Identification of an anti-aldolase autoantibody as a diagnostic marker for diabetic retinopathy by immunoproteomic analysis

Serum autoantibodies against hexokinase 1 manifest secondary to diabetic macular edema onset

AIMS

Autoantibodies against hexokinase 1 (HK1) were recently proposed to be associated with diabetic macular edema (DME). We hypothesized that anti-HK1 autoantibodies can be used as DME markers and to predict DME onset.

MATERIALS AND METHODS

Serum from patients with 1) DME, 2) diabetes mellitus (DM), 3) allergies or autoimmunities, and 4) control subjects was tested for anti-HK1 and anti-hexokinase 2 (HK2) autoantibodies by immunoblotting. Patients with DM were prospectively followed for up to nine years, and the association of anti-HK1 antibodies with new-onset DME was evaluated. The vitreous humor was also tested for autoantibodies.

RESULTS

Among patients with DME, 32 % were positive for anti-HK1 autoantibodies (42 % of those with underlying type 1 DM and 31 % of those with underlying type 2 DM), and 12 % were positive for anti-HK2 autoantibodies, with only partial overlap of these two groups of patients. Anti-HK1 positive were also 7 % of patients with DM, 6 % of patients with allergies and autoimmunities, and 3 % of control subjects. The latter three groups were anti-HK2 negative. Only one of seven patients with DM who were initially anti-HK1 positive developed DME.

CONCLUSIONS

Anti-HK1 autoantibodies can be used as DME markers but fail to predict DME onset.

Nutrient sensors and their crosstalk

The macronutrients glucose, lipids, and amino acids are the major components that maintain life. The ability of cells to sense and respond to fluctuations in these nutrients is a crucial feature for survival. Nutrient-sensing pathways are thus developed to govern cellular energy and metabolic homeostasis and regulate diverse biological processes. Accordingly, perturbations in these sensing pathways are associated with a wide variety of pathologies, especially metabolic diseases. Molecular sensors are the core within these sensing pathways and have a certain degree of specificity and affinity to sense the intracellular fluctuation of each nutrient either by directly binding to that nutrient or indirectly binding to its surrogate molecules. Once the changes in nutrient levels are detected, sensors trigger signaling cascades to fine-tune cellular processes for energy and metabolic homeostasis, for example, by controlling uptake, de novo synthesis or catabolism of that nutrient. In this review, we summarize the major discoveries on nutrient-sensing pathways and explain how those sensors associated with each pathway respond to intracellular nutrient availability and how these mechanisms control metabolic processes. Later, we further discuss the crosstalk between these sensing pathways for each nutrient, which are intertwined to regulate overall intracellular nutrient/metabolic homeostasis.

Correlation of photoreceptor damage with anti-retina antibodies level in aqueous humor in macular edema patients

This study aimed to investigate the correlation between the severity of photoreceptor damage and the level of anti-retina antibodies (ARAs) in aqueous humor, including recoverin, CA II and enolase-α IgG antibody of macular edema patients. Aqueous humor samples were collected from macular edema patients and from cataract patients. Patients were divided into three groups according to the severity of discontinuity of ellipsoid zone (EZ) shown on optical coherence tomography (OCT) imaging: cataract patients with intact EZ, macular edema patients with mild EZ damage, and macular edema patients with severe EZ damage. The level of ARAs was determined with enzyme-linked immunosorbent assay (ELISA). The correlation between the level of ARAs and the degree of photoreceptor damage was analyzed. The level of ARAs of the intact EZ group was significantly lower than that in the severely damaged group (P < 0.05). The level of recoverin IgG of the intact EZ group was significantly lower than mildly damaged group (P = 0.030). In a subgroup analysis, the level of recoverin IgG of DME patients was correlated with their central retinal thickness (CRT) (r = 0.462, P = 0.035). The level of ARAs in aqueous humor of patients with DME and RVO-ME was correlated with the degree of photoreceptor damage.

