EXPRESSION OF TRANSFORMING GROWTH-FACTOR-BETA-1 DURING DIABETIC RENALHYPERTROPHY

Expression of transforming growth factor-beta 1 during diabetic renal hypertrophy. Experimental type I diabetes mellitus is characterized by an early increase in kidney weight and glomerular volume, but changes in gene expression accompanying diabetic renal growth have not been f ully elucidated. In the current study, total RNA was extracted from re nal cortex and isolated glomeruli of streptozotocin-induced diabetic r ats 24 hours, 48 hours, 96 hours, one and two weeks after the onset of hyperglycemia (blood glucose >15 mmol/liter), insulin-treated diabeti c rats (blood glucose <6.0 mmol/liter), and normal rats. RNA samples w ere reverse transcribed (RT) and subjected to polymerase chain reactio n (PCR) amplication with specific 5' and 3' primers for rat transformi ng growth factor (TGF-beta 1) and beta-actin. RT-PCR analysis revealed that glomerular TGF-beta 1 mRNA levels increased relative to beta-act in as early as 24 hours after the onset of hyperglycemia, reaching a p lateau after 96 hours that was sustained at one and two weeks. In cort ical samples, TGF-beta 1 mRNA levels increased less abruptly, reaching a peak one week after the onset of hyperglycemia. Intensive insulin t reatment to normalize blood glucose levels attenuated the rise in glom erular and renal cortical TGF-beta 1 mRNA. Cryostat sections of rat ki dneys were immunostained for TGF-beta 1 utilizing a polyclonal anti-po rcine TGF-beta 1 antibody and semiquantitative scoring of TGF-beta 1 i mmunostaining revealed a twofold increase in diabetic glomeruli after two weeks compared to normal glomeruli. Increased segmental immunostai ning for TGF-beta 1 was also evident in cortical tubules of diabetic r ats. These studies establish that TGF-beta 1 expression in the kidney increases during the phase of rapid renal hypertrophy in diabetic rats . Normalization of blood glucose levels with insulin treatment attenua tes the increase in TGF-beta 1 expression.