Fetal growth restriction (FGR) is a prevalent pregnancy complication that significantly increases the risk of infant morbidity and mortality. FGR is characterised by placental oxidative stress resulting from impaired placentation and subsequent exposure to intermittent hypoxia and reoxygenation (H/R). The expression of the critical antioxidant, angiotensin-converting enzyme 2 (ACE2), is reduced in FGR placentae. We aimed to determine the role of placental ACE2 in driving antioxidant capacity in FGR, using an in vitro model of H/R in combination with ACE2 activation or replacement.
Healthy term placental explants (n=8/group) were cultured for 24hrs under normoxic (8% O2) or repeated H/R conditions (alternating 6hr periods of 1% and 8% O2) and concurrently treated with either a) control media alone, b) an ACE2 activator, diminazene aceturate (DIZE), or c) recombinant human (rh)ACE2. ACE2 expression and oxidative and antioxidant markers were then assessed via qPCR, immunoblot, and activity assays.
Exposure to H/R for 24hrs reduced placental ACE2 protein levels (p=0.001). The mRNA expression of key oxidative markers NOX5 and XDH, and the protein levels of NOX4 were all increased by H/R (p=0.008, 0.006, and 0.029). The mRNA expression of the antioxidants SOD1, GSR, NRF2, HO-1 and NQO1 were all increased by H/R (all p<0.01), a finding not conserved when examining activity levels of total SOD and CAT, which were both reduced by H/R (both p<0.01). Treatment with DIZE and rhACE2 partially mitigated H/R induced oxidative stress by reducing NOX5 mRNA and NOX4 protein levels (both p<0.05) and increasing SOD and CAT activities (both p<0.01).
Collectively, this data reveals that ACE2 treatments like DIZE and rhACE2 can mitigate placental oxidative stress in vitro, by reducing oxidative markers and enhancing antioxidant capacity. Ultimately these findings highlight the stimulation of ACE2 as a potential therapeutic target for improving outcomes for pregnancies complicated by FGR.