Anti-retinal IgG antibodies in patients with early and advanced type 2 macular telangiectasia

Type 2 idiopathic macular telangiectasia (MacTel-2) is a progressive adult-onset macular disease associated with bilateral perifoveal vascular changes, Muller cell degeneration and increased blood-retinal barrier permeability. The pathophysiological mechanisms of MacTel-2 remain unclear, however it was previously reported that anti-retinal antibodies in MacTel-2 patients was a significant feature of the disease. In this study, we aimed to compare the prevalence of anti-retinal antibodies in patients MacTel-2, healthy controls and patients with other retinal diseases. MacTel-2 patients diagnosed with multimodal imaging were enrolled and their disease severities were graded using spectral-domain optical coherence tomography. For comparison, patients with age-related macular degeneration (AMD), inherited retinal diseases (IRDs) or no retinal disease (healthy controls) were recruited as controls. Blood serum samples were screened for immunoglobulin G anti-retinal antibodies by western blotting, followed by densitometry analysis. Odds ratios (OR) with 95% confidence intervals (CI) were calculated and p < 0.05 considered statistically significant. Overall, anti-retinal antibody-positive cases were older (64 ± 15 vs 53 ± 17 years, p < 0.001) and females were more likely to develop anti-retinal antibodies (OR: 2.41, CI: 1.12-5.18). The frequency of anti-retinal antibody detection in MacTel-2 patients (n = 42, 36%) was not significantly different from healthy controls (n = 52, 25%) or IRDs patients (n = 18, 25%) and the majority of MacTel-2 patients had no anti-retinal antibodies. In contrast, the frequency of anti-retinal antibody detection was significantly higher in patients with AMD (n = 15, 73%, p < 0.001). The lack of a greater anti-retinal antibody frequency or specificity in the MacTel-2 cohort suggests that antibody mediated immunological mechanisms may play a less significant role in MacTel-2 disease pathogenesis.

Immune regulation in the aging retina

The retina is an immune privileged tissue, which is protected from external and internal insults by its blood-retina barriers and immune suppressive microenvironment. Apart from the avoidance and tolerance strategies, the retina is also protected by its own defense system, i.e., microglia and the complement system. The immune privilege and defense mechanisms work together to maintain retinal homeostasis. During aging, the retina is at an increased risk of developing various degenerative diseases such as age-related macular degeneration, diabetic retinopathy, and glaucomatous retinopathy. Previously, we have shown that aging induces a para-inflammatory response in the retina. In this review, we explore the impact of aging on retinal immune regulation and the connection between homeostatic control of retinal immune privilege and para-inflammation under aging conditions and present a view that may explain why aging puts the retina at risk of developing degenerative diseases.

Autoantibody profiling in intraocular fluid of patients with uveitis

A high prevalence of serum antiretinal antibodies (ARAs) in patients with uveitis has been previously described, though their clinical role remains elusive. Assessment of intraocular ARAs may provide further insight into the pathogenesis of diverse uveitis entities. In this study we investigate the prevalence of multiple specific anti-ocular antibodies (AOcAs), including ARAs, in intraocular fluid of patients with uveitis. Autoantibody profiling with 188 different ocular antigens was performed by a multiplex immunoassay with intraocular fluid samples of 76 patients with uveitis. Clinical data from uveitis patients were collected and statistical analyses were executed to evaluate associations between intraocular AOcAs and clinical characteristics. Controls consisted of 19 intraocular fluid samples from cataract patients. A spectrum of 22 different AOcAs was present in higher levels in patients with uveitis than in controls (p < 0.05), but in moderately elevated titers (<2x). High elevations of intraocular AOcAs in uveitis (>5x compared to cataract) were observed in varicella zoster virus-induced uveitis, multiple sclerosis-associated uveitis and patients with unexplained uveitis but positive quantiferon test. Presence of macular edema was associated with increased intraocular levels of tyrosinase antibodies. Our results show that patients with uveitis are characterized by the presence of a broad spectrum of moderately elevated levels of intraocular AOcAs, and high intraocular AOcA levels were found in several specific uveitis entities. This study favors secondary production of AOcAs and not their inciting role.

