Abstract
AimsMonocytes play an important role in hypertension. Circulating monocytes in humans exist as classical, intermediate, and non-classical forms. Monocyte differentiation can be influenced by the endothelium, which in turn is activated in hypertension by mechanical stretch. We sought to examine the role of increased endothelial stretch and hypertension on monocyte phenotype and function.Methods and resultsHuman monocytes were cultured with confluent human aortic endothelial cells undergoing either 5% or 10% cyclical stretch. We also characterized circulating monocytes in normotensive and hypertensive humans. In addition, we quantified accumulation of activated monocytes and monocyte-derived cells in aortas and kidneys of mice with Angiotensin II-induced hypertension. Increased endothelial stretch enhanced monocyte conversion to CD14++CD16+ intermediate monocytes and monocytes bearing the CD209 marker and markedly stimulated monocyte mRNA expression of interleukin (IL)-6, IL-1β, IL-23, chemokine (C-C motif) ligand 4, and tumour necrosis factor α. STAT3 in monocytes was activated by increased endothelial stretch. Inhibition of STAT3, neutralization of IL-6 and scavenging of hydrogen peroxide prevented formation of intermediate monocytes in response to increased endothelial stretch. We also found evidence that nitric oxide (NO) inhibits formation of intermediate monocytes and STAT3 activation. In vivo studies demonstrated that humans with hypertension have increased intermediate and non-classical monocytes and that intermediate monocytes demonstrate evidence of STAT3 activation. Mice with experimental hypertension exhibit increased aortic and renal infiltration of monocytes, dendritic cells, and macrophages with activated STAT3.ConclusionsThese findings provide insight into how monocytes are activated by the vascular endothelium during hypertension. This is likely in part due to a loss of NO signalling and increased release of IL-6 and hydrogen peroxide by the dysfunctional endothelium and a parallel increase in STAT activation in adjacent monocytes. Interventions to enhance bioavailable NO, reduce IL-6 or hydrogen peroxide production or to inhibit STAT3 may have anti-inflammatory roles in hypertension and related conditions.
Highlights
In 2016, hypertension was ranked as the leading risk factor for global burden of disease in both developed and underdeveloped countries.[1]
These findings provide insight into how monocytes are activated by the vascular endothelium during hypertension
This is likely in part due to a loss of nitric oxide (NO) signalling and increased release of IL-6 and hydrogen peroxide by the dysfunctional endothelium and a parallel increase in STAT activation in adjacent monocytes
Summary
In 2016, hypertension was ranked as the leading risk factor for global burden of disease in both developed and underdeveloped countries.[1]. The mechanism by which monocytes promote hypertension remains undefined but likely involves transformation into activated states or into other cell types, including macrophages and monocyte-derived dendritic cells (DCs). De Ciuceis et al found that mice lacking macrophage colony-stimulating factor, required for the stimulation of macrophage formation from monocytes, are protected against blood pressure (BP) elevation.[4] these mice are protected from vascular remodelling, vascular superoxide production and the alteration of endothelium-dependent vasodilation that normally accompanies hypertension.[4] Likewise, monocyte-derived DCs seem to play a critical role in hypertension. The production of IL-17 by T cells is critical for maintenance of Ang II-induced hypertension and vascular dysfunction.[8] we have observed increased IL-17A producing T cells in the circulation of hypertensive humans.[9]
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