Losartan, an AT1 antagonist, prevents aortic aneurysm in a mouse model of Marfan syndrome

Abstract

Aortic aneurysm and dissection are manifestations of Marfan syndrome (MFS), a disorder caused by mutations in the gene that encodes fibrillin-1. Selected manifestations of MFS reflect excessive signaling by the transforming growth factor-beta (TGF-beta) family of cytokines. We show that aortic aneurysm in a mouse model of MFS is associated with increased TGF-beta signaling and can be prevented by TGF-beta antagonists such as TGF-beta-neutralizing antibody or the angiotensin II type 1 receptor (AT1) blocker, losartan. AT1 antagonism also partially reversed noncardiovascular manifestations of MFS, including impaired alveolar septation. These data suggest that losartan, a drug already in clinical use for hypertension, merits investigation as a therapeutic strategy for patients with MFS and has the potential to prevent the major life-threatening manifestation of this disorder.

Fig. 1

Postnatal treatment with TGF-β NAb. (A to H) Characterization of the ascending aorta in untreated wild-type mice [(A) and (E)] and Fbn1^C1039G/+ mice treated with placebo [(B) and (F)], 1 mg/kg TGF-β NAb [(C) and (G)], and 10 mg/kg TGF-β NAb [(D) and (H)]. In (A) to (D), Verhoeff's–van Gieson (VVG) stain reveals diffuse disruption of elastic fiber architecture and thickening of the aortic media (delineated by arrows) in placebo-treated Fbn1^C1039G/+ mice (B) relative to the normal elastic fiber architecture observed in wild-type mice (A). Improvement in both parameters is seen in NAb-treated Fbn1^C1039G/+ mice [(C) and (D)]. Scale bars, 40 μm. In (E) to (H), immunohisto-chemistry (IH) reveals nuclear pSmad2, a marker for TGF-β signaling (arrows indicate representative positive nuclei). Increased pSmad2 is observed in the placebo-treated Fbn1^C1039G/+ mice (F) relative to wild-type mice (E). Normalized pSmad2 staining is observed in the NAb-treated Fbn1^C1039G/+ mice [(G) and (H)]. Scale bars, 50 μm. (I) Average aortic root growth (±SD) measured by echocardiogram over the 2-month treatment period. Note the reduced rate of growth in the NAb-treated mice relative to the placebo-treated Fbn1^C1039G/+ mice. *P < 0.0001, **P < 0.03, †P = 0.11, ‡P = 1.0. (J) Average thickness (±SD) of the proximal ascending aortic media of four representative sections measured by an observer blinded to genotype and treatment arm. Note full normalization of thickness in NAb-treated Fbn1^C1039G/+ mice. *P < 0.01, †P = 0.91, ‡P = 0.38. (K) Average aortic wall architecture score (±SD) of the proximal ascending aorta. Three separate observers who were blinded to genotype and treatment arm graded elastic fiber architecture in four representative areas on a scale from 1 (completely intact elastic lamellae) to 4 (extensive fragmentation). Note the improvement in NAb-treated Fbn1^C1039G/+ mice. *P < 0.007, **P < 0.0001, ***P < 0.001, †P = 0.21.

Fig. 2

Prenatal treatment with losartan and propranolol. (A to D) VVG staining highlights intact elastic fiber architecture and normal ascending aortic wall thickness (arrows) in wild-type mice (A) and losartan-treated Fbn1^C1039G/+ mice (D). Marked elastic fiber disruption and wall thickening is apparent in the placebo- and propranolol-treated Fbn1^C1039G/+ mice [(B) and (C).] Scale bars, 40 μm. (E) Average aortic wall thickness (±SD) after 10 months of treatment. Note full normalization of wall thickness in losartan-treated Fbn1^C1039G/+ mice relative to mice that received placebo or propranolol treatment. *P < 0.0001, **P < 0.002, †P = 0.24, ‡P = 0.19. (F) Average aortic wall architecture score (±SD) after treatment. Note the improvement in losartan-treated Fbn1^C1039G/+ mice. *P < 0.02, **P < 0.0001, †P = 0.16.

Fig. 3

Postnatal treatment with losartan and propranolol. (A to H) VVG staining [(A) to (D)] and pSmad2 immunostaining [(E) to (H)] of aortic wall. Elastic lamellae are intact and aortic media is of normal thickness in the wild-type (A) and losartan-treated Fbn1^C1039G/+ mice (D). Placebo-and propranolol-treated Fbn1 ^C1039G/+ mice [(B) and (C)] have diffuse fragmentation of elastic fibers and thickening of the aortic media (arrows). Scale bars, 50 μm. Nuclear pSmad2 staining is decreased in the aortic media of wild-type (E) and losartan-treated Fbn1^C1039G/+ mice (H). Marked increase in nuclear staining for pSmad2 (representative positive cells denoted by arrowheads) is seen in the Fbn1^C1039G/+ mice treated with placebo (F) and propranolol (G). Scale bars, 40 μm. (I) Average aortic root growth (±SD) during the 6 months of treatment. Note that aortic root growth in Fbn1^C1039G/+ mice treated with propranolol is less than that with placebo, yet remains greater than that seen in wild-type mice. Losartan treatment normalizes growth rate. *P < 0.0001, **P < 0.001, ***P < 0.02, †P = 0.55. (J) Average aortic wall thickness (±SD). Aortic wall thickness in losartan-treated Fbn1^C1039G/+ mice is reduced relative to placebo- and propranolol-treated mice and is indistinguishable from that seen in wild-type mice. *P < 0.002, **P < 0.0001, ***P < 0.05, †P = 0.67, ‡P = 0.17. (K) Average aortic wall architecture (±SD). Note full normalization achieved with losartan treatment. *P < 0.002, **P < 0.0001, ***P < 0.05, †P = 0.20, ‡P = 0.47.

Fig. 4

Postnatal losartan treatment of lung disease in Fbn1^C1039G/+ mice. Histologic analysis of lung in wild-type mice (A) shows normal airspace caliber. Fbn1^C1039G/+ mice treated with placebo (B) show diffuse distal airspace widening (example delineated with arrows). Distal airspace caliber is reduced in Fbn1^C1039G/+ mice treated with losartan (C). Scale bars, 500 μm. (D) Average mean linear intercept, a marker of airspace caliber, is greater for placebo-treated Fbn1^C1039G/+ mice than for untreated wild-type and losartan-treated Fbn1^C1039G/+ mice. *P < 0.01, **P < 0.001.