Obesity promotes inflammation in periaortic adipose tissue and angiotensin II-induced abdominal aortic aneurysm formation

Abstract

Objective: Obesity promotes macrophage infiltration into adipose tissue and is associated with increases in several cardiovascular diseases. Infusion of angiotensin II (AngII) to mice induces formation of abdominal aortic aneurysms (AAAs) with profound medial and adventitial macrophage infiltration. We sought to determine whether obesity promotes macrophage infiltration and proinflammatory cytokines in periaortic adipose tissue surrounding abdominal aortas and increases AngII-induced AAAs.

Methods and results: Hypertrophied white adipocytes surrounded abdominal aortas, whereas brown adipocytes surrounded thoracic aortas of obese mice. mRNA abundance of macrophage proinflammatory chemokines and their receptors were elevated with obesity to a greater extent in abdominal compared to thoracic periaortic adipose tissue. Periaortic adipose tissue explants surrounding abdominal aortas of obese mice released greater concentrations of MCP-1 and promoted more macrophage migration than explants from thoracic aortas. Male C57BL/6 mice were fed a high-fat (HF) diet for 1, 2, or 4 months and then infused with AngII (1000 ng/kg/min) for 28 days. AAA incidence increased progressively with the duration of HF feeding (18%, 36%,and 60%, respectively). Similarly, AngII-infused ob/ob mice exhibited increased AAAs compared to lean controls (76% compared to 32%, respectively, P<0.05). Infusion of AngII to obese mice promoted further macrophage infiltration into periaortic and visceral adipose tissue, and obese mice exhibiting AAAs had greater macrophage content in visceral adipose tissue than mice not developing AAAs.

Conclusions: Increased macrophage accumulation in periaortic adipose tissue surrounding abdominal aortas of AngII-infused obese mice is associated with enhanced AAA formation.

Figure 1. Regional differences in adipocyte morphology in periaortic adipose tissue surrounding thoracic versus abdominal aortas of lean and obese mice

Top, Panel A illustrates aortic regions with intact periaortic adipose tissue (thoracic and abdominal) dissected for analyses from lean (ob/+) and obese (ob/ob) mice. Thoracic (B,C) and abdominal (D,E) aortic sections (5 m) from ob/+ (B,D) and ob/ob (C,E) mice were stained with hematoxylin and eosin (H&E). Adipose tissue surrounding thoracic aortas was composed of multilocular brown adipocytes (B: 40X; insets: 10X). In contrast, adipocytes surrounding abdominal aortas were primarily unilocular (C: 40X; insets: 10X). With obesity (C,F), both brown and white adipocytes surrounding aortas were hypertrophied.

Figure 2. Effects of obesity on mRNA abundance of macrophage markers and proinflammatory chemokines in periaortic adipose tissue surrounding thoracic versus abdominal aortas

Periaortic adipose tissue surrounding thoracic versus abdominal aortas of LF- and HF-fed mice (4 months) was analyzed for mRNA abundance by real-time PCR. A, mRNA abundance in periaortic adipose tissue surrounding thoracic aortas from LF and HF-fed mice. B, mRNA abundance in periaortic adipose tissue surrounding abdominal aortas of LF and HF-fed mice. F4/80 mRNA abundance increased to a greater extent in periaortic adipose tissue surrounding abdominal than thoracic aortas. Similarly, obesity-induced elevations in mRNA abundance of CCL2, CCR2, and leptin were greater in adipose tissue surrounding abdominal than thoracic aortas. mRNA abundance of UCP-1 was increased by obesity in thoracic periaortic adipose tissue, but decreased in abdominal. Data are mean ± SEM from n = 5 mice/group. *, P < 0.05 compared to LF.

Figure 3. MCP-1 release (A) and macrophage migration (B) in periaortic adipose tissue explants from abdominal aortas are increased by obesity

Periaortic adipose tissue explants were prepared from thoracic or abdominal aortas of LF- and HF-fed mice (4 months) and incubated as described. A, MCP-1 release into the media was increased in periaortic explants of abdominal aortas from HF compared to LF-fed mice. There was no effect of HF-feeding on MCP-1 release from thoracic periaortic adipose tissue explants. B, Mouse peritoneal macrophage migration was increased by conditioned media from abdominal periaortic adipose explants of HF compared to LF-fed mice.*, significantly different from LF abdominal. , significantly different from HF-thoracic. Data are mean ± SEM from n = 5 mice/group.

Figure 4. Diet-induced and genetic obesity increase AngII-induced AAAs

A, C57BL/6 mice were fed control or HF diets for 1, 2 or 4 months. Age-matched LDLr-/- mice were fed the HF diet for 4 months. AAA incidence increased progressively with longer durations of HF-feeding in C57BL/6 mice (18%, 36% and 60% AAA incidence, respectively). AAA incidence was similar in both C57BL/6 and LDLr-/- mice fed a HF diet for 4 months (57% and 60%, respectively). B, AAA incidence was increased in ob/ob (76%) compared to ob/+ mice (32%). Data are mean ± SEM from n = 10/group. *, P < 0.05 vs ob/+. **, P < 0.05 compared to control, 1 month HF.

Figure 5. Infusion of AngII promotes inflammation in aneurysms and adipose tissue from obese mice

A-D, Aneurysmal sections with isotype-matched IgG control (A, B) and cd68-positive immunostaining in an aneurysmal tissue section from an AngII-infused ob/ob mice (C, D). Macrophages are present in adventitia and periaortic adipose tissue. Boxes represent regions illustrated at higher magnification in B, D. E, AngII infusion promotes macrophage infiltration into the stromal vascular fraction of retroperitoneal white adipose tissue from ob/ob mice (n = 5/group). F, Macrophage infiltration into the stromal vascular fraction of white adipose tissue from mice who developed AAAs compared to mice that did not develop AAAs (n = 4 no AAA; n = 3 AAA). Data are mean ± SEM; *, denotes significantly different from saline or no AAA, P < 0.05.