In summary we have identified
In summary, we have identified a series of amides as ERRγ agonists with suitable potency for further development. Our SAR studies of this chemotype identified SR19881 as the most potent full agonist of ERRγ with an EC=0.39 μM in a binding assay and an EC=4.7 μM in a cell-based assay. SR19881 was also equipotent on ERRβ with an EC=0.63 μM making it an equipotent dual agonist of ERRβ/γ. HDX studies help explain how subtle changes to the molecule translate into improved potency by increased stabilization of the receptor. These studies provided valuable information and an opportunity to expand the series in search of more potent, selective, and druglike molecules. Further investigations of new chemotypes and pharmacokinetic properties continue in an effort to explore the role of ERRγ and . These results will be reported in due course.
Introduction Skeletal muscle originates from muscle progenitor BCATc Inhibitor 2 that undergo expansion and migration; then they differentiate into myoblasts that eventually fuse to generate multinucleated myotubes . The maturation of myotubes ultimately gives rise to contractive skeletal myofibers . Among all of these stages of development, differentiation is a crucial process that determines muscle cell fate and final muscle formation. In mammals, muscle fibers are broadly characterized as slow-twitch (oxidative) or fast-twitch (glycolysis), which express the MyHC isoform I and MyHC isoforms IIa, IIx, and IIb, respectively [2,3]. The highly complicated process of myogenesis is orchestrated by the muscle specific regulatory transcription factors (MRFs) and myocyte enhancer factor 2 (MEF2) families. The MRFs family includes myogenic differentiation antigen (MyoD), myogenin (MyoG), myogenic factor 5 (Myf5), and myogenic regulatory factor 4 (MRF4). The MEF2 family includes MEF2A, -B, -C and –D [, , ]. These two classes of transcription factors interact directly to establish a unique transcriptional code for skeletal muscle gene activation . The MEF2C gene serves to further reinforce the decision of myoblasts to differentiate . Estrogen-related receptor gamma (ERRγ) is an orphan nuclear hormone receptor that belongs to the ERR subfamily of transcription factors. Studies have shown that ERRγ expression in skeletal muscle is sufficient and necessary to increase exercise capacity and activate mitochondrial function . Recently, microRNAs (miRNAs), a class of conserved small non-coding RNAs , have emerged as novel and essential regulators of myogenesis . They vary from 17 to 24 nucleotides in length and induce mRNA degradation or translation inhibition by interacting with the 3′UTRs of their target mRNAs . miRNAs may regulate myogenesis by regulating the process of myoblast proliferation and differentiation . miR-206 and miR-486 can cause myoblasts to exit the proliferation and cell cycle stage, and subsequently enter the differentiation phase by directly suppressing Pax7 expression . Eric Olson et al. reported that several miRNAs are involved in muscle fiber type programs . Especially, miR-208b and miR-499 are involved in slow-twitch fiber programming by modulating contractile protein gene expression [13,14]. Interestingly, our previous studies from porcine skeletal muscle high-throughput sequencing found that the expression of miR-204-5p gradually decreased with age . Sheng et al.  reported that the expression of miR-204-5p was significantly increased in skeletal muscle at all postnatal stages in Min pigs, which has low lean meat percentage, compared to its expression in Large White pigs, which contains high lean meat percentage. These studies imply that miR-204-5p has a potential function in regulating muscle development. However, the role of miR-204-5p in myoblast differentiation, which is the critical process of determining muscle cell fate and final muscle formation, has not been reported yet. In the current study, we found that miR-204-5p is negatively correlated with myoblast differentiation. We suppose that miR-204-5p blunts myoblast differentiation and reduces the composition of MyHC in slow-twitch fibers by targeting MEF2C and ERRγ. We provide evidence that miR-204-5p affects myoblast differentiation.