These results support the idea that ACE2 might function as a sensor of an inflammatory/fibrotic environment in the muscle tissue, with its expression being elevated in fibrotic situations or decreased when anti-inflammatory molecules are released. Together, the results presented here suggest that muscle tissue maintains homeostasis by modulating ACE2 levels. Moreover, we provide novel evidence that augmenting ACE2 levels PI-103 beyond the already elevated levels detected in the mdx muscle improves some aspects of the dystrophic phenotype, such as ECM deposition and infiltration of inflammatory cells. The relevance of the RAS goes beyond its role in the physiology of the kidney and control of vascular tone. Considerable data suggest its importance in normal skeletal muscle function and tissue architecture. However, little is known about the regulation of the RAS components in skeletal muscle in the context of disease. Ang- acting through its Mas receptor plays a critical role in controlling skeletal muscle fibrosis in DMD. ACE2, a key component of the alternative RAS, catalyzes the conversion of Ang II to Ang-; therefore, we investigated whether ACE2 expression and activity are subject to regulation in muscular dystrophy. ACE2 is normally expressed in skeletal muscle. Here, we report that ACE2 protein levels and concomitant activity are increased in dystrophic muscles compared with wt. It has been reported that the phenotype of mdx mice is milder than that of DMD. It would be interesting to evaluate the level of ACE2 activity and expression of the Mas receptor in samples from DMD patients, since it could be hypothesized that in DMD ACE2 levels are not increased, given a more aggressive phenotype. As a consequence of augmented ACE2 expression in the dystrophic muscle, we might expect increased local production of Ang-. Since Ang- is an anti-fibrotic molecule, it might seem counterintuitive to have a simultaneous increase in ACE2 activity and excessive deposition of fibrotic constituents. However, results obtained from the analysis of mdx-Mas-KO muscle give some insight to help us understand these observations. Muscle from the double knockout mice LY2109761 exhibits a worse phenotype than mdx-derived muscle, with stronger TGF-b signaling, more fibrosis, and a further decrease in muscle function. These findings suggest that production of endogenous Ang- and its signaling through the Mas receptor are required to compensate for the progression of fibrosis in the mdx skeletal muscle. Thus, augmented ACE2 activity in dystrophic muscle or in wt muscle subjected to chronic damage seems necessary to protect the tissue from more severe damage such as that observed in the double knockout mouse. It will be helpful to quantify the amount of Ang- generated in the skeletal muscle in future studies. Following this line of reasoning, we hypothesized that we could reduce muscle fibrosis and inflammation by overexpressing ACE2 in dystrophic muscle. Indeed, we demonstrate for the first time that ACE2 gain of function correlates with decreased levels of fibrotic proteins and an important decrease in the number of inflammatory M1 macrophages, validating the anti-fibrotic and anti-inflammatory roles of ACE2 in 
skeletal muscle and supporting the idea of a beneficial effect of Ang- in the context of disease.