Cardiac protective effects of irbesartan via the PPAR-gamma signaling pathway in angiotensin-converting enzyme 2-deficient mice

Background: Angiotensin-converting enzyme 2 (ACE2), a monocarboxypeptidase which metabolizes angiotensin II (Ang II) to generate Ang-(1-7), has been shown to prevent cardiac hypertrophy and injury but the mechanism remains elusive. Irbesartan has the dual actions of angiotensin receptor blockade and peroxisome proliferatoractivated receptor-. (PPAR.) activation. We hypothesized that irbesartan would exert its protective effects on ACE2 deficiency-mediated myocardial fibrosis and cardiac injury via the PPAR. signaling. Methods: 10-week-old ACE2 knockout (ACE2KO; Ace2-/y) mice received daily with irbesartan (50 mg/kg) or saline for 2 weeks. The wild-type mice (Ace2+/y) were used to the normal controls. We examined changes in myocardial ultrastructure, fibrosis-related genes and pathological signaling by real-time PCR gene array, Western blotting, Masson trichrome staining and transmission electron microscope analyses, respectively. Results: Compared with the Ace2(+/y) mice, cardiac expression of PPARa and PPAR. were reduced in Ace2(-/y) mice and the myocardial collagen volume fraction (CVF) and expression of fibrosis-related genes were increased, including transforming growth factor-beta 1 (TGF beta 1), connective tissue growth factor (CTGF), collagen I and collagen III. Moreover, ACE2 deficiency triggered cardiac hypertrophy, increased myocardial fibrosis and adverse ultrastructure injury in ACE2KO hearts with higher levels of atrial natriuretic factor (ANF) and phosphorylated extracellular signalregulated kinase 1/2 (ERK1/2), without affecting cardiac systolic function. Intriguingly, treatment with irbesartan significantly reversed ACE2 deficiency-mediated pathological hypertrophy and myocardial fibrosis in Ace2(-/y) mice linked with enhancement of plasma Ang-(1-7) level and downregulation of AT1 receptor in heart. Consistent with attenuation of myocardial fibrosis and ultrastructure injury, the myocardial CVF and levels of ANF, TGF beta 1, CTGF, collagen I, collagen III and phosphorylated ERK1/2 were lower, and expression of PPAR gamma was higher in ACE2KO mice in response to irbesartan treatment, without affecting cardiac expression of PPAR alpha, PPAR delta, beta-myosin heavy chain, TGF beta 2 and fibronectin. Conclusions: We conclude that irbesartan prevents ACE2 deficiency- mediated pathological hypertrophy and myocardial fibrosis in ACE2 mutant mice via activation of the PPAR. signaling and suppression of the TGF beta-CTGF -ERK signaling, resulting in attenuation of myocardial injury. Drugs targeting ACE2 and PPAR. represent potential candidates to prevent and treat myocardial injury and related cardiac disorders.