Aging of the skeletal muscle extracellular matrix drives a stem cell fibrogenic conversion

Aging Cell. 2017 Jun;16(3):518-528. doi: 10.1111/acel.12578. Epub 2017 Mar 30.

Abstract

Age-related declines in skeletal muscle regeneration have been attributed to muscle stem cell (MuSC) dysfunction. Aged MuSCs display a fibrogenic conversion, leading to fibrosis and impaired recovery after injury. Although studies have demonstrated the influence of in vitro substrate characteristics on stem cell fate, whether and how aging of the extracellular matrix (ECM) affects stem cell behavior has not been investigated. Here, we investigated the direct effect of the aged muscle ECM on MuSC lineage specification. Quantification of ECM topology and muscle mechanical properties reveals decreased collagen tortuosity and muscle stiffening with increasing age. Age-related ECM alterations directly disrupt MuSC responses, and MuSCs seeded ex vivo onto decellularized ECM constructs derived from aged muscle display increased expression of fibrogenic markers and decreased myogenicity, compared to MuSCs seeded onto young ECM. This fibrogenic conversion is recapitulated in vitro when MuSCs are seeded directly onto matrices elaborated by aged fibroblasts. When compared to young fibroblasts, fibroblasts isolated from aged muscle display increased nuclear levels of the mechanosensors, Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ), consistent with exposure to a stiff microenvironment in vivo. Accordingly, preconditioning of young fibroblasts by seeding them onto a substrate engineered to mimic the stiffness of aged muscle increases YAP/TAZ nuclear translocation and promotes secretion of a matrix that favors MuSC fibrogenesis. The findings here suggest that an age-related increase in muscle stiffness drives YAP/TAZ-mediated pathogenic expression of matricellular proteins by fibroblasts, ultimately disrupting MuSC fate.

Keywords: aging; extracellular matrix; muscle stem cells; satellite cells; skeletal muscle.

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Aging / metabolism*
  • Aging / pathology
  • Animals
  • Biomechanical Phenomena
  • Cell Cycle Proteins
  • Cell Differentiation
  • Extracellular Matrix / metabolism*
  • Extracellular Matrix / pathology
  • Fibroblasts / metabolism*
  • Fibroblasts / pathology
  • Fibrosis
  • Gene Expression Regulation
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Muscle Development / genetics
  • Muscle, Skeletal / growth & development
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / pathology
  • Myoblasts / metabolism*
  • Myoblasts / pathology
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism
  • Primary Cell Culture
  • Stem Cells / metabolism*
  • Stem Cells / pathology
  • Torsion, Mechanical
  • Transcription Factors / genetics
  • Transcription Factors / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • Cell Cycle Proteins
  • Phosphoproteins
  • Taz protein, mouse
  • Transcription Factors
  • Yap1 protein, mouse