Heterogeneity of Phospholipase D Activation by Angiotensin II, Lysophosphatidylcholine, and Insulin in Human Endothelial Cells

An improved and reliable method for isolation of microvascular endothelial cells from human omentum

OBJECTIVES

Despite an increasing research demand for human microvascular endothelial cells, isolation of primary endothelial cells from human tissue remains difficult. The omentum, a highly vascular visceral adipose tissue, could provide an excellent source of these cells.

METHODS

A reliable method to isolate HOMECs has been developed. It consists of initial enzymatic digestion (to deplete cell contaminants), followed by further digestion, selective filtration, and immunoselection using Dynabeads coated with CD31 antibody. Cultures were characterized for expression of endothelial cell markers and their ability to undergo VEGF-dependent in vitro tube structure formation.

RESULTS

Omental-derived cultures of microvascular endothelial cells were achieved with <5% contamination of other cell types. The endothelial origin of cells was confirmed by the constitutive expression of a range of vascular endothelial markers (CD31, CD105, vWF) and internalization of DiI-AcLDL. Furthermore, cultures were negative for lymphatic endothelial markers, underwent in vitro angiogenesis, and exhibited typical endothelial morphology.

CONCLUSIONS

This isolation method produces homogeneous HOMEC cultures that can be maintained in vitro for at least six passages without loss of cellular features characterizing endothelial cells.

The stimulatory effect of angiotensin II on Na(+)-ATPase activity involves sequential activation of phospholipases and sustained PKC activity

Angiotensin II (Ang II) stimulates the proximal tubule Na(+)-ATPase through the AT(1) receptor/phosphoinositide phospholipase Cbeta (PI-PLCbeta)/protein kinase C (PKC) pathway. However, this pathway alone does not explain the sustained effect of Ang II on Na(+)-ATPase activity for 30 min. The aim of the present work was to elucidate the molecular mechanisms involved in the sustained effect of Ang II on Na(+)-ATPase activity. Ang II induced fast and correlated activation of Na(+)-ATPase and PKC activities with the maximal effect (115%) observed at 1 min and sustained for 30 min, indicating a pivotal role of PKC in the modulation of Na(+)-ATPase by Ang II. We observed that the sustained activation of PKC by Ang II depended on the sequential activation of phospholipase D and Ca(2+)-insensitive phospholipase A(2), forming phosphatidic acid and lysophosphatidic acid, respectively. The results indicate that PKC could be the final target and an integrator molecule of different signaling pathways triggered by Ang II, which could explain the sustained activation of Na(+)-ATPase by Ang II.