Expression of Smad1 is directly associated with mesangial matrix expansion in rat diabetic nephropathy.
Diabetic nephropathy is the leading cause of end-stage renal disease, and glomerular mesangial matrix expansion is the hallmark in diabetic nephropathy. However, the precise mechanism for the development of mesangial matrix expansion has remained unknown. The key component involved in mesangial matrix expansion is type IV collagen (Col4). Recently, we have reported that Smad1 transcriptionally regulates expression of Col4 under diabetic conditions in vitro. Here we show that this direct regulator of Col4 also plays a crucial role for mesangial matrix expansion in vivo. Streptozotocin-induced diabetic rats are the model of incipient diabetic nephropathy, and showed various levels of mesangial matrix expansion at 24 weeks. The glomerular expression of Smad1 was significantly increased in diabetic rats with more mesangial matrix expansion by Western blot and immunohistochemical analysis. Furthermore, the glomerular expression of Smad1 was closely correlated with the glomerular expression of Col4 and smooth muscle alpha actin (alpha-SMA), while albuminuria or glomerular filtration rate was not correlated with mesangial matrix expansion. We also found that urinary excretion of Smad1 was closely associated with the severity of mesangial matrix expansion. In cultured mesangial cells expression of Smad1 upregulated the transcriptional activity of key molecules in mesangial matrix expansion, such as Col4 and alpha-SMA. These data indicate the critical involvement of Smad1 in mesangial matrix expansion in the early phase of diabetic nephropathy. Our data imply that urinary Smad1 might be a representative diagnostic marker for mesangial matrix expansion in diabetic nephropathy.
Matsubara
Takeshi
T
Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Abe
Hideharu
H
Arai
Hidenori
H
Nagai
Kojiro
K
Mima
Akira
A
Kanamori
Hiroshi
H
Sumi
Eriko
E
Takahashi
Toshikazu
T
Matsuura
Motokazu
M
Iehara
Noriyuki
N
Fukatsu
Atsushi
A
Kita
Toru
T
Doi
Toshio
T
D000199:Actins / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D024141:Collagen Type IV / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D015870:Gene Expression; D005920:Glomerular Mesangium / Q000503:physiopathology*; D007676:Kidney Failure, Chronic / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D007678:Kidney Glomerulus / Q000378:metabolism* / Q000473:pathology; D008297:Male; D050527:Mesangial Cells / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D051898:Smad1 Protein / Q000378:metabolism* / Q000502:physiology / Q000652:urine
D000199:Actins; D024141:Collagen Type IV; D051898:Smad1 Protein; C497400:Smad1 protein, rat; C498862:Acta2 protein, rat