Project description:Skeletal aging and disease are associated with a misbalance in the opposing actions of osteoblasts and osteoclasts that are responsible for maintaining the integrity of bone tissues. Here, we show through detailed functional and single-cell genomic studies that intrinsic aging of bona fide mouse skeletal stem cells (SSCs) alters bone marrow niche signaling and skews bone and blood lineage differentiation leading to fragile bones that regenerate poorly. Aged SSCs have diminished bone and cartilage forming potential but produce higher frequencies of stromal lineages that express high levels of pro-inflammatory and pro-resorptive cytokines. Single-cell transcriptomic studies reveal a distinct population of SSCs in aged mice that gradually outcompete their younger counterparts in the bone marrow niche. While systemic exposure to a youthful circulation through heterochronic parabiosis reduced local expression of inflammatory cytokines, it did not reverse the diminished osteochondrogenic activity of aged SSCs and was insufficient to improve bone mass and skeletal-healing parameters in aged mice. Hematopoietic reconstitution of aged mice with young hematopoietic stem cells (HSC) also did not improve bone integrity and repair. We find that deficient bone regeneration in aged mice could only be reversed by the local application of a combinatorial treatment that re-activates aged SSCs and simultaneously abates crosstalk to hematopoietic cells favoring an inflammatory milieu. This treatment expanded aged SSC pools, reduced osteoclast activity, and enhanced bone healing to youthful levels. Our findings provide mechanistic insight into the complex, multifactorial mechanisms underlying skeletal aging and offer new prospects for rejuvenating the aged skeletal system.
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:Age-related delays in fracture healing are prevalent and contribute to morbidity and mortality in elderly populations. Clinical and preclinical studies demonstrate that aging is associated with slower and less complete fracture repair characterized by delayed cartilage and bone formation, impaired matrix resorption, and an increased risk of delayed union or nonunion. Matrix Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI MSI) enables spatially resolved, in situ molecular analysis of proteins directly from murine fracture tissue sections. We applied collagenase type III (MMP 13) mediated proteolytic digestion to formalin fixed, paraffin embedded (FFPE) tibia fracture callus sections harvested 10 days post tibial fracture from young (3 month old) and aged (18 month old) mice to perform spatially resolved proteomic profiling. MALDI MSI revealed pronounced age dependent differences in extracellular matrix protein composition and remodeling within the fracture callus. We identified up regulation of canonical bone and matrix proteins, including Col1a1 and Col1a2 specifically in the young fracture callus demonstrating advancement into harden callus formation. Conversely, Col2a1 and other soft callus proteins were only seen in the aged callus tissues. Further, protein indicators of tissue state, such as fibronectin (up regulated) and calreticulin (down regulated) were selectively regulated aged tissues, demonstrating a failure for aged tissues to fully progress into harden calluses. Spatial proteomic patterns demonstrated a marked delay in progression from cartilaginous to osseous callus in aged mice, consistent with impaired matrix remodeling during fracture repair. Together, these findings establish MALDI MSI based spatial proteomics as a powerful approach to elucidate age related alterations in fracture healing and to identify molecular regulators of impaired skeletal regeneration.
Project description:Study of rat femur fracture healing in young (6 weeks old), adult (26 weeks old), and older (52 weeks old) rats with samples collected at 0 time (no fracture) and at 0.4, 1, 2, 4, and 6 weeks after fracture. RNA from two rats were pooled for each array. Keywords = rat, femur, fracture, age, time Keywords: time-course
Project description:The association between DM and impaired fracture healing including delayed union and nonunion has been documented in clinical and experimental settings. We examine miRNA expression specific for impaired fracture healing in diabetic rat.
Project description:The association between DM and impaired fracture healing including delayed union and nonunion has been documented in clinical and experimental settings. We examine mRNA expression specific for impaired fracture healing in diabetic rat.
Project description:mRNA gene expression was measured in intact female Sprague-Dawley rats at 6 (young), 26 (adult) and 52 (older) weeks of age at the time of fracture. Samples were collected at 0, 0.4, 1, 2, 4, and 6 weeks after fracture. RNA from two rats were pooled for each Affymetrix Rat U34A array. Mid-shaft, simple, transverse left femoral fractures were induced after retrograde intramedullary rod fixation with a Bonnarens and Einhorn device. Samples were collected from one third of the femoral length, centered on the fracture site, including the external callus, cortical bone, and marrow elements. Keywords = rat Keywords = fracture Keywords = age Keywords = time Keywords = femur Keywords: other
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: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.
Project description:Phosphate is essential for healthy bone growth and plays an essential role in fracture repair. Although phosphate deficiency has been shown to impair fracture healing, the mechanisms involved in impaired healing are unknown. More recently, studies have shown that the effect of phosphate deficiency on the repair process varied based on the genetic strain of mice, which is not characterized. We used data from microarrays to (1) determine the effects of phosphate restriction on the biologic functions identified from the gene expression in fracture calluses; and (2) examine whether there are genetic differences within the primary biologic functions.