Relevant Role of Von Willebrand Factor in Ischemia-Reperfusion Model of Acute Kidney Injury in Mice

Acute kidney injury (AKI), an abrupt loss of renal function, is often seen in clinical settings and its mortality remains high even in the developed countries. An adhesive protein von Willebrand factor (VWF) plays a pivotal role in platelet thrombus formation and is recently understood as a key protein in a cross-talk between inflammation and thrombosis. Recent mouse model studies demonstrated that VWF-mediated thrombotic and inflammatory responses could play a role in the disease progression of myocardial infarction or brain stroke. Thus, we assumed that VWF may also be involved in the pathophysiology of AKI, the major cause of which could be an insufficient renal circulation and/or inflammatory cell infiltration in the kidney. To test this hypothesis, we studied the relevant role of VWF in AKI in mouse model of acute ischemia-reperfusion (I/R) kidney injury. All mice used were male, 8-12 weeks of age, healthy and whose right kidney was surgically removed by the standard mouse nephrectomy procedure 1 week prior to the kidney I/R experiment. The preliminary experiments confirmed that surgical removal of mouse right kidney did not affect their general conditions including renal functions. Mice were anesthetized with inhaled isoflurane and then placed in an abdominal position on a heating pad. Surgical incision was given on the left side of back and the left kidney was brought out and kept outside during the operation. Both renal artery and vein were clamped at the renal hilus by a clamping clip for 30 min ischemia. Then a clip was taken off to provoke the reperfusion of renal blood flow, which was monitored by Laser Doppler flowmetry (ALF21, Advance Co, Tokyo, Japan). The kidney was then put back in a body and skin incision was closed. The renal blood flow was measured again 30 h after reperfusion and mice were then sacrificed for blood collection. We compared 15 wild-type (WT) and 16 VWF-gene deleted (knock-out; KO) mice (from The Jackson Laboratory, Bar Harbor, ME). Excess blood loss was not observed in all mice (WT or KO) during whole surgical process. Although no difference was seen immediately after reperfusion, significantly (p < 0.05) higher renal blood flow at 30 h after reperfusion was confirmed in VWF-KO mice, as compared to WT (KO; 24.0±2.3 vs. WT; 15.1±1.46 ml/min/100g of kidney weight, and the reperfusion/base flow ratio: KO; 1.0±0.07 vs. WT; 0.6 ±0.07). Consistent with the renal blood flow data, the serum creatinine value at 30 h after reperfusion were significantly (p < 0.05) lower in VWF-KO mice than WT (KO; 2.77±0.11 vs. WT; 3.15±0.11 mg/dl). Our results suggest that VWF does play a role in the pathogenesis of AKI, in which VWF-dependent thrombotic or inflammatory responses may trigger thrombotic ischemia or endothelial damages of vascular bed in the kidney. Thus, proper functional regulation of VWF would be beneficial for better microcirculation and vessel functions in the kidney, suggesting a novel therapeutic potential against AKI.