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

Abstract

SummaryAge‐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.

In Vitro Tissue‐Engineered Skeletal Muscle Models for Studying Muscle Physiology and Disease

“…[126] This is consistent with findings that fibrosis, in which collagen levels are highly elevated, is associated with poor regeneration and function of native muscle. [127] Furthermore, collagen I is not easily remodeled, does not stimulate endogenous ECM secretion, and may not provide the optimal stiffness for muscle differentiation. [128] Consequently, the collagen hydrogel is being used less frequently for engineering of functional skeletal muscle as superior ECM choices have been identified.…”

Chronic inflammation in skeletal muscle impairs satellite cells function during regeneration: can physical exercise restore the satellite cell niche?

“…However, in conditions where chronic inflammation is observed in the skeletal muscle, such as obesity, aging, muscle dystrophy, and inflammatory myopathies, the balance of macrophages is lost with an increase in both the pro-and anti-inflammatory phenotypes [16,[20][21][22]24,25,65,66]. This pattern is followed by impaired satellite cell activation and a fibro fatty deposit, with a consequent reduction in skeletal muscle regeneration [67][68][69].…”

Obstacles and challenges for tissue engineering and regenerative medicine: Australian nuances

“…These concepts were expanded by Mina Bissell in the 1990s through her studies on mammary cancer cells, to show that the ECM exerts physical and biochemical influences which are transduced by cell surface receptors through the cytoskeleton to the nucleus to effect changes in gene expression that can alter cell phenotype: this led to a greater appreciation of the microenvironment of a cell (often called a niche) and the influence of 3D cultures . The effect of matrix on phenotype is further demonstrated by an altered fibrotic environment (with increasing glycation and cross‐linking as occurs in ageing and some muscular dystrophies) that can convert myogenic precursor cells into a fibrogenic fate and prevent myogenesis; thus the extrinsic ECM can trump the intrinsic initial cell programming . The ECM may exert these effects on many cell types through the molecular and protein composition and signalling interactions (that have been widely studied), biomechanical properties (eg, stiffness or elasticity) nanotypography and also electric fields, and it can be difficult to separate out these potentially different roles of the ECM in vivo.…”

“…58 The effect of matrix on phenotype is further demonstrated by an altered fibrotic environment (with increasing glycation and cross-linking as occurs in ageing and some muscular dystrophies) that can convert myogenic precursor cells into a fibrogenic fate and prevent myogenesis; thus the extrinsic ECM can trump the intrinsic initial cell programming. 59 The ECM may exert these effects on many cell types through the molecular and protein composition and signalling interactions (that have been widely studied), biomechanical properties (eg, stiffness or elasticity) nanotypography and also electric fields, 60 and it can be difficult to separate out these potentially different roles of the ECM in vivo. There is huge interest in the effects of new biomaterials on the biology of cells and tissues with an emphasis on the need to develop ECM-mimicking biomaterials.…”