GRANULOCYTE-COLONY STIMULATING FACTOR ENHANCES BONE FRACTURE HEALING

International audienceBackgroundCirculating mesenchymal stem cells contribute to bone repair. Their incorporation in fracture callus is correlated to their bioavailability. In addition, Granulocyte-colony stimulating factor induces the release of vascular and mesenchymal progenitors. We hypothesized that this glycoprotein stimulates fracture healing, and analyzed the effects of its administration at low doses on bone healing. Methods27 adult male Sprague-Dawley rats underwent mid-femur osteotomy stabilized by centromedullar pinning. In a post (pre) operative group, rats were subcutaneously injected with 5µg/kg per day of Granulocyte-colony stimulating factor for 5 days after (before) surgery. In a control group, rats were injected with saline solution for 5 days immediately after surgery. A radiographic consolidation score was calculated. At day 35, femurs were studied histologically and underwent biomechanical tests. Findings5 weeks after surgery, mean radiographic scores were significantly higher in the Preop group 7.75 (SD 0.42) and in the Postop group 7.67 (SD 0.52) than in the control group 6.75 (SD 0.69). Biomechanical tests showed femur stiffness to be more than three times higher in both the Preop 109.24N/mm (SD 51.86) and Postop groups 100.05N/mm (SD 60.24) than in control 32.01N/mm (SD 15.78). Mean maximal failure force was twice as high in the Preop group 68.66 N (SD 27.78) as in the control group 34.21N (SD 11.79). Histological results indicated a later consolidation process in control than in treated groups. InterpretationGranulocyte-colony stimulating factor injections strongly stimulated early femur fracture healing, indicating its potential utility in human clinical situations such as programmed osteotomy and fracture

Caractérisation de tissu osseux et de biomatériaux pour la régénération osseuse sur gros volume.

L’objectif de cette étude est de développer un processus expérimental de régénération de tissus osseux de grand volume. Une première étape vise à produire du matériau osseux à partir de lambeau de périoste vascularisé et à le caractériser grâce a des essais d’indentation. Ensuite, nous développons un process impliquant un biomatériau poreux et biodégradable utilisé comme réceptacle de cellules mésenchymateuses. Dans les deux cas, le nouveau matériau obtenu est étudié grâce à des tests mécaniques et biologiques

Distinct Articular and Endochondral Differentiation Pathways in Bone Marrow Chondrogenic Progenitor Cells

International audienceBone marrow contains skeletal progenitor cells (mesenchymal stem cells) which are important actors in skeletal repair. Nevertheless the therapeutic use of mesenchymal stem cells for articular cartilage repair remains a challenge with a limited efficacy on both clinical outcomes and cartilage regeneration. In rabbit periosteal graft models we show that such skeletal progenitor cells are recruited and undergo differentiation through different skeletal tissue pathways (bone, cartilage, skeletal muscle) in bone marrow areas that are under periosteal graft influence. Moreover histological observations show among cartilage differentiated cells two different cartilage pathways, corresponding respectively to articular cartilage formations and to endochondral cartilage formations. This underline the presence in bone marrow of cartilage progenitor cells that escape from the intrinsic endochondral differentiation program resulting in transient rather than permanent cartilage, and follow a specific articular cartilage differentiation pathway. With respect to tissue engineering, and while extremely complex techniques are being developed to artificially generate functionally integrated, stratified articular cartilage like structures, our observations urge the development of protocols that select the proper population of articular cartilage progenitor cells before its use as cartilage building units

