Natural Killer Lymphocytes Mediate Renal Fibrosis Due to Acute Cardiorenal Syndrome

Background: The acute kidney injury (AKI) to chronic kidney disease (CKD) transition presents an opportunity for intervention to prevent CKD. Our lab developed a novel murine model of AKI-CKD transition, cardiac arrest and cardiopulmonary resuscitation (CA/CPR), in which all Animals develop CKD at 7 weeks. The purpose of this study was to identify potential immune drivers of fibrosis after CA/CPR.

Methods: Cardiac arrest was induced by potassium chloride and mice were resuscitated with chest compressions and epinephrine. The kidney immune landscape after CA/CPR was profiled using 11-color flow cytometry analysis and immunofluorescence. Immune cell-derived mediators of fibrosis were identified by analyzing data from three previously published single cell or single nuclear RNA sequencing (sc/snRNASeq) studies. NRK49F fibroblasts were treated with granzyme A (GzA) in vitro, then cell proliferation was quantified using 5-ethynyl-2'-deoxyuridine. GzA was pharmacologically inhibited both in vitro and in vivo.

Results: Immune cells infiltrated the kidney after CA/CPR, consisting primarily of innate immune cells, including monocytes/macrophages, neutrophils, and natural killer (NK) cells. NK cell infiltration immediately preceded mesenchymal cell expansion, which occurred starting 7 days after CA/CPR. Immune cells colocalized with mesenchymal cells, accumulating in areas of fibrosis. Analysis of previously published sc/snRNASeq data revealed GzA as a potential mediator of immune to mesenchymal communication. GzA administration to fibroblasts in vitro induced cell growth and proliferation. Pharmacologic blockade of GzA signaling in vivo attenuated fibrosis and improved renal function after CA/CPR.

Conclusion: Renal inflammation occurs during cardiorenal syndrome, which correlates with mesenchymal cell expansion. GzA, produced by NK cells, presents a novel therapeutic target to prevent the transition to CKD after AKI.