Five days after injury, the average CSA of muscle fibers was significantly decreased inPax7-CreER:Islrfl/flmice compared to theIslrfl/flmice (Fig.5e). as an important regulator for skeletal muscle regeneration. Satellite cells are crucial for skeletal muscle regeneration. Here the authors show that immunoglobulin superfamily containing leucine-rich repeat (Islr) promotes skeletal muscle regeneration via a mechanism involving Dishevelled-2 stabilization in satellite cells and protection from autophagy. == Introduction == Regeneration is critical to maintain the homeostasis of adult skeletal muscle in animals, and satellite cells (SCs) play an important role during this process. Adult skeletal muscle fails to regenerate by genetic ablation of SCs postnatally13. Upon adult skeletal muscle injury, quiescent Pax7+SCs are activated and give rise to a population of Pax7+/Myf5+committed Edotecarin SCs4,5. These progenitor cells proliferate into Pax7+/MyoD+myoblast cells6,7and differentiate into the myogenin+(MyoG+) cells that fuse to form multinucleated myotubes8,9. SC differentiation is essential for skeletal muscle regeneration, and it is increasingly clear that SC differentiation is regulated by many signaling pathways. In particular, the canonical Wnt signaling pathway is important for promoting SC differentiation during skeletal muscle regeneration10,11. When Wnt ligands bind to Frizzled receptors and members of the low-density lipoprotein receptor-relayed protein (LRP) family, the canonical Wnt signaling is activated. The cytoplasmic part of Frizzled interacts with Disheveled-2 (Dvl2), facilitating interaction between Axin and the LRP tail, which destroys the -catenin destruction complex and blocks the ubiquitination of -catenin. Subsequently, -catenin translocates into the nucleus and further forms a complex with the TCF transcription factors to activate transcription of Wnt target genes1214. Dvl2 is the hub of the canonical Wnt signaling pathway; autophagy mediates the degradation of Dvl2 and further negatively regulates Rabbit Polyclonal to Ik3-2 canonical Wnt signaling in response to cellular metabolic stress15,16. The deletion of some components of the canonical Wnt signaling pathway delays skeletal muscle regeneration11. Inactivation of -catenin or BCL9 inhibits the differentiation of SCs17,18. It is well-known that autophagy is crucial for maintaining the energy balance and stability of the cellular environment19,20. Interestingly, autophagy regulates SC activation and skeletal muscle regeneration21,22. Given this, we wanted to know whether autophagy regulates muscle regeneration by affecting the stabilization of Dvl2 and how this process is precisely controlled during skeletal muscle regeneration. Recently, the immunoglobulin superfamily containing leucine-rich repeat (Islr) gene was identified as a new marker of mesenchymal stem cells and is expressed in SCs23.IslrmRNA is also detected in muscle tissues24,25. It is well-known that Duchenne muscular dystrophy (DMD) patients and dystrophin-null (mdx) mice have continuous regeneration of muscle and activation of SCs in humans and mice, respectively2628.IslrmRNA is highly expressed in DMD patients andmdxmice in the Gene Expression Omnibus (GEO) database, suggesting a potential role ofIslrin skeletal muscle regeneration. However, the in vivo functions ofIslrin skeletal muscle regeneration are entirely unknown. In this study, we found that Islr was highly expressed in differentiated myogenic cells. Utilizing anIslrloss-of-function mouse model, we demonstrated thatIslrwas required for skeletal muscle regeneration. Mechanistically, Islr activated the canonical Wnt signaling pathway by antagonizing autophagy to stabilize Dvl2. == Results == == Islr is highly expressed in differentiated myogenic cells == The GEO database shows thatIslrmRNA is highly expressed inmdxmice, thus we validated this information and found that Islr was indeed upregulated inmdxmice (Supplementary Fig.1a, b), indicating that it might Edotecarin be involved in skeletal muscle regeneration. To examine the expression of Islr during skeletal muscle regeneration, the tibial anterior (TA) muscles were injured with an injection of cardiotoxin Edotecarin (CTX) and allowed to regenerate. Islr protein levels were higher in the injured than in the contralateral TA muscles (CTL) at 3 d postinjury (Supplementary Fig.1c). The expression level of Islr increased between 3 and 5 day postinjury, which is a critical stage during which SCs participate in skeletal muscle regeneration (Supplementary Fig.1d). To analyze the expression of Islr during myogenesis, we carried out immunohistochemical staining for Islr, Pax7, and MyoG on serial sections of TA muscles. No Islr protein expression was detected in Pax7+quiescent SCs (Fig.1a). However, Edotecarin Islr protein was expressed in Pax7+activated SCs and MyoG+muscle progenitors (Fig.1b, c). A combination of cell surface markers (CD45, CD31, Sca1, and 7-integrin+) is widely used to purify SCs in skeletal muscle. Specifically, we isolated SCs from wild-type (WT) mice using fluorescence-activated cell sorting (FACS)29(Fig.1d). AlthoughIslrmRNA was not significantly different between freshly isolated SCs and activated SCs cultured for 24 h, the mRNA and protein levels ofIslrwere higher in differentiating cells as compared to proliferating cells (Fig.1eand Supplementary Fig.1e). == Fig. 1. == Islr is upregulated during satellite cell differentiation and C2C12 differentiation.aImmunohistochemistry analysis of Islr and Pax7 in uninjured TA muscles of wild-type (WT) mice. Scale bar = 10 m.bImmunohistochemistry analysis of Islr and Pax7 in injured TA muscles of wild-type mice at 5 d postinjury using serial sections. Scale bar = 10 m.cImmunohistochemistry analysis of Islr and MyoG in injured TA muscles of WT mice at 5 d.