#855 Cyclophilin D in cholesterol crystal-induced acute kidney injury
Authors: LI Cong , Mammadova-Bach Elmina , Anders Hans Joachim 
Published: May 2024

Abstract

Background and Aims
Cholesterol crystal embolism (CCE) occurs when cholesterol crystal (CC) clots move from an atherosclerotic plaque in a large artery to a smaller artery, leading to obstruction, ischemia, and organ failure. CCE directly impairs blood flow by provoking a local inflammatory response and triggering arterial thrombus formation, consisting of collagen and fibrin mesh, platelet and neutrophil activation, and extracellular DNA trap formation. Activated platelets form a procoagulant surface that supports adhesion to collagen and fibrin mesh, promoting thrombus growth and the recruitment of immune cells. CCE often targets kidney tissue, leading to thrombotic angiopathy, acute loss of glomerular filtration rate (GFR), and necrosis in tubular cells. Cyclophilin D (CypD) plays a central role in regulating platelet procoagulant activity by triggering calcium bursts and mitochondrial depolarization. While the increased number of procoagulant platelets contributes to thrombosis, CypD-mediated procoagulant pathomechanisms in the kidney during CCE remain unknown. In our study presented here, we hypothesized that CypD deficiency might attenuate procoagulant platelet activity, thereby inhibiting CCE-induced kidney infarction and organ injury.

Method
6-week-old wild-type (WT) and CypD-/- mice were administered 10 mg/kg CC through injections into the left kidney arteries in vivo. Kidneys were collected 24 hours later, and kidney function, infarct size, necroinflammation and kidney injury were evaluated using GFR measurements, TTC colorimetric assay, immunohistochemistry, and immunofluorescence microscopy. For in vitro studies, whole blood samples were isolated from WT and CypD-/- mice and perfused on a collagen-coated surface in the presence or absence of CC under arterial shear conditions of 1000s-1.

Results
After CC injection in mice, CypD deficiency ameliorated immunothrombosis, acute kidney injury, and organ failure. CypD-/- mice were protected from the sudden drop in GFR, i.e., acute kidney injury, which resulted from the reduced number of arteries obstructed by crystal clots. Kidney infarct size consistently decreased in CypD-/- mice. CypD-/- mice displayed reduced neutrophil recruitment to thrombotic microangiopathic lesions, indicating diminished immunothrombosis. Preemptive injection of the CypD inhibitor cyclosporin A could prevent CC-mediated vessel obstruction and infarct size, thereby improving kidney function. Interestingly, WT platelets showed increased platelet adhesion and phosphatidylserine (PS) exposure on a collagen-coated surface in the presence of CC under shear conditions in whole blood, suggesting increased procoagulant activity, which was strongly reduced in CypD-/- platelets.

Conclusion
During CCE-mediated kidney injury, CypD-mediated platelet activation and consequent procoagulant activity accelerate ischemic tissue necrosis and the recruitment of neutrophils. Inhibition of CypD-mediated signaling could be a potential therapeutic approach to inhibit acute kidney injury in patients with CCE.