Studies were undertaken to examine any role for the hepcidin/ferroportin axis in proliferative responses of human pulmonary artery smooth muscle cells (hPASMCs). Entirely novel findings have demonstrated the presence of ferroportin in hPASMCs. Hepcidin treatment caused increased proliferation of these cells most likely by binding ferroportin resulting in internalisation and cellular iron retention. Cellular iron content increased with hepcidin treatment. Stabilisation of ferroportin expression and activity via intervention with the therapeutic monoclonal antibody LY2928057 reversed proliferation and cellular iron accumulation. Additionally, IL-6 treatment was found to enhance proliferation and iron accumulation in hPASMCs; intervention with LY2928057 prevented this response. IL-6 was also found to increase hepcidin transcription and release from hPASMCs suggesting a potential autocrine response. Hepcidin or IL-6 mediated iron accumulation contributes to proliferation in hPASMCs; ferroportin mediated cellular iron excretion limits proliferation. Haemoglobin also caused proliferation of hPASMCs; in other novel findings, CD163, the haemoglobin/haptoglobin receptor, was found on these cells and offers a means for cellular uptake of iron via haemoglobin. Il-6 was also found to modulate CD163 on these cells. These data contribute to a better understanding of how disrupted iron homeostasis may induce vascular remodelling, such as in pulmonary arterial hypertension.

The interplay between iron and oxygen is longstanding and central to all aerobic life. Tight regulation of these interactions including homeostatic regulation of iron utilization ensures safe usage of this limited resource. However, when control is lost adverse events can ensue, which are known to contribute to an array of disease processes. Recently, associations between disrupted iron homeostasis and pulmonary artery hypertension (PAH) have been described with the suggestion that there is a contributory link with disease. This review provides a background for iron regulation in humans, describes PAH classifications, and discusses emerging literature, which suggests a role for disrupted iron homeostatic control in various sub-types of PAH, including a role for decompartmentalization of hemoglobin. Finally, the potential for therapeutic options to restore iron homeostatic balance in PAH are discussed.

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Emerging studies from the ongoing covid-19 pandemic have implicated vascular dysfunction and endotheliitis in many patients presenting with severe disease. However, there is limited evidence for the expression of ACE2 (the principal co-receptor for Sars-Cov-2 cellular attachment) in vascular endothelial cells which has prompted the suggestion that the virus does not infect these cell types. However, the studies presented here demonstrate enhanced expression of ACE2 at the level of both mRNA and protein, in human pulmonary artery endothelial cells (PAECs) challenged with either IL-6 or hepcidin. Notably elevated levels both these iron-regulatory elements have been described in Covid-19 patients with severe disease and are further associated with morbidity and mortality. Additionally, levels of both IL-6 and hepcidin are often elevated in the elderly and in chronic disease settings, these populations being at greater risk of adverse outcomes from Sars-Cov-2 infection. A role for IL-6 and hepcidin as modulators of ACE2 expression seems plausible, additional, studies are required to determine if viral infection can be demonstrated in PAECs challenged with either of these iron-regulatory elements.