Photopolymerizable Hydrogel-Encapsulated Fibromodulin-Reprogrammed Cells for Muscle Regeneration

A central challenge in tissue engineering is obtaining a suitable cell type with a capable delivery vehicle to replace or repair damaged or diseased tissues with tissue mimics. Notably, for skeletal muscle tissue engineering, given the inadequate availability and regenerative capability of endogenous myogenic progenitor cells as well as the tumorigenic risks presented by the currently available pluri- and multipotent stem cells, seeking a safe regenerative cell source is urgently demanded. To conquer this problem, we previously established a novel reprogramming technology that can generate multipotent cells from dermal fibroblasts using a single protein, fibromodulin (FMOD). The yield FMOD-reprogrammed (FReP) cells exhibit exceeding myogenic capability without tumorigenic risk, making them a promising and safe cell source for skeletal muscle establishment. In addition to using the optimal cell for implantation, it is equally essential to maintain cellular localization and retention in the recipient tissue environment for critical-sized muscle tissue establishment. In this study, we demonstrate that the photopolymerizable methacrylated glycol chitosan (MeGC)/type I collagen (ColI)-hydrogel provides a desirable microenvironment for encapsulated FReP cell survival, spreading, extension, and formation of myotubes in the hydrogel three-dimensionally in vitro, without undesired osteogenic, chondrogenic, or tenogenic differentiation. Furthermore, gene profiling revealed a paired box 7 (PAX7) -> myogenic factor 5 (MYF5) -> myogenic determination 1 (MYOD1) -> myogenin (MYOG) -> myosin cassette elevation in the encapsulated FReP cells during myogenic differentiation, which is similar to that of the predominant driver of endogenous skeletal muscle regeneration, satellite cells. These findings constitute the evidence that the FReP cell-MeGC/ColI-hydrogel construct is a promising tissue engineering mimic for skeletal muscle generation in vitro, and thus possesses the extraordinary potential for further in vivo validation. Impact statement The present study revealed the promising potential of methacrylated glycol chitosan (MeGC)/ColI-hydrogel-encapsulated fibromodulin-reprogrammed (FReP) cells for skeletal muscle tissue engineering. Moreover, the excellent biocompatibility of MeGC/ColI-hydrogel with FReP cells-a novel induced multipotent cell type that is generated through innovative protein-based technology-makes it a suitable cell delivery vehicle for FReP cell-based tissue engineering. The development of various photopolymerizable MeGC/ColI-hydrogel/FReP cell constructs may also shift the paradigm of regenerative medicine into a feasible, safe, and efficient procedure with controllable in situ cell delivery.