Antibodies to T- and L-isoforms of the cytoskeletal protein, fimbrin, in patients with systemic lupus erythematosus

Targeting actin-bundling protein L-plastin as an anabolic therapy for bone loss

The actin-bundling protein L-plastin (LPL) mediates the resorption activity of osteoclasts, but its therapeutic potential in pathological bone loss remains unexplored. Here, we report that LPL knockout mice show increased bone mass and cortical thickness with more mononuclear tartrate-resistant acid phosphatase-positive cells, osteoblasts, CD31^hiEmcn^hi endothelial vessels, and fewer multinuclear osteoclasts in the bone marrow and periosteum. LPL deletion impeded preosteoclasts fusion by inhibiting filopodia formation and increased the number of preosteoclasts, which release platelet-derived growth factor-BB to promote CD31^hiEmcn^hi vessel growth and bone formation. LPL expression is regulated by the phosphatidylinositol 3-kinase/AKT/specific protein 1 axis in response to receptor activator of nuclear factor-κB ligand. Furthermore, we identified an LPL inhibitor, oroxylin A, that could maintain bone mass in ovariectomy-induced osteoporosis and accelerate bone fracture healing in mice. In conclusion, we showed that LPL regulates osteoclasts fusion, and targeting LPL serves as a novel anabolic therapy for pathological bone loss.

Enhanced reactivity to malondialdehyde-modified proteins by systemic lupus erythematosus autoantibodies

OBJECTIVE

Evaluation of the reactivity of autoantibodies of systemic lupus erythematosus (SLE) patients directed against malondialdehyde (MDA)-modified catalase, superoxide dismutase (SOD), and different Hep2 protein fractions (hydrophobic, hydrophilic, and nuclear).

METHOD

Thiol groups and MDA-protein adducts were first assessed among 65 SLE patients and 60 healthy controls. Then, the reactivities of SLE immunoglobulin (Ig)G autoantibodies towards MDA-modified and unmodified proteins were compared using a standard enzyme-linked immunosorbent assay (ELISA).

RESULTS

An increase in the levels of MDA-modified proteins and a decrease in the concentration of thiol groups among SLE patients (p < 0.05) were observed. IgG circulating autoantibodies in the sera of SLE patients exhibited a significant enhanced reactivity (p < 0.05) against catalase and SOD-modified proteins. The same data were observed in the different protein fractions extracted from cultured cells (p < 0.05).

CONCLUSION

These data reinforce the role of oxidative stress and especially lipid peroxidation products in the progression of SLE disease.

Identification of L-plastin autoantibody in plasma of patients with non-Hodgkin's lymphoma using a proteomics-based analysis

Background

The diagnosis of malignant lymphoma (ML) such as non-Hodgkin's lymphoma (NHL) and Hodgkin's lymphoma (HL) was mainly performed by morphological examination and gene analysis. There are only a few serum/plasma biomarkers such as lactate dehydrogenase and soluble interleukin-2 receptor α to diagnose ML. The classifications are various, and therefore the cell surface markers using flow cytometry or lymph node biopsy have been examined. It is difficult, however, to distinguish the two diseases, NHL and HL, from each other.

Methods

In order to identify the haematological malignancy-associated autoimmunoreactivity (autoantibodies) in patients' plasma, a novel proteomics-based approach using electrophoresis/mass spectrometry was applied. Solubilized proteins from a Burkitt's lymphoma cell line (Raji) were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blotting analysis, in which the plasma of individual patients with haematological malignancies was tested for primary antibodies, followed by visualization with anti-IgG antibody conjugated with horseradish peroxidase.

Results

Two proteins, L-plastin and α-enolase, capable of reacting with the antibodies in plasma of patients with NHL, were detected using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry and tandem mass spectrometry. The rates of the detections of an anti L-plastin autoantibody were significantly higher: 0.84 (21/25) in patients with NHL; 0.00 (0/4) in HL; 0.38 (5/13) in autoimmune diseases; 0.20 (2/10) in leukaemia; and 0.13 (1/8) in healthy controls. In contrast, those of anti α-enolase antibody were not specific to NHL.

Conclusions

We first identified autoantibody against L-plastin in plasma of patients with NHL, suggesting that the autoantibody can be a new diagnostic biomarker for NHL.

Plastins: versatile modulators of actin organization in (patho)physiological cellular processes

Many actin-binding proteins are expressed in eukaryotic cells. These polypeptides assist in stabilizing and rearranging the organization of the actin cytoskeleton in response to external stimuli, or during cell migration and adhesion. Here we review a particular set of actin-binding proteins called plastins. Plastins (also called fimbrins) belong to a subclass of actin-binding proteins known as actin bundling proteins. Three isoforms have been characterized in mammals: T-plastin is expressed in cells from solid tissue, whereas L-plastin occurs predominantly in hematopoietic cells. The third isoform, I-plastin, is specifically expressed in the small intestine, colon and kidney. These proteins share the unique property of cross-linking actin filaments into tight bundles. Although plastins are primarily involved in regulation of the actin cytoskeleton, they possess some unique features. For instance, they are implicated in invasion by pathogenic bacteria such as Shigella flexneri and Salmonella typhimurium. Also, L-plastin plays an important role in leukocyte function. T-plastin, on the other hand, is possibly involved in DNA repair. Finally, both T- and L-plastin are implicated in several diseases, and L-plastin is considered to be a valuable marker for cancer.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Detection of anti-acetylcholine receptor antibody by an ELISA using human receptor from a rhabdomyosarcoma cell line

A simple and reliable enzyme-linked immunosorbent assay (ELISA) has been developed for the measurement of anti-acetylcholine receptor (AChR) antibodies. The test utilizes a membrane-bound AChR obtained from a human rhabdomyosarcoma cell line (TE671) as antigen and employs an affinity-purified rabbit anti-human immunoglobulin G alkaline phosphatase-conjugated antibody as labelled antibody. To assess the sensitivity and the specificity of our assay we tested serum samples from 13 anti-AChR antibody-positive myasthenia gravis (MG) patients known to contain between 2 and 120 nmol/l of anti-AChR antibody, three anti-AChR antibody-negative MG patients, and 70 control subjects including patients with other neurological and autoimmune diseases. A panel of six different anti-AChR monoclonal antibodies and membranes from a AChR-negative rat adrenal pheochromocytoma cell line (PC 12) were also used in competitive studies. The test showed to be specific and able to detect as low as 2.0 nmol/l of anti-AChR antibodies. Moreover, we found a good correspondence between anti-AChR antibody levels measured in the serum samples tested by our assay and levels measured by the routinely adopted radioimmuno assay (RIA) using human-AChR (r = 0.96). Cross-reaction phenomena were observed only using serum samples containing high-titer anti-DNA antibodies. The proposed ELISA, circumventing the limitation of the commonly used RIA (radioactivity and amputated legs as source of human antigen), can be considered as an useful screening test for the diagnosis of myasthenia gravis.