| dc.description.abstract | Systemic lupus erythematosus (SLE) is a complicated chronic inflammatory autoimmune disease with unknown etiology. It distresses the body′s immune system and mistakenly attacks healthy tissues. Consequently, it affects the skin, joints, kidneys, brain, and other organs of the body. Human plasma is comprised of ten orders of magnitude concentration of proteins and tissue leakages. The change of the abundance and modifications of these proteins have been playing important roles in various human diseases. Therefore, the differential expression of proteins in the serum/plasma has potential clinical applications including in serving as diagnosis or treating targets. Thus, the research objective of this study is to identify the significantly altered expressions in both abundance and posttranslational modifications of plasma proteins from SLE patients. We compared those aspects to the healthy controls using proteomics approach. The 19 SLE patients had been shown to be in active disease stage with average systemic lupus erythematosus activity index (SLEDAI) score of more than 8. All the recruited patients showed high titers of anti-ds DNA antibodies along with anti-nuclear antibodies (ANA test of ≥1:640) plus low levels of complement indicating the presence of proteinuria along with nephritis symptoms. In this study, the patient plasma samples were compared to 12 healthy controls. The plasma proteome were analyzed using both gel-based and gel-free proteomic methodologies. The high-resolution electrospray ionization liquid chromatography-tandem mass spectrometry followed by label-free quantification and post-translational modifications (PTMs) analysis was employed to identify the significantly altered proteins. A total of 29 proteins showed a significant level of differential expressions combining the results from both electrophoresis and liquid chromatography separating methods. The 21 proteins including complement C4, complement factor H, apolipoprotein B-100, immunoglobulin heavy and light chains, few glycoproteins and several acute phase reactant proteins had > 1.5-3 fold up-regulation. Eight proteins including transthyretin, clusterin, fibrinogen gamma chain, hemoglobin subunit alpha, serotransferrin, serum albumin, alpha-1 antitrypsin and hemopexin have been shown to be down-regulated with <0.2-0.6 fold. The GO and DAVID functional enrichment analysis revealed that these proteins involved in several important biological processes including acute phase inflammatory responses, complement activation, homeostasis, and immune system regulation. Thus, the identified differentially expressed proteins are relevant to SLE patient’s cohort and that are proposed to be involved in the imbalance of the immune system and inflammatory responses. Some might be potential candidates for the renal system involvement in SLE pathogenesis. In addition, a total of 3,850 unique peptides mapped to 83 proteins with PTMs were identified in SLE plasma compared to healthy controls using both MODa and PEAKS 8.5 software. The annotations of the identified proteins were further confirmed using Universal Protein Resource Website. Furthermore, the PTMs were also found in several up-regulated proteins identified by our proteomics approach. They are immunoglobulin heavy and light chains, alpha-2 macroglobulin, ceruloplasmin, hemoglobin subunit beta, haptoglobin, apolipoprotein B, alpha-1 acid glycoproteins. The PTMs also found in the down-regulated proteins including fibrinogen gamma chain, complement C4, serotransferrin. The modifications include acetylation, carboxylation, methylation, dehydration, phosphorylation, hydroxylation, formylation, amidation and sulfation. The PTMs might play roles in modulating the functions of the proteins in various biological activities including regulation, localization and interactions with other cellular components of the immune system. In summary, these findings have the potential to be further investigated to be used as prognostic/diagnostic markers for SLE. | en_US |