MLKL preserves the splenic microenvironment to repress hematopoiesis during atherosclerosis

Dysregulation of the hematopoietic niche during hyperlipidemia facilitates pathologic leukocyte production, driving atherogenesis. While definitive hematopoiesis primarily occurs in the bone marrow, during atherosclerosis this also occurs in the spleen. Cells of the bone marrow niche, in particular endothelial cells, have been studied in atherosclerosis, while little is known about how splenic endothelial cells respond to the atherogenic environment. Here we show unique dysregulated pathways in splenic compared to bone marrow endothelial cells during atherosclerosis, including perturbations of lipid metabolism and endocytic trafficking pathways. As part of this response, we identified MLKL as a repressor of splenic, but not bone marrow, myelopoiesis. Silencing MLKL in splenic endothelial cells results in inefficient endosomal trafficking and lipid accumulation, ultimately promoting the production of myeloid cells that participate in plaque development. These studies identify endocytic trafficking by MLKL as a key mechanism of splenic endothelial cell maintenance, splenic hematopoiesis, and subsequently atherosclerosis.