LACK OF ANGIOPOIETIN LIKE-2 PROTECTS AGAINST ANGIOTENSIN II-INDUCED CEREBRAL ENDOTHELIAL DYSFUNCTION IN MICE

Abstract

Angiopoietin like-2 (angptl2) is a recently identified pro-inflammatory and pro-oxidative protein that is elevated in patients with chronic inflammatory and cardiovascular diseases. Its role in regulating endothelial function is largely unknown, and there is no report of the impact of angptl2 in the cerebrovasculature. We hypothesized that the lack of angptl2 improves endothelial cell stress resistance and prevents cerebral endothelial dysfunction induced by a sub-pressor dose of angiotensin II (angII). Subcutaneous infusion of angII (200 ng/kg/min, n=15; osmotic mini-pump), or saline as control (n=15), was performed in 20- to 22-week-old angptl2 knock-down (KD) mice and wild-type (WT) littermates for 14 days. In isolated cerebral arteries of saline-treated KD and WT mice, global acetylcholine (ACh)-induced vasodilations were similar. However, the contribution of endothelium-derived relaxing factors differed: while eNOS-derived O2-/H2O2 contributed to dilation in WT, eNOS-derived NO (P<0.001) was involved in KD mice. Furthermore, angII induced endothelial dysfunction only in WT mice (P<0.01). This was reversed by acute addition of either N-acetylcysteine (10 μM), an anti-oxidant, apocynin (10 μM), a non-selective NADPH oxidase (Nox) inhibitor, or indomethacin (10 μM), a non-selective cyclooxygenase (COX) inhibitor, suggesting that angII-induced endothelial dysfunction in WT mice was related to oxidative stress, Nox activity and/or COX-derived constrictor-derivatives. In KD mice treated with angII, on the other hand, apocynin worsened endothelium-dependent dilation, while N-acetylcysteine and indomethacin were ineffective, suggesting remodeling of the Nox systems, low levels of oxidative stress and COX-derived constrictor derivatives. The demonstration that the lack of angptl2 expression is associated with NO-dependent dilation, prevented angII-induced endothelial dysfunction, and led to a deleterious effect of apocynin, suggests that lowering angptl2 protects cerebral endothelial function and leads to a potential compensatory Nox dilatory pathway, ultimately reinforcing cerebral endothelial cell stress resistance.