Normal Sirt1 and WT mice had similar glucose and HDL levels, and the severity of hyperglycemia (blood glucose and glycated hemoglobin) was also similar in WT and Sirt1 mice with diabetes ( Supplementary Table 1). Glycated hemoglobin was measured after the mice had diabetes for ∼6 months using a kit from Helena Laboratories (Beaumont, TX), and serum HDL was quantified as described previously ( 23). Mice were sacrificed ∼8 months after diabetes was induced one eye was fixed in 10% buffered formalin, and the retina from the other eye was removed immediately to obtain biochemical measurements. Compared with normal WT mice, although Sirt1 expression was significantly increased in the retina of Sirt1 mice, we found no increase in kidneys from the same animals ( Supplementary Fig. Age-matched normal WT and Sirt1 mice were used as their respective controls. Mice presenting blood glucose >250 mg/dL 2 days after the last injection were considered to have diabetes ( 19, 22). Thus strategies targeted to ameliorate Sirt1 inhibition have the potential to maintain retinal vascular and neuronal homeostasis, providing opportunities to retard the development of diabetic retinopathy in its early stages.ĭiabetes was induced in wild-type C57BL/6J (WT) and Sirt1-overexpressing ( St, C57BL/6-Actbtm3.1 Npa/J Sirt1) mice (The Jackson Laboratory, Bar Harbor, ME), with a body weight (BW) of ∼20 g (either sex), by streptozotocin injection (55 mg/kg BW for four consecutive days). Diabetic wild-type mice had hypermethylated Sirt1 promoter DNA, which was alleviated in diabetic Sirt1 mice, suggesting a role for epigenetics in its transcriptional suppression. Diabetic Sirt1 mice were also protected from mitochondrial damage and had normal electroretinography responses and ganglion cell layer thickness. Compared with diabetic wild-type mice, retinal vasculature from diabetic Sirt1 mice did not present any increase in the number of apoptotic cells or degenerative capillaries or decrease in vascular density. The role of epigenetics in Sirt1 transcriptional suppression was investigated in retinal microvessels. Using Sirt1-overexpressing mice that were diabetic for 8 months, structural, functional, and metabolic abnormalities were investigated in vascular and neuronal retina. Our aim was to determine the role of Sirt1 in the development of diabetic retinopathy and to elucidate the molecular mechanism of its downregulation. Sirtuin 1 (Sirt1), a multifunctional deacetylase, is implicated in the regulation of many cellular functions and in gene transcription, and retinal Sirt1 is inhibited in diabetes. Diabetic retinopathy is a multifactorial disease, and the exact mechanism of its pathogenesis remains obscure.
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