Studies of ADAMTS13 expression and activity in the kidney

Sammanfattning: Von Willebrand factor (VWF) is an abundant plasma glycoprotein involved in platelet adhesion and aggregation at sites of vascular injury. ADAMTS13 is the sole physiological VWF-cleaving protease, thus regulating the size of thrombus growth. Dysfunctional ADAMTS13 leads to thrombotic thrombocytopenic purpura (TTP), which is either due to mutations (congenital TTP) or auto-antibodies (acquired TTP). The histopathological lesion is termed thrombotic microangiopathy and characterized by disseminated hyaline thrombi in the microvasculature of various organs including the kidney. The present study aimed to investigate ADAMTS13 expression and activity in the kidney. Cultured renal tubular epithelial cells were shown to express biologically active ADAMTS13. Renal tissues from patients with tubulopathy exhibited an altered ADAMTS13 expression pattern in comparison to controls. ADAMTS13 was detected in urine from patients with tubulopathy suggesting local synthesis. Cultured glomerular endothelial cells were also shown to express biologically active ADAMTS13. ADAMTS13-deficiency in mice led to glomerular capillary vessel wall thickening and platelet deposition as demonstrated by electron microscopy. ADAMTS13 was also detected in the glomerular basement membrane (GBM), however its role in VWF-cleavage in the GBM appeared to be minimal, whereas serine protease activity accounted for most of the cleavage. ADAMTS13 deficiency led to complement deposition in kidney from TTP patients and from ADAMTS13-deficient mice. Plasma from TTP patients contained high levels of complement (C3 and C9)-coated endothelial microparticles. Experiments using plasma/serum samples from the patients with added normal platelets perfused over glomerular endothelial cells demonstrated C3 deposition on VWF-platelet strings and on the endothelial cells. Perfusion of patient plasma induced more release of C3- and C9-coated endothelial microparticles than control plasma. The experimental work in this thesis provides evidence for ADAMTS13 in renal tissue including tubular cells, GBM and glomerular endothelial cells. Local production of the protease may contribute to protection of glomerular vessels from injury, in addition to circulatory ADAMTS13. ADAMTS13 deficiency promoted complement deposition which may further aggravate the vascular damage.