Abstract
ObjectiveMouse models possessing green fluorescent protein (GFP) and/or human aldose reductase (hAR) in vascular tissues have been established and crossed with naturally diabetic Akita mice to produce new diabetic mouse models.Research Design and MethodsColonies of transgenic C57BL mice expressing GFP (SMAA-GFP), hAR (SMAA-hAR) or both (SMAA-GFP-hAR) in vascular tissues expressing smooth muscle actin were established and crossbred with C57BL/6-Ins2Akita/J (AK) mice to produce naturally diabetic offspring AK-SMAA-GFP and AK-SMAA-GFP-hAR. Aldose reductase inhibitor AL1576 (ARI) was administered in chow. Retinal and lenticular sorbitol levels were determined by HPLC. Retinal functions were evaluated by electroretinography (ERGs). Growth factor and signaling changes were determined by Western Blots using commercially available antibodies. Retinal vasculatures were isolated from the neural retina by enzymatic digestion. Flat mounts were stained with PAS-hematoxylin and analyzed.ResultsAkita transgenics developed DM by 8 weeks of age with blood glucose levels higher in males than females. Sorbitol levels were higher in neural retinas of AK-SMAA-GFP-hAR compared to AK-SMAA-GFP mice. AK-SMAA-GFP-hAR mice also had higher VEGF levels and reduced ERG scotopic b-wave function, both of which were normalized by AL1576. AK-SMAA-GFP-hAR mice showed induction of the retinal growth factors bFGF, IGF-1, and TGFβ, as well as signaling changes in P-Akt, P-SAPK/JNK and P-44/42 MAPK that were also reduced by ARI treatment. Quantitative analysis of flat mounts in 18 week AK-SMAA-GFP-hAR mice revealed increased loss of nuclei/capillary length and a significant increase in the percentage of acellular capillaries present which was not seen in AK-SMAA-GFP-hAR treated with ARI.Conclusions/SignificanceThese new mouse models of early onset diabetes may be valuable tools for assessing both the role of hyperglycemia and AR in the development of retinal lesions associated with diabetic retinopathy.
Highlights
Diabetic Retinopathy (DR) is primarily a microvascular complication where a selective degeneration of retinal capillary pericytes occurs
Quantitative analysis of flat mounts in 18 week AKSMAA-green fluorescent protein (GFP)-human aldose reductase (hAR) mice revealed increased loss of nuclei/capillary length and a significant increase in the percentage of acellular capillaries present which was not seen in AK-SMAA-GFP-hAR treated with aldose reductase inhibitors (ARIs)
A colony of transgenic mice (SMAA-GFP) where green fluorescent protein (GFP) was introduced in all vascular tissues containing smooth muscle actin to aid in the identification of retinal capillary pericytes was established from a breeding pair of transgenic C57BL6-SMAA-GFP mice expressing GFP under the control of smooth muscle alpha actin promoter
Summary
Diabetic Retinopathy (DR) is primarily a microvascular complication where a selective degeneration of retinal capillary pericytes occurs. This results in a retinal capillary pericyte to endothelial cell ratio increase from 1:1 in nondiabetics to up to 1:18 in diabetic patients [1,2]. Control retinal capillary blood flow through their contractile nature (presence of smooth muscle actin) and control neovasculogenesis by suppressing the growth of endothelial cells [3,4,5]. Pericyte loss is followed by either an adjacent increased focal growth of endothelial cells to form microaneurysms, or the subsequent degeneration of endothelial cells to form acellular capillaries through which blood, oxygen and nutrients no longer flow. Further studies with canine retinal capillary cells indicate that aldose reductase (AR) is expressed in pericytes and that exposure of retinal capillary cells to high sugar levels initiates apoptosis in pericytes that is prevented by treatment with aldose reductase inhibitors (ARIs) [13,14,15]
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