Weight loss in obese C57BL/6 mice limits adventitial expansion of established angiotensin II-induced abdominal aortic aneurysms

Abstract

Previous studies demonstrated that obesity increases inflammation in periaortic adipose tissue and promotes angiotensin II (ANG II)-induced abdominal aortic aneurysms (AAAs). We sought to determine whether weight loss of obese C57BL/6 mice would influence the progression of established AAAs. Male C57BL/6 mice were fed a high-fat diet (HF) for 4 mo and then infused with either saline or ANG II (1,000 ng x kg(-1) x min(-1)) for 3 mo. Mice with dilated suprarenal aortas at 28 days of ANG II infusion were designated to groups fed the HF (HF/HF) or a low-fat diet (LF; 10% kcal as fat; HF/LF) to induce weight loss for the last 2 mo of infusions. Suprarenal aortic lumen diameters of obese mice were increased by ANG II infusion at day 28 (day 0: 1.03 + or - 0.02; day 28: 1.86 + or - 0.14 mm; P < 0.05), but did not progress with continued infusion in HF/HF mice. Moreover, aortic lumen diameters were not different between groups (HF/HF: 1.89 + or - 0.15; HF/LF: 1.79 + or - 0.18 mm). However, maximal diameters of excised AAAs were decreased with weight loss (HF/HF: 2.00 + or - 0.11; HF/LF: 1.55 + or - 0.13 mm; P < 0.05) and had reduced adventitial areas (HF/HF: 1.18 + or - 0.10; HF/LF: 0.54 + or - 0.02 mm(2); P < 0.05). Neovascularization of aortic adventitias was strikingly decreased in HF/LF mice (HF/HF: 43 + or - 5; HF/LF: 12 + or - 2 endothelial cells/adventitial area; P < 0.05). ANG II-induced elevations in adipose mRNA abundance of CD105, an adipose-derived stem cell marker, were abolished with weight loss. These results demonstrate that weight loss limits adventitial expansion of ANG II-induced AAAs. Reduced neovascularization from weight loss may limit progression of AAAs.

Fig. 1.

Weight loss and angiotensin (ANG) II infusion decreased body weight in obese mice. C57BL/6 mice gained weight over 16 wk of high-fat (HF) feeding. At 16 wk, mice were implanted with pumps infusing either saline or ANG II, with replacement of pumps at weeks 20 and 24. At week 20, mice were assigned to groups fed the HF (HF/HF) or low-fat (LF; HF/LF) diet to induce weight loss. The LF diet promoted weight loss in both saline and ANG II-infused mice. In addition, infusion of ANG II decreased body weight in HF/HF and HF/LF mice. Values are means ± SE from n = 10–15 mice/group.

Fig. 2.

Weight loss has no effect on aortic lumen diameter, but decreased external diameters of established ANG II-induced abdominal aortic aneurysms (AAAs). A: lumen diameters of suprarenal aortas were measured by ultrasound. ANG II infusion increased lumen diameters at day 28 compared with baseline, but lumen dilation remained constant from day 28 through day 84 of continued ANG II infusions. B: suprarenal external aortic diameters were measured on excised, cleaned tissue. Weight loss decreased external aortic diameters. Values are means ± SE from n = 10–15 mice/group. *P < 0.05 compared with saline, within diet. **P < 0.05 compared with HF/HF, within treatment.

Fig. 3.

Weight loss reduced adventitial thickening of established ANG II-induced AAAs. A and B: representative AAA sections stained with hematoxylin and eosin from HF/HF (A) and HF/LF (B) mice. C: medial areas were not different in AAA sections from HF/HF and HF/LF mice. D: adventitial areas were decreased with weight loss in AAA sections from HF/LF compared with HF/HF mice. Values are means ± SE from 3 tissue sections from n = 3 mice/group. *P < 0.05 compared with HF/HF.

Fig. 4.

Weight loss markedly reduced adventitial neovascularization of established ANG II-induced AAAs. A: endothelial cell numbers (positive Von Willebrand immunostaining) in adventitias of AAA sections were strikingly reduced with weight loss in HF/LF compared with HF/HF mice. B: whole vessel CD31 immunostaining demonstrates reduced vasa vasorum in aortas from HF/LF compared with HF/HF mice. Specificity of staining is demonstrated by incubation of aorta without primary antibody (Control). Values are means ± SE from 4 fields of 3 sections (B) from n = 3 mice/group. *P < 0.05 compared with HF/HF.

Fig. 5.

Weight loss reduced ANG II-induced elevations in CD105 mRNA abundance in stromal vascular fraction (SVF) from adipose tissue. A: mRNA abundance of CD34, a bone marrow-derived stem cell marker, is reduced in SVF with weight loss in saline, but not ANG II-infused mice. B: mRNA abundance of CD105, an adipose-derived stem cell marker, is increased by ANG II in SVF from HF/HF, but not HF/LF mice. Values are means ± SE from n = 3–5 mice/group. *P < 0.05 compared with HF/LF within infusion. **P < 0.05 compared with saline within diet.