Impact of oxLDL and LPS on C-type natriuretic peptide system is different between THP-1 cells and human peripheral blood monocytic cells.

BACKGROUND

The C-type natriuretic peptide (CNP) has anti-inflammatory, anti-proliferative, and anti-migratory properties. The purpose of this study was to investigate the occurrence of CNP and its receptors (NPR2 and NPR3) in a human monocytic cell line (THP-1 cells) as well as in peripheral blood monocytic cells (PBMC). Impact of both, LPS and human oxLDL on expression pattern of CNP and its receptors shall be studied.

METHODS

Cells were cultured in standard medium with or without LPS or oxLDL. Expression levels of CNP, NPR2, NPR3, TNF-α, IL-1β, IL-6, CD14 and CD68 were measured at baseline, 24h, and 48h.

RESULTS

Baseline expression of all analysed genes was significantly higher in PBMC compared to THP-1 cells (all p<0.05). Expression levels of CNP, IL-1β, IL-6, and CD14 were significantly increased in PBMC following stimulation with LPS. In contrast, in THP-1 cells stimulated by LPS, significant increase in expression was found only for IL-6 (p=0.007). In THP-1 cells, oxLDL increased the expression levels of NPR3, TNF-α, IL-1β, IL-6, CD14, and CD68 significantly. In contrast, expression level of NPR2 was diminished by oxLDL (p=0.007). In PBMC NPR3 was significantly down-regulated (p=0.002). Treatment with oxLDL for 48h increased NPR2/3-ratio significantly in PBMC (22.5 vs. 4.8, p=0.010). In contrast, in THP-1 cells, NPR2/3-ratio was lowered significantly by oxLDL (0.31 vs. 17.0, p=0.008).

CONCLUSION

Treatment with LPS or oxLDL leads to diverging changes in gene expression PBMC and THP-1 cells. With respect to CNP and its receptors, data gained from THP-1 cells should be further validated using naive human peripheral blood monocytes. However, THP-1 cells can serve as a negative control for e.g. future signalling pathway studies related to oxLDL effect on CNP system in monocytes/macrophages.