# Endothelial MerTK impairment accelerates the development of atherosclerosis

## TL;DR

This study shows that impaired MerTK in endothelial cells promotes atherosclerosis through increased inflammation and mitochondrial dysfunction.

## Contribution

The novel finding is that endothelial MerTK deficiency directly contributes to atherosclerosis via specific molecular pathways.

## Key findings

- Endothelial MerTK deficiency increases proinflammatory signaling and mitochondrial dysfunction.
- MerTK impairment activates MAPK pathways and NADPH oxidases, promoting atherosclerosis.
- The miR-218–5p/ECMerTK/MAPK axis is implicated in MerTK-mediated atherosclerosis.

## Abstract

Atherosclerosis is a chronic inflammatory disease primarily affecting large arteries and is the leading cause of cardiovascular disease. MER proto-oncogene tyrosine kinase (MerTK) plays a key role in regulating efferocytosis, a process for the clearance of apoptotic cells. This study investigates the specific contribution of endothelial MerTK to atherosclerosis development.

Big data analytics, human microarray analyses, proteomics, and a unique mouse model with MerTK deficiency in endothelial cells (MerTKflox/floxTie2Cre) were utilized to elucidate the role of endothelial MerTK in atherosclerosis development.

Our big data analytics, encompassing approximately 98,881 cross analyses including 234 analyses for atherosclerosis in the aortic arch, along with human microarray data, reveal that inflammatory responses play a predominant role in atherosclerosis. In vivo, MerTKflox/floxTie2Cre mice and the littermate control MerTKflox/flox mice were used to establish an early stage of atherosclerosis model through a high-fat diet combined with AAV8-PCSK9 treatment. Consistent with big data analytics and human microarray analyses, our proteomics data showed that MerTKflox/floxTie2Cre mice demonstrated significantly enhanced proinflammatory signaling, mitochondrial dysfunction, and activated mitogen-activated protein kinase (MAPK) pathway compared to that of MerTKflox/flox mice. Endothelial MerTK deficiency induces endothelial dysfunction (enhanced endothelial inflammation, mitochondrial dysfunction, and activation of NADPH oxidases and MAPK signaling pathways) and subsequently causes smooth muscle cell (SMC) phenotypic alterations, ultimately promoting atherosclerosis development. The mechanism studies showed that the miR-218–5p/ECMerTK/MAPK axis may play an important role in endothelial MerTK-mediated atherosclerosis.

Our findings provide strong evidence that endothelial MerTK impairment serves as a novel mechanism in promoting atherosclerosis development.