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G.M. Seigel, S. Lupien, L.M. Campbell, D.N. Ishii; Systemic IGF-1 Treatment Inhibits Neuroretinal Cell Death in Diabetic Rat Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1083.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It is known that progressive diabetic retinopathy can result in apoptotic cell death of retinal neurons, as well as significant visual loss. It is further known that insulin-like growth factor-1 (IGF-1) is reduced in diabetes, and that IGF-1 can prevent cell death in a variety of neuron types. In this study, we tested the hypothesis that systemic treatment with IGF-1 could inhibit apoptotic death of neuroretinal cells in diabetic rats.Methods: Wistar rats (12 weeks old) were randomly assigned to treatment (6 rats per group): ND, non-diabetic; STZ-veh, diabetic with subcutaneous osmotic minipumps releasing vehicle (1 mM acetate, pH 6); or STZ-IGF-1, diabetic rats with pumps releasing IGF-1 (20 µg/rat/day). Rats were diabetic for 11.5 weeks and received vehicle or IGF-1 treatment continuously during the final 7.5 weeks. Eleven-and-a-half weeks later, the animals were killed and their eyes placed in 4% paraformaldehyde. The fixed eyes were embedded in paraffin and 4 mm thin histological sections were made. Neuroretinal cell death was assessed using TUNEL reactivity, as well as immunoreactivity to phospho-Akt (Thr 308), activated caspase-3 and BAD. After staining, cell counts in the ganglion cell layer (GCL), the inner nuclear layer (INL) and photoreceptor layer (PHL) were made for each retinal section. Cell counts were statistically analyzed with Fisher's post hoc least significant differences.Results: For TUNEL measurements, the number of reactive cells increased approximately 12-fold in the PHL (p = 0.0002) and 8-fold in the INL (p = 0.0033) in retinas from STZ-veh vs. ND. For phospho-Akt, immunoreactivity increased 6-fold in the GCL (p< 0.0001) and 3-fold in the INL (p=0.0153) in STZ-veh vs. N.D. For both TUNEL and phospho-Akt, systemic IGF-1 treatment significantly reduced the number of reactive cells approximately to the level of the ND group (STZ-IGF-I vs. STZ-veh; p < 0.014). Activated caspase-3 and BAD immunoreactivities were also qualitatively reduced in IGF-1-treated animals. IGF-1 treatment did not alter ongoing hyperglycemia and weight loss in STZ-IGF-1 vs. STZ-Veh rats. Conclusions: 1) TUNEL and phospho-Akt reactive cells are elevated and localized to distinct cell layers in the retina of STZ diabetic rats. 2) Early intervention with systemic IGF-1 can reduce the presence of pro-apoptotic markers indicative of neuroretinal cell death, despite ongoing hyperglycemia and weight loss in diabetic rats. Future experiments will examine further the effects of IGF-1 on the progression of diabetic retinopathy.
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