Identification of Novel Functional Differences in Monocyte Subsets Using Proteomic and Transcriptomic Methods

Abstract

Human blood monocytes can be broadly divided into two distinct subsets: CD14+CD16- and CD14+/lowCD16+ subsets. Perturbation in their proportions in the blood has been observed in several disease conditions. Although numerous phenotypic and functional differences between the two subsets have already been described, the roles contributed by each subset during homeostasis or disease conditions are still largely unclear. To uncover novel differences to aid in elucidating their functions, we perform a global analysis of the two subsets utilizing both proteomics and transcriptomics approaches. From the proteomics and transcriptomics data, the expression of 613 genes by the two subsets is detected at both the protein and mRNA levels. These 613 genes are assessed for up-regulation in each subset at the protein and mRNA levels using a cutoff fold change of > or =|1.5| between subsets. Proteins and mRNAs up-regulated in each subset are then mapped in silico into biological functions. This mapping reveals copious functional differences between the subsets, many of which are seen at both protein and mRNA levels. For instance, expression of genes involved in F(CY) receptor-mediated phagocytosis are up-regulated in the CD14+/lowCD16+ subset, while those involved in antimicrobial function are up-regulated in the CD14+CD16- subset. We uncover novel functional differences between the monocyte subsets from differences in gene expression at the protein and mRNA levels. These functional differences would provide new insights into the different roles of the two monocyte subsets in regulating innate and adaptive immune responses.

Comparative Analysis of Monocyte Subsets in the Pig

“…The proposed functional equivalence of the human CD16 + and mouse Ly6C 2 cells (nonclassical) is mainly supported by the differential expression of a few key markers (12)(13)(14) and more recently by gene expression profiling (4,15). Several separate studies have compared array profiles of human monocyte subsets (5,(15)(16)(17). They found broad similarities between genes preferentially expressed by classical CD14 high monocytes, but differed somewhat in the profiles attributed to the nonclassical cells, due in part to differences in definition of the intermediate phenotype.…”

Monocyte Subsets and Their Role in Tumor Progression

“…In recent years the improvement in cell isolation techniques has allowed great advances in the understanding of transcriptomes in circulating monocytes helping identify unique signatures for different monocyte subsets and share remarkably transcriptional similarity (Ancuta et al, 2009;Mobley et al, 2007;Zhao et al, 2009). Genome wide studies on monocytes transcriptomes suggest that both CD16 -and CD16 + monocytes share a common precursor (Ancuta et al, 2009).…”

“…MARCO (macrophage receptor with collagenous structure) is also one of the highly expressed gene (Wong et al, 2011). CD16 + monocytes express higher levels of TNF- and chemokine receptor CX3CR1, CX3CR2 and colony-stimulating factor 1 receptor (CSF1R), the receptor for macrophage colony-stimulating factor (M-CSF) than classical CD16 -monocytes (Ancuta et al, 2009;Wong et al, 2011;Zhao et al, 2009). Proteomic analysis also showed small differences with only 235 proteins differentially expressed between the monocyte subsets (Martinez, 2009).…”

Overview of Current Proteomic Approaches for Discovery of Vascular Biomarkers of Atherosclerosis

“…In this respect, cell culture systems could represent a useful tool to partially overcome drawbacks of tissue analyses, allowing researchers to study single aspects of the atherosclerotic process in very controlled conditions. In the last years, studies on proteome (the intracellular proteins) and secretome (the proteins released into the cell culture medium) by 2DE and MS of ECs (Bruneel et al, 2003;Chen et al, 2007;Tunica et al, 2009), VSMCs (McGregor et al, 2001Dupont et al, 2005;Lee et al, 2006), and monocytes/macrophages (Dupont et al, 2004;Fach et al, 2004;Slomianny et al, 2006;Zhang et al, 2007;Zhao et al, 2009) have been performed. Moreover, in the attempt to help in elucidating the mechanisms of atherogenesis, several proteomic studies have been carried out on vascular cells cultured in different experimental conditions (table 3).…”

“…Very few studies applied gel free proteomic approaches such as LC MS/MS (Fach et al, 2004;X.L. Wang et al, 2007;Zhao et al, 2009;Tunica et al, 2009;Zimman et al, 2010) and microarrays (Sukhanov et al, 2005).…”