Endothelial Progenitors: A Consensus Statement on Nomenclature

Endothelial progenitor cell (EPC) nomenclature remains ambiguous and there is a general lack of concordance in the stem cell field with many distinct cell subtypes continually grouped under the term “EPC.” It would be highly advantageous to agree on standards to confirm an endothelial progenitor phenotype and this should include detailed immunophenotyping, potency assays, and clear separation from hematopoietic angiogenic cells which are not endothelial progenitors. In this review, we seek to discourage the indiscriminate use of “EPCs,” and instead propose precise terminology based on defining cellular phenotype and function. Endothelial colony forming cells and myeloid angiogenic cells are examples of two distinct and well‐defined cell types that have been considered EPCs because they both promote vascular repair, albeit by completely different mechanisms of action. It is acknowledged that scientific nomenclature should be a dynamic process driven by technological and conceptual advances; ergo the ongoing “EPC” nomenclature ought not to be permanent and should become more precise in the light of strong scientific evidence. This is especially important as these cells become recognized for their role in vascular repair in health and disease and, in some cases, progress toward use in cell therapy. Stem Cells Translational Medicine 2017;6:1316–132

Homocysteine Induces Phosphatidylserine Exposure in Cardiomyocytes through Inhibition of Rho Kinase and Flippase Activity.

AIMS: Increased levels of homocysteine (Hcy) form an independent risk factor for cardiovascular disease. In a previous study we have shown that Hcy induced phosphatidylserine (PS) exposure to the outer leaflet of the plasma membrane in cardiomyocytes, inducing a pro-inflammatory phenotype. In the present study the mechanism(s) involved in Hcy-induced PS exposure were analyzed. METHODS: H9c2 rat cardiomyoblasts were subjected to 2.5 mM D,L-Hcy and analyzed for RhoA translocation and activity, Rho Kinase (ROCK) activity and expression and flippase activity. In addition, the effect of ROCK inhibition with Y27632 on Hcy-induced PS exposure and flippase activity was analyzed. Furthermore, GTP and ATP levels were determined. RESULTS: Incubation of H9c2 cells with 2.5 mM D,L-Hcy did not inhibit RhoA translocation to the plasma membrane. Neither did it inhibit activation of RhoA, even though GTP levels were significantly decreased. Hcy did significantly inhibit ROCK activation, but not its expression, and did inhibit flippase activity, in advance of a significant decrease in ATP levels. ROCK inhibition via Y27632 did not have significant added effects on this. CONCLUSION: Hcy induced PS exposure in the outer leaflet of the plasma membrane in cardiomyocytes via inhibition of ROCK and flippase activity. As such Hcy may induce cardiomyocytes vulnerable to inflammation in vivo in hyperhomocysteinaemia patients

Synthesis and secretion of plasminogen activators and plasminogen activator inhibitor by endothelial cells

The vascular endothelium is generally thought to be the main source of t-PA in the blood, and to be involved in the regulation of the extrinsic fibrinolysis route. 1 This view has been developed over a 30-year period, after Astrup and Permin 2 demonstrated that human tissues contain an activator of plasminogen.* The first evidence that the endothelial cells are involved in fibrinolytic activity was given by Todd, 4 who developed a histological technique for the localization of fibrinolytic activity in tissue sections. Further evidence for the role of endothelial cells in fibrinolysis was obtained by immunolocalization studies, which demonstrated the presence of t-PA in endothelial cells of tissue slices, and by investigations on cultured endothelial cells. The latter studies have mainly been done on human and bovine endothelial cells. Endothelial cells in vitro not only produce t-PA, but also synthesize a potent PA inhibitor and are able to synthesize u-PA. The endothelial cell PA inhibitor is similar to the PA inhibitor in blood plasma and appears to be an important factor in the regulation of fibrinolysis. 5

Mevastatin increases eNO synthase expression and inhibits lipid peroxidation in human endothelial cells

Statins can protect endothelial activation independent from their lipid-lowering effects. To gain more insight in mechanisms via which HMG-CoA inhibition may attenuate endothelial activation, we assessed the effects of mevastatin on eNOS expression of non- and modified-LDL treated endothelial cells and on basal and hydrogen peroxide-induced lipid peroxidation. Oxidized-LDL (Ox-LDL), but not glycated or acylated LDL decreased eNOS expression in human endothelial cells. The extent to which Ox-LDL decreases eNOS expression depends on the extent of modification of Ox-LDL. Mevastatin increased eNOS-expression, both in the presence and absence of Ox-LDL. In addition, mevastatin decreased the H2O2-induced (100 μM) lipid peroxidation in endothelial cells. This study shows that mevastatin has protective effects on endothelial cells by inducing eNOS and by inhibiting lipid peroxidation