Current research has suggested that monocyte/macrophages can coexist as different phenotypes which display an array of disparate properties. Monocyte/macrophage subsets may also divergently harbour the ability to acquire characteristics of other vascular cell types, such as vascular smooth muscle cells (VSMC) and endothelial cells. These findings imply that monocytes yield progenitor potential which could be potentially exploited for therapeutic purposes. The aim of this study is to robustly assess the progenitor potential of different in vitro monocyte/macrophage subsets into other vascular cells, namely, VSMCs and endothelial cells. Cultured human primary monocytes with subsequent polarisation with macrophage-colony stimulating factor (M-CSF) and termed M-Mac, or granulocyte-macrophage colony stimulating factor (GM-CSF) and termed GM-Mac, can appear like VSMCs based on the expression of genes/proteins considered specific to VSMCs (namely a-SMactin, caldesmon, calmodulin, myosin heavy chain-11, smoothelin, and vimentin). GM-Macs display a greater VSMC-like gene expression pattern compared to their M-Mac counterparts, through up- regulation of α-SMactin, caldesmon, calmodulin, myosin heavy chain-11, smoothelin, and vimentin. Interestingly, gene and protein expression of the endothelial cell (EC)-specific markers PECAM-1 (CD31) and VE-cadherin (CDH5) are also expressed by cultured macrophages. Mirroring the VSMC- like cell experiments, GM-Macs display greater expression of EC markers than M-Macs. These findings infer that pro-inflammatory GM-Macs already harbour the ability to express VSMC-like and EC-like genes/proteins, whereas their anti-inflammatory M-Mac counterparts do not. Accordingly, we propose that GM-Macs may foster the ability to mimic vascular cells (VSMCs and/or ECs) in response to injury or under angiogenic conditions, to provide temporary barrier function for example. Interestingly, the growth factors FGF2 and VEGF-A were shown to upregulate PECAM-1 and VE-cadherin expression in M-Mac but not GM-Mac. We also observed an inverse relation between expression of VE-cadherin mRNA and protein expression in M-Mac after stimulation with FGF2, suggesting the involvement of a post-transcriptional regulatory mechanism. Indeed, M-Mac VE-cadherin protein expression was identified to be dependent upon microRNA (miR)-27a-3p. Moreover, miR-27a-3p levels appear to be regulated through a FGF-receptor type-1 and signal transducer and activator of transcription-3 (Stat3) signalling pathway. Finally, GM-Macs and FGF2- stimulated M-Macs harboured the ability to form angiogenic sprouts, supporting their transition towards an endothelial cell-like phenotype. In conclusion, the novel findings within this thesis demonstrate the divergent progenitor capacity of macrophage subsets, which may be utilised for cardiovascular therapeutic purposes.
Evaluation of the progenitor potential of monocyte/macrophage subsets in cardiovascular disease
Mat Noh, M. A. (Author). 28 Sept 2021
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)