RAS plays a vital role in regulating many physiological processes of the vascular system. Angiotensin II (Ang II), a product of angiotensin converting enzyme (ACE), mediates its effects through activation of either the AT1 receptor – to induce vasoconstriction, proliferation, fibrosis, and inflammation – or the AT2 receptor to promote NO generation. The protective arm of RAS involves ACE2, which produces angiotensin-(1-7) [Ang-(1-7)]. Ang-(1-7) activates the MAS receptor to promote vascular health. Because diabetic endothelial progenitor cells are dysfunctional and this limits their utility in autologous cell therapy, we asked whether angiotensin (Ang)-(1-7) could restore the vasoreparative function of diabetic CD34+cells.
Healthy nondiabetic (ND) and diabetic (D) Lin−CD45midCD34+ cells were obtained from peripheral blood mononuclear cells (PB-MNCs) by FACS. The effect of Ang-(1-7) on migration, proliferation, NO bioavailability, reactive oxygen species (ROS) levels and NADPH oxidase activity were evaluated in ND- and D-CD34+ cells. The effect of Ang-(1-7) on the formation of ECFCs from ND- and D-MNCs was evaluated. Ang-(1-7) production by cells was analyzed and the expression of ACE2 and Mas-receptor were assessed by real-time PCR and flow cytometry. Effects of ACE2 activators XNT and DIZE in CD34+ cells were also evaluated. D-CD34+ cells were genetically modified to overexpress Ang-(1-7) by lentiviral Ang-(1-7)-fusion transgene and their function was evaluated in vitro. The effect of transduction on the surface expression of CD133, CD34 and CD309 was assessed. In vivo homing function was assessed in a mouse model of ischemia-reperfusion (I/R). After one week of I/R insult, when retinal capillary damage was appreciable, CD34 cells were intravitreally injected. Neural retinas were harvested after 48 hours and human cells within the mouse vasculature were localized by immunohistochemistry.
Migration to SDF1- and VEGF-were impaired in D-CD34+ cells. In contrast, Ang-(1-7)-induced migration in both D-CD34+ and ND-CD34+cells was dependent on Mas receptor expression and eNOS. ROS levels and NADPH oxidase activity were reduced and proliferation and NO bioavailability were restored in D-CD34+ cells by Ang-(1-7). ECFCs from D-MNCs were appeared only in the presence of Ang-(1-7). Migration, NO release and Ang-(1-7) release by ACE2 activators, XNT and DIZE, were significantly decreased in D-CD34+ cells. Ang-(1-7) release and ACE2 expression were decreased in D-cells while Mas-receptor expression was similar that in ND-cells. Ang-(1-7) gene-modified cells showed reduced ROS levels, increased NO bioavailability, enhanced migration to SDF-1 and proliferation. Lentiviral transduction did not alter surface expression of CD133, CD34 and CD309. Ang-(1-7)-overexpression restored the homing efficiency of D-CD34+ cells similar to that of ND-CD34+ cells in vivo.
Ang-(1-7) stimulates the vasoreparative functions in CD34+ cells. Ang-(1-7) bypasses the reduced ACE2 seen in diabetic CD34+ cells and restores the vasoreparative potential of these cells by decreasing oxidative stress and normalizing NO bioavailability. Pharmacological strategies that either increase ACE2 or Ang-(1-7) in diabetic CD34+ cells will improve their therapeutic utility for autologous cell therapy in treatment of diabetic complications.
No relevant conflicts of interest to declare
Asterisk with author names denotes non-ASH members.