With Ang- was associated with increased skeletal muscle force and better performance in endurance tests. However, the adenovirus approach involving injection into the TA does not allow us to enrich all muscle fibers, therefore when we assayed muscle strength in isolated muscles injected with either Ad-GFP or Ad-hACE2 we did not observe significant differences. The membrane localization of ACE2 is relevant for its function. Here, we show that endogenous and overexpressed ACE2 protein was localized at the sarcolemma of individual fibers. 
It has been reported that ACE2 located at the plasma membrane enhances cell adhesion in an integrin-dependent manner. Indeed, soluble ACE2 is capable of suppressing integrin signaling mediated by FAK. It has also been shown that integrins are involved in the regulation of fibrosis, suggesting that pharmacologic targeting of all av integrins may have clinical utility in the treatment of patients with a broad range of fibrotic diseases. It would be interesting to determine whether sarcolemmal ACE2 participates in muscle fiber adhesion. Under fibrotic conditions, ACE2 is present in the interstitial space and most likely associated with the plasma membrane of ECMproducing cells, myofibroblasts, and/or inflammatory cells. As mentioned above, ACE2 exists in a soluble form in the plasma when shed from the cell membrane. Studies have linked elevated levels of sACE2 to myocardial dysfunction in heart BU 4061T inquirer failure patients. Moreover, ADAM17-mediated shedding of membrane ACE2 contributes to the development of neurogenic hypertension. The authors of these studies proposed a protective role for ACE2 when it is associated with the plasma membrane, which is consistent with the findings presented here. The large amounts of ACE2 in the interstitial space lead us to speculate about a signaling role of ACE2 in addition to its catalytic role. In this vein it has been demonstrated that overexpression of ADAM17 has a deleterious effect in mdx mice and mice with laminin alpha2deficient muscular dystrophy. It is intriguing that ACE2 activity is higher in skeletal muscles that exhibit more fibrosis in both the mdx mouse and the model of chronic induction of fibrosis. One plausible explanation is that some of the enhanced total ACE2 activity corresponds to enzyme associated with ECM-producing cells. This could be experimentally verified in dystrophic models in which fibrosis can be reduced. In fact, our results in mdx mice infused with Ang- support this idea because ACE2 staining was lower than in nontreated mdx mice. Another explanation is that ACE2 activity is enhanced as a compensatory mechanism to produce more Ang- and therefore decrease the amount of fibrotic proteins. Fibrosis is a deleterious feature of several chronic OTX015 diseases including DMD. Understanding the cellular and molecular mechanisms underlying muscle fibrosis is essential to develop effective antifibrotic therapies for DMD. Administration of Ang via systemic infusion has been shown to be a promissory approach for muscular disorders. However, given its short half-life in plasma and its putative effects in other organs, we believe that modulating ACE2 activity in the skeletal muscle to increase local skeletal muscle levels of Ang- may represent a new therapeutic approach. In conclusion, this work shows for the first time that ACE2 protein levels and activity are augmented in fibrotic.