Diabetic Retinopathy and Laser Therapy in Rats: A Protein-Protein Interaction Network Analysis

Introduction: Diabetic retinopathy (DR) is a serious microvascular complication of diabetes which can cause vision loss or blindness ultimately. Non enzymatic glycation of proteins leads to advanced glycation end products (AGEs) in DR. Since laser therapy is a well-established method, in this study, protein-protein interaction (PPI) network is applied for protein targets in DR disease in rats treated by laser. Methods: In this study, we focused on articles that investigated and compared the proteome profiles of DR rats with healthy control and also DR rats before and after laser therapy. The networks of related differentially expressed proteins were explored using Cytoscape version 3.3.0, the PPI analysis methods and ClueGO. Results: Analysis of PPI network of 37 related proteins to DR rats including 108 nodes, introduced 10 hub-bottleneck proteins and 5 concerned biochemical pathways. On the other hand, PPI analysis of related proteins to DR rats before and after laser therapy corresponded to 33 proteins and 2 biological pathways. Discussion: Centrality and cluster screening identified hub-bottelneck genes, including Aldoa, HSPD1, Pgam2, Mapk3, SLC2A4, Ctnnb1, Ywhab, HSPA8, GAPDH and Actb for DR rats versus healthy control and ENO1, Aldoa, GAPDH for DR samples after laser therapy.

CONCLUSION

Gene expression analysis of the DR samples treated via laser therapy provides a molecular evidence in support of the therapeutic effect of laser.

Efficacy of rituximab in non-paraneoplastic autoimmune retinopathy

Background

Autoimmune retinopathy (AIR) is a rare but potentially blinding condition that is often underdiagnosed. Common features in AIR presentation include rapidly progressive vision loss with abnormal electrophysiological responses of the retina associated with positive anti-retinal antibodies. AIR is also challenging to treat, and thus, the introduction of new potential therapeutic agents is welcomed. The goal of this communication is to assess the effects of rituximab infusions on electroretinogram (ERG) responses and visual function outcomes in patients with non-paraneoplastic autoimmune retinopathy (npAIR).

Results

Following infusion(s), three out of five patients showed no evidence of disease progression or improved, while two patients continued to progress on ERG. One patient demonstrated improvement in visual acuity (2 lines) in both eyes. ERG responses provided objective monitoring of patients’ visual function and response to immunosuppression over time.

Conclusions

These findings suggest that patients with npAIR unresponsive to other immunosuppression therapies may benefit from rituximab infusion, although stabilization rather than improvement was more frequently the outcome in our case series. Furthermore, regularly scheduled ERG follow-up examinations are recommended for monitoring patients’ progression during treatment.

Diabetic retinopathy and dysregulated innate immunity

Diabetic retinopathy (DR) is the progressive degeneration of retinal blood vessels and neurons. Inflammation is known to play an important role in the pathogenesis of DR. During diabetes, metabolic disorder leads to the release of damage-associated molecular patterns (DAMPs) both in the retina and elsewhere in the body. The innate immune system provides the first line of defense against the DAMPs. In the early stages of DR when the blood retinal barrier (BRB) is intact, retinal microglia and the complement system are activated at low levels. This low-level of inflammation (para-inflammation) is believed to be essential to maintain homeostasis and restore functionality. However, prolonged stimulation by DAMPs in the diabetic eye leads to maladaptation of the innate immune system and dysregulated para-inflammation may contribute to DR development. In the advanced stages of DR where immune privilege is comprised, circulating immune cells and serum proteins may infiltrate the retina and participate in retinal chronic inflammation and retinal vascular and neuronal damage. This review discusses how the innate immune system is activated in diabetes and DR. The view also discusses why the protective immune response becomes detrimental in DR.

Impact of Autoantibodies against Glycolytic Enzymes on Pathogenicity of Autoimmune Retinopathy and Other Autoimmune Disorders

Autoantibodies (AAbs) against glycolytic enzymes: aldolase, α-enolase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase are prevalent in sera of patients with blinding retinal diseases, such as paraneoplastic [cancer-associated retinopathy (CAR)] and non-paraneoplastic autoimmune retinopathies, as well as in many other autoimmune diseases. CAR is a degenerative disease of the retina characterized by sudden vision loss in patients with cancer and serum anti-retinal AAbs. In this review, we discuss the widespread serum presence of anti-glycolytic enzyme AAbs and their significance in autoimmune diseases. There are multiple mechanisms responsible for antibody generation, including the innate anti-microbial response, anti-tumor response, or autoimmune response against released self-antigens from damaged, inflamed tissue. AAbs against enolase, GADPH, and aldolase exist in a single patient in elevated titers, suggesting their participation in pathogenicity. The lack of restriction of AAbs to one disease may be related to an increased expression of glycolytic enzymes in various metabolically active tissues that triggers an autoimmune response and generation of AAbs with the same specificity in several chronic and autoimmune conditions. In CAR, the importance of serum anti-glycolytic enzyme AAbs had been previously dismissed, but the retina may be without pathological consequence until a failure of the blood–retinal barrier function, which would then allow pathogenic AAbs access to their retinal targets, ultimately leading to damaging effects.

