Anti-inflammatory effect of Angiotensin 1-7 in white adipose tissue

Abstract

Obesity is a global health concern that promotes chronic low-grade inflammation, leading to insulin resistance, a key factor in many metabolic diseases. Angiotensin 1-7 (Ang 1-7), a component of the renin-angiotensin system (RAS), exhibits anti-inflammatory effects in obesity and related disorders, though its mechanisms remain unclear. In this study, we examined the effect of Ang 1-7 on inflammation of white adipose tissue (WAT) in dietary-induced obese mice. Monocyte chemoattractant protein-1 (MCP-1) produced by white adipocytes and tumour necrosis factor-α (TNF-α) produced by macrophages are pro-inflammatory cytokines and interact to form a pathogenic loop to exacerbate obesity-induced inflammation. We found that Ang 1-7 reduced MCP-1 and TNF-α gene expressions and the number of crown-like structures, which are histological hallmarks of the pro-inflammatory process, in visceral epididymal WAT (eWAT) and reduced circulating MCP-1 and TNF-α levels, accompanied by improvement in insulin resistance, in dietary-induced obese mice. Furthermore, Ang 1-7 reduced MCP-1 and TNF-α secretions in 3T3-L1 white adipocytes and RAW 264.7 macrophages, respectively, which are in vitro experimental models mimicking obesity condition. Our results suggest that Ang 1-7 directly acts on WAT to mitigate obesity-induced inflammation. Thus, this study provides novel insights into the underlying mechanism of anti-obesity effects of Ang 1-7.

Keywords: Angiotensin 1-7; MCP-1; TNF-α; anti-inflammatory effect; obesity.

Figure 1.

Angiotensin 1–7 (Ang 1–7) improves insulin resistance and glucose tolerance without affecting body weight, food intake, and epididymal white adipose tissue (eWAT) weight in dietary-induced obese mice. (a) Food intake, n = 4. (b) Body weight, n = 11–16. (c) Weight of eWAT, n = 11–15. (d) Levels of blood glucose during intraperitoneal glucose tolerance test (IPGTT), n = 10–15. (e) Levels of blood glucose during intraperitoneal insulin tolerance test (IPITT), n = 9–15. (f) Levels of blood glucose, serum insulin, and homeostasis model assessment of insulin resistance (HOMA-IR), with sample sizes of n = 11–15, n = 10–14, and n = 10–14, respectively. *p < 0.05, **p < 0.01. ^#p < 0.05 vs. NC. ^$p < 0.05 vs. HF. NC, mice fed a normal chow diet; HF, mice fed a high-fat diet alone; HFA, mice fed a high-fat diet and treated with Ang 1–7.

Figure 2.

Ang 1–7 reduces inflammation in visceral eWAT in HFD-induced obese mice. (a) Relative mRNA level of MCP-1 (n = 6–7), TNF-α (n = 6–7), IL6 (n = 6–8) and IL1-β (n = 6–8) determined using real-time PCR. (b) Serum levels of MCP-1 (n = 6–8) and TNF-α (n = 6–8). (c) Left panel: representative histology of crown-like structures (CLS, indicated by black arrows) in eWAT of NC, HF,and HFA mice. NC, mice fed a normal chow diet alone; HF, mice fed a high-fat diet alone; HFA, mice fed a high-fat diet and treated with Ang 1–7. Scale bars, 100 μm. Right panel: number of CLS in eWAT (n = 5–8). Data are presented as means ± SE. *p < 0.05, **p < 0.01.

Figure 3.

Ang 1–7 reduces MCP-1 secretion in an obese model of 3T3-L1 white adipocytes. (a) MCP-1 concentration in the culture medium of 3T3-L1 adipocytes at 1, 2, and 3 weeks after differentiation, determined by ELISA. CON, control group (vehicle-treated cells), n = 7–8; Ang 1–7, cells treated with Ang 1–7 alone, n = 7–8; Ang 1–7+A779, cells treated with Ang 1–7 and A779, n = 7–8. (b) MCP-1 concentration in the culture medium of TNF-α-treated 3T3-L1 adipocytes, determined by ELISA. CON, control group (vehicle-treated cells), n = 7; TNF-α (cells treated with TNF-α), n = 6; TNF-α+Ang 1–7, cells treated with TNF-α and Ang 1–7, n = 5; TNF-α+Ang 1–7+A779’, cells treated with TNF-α, TNF-α+Ang 1–7+A779, n = 5. Data are presented as means ± SE. *p < 0.05, **p < 0.01.

Figure 4.

Ang 1–7 reduces TNF-α secretion in a model of macrophage lipotoxicity. (a) TNF-α concentrations in the culture medium of LPS- and PA-treated RAW264.7 cells. CON, cells treated with only LPS and PA (control group); Ang 1–7, cells treated with LPS, PA, and Ang 1–7; Ang 1–7+A779, cells treated with LPS, PA, Ang 1–7, and A779. n = 14 for each group. Data are presented as means ± SE. **p < 0.01. (b) Schematic diagram showing the mechanism by which Ang 1–7 reduces inflammation in WAT in obesity. Macrophage-derived TNF-α not only impairs insulin signalling but also stimulates adipocytes to enhance more MCP-1 secretion in obesity. Interaction between adipocyte and macrophage forms a vicious cycle to augment inflammation. Ang 1–7 breaks this vicious cycle by acting on adipocytes and macrophages to reduce MCP-1 and TNF-α secretion, respectively.