Background: Atherosclerotic lesions preferably form at sites of disturbed blood flow resulting in decreased endothelial shear stress. However, the molecular mechanism of this atherogenic mechanotransduction linking reduced shear stress to atherosclerotic lesion formation is largely unknown. We have recently discovered that endothelial G-proteins of the G_q/11 family are involved in sensing and/or transduction of atherogenic shear stress, and an endothelial-specific G_q/11-deficiency protected mice from atherosclerotic plaque formation in murine models of disturbed flow and atherosclerosis. While this signaling pathway appears to be a promising target, due to their central involvement in many key cellular processes, G-proteins themselves barely qualify as pharmacological targets. Thus, in this project we aimed to identify more „drugable“ downstream effectors of G_q/11, focusing on chromatin modifying enzymes.

Methods and results: Using special flow chambers that allowed us to expose cultured endothelial cells (HUVECs) to different physiological as well as atherogenic flow patterns, we performed a genome-wide microarray to identify genes that are transcriptionally regulated upon atherogenic shear stress in a G_q/11-dependent manner. Indeed, we found a number of chromatin modifyers to be dynamically regulated upon atherogenic flow in a Gq/11-dependent manner. Of those, the histone demethylase KDM2B was the most strongly downregulated upon atherogenic flow conditions. Subsequent RNAi loss-of-function studies showed that KDM2B, controls the endothelial switch towards atherogenic phenotypes: Upregulation of inflammatory genes like Ccl2 or Endothelin-1 (Edn1) upon atherogenic flow was strongly intensified in endothelial cells transfected with Kdm2b siRNA compared to scramble control.

In order to test the relevance of KDM2B in the context of atherogenic flow in vivo, we established a transgenic mouse line with conditional endothelial-specific Kdm2b-deficiency and constitutive ApoE-deficiency (EC-Kdm2b-KO). Those mice were fed with western diet and exposed to a model of accelerated atherosclerosis, in which partial carotid ligation is performed to establish atherogenic blood flow resulting in atherosclerotic plaque formation within 3 weeks. In EC-Kdm2b-KO mice plaque formation was significantly accelerated compared with the respective control mice (Figure 1).

Conclusion: Our in vitro and vivo data indicate that the histone demethylase KDM2B controls endothelial phenotypes in a flow-sensitive, antiinflammatory and atheroprotective manner. It may therefore qualify as a potential drug target for the treatment of atherosclerosis.