Macrophage Function in Processing of Excess Dietary Fat

Abstract

Background: Chronic low-grade metabolic inflammation is one of the hallmarks of metabolic diseases. The risk of periodontitis is approximately threefold higher in diabetic individuals. To examine this relationship, we used a strain of transgenic mice overexpressing the receptor for Resolvin E1 (ERV1tg) that have a reduced inflammatory phenotype depicted by higher resolving (M2) to inflammatory macrophage (M1) ratio and are resistant to periodontitis and compared them to wild type (WT). Objective: investigate the role of resolving macrophages in processing of excess dietary fat in ERV1 tg mice and determine the difference that leads to sexual dimorphism in energy utilization by metabolic organs. Materials and Methods: 6-week-old ERV1tg and WT male and female mice were fed HFD for 16 weeks, 5 mice per group. Differences in expression of uncoupling protein 1 (UCP-1), peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1⍺), nuclear respiratory factor 1 (NRF-1), sirtuin1 (SIRT1) and estrogen-related receptor alpha (ERRα) in visceral adipose tissue (VAT), liver and brown adipose tissue (BAT) were assessed using real-time quantitative PCR and western blot. mRNA expression was normalized to peptidylprolyl isomerase A (PPIA) as a reference gene. Protein expression was normalized to Actin-B. to investigate the impact of RvE1 on cholesterol uptake by macrophages and efflux to HDL, we used RAW264.7 murine macrophage cell line and performed in vitro cholesterol uptake and efflux assay and investigated the impact of varying concentrations of RvE1 on cholesterol uptake and efflux to HDL. Statistical analysis: One-way ANOVA with ⍺=0.05. Results: Expression of PGC1-α mRNA in VAT was significantly higher in ERV1 tg female mice (4.4-fold ± 0.66) compared to ERV1 tg male mice (0.65-fold ± 0.12, p <0.0001). Relative NRF- 1 mRNA expression in VAT was significantly higher in ERV1 tg female mice (1.6-fold ± 0.12) compared to ERV1 tg male mice (0.65 ± 0.13, p < 0.0001). ERV1 tg female mice showed significantly higher expression of Sirt-1 mRNA in VAT (3.1-fold ± 0.26) compared to ERV1 tg male mice (1.7-fold ± 0.29, p < 0.0001). NRF-1 mRNA expression in the liver was significantly higher in ERV1 tg female mice (2.5-fold ± 0.21) compared to ERV1 tg male mice (2.0-fold ± 0.59, p = 0.0002). Relative Sirt-1 mRNA expression in BAT was significantly higher in ERV1 tg female mice (2.2-fold ± 0.12) compared to WT female (0.5-fold ± 0.08, p < 0.0001), and ERV1 tg male mice (1.3-fold ± 0.29) compared to WT male mice (0.47-fold ± 0.09, p < 0.0001). Conclusions: This study provides direct evidence for molecular targets of RvE1-mediated regulation of obesity that display sexual dimorphism suggesting that female ERV1 tg mice have higher metabolic flexibility through increased mitochondrial function to adapt to excess energy.