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Research focus

Stem cells in musculoskeletal development, regeneration and diseases

Musculoskeletal disorders affect 1 in 7 people (10 million people in Europe) and are the second cause of disability worldwide. Fractures due to genetic diseases, osteoporosis or trauma have a prevalence of 1 in 50 people affected annually. Large bone defects caused by trauma, resection of bone tumors, osteonecrosis and severe skeletal dysplasia represent significant clinical challenges, as bone does not regenerate spontaneously in these situations. In order to enhance musculoskeletal regeneration, our research concentrates on the role of skeletal stem cells in bone development, growth and regeneration in order to improve our understanding of skeletal repair defects both in children and adult, using genetic mouse models, genomics and cellular approaches.

Role of skeletal stem/progenitor cells in periosteum

The process of bone formation begins during embryogenesis and continues throughout bone growth, homeostasis and aging, and during bone regeneration and repair. We study the ontogeny of skeletal stem cells, how they are established during the development and growth of the skeleton and how they are affected in genetic diseases and skeletal repair disorders. Skeletal stem cells have been identified in several bone compartments of the adult skeleton. 

We showed that periosteum, the tissue lining the outer surface of bone, is a key component of bone repair and contains skeletal stem/progenitor cells (SSPCs) with higher bone regenerative potential compared to bone marrow (Duchamp de Lageneste et al., 2018). .

In mice carrying the Fgfr3Y367C activating mutation in Prx1-derived skeletal stem/progenitor cells, we observed a severe bone repair phenotype due to functional impairment of periosteal cells in mediating cartilage to bone transformation. Transplantation of wild type periosteal cells can rescue this phenotype thus uncovering an essential role of periosteal cells in bone healing (Julien et al, Stem Cell Reports, 2020).

We developed scRNAseq and snRNAseq to elucidate the heterogeneity of SSPC populations and their response to injury. In response to fracture, periosteal SSPCs transition via an injury-induced fibrogenic phase prior to undergoing osteogenesis or chondrogenesis (Julien et al., NatComms, 2021, Julien et al., JBMR 2022, Perrin et al. biorixv 2023)

Role of muscle-bone interactions in musculoskeletal regeneration

The recruitment of skeletal stem cells in bone defects or injuries occurs in an inflammatory environment and is influenced by environmental mechanical signals and the surrounding tissues such as muscle. Bone and skeletal muscle are closely linked across development, growth and aging. The delay in bone consolidation is increased up to 10-fold in patients with severe trauma to adjacent muscles.

Genetic disorders affecting muscle such as Duchenne Muscular Dystrophy (DMD) also impact bone and we have shown that bone regeneration is deficient in a mouse model of DMD. Similarly, loss of bone quality in osteoporosis is linked with sarcopenia. However, the biological mechanisms underlying the role of muscle in bone repair remain poorly understood.

We showed that muscle stem cells, the satellite cells, play a role in skeletal regeneration via paracrine effects of secreted factors in response to bone injury.

We showed that skeletal stem/progenitor cells that repair bone reside not only in bone compartments but also in skeletal muscle adjacent to bone. Cells recruited from skeletal muscle also become pro-fibrotic in the context of musculoskeletal trauma, a process that can be targeted pharmacologically to improve bone repair.

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