Age Dependence of Systemic Bone Loss and Recovery Following Femur Fracture in Mice

Altered post-fracture systemic bone loss in a mouse model of osteocyte dysfunction

Femur fracture leads to loss of bone at uninjured skeletal sites, which may increase risk of subsequent fracture. Osteocytes, the most abundant bone cells, can directly resorb bone matrix and regulate osteoclast and osteoblast activity, but their role in systemic bone loss after fracture remains poorly understood. In this study we used a transgenic (TG+) mouse model that overexpresses human B-cell lymphoma 2 (BCL-2) in osteoblasts and osteocytes. This causes enhanced osteoblast proliferation, followed by disruption in lacunar-canalicular connectivity and massive osteocyte death by 10 wk of age. We hypothesized that reduced viable osteocyte density would decrease the magnitude of systemic bone loss after femur fracture, reduce perilacunar remodeling, and alter callus formation. Bone remodeling was assessed using serum biomarkers of bone formation and resorption at 5 d post-fracture. We used micro-computed tomography, high resolution x-ray microscopy, mechanical testing, and Raman spectroscopy to quantify the magnitude of systemic bone loss, as well as changes in osteocyte lacunar volume, bone strength, and bone composition 2 wk post-fracture. Fracture was associated with a reduction in circulating markers of bone resorption in non-transgenic (TG-) animals. TG+ mice exhibited high bone mass in the limbs, greater cortical elastic modulus and reduced post-yield displacement. After fracture, TG+ mice lost less trabecular bone than TG- mice, but conversely TG+ mice exhibited trends toward a lower yield point and reduced femoral cortical thickness after fracture, though these were not statistically significant. Lacunar density was greater in TG+ mice, but fracture did not alter lacunar volume in TG+ or TG- mice. These findings suggest that osteocytes potentially play a significant role in the post-traumatic systemic response to fracture, though the effects differ between trabecular and cortical bone.

Fracture severity dependence of bone and muscle performance in patients following single or multiple vertebral fractures

Background

Few studies focus on the clinical, laboratory, radiological, and biological characteristics of bone and muscle of multiple vertebral fractures, which are associated with a more poor prognosis compared with single fracture.

Purpose

To compare the BMD, bone turnover, muscularity, fatty infiltration of muscle, and prevalence of co-morbidities in patients with single and multiple vertebral fractures.

Methods

We recruited 100 patients with single fracture (age 66.96 ± 8.24 years) and 100 with multiple fractures (age 69.90 ± 7.80 years); performed dual-energy X-ray absorptiometry of the femoral neck, hip, and lumbar vertebrae; and measured biochemical markers of bone turnover, muscularity, and fatty infiltration.

Results

Patients with multiple vertebral fractures had lower hip BMD (p=0.010) than those with single fractures, but there was no difference in femoral neck and lumbar vertebral BMD nor in muscularity. However, fatty infiltration, an indicator of muscle quality, was significantly higher in participants with multiple fractures (p=0.006). Diabetes was significantly more common in patients with multiple fractures (p=0.042). There were no significant differences in markers of bone turnover, and Seperman analyses showed no correlations of CTX-1 or tPINP with the BMD of the hip, femoral neck, or lumbar spine. However, high CTX-1 was associated with high tPINP (r=0.4805; p<0.0001), and marked fatty infiltration was associated with low hip, lumbar vertebral, and femoral neck BMD. Cox regression analyses showed that age (OR 1.057; 95% CI 1.016-1.101; p=0.006) and low hip BMD (OR 0.016; 95% CI, 0.000-0.549; p=0.022) were associated with a higher risk of multiple fractures.

Conclusion

Patients with multiple fractures tend to have lower hip BMD, a history of type 2 diabetes, and more substantial fatty infiltration of muscle than in those with single fractures. Age and hip BMD rather than lumbar vertebrae BMD were found to be independent risk factors for multiple vertebral compression fractures, implying that hip BMD may be a more sensitive predictor for multiple vertebral fractures. More improvements in hip BMD and focus on older persons may be useful means of preventing multiple fractures.

[Perioperative changes of serum interleukin 6 levels in elderly male patients with intertrochanteric fracture]

Objective

To investigate the perioperative changes in serum interleukin 6 (IL-6) levels in elderly male patients with intertrochanteric fractures, and provide evidence for inflammatory control in this patient population.

Methods

The clinical data of 40 male patients aged more than 60 years with intertrochanteric fractures who met the selection criteria between January 2021 and December 2022 were retrospectively analyzed, including 25 non-osteoporosis patients (T value>-2.5, group A) and 15 osteoporosis patients (T value≤-2.5, group B). In addition, 40 healthy men aged more than 60 years old were included as controls (group C) according to the age matching rule. There was no significant difference in age, smoking history, drinking history, body mass index, complications (hypertension and diabetes), alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, creatinine, and total protein among the 3 groups ( P>0.05). Serum samples were collected from group C subjects and from groups A and B patients preoperatively and on postoperative days 1, 3, 5, and 7. IL-6 levels were measured using ELISA assay. Pearson correlation analysis was used to assess the relationship between IL-6 levels and T values at various time points in groups A and B. Postoperative complications during hospitalization and 1-year mortality rates were recorded for groups A and B.

Results

Preoperative IL-6 levels were significantly higher in groups A and B than in group C ( P<0.05), with group B being significantly higher than group A ( P<0.05). In groups A and B, IL-6 levels increased significantly on postoperative day 1 compared to preoperative levels and then gradually decreased, approaching preoperative levels by postoperative day 7. IL-6 levels in group B were significantly higher than those in group A at all postoperative time points ( P<0.05). Correlation analysis showed that IL-6 levels were negatively correlated with T values at all perioperative time points in all patients from groups A and B ( P<0.05). Complications occurred in 4 patients (16.0%) in group A, including 2 cases of pulmonary infection, 1 case of urinary tract infection, and 1 case of heart failure, and in 3 patients (20.0%) in group B, including 2 cases of pulmonary infection and 1 case of gastrointestinal bleeding. There was no significant difference in the incidence of complications between the two groups ( χ 2=0.104, P=0.747). There were 2 cases (8.0%) and 4 cases (26.7%) died within 1 year after operation in groups A and B, respectively, and there was no significant difference in 1-year mortality rates between the two groups ( χ 2=2.562, P=0.109).

Conclusion

Serum IL-6 levels significantly increase in the early postoperative period in elderly male patients with intertrochanteric fractures, especially in those with osteoporosis. Monitoring the inflammatory state and promptly controlling the inflammatory response during the perioperative period, may reduce complications and improve postoperative survival in this patient population.

The hyaluronic acid-gelatin hierarchical hydrogel for osteoporotic bone defect repairment

Osteoporotic bone defects are serious medical problems due to their sparse bone structure, difficulty in restoration and reconstruction, and high recurrence rates, which also result in heavy economic and social burdens. Herein, we developed a hierarchical hydrogel composed of alendronate sodium (AS)/Mg2+-loaded inverse opal methylpropenylated gelatin (GelMA) hydrogel microspheres (IOHM-AS-Mgs) within methylpropenylated poly(hyaluronic acid) (HAMA) for osteoporotic bone defect treatment. The IOHM-AS-Mgs displayed good cytocompatibility and cell adhesion and strongly stimulated osteogenesis at the transcriptomic and protein levels. When this treatment was applied to the osteoporotic bone defect area, HAMA was used to fix the microspheres. The results of the microcomputed tomography (micro-CT) and histological analyses indicated that the hierarchical hydrogel had the best therapeutic effect. Therefore, this hydrogel is a new candidate for osteoporotic bone defect treatment.

β-Receptor blocker enhances the anabolic effect of PTH after osteoporotic fracture

The autonomic nervous system plays a crucial role in regulating bone metabolism, with sympathetic activation stimulating bone resorption and inhibiting bone formation. We found that fractures lead to increased sympathetic tone, enhanced osteoclast resorption, decreased osteoblast formation, and thus hastened systemic bone loss in ovariectomized (OVX) mice. However, the combined administration of parathyroid hormone (PTH) and the β-receptor blocker propranolol dramatically promoted systemic bone formation and osteoporotic fracture healing in OVX mice. The effect of this treatment is superior to that of treatment with PTH or propranolol alone. In vitro, the sympathetic neurotransmitter norepinephrine (NE) suppressed PTH-induced osteoblast differentiation and mineralization, which was rescued by propranolol. Moreover, NE decreased the PTH-induced expression of Runx2 but enhanced the expression of Rankl and the effect of PTH-stimulated osteoblasts on osteoclastic differentiation, whereas these effects were reversed by propranolol. Furthermore, PTH increased the expression of the circadian clock gene Bmal1, which was inhibited by NE-βAR signaling. Bmal1 knockdown blocked the rescue effect of propranolol on the NE-induced decrease in PTH-stimulated osteoblast differentiation. Taken together, these results suggest that propranolol enhances the anabolic effect of PTH in preventing systemic bone loss following osteoporotic fracture by blocking the negative effects of sympathetic signaling on PTH anabolism.

Impact of age on the host response to sepsis in a murine model of fecal-induced peritonitis

INTRODUCTION

Despite older adults being more vulnerable to sepsis, most preclinical research on sepsis has been conducted using young animals. This results in decreased scientific validity since age is an independent predictor of poor outcome. In this study, we explored the impact of aging on the host response to sepsis using the fecal-induced peritonitis (FIP) model developed by the National Preclinical Sepsis Platform (NPSP).

METHODS

C57BL/6 mice (3 or 12 months old) were injected intraperitoneally with rat fecal slurry (0.75 mg/g) or a control vehicle. To investigate the early stage of sepsis, mice were culled at 4 h, 8 h, or 12 h to investigate disease severity, immunothrombosis biomarkers, and organ injury. Mice received buprenorphine at 4 h post-FIP. A separate cohort of FIP mice were studied for 72 h (with buprenorphine given at 4 h, 12 h, and then every 12 h post-FIP and antibiotics/fluids starting at 12 h post-FIP). Organs were harvested, plasma levels of Interleukin (IL)-6, IL-10, monocyte chemoattract protein (MCP-1)/CCL2, thrombin-antithrombin (TAT) complexes, cell-free DNA (CFDNA), and ADAMTS13 activity were quantified, and bacterial loads were measured.

RESULTS

In the 12 h time course study, aged FIP mice demonstrated increased inflammation and injury to the lