Limiting pro-atherogenic macrophage formation: Taming Quaking and inflammation

A critical part of the RNAissance (a period in which the realization has developed that RNA is not merely an intermediate) is the invention of commercial microarrays (link to de Bruin et al., European Heart Journal, 2016). This technological advancement, albeit slightly dated now in 2016, enabled scientists worldwide to identify changes in coding-gene expression levels in diverse cell types and disease settings. We used this approach to identify genes that were differentially expressed in CD68+ macrophages of early and advanced atherosclerotic lesions. Importantly, this initial screen formed the basis of my Quaking research focus, as this experiment uncovered a 4.2-fold increase in the expression levels of the RNA-binding protein Quaking. In mice, reducing QKI expression levels in hematopoietic progenitor cells led to a reduction in atherosclerotic lesion formation, due to a reduction in monocyte/macrophage accumulation in the aortic root. In vitro, we confirmed that a reduction in QKI expression limited monocyte adhesion, (transwell) migration, differentiation in pro-inflammatory macrophages, and foam cell formation (in particular with oxidized LDL as substrate).

To gain post-transcriptional insight into how QKI was mediating these effects, together with our scientific colleagues at Leuven University (Prof. Hilde van Esch) and University of Santa Cruz in California (Prof. Manny Ares Jr.), we proceded to characterize the RNA expression profiles from monocytes and macrophages derived from a unique, QKI haploinsufficient individual and her age- and sex-matched sibling. Here we pinpointed numerous QKI-mediated changes in splicing as well as gene expression that could impact various aforementioned aspects of monocyte to macrophage differentiation.

This work was recently published in Nature Communications (link to de Bruin et al., Nature Communications, 2016). We are currently investigating the functional consequences of a select number of splicing and gene expression changes observed in these studies.