Placenta growth factor (PlGF) induces vascular endothelial growth factor (VEGF) secretion from mononuclear cells and is co-expressed with VEGF in synovial fluid

Abstract

The aims of this study were (i) to determine whether PlGF, VEGF and PlGF/VEGF heterodimers are detected in synovial fluid (SF) and plasma samples from patients with a range of arthropathies; (ii) to describe whether any correlation exists between SF PlGF, VEGF and PlGF/VEGF heterodimer levels and the total and differential SF leucocyte counts; and (iii) to investigate the regulation of peripheral blood mononuclear cell (PBMC) VEGF secretion by stimuli relevant to inflammatory joints. PlGF, VEGF and PlGF/VEGF heterodimer levels were measured in the SF and plasma of patients with a range of arthropathies and normal controls by ELISA. Western blotting for PlGF was performed on SF from three patients with rheumatoid arthritis (RA) and primary inflammatory arthropathies. VEGF was quantified in cell culture supernatants after stimulation with lipopolysaccharide (LPS), PlGF or cobalt ions of PBMC isolated from RA patients and controls. PlGF and VEGF were detected in all SF samples. PlGF/VEGF heterodimers were detected in 10.2% of SF samples, most frequently in RA samples. Western blotting confirmed the presence of PlGF in RA SF. PlGF was detected in 52% of RA and 31% of control plasma samples, and VEGF was detected in 38% of RA and 38% of control plasma samples. PlGF/VEGF heterodimers were detected in 21% of RA samples and none of the control samples. In primary inflammatory arthropathy patients, SF PlGF and VEGF levels correlated significantly with the SF total leucocyte count and the neutrophil count. PlGF was the most potent inducer of PBMC VEGF production in both RA and control subjects. This is the first report of the detection of PlGF and PlGF/VEGF heterodimers in the SF of patients with inflammatory arthropathies, and we have shown for the first time that PlGF up-regulates PBMC VEGF production. PlGF may therefore play a key role in the production of VEGF in the inflammatory joint.

Fig. 1

Synovial fluid levels (mean ± s.e.m.) of PlGF (a) (*P < 0.05 compared with non-inflammatory arthropathy (NI) group, one-way anova with Bonferroni correction), VEGF (b) (*P < 0.05 compared with NI and osteoarthritis (OA) groups, one-way anova with Bonferroni correction) and PlGF/VEGF heterodimers (c) (P = NS). RA, Rheumatoid arthritis; PA, primary inflammatory arthropathy; JRA, juvenile rheumatoid arthritis; CA, crystal arthropathy; SN, seronegative arthritis.

Fig. 2

Western blot of PlGF detected in synovial fluid (SF). Lane 1, rPlGF-positive control; lanes 2–4, SF from three patients with rheumatoid arthritis; lanes 5–7, SF from three patients with primary inflammatory arthropathies.

Fig. 3

Correlation between synovial fluid (SF) PlGF and total leucocyte and neutrophil counts (a) (total leucocyte count r = 0.69, P = 0.006 and neutrophil count r = 0.67, P = 0.009) and correlation between SF VEGF and total leucocyte and neutrophil counts (b) (total leucocyte count r = 0.76, P = 0.001 and neutrophil count r = 0.79, P < 0.001). ▪, Leucocytes; ▴, neutrophils.

Fig. 4

VEGF secretion (mean ± s.e.m.) by lipopolysaccharide (LPS), cobalt and PlGF-stimulated peripheral blood mononuclear cells isolated from 10 rheumatoid arthritis (RA) patients and 10 normal controls after 24 h culture (a) (*P < 0.05 compared with LPS and cobalt, one-way anova with Bonferroni correction) and 72 h culture (b) (*P < 0.05 compared with cobalt, one-way anova with Bonferroni correction).