Neutrophil-platelet cross-talk in acute renal inflammation

Glomerulonephritis is a leading cause of end-stage renal failure and is characterised by inflammation of glomeruli (tufts of capillaries which carry blood within the kidneys for filtration). In this disease white blood cells (e.g. neutrophils) incorrectly get activated and start to fight against us by attacking and damaging tissue in the kidney, which eventually leads to leakage of blood into the urine. Neutrophils are considered as the primary immune cells to cause injury and dysfunction of the kidney in acute glomerulonephritis via the release of chemically reactive molecules (i.e. reactive oxygen species (ROS)). Furthermore, neutrophils have been shown in other inflammatory diseases to produce neutrophil extracellular traps (NETs) in dependence of ROS. NETs are a network of fibres primarily composed of DNA, which can bind and eliminate infectious agents, but can also cause tissue injury if uncontrolled. It is possible that these NETs are also formed during glomerulonephritis and promote kidney damage in this disease. Besides neutrophils, also platelets accumulate in inflamed glomeruli, facilitating neutrophil recruitment and activation. However, the precise mechanisms of these processes and how platelets contribute to the development of the disease are not understood. It is hypothesised that intercellular cross- talk between platelets and neutrophils via direct contacts initiate the release of harmful factors by neutrophils and promote NET formation. The aim of this project is to define the dynamics of neutrophil-platelet interactions in acute glomerular inflammation and to investigate the underlying mechanisms in mediating kidney damage. Using advanced microscopy techniques these neutrophil-platelet contacts will be directly visualised in the renal microvasculature and examined in a mouse model of glomerulonephritis. This method allows us to monitor the formation of platelet-neutrophil aggregates and cellular responses (e.g. ROS production and NET formation) in response to inflammatory stimuli in real time in the live kidney. Hence, it provides a potential tool to analyse cellular behaviour within the body. The molecules produced by platelets and neutrophils that are likely to be activating neutrophils and NET release, and thereby causing the disease will be assessed in more detail using isolated blood cells and specialised in vitro techniques (i.e. flow chamber assays). This allows us to analyse specific molecules individually in order to decipher the intricacies of these self-injuring processes. Together, these experiments will provide an unparalleled understanding of how platelets and neutrophils interact during acute renal inflammation to injure the glomerulus. These discoveries will help to find selective ways of blocking these injurious pathways to develop more effective and saver therapies to treat inflammatory diseases such as glomerulonephritis.

Glomerulonephritis is a leading cause of end-stage kidney failure. In this disease immune cells (such as neutrophils in acute glomerulonephritis) are incorrectly activated and start to fight against us by attacking and damaging tissue in the kidney. In the present FWF-funded project, we found that cross-talk between different cells (e.g. between platelets and immune cells called neutrophils) initiate inflammation and the release of harmful factors by neutrophils, thereby contributing to this disease. Highly advanced microscopy techniques allowed us to visualise these interactions and to study the behaviour of the cells involved in real time. In this context, interactions between platelet and neutrophils occurred within small blood vessels in the kidney compromising a structure called glomerulus. These structures in the kidney play a very important role filtrating blood and removing unwanted chemicals or waste. During acute glomerulonephritis, we found that platelets physically interact with neutrophils for a prolonged time and release stimuli, which lead to neutrophil activation and their release of harmful factors such as reactive oxygen species damaging these structures. This eventually leads to a loss of kidney function by leakage of blood and protein into the urine. Thereby, our findings demonstrate that platelets in the blood directly contribute to immune cell activation and inflammation in the kidney and describe a previously unknown mechanism leading to the development of glomerulonephritis. We hope that data arising from this work will help to better understand the cause of glomerulonephritis and help to develop more effective and saver therapies to block these injurious pathways in patients in the future.