No abstract

CD34 + hematopoietic stem/progenitor cells (HSPCs) are vasculogenic and hypoxia is a strong stimulus for the vasoreparative functions of these cells. Angiotensinconverting enzyme 2 (ACE2)/angiotensin-(1-7)/Mas receptor (MasR) pathway stimulates vasoprotective functions of CD34 + cells. This study tested if ACE2 and MasR are involved in the hypoxic stimulation of CD34 + cells. Cells were isolated from circulating mononuclear cells derived from healthy subjects (n = 46) and were exposed to normoxia (20% O 2 ) or hypoxia (1% O 2 ). Luciferase reporter assays were carried out in cells transduced with lentivirus carrying ACE2-or MasR-or a scramble-3′-untranslated region gene with a firefly luciferase reporter. Expressions or activities of ACE, angiotensin receptor Type 1 (AT1R), ACE2, and MasR were determined. In vitro observations were verified in HSPCs derived from mice undergoing hindlimb ischemia (HLI). In vitro exposure to hypoxia-increased proliferation and migration of CD34 + cells in basal conditions or in response to vascular endothelial growth factor (VEGF) or stromal-derived factor 1α (SDF) compared with normoxia. Expression of ACE2 or MasR was increased relative to normoxia while ACE or AT1R expressions were unaltered. Luciferase activity was increased by hypoxia in cells transfected with the luciferase reporter plasmids coding for the ACE2-or MasR promoters relatively to the control. The effects of hypoxia were mimicked by VEGF or SDF under normoxia. Hypoxia-induced ADAM17-dependent shedding of functional ACE2 fragments. In mice undergoing HLI, increased expression/activity of ACE2 and MasR were observed in the circulating HSPCs. This study provides compelling evidence for the hypoxic upregulation of ACE2 and MasR in CD34 + cells, which likely contributes to vascular repair. K E Y W O R D S ACE2, CD34 + cells, hypoxia, Mas receptor 1 | BACKGROUND Accumulated evidence based on numerous laboratory and clinical studies strongly support the vasoregenerative functions of bone marrow-derived CD34 + hematopoietic stem/progenitor cells (HSPCs) and their therapeutic potential for the treatment of ischemic vascular disorders (Mackie & Losordo, 2011; Schachinger

Angiotensin-converting enzymes, ACE and ACE2, are key members of renin angiotensin system. Activation of ACE2/Ang-(1-7) pathway enhances cardiovascular protective functions of bone marrow-derived stem/progenitor cells. The current study evaluated the selectivity of ACE2 inhibitors, MLN-4760 and DX-600, and ACE and ACE2 activities in human (hu) and murine (mu) bone marrow cells. Assays were carried out in hu and mu mononuclear cells (MNCs) and huCD34+ cells or mu-lineage-depleted (muLin-) cells, human-recombinant (rh) enzymes, and mu-heart with enzyme-specific substrates. ACE or ACE2 inhibition by racemic MLN-4760, its isomers MLN-4760-A and MLN-4760-B, DX600 and captopril were characterized. MLN-4760-B is relatively less efficacious and less-selective than the racemate or MLN-4760-A at hu-rhACE2, and all three of them inhibited 43% rhACE. In huMNCs, MLN-4760-B detected 63% ACE2 with 28-fold selectivity over ACE. In huCD34+ cells, MLN-4760-B detected 38% of ACE2 activity with 63-fold selectivity. In mu-heart and muMNCs, isomer B was 100- and 228-fold selective for ACE2, respectively. In muLin- cells, MLN-4760-B detected 25% ACE2 activity with a pIC50 of 6.3. The racemic mixture and MLN-4760-A showed lower efficacy and poor selectivity for ACE2 in MNCs and mu-heart. ACE activity detected by captopril was 32 and 19%, respectively, in huCD34+ and muLin- cells. DX600 was less efficacious, and more selective for ACE2 compared to MLN-4760-B in all samples tested. These results suggest that MLN-4760-B is a better antagonist of ACE2 than DX600 at 10μM concentration in human and murine bone marrow cells, and that these cells express more functional ACE2 than ACE.

CD34(+) stem/progenitor cells have been identified as a promising cell population for the autologous cell-based therapies in patients with cardiovascular disease. The counter-regulatory axes of renin angiotensin system, angiotensin converting enzyme (ACE)/Ang II/angiotensin type 1 (AT1) receptor and ACE2/Ang-(1-7)/Mas receptor, play an important role in the cardiovascular repair. This study evaluated the expression and vascular repair-relevant functions of these two pathways in human CD34(+) cells. CD34(+) cells were isolated from peripheral blood mononuclear cells (MNCs), obtained from healthy volunteers. Expression of ACE, ACE2, AT1, and angiotensin type 2 and Mas receptors were determined. Effects of Ang II, Ang-(1-7), Norleu(3)-Ang-(1-7), and ACE2 activators, xanthenone (XNT) and diminazene aceturate (DIZE) on proliferation, migration, and adhesion of CD34(+) cells were evaluated. ACE2 and Mas were relatively highly expressed in CD34(+) cells compared with MNCs. Ang-(1-7) or its analog, Norleu(3)-Ang-(1-7), stimulated proliferation of CD34(+) cells that was associated with decrease in phosphatase and tensin homologue deleted on chromosome 10 levels and was inhibited by triciribin, an AKT inhibitor. Migration of CD34(+) cells was enhanced by Ang-(1-7) or Norleu(3)-Ang-(1-7) that was decreased by a Rho-kinase inhibitor, Y-27632. In the presence of Ang II, XNT or DIZE enhanced proliferation and migration that were blocked by DX-600, an ACE2 inhibitor. Treatment of MNCs with Ang II, before the isolation of CD34(+) cells, attenuated the proliferation and migration to stromal derived factor-1α. This attenuation was reversed by apocynin, an NADPH oxidase inhibitor. Adhesion of MNCs or CD34(+) cells to fibronectin was enhanced by Ang II and was unaffected by Ang-(1-7). This study suggests that ACE2/Ang-(1-7)/Mas pathway stimulates functions of CD34(+) cells that are cardiovascular protective, whereas Ang II attenuates these functions by acting on MNCs. These findings imply that activation of ACE2/Ang-(1-7)/Mas axis is a promising approach for enhancing reparative outcomes of cell-based therapies.