The TetO-IR rat as a model for diabetic retinopathy in type-2 diabetes

Abstract

Purpose: There is an urgent need for rodent models exhibiting early retinal changes in type 2 diabetes. While STZ-induced diabetes (resembling type 1) shows an early inflammatory reaction and macrophage recruitment in the retina (Joussen et al. 2001, 2003 a,b), conditional insulin-receptor knock-out resembles many of the systemic features of type 2 diabetes. We assess here the ocular phenotype of TetO-IR rats and their suitability for pathophysiological and pharmacological investigations.

Methods: We used a tetracycline-inducible shRNA expression system targeting the insulin receptor (IR). Doxycycline treatment of the rats led to a dose-dependent and reversible increase in blood glucose (>400mg/dl) caused by systemic inhibition of IR expression and signaling (Kotnik et al 2009). TetO rats were examined 4-6 weeks after the onset of diabetes and age-matched non-transgenic Sprague-Dawley (SD) rats served as control. Rats were investigated in vivo by fluorescein angiography (FAG), and GanzfeldERG as functional measures. Ganglion cells were quantified on histological sections. Immunohistochemistry on sagittal sections or flatmounts of the retina and the RPE were performed against GFAP, Vimentin, Kir4.1, Iba-1, NG2, Desmin and ZO-1. Gene expression was assessed by taqmanPCR.

Results: <br /> We detected a reduction in the ganglion cell counts. GFAP-Vimentin co-staining revealed an activation of astrocytes and Müller cells in TetO. Kir 4.1 was dislocated in TetO. These findings were associated with a reduction of both the a and the b-wave of the scotopic GanzfeldERG. The b-a wave ratio was increased suggesting a loss of photoreceptor function. Photopic ERG was also decreased. FAG exhibits vascular irregularities including capillary occlusions in TetO rats. There is no sign of microglia activation in retina flatmounts and sagittal sections. On RPE flatmounts, loss of ZO-1 expression as well as morphological alterations of RPE cells were visible indicating a disruption of the blood retina barrier.

Conclusions: The TetO IR rat exhibits several features of diabetic retinopathy. Very early in the course of diabetes, alterations of ganglion cells and Müller cells are present. This indicates, that in type II diabetes, neuronal and vascular alterations are progressing simultaneously.