Mineralocorticoid Receptor Signaling Contributes to Normal Muscle Repair After Acute Injury

Abstract

Acute skeletal muscle injury is followed by a temporal response of immune cells, fibroblasts, and muscle progenitor cells within the muscle microenvironment to restore function. These same cell types are repeatedly activated in muscular dystrophy from chronic muscle injury, but eventually, the regenerative portion of the cycle is disrupted and fibrosis replaces degenerated muscle fibers. Mineralocorticoid receptor (MR) antagonist drugs have been demonstrated to increase skeletal muscle function, decrease fibrosis, and directly improve membrane integrity in muscular dystrophy mice, and therefore are being tested clinically. Conditional knockout of MR from muscle fibers in muscular dystrophy mice also improves skeletal muscle function and decreases fibrosis. The mechanism of efficacy likely results from blocking MR signaling by its endogenous agonist aldosterone, being produced at high local levels in regions of muscle damage by infiltrating myeloid cells. Since chronic and acute injuries share the same cellular processes to regenerate muscle, and MR antagonists are clinically used for a wide variety of conditions, it is crucial to define the role of MR signaling in normal muscle repair after injury. In this study, we performed acute injuries using barium chloride injections into tibialis anterior muscles both in myofiber MR conditional knockout mice on a wild-type background (MRcko) and in MR antagonist-treated wild-type mice. Steps of the muscle regeneration response were analyzed at 1, 4, 7, or 14 days after injury. Presence of the aldosterone synthase enzyme was also assessed during the injury repair process. We show for the first time aldosterone synthase localization in infiltrating immune cells of normal skeletal muscle after acute injury. MRcko mice had an increased muscle area infiltrated by aldosterone synthase positive myeloid cells compared to control injured animals. Both MRcko and MR antagonist treatment stabilized damaged myofibers and increased collagen infiltration or compaction at 4 days post-injury. MR antagonist treatment also led to reduced myofiber size at 7 and 14 days post-injury. These data support that MR signaling contributes to the normal muscle repair process following acute injury. MR antagonist treatment delays muscle fiber growth, so temporary discontinuation of these drugs after a severe muscle injury could be considered.

Mineralocorticoid Receptor Signaling in the Inflammatory Skeletal Muscle Microenvironments of Muscular Dystrophy and Acute Injury

“…Defining myofiber MR signaling during acute muscle injury also elucidates mechanistic insights contributing to MRA efficacy in muscular dystrophy. CYP11B2 is transiently expressed during a very brief period at the peak of myeloid cell infiltration after acute muscle injury in normal mice ( Hauck et al, 2019a ). Conditional knockout of myofiber MR in wild-type mice after muscle injury hampers muscle regeneration by increasing the density of collagen in fibrotic areas as well as reducing myofiber size post-injury, suggesting a delay in wound healing.…”

“…Increased infiltration of immune cells expressing CYP11B2 is also observed, supporting that MR activation by aldosterone contributes to efficient coordination of regeneration during the skeletal muscle repair process. Treatment with MRAs has similar effects, suggesting that MRAs in chronic versus acute skeletal muscle injuries have contrasting effects ( Hauck et al, 2019a ).…”

Micro-dystrophin gene therapy prevents heart failure in an improved Duchenne muscular dystrophy cardiomyopathy mouse model

“…All ( n = 8) μDys-treated samples were used for dystrophin and α-sarcoglycan immunofluorescence. For quantification, transverse ventricular sections were imaged on a Nikon Eclipse 800 microscope under a 10× objective using a Nikon DS-Ri2 digital camera driven by Nikon NIS-Elements Br software and analyzed using Adobe Photoshop CS6 as previously described ( 50 , 51 ).…”

Current state of cardiac troponin testing in Duchenne muscular dystrophy cardiomyopathy: review and recommendations from the Parent Project Muscular Dystrophy expert panel

“…[51][52][53] Some of these benefits are related to membrane stabilisation properties that could also slow troponin release from myocardial cells. [54][55][56] Increased steroid dosing showed benefits in two case reports. 37 38 A new steroid derivative therapeutic also demonstrated membrane stabilisation properties and could provide an alternative to steroid therapy in subjects with elevated cTnI levels.…”