Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Gene expression in alpha SMA Cre-labeled cells in periosteum during early fracture callus formation

ABSTRACT: Fracture healing is a process that involves many cell populations. In this study we characterized gene expression in a subset of cells involved in fracture healing. αSMACreERT2 mice crossed with Ai9 reporter mice that express tdTomato fluorescent protein after Cre-mediated activation were used as an experimental model. αSMA-expressing cells were labeled by tamoxifen administration, then periosteal cells from the tibia were isolated two days later (controls), or tibial fractures were performed and periosteum/soft callus tissue was collected after 2 and 6 days. The tdTomato positive cell population was isolated by flow cytometry, and subjected to microarray analysis. Histology and cell surface marker analysis indicates that αSMACreERT2 labels a mainly mesenchymal population in the periosteum that expands after fracture, and contributes to both osteogenic and chondrogenic elements of the fracture callus. We were therefore able to examine gene expression in a defined population during the early stages of fracture healing. Total RNA was obtained from the tomato positive cells within the periosteal compartment of fractures from αSMACreERT2/Ai9 mice. Control animals were given 2 doses of tamoxifen, and periosteum was collected and labeled cells sorted (8-9 sex-matched mice per group). Fractures were performed after the second dose of tamoxifen, and tomato positive cells from periosteum/callus tissue were isolated 2 and 6 days after fracture (4-8 animals per sample pooled). 3 replicates for each sample are included.

ORGANISM(S): Mus musculus

SUBMITTER: Brya Matthews

PROVIDER: E-GEOD-45156 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Analysis of αSMA-labeled progenitor cell commitment identifies notch signaling as an important pathway in fracture healing.

Matthews Brya G BG Grcevic Danka D Wang Liping L Hagiwara Yusuke Y Roguljic Hrvoje H Joshi Pujan P Shin Dong-Guk DG Adams Douglas J DJ Kalajzic Ivo I

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 20140101 5

Fracture healing is a regenerative process that involves coordinated responses of many cell types, but characterization of the roles of specific cell populations in this process has been limited. We have identified alpha smooth muscle actin (αSMA) as a marker of a population of mesenchymal progenitor cells in the periosteum that contributes to osteochondral elements during fracture healing. Using a lineage tracing approach, we labeled αSMA-expressing cells, and characterized changes in the perio ...[more]

PMID: 24190076

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Project description:The phases of fracture healing have been well characterized. However, the exact source and genetic profile of the skeletal progenitors that participate in bone repair is somewhat unclear. Sox9 expression in skeletal elements precedes bone and cartilage formation and a Sox9+ cell type is retained in the adult periosteum. We hypothesized that Sox9+ periosteal cells are multipotent skeletal progenitors normally participating in fracture repair. To test this hypothesis we used tamoxifen (TM)-mediated lineage tracing of Sox9+ cells in Sox9CreErt2:Td-Tomato mice. TM injection indelibly labels Sox9+ cells and all their descendants with the fluorescent reporter protein Td-Tomato. Intact mouse femora were harvested 2 weeks after TM injection and analyzed by histology and immunostaining and RNA sequencing, to evaluate the skeletal distribution and gene expression profile of Td-Tomato positive cells in the adult femur. To assess the role of these cells in fracture repair, mice underwent a closed mid-diaphyseal femoral fracture and their hind limbs were harvested at 3, 9 or 56 days post-fracture to assess the contribution of Sox9+ and Td-tomato+ cells in the fracture healing process. In the intact adult mouse femur, Td-Tomato-labelled cells were observed in articular and growth plate cartilage where Sox9 is known to be expressed, but also in the primary spongiosa, periosteum, and endosteum. RNA sequencing and subsequent analysis showed that Td-Tomato positive periosteal cells were enriched in Sox9 transcripts, and transcripts for various osteogenic and chondrocyte specific genes. In a femoral fracture model, we showed that pre-labeled Td-Tomato positive descendent cells were mobilized during the fracture repair process, expanding and migrating towards the fracture site 3 days post-fracture. Here, Td-Tomato positive cells differentiate into chondrocytes and osteoblasts in the soft and hard callus, respectively, 9 days post-fracture. By 2 months post-fracture, descendants of the original Sox9 labelled cell population were prevalent in the cortex and periosteum, and amongst the differentiated osteocyte population embedded within the cortical bone. Thus, a Sox9+ progenitor population resides in the adult periosteum. Fate tracing shows that these cells likely play a substantial role in repair of the fractured femur giving rise to chondrocytes, osteoblasts and mature cortical osteocytes. To our knowledge this is the first report of this Sox9+ cell population in the periosteum of the adult long bone. Taken together with developmental studies on skeletal formation, our data suggest that Sox9+ osteochondroprogenitors play a continuous role in skeletal formation throughout life.

Project description:Bone fractures, the most common musculoskeletal injuries, heal through three main phases: inflammatory, repair, and remodeling. Around 10% of fracture patients suffer from impaired healing that requires surgical intervention, a huge burden on the healthcare system. The rate of impaired healing increases with metabolic diseases such as obesity-associated hyperglycemia/type 2 diabetes (T2D), an increasing concern given the growing incidence of obesity/T2D. Immune cells play pivotal roles in fracture healing, and obesity/T2D is associated with defective immune-cell functions. However, there is a gap in knowledge regarding the stoichiometry of immune cells that populate the callus and how that population changes during different phases of healing. Here, we used complementary global and single-cell techniques to characterize the repertoire of immune cells in the fracture callus and to identify populations specifically enriched in the fracture callus relative to the unfractured bone or bone marrow. Our analyses identified two clear waves of immune-cell infiltration into the callus: the first wave occurs during the early inflammatory phase of fracture healing, while the second takes place during the late repair/early remodeling phase. Innate immune cells were activated during the early inflammatory phase, but in later phases they returned to homeostatic numbers and activation levels. Of the innate immune cells, distinct subsets of activated dendritic cells were particularly enriched in the inflammatory healing hematoma. In contrast to innate cells, lymphocytes, including B and T cells, were enriched and activated in the callus primarily during the late repair phase. The Diet-Induced Obesity (DIO) mouse, an established model of obesity-associated hyperglycemia and insulin resistance, suffers from multiple healing defects. Our data demonstrate that DIO mice exhibit dysregulated innate immune responses during the inflammatory phase, and defects in all lymphocyte compartments during the late repair phase. Taken together, our data characterize, for the first time, immune populations that are enriched/activated in the callus during two distinct phases of fracture healing and identify defects in the healing-associated immune response in DIO mice, which will facilitate future development of immunomodulatory therapeutics for impaired fracture healing.

Dataset Information

Gene expression in alpha SMA Cre-labeled cells in periosteum during early fracture callus formation

Publications

Analysis of αSMA-labeled progenitor cell commitment identifies notch signaling as an important pathway in fracture healing.

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