Matrix stiffness and architecture drive fibro-adipogenic progenitors’ activation into myofibroblasts

Abstract

Fibro-adipogenic progenitors (FAPs) are essential in supporting regeneration in skeletal muscle, but in muscle pathologies FAPs the are main source of excess extracellular matrix (ECM) resulting in fibrosis. Fibrotic ECM has altered mechanical and architectural properties, but the feedback onto FAPs of stiffness or ECM properties is largely unknown. In this study, FAPs’ sensitivity to their ECM substrate was assessed using collagen coated polyacrylamide to control substrate stiffness and collagen hydrogels to engineer concentration, crosslinking, fibril size, and alignment. FAPs on substrates of fibrotic stiffnesses had increased myofibroblast activation, depicted by αSMA expression, compared to substrates mimicking healthy muscle, which correlated strongly YAP nuclear localization. Surprisingly, fibrosis associated collagen crosslinking and larger fibril size inhibited myofibroblast activation, which was independent of YAP localization. Additionally, collagen crosslinking and larger fibril diameters were associated with decreased remodeling of the collagenous substrate as measured by second harmonic generation imaging. Inhibition of YAP activity through verteporfin reduced myofibroblast activation on stiff substrates but not substrates with altered architecture. This study is the first to demonstrate that fibrotic muscle stiffness can elicit FAP activation to myofibroblasts through YAP signaling. However, fibrotic collagen architecture actually inhibits myofibroblast activation through a YAP independent mechanism. These data expand knowledge of FAPs sensitivity to ECM and illuminate targets to block FAP’s from driving progression of muscle fibrosis.

Collagen architecture and biomechanics of gracilis and adductor longus muscles from children with cerebral palsy

“…If collagen fibres started highly aligned within the in vivo operating range of motion, further strain on the muscle could result in increased collagen molecular sliding instead of changes in alignment, which would correspond to higher passive tension and stiffness according to typical mechanical behaviour of collagen fibrils (Depalle et al., 2015). Increased passive tension and alignment of collagen fibrils could contribute to increased resistance of collagen fibres to enzymatic degradation (Saini et al., 2020) and the mechanosensitive actions of satellite cells and fibro‐adipogenic progenitors within muscle (Hu et al., 2021; Loomis & Smith, 2023; Loomis et al., 2022). For these reasons, the intrinsic strain imposed on CP muscle via longer in vivo sarcomere lengths could have large impacts on collagen architecture and biomechanics that were not observed in our ex vivo muscle biopsy mechanical and visual experiments.…”

Denervation Drives YAP/TAZ Activation in Muscular Fibro/Adipogenic Progenitors

“…Fibrotic skeletal muscle ECM exhibits high stiffness [ 53 , 54 , 55 ]. Recently, the pro-fibrotic response of FAPs to ECM stiffness was reported for the first time [ 56 ]. In response to biomimetic substrates of high stiffness, FAPs display nuclear accumulation of YAP and induction of myofibroblast differentiation, which can be prevented by VP addition.…”

Engineering Cell–ECM–Material Interactions for Musculoskeletal Regeneration

“…In this study, the ECM of the pulmonary arteries was engineered to mimic disease progression. The engineered ECM and polyethylene glycol-based model allowed for unprecedented recreation of the mechanical properties of both PAH and healthy tissue [ 148 , 149 , 150 ], providing a new in vitro tool for understanding how fibrotic pathogenesis initiates. The phototunable constructs developed to mimic the mechanical properties of normal and diseased arteries could be adapted for use in musculoskeletal applications, providing an existing and validated platform for interrogating the role of the ECM in musculoskeletal health and disease.…”