Increased phosphatidylserine-exposing microparticles and their originating cells are associated with the coagulation process in patients with IgA nephropathy.

Abstract

Relatively little information is available about phosphatidylserine positive (PS(+)) microparticles (MPs) and their originating cells in IgA nephropathy (IgAN) despite well-established intraglomerular coagulation. Our objectives were to detect PS exposure on MP membranes and MP-origin cells and to evaluate its role in procoagulant activity (PCA) and fibrin formation and their association with pathological lesions in the disease. Patients with IgAN and healthy controls were studied. Lactadherin was used to quantify PS exposure on MPs and MP-origin cells. PCA of MPs and MP-origin cells was evaluated by clotting time and purified coagulation complex assays. Fibrin production was determined by turbidity. PS exposure, fibrin strands and FVa/Xa binding were observed on MPs/cells using confocal microscopy. Using flow cytometry, we found that IgAN patients had high levels of PS(+) MPs derived from lymphocytes, monocytes, neutrophils, platelets, erythrocytes and endothelial cells (ECs). The PS exposure on MP-origin cells also increased in these patients. MPs and MP-origin cells (leukocytes, platelets and erythrocytes) isolated from IgAN patients and ECs cultured with IgAN serum had a significantly shorter median coagulation time (P < 0.001), higher median intrinsic FXa (P < 0.001) and higher thrombin (P < 0.001) generation than controls. These coagulation functional assays were associated with the glomerular lesions. The lesions were also correlated with glomerular fibrin deposition (all P < 0.05). In the presence of patient MPs or their related cells, fibrin formation peaked faster with a higher maximum turbidity when compared with healthy controls. Blocking PS with lactadherin in the IgAN group prolonged coagulation time to control levels, inhibited the PCA up to 80% and markedly reduced fibrin formation. More importantly, we observed that fibrin strands formed on MPs and ECs in the same regions that bound lactadherin, similar to the FVa/Xa costaining. We find that high levels of PS(+) MPs and the MP-origin cells are associated with the coagulation process in IgAN, and this may provide a previously unrecognized contribution to intraglomerular coagulation.