Expression of Transforming Growth Factor-beta1 in Spontaneously Developed Diabetic Rats

Kim, Hyung Yup; Jang, Jae Hwi; Han, Sang Mi; Ahn, Ki Sung; Park, Sung Bae; Kim, Hyun Chul; Park, Kwan Kyu

Abstract

BACKGROUND
Diabetic nephropathy is a common cause of end-stage renal disease by means of glomerular and interstitial fibrosis. Increases in extracellular matrix (ECM) and changes in its components have been documented in the glomeruli of diabetic nephropathy. Fibrogenic cytokines, particularly transforming growth factor (TGF)-beta1, play a central role in progressive renal fibrosis. Activated TGF-beta1 is known to increase the production of ECM as collagen and fibronectin. Otsuka Long-Evans Tokushima Fatty (OLETF) rat is an inbred strain that spontaneously develops non-insulin-dependent diabets mellitus which progresses to diabetic glomerulosclerosis. This study is examined the time points and localization of TGF-beta1 in diabetic glomerulosclerosis of OLETF rats. METHODS: OLETF rats, a chronic model for human type 2 diabetes mellitus, and age-matched control (LETO) rats were used. Blood was assayed for glouse and body weight were measured. From rats aged 30 to 60 weeks, animals were sacrificed under ether anesthesia, and both kidneys were removed. Portions of these tissues were processed for light microscopy and immunohistochemistry of TGF-beta1. TGF-beta1 mRNA levels were measured by reverse transcription polymerase chain reaction.
RESULTS
The body weights of OLETF rats were significantly greater than those of LETO rats from the age of 30 to 40 weeks, but those of OLETF rats gradually decreased after 40 weeks of age. There were no differences in body weights between these two strains at 50 weeks of age. Blood glucose levels of OLETF rats increased significantly with aging and were significantly higher than those of LETO rats after 32 weeks of age. There was no significant fibrosis in kidney of OLETF and LETO rats at all ages examined. The TGF-beta1 protein was detected in the glomerular endothelial cells and tubular epithelial cells of OLETF rats at 35 to 38 weeks of age. The TGF-beta1 protein in tubular epithelial cells of OLETF rats was strongly expressed at 60 weeks of age, whereas the glomerular endothelial cells scarcely detected the expression of TGF-beta1 protein. In LETO rat kidneys, the TGF-beta1 protein is detected in the glomerular endothelial cells at 35 weeks of ages, but is not detected in any other cells. The TGF-beta1 mRNA of OLETF rats were increased at 32 weeks of age, higher than that of control LETO rats.
CONCLUSION
Until 60 weeks of age, glomerular sclerosis became very weakly in OLETF rats. However, in 30-week-old OLETF rats, the blood gloucose levels and TGF-beta1 protein increased significantly. The TGF-beta1 protein was detected in the glomerular endothelial cells and tubular epithelial cells of OLETF rats at 37 weeks of age.