Histopathological study of time course changes in inter-renal aortic banding-induced left ventricular hypertrophy of mice

Abstract

The left ventricular hypertrophy (LVH) in response to pressure overload is an important risk factor in cardiac morbidity and mortality. To investigate the time course of histopathological alterations in the LVH in response to pressure overload, histopathological and immunohistochemical examination was performed using the aortic banding-induced mouse LVH model. Five-week-old male CD-1 mice were subjected to the inter-renal aortic banding. Major organs were sampled on 3, 10, 14, 21, 28 or 42 days after banding. Haematoxylin and eosin (H&E) staining, Masson's trichrome staining and immunohistochemistry for proliferating cell nuclear antigen (PCNA), alpha-smooth muscle actin (aSMA), ICAM-1, type I collagen and CD31 was performed and microscopically examined. Three days after aortic banding, acute inflammatory changes, such as macrophages/neutrophil infiltration and vascular wall injury were observed on/around the coronary arteries/arterioles of both ventricles. Intense ICAM-1 immunostaining was observed on the endothelium of the coronary arteries/arterioles. After day 10, vascular wall thickening and perivascular fibrosis was induced on the coronary arteries/arterioles. Immunohistochemistry for aSMA and PCNA demonstrated the proliferation of vascular smooth muscle cells in the media. After day 28, minimal cardiomyocyte hypertrophy was observed at the light microscope level. In the inter-renal aortic banding LVH model, histopathological alterations in early phase were mainly observed on coronary arteries/arterioles. These early phase alterations were thought to be hypertension-related changes in the coronary vasculatures. The cardiomyocyte hypertrophy observed in later phase was minimal at the light microscope level. These evidences would facilitate the understanding of pathophysiology of pressure overload LVH.

Figure 1

Cellular infiltration and vascular wall thickening observed in the inter-renal aortic banding-induced LVH model. (a) Cellular infiltration dominated by macrophages and neutrophils around coronary artery observed on day 3. (b) Transmigration and infiltration of macrophages/neutrophils observed on day 3. (c) ICAM-1 immunostaining on endothelium of the coronary artery. (d) Mild cellular infiltration dominated around coronary arteries observed on day 10. (e) Moderate coronary artery thickening observed on day 14. HE staining (a, b and d–f), Original magnification ×200 (a, c and e), ×400 (b, d and f).

Figure 2

Immunohistochemistry for CD31, aSMA, type I collagen and PCNA in the inter-renal aortic banding-induced LVH model. (a) Endothelium marker, CD31. (b) Vascular smooth muscle cell marker, aSMA. (c) Type I collagen immunostaining. (d) Cell proliferation marker, PCNA. Increase in the number of aSMA-positive vascular smooth muscle cells is observed. PCNA immunostaining preferentially localized to vascular smooth muscle cells. Original magnification ×200 (a–d).

Figure 3

Masson' trichrome staining in the inter-renal aortic banding-induced LVH model. Perivascular fibrosis observed on coronary artery of right ventricle (RV) and left ventricle (LV) at 14 days or 42 days after banding (a and b or c and d respectively). Perivascular area of LV and RV in sham-operated animals on day 14 (e and f) Masson' trichrome staining (a–f). Original magnification ×200 (a–e), bar 50 μm.

Figure 4

Cardiomyocyte hypertrophy in the inter-renal aortic banding-induced LVH model. (a) Cardiomyocytes of sham-operated animal on day 42. (b) Cardiomyocytes of banded animal on day 42. Note minimal increase in the size of cardiomyocytes in the banded animal. HE staining (a and b), original magnification ×200 (a and b), bar 50 μm.