Mineralocorticoid receptor antagonists improve membrane integrity independent of muscle force in muscular dystrophy

Abstract

Mineralocorticoid receptor (MR) drugs have been used clinically for decades to treat cardiovascular diseases. MR antagonists not only show preclinical efficacy for heart in Duchenne muscular dystrophy (DMD) models but also improve skeletal muscle force and muscle membrane integrity. The mechanisms of action of MR antagonists in skeletal muscles are entirely unknown. Since MR are present in many cell types in the muscle microenvironment, it is critical to define cell-intrinsic functions in each cell type to ultimately optimize antagonist efficacy for use in the widest variety of diseases. We generated a new conditional knockout of MR in myofibers and quantified cell-intrinsic mechanistic effects on functional and histological parameters in a DMD mouse model. Skeletal muscle MR deficiency led to improved respiratory muscle force generation and less deleterious fibrosis but did not reproduce MR antagonist efficacy on membrane susceptibility to induced damage. Surprisingly, acute application of MR antagonist to muscles led to improvements in membrane integrity after injury independent of myofiber MR. These data demonstrate that MR antagonists are efficacious to dystrophic skeletal muscles through both myofiber intrinsic effects on muscle force and downstream fibrosis and extrinsic functions on membrane stability. MR antagonists may therefore be applicable for treating more general muscle weakness and possibly other conditions that result from cell injuries.

Mineralocorticoid Receptor Signaling Contributes to Normal Muscle Repair After Acute Injury

“…The muscle microenvironment in chronic muscle injury attempts to compensate for the repeated damage and regenerate muscle in a similar manner to acute muscle injury (Bentzinger et al, 2013; Tidball et al, 2018). The mineralocorticoid receptor (MR) has been identified as an important therapeutic target for modifying disease severity in Duchenne muscular dystrophy (Duboc et al, 2005; Rafael-Fortney et al, 2011, 2016; Sayer and Bhat, 2014; Chadwick et al, 2015, 2017a; Lowe et al, 2016; Raman et al, 2017; Hauck et al, 2019). The MR, a nuclear steroid hormone receptor, is expressed in many cell types in the skeletal muscle microenvironment including myofibers, muscle progenitor cells, immune cells, fibroblasts, and endothelial cells (Duboc et al, 2005; Rickard et al, 2009, 2014; Yang and Young, 2009; Usher et al, 2010; Lother et al, 2011; Chadwick et al, 2015; Mueller et al, 2015; Hauck et al, 2019).…”

“…The mineralocorticoid receptor (MR) has been identified as an important therapeutic target for modifying disease severity in Duchenne muscular dystrophy (Duboc et al, 2005; Rafael-Fortney et al, 2011, 2016; Sayer and Bhat, 2014; Chadwick et al, 2015, 2017a; Lowe et al, 2016; Raman et al, 2017; Hauck et al, 2019). The MR, a nuclear steroid hormone receptor, is expressed in many cell types in the skeletal muscle microenvironment including myofibers, muscle progenitor cells, immune cells, fibroblasts, and endothelial cells (Duboc et al, 2005; Rickard et al, 2009, 2014; Yang and Young, 2009; Usher et al, 2010; Lother et al, 2011; Chadwick et al, 2015; Mueller et al, 2015; Hauck et al, 2019). Chronic overactivation of MR by the endogenous hormone aldosterone, primarily produced from the adrenal gland, is known to exacerbate cell damage in cardiovascular diseases and promote fibrosis (Mizuno et al, 2001; Pitt, 2012; McCurley et al, 2013; Gomez-Sanchez and Gomez-Sanchez, 2014).…”

“…Chronic overactivation of MR by the endogenous hormone aldosterone, primarily produced from the adrenal gland, is known to exacerbate cell damage in cardiovascular diseases and promote fibrosis (Mizuno et al, 2001; Pitt, 2012; McCurley et al, 2013; Gomez-Sanchez and Gomez-Sanchez, 2014). We have shown in mouse models of muscular dystrophy that genetic inactivation of myofiber MR improves skeletal muscle force and alters fibrosis (Rafael-Fortney et al, 2011; Lowe et al, 2016; Hauck et al, 2019). Additionally, our findings indicate that MR antagonist treatment improves muscle membrane integrity in muscular dystrophy (Chadwick et al, 2017a; Hauck et al, 2019).…”

“…We have shown in mouse models of muscular dystrophy that genetic inactivation of myofiber MR improves skeletal muscle force and alters fibrosis (Rafael-Fortney et al, 2011; Lowe et al, 2016; Hauck et al, 2019). Additionally, our findings indicate that MR antagonist treatment improves muscle membrane integrity in muscular dystrophy (Chadwick et al, 2017a; Hauck et al, 2019). We have also demonstrated that myeloid immune cells in dystrophic skeletal muscle contain the enzyme aldosterone synthase (CYP11B2) and have the capacity to synthesize aldosterone (Chadwick et al, 2016).…”

Muscle Twitch Kinetics Are Dependent on Muscle Group, Disease State, and Age in Duchenne Muscular Dystrophy Mouse Models

“…Widely used mouse models for DMD preclinical studies include the dystrophin deficient mdx mouse ( Bulfield et al, 1984 ; Yucel et al, 2018 ) and the dystrophin deficient and utrophin haplo-insufficient ( utrn +/– ; mdx ) “het” mouse ( Zhou et al, 2008 ; van Putten et al, 2012 ). Maximal tetanic contractions are the most commonly used protocol to assess muscle function ( Hibaoui et al, 2011 ; Janssen et al, 2014 ; Lowe et al, 2016 , 2018 ; Hauck et al, 2019 ; Lindsay et al, 2019 ; Trajanovska et al, 2019 ). However, in vivo , the vast majority of muscle function occurs not at maximal, but at sub-maximal contraction conditions.…”