Lack of glutathione peroxidase 1 accelerates cardiac-specific hypertrophy and dysfunction in angiotensin II hypertension

Abstract

Glutathione peroxidase 1 (Gpx1) plays an important role in cellular defense by converting hydrogen peroxide and organic hydroperoxides to nonreactive products, and Gpx1(-/-) mice, which are characterized by reduced tissue glutathione peroxidase activity, are known to exhibit enhanced oxidative stress. Peroxides participate in tissue injury, as well as the hypertrophy of cultured cells, yet the role of Gpx1 to prevent end organ damage in cardiovascular tissue is not clear. We postulated that Gpx1 deletion would potentiate both aortic and cardiac hypertrophy, as well as mean arterial blood pressure, in response to angiotensin II (AngII). Our results show that short-term AngII markedly increased left ventricular mass, myocyte cross-sectional area, and interventricular septum thickness and decreased shortening fraction in Gpx1(-/-) mice as compared with wild-type animals. On the other hand, AngII resulted in a similar increase in mean arterial blood pressure in wild-type and Gpx1(-/-) mice. Collagen deposition increased in response to AngII, but no differences were found between strains. Vascular hypertrophy increased to the same extent in Gpx1(-/-) and wild-type mice. Collectively, our results indicate that Gpx1 deficiency accelerates cardiac hypertrophy and dysfunction but has no effect on vascular hypertrophy and mean arterial blood pressure and suggest a major role for Gpx1 in cardiac dysfunction in AngII-dependent hypertension.

Figure 1. MABP changes in wildtype and Gpx1 −/− mice

MABP was measured by radio-telemetry from days -1 to 7 in wildtype and Gpx1 −/− mice treated with AngII (521 ng/kg*min, s.c.) or vehicle for 7 d. Data are expressed as mean ± SEM. # p <0.05 vs. wildtype + vehicle; * p < 0.05 vs. Gpx1 −/− + vehicle (n = 6 – 7).

Figure 2. Comparison of cardiac mass in wildtype vs. Gpx1 −/− mice

Hearts were harvested after 7 days treatment with vehicle or AngII (521 ng/kg*min, s.c.). Representative cross-sections of hearts from wildtype + vehicle (A), Gpx1−/− + vehicle (B), wildtype + AngII (C) and Gpx1−/− + AngII (D) stained with picrosirius red. Total Heart Weight/ Body Weight (THW/BW) ratio was tabulated for hearts from vehicle- and AngII-treated wildtype and Gpx1 −/− mice (E). Data are expressed as mean ± SEM (n = 9 – 10).

Figure 3. Echocardiographic Measurement of Cardiac Hypertrophy and Function

A). Changes in diastolic interventricular septum thickness (IVSTd) in wildtype and Gpx1 −/− mice. Values were quantified from 3 separate M-mode measurements by echocardiography on conscious mice before (day 0) and after vehicle or AngII treatment (day 7). B) Changes in left ventricular mass (LV mass) in wildtype mice and Gpx1 −/− mice treated with vehicle or AngII. Measurements were performed using echocardiography on conscious mice before (day 0) and after vehicle or AngII (day 7). C) Comparison of shortening fraction (SF) in wildtype and Gpx1 −/− mice. Echocardiographic measurements were taken before (day 0) and after vehicle or AngII treatment (day 7). Data expressed as mean ± SEM (n = 9 – 10) (* p <0.05, ** p <0.001).

Figure 4. Left ventricular myocyte cross-sectional area (MCSA) in wildtype mice and Gpx1 −/− mice

Mice were treated with AngII or vehicle and cardiac sections were evaluated for MCSA. Panels show representative heart sections from wildtype + vehicle (A), Gpx1 −/− + vehicle (B), wildtype + AngII (C), and Gpx1 −/− + AngII (D) mice. Picrosirius red stain was used to demarcate myocytes as well as stain for collagen MCSA was measured after 7 days of vehicle or Ang II treatment. MCSA (µm₂) was digitally measured and expressed as mean ± SEM (E) (n = 9 – 10). Original magnification ×200.

Figure 5. Left ventricular interstitial collagen fraction (ICF %) in wildtype mice and Gpx1 −/− mice

Mice were treated with AngII or vehicle and cardiac sections were stained with picrosirius red. Panels show representative heart sections from wildtype + vehicle (A), Gpx1 −/− + vehicle (B), wildtype + AngII (C), and Gpx1 −/− + AngII (D) mice. ICF % of total area was digitally measured and expressed as mean ± SEM (E) (n = 9 – 10). Original magnification ×200.

Figure 6. Comparisons of aortic wall thickness to lumen ratio (Wm/L) and cross sectional area (CSA) in wildtype mice and Gpx1 −/− mice

Mice were treated with AngII or vehicle for 7 days. Thoracic aortas were stained with Masson Trichrome and parameters digitally obtained by image analysis. Data are expressed as mean ± SEM. * p < 0.05 vs. vehicle (n = 9 – 10).