Age- and gender-related difference of ACE2 expression in rat lung

Abstract

Epidemiologic data suggested that there was an obvious predominance of young adult patients with a slight female proneness in severe acute respiratory syndrome (SARS). The angiotensin-converting enzyme 2 (ACE2) was very recently identified as a functional receptor for SARS virus and is therefore a prime target for pathogenesis and pharmacological intervention. Rats of both genders at three distinct ages (young-adult, 3 months; middle-aged, 12 months; old, 24 months) were evaluated to determine the characteristic of ACE2 expression in lung and the effect of aging and gender on its expression. ACE2 was predominantly expressed in alveolar epithelium, bronchiolar epithelium, endothelium and smooth muscle cells of pulmonary vessels with similar content, whereas no obvious signal was detected in the bronchiolar smooth muscle cells. ACE2 expression is dramatically reduced with aging in both genders: young-adult vs. old P < 0.001 (by 78% in male and 67% in female, respectively) and middle-aged vs. old P < 0.001 (by 71% in male rats and 59% in female rats, respectively). The decrease of ACE2 content was relatively slight between young-adult and middle-aged groups (by 25% in male and 18% in female, respectively). Although there was no gender-related difference of ACE2 in young-adult and middle-aged groups, a significantly higher ACE2 content was detected in old female rats than male. In conclusion, the more elevated ACE2 in young adults as compared to aged groups may contribute to the predominance in SARS attacks in this age group.

Fig. 1

The immunohistochemical analysis of ACE2 expression in normal rat lung. A: Positive staining for ACE2 in alveolar epitheliums (empty arrowhead) and bronchiolar epitheliums (arrow), but no obvious signal in the bronchiolar smooth muscle cells (black arrowhead). B: ACE2 present in alveolar epithelial cells (type I black arrow and type II empty arrowhead) and capillary endothelium (black arrowhead) in larger magnification. C: Control section stained with normal rabbit serum instead of anti-ACE2 shows no staining in rat lung. Original magnification A and C, × 400; B × 800.

Fig. 2

ACE2 protein content was decreased with age in rat lung tissue of both genders: male (A) and female (B). The amounts of ACE2 were determined by Western analysis as described in Methods section. β-actin was used as loading control. Values represent means ± SEM (n = 10). 3 m, young-adult group (3 months); 12 m, middle-aged group(12 months); 24 m, old group (24 months). The sizes of the molecular weight markers are shown to the right and indicate the 100 kDa and 86 kDa proteins. **, P < 0.01; ***, P < 0.001.

Fig. 3

Immunohistochemical staining of ACE2 in rat lung of both genders at three distinct ages: female young-adult (A), male young-adult (B), female middle-aged (C), male middle-aged (D), female old (E) and male old (F). Original magnification: × 400.

Fig. 4

Effect of gender on ACE2 expression in rat lung tissue during aging process. A: young adult group (3 months); B: middle-aged group (12 months); C: old group (24 months). β-actin was used as loading control. Values represent means ± SEM (n = 10). The sizes of the molecular weight markers are shown to the right and indicate the 100 kDa and 86 kDa proteins. *, P < 0.05.