Diagnostic features of the autoimmune retinopathies

The term autoimmune retinopathy encompasses a spectrum of rare autoimmune diseases that affect retinal function, often but not exclusively at the level of the photoreceptor. They typically present with painless visual loss, which may be accompanied by normal fundus examination. Some are progressive, often rapidly. They present a diagnostic challenge because there are no standardised clinical or laboratory based diagnostic criteria. Included within the spectrum are cancer-associated retinopathy, melanoma-associated retinopathy and presumed non-paraneoplastic autoimmune retinopathy. Differentiation from other retinopathies can be challenging, with overlap in symptoms, signs, and investigation findings, and an absence of pathognomonic features. However, technological developments in ophthalmic imaging and serological investigation over the past decade are adding novel dimensions to the investigation and classification of patients with these rare diseases. This review addresses the clinical, imaging, and serological features of the autoimmune retinopathies, and discusses the relative strengths and limitations of candidate diagnostic features.

Autoimmune retinopathy

PURPOSE OF REVIEW

Autoimmune retinopathy (AIR) is an immune-mediated disorder characterized by progressive visual loss, abnormal electroretinographic and visual field findings in the presence of circulating anti-retinal antibodies. This review highlights advances made toward understanding the pathophysiology, clinical manifestations, and trends in the management of AIR.

RECENT FINDINGS

The pathophysiology of AIR is likely antibody-mediated. AIR serum autoantibodies are variable in their size and retinal tissue they target and can also be present in healthy controls and multiple autoimmune diseases. Rarely, AIR may be associated with dysregulated self-tolerance mechanisms in the thymus. Despite progress in research, our understanding of AIR remains incomplete. Lack of standardized methods for anti-retinal antibody testing continues to challenge the interpretation of seropositivity. Conventional immunosuppressives have been further studied, and promising immunomodulatory therapies, such as targeted B-cell therapy, have been introduced. Newer imaging modalities such as fundus autofluorescence and spectral domain optical coherence tomography may be helpful in diagnosis, monitoring progression of disease and response to treatment.

SUMMARY

AIR is a rare but vision-threatening disease whose pathogenesis is poorly defined. Lack of standardized clinical or laboratory criteria further complicates the diagnosis and management. Despite recent progress, further basic science research into the autoimmune process is needed. Prospective controlled clinical trials with immunomodulatory therapy can help define future treatment paradigms.

Proteomic identification of aldolase A as an autoantibody target in patients with atypical movement disorders

We tried to identify the target/s of autoantibodies to basal ganglia neurons found in a patient with hyperkinetic movement disorders (HMD) characterized by rapid, rhythmic involuntary movements or spasms in both face and neck. Patient and control sera were used in Western blot to probe mouse brain homogenates. Two-dimensional gel electrophoresis (2-DE) SDS-PAGE protein spots recognized by the patient's antibodies were excised and sequenced by mass spectrometry analysis, and the glycolytic enzyme aldolase A was identified as the antigen recognized by the patient's autoantibodies. To assess relevance and specificity of these antibodies to the identified targets as biomarkers of autoimmunity in movement disorders, autoantibody responses to the identified target were then measured by ELISA in various diseases of the central nervous system. Anti-aldolase A autoantibodies were associated mainly with HMD (7/17, 41%) and Parkinson's disease (4/30, 13%) patients, and undetectable in subjects with other inflammatory and non-inflammatory central nervous system diseases. We, thus, identified aldolase A as an autoantigen in a sub-group of patients with HMD, a clinically ill-defined syndrome. Anti-aldolase A antibodies may represent a useful biomarker of autoimmunity in HMD patients.

