Institute of Proteomics (PROTEORED). We are grateful to L. M. Sánchez (University of Oviedo, Spain), for providing us with rabbit anti-human ZAG, and to J. M. Nickerson (Emory University, Atlanta, GA, USA), for providing us with the antibodies against IRBP.
Duality of interest
We declare that we have no duality of interest.
The first two authors contributed equally to this work.
Electronic supplementary material
Below is the link to the Electronic supplementary material
(DOC 59 kb).
About this article
Cite this article
García-Ramírez, M., Canals, F., Hernández, C. et al. Proteomic analysis of human vitreous fluid by fluorescence-based difference gel electrophoresis (DIGE): a new strategy for identifying potential candidates in the pathogenesis of proliferative diabetic retinopathy. Diabetologia 50, 1294–1303 (2007). https://doi.org/10.1007/s00125-007-0627-y
- Diabetic retinopathy
- Type 1 diabetes
- Vitreous fluid