ADAMTS13/ VWF Axis Potentially Contributes to Diabetic Nephropathy By Regulating PAI-1 Levels

Background and objective: ADAMTS13 (A Disintegrin And Metalloprotease with Thrombospondin type I repeats-13) cleaves von Willebrand factor (VWF), a large multimeric protein that plays an important role in hemostasis and thrombosis. Severe deficiency or very low levels of ADAMTS13 in presence of external stimuli results in accumulation of thrombogenic ultra large VWF multimers (which are released from activated endothelium) known to trigger thrombotic microangiopathy. Activated endothelium/dysfunction is a prominent feature of diabetic nephropathy, and advanced diabetic glomerulopathy often exhibits thrombotic microangiopathy. Significantly reduced ADAMTS13 and increased plasma VWF levels have been found in diabetic patients with nephropathy. Although major site of ADAMTS13 synthesis is liver, ADAMTS13 is also expressed by podocytes in normal renal cortex. It remains unknown, however, whether VWF and ADAMTS13 imbalance plays a causal role in development of nephropathy in diabetic patients or rather is simply an associate marker of disease status, possibly secondary to endothelial function. We performed experiments in genetic models to determine whether ADAMTS13 and VWF axis contributes to diabetic nephropathy.

Methods: Male, 8-10 weeks old wild-type (WT), Adamts13^-/- and Vwf ^-/- mice were made diabetic by injecting multiple low doses of streptozotocin (60 mg/kg, i.p. for five consecutive days). Successful diabetes induction was tested after 2 weeks by measuring blood glucose. Mice having blood glucose levels above 300 mg/dL were included in the study. Controls were nondiabetic littermate mice treated with citrate buffer. The extent of renal injury was evaluated after 28 weeks of diabetes induction by measuring albuminuria and kidney to body weight ratio. Renal hypertrophy and extracellular matrix deposition was quantified by hematoxylin and immunostaining. PAI-1 mRNA and protein levels were measured by real time quantitative RT-PCR and ELISA.

Results: Adamts13^-/- diabetic mice exhibited significantly increased kidney to body weight ratio (P<0.05 vs. WT diabetic mice). Urine albuminuria, an index of renal injury was significantly elevated in Adamts13^-/- diabetic mice (P<0.05 vs. WT diabetic mice). Increased renal injury in Adamts13^-/- diabetic mice was concomitant with increased renal hypertrophy and extracellular matrix (ECM) deposition within glomeruli (P<0.05 vs. WT diabetic mice). Murine studies have shown that PAI-1 contributes to diabetic nephropathy by regulating TGF-beta and ECM deposition. A positive association exists between increased PAI-1 levels in glomeruli and microangiopathy in patients with diabetic nephropathy. We determined whether ADAMTS13 deficiency-induced microangiopathy in glomeruli increases PAI-1 levels. Adamts13^-/- diabetic mice exhibited increased PAI-1 mRNA and protein levels (P<0.05 vs. WT diabetic mice). VWF remains the only known substrate of ADAMTS13 and increased plasma VWF levels have been associated with diabetic nephropathy. We determined the role of VWF in diabetic nephropathy. Vwf ^-/- diabetic mice exhibited significantly decreased kidney weight/body weight ratio, less urinary albuminuria, decreased kidney PAI-1 expression levels concomitant with improved kidney morphological changes (P<0.05 vs. WT diabetic mice).

Conclusion: These findings provide experimental evidence for the first time that ADAMTS13/ VWF axis potentially contributes to diabetic nephropathy, most likely by regulating PAI-1 levels.