Thrombospondin-1 Is an Endogenous Activator of TGF-β in Experimental Diabetic Nephropathy In Vivo

Abstract

OBJECTIVE—Transforming growth factor-β (TGF-β), the central cytokine responsible for the development of diabetic nephropathy, is usually secreted as a latent procytokine complex that has to be activated before it can bind to its receptors. Recent studies by our group demonstrated that thrombospondin-1 (TSP-1) is the major activator of latent TGF-β in experimental glomerulonephritis in the rat, but its role in diabetic nephropathy in vivo is unknown. RESEARCH DESIGN AND METHODS—Type 1 diabetes was induced in wild-type (n = 27) and TSP-1–deficient mice (n = 36) via streptozotocin injection, and diabetic nephropathy was investigated after 7, 9.5, and 20 weeks. Renal histology, TGF-β activation, matrix accumulation, and inflammation were assessed by immunohistology. Expression of fibronectin and TGF-β was evaluated using real-time PCR. Furthermore, functional parameters were examined. RESULTS—In TSP-1–deficient compared with wild-type mice, the amount of active TGF-β within glomeruli was significantly lower, as indicated by staining with specific antibodies against active TGF-β or the TGF-β signaling molecule phospho-smad2/3 or the typical TGF-β target gene product plasminogen activator inhibitor-1. In contrast, the amount of glomerular total TGF-β remained unchanged. The development of diabetic nephropathy was attenuated in TSP-1–deficient mice as demonstrated by a significant reduction of glomerulosclerosis, glomerular matrix accumulation, podocyte injury, renal infiltration with inflammatory cells, and renal functional parameters. CONCLUSIONS—We conclude that TSP-1 is an important activator of TGF-β in diabetic nephropathy in vivo. TSP-1–blocking therapies may be considered a promising future treatment option for diabetic nephropathy.

Blockade of TSP1-Dependent TGF-β Activity Reduces Renal Injury and Proteinuria in a Murine Model of Diabetic Nephropathy

“…8,9 The increase in nephrin expression in LSKL-treated Akita kidneys suggests that one mechanism by which LSKL reduces proteinuria is by preventing TGF-␤-mediated podocyte damage. This would be consistent with the observations of Daniel et al, 36 who showed that diabetic TSP1 knockout mice have increased staining for the podocyte antigen desmin. LSKL treatment of rats with mesangioproliferative glomerulonephritis also preserved podocyte marker expression as measured by Wilms Tumor suppressor gene staining.…”

“…7,30,35,36,38,39,53,54 In the present studies, we addressed whether selective targeting of only TGF-␤ activated by TSP1 would be an effective approach to reduce renal dysfunction in a mouse model of type 1 diabetes. These studies showed that i.p.…”

“…61 The present findings are unusual in that mesangial sclerosis was not affected by LSKL treatment but albuminuria was reduced. Given the known effects of TSP1 and LSKL peptide on blockade of glucose-stimulated TGF-␤ activity and matrix production by cultured mesangial cells and the reduced mesangial sclerosis in diabetic TSP1 knockout mice, 33,36,64 it is possible that mesangial accessibility of LSKL peptide administered i.p. was insufficient to attenuate glomerulosclerosis, although the effects of LSKL on nephrin expression and glomerular phospho-Smad levels suggest that the peptide is accessible.…”

“…7,31,33 There is also evidence that TSP1-mediated latent TGF-␤ activation is involved in the development of diabetic nephropathy: TSP1 protein is increased in the glomeruli of patients with types 1 and 2 diabetic nephropathy, which correlates with increased TGF-␤ activity. 34,35 Moreover, streptozotocin-treated TSP1 null mice do not develop glomerulosclerosis or podocyte loss, 36 and mice with induced expression of USF2 have increased TSP1 expression, TGF-␤ activity, and renal fibrosis. 37 TSP1 expression correlates with proteinuria in patients with type 2 diabetes, 34 and glycated albumin stimulates increased TSP1 expression and tubular hypertrophy.…”

Rôle de la thrombospondine-1 dans le développement des maladies rénales

“…L'injection intrarénale d'oligonucléotides antisens anti-TSP-1 permet une réduction de l'activation glomérulaire du TGF- et de l'accumulation de protéines de la MEC (collagènes I et IV, fibronectine) dans un modèle de glomérulonéphrite membrano-proliférative induite par des anticorps antiThy1 chez le rat [43]. Après induction d'un diabète par la streptozocine chez les souris TSP-1 KO, l'expression glomérulaire de TGF-, des Smad2 et -3 phosphorylées et de PAI-1 (plasminogen activator inhibitor-1), l'accumulation mésangiale de fibronectine et de collagène IV, les lésions podocytaires, l'infiltration interstitielle par les macrophages et les lymphocytes, et la protéinurie sont réduites [44]. Enfin, l'activation rénale du TGF- et les lésions tubulo-interstitielles induites par l'obstruction urété-rale unilatérale sont atténuées chez la souris TSP-1 KO [29].…”