Project description:Genome-wide comparative gene expression analysis of callus tissue of osteoporotic mice (Col1a1-Krm2 and Lrp5-/-) and wild-type were performed to identify candidate genes that might be responsible for the impaired fracture healing observed in Col1a1-Krm2 and Lrp5-/- mice. To investigate bone healing in osteoporosis, we performed fracture healing studies in wild-type mice (C57BL/6 genetic background) and the low bone mass strains Col1a1-Krm2 and Lrp5-/- (Schulze et al., 2010; Kato et al., 2002). Osteotomy was set in femora of female mice and stabilized by a semi-rigid fixator to allow fast bone healing (RM-CM-6ntgen et al., 2010). 21 days post surgery we analyzed the fracture calli by biochemical/histological methods, as well as micro-computed tomography, and observed impaired fracture healing in Col1a1-Krm2 and Lrp5-/- mice in comparison to wild-type. To identify genes that may be responsible for the impaired healing in osteoporotic mice, we performed microarray analysis of three independent callus samples of each genotype. The callus tissue was taken 10 days after surgery, because extensive bone formation took place at this point.
Project description:Traumatic brain injury (TBI) accelerates fracture healing, but the underlying mechanism remains largely unknown. Accumulating evidence indicates that the central nervous system plays a pivotal role in regulating immune system and skeleton, however, the impact of TBI on hematopoiesis commitment was overlooked. Here, we found that the dramatically elevated sympathetic tone accompanied with TBI-accelerated fracture healing; chemical sympathectomy blocks TBI-induced fracture healing. Importantly, the adrenergic hypersensitivity swiftly skews bone marrow hematopoietic lineage cells toward anti-inflammation myeloid cells within 14 days, which favor fracture healing. Knockout of β3- or β2-adrenergic receptors (ARs) eliminate TBI mediated anti-inflammation macrophage expansion and TBI-accelerated fracture healing. Moreover, β3- and β2-ARs agonists synergistically promote M2 macrophages infiltration in callus and accelerate bone healing process. Our results suggest that TBI shapes the anti-inflammation environment during early stage of fracture healing, implicating the sympathetic nerve system as a potential target that can be exploited to treat fracture.
Project description:Elevated bone resorption and diminished bone formation have been recognized as the primary features of glucocorticoid-associated skeletal disorders. However, the direct effects of excess glucocorticoids on bone turnover remains unclear. Here, we explored the outcomes of exogenous glucocorticoid treatment on bone loss and delayed fracture healing in mice and found that reduced bone turnover was a dominant feature, resulting in a net loss of bone mass. We investigated the single-cell gene expression profiles of these two models. In the glucocorticoid-induced bone loss model, we sequenced the cell population digested from the bone surface. In the glucocorticoid-associated fracture healing model, we sequenced the cell population digested from the callus. Overall, the cell population on the bone surface was predominantly composed of hematopoietic cells, while only a small fraction represented the bone progenitor cells. In the fracture healing model, the callus contained a significant number of osteogenic and osteoclastic lineage cells. We primarily analyzed the gene expression of functional genes in the fracture healing model and characterized the metabolic profiles. These data provide insights into the multifactorial metabolic mechanisms by which glucocorticoids generate skeletal disorders.
Project description:alpha-CGRP is a neuropeptide that is also expressed in the fracture callus during bone regeneration. Our aim was to evaluate the role of alpha-CGRP in the context of fracture healing. Therefore we investigated the effect of alpha-CGRP deficiency on fracture callus formation. We used microarray analysis to compare the global gene expression of fracture calli from alpha-CGRP deficient mice and WT mice.
Project description:A study of rat femoral fracture healing in young (6 weeks old at fracture), adult (26 weeks old at fracture), and old (52 weeks old at fracture) rats. Samples were collected at time of surgery (intact controls) and at 3 days, 1 week, 2 weeks, 4 weeks, and 6 weeks after fracture. Samples were the mid third of the femoral length including the external callus, cortical bone and marrow elements. Fracture was stabilized with an intramedullary rod prior to fracture with a Bonnarens and Einhorn device.
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.
Project description:Cells expressing features of cellular senescence, including upregulation of p21 and p16, appear transiently following tissue injury, yet the properties of these cells or how they contrast with age-induced senescent cells remains unclear. Using skeletal fracture as a model of acute injury, we identified rapidly-appearing senescent-like cells, marked by p21 expression, that negatively affected fracture healing. p21+ callus cells, which consisted predominantly of neutrophils and osteochondroprogenitors, existed as transient cells specific to injury and expressed high levels of senescence-associated factors known to impair bone formation and induce paracrine senescence. Targeted genetic clearance of p21+ cells suppressed senescence-associated signatures within the fracture callus and accelerated fracture healing. By contrast, p21+ cell clearance did not alter bone loss due to aging; conversely, p16+ cell clearance, known to alleviate skeletal aging, did not affect fracture healing. Together, our findings establish contextual roles of senescent/senescent-like cells that may be leveraged for therapeutic opportunities.
Project description: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.
Project description:We reported the application of single-cell mRNA sequencing to identify a unique population of fibroblasts that exits in the fracture callus of bisphosphonate-treated rats. Such unique population of fibroblasts prevented fracture healing by secreting ECM. Further, it was found that these ECM-secreting fibroblasts were enriched for myeloid genes, suggesting a bone marrow orgin. After fractures were treated with local CGRP injection or Magnesium based biometal, such population of fibroblasts was cleared off, resulting in facilitated fracture healing of bisphosphonate-treated rats.
Project description:Bone regeneration involves skeletal stem/progenitor cells within periosteum and bone marrow, the formation of a fibrous callus followed by the deposition of cartilage and bone matrix to consolidate the fracture. Interactions between bone and skeletal muscle are known to play a role in bone repair but the underlying mechanisms are poorly understood. To better understand the role of skeletal muscle during bone repair, we characterized stem/progenitor cells within skeletal muscle that participate in bone repair. We show that cells originating from bone marrow, periosteum and skeletal muscle are all derived from the Prx1 embryonic lineage. We developed a mouse polytrauma model combining a non-stabilized tibial fracture and mechanical injury to adjacent skeletal muscles. In this polytrauma model, bone fracture healing is impaired. We characterized the Prx1-derived cell population within skeletal muscle in response to fracture and to polytrauma. To do so, we performed fracture and polytrauma in Prx1Cre;Rosa mTmG mice. We harvested skeletal muscle surrounding the tibia at d0 (uninjured), and surrounding the fracture site at d3 and d5 post-fracture or post-polytrauma. Following enzymatic and mechanical digestion of skeletal muscle tissue, we FACS sorted Prx1-derived GFP+ cells and sequenced them using the 10X Chromium technology.