Abstract
Purpose:
We have previously demonstrated morphological changes to retinal microglia and the disruption of microglial networks in response to hyperglycemia in Ins2Akita mice. Here we sought to determine whether exposure to toll-like receptor (TLR) 4 ligand lipopolysaccharide (LPS) or TLR 9 ligand CpG-ODN enhances microglial responses to hyperglycemia and further, drives the development of retinopathy in the Ins2Akita mouse.
Methods:
Ins2Akita mice bear a point mutation in the insulin2 gene, resulting in spontaneous development of hyperglycemia by 4 weeks of age. For this study, Ins2Akita mice were crossed with C57BL/6J Cx3cr1+/gfp mice, allowing for the clinical (Micron III Fundus Camera) and microscopic visualization of Cx3cr1+ microglia. Non-diabetic Cx3cr1+/gfp and diabetic Cx3cr1+/gfp Ins2Akita mice were injected with either 9 μg/g Ultrapure LPS (or PBS control) or 40 μg CpG-ODN (or control Oligo GpC-ODN) and were clinically examined after 24 hours and 1 week respectively. Analysis of changes to microglia and macroglia were performed using a range of monocytic and glial cell markers.
Results:
Clinical evaluation at 24 hours after LPS and 1 week after CpG-ODN treatment revealed no overt changes to the retinal fundus or vasculature in non-diabetic Cx3cr1+/gfp mice or diabetic Cx3cr1+/gfp Ins2Akita mice. Whilst LPS and CpG-ODN treatment of non-diabetic mice resulted in characteristic changes to microglial morphology indicative of activation, microglial reactivity was not further enhanced in Ins2Akita mice. The upregulation of MHC Class II expression was observed on the inner retinal vasculature of non-diabetic Cx3cr1+/gfp mice following CpG-ODN treatment, a phenomenon that was absent in Ins2Akita mice. Muller cell activation was evident in both non-diabetic and diabetic mice 1 week after CpG-ODN treatment, but not 24 hours after treatment with LPS.
Conclusions:
Systemic treatment with LPS or CpG-ODN does not significantly alter microglial reactivity or drive the development of retinopathy in the Ins2Akita mouse.
Keywords: 595 microglia •
499 diabetic retinopathy •
557 inflammation