Approche biomécanique de la régénération tissulaire squelettique

L étude de la régénération des tissus squelettiques ne peut se concevoir sans une approche biomécanique des processus de régulation de la prolifération et de la différenciation des cellules progénitrices mésenchymateuses. Dans l organisme mature, ces cellules souches sont en mesure de donner naissance à la totalité des tissus squelettiques en reproduisant de nombreuses cascades cellulaires et moléculaires de leur embryogenèse. Parallèlement à la régulation biologique reposant sur des signaux moléculaires, la régulation mécanique joue un rôle de premier ordre dans la modulation du métabolisme, des synthèses et de la différenciation des cellules progénitrices jusqu à l organisation structurale, anatomique et histologique des tissus régénérés. Les observations empiriques ont établi une relation entre les déformations tissulaires et la différenciation fibreuse, les pressions hydrostatiques et la différenciation cartilagineuse. Cependant, les travaux actuels issus de modélisations ne permettent qu une ébauche des facteurs d organisation fonctionnelle des tissus. Dans la première partie de ce travail, les résultats des expérimentations empiriques in vivo ont démontré le vaste potentiel de régénération des tissus mésenchymateux et en particulier, du cartilage, sous certaines conditions de chargement complexes. Les caractéristiques descriptives de cet environnement spécifique ne peuvent être approchées que par la modélisation. Cependant, elle nécessite que le comportement mécanique du régénérat soit connu. Ce travail s inscrit dans une démarche de caractérisation du matériau évolutif constitué par le régénérat squelettique afin d en permettre une modélisation fiable.Skeletal tissue regeneration cannot be studied without taking account of the effect of biomechanics in regulating mesenchymal progenitor cell proliferation and differentiation. In the mature organism, stem cells produce skeletal tissues by reproducing the cellular and molecular cascades of embryogenesis. In parallel with regulation mediated by molecular signals, mechanical factors also influence the modulation and differentiation of progenitor cells and the structure of the regenerated tissue. Empirical observation has established relationships between tissue deformation and fibrous differentiation, hydrostatic pressures and cartilage differentiation. However, current modelling studies produce only the early development phase of tissue functional organisation factors. In the first part of this work, in vivo experiments showed the great regeneration potential of mesenchymal tissue, particularly cartilage, under certain complex loading conditions. Only modelling can simulate the characteristics of this process, but first the mechanical characteristics of the regenerated tissue must be known. This work aims to characterise the developmental characteristics of regenerated skeletal tissue to permit reliable modelling.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

GRANULOCYTE-COLONY STIMULATING FACTOR ENHANCES BONE FRACTURE HEALING

International audienceBackgroundCirculating mesenchymal stem cells contribute to bone repair. Their incorporation in fracture callus is correlated to their bioavailability. In addition, Granulocyte-colony stimulating factor induces the release of vascular and mesenchymal progenitors. We hypothesized that this glycoprotein stimulates fracture healing, and analyzed the effects of its administration at low doses on bone healing. Methods27 adult male Sprague-Dawley rats underwent mid-femur osteotomy stabilized by centromedullar pinning. In a post (pre) operative group, rats were subcutaneously injected with 5µg/kg per day of Granulocyte-colony stimulating factor for 5 days after (before) surgery. In a control group, rats were injected with saline solution for 5 days immediately after surgery. A radiographic consolidation score was calculated. At day 35, femurs were studied histologically and underwent biomechanical tests. Findings5 weeks after surgery, mean radiographic scores were significantly higher in the Preop group 7.75 (SD 0.42) and in the Postop group 7.67 (SD 0.52) than in the control group 6.75 (SD 0.69). Biomechanical tests showed femur stiffness to be more than three times higher in both the Preop 109.24N/mm (SD 51.86) and Postop groups 100.05N/mm (SD 60.24) than in control 32.01N/mm (SD 15.78). Mean maximal failure force was twice as high in the Preop group 68.66 N (SD 27.78) as in the control group 34.21N (SD 11.79). Histological results indicated a later consolidation process in control than in treated groups. InterpretationGranulocyte-colony stimulating factor injections strongly stimulated early femur fracture healing, indicating its potential utility in human clinical situations such as programmed osteotomy and fracture

Temporal evolution of skeletal regenerated tissue: what can mechanical investigation add to biological?

International audienceThe objective here was to experimentally characterize the temporal evolution of the structural and mechanical properties of large volume immature regenerated tissues. We studied these evolving tissues from their genesis in controlled mechanical conditions. We developed an animal model based on the periosteal properties leading to unloaded regenerated skeletal tissue. To characterize the temporal evolution of mechanical properties, we carried out indentation tests coupled with macroscopic examinations and histological studies. This combined methodology yielded a range of information on osteogenesis at different scales: macroscopic by simple observation, mesoscopic by indentation test and microscopic by histological study. Results allowed us to identify different periods, providing a link between biological changes and material property evolution in bone tissue regeneration. The regenerated tissue evolves from a viscous, homogeneous, soft material to a heterogeneous stiffer material endowed with a lower viscosity. From a biological point of view, cell organization progresses from a proliferated cell clot to a mature structure closer to that of the bone. During the first 7 days, mechanical and biological results revealed the same evolution: first, the regenerated tissue grew, then, differentiated into an osteochondral tissue and finally calcification began. While our biological results confirm those of other studies, our mechanical results provide the first experimental mechanical characterization by reduced Young's modulus of such tissue