Characterisation of the vitreous proteome in proliferative diabetic retinopathy

Background

Diabetes can lead to serious microvascular complications such as proliferative diabetic retinopathy (PDR), which results in severe vision loss. The diabetes-induced alterations in the vitreous protein composition in diabetic patients with PDR may be responsible for the presence of PDR. The vitreous humour can be utilised in a variety of studies aimed toward the discovery of new targets for the treatment or prevention of PDR and the identification of novel disease mechanisms. The aim of this study was to compare the protein profile of vitreous humour from diabetic patients with PDR with that of vitreous humour from normal human eyes donated for corneal transplant.

Results

Vitreous humour from type 2 diabetic patients with PDR (n = 10) and from normal human eyes donated for corneal transplant (n = 10) were studied. The comparative proteomic analysis was performed using two-dimensional fluorescence difference gel electrophoresis (2-D DIGE). Differentially produced proteins (abundance ratio > 2 or < -2, p < 0.01) were identified by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and MALDI-TOF tandem mass spectrometry. A total of 1242 protein spots were detected on the 2-D master gel of the samples, and 57 spots that exhibited statistically significant variations were successfully identified. The spots corresponded to peptide fragments of 29 proteins, including 8 proteins that increased and 21 proteins that decreased in PDR. Excluding the serum proteins from minor vitreous haemorrhage, 19 proteins were found to be differentially produced in PDR patients compared with normal subjects; 6 of these proteins have never been reported to be differentially expressed in PDR vitreous: N(G),N(G)-dimethylarginine dimethylaminohydrolase 1 (DDAH 1), tubulin alpha-1B chain, gamma-enolase, cytosolic acyl coenzyme A thioester hydrolase, malate dehydrogenase and phosphatidylethanolamine-binding protein 1 (PEBP 1). The differential production of pigment epithelium-derived factor (PEDF) and clusterin was confirmed by Western blot analysis.

Conclusions

These data provide an in-depth analysis of the human vitreous proteome and reveal protein alterations that are possibly involved in the pathogenesis of PDR. Further investigation of these special proteins may provide potential new targets for the treatment or the prevention of PDR.

Proteomic analysis of human serum from diabetic retinopathy

AIM

To establish and compare serum proteomic of diabetic retinopathy (DR) patients in various phases and discuss pathogenesis of DR so as to find out possible serum specific molecular markers for early diagnosis of DR.

METHODS

Thirty-two subjects were divided into four groups: one group of eight type 2 diabetes mellitus (T2DM) patients without apparent DR (No-DR, NDR), one group of eight T2DM patients with non-proliferative diabetic retinopathy (NPDR), one group of eight T2DM patients with proliferative diabetic retinopathy (PDR) and one group of eight healthy volunteer participants. Two dimensional fluorescence difference gel electrophoresis (2D-DIGE) was applied to establish differential protein expression profiles in four groups. Matrix-assisted laser desorption/ionization time of flight tandem mass spectrometry (MALDI-TOF-TOF MS) was applied to identify mass spectrometry of differential proteins and analyze follow-up bioinformatics.

RESULTS

2D-DIGE maps of serum protein were satisfactory obtained from NDR, NPDR, PDR and normal control groups. Twenty-six different proteins spots were screened (the volume ratio was >1.5 based on DeCyder software analysis). Twenty-four of them were verified and two of them were not. Fifteen proteins were verified. Most of them were high-abundant proteins in serum. The four relatively low-abundant ones were beta 2-glycoprotein I (β(2)-GPI), alpha2-HS-glycoprotein(AHSG), alpha1-acid glycoprotein(α(1)-AGP) and apolipoprotein A-1(apo A-1). β(2)-GPI expression was gradually increased in the development of DR but unrelated to the severity of DR. The volume ratio of β(2)-GPI is 1.54, 2.43, and 2.84 in NDR, NPDR and PDR group respectively compared with normal control group.

CONCLUSION

Serum proteomic analysis of 2D-DIGE combined with MALDI-TOF-TOF MS is feasible to be applied in the study of DR. β(2)-GPI probably takes part in the process of DR occurrence and development and it could be a candidate biomarker on DR diagnosis in early phase.

Comparison of tear proteins between healthy and early diabetic retinopathy patients

OBJECTIVES

To identify potential prognostic or diagnostic marker tear proteins for early diabetic retinopathy (DR) and to investigate the pathogenesis of this disease using proteomics techniques.

DESIGN AND METHODS

The tear proteins expressed in patients suffering from diabetes mellitus without the retinopathy symptoms, nonproliferative diabetic retinopathy and healthy volunteers were analyzed by 2-DE. The differentially expressed proteins in patients were identified by ESI-Q-TOF and confirmed by Western blotting.

RESULTS

Proteins which were differentially expressed with statistical significance (P<0.05) in two diabetic groups as compared to those in healthy group were selected and identified by ESI-Q-TOF MS/MS. Among these proteins, three proteins (LCN-1, HSP27 and B2M) were found to exhibit a progressive reduction in two disease groups. The expression levels of which might be useful as diagnostic biomarkers of DR were verified by Western blotting

CONCLUSIONS

Proteomic analysis using tear is a novel approach that can provide insight into possible biomarker and the pathogenesis of early DR.

Melanoma-associated retinopathy: a paraneoplastic autoimmune complication

OBJECTIVES

To study 11 patients with melanoma-associated retinopathy (MAR) to clarify the reliability of various methods of diagnostic testing, to determine the underlying antigenic retinal proteins, and to study the clinical histories and types of associated melanomas.

METHODS

Clinical data were obtained from patients with melanoma who developed marked visual problems. Testing included electroretinography, kinetic visual fields, comparative studies of Western blots, and indirect immunohistologic examination to detect antiretinal antibodies, as well as proteomic studies to identify underlying antigenic retinal proteins.

RESULTS

Patients with MAR typically have rapid onset of photopsias, scotomata, and loss of central or paracentral vision. Ophthalmoscopy seldom shows significant changes early, but electroretinograms are abnormal. Results of Western blots and immunohistologic examination can show antiretinal antibodies but not always. Most patients (9 of 11) had a strong family history of autoimmune disorders. Any type of melanoma (cutaneous, choroidal, ciliary body, or choroidal nevi) may be associated with this paraneoplastic autoimmune reactivity. MAR may precede or follow the diagnosis of melanoma. Patients with MAR have the same antigenic retinal proteins that have been associated with cancer-associated retinopathy. In addition, 2 new antigenic retinal proteins, aldolase A and aldolase C, were found.

CONCLUSIONS

There was a high prevalence of positive family histories of autoimmune disease in patients with MAR. To confirm the disorder, multiple clinical and serum diagnostic techniques (Western blot or indirect immunohistologic examination) are needed. Two newly observed antigenic retinal proteins, aldolase A and aldolase C, are associated with MAR.

Autoimmunity in retinal degeneration: autoimmune retinopathy and age-related macular degeneration

Autoantibody production is associated with a variety of ocular disorders, including autoimmune retinopathy (AIR) and age-related macular degeneration (AMD). A breakdown of immunologic tolerance (ocular immune privilege), including the blood-retinal barrier, anti-immune and anti-inflammatory proteins, and anterior chamber-associated immune deviation may play important roles in these disorders. Although the exact triggers for ocular autoimmunity are unknown, autoimmune targeting of retinal tissue is clearly associated with and may contribute to the pathogenesis of both AIR and AMD. Autoantibody production has long been associated with AIR, a collection of disorders that includes cancer-associated retinopathy, melanoma-associated retinopathy and non-paraneoplastic autoimmune retinopathy. A growing body of evidence indicates that AMD pathogenesis, too, involves ocular inflammation and autoimmunity. Identification and quantification of autoantibodies produced in patients with AIR and AMD may assist with diagnosis, prognosis, and choice of treatments. Animal models that allow investigation of ocular autoimmunity will also be needed to better understand the disease processes and to develop novel therapies. In this review we discuss ocular immune privilege and potential mechanisms of autoimmunity in the eye. We describe how autoimmunity relates to the pathogenesis of AIR and AMD. We explain how the antigen microarray technique is used to detect autoantibodies in patient serum samples, and discuss how current animal models for AMD can be used to investigate autoimmune pathogenesis. Finally, we outline unanswered questions and exciting areas of future study related to autoimmune retinal degeneration.

Multidimensional degradomics identifies systemic autoantigens and intracellular matrix proteins as novel gelatinase B/MMP-9 substrates

The action radius of matrix metalloproteinases or MMPs is not restricted to massive extracellular matrix (ECM) degradation, it extends to the proteolysis of numerous secreted and membrane-bound proteins. Although many instances exist in which cells disintegrate, often in conjunction with induction of MMPs, the intracellular MMP substrate repertoire or degradome remains relatively unexplored. We started an unbiased exploration of the proteolytic modification of intracellular proteins by MMPs, using gelatinase B/MMP-9 as a model enzyme. To this end, multidimensional degradomics technology was developed by the integration of broadly available biotechniques. In this way, 100-200 MMP-9 candidate substrates were isolated, of which 69 were identified. Integration of these results with the known biological functions of the substrates revealed many novel MMP-9 substrates from the intracellular matrix (ICM), such as actin, tubulin, gelsolin, moesin, ezrin, Arp2/3 complex subunits, filamin B and stathmin. About 2/3 of the identified candidates were autoantigens described in multiple autoimmune conditions and in cancer (e.g. annexin I, nucleolin, citrate synthase, HMGB1, alpha-enolase, histidyl-tRNA synthetase, HSP27, HSC70, HSP90, snRNP D3). These findings led to the insight that MMPs and other proteases may have novel (immuno)regulatory properties by the clearance of toxic and immunogenic burdens of abundant ICM proteins released after extensive necrosis. In line with the extracellular processing of organ-specific autoantigens, proteolysis might also assist in the generation of immunodominant 'neo-epitopes' from systemic autoantigens. The study of proteolysis of ICM molecules, autoantigens, alarmins and other crucial intracellular molecules may result in the discovery of novel roles for proteolytic modification.

QUADOMICS: an adaptation of the Quality Assessment of Diagnostic Accuracy Assessment (QUADAS) for the evaluation of the methodological quality of studies on the diagnostic accuracy of '-omics'-based technologies

OBJECTIVES

To adapt the Quality Assessment of Diagnostic Accuracy Assessment (QUADAS) to the particular methodological challenges posed by research on '-omics'-based diagnostic tests.

DESIGN AND METHODS

We generated new guidelines by appraising the suitability of each criterion from QUADAS to '-omics'-based diagnostic research, and by adding new items that addressed specific sources of error. In addition, we defined four phases in the evaluation of a diagnostic test.

RESULTS

Twelve of the 14 criteria from QUADAS were retained in the new tool. The items relating to selection criteria and the description of the test were reformulated, and the criteria about external validation and the availability of clinical data were applied only in studies in the last research phase. Four new items were incorporated to QUADOMICS related to pre-analytical conditions and methods to avoid overfitting.

CONCLUSIONS

QUADOMICS is an adaptation of QUADAS to the special nature of '-omics'-based diagnostic research. The tool adds new items that assess quality issues specific to this research, and may enhance the application of '-omics'-based discoveries to clinical \and public health practice.

Autoantibody profiling of Chinese patients with autoimmune hepatitis using immunoproteomic analysis

In the present study, immunoproteomic analysis was utilized to systemically characterize global autoantibody profiles in autoimmune hepatitis (AIH). Sera from 21 patients with AIH and 15 healthy controls were analyzed for the antibody reactivity against the protein antigens of HepG2, a human hepatoma cell line. The lysates of HepG2 cells were separated by two-dimensional electrophoresis and then immunoblotted with each serum sample. Matrix-assisted laser desorption/ionization mass spectrometry or/and nanoelectrospray ionization MS/MS were then used to identify antigens, among which a bifunctional enzyme in mitochondrial, fumarate hydratase (FH), was further analyzed by ELISA using recombinant FH as a coating antigen. A total of 18 immunoreactive spots were identified as 13 proteins, 8 of which have not been reported in AIH. Immune reactivity to FH was detected in 66.67% of patients with AIH, 19.35% of patients with primary biliary cirrhosis (PBC), 12.31% of patients with chronic hepatitis B (CHB), 6.35% of patients with chronic hepatitis C (CHC), 11.32% of patients with systemic lupus erythematosus (SLE), and 3.57% of normal individuals. The differences of prevalence between AIH patients and healthy controls as well as other diseases were of statistical significance (P<0.001). These data demonstrate the serological heterogeneity in AIH and suggest the diversity of the mechanisms underlying AIH. FH, recognized mainly in AIH rather than in viral hepatitis and other autoimmune diseases, may have utility in improved diagnosis of AIH.

Using proteomics to identify targets of antiendothelial cell antibodies

Antiendothelial cell antibodies represent a heterogeneous group of antibodies directed against a variety of antigen determinants of endothelial cells. Antibodies reacting with endothelial structures have been detected in sera from patients with autoimmune vasculitis, both primary and secondary to systemic connective tissue diseases. It may interfere with several functions and, therefore, may be a pathophysiological relevance. The analysis of the antigens recognized by antiendothelial cell antibodies showed that the antibodies are directed against a heterogeneous family of both constitutive and nonconstitutive surface endothelial proteins. Proteomics is a field of science that evaluates a large number of proteins expressed from a given cell line or organism. The technology of proteomics has been used as a method for discovering the target protein specific to a particular disease by searching for the expression or modification of the protein. Recently, progress has been made in defining the target antigens of these antibodies and proteomic technologies is one of them. This review will focus on the proteomic technologies in searching autoantigens/autoantibodies associated with disease of the endothelium.

Protein kinase C delta regulates anti-apoptotic alphaB-crystallin in the retina of type 2 diabetes

We investigated the relationship between phosphorylation of alphaB-crystallin (alphaBC) and retinal apoptosis in type 2 diabetes. The retinas of male Otsuka Long-Evans Tokushima fatty (OLETF) rats at 24 and 35 weeks were used as an animal model for type 2 diabetes and sex- and age-matched Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In the retinas of 35-week OLETF rats, the interaction between alphaBC and protein kinase C delta (PKC delta) among the PKC isozymes, alphaBC phosphorylation at Ser45 (S45p-alphaBC), TUNEL-positive apoptotic ganglion cells, several apoptotic signs, and co-localization of S45p-alphaBC and TUNEL significantly increased as compared with other groups while the alphaBC-Bax interaction greatly decreased. These changes were abolished by rottlerin treatment, a highly specific PKC delta inhibitor. These results suggest that PKC delta is involved in regulation of anti-apoptotic function of alphaBC in the retina of type 2 diabetes.

Proteomic surveillance of autoimmunity in Behcet's disease with uveitis: selenium binding protein is a novel autoantigen in Behcet's disease

Autoimmune response to retinal antigens is considered to be one of the pathogenesis of uveitis in Behcet's disease (BD). In the present study, we comprehensively compared retinal autoantigens recognized by sera from BD patients with uveitis or healthy donors using proteomic technique, 2-dimensional electrophoresis (2DE) followed by Western blotting (WB). Six protein spots showing high reactivity with the serum from the BD patients were detected as candidate retinal autoantigens, and three of them were identified by mass spectrometry. Two of them were previously reported BD autoantigens, S-antigen and alpha-enolase, whereas the third one was selenium binding protein (SBP), a new candidate retinal autoantigen. Autoantigenicity of SBP was examined by WB and enzyme-linked immunosorbent assay (ELISA) using a recombinant protein. We found that 20 and 16% of the BD patients with uveitis were positive for the anti-SBP antibody by WB and ELISA, respectively. Comparison of clinical parameters between anti-SBP antibody-positive and -negative patients revealed that the anti-SBP antibody-positive patient group showed more frequent ocular inflammation than the antibody-negative patient group. Autoimmunity against the retinal SBP may contribute to the pathogenesis of uveitis in BD patients.

Use of proteomics in analysis of autoimmune diseases

Autoimmune diseases are common by diseases characterized by disorders of immune responses and autoimmune impairment involving multiple tissues, organs and systems. The autoantigens (Ags)/autoantibodies (Abs) are not only hallmarks but also involved in pathogenesis of autoimmune diseases. In recent years, proteomics technologies have been used and demonstrated effective in searching new Ags/Abs as well as disease biomarkers in autoimmune diseases.