Project Summary Cardiovascular diseases are among the nation's leading causes of death and disability, with an estimated cost of more than $351 billion in the USA. Ischemia-induced angiogenesis plays an important role in the recovery of many vascular diseases. The endothelium plays an even more important role in vascular homeostasis as it regulates vascular tone, thrombosis, leukocyte trafficking, metabolism, and angiogenesis. Maintaining normal endothelial function requires balancing numerous physiological and pathophysiological stresses such as shear, hypoxia, and inflammation. Among the pathways mediating cellular stress, responses are the stress-activated members of the MAP kinase (MAPK) superfamily, which includes c-Jun N-terminal kinase (JNK) and p38 MAPK. JNK protein plays an important role in collateral artery formation during development. Recently, we have shown that neural JNK3 plays a significant role in blood flow recovery after hindlimb ischemia. In probing upstream components of the MAPK signaling cascade (MAP2K and MAP3K), we found that Mixed Lineage Kinase 2 (MLK2), a MAP3K and upstream regulator of MAPK, is expressed in endothelium and required for normal postnatal endothelial function. In fact, MLK2-deficient endothelial cells exhibit profound defects in angiogenesis as well as endothelial proliferation and migration. MLK2 also plays a significant role in VEGF signaling, which is required for proper endothelium function. RNA-seq data indicates that MLK2-deficient endothelial cells exhibit both basal and VEGF- induced upregulation of a broadly conserved microRNA, miR-146a, that has previously been linked to inflammation. Mimics of this miR-146a miRNA administered to wild-type endothelial cells recapitulate a broad spectrum of the MLK2-deficient phenotype, including defects in proliferation and VEGF signaling. Using these strategies, we should be able to develop a clear picture of how MLK2 influences endothelial function and vascular homeostasis. These data will be important as MLK inhibitors are being tested in the cancer field since very little data is understood regarding their cardiovascular consequences. Moreover, how Mlk2 influences the vasculature is a large gap in knowledge that we will address.

Cardiovascular diseases are the number one cause of morbidity worldwide, and endothelium plays an important role in cardiovascular health. This project investigates a pathway known as Mixed Lineage Kinase 2 and how it impacts the endothelium and is based on our findings that Mixed Lineage Kinase 2 is needed for normal endothelial function and control signals needed for new blood vessel formation.