Introduction Pulmonary arterial hypertension (PAH) is characterised by vascular remodelling of pulmonary arterioles. Disrupted iron homeostasis as well as subclinical haemolysis are implicated in PAH, although exact mechanisms remain unknown. IL-6, a proinflamatory cytokine and regulator of iron homeostasis is elevated in PAH patients and also been implicated in pulmonary vascular remodelling in murine models.
Objectives In this study we explored the influences of free haemoglobin (Hb) on proliferative responses and secondary mediator, IL-6 release in human pulmonary artery endothelial cells (hPAECs).
Methods Cells were challenged with Hb (10 uM) and/or IL-6 (1–10 ng/mL). Transcriptional regulation was analysed by RT-PCR, protein expression by immunocytochemistry, secretion by ELISA and proliferation by BrdU incorporation.
Results Novel findings demonstrate that Hb and IL-6 individually and in combination increased proliferation of hPAECs (by 32%, 47% and 63% respectively; p < 0.05). CD163, a Hb scavenger receptor, was basally expressed as mRNA and protein (cell surface) on hPAECs and further modulated by Hb or IL-6 exposure. Hb treatment also caused increased transcription (30%; p < 0.05) and release of IL-6 (107%; p < 0.01) from hPAECs.
Conclusion This is the first report of Hb-mediated proliferation, CD163 expression and IL-6 release in hPAECs with potential implications for autocrine and paracrine signalling in pulmonary vasculature. Hb uptake may be facilitated via CD163. These studies may provide novel insights regarding mechanisms for haemoglobin driven proliferative and second messenger responses of relevance to PAH.