The Protective Role of Smad7 in Diabetic Kidney Disease: Mechanism and Therapeutic Potential

Abstract

OBJECTIVEAlthough Smad3 has been considered as a downstream mediator of transforming growth factor-β (TGF-β) signaling in diabetes complications, the role of Smad7 in diabetes remains largely unclear. The current study tests the hypothesis that Smad7 may play a protective role and has therapeutic potential for diabetic kidney disease.RESEARCH DESIGN AND METHODSProtective role of Smad7 in diabetic kidney disease was examined in streptozotocin-induced diabetic mice that have Smad7 gene knockout (KO) and in diabetic rats given Smad7 gene transfer using an ultrasound-microbubble-mediated technique.RESULTSWe found that mice deficient for Smad7 developed more severe diabetic kidney injury than wild-type mice as evidenced by a significant increase in microalbuminuria, renal fibrosis (collagen I, IV, and fibronectin), and renal inflammation (interleukin-1β [IL-1β], tumor necrosis factor-α [TNF-α], monocyte chemoattractant protein-1 [MCP-1], intracellular adhesion molecule-1 [ICAM-1], and macrophages). Further studies revealed that enhanced renal fibrosis and inflammation in Smad7 KO mice with diabetes were associated with increased activation of both TGF-β/Smad2/3 and nuclear factor-κB (NF-κB) signaling pathways. To develop a therapeutic potential for diabetic kidney disease, Smad7 gene was transferred into the kidney in diabetic rats by an ultrasound-microbubble-mediated technique. Although overexpression of renal Smad7 had no effect on levels of blood glucose, it significantly attenuated the development of microalbuminuria, TGF-β/Smad3-mediated renal fibrosis such as collagen I and IV and fibronectin accumulation and NF-κB/p65-driven renal inflammation including IL-1β, TNF-α, MCP-1, and ICAM-1 expression and macrophage infiltration in diabetic rats.CONCLUSIONSSmad7 plays a protective role in diabetic renal injury. Overexpression of Smad7 may represent a novel therapy for the diabetic kidney complication.

Loss of angiotensin-converting enzyme 2 enhances TGF-β/Smad-mediated renal fibrosis and NF-κB-driven renal inflammation in a mouse model of obstructive nephropathy

“…38,39 In contrast, deletion of Smad7 promotes NF-kB-dependent renal inflammation in a mouse model of UUO. 12 Taken together, loss of Smad7 promotes, while overexpression of Smad7 inhibits, TGF-b/ Smad-mediated progressive renal fibrosis and NF-kB-driven renal inflammation as evidenced in a number of kidney disease models including UUO nephropathy, 12,37,40 hypertension-associated remnant kidney disease, 38,41 diabetic nephropathy, 14 and immunologically-mediated glomerulonephritis. 42 Therefore, loss of Ace2 promoted Ang II-induced Smurf2-dependent ubiquitin degradation of renal Smad7 may be another essential mechanism by which Ace2 À/y mice were promoted TGF-b/Smad-mediated renal fibrosis and NF-kB-driven renal inflammation in a mouse model of UUO nephropathy.…”

“…[12][13][14] The number of F4/80 þ cells in the tubulointerstitium was counted under high-power fields ( Â 40 objective) by means of a 0.0625-mm 2 graticule fitted in the eyepiece of the microscope and expressed as cells per millimeters squared (mm 2 ).…”

“…[12][13][14] Briefly, after the protein was transferred onto a nitrocellulose membrane, the membrane was incubated overnight with primary antibodies against phospho-Smad3, phospho-IkBa (ser32), phospho-NF-kB/p65 (ser276), ERK1/2 (Cell Signaling Technology, MA, USA); IkBa, NF-kB/p65, phospho-ERK1/2, Smad2/3, Smad7, ACE2, Smurf2, Ang II receptor-1 (AT1) (Santa Cruz Biotech); a-SMA (Sigma), collagen I (Southern Tech), and GAPDH (Chemicon, Temecula, CA, USA) followed by the LI-COR IRDye 800-labeled secondary antibodies (Rockland Immunochemicals, Gilbertsville, PA, USA) in dark for 1 h at room temperature. Signals were scanned and visualized by Odyssey Infrared Imaging System (LiCor, Lincoln, NE, USA).…”

“…Renal mRNA expression was quantitatively analyzed by realtime PCR with primers against mouse mRNA of IL-1b, TNF-a, MCP-1, TGF-b1, Smad7, collagen I, a-SMA, and GAPDH as Ace2 protects renal fibrosis and inflammation Z Liu et al described previously, [12][13][14] whereas the primers for AT1 and Ace2 were described below: AT1:…”

All-Trans Retinoic Acid Attenuates the Renal Interstitial Fibrosis Lesion in Rats but Not By Transforming Growth Factor-β1/Smad3 Signaling Pathway

“…8 TGF-β/Smad3 signaling plays a central role in tissue fibrogenesis, acting as a potent stimulus of extracellular matrix accumulation. 9 Transforming growth factor-β1 (TGF-β1) is an important subtype of TGF-β.…”