Muscle cell identity requires Pax7-mediated lineage-specific DNA demethylation

Abstract

BackgroundSkeletal muscle stem cells enable the formation, growth, maintenance, and regeneration of skeletal muscle throughout life. The regeneration process is compromised in several pathological conditions, and muscle progenitors derived from pluripotent stem cells have been suggested as a potential therapeutic source for tissue replacement. DNA methylation is an important epigenetic mechanism in the setting and maintenance of cellular identity, but its role in stem cell determination towards the myogenic lineage is unknown. Here we addressed the DNA methylation dynamics of the major genes orchestrating the myogenic determination and differentiation programs in embryonic stem (ES) cells, their Pax7-induced myogenic derivatives, and muscle stem cells in proliferating and differentiating conditions.ResultsOur data showed a common muscle-specific DNA demethylation signature required to acquire and maintain the muscle-cell identity. This specific-DNA demethylation is Pax7-mediated, and it is a prime event in muscle stem cells gene activation. Notably, downregulation of the demethylation-related enzyme Apobec2 in ES-derived myogenic precursors reduced myogenin-associated DNA demethylation and dramatically impaired the expression of differentiation markers and, ultimately, muscle differentiation.ConclusionsOur results underscore DNA demethylation as a key mechanism driving myogenesis and identify specific Pax7-mediated DNA demethylation signatures to acquire and maintain the muscle-cell identity. Additionally, we provide a panel of epigenetic markers for the efficient and safe generation of ES- and induced pluripotent stem cell (iPS)-derived myogenic progenitors for therapeutic applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0250-9) contains supplementary material, which is available to authorized users.

APOBEC2 is a Transcriptional Repressor required for proper Myoblast Differentiation

“…Thus, APOBEC2 downregulation impaired myoblast-to-myotube differentiation. These observations match those previously reported using mouse embryonic stem cell-derived myogenic precursors (Carrió et al, 2016).…”

Myogenic progenitor specification from pluripotent stem cells

“…The myogenic vs. cardiac fate decision process involves Pax3-induced repression of the cardiac master regulators Nkx2–5, Gata4 and Tbx5, and this can be partially rescued solely upon Tbx5 up-regulation [112, 113]. In addition, the transition from PDGFRα+FLK1− to Myod+ cell is accompanied by DNA demethylation at the regulatory regions of important muscle specific genes, including the Myf5 and MyoD enhancers, and the MyoG and Ckm promoters [114]. ES-derived myogenic progenitors are also characterized by Pax7-dependent chromatin remodeling at a subset of sites, which correlates with Pax7’s ability to maintain the undifferentiated status of these cells [115].…”

Epigenetics of cancer-associated muscle catabolism

“…FAPs are generally quiescent within muscle tissue but, mounting evidence supports a role for FAPs in muscle fiber regeneration by: creating a scaffold that supports muscle repair and releasing cytokines that stimulate satellite cell regeneration [35]. Mouse models show that FAP cells can mediate fibrotic and fat deposition, a phenotype regulated at the epigenetic level by targeting the SWI/SNF chromatin remodeling complex via HDAC activity [29]. Trichostatin A, an HDAC inhibitor can alter the epigenetic landscape of FAPs, promoting muscle regeneration through repression of MyoD and follistatin expression in mouse models (Figure 1) [32,35].…”

“…In cachexia, extrinsic factors are thought to stimulate NF-κB signaling resulting in persistent Pax7 expression ( Figure 1) [29]. Ultimately, myogenic factors are subject to extensive epigenetic regulation, ranging from regulation of myogenic loci by histone modifying enzymes, to post-transcriptional mRNA stability and translational control [29][30][31]. As such, recent attention has turned to epigenetic pathways as potential therapeutic targets aimed at reversing the wasting phenotype by augmenting muscle regeneration.…”

“…While Pax7 is critical for satellite cell self-renewal, its persistent expression results in muscle atrophy by preventing myogenic pathways. In cachexia, extrinsic factors are thought to stimulate NF-κB signaling resulting in persistent Pax7 expression ( Figure 1) [29]. Ultimately, myogenic factors are subject to extensive epigenetic regulation, ranging from regulation of myogenic loci by histone modifying enzymes, to post-transcriptional mRNA stability and translational control [29][30][31].…”