Evaluation of macrophage plasticity in brown and white adipose tissue

Abstract

There are still questions about whether macrophage differentiation is predetermined or is induced in response to tissue microenvironments. C2D macrophage cells reside early in the macrophage lineage in vitro, but differentiate to a more mature phenotype after adoptive transfer to the peritoneal cavity (PEC-C2D). Since C2D macrophage cells also traffic to adipose tissue after adoptive transfer, we explored the impact of white adipose tissue (WAT), brown adipose tissue (BAT) and in vitro cultured adipocytes on C2D macrophage cells. When PEC-C2D macrophage cells were cultured with preadipocytes the cells stretched out and CD11b and Mac-2 expression was lower compared to PEC-C2D macrophage cells placed in vitro alone. In contrast, PEC-C2D cells co-cultured with adipocytes maintained smaller, round morphology and more cells expressed Mac-2 compared to PEC-C2D co-cultured with preadipocytes. After intraperitoneal injection, C2D macrophage cells migrated into both WAT and BAT. A higher percentage of C2D macrophage cells isolated from WAT (WAT-C2D) expressed Ly-6C (33%), CD11b (11%), Mac-2 (11%) and F4/80 (29%) compared to C2D macrophage cells isolated from BAT (BAT-C2D). Overall, BAT-C2D macrophage cells had reduced expression of many cytokine, chemokine and receptor gene transcripts when compared to in vitro grown C2D macrophages, while WAT-C2D macrophage cells and PEC-C2D up-regulated many of these gene transcripts. These data suggest that the C2D macrophage phenotype can change rapidly and distinct phenotypes are induced by different microenvironments.

Intrinsic Properties of Brown and White Adipocytes Have Differential Effects on Macrophage Inflammatory Responses

“…Prior studies have shown that macrophages isolated from murine BAT following adoptive transfer experiments have reduced expression of cytokine, chemokine, and receptor transcripts compared to their in vitro counterparts or those isolated from WAT [17]. Similarly, in the present study, white adipocytes induced expression of several inflammatory transcripts in macrophages, while brown adipocytes either reduced or did not significantly affect gene expression in both U937 and THP-1 macrophages regardless of stimulation state (Figures 3 and 4).…”

“…Of interest is that macrophage infiltration in BAT was found to be significantly less than that in WAT [16] and enhanced mRNA expression of inflammatory molecules, including tumor necrosis factor (TNF) α , interleukin-6 (IL-6), and monocyte chemotactic protein (MCP-1), was nearly 10–100-fold less in BAT than that in WAT in DIO mice. In addition, others have shown that expression of proinflammatory cytokines is lower in BAT than in WAT in normal mice [17] and expression of several cytokines has been found to be lower in C2D macrophage cells that were isolated after in vivo injection into BAT compared to injection into WAT [17]. However, as adipose tissue is a heterogeneous organ, it is unknown which specific type(s) of cell(s) in the adipose tissue environment is(are) contributing to the observed differences between WAT and BAT.…”

The Role of Tissue Macrophage-Mediated Inflammation on NAFLD Pathogenesis and Its Clinical Implications

“…In vitro, preadipocytes inhibited the expression of galectin-3 by a specific subpopulation of macrophages, known as peritoneal-C2D macrophages, which retains plasticity in response to different microenvironments. Peritoneal-C2D macrophages that migrated to WAT expressed higher levels of galectin-3 than macrophages that moved to brown adipose tissue [93]. Moreover, in the course of monocyte-to-macrophage differentiation, galectin-3 mRNA and protein levels are substantially upregulated by M2 macrophages when compared with M1 macrophages [94].…”

Overexpression of IL-10 in C2D Macrophages Promotes a Macrophage Phenotypic Switch in Adipose Tissue Environments

“…Cells were stained with carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) according to the manufacturer’s protocol and as described before [4].…”

“…Because the adoptive transfer of C2D macrophages can ameliorate the impact of infection [22] and C2D macrophages trafficked to adipose tissue [4], we wondered if the cells would be able to influence the adipose tissue environment if they overexpressed IL-10. Therefore, we constructed a C2D macrophage cell line that stably overexpresses IL-10 (C2D-IL10).…”