ACE2 and Ang-(1-7) Confer Protection Against Development of Diabetic Retinopathy

Abstract

Despite evidence that hyperactivity of the vasodeleterious axis (ACE/angiotensin II (Ang II)/AT1 receptor) of the renin-angiotensin system (RAS) is associated with the pathogenesis of diabetic retinopathy (DR) use of the inhibitors of this axis has met with limited success in the control of this pathophysiology. We investigated the hypothesis that enhancing the local activity of the recently established protective axis of the RAS, ACE2/Ang-(1-7), using adeno-associated virus (AAV)-mediated gene delivery of ACE2 or Ang-(1-7) would confer protection against diabetes-induced retinopathy. Genes expressing ACE2 and Ang-(1-7) were cloned in AAV vector. The effects of ocular AAV-ACE2/Ang-(1-7) gene transfer on DR in diabetic eNOS(-/-) mice and Sprague-Dawley (SD) rats were examined. Diabetes was associated with approximately tenfold and greater than threefold increases in the ratios of ACE/ACE2 and AT1R/Mas mRNA levels in the retina respectively. Intraocular administration of AAV-ACE2/Ang-(1-7) resulted in significant reduction in diabetes-induced retinal vascular leakage, acellular capillaries, infiltrating inflammatory cells and oxidative damage in both diabetic mice and rats. Our results demonstrate that DR is associated with impaired balance of retinal RAS. Increased expression of ACE2/Ang-(1-7) overcomes this imbalance and confers protection against DR. Thus, strategies enhancing the protective ACE2/Ang-(1-7) axis of RAS in the eye could serve as a novel therapeutic target for DR.

Adeno-Associated Virus Overexpression of Angiotensin-Converting Enzyme-2 Reverses Diabetic Retinopathy in Type 1 Diabetes in Mice

“…A secreted form of human ACE2 lacking the membrane domain, which has been previously characterized, 17 was cloned into an AAV vector under the control of the chicken b-actin promoter and packaged into serotype 2 viral particles, as previously described. 10 Serotype 2 typically infects ganglion cells in the ganglion cell layer and horizontal and amacrine cells in the inner nuclear layer. 10 Previously, we found that this secreted, truncated ACE2 had approximately fourfold higher activity in media from transfected cells and approximately eightfold higher activity in serum collected from systemically injected neonatal rats when compared with the membrane-bound enzyme.…”

“…10 Serotype 2 typically infects ganglion cells in the ganglion cell layer and horizontal and amacrine cells in the inner nuclear layer. 10 Previously, we found that this secreted, truncated ACE2 had approximately fourfold higher activity in media from transfected cells and approximately eightfold higher activity in serum collected from systemically injected neonatal rats when compared with the membrane-bound enzyme. 17 This viral vector, delivered by intravitreal injection, resulted in a greater than twofold increase of ACE2 activity with a approximately 50% decrease of Ang II and a 2.3-fold increase of Ang(1-7) levels.…”

“…17 This viral vector, delivered by intravitreal injection, resulted in a greater than twofold increase of ACE2 activity with a approximately 50% decrease of Ang II and a 2.3-fold increase of Ang(1-7) levels. 10 The control vector contained a GFP coding region in reverse sequence.…”

“…12,13 The most widely proposed explanation for this shortcoming is that the blood-retinal barrier limits access of therapeutic concentrations of systemically administered pharmaceuticals, such that suppression of the classic RAS in ocular tissues fails to occur. 10 From these data, the notion has emerged that restoring the balance between the classic RAS and its endogenous counterbalance, the vasoprotective RAS, represents a viable strategy for controlling DR in humans. The crucial enzyme in this axis is ACE2, which converts the vasoconstrictive and proinflammatory peptide, Ang II, into the vasodilatory and anti-inflammatory peptide, angiotensin-(1-7) [Ang(1-7)], which mediates its effects primarily through the receptor Mas.…”

“…9,10 Accordingly, systemically administered ACE1 inhibitors and AGTR1 antagonists attenuate retinal microvascular disease in diabetic rodents by decreasing vascular hyperpermeability, acellular capillaries, and the expression of angiogenic factors, such as vascular endothelial growth factor. 9,11 Despite the clear success of systemic RAS blockade in diabetic rodents, systemic suppression in humans has led to only marginal improvement.…”