Neural and Glial Change at Early Stage in Spontaneous Diabetes Torii Rats

Abstract

Purpose: : A spontaneous diabetic Torii (SDT) rats is a recently established strain from Sprague–Dawley rats, which spontaneously develops diabetes mellitus (DM) at 10 w postnatally and neovascularization in retina at later stage. DM is known to cause neurodegeneration at early stage in addtion to the vascular change in retina. The purpose of this study is to examine the retinal neuronal cell death and glial reactivity at the pre– and early stage of DM in SDT rat retina.

Methods: : SDT rats of postnatal 10, 20, 40 w without treatment and of 40 w with insulin therapy were used. Retinal neuronal cell death was assessed by terminal dUTP nick end labeling (TUNEL) in flat mounted retina. Retinal cryosections were subjected to immunohistochemistry against activated caspase3. Immunohistochemistory against glial fibrillary acidic protein (GFAP) on retinal flat mount and cryosection as well as western blotting probing for GFAP were employed to evaluate glial reactivity.

Results: : SDT rats showed hyperglycemia and glucosuria from 17 w and older. TUNEL positive cells were 10.3±1.5, 6.1±3.7, and 18.2±7.1 per 0.5 cm² retina area in 10, 20, and 40 w without treatment, whereas that was reduced to 8.8±3.9 per 0.5 cm² retina area when treated with insulin. The ratio of the activated caspase 3 immunoreactivity cells relative to total cells in ganglion cell layer and inner nuclear layer was 13.1±6.5, 13.9±4.3, 21.5±4.6 in 10, 20, and 40 w rats without treatment, whereas that was 15.3±3.8 % in 40 w rats with insulin therapy. Thus, there was a tendency of increasing apoptosis of retinal cells with increasing age. Up–regulated GFAP immunoreactivity was detected in Muller cells as early as 20 w. GFAP protein content significantly increased along with DM duration (p= 0.009), which was reversed by insulin therapy.

Conclusions: : Altered glial reactivity preceded neuronal cell death in SDT rat retina. Insulin treatment ameliorated both glial and neuronal change in SDT rats retina.

Keywords: diabetic retinopathy • apoptosis/cell death