ATR1 blockage ameliorates neuronal but not vascular degeneration in diabetic retinopathy in TetO rats

Abstract

Purpose : TetO rats show early neurovascular degeneration and inflammation as hallmarks of diabetic retinopathy (DR) in Type-2 Diabetes (T2D). Although the renin-angiotensin system plays an important role in the progression of DR, its influence on the neurovascular changes in DR has not been systematically evaluated. Here we address the role of angiotensin-II receptor 1 (ATR1) blockage on the neurovascular unit in vivo and ex vivo.

Methods : Diabetes was provoked by tetracycline-inducible shRNA targeting the insulin receptor. TetO rats were used 6 weeks after the onset of T2D. One experimental group received oral ATR1-antagonist at the onset of T2D (Losartan, 10 mg/kg/d). Age-matched Sprague-Dawley (SD) rats served as controls. Neurovascular unit in the retina was evaluated ex vivo in whole-mounts and sagittal sections. Retina was analyzed in vivo by optical coherence tomography (OCT) and fluorescence angiography (FAG). Retinal function was assessed by GanzfeldERG.

Results : Retina of TetO rats did not present severe structural differences compared to SD controls; however, OCT revealed a relative retinal thinning of 16%. Vasculature in diabetic retinae presented acellular capillaries and differences in venous stiffness and caliber. Leakage was not detectable in FAG but ex vivo via albumin extravasation in sagittal sections. TetO rats showed signs of Müller cell activation. The total number as well as the proportion of activated mononuclear phagocytes was increased in TetO, especially in the superficial retina. TetO rats presented significant loss of retinal ganglion cells (RGC) compared to SD controls. Decrease of both scotopic a- and b-waves combined with an increase in b/a-wave ratio in TetO indicated photoreceptor malfunction. The decrease in oscillatory potentials implied hypoxia in the TetO retina.
The losartan-treated group presented reduced Müller cell activation and an overall improvement of the retinal function together with RGC recovery. No significant effects were found on vascular and inflammatory features.

Conclusions : TetO rats represent a promising model for early changes of DR in T2D. Neurovascular degeneration was assessed in vivo and ex vivo. ATR1 blockage revealed an effect on the neuronal component but not on the vascular one.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.