Immature mice are more susceptible to the detrimental effects of high fat diet on cancellous bone in the distal femur

AbstractWith the increasing prevalence of obesity among children and adolescents, it is imperative to understand the implications of early diet-induced obesity on bone health. We hypothesized that cancellous bone of skeletally immature mice is more susceptible to the detrimental effects of a high fat diet (HFD) than mature mice, and that removing excess dietary fat will reverse these adverse effects. Skeletally immature (5weeks old) and mature (20weeks old) male C57BL/6J mice were fed either a HFD (60% kcal fat) or low fat diet (LFD; 10% kcal fat) for 12weeks, at which point, the trabecular bone structure in the distal femoral metaphysis and third lumbar vertebrae were evaluated by micro-computed tomography. The compressive strength of the vertebrae was also measured. In general, the HFD led to deteriorations in cancellous bone structure and compressive biomechanical properties in both age groups. The HFD-fed immature mice had a greater decrease in trabecular bone volume fraction (BVF) in the femoral metaphysis, compared to mature mice (p=0.017 by 2-way ANOVA). In the vertebrae, however, the HFD led to similar reductions in BVF and compressive strength in the two age groups. When mice on the HFD were switched to a LFD (HFD:LFD) for an additional 12weeks, the femoral metaphyseal BVF in immature mice showed no improvements, whereas the mature mice recovered their femoral metaphyseal BVF to that of age-matched lean controls. The vertebral BVF and compressive strength of HFD:LFD mouse bones, following diet correction, were equivalent to those of LFD:LFD mice in both age groups. These data suggest that femoral cancellous metaphyseal bone is more susceptible to the detrimental effects of HFD before skeletal maturity and is less able to recover after correcting the diet. Negative effects of HFD on vertebrae are less severe and can renormalize with LFD:LFD mice after diet correction, in both skeletally immature and mature animals

NOTCH signaling in skeletal progenitors is critical for fracture repair

Fracture nonunions develop in 10%–20% of patients with fractures, resulting in prolonged disability. Current data suggest that bone union during fracture repair is achieved via proliferation and differentiation of skeletal progenitors within periosteal and soft tissues surrounding bone, while bone marrow stromal/stem cells (BMSCs) and other skeletal progenitors may also contribute. The NOTCH signaling pathway is a critical maintenance factor for BMSCs during skeletal development, although the precise role for NOTCH and the requisite nature of BMSCs following fracture is unknown. Here, we evaluated whether NOTCH and/or BMSCs are required for fracture repair by performing nonstabilized and stabilized fractures on NOTCH-deficient mice with targeted deletion of RBPjk in skeletal progenitors, maturing osteoblasts, and committed chondrocytes. We determined that removal of NOTCH signaling in BMSCs and subsequent depletion of this population result in fracture nonunion, as the fracture repair process was normal in animals harboring either osteoblast- or chondrocyte-specific deletion of RBPjk. Together, this work provides a genetic model of a fracture nonunion and demonstrates the requirement for NOTCH and BMSCs in fracture repair, irrespective of fracture stability and vascularity

Biomechanical comparison of plate and screw fixation in anterior pelvic ring fractures with low bone mineral density

Introduction: Osteosynthesis of anterior pubic ramus fractures can be challenging, especially in poor bone quality. The aim of the present study was to compare plate and retrograde endomedullary screw fixation of the superior pubic ramus with low bone mineral density (BMD). Materials and methods: Twelve human cadaveric hemi-pelvises were analyzed in a matched pair study design. BMD of the specimens was 35 +/- 30 mgHA/cm(3), as measured in the fifth lumbar vertebra. A simulated two-fragment superior pubic ramus fracture model was fixed with either a 7.3-mm cannulated retrograde screw (Group 1) or a 10-hole 3.5-mm reconstruction plate (Group 2). Cyclic progressively increasing axial loading was applied through the acetabulum. Relative interfragmentary movements were captured using an optical motion tracking system. Results: Initial axial construct stiffness was 424 +/- 116.1 N/mm in Group 1 and 464 +/- 69.7 N/mm in Group 2, with no significant difference (p = 0.345). Displacement and gap angle at the fracture site during cyclic loading were significantly higher in Group 1 compared to Group 2. Cycles to failure, based on clinically relevant criteria, were significantly lower in Group 1 (3469 +/- 1837) compared to Group 2 (10,226 +/- 3295) (p = 0.028). Failure mode in Group 1 was characterized by screw cutting through the cancellous bone. In Group 2 the specimens exclusively failed by plate bending. Conclusions: From biomechanical point of view, pubic ramus stabilization with plate osteosynthesis is superior compared to a single retrograde screw fixation in osteoporotic bone. However, the extensive surgical approach needed for plating must be considered. (C) 2016 Elsevier Ltd. All rights reserved

Insulin receptors are expressed by cells involved in the FDL tendon repair process.

<p>Longitudinal sections of FDL tendons from lean (A) and HF (B) diet-fed mice at day 28 post-injury were stained for insulin receptors (20× magnification). Strong positive staining (brown) was present in the majority of cells in the repair zone regardless of dietary treatment.</p

Murine “Stab Injury” model.

<p>A 23-gauge needle (outlined by blue dotted line) approaches the surface of an exposed and elevated FDL tendon (A) prior to creating the stab injury defect (depicted by black oval). Picrosirius red stained longitudinal sections of (B) injured (blue arrow) and (C) uninjured, sham operated FDL tendons are visualized under polarized light (5× magnification). Note that the tissue section in (B) is oriented through the center of the stab injury. Maximum force (D), work to maximum force (E) and stiffness (F) were measured in isolated FDL tendons immediately following a puncture injury produced by various needle gauge sizes. Results are represented as mean ± SEM (n = 7–9). *** p<0.001, ** p<0.01 and * p<0.05.</p

Effect of high fat diet on tissue repair, cellular recruitment and collagen organization/fiber alignment during the FDL tendon repair process.

<p>Mice were placed on HF or lean control diets for 12 weeks. Following stab injury, mice were maintained on their respective diets until sacrifice. FDL tendons were harvested at 7 day intervals for 28 days and processed for histologic analysis. Longitudinal sections of injured FDL tendons at day 14 from mice on lean (A) or HF (B) diets were stained with hematoxylin-eosin (5× magnification). Area of repair tissue (increased cellularity) was quantitated as a fraction of total tendon area (C). The number of cells per unit area of repair tissue was determined (D). Longitudinal sections of uninjured (E,F) and injured FDL (G–H) tendons at day 28 were stained with picrosirius red and visualized under polarized light (20× magnification). Brighter color intensities indicate organized and aligned collagen fibers while zones of disorganized or absent collagen appear dark. Results are represented as mean ± SEM (n = 2–4). * p<0.05.</p