Use of proteomics in analysis of autoimmune diseases

Autoimmunoreactive IgGs from patients with postural orthostatic tachycardia syndrome

PURPOSE

Autoantibodies are implicated in the pathogenesis of cardiovascular diseases and cardiac arrhythmias. In this pilot study, we tested the hypothesis that autoantibodies are present in patients with postural orthostatic tachycardia syndrome (POTS).

EXPERIMENTAL DESIGN

Seven control subjects (6 F:1 M, average age 36.1 years) and ten patients with the diagnosis of POTS (7 F: 3 M, average age 35.1 years) provided informed consent and 30 mL of venous blood. Human heart membrane proteins were resolved by 2DE and immunoblotted against purified IgGs from controls and patients.

RESULTS

Eighteen protein spots immunoreactive specifically against patient IgGs were detected and they were excised from gels, trypsin-digested, and analyzed by nanoLC-electrospray MS/MS. Forty unique proteins were identified and these include proteins that are associated with cardiac hypertrophy (mimecan, myozenin), cardiac remodeling (periostin), cardiomyopathy (desmin, desmoplakin), cell survival (laminin), structural integrity (filamin), chaperone proteins (crystalline, HSP70), mitochondrial enzymes, and channel proteins. Ingenuity Pathway Analysis showed multiple pathways were involved including those that regulate energy metabolism, redox, fibrosis, cardiac hypertrophy, and degeneration.

CONCLUSIONS AND CLINICAL RELEVANCE

Autoantibodies are present in patients with POTS. These autoantibodies cross-react with a wide range of cardiac proteins and may induce alterations in cardiac function. Autoimmune pathogenetic mechanisms should be further explored in these patients.

A comparative proteomic study of sera in paediatric systemic lupus erythematosus patients and in healthy controls using MALDI-TOF-TOF and LC MS-A pilot study

BACKGROUND

Paediatric systemic lupus erythematosus (pSLE) exhibits an aggressive clinical phenotype with severe complications and overall poor prognosis. The aim of this study was to analyse differential expression of low molecular weight (LMW) serum protein molecules of pSLE patients with active disease in comparison to sera of healthy age matched controls. Further, some of the differential expressed spots were characterised and identified by Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) and liquid chromatography (LC-MS).

METHODS

2D-PAGE was performed using pooled sera of active pSLE and age matched healthy controls. Gels were silver-stained and differentially expressed protein spots were detected by automated image master platinum 2D software. 79 ± 17 protein spots were detected for control gels and 78 ± 17 protein spots for patient gels. Of these eleven protein spots were selected randomly and characterized by MALDI-TOF MS (five protein spots) and LC MS (six protein spots) techniques.

RESULTS

Out of the 11 protein spots, 5 protein spots were significantly upregulated viz., leiomodin 2 (LMOD2); epidermal cytokeratin 2; immunoglobulin kappa light chain variable region; keratin 1 and transthyretin (TTR). Three protein spots were significantly down regulated e.g., apolipoprotein A1 (APOA1); chain B human complement component C3c; campath antibody antigen complex. Two protein spots (complement component C3; retinol binding protein (RBP) were found to be expressed only in disease and one protein spot cyclohydrolase 2 was only expressed in controls.

CONCLUSIONS

We conclude that 2-D maps of patients with active pSLE and controls differ significantly. In this pilot study, using proteomic approach we have identified differential expressed proteins (of LMW) e.g., RBP, LMOD 2, TTR, Component C3c Chain B and APO A1. However, in future, further studies need to confirm the physiological and pathological role of these proteins in similar cohorts of pSLE.

Proteomics analysis in 28 patients with systemic IgG4-related plasmacytic syndrome

It is considered that autoimmune pancreatitis (AIP), Mikulicz's disease (MD) and IgG4-related tubulointerstitial nephritis (TIN) comprise systemic IgG4-related plasmacytic syndrome (SIPS), of which the origin remains unknown. We analyzed these patients with focus on serological aspects to invest whether there are autoantigens in SIPS. We evaluated 28 patients with SIPS who presented at Sapporo Medical University Hospital and the collaborated institutions. They were mainly middle-aged (eight male), and consisted of 26 patients with MD and two patients with AIP. The three among 26 patients diagnosed with MD were complicated to AIP, and another three patients had IgG4-related TIN. As a control, healthy volunteers and the patients with Sjögren's syndrome were examined. At first, we measured the levels of serum complements and circulating immune complexes in these patients. Next, immune complexes were collected from the serum of patients and healthy controls by immunoprecipitation. They were divided into immunoglobulin and the antigens by glycine-HCl solution. The divided samples including the antigens were analyzed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS). Nine patients had hypocomplementemia and 15 had elevated levels of circulating immune complexes in the group of SIPS. In the groups of healthy volunteers and SS, all showed that the levels of serum complements and circulating immune complexes were normal. SELDI-TOF-MS detected a 13.1-kDa protein from all samples of SIPS, and not in normal control and SS. It is possible that the 13.1-kDa protein is one of the autoantigens of SIPS.

Challenges to the use of autoantibodies as predictors of disease onset, diagnosis and outcomes

Autoantibodies (AA) are a serological hallmark of most autoimmune diseases. In contrast to genetic markers that show a predisposition for disease development, certain AA serve as diagnostic biomarkers and classification criteria for a number of these conditions. The role of AA is still not clearly understood: some are pathogenic, some disease specific and others serve as predictors of disease outcome, but little is known about those that protect against disease or serve as signatures of the inciting agent of autoimmunity. Because of growing evidence that some AA antedate clinical diagnosis, significant effort is being spent on gathering evidence regarding their value as predictors of disease onset and outcome. Although many studies have shown that specific AA are detected in the pre-clinical phase and are biomarkers of increased risk of developing an autoimmune disease, they are currently not widely used to determine risk or as a pre-clinical screen. Additional prospective and retrospective studies are urgently needed to determine the precise risk of developing autoimmune disease in the presence of various AA. Such studies must be attended by the development of strategies for earlier diagnosis and novel therapeutic interventions of early disease.