Protocol for the induction of innate immune memory in human smooth muscle cells and endothelial cells in vitro.

Non-immune cells, like innate immune cells, can develop a memory-like phenotype in response to priming with microbial compounds or certain metabolites, which enables an enhanced response to a secondary unspecific stimulus. This paper describes a step-by-step protocol for the induction and analysis of trained immunity in human endothelial and smooth muscle cells. We then describe steps for cell culture with cryopreserved vascular cells, subcultivation, and induction of trained immunity. We then provide detailed procedures for downstream analysis using ELISA and qPCR. For complete details on the use and execution of this protocol, please refer to Sohrabi et al. (2020)1 and Shcnack et al.2.

Transforming growth factor-ß1 signalling triggers vascular endothelial growth factor resistance and monocyte dysfunction in type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM) leads to monocyte dysfunction associated with atherogenesis and defective arteriogenesis. Transforming growth factor (TGF)-ß1, placenta growth factor (PlGF)-1 and vascular endothelial growth factor (VEGF)A play important roles in atherogenesis and arteriogenesis. VEGF-receptor (VEGFR)-mediated monocyte migration is inhibited in T2DM (VEGFA resistance), while TGF-ß1-induced monocyte migration is fully functional. Therefore, we hypothesize that TGF-ß antagonises the VEGFA responses in human monocytes. We demonstrate that monocytes from T2DM patients have an increased migratory response towards low concentrations of TGF-ß1, while PlGF-1/VEGFA responses are mitigated. Mechanistically, this is due to increased expression of type II TGF-ß receptor in monocytes under high-glucose conditions and increased expression of soluble (s)VEGFR1, which is known to interfere with VEGFA signalling. VEGFA resistance in monocytes from T2DM patients can be rescued by either experimental down-regulation of TGF-ß receptor expression in vitro or by functional blocking of TGF-ß signalling using either a TGF-ß receptor kinase inhibitor or a TGF-ß neutralizing antibody. Our data demonstrate that both T2DM and high-glucose potentiate the TGF-ß pathway. TGF-ß signalling impairs VEGFR-mediated responses in T2DM monocytes and in this way contributes to mononuclear cell dysfunction, provide novel insights into T2DM vascular dysfunction.

BMP-2 induces human mononuclear cell chemotaxis and adhesion and modulates monocyte-to-macrophage differentiation.

Type 2 diabetes mellitus (T2DM) is a cardiovascular risk factor which leads to atherosclerosis, an inflammatory disease characterized by the infiltration of mononuclear cells in the vessel. Bone morphogenetic protein (BMP)-2 is a cytokine which has been recently shown to be elevated in atherosclerosis and T2DM and to contribute to vascular inflammation. However, the role of BMP-2 in the regulation of mononuclear cell function remains to be established. Herein, we demonstrate that BMP-2 induced human monocyte chemotaxis via phosphoinositide 3 kinase and mitogen-activated protein kinases. Inhibition of endogenous BMP-2 signalling, by Noggin or a BMP receptor inhibitor, interfered with monocyte migration. Although BMP-2 expression was increased in monocytes from T2DM patients, it could still stimulate their migration. Furthermore, BMP-2 interfered with their differentiation into M2 macrophages. Finally, BMP-2 both induced the adhesion of monocytes to fibronectin and endothelial cells (ECs), and promoted the adhesive properties of ECs, by increasing expression of adhesion and pro-inflammatory molecules. Our data demonstrate that BMP-2 could exert its pro-inflammatory effects by inducing monocyte migration and adhesiveness to ECs and by interfering with the monocyte differentiation into M2 macrophages. Our findings provide novel insights into the mechanisms by which BMP-2 may contribute to the development of atherosclerosis.

Leptin-induced transphosphorylation of vascular endothelial growth factor receptor increases Notch and stimulates endothelial cell angiogenic transformation.

Leptin increases vascular endothelial growth factor (VEGF), VEGF receptor-2 (VEGFR-2), and Notch expression in cancer cells, and transphosphorylates VEGFR-2 in endothelial cells. However, the mechanisms involved in leptin's actions in endothelial cells are not completely known. Here we investigated whether a leptin-VEGFR-Notch axis is involved in these leptin's actions. To this end, human umbilical vein and porcine aortic endothelial cells (wild type and genetically modified to overexpress VEGFR-1 or -2) were cultured in the absence of VEGF and treated with leptin and inhibitors of Notch (gamma-secretase inhibitors: DAPT and S2188, and silencing RNA), VEGFR (kinase inhibitor: SU5416, and silencing RNA) and leptin receptor, OB-R (pegylated leptin peptide receptor antagonist 2: PEG-LPrA2). Interestingly, in the absence of VEGF, leptin induced the expression of several components of Notch signaling pathway in endothelial cells. Inhibition of VEGFR and Notch signaling significantly decreased leptin-induced S-phase progression, proliferation, and tube formation in endothelial cells. Moreover, leptin/OB-R induced transphosphorylation of VEGFR-1 and VEGFR-2 was essential for leptin's effects. These results unveil for the first time a novel mechanism by which leptin could induce angiogenic features via upregulation/trans-activation of VEGFR and downstream expression/activation of Notch in endothelial cells. Thus, high levels of leptin found in overweight and obese patients might lead to increased angiogenesis by activating VEGFR-Notch signaling crosstalk in endothelial cells. These observations might be highly relevant for obese patients with cancer, where leptin/VEGFR/Notch crosstalk could play an important role in cancer growth, and could be a new target for the control of tumor angiogenesis.