Expression of transforming growth factor-β1 during diabetic renal hypertrophy

Abstract

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 fully elucidated. In the current study, total RNA was extracted from renal cortex and isolated glomeruli of streptozotocin-induced diabetic rats 24 hours, 48 hours, 96 hours, one and two weeks after the onset of hyperglycemia (blood glucose > 15 mmol/liter), insulin-treated diabetic rats (blood glucose < 6.0 mmol/liter), and normal rats. RNA samples were reverse transcribed (RT) and subjected to polymerase chain reaction (PCR) amplication with specific 5' and 3' primers for rat transforming growth factor (TGF-beta 1) and beta-actin. RT-PCR analysis revealed that glomerular TGF-beta 1 mRNA levels increased relative to beta-actin as early as 24 hours after the onset of hyperglycemia, reaching a plateau after 96 hours that was sustained at one and two weeks. In cortical samples, TGF-beta 1 mRNA levels increased less abruptly, reaching a peak one week after the onset of hyperglycemia. Intensive insulin treatment to normalize blood glucose levels attenuated the rise in glomerular and renal cortical TGF-beta 1 mRNA. Cryostat sections of rat kidneys were immunostained for TGF-beta 1 utilizing a polyclonal anti-porcine TGF-beta 1 antibody and semiquantitative scoring of TGF-beta 1 immunostaining revealed a twofold increase in diabetic glomeruli after two weeks compared to normal glomeruli. Increased segmental immunostaining for TGF-beta 1 was also evident in cortical tubules of diabetic rats. 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 attenuates the increase in TGF-beta 1 expression.

Alterations in the expression of the a 3 b 1 integrin in certain membrane domains of the glomerular epithelial cells (podocytes) in diabetes mellitus

“…However, a down-regulation of the a 3 by TGF-b1 has been reported in glomeruli from nephrotic rats [23], and rat alveolar epithelial cells cultured in the presence of this factor [49]. Our finding of a decreased expression of the a 3 in podocytes of hyperglycaemic animals, might thus be considered as an early effect of the high glucose levels and/or overexpression of TGF-b1 [46]. Early alteration of podocyte integrins in diabetes and particularly in the domain facing the GBM could influence the alterations occurring in the glomerular wall and in the progress of the diabetic nephropathy.…”

“…High glucose levels and TGF-b1 seem to act on glomerular cells by increasing production of ECM components [41][42][43] and by reducing the expression and activity of metalloproteinases [44] and cathepsins [44,45]. An overexpression of the TGF-b1 has been reported to occur in diabetic rat kidneys as early as 2-3 days after the induction of hyperglycaemia [46]. Although there is a large body of evidence correlating hyperglycaemia and TGF-b1 with the ECM accumulation in diabetic glomerulopathy [41][42][43], little is known about the action of these factors on b 1 integrin expression in renal cells [47,23].…”

Glucosamine activates the plasminogen activator inhibitor 1 gene promoter through Sp1 DNA binding sites in glomerular mesangial cells.

“…Analogous to the pivotal role played by TGF-␤ in many pathological conditions associated with scarring, in vivo and in vitro studies have implicated TGF-␤1 overexpression in the pathogenesis of diabetic nephropathy (8,15,81). Glucosamine increases TGF-␤1 mRNA and protein levels (25,26).…”

Advanced glycation end products and their receptors co-localise in rat organs susceptible to diabetic microvascular injury

“…The amount of staining for AGEs was defined as the area of brown pigment detected by the videoimaging system [17]. The degree of AGE staining within glomeruli was expressed as a proportion, which was calculated as the quotient of the area of the AGE staining and the total glomerular area.…”