Enhanced TGF-beta/Smad signaling in the early stage of diabetic nephropathy is independent of the AT1a receptor.
BACKGROUND
Angiotensin II (AII) and transforming growth factor-beta (TGF-beta) are closely involved in the pathogenesis of diabetic nephropathy (DN). AII is known to induce TGF-beta production in resident renal cells, including glomerular mesangial cells and tubular epithelial cells. TGF-beta receptor types I and II (TGF-betaRI, II) are up-regulated in the diabetic kidney. The aim of this study was to clarify the role of AII in the regulation of the TGF-beta system in the early stage of DN using AII type1a receptor-deficient(AT1a(-/-)) mice.


METHODS
We investigated the expression of TGF-beta1, TGF-betaRI, II, and Smad signaling in AT1a(-/-) mice with streptozotocin (STZ)-induced DN. Mice were killed 10 and 20 days after the induction of hyperglycemia. The expression of TGF-beta receptors was analyzed by immunohistochemical staining and reverse transcriptase-polymerase chain reaction (RT-PCR). TGF-beta-specific Smad signaling was analyzed by electrophoretic mobility shift assay and Western blotting.


RESULTS
The expression of both TGF-betaRI and RII was up-regulated in the glomerular tufts and vasculature in diabetic AT1a(+/+) mice kidney by immunohistochemistry. RT-PCR revealed that mRNAs for TGF-betaRI and RII were also up-regulated. Smad2 and 4 protein levels were reduced in the renal cortex after the induction of diabetes, with an increase of Smad 3/4 complex in the nucleus. The expression of TGF-beta receptors increased in both diabetic AT1a(-/-) and AT1a(+/+) mice. Smad signaling in AT1a(-/-) mice was also enhanced.


CONCLUSIONS
Our results suggest that the complete blockade of the AT1a-mediated pathway has a minimal effect on the enhanced TGF-beta/Smad signaling in the early stage of DN, at least in the AT1a(-/-) model.
Okazaki
Yuko
Y
Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8558, Japan. yahman-a-and-y@r5.dion.ne.jp
Yamasaki
Yasushi
Y
Uchida
Haruhito A
HA
Okamoto
Kazunori
K
Satoh
Minoru
M
Maruyama
Keisuke
K
Maeshima
Yohei
Y
Sugiyama
Hitoshi
H
Sugaya
Takeshi
T
Kashihara
Naoki
N
Makino
Hirofumi
H
D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology; D015870:Gene Expression; D007668:Kidney / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism*; D012084:Renin-Angiotensin System / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051785:Smad Proteins / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism
D044140:Receptor, Angiotensin, Type 1; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D000804:Angiotensin II