Angiotensin II type 1 and 2 receptors and lymphatic vessels modulate lung remodeling and fibrosis in systemic sclerosis and idiopathic pulmonary fibrosis

Abstract

Objective: To validate the importance of the angiotensin II receptor isotypes and the lymphatic vessels in systemic sclerosis and idiopathic pulmonary fibrosis.

Methods: We examined angiotensin II type 1 and 2 receptors and lymphatic vessels in the pulmonary tissues obtained from open lung biopsies of 30 patients with systemic sclerosis and 28 patients with idiopathic pulmonary fibrosis. Their histologic patterns included cellular and fibrotic non-specific interstitial pneumonia for systemic sclerosis and usual interstitial pneumonia for idiopathic pulmonary fibrosis. We used immunohistochemistry and histomorphometry to evaluate the number of cells in the alveolar septae and the vessels stained by these markers. Survival curves were also used.

Results: We found a significantly increased percentage of septal and vessel cells immunostained for the angiotensin type 1 and 2 receptors in the systemic sclerosis and idiopathic pulmonary fibrosis patients compared with the controls. A similar percentage of angiotensin 2 receptor positive vessel cells was observed in fibrotic non-specific interstitial pneumonia and usual interstitial pneumonia. A significantly increased percentage of lymphatic vessels was present in the usual interstitial pneumonia group compared with the non-specific interstitial pneumonia and control groups. A Cox regression analysis showed a high risk of death for the patients with usual interstitial pneumonia and a high percentage of vessel cells immunostained for the angiotensin 2 receptor in the lymphatic vessels.

Conclusion: We concluded that angiotensin II receptor expression in the lung parenchyma can potentially control organ remodeling and fibrosis, which suggests that strategies aimed at preventing high angiotensin 2 receptor expression may be used as potential therapeutic target in patients with pulmonary systemic sclerosis and idiopathic pulmonary fibrosis.

Figure 1

Cellular expression of the angiotensin II type 1 receptor (AGTR-1) and AGTR-2 divided in septal areas and intrapulmonary vessels from normal control lungs, systemic sclerosis (SSc) and idiopathic pulmonary fibrosis (IPF). In (A) and (B), we observe a diffuse and minimal AGTR-1 (arrows) expression in the alveolar septal areas and in the intrapulmonary vessels of the controls. The AGTR-1 expression shows greater increases in the thickened alveolar septal region from the cellular SSc-NSIP (arrows, E) than in the fibrotic SSc-NSIP (arrows, I). In the intrapulmonary vessels, the expression of AGTR-1 (arrows) is minimal and similar in both groups (cellular SSc-NSIP, F and fibrotic SSc-NSIP, J). Increased expression of AGTR-1 (arrows) is observed in the septal areas (M) and intrapulmonary vessels (N) of IPF-UIP. In (C) and (D), we observed AGRT-2 (arrows) expression in the septal areas and intrapulmonary vessels from the controls. In (G) and (K), we observed a similar expression of AGTR-2 (arrows) in the septal areas of cellular and fibrotic SSc-NSIP. Increased expression of AGTR-2 (arrows) is observed in the intrapulmonary vessels of fibrotic SSc-NSIP (L) compared to cellular SSc-NSIP (H). The expression of AGTR-2 (arrows) is more evident in the septal areas of IPF-UIP (O) than in the intrapulmonary vessels (P) of this histologic pattern. Q and R show the total values of AGTR-1 and AGTR-2 and the results analyzed by a one-way ANOVA with the Bonferroni multiple comparisons test for the control, SSc-NSIP and IPF-UIP groups. (*) Significantly higher AGTR-1 expression was observed in the SSc-NSIP and IPF-UIP lungs compared with the control group (p = 0.001 and p = 0.001, respectively). A similar situation was observed with AGTR-2 expression from the SSc-NSIP and IPF-UIP patterns compared to the control group (p<0.001 and p<0.001, respectively). (†) Significantly higher expression of AGTR-2 in the SSc-NSIP group was observed when compared with the IPF-UIP group (p = 0.04) by Student's t-test.

Figure 2

D2-40 cell expression in the lymphatic vessels of the normal control lungs, systemic sclerosis (SSc) and idiopathic pulmonary fibrosis (IPF). The lymphatic vessels (arrows) were observed in the sub pleural (A) and interlobular septal interstitium (B) in the control lungs. In cellular SSc-NSIP, the lymphatic vessels (arrows) were observed in the thickened alveolar septal region (C) and were infrequent compared to the fibrotic SSc-NSIP pattern (arrows, D). In the UIP pattern, we observed a higher proportion of lymphatic vessels (arrows) in the interlobular and subpleural spaces (E and F). G and H represent the total values of the lymphatic dilatation and density, and the results analyzed by the one-way ANOVA followed by the Bonferroni multiple comparisons test for the control, SSc-NSIP and IPF-UIP groups. (*) A significantly increased lymphatic dilatation (G) was observed in the IPF-UIP group compared to the SSc-NSIP (p = 0.01) and control (p = 0.01) groups. Similarly, a significantly higher lymphatic density (H) was observed in the IPF-UIP group compared to the SSc-NSIP (0.02) and control (0.01) groups.