Effects of calcitonin gene-related peptide on apoptosis of peripheral blood mononuclear cells from patients with systemic lupus erythematosus

Abstract

Background: Systemic lupus erythematosus (SLE) is an autoimmune disease with abnormal apoptosis and autoantibody production. Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by the central and peripheral nervous systems and by endocrine cells. It can influence cell death in thymocytes and cultured smooth muscle cells, and inhibits the production of interleukin (IL)-2, which inhibits apoptosis.

Aims: To investigate the effects of calcitonin gene-related peptide (CGRP) on apoptosis of peripheral blood mononuclear cells (PBMCs) from patients with SLE.

Methods: The percentage of apoptosis of PBMCs from patients with SLE and healthy blood donors were examined using annexin-V/propidine iodide staining 48 h after culturing with CGRP and/or its receptor antagonist CGRP(8-37) at various concentrations. IL-2 activity in culture supernatants was determined using the incorporation of 3H-TdR by the IL-2-dependent cell line CTLL and evaluated by ELISA.

Results: The percentage of spontaneous apoptosis of PBMCs from patients with SLE was higher than that of healthy blood donors (34.18 +/- 2.86 vs. 18.23 +/- 0.81, P < 0.001). CGRP, at all tested concentrations, had no effect on apoptosis of PBMCs from healthy blood donors, but significantly inhibited apoptosis of PBMCs from patients with SLE at concentrations of >or= 0.5 x 10(-8) mol/L (0.5 x 10(-8) mol/L: 32.01 +/- 3.98 vs. 34.18 +/- 2.86, P < 0.05; 1.0 x 0(-8) mol/L: 26.76 +/- 2.69 vs. 34.18 +/- 2.86, P < 0.001; 1.5 x 10(-8) mol/L: 25.97 +/- 2.65 vs. 34.18 +/- 2.86, P < 0.001), and the effect plateaued at 1.0 x 10(-8) mol/L, at which level inhibition was not significantly increased with increasing concentration. However, CGRP, at any concentration tested, could not reduce the rate of apoptosis of PBMCs from patients with SLE to the normal range. There were significant positive relationships between the effect of CGRP, on apoptosis of PBMCs and SLE Disease Activity Index (0.5 x 10(-8) mol/L: r(s) = 0.328, P < 0.05; 1.0 x 10(-8) mol/L: r(s) = 0.431, P < 0.01; 1.5 x 10(-8) mol/L: r(s) = 0.419, P < 0.01). CGRP(8-37) itself had no effect on apoptosis, but was able to block the effects of CGRP on PBMCs (0.5 x 10(-8) mol/L: 32.01 +/- 3.98 vs. 33.12 +/- 2.37, P < 0.05; 1.0 x 10(-8) mol/L: 26.76 +/- 2.69 vs. 34.73 +/- 2.32, P < 0.001; 1.5 x 10(-8) mol/L: 25.97 +/- 2.65 vs. 35.25 +/- 3.37, P < 0.001). There was no effect of CGRP on IL-2 production.

Conclusions: These results indicate that CGRP plays an important role in the apoptosis of PBMCs from patients with SLE via its receptor; low plasma levels of CGRP may cause accelerated apoptosis. This regulation does not seem to be related to IL-2.