title: Upregulated IL-1β in dysferlin-deficient muscle attenuates regeneration by blunting the response to pro-inflammatory macrophages.
abstract: BACKGROUND
  Loss-of-function mutations in the dysferlin gene (DYSF) result in a family of muscle disorders known collectively as the dysferlinopathies. Dysferlin-deficient muscle is characterized by inflammatory foci and macrophage infiltration with subsequent decline in muscle function. Whereas macrophages function to remove necrotic tissue in acute injury, their prevalence in chronic myopathy is thought to inhibit resolution of muscle regeneration. Two major classes of macrophages, classical (M1) and alternative (M2a), play distinct roles during the acute injury process. However, their individual roles in chronic myopathy remain unclear and were explored in this study.
  
  
  METHODS
  To test the roles of the two macrophage phenotypes on regeneration in dysferlin-deficient muscle, we developed an in vitro co-culture model of macrophages and muscle cells. We assayed the co-cultures using ELISA and cytokine arrays to identify secreted factors and performed transcriptome analysis of molecular networks induced in the myoblasts.
  
  
  RESULTS
  Dysferlin-deficient muscle contained an excess of M1 macrophage markers, compared with WT, and regenerated poorly in response to toxin injury. Co-culturing macrophages with muscle cells showed that M1 macrophages inhibit muscle regeneration whereas M2a macrophages promote it, especially in dysferlin-deficient muscle cells. Examination of soluble factors released in the co-cultures and transcriptome analysis implicated two soluble factors in mediating the effects: IL-1β and IL-4, which during acute injury are secreted from M1 and M2a macrophages, respectively. To test the roles of these two factors in dysferlin-deficient muscle, myoblasts were treated with IL-4, which improved muscle differentiation, or IL-1β, which inhibited it. Importantly, blockade of IL-1β signaling significantly improved differentiation of dysferlin-deficient cells.
  
  
  CONCLUSIONS
  We propose that the inhibitory effects of M1 macrophages on myogenesis are mediated by IL-1β signals and suppression of the M1-mediated immune response may improve muscle regeneration in dysferlin deficiency. Our studies identify a potential therapeutic approach to promote muscle regeneration in dystrophic muscle.
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA ; Center for Genetic Muscle Disorders, Kennedy Krieger Institute, 707 N. Broadway, Baltimore, MD 21205 USA ; Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205 USA.
authors.forename: Tatiana V
authors.identifier: 0000-0002-1354-2437
authors.initials: TV
authors.lastname: Cohen
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA.
authors.forename: Gina M
authors.initials: GM
authors.lastname: Many
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742 USA.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Fleming
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA.
authors.forename: Viola F
authors.initials: VF
authors.lastname: Gnocchi
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Ghimbovschi
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742 USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Mosser
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA.
authors.forename: Eric P
authors.initials: EP
authors.lastname: Hoffman
authors.affiliation: Center for Genetic Medicine Research, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010 USA.
authors.forename: Terence A
authors.initials: TA
authors.lastname: Partridge
keywords: Cell-cell interactions; Dysferlin; LGMD2B; Macrophages; Muscular dystrophy; Myoblasts; Skeletal muscle