Resolvin D1 and Its Precursor Docosahexaenoic Acid Promote Resolution of Adipose Tissue Inflammation by Eliciting Macrophage Polarization toward an M2-Like Phenotype

Abstract

We recently demonstrated that ω-3-polyunsaturated fatty acids ameliorate obesity-induced adipose tissue inflammation and insulin resistance. In this study, we report novel mechanisms underlying ω-3-polyunsaturated fatty acid actions on adipose tissue, adipocytes, and stromal vascular cells (SVC). Inflamed adipose tissue from high-fat diet-induced obese mice showed increased F4/80 and CD11b double-positive macrophage staining and elevated IL-6 and MCP-1 levels. Docosahexaenoic acid (DHA; 4 μg/g) did not change the total number of macrophages but significantly reduced the percentage of high CD11b/high F4/80-expressing cells in parallel with the emergence of low-expressing CD11b/F4/80 macrophages in the adipose tissue. This effect was associated with downregulation of proinflammatory adipokines in parallel with increased expression of IL-10, CD206, arginase 1, resistin-like molecule α, and chitinase-3 like protein, indicating a phenotypic switch in macrophage polarization toward an M2-like phenotype. This shift was confined to the SVC fraction, in which secretion of Th1 cytokines (IL-6, MCP-1, and TNF-α) was blocked by DHA. Notably, resolvin D1, an anti-inflammatory and proresolving mediator biosynthesized from DHA, markedly attenuated IFN-γ/LPS-induced Th1 cytokines while upregulating arginase 1 expression in a concentration-dependent manner. Resolvin D1 also stimulated nonphlogistic phagocytosis in adipose SVC macrophages by increasing both the number of macrophages containing ingested particles and the number of phagocytosed particles and by reducing macrophage reactive oxygen species production. No changes in adipocyte area and the phosphorylation of hormone-sensitive lipase, a rate-limiting enzyme regulating adipocyte lipolysis, were observed. These findings illustrate novel mechanisms through which resolvin D1 and its precursor DHA confer anti-inflammatory and proresolving actions in inflamed adipose tissue.

Resolvin D1 Polarizes Primary Human Macrophages toward a Proresolution Phenotype through GPR32

“…In the same mouse model, peritoneal injection of RvD1 induced the formation of CD11b low macrophages with high phagocytic activity, reduced TNF-a, and increased IL-10 secretion, reflecting the proresolution effect of RvD1 on mouse macrophages (34). Similarly, RvD1 treatment of obese mice lowered adipose tissue inflammation, accompanied by a repolarization of adipose tissue M1 macrophages to a proresolution macrophage with lower proinflammatory cytokines, higher arginase 1, and higher phagocytic activity (35).…”

“…In clinical conditions, coexistence of cells in different activation states and unique or mixed phenotypes have been observed as a reflection of dynamic changes and complex tissue-derived signals (5). One of these macrophages is the resolution phase macrophage, for which there is in vivo evidence for its presence during the resolution phase of inflammation in mouse models (7,29,34,35). Those isolated resolution phase macrophages secrete low levels of proinflammatory cytokines and high levels of the anti-inflammatory IL-10, and express high levels of the mannose receptor CD206 on their surface, all proprieties of M2 polarization (7).…”

Coordinate Functional Regulation between Microsomal Prostaglandin E Synthase-1 (mPGES-1) and Peroxisome Proliferator-activated Receptor γ (PPARγ) in the Conversion of White-to-brown Adipocytes

“…Explants were washed with DPBS at 37°C by centrifugation for 1 min at 400 ϫ g to remove blood cells and pieces of tissue containing insufficient adipocytes to float as described in Refs. 23 Analysis of Gene Expression-Total RNA was isolated using the TRIzol reagent. RNA concentration was assessed in a NanoDrop-1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE), and its integrity was tested with a RNA 6000 Nano Assay in a Bioanalyzer 2100 (Agilent Technologies, Santa Clara, CA).…”

“…Tissue suspensions (300 -600 mg) were placed in 5 ml of digestion buffer containing Krebs-Ringer supplemented with 1% fatty acid-free BSA and 1 mg/ml collagenase A (Roche Applied Science) and incubated at 37°C for 30 min as described (23). Cell pellets corresponding to the SVC were incubated with erythrocyte lysis buffer (0.15 M NH 4 Cl, 10 mM KHCO 3 , and 0.1 mM EDTA) for 5 min and centrifuged at 500 ϫ g for 5 min.…”

Role of bioactive lipid mediators in obese adipose tissue inflammation and endocrine dysfunction

“…In vitro, nanomolar concentrations of RvD1 stimulate macrophage nonphlogistic phagocytosis, a critical process in the resolution of inflammation, and enhance the phagocytic activity of macrophages isolated from the adipose tissue stromal vascular cell fraction (Titos et al, 2011). In human monocyte-adipocyte co-incubations, both RvD1 and RvD2 reduce MCP-1 and LTB 4 -stimulated monocyte adhesion to adipocytes as well as monocyte transadipose migration, which are critical for the recruitment of monocytes/ macrophages into the inflamed adipose tissue (Claria et al, 2012).…”