Profiling of the Three Circulating Monocyte Subpopulations in Human Obesity

Abstract

Three subpopulations of circulating monocytes have been described: CD14(2+)CD16(-) (classical monocytes [CM]), CD14(2+)CD16(+) (intermediate monocytes [IM]), and CD14(+)CD16(2+) (nonclassical monocytes [NCM]). We previously showed that obesity is associated with an increased proportion of IM and NCM. Our objective is to decipher the migratory and inflammatory functions of each monocyte subset in obesity-related low-grade inflammation. Twenty-six healthy, normal-weight and nondiabetic volunteers (C) and 40 obese nondiabetic (Ob) individuals were included in this study. We explored the gene expression profile of 18 inflammatory genes in each subset of C and Ob subjects and measured protein expression of the upregulated genes. We then tested their functional response to TLR signaling in both groups. We showed an increased expression of CX3CR1 in all monocyte subpopulations and of CCR2 and CCR5 in CM and IM in the Ob group. We found negative correlation between CCR2 and CX3CR1 expressions and high-density lipoprotein-cholesterol, whereas CCR5 expression was positively linked to obesity-related metabolic traits. Production of inflammatory proteins upon bacterial LPS and viral ssRNA stimulation was higher in CM and NCM of the Ob group compared with the C group. Our work highlights an enhanced inflammatory phenotype of monocytes with a higher response to TLR4 and TLR8 stimulations in obesity. Moreover, it suggests an increased migration capacity of CM and IM subpopulations.

Increased adipose tissue expression of TLR8 in obese individuals with or without type-2 diabetes: significance in metabolic inflammation

“…Our data showing elevated macrophage markers expression in the adipose tissue in obesity/T2D are corroborated, at least in part, by other studies as well [2, 22, 23]. Of note, Devevre et al reported three distinct monocytic populations in human obesity named as classical, intermediate, and non-classical monocytes while a 2–4 fold increased expression of TLR4/TLR8 was found in all three subsets [24]. These observations partially support our data showing enhanced TLR8 expression in the obese adipose tissue.…”

“…The white adipose tissue is a site for excessive energy storage and active biosynthesis of adipokines that act via autocrine/paracrine mechanisms in adipocyte-macrophage crosstalk to amplify the local and systemic inflammatory responses in obesity/T2D [25]. The proinflammatory cytokines TNF-α and IL-18 are known to be elevated in obesity/T2D [26, 27] while IL-8 or CXC chemokine ligand (CXCL)-8 is an inflammatory protein and increased circulatory numbers of IL8-expressing monocytes were also reported in human obesity [24]. CRP is a typical systemic inflammatory marker and its increased levels were linked with obesity, blood pressure, and hyperlipidemia [28].…”

Monocyte isolation techniques significantly impact the phenotype of both isolated monocytes and derived macrophages in vitro

“…More importantly, because of the specific removal of CD16 pos cells by negative selection, the distribution of resultant monocyte subpopulations was very different from PBMCs, consisting almost exclusively of classical monocytes. As intermediate and non‐classical monocytes are believed to have specific functions in vivo , negative selection should not be employed when ex vivo studies require representative monocyte populations. On the other hand, CD14 pos selection may carry the risk of altering the cells' phenotype and potentially induce cell activation .…”

Role of immune activation in progression to AIDS

“…High expression of the PD1 homologue (PD-1H), which is associated with increased production of TNF, IL-1β, and IL-6, may also contribute to the pro-inflammatory state of these monocytes [44]. CD16+ non-classical and intermediate monocytes have a high migratory capacity, which has been attributed to expression of the chemokine receptors CCR2, CCR5, [45, 46] and CX3CR1 [47]. Indeed, higher expression of the monocyte adhesion molecule CXCL8 was associated with death in SMART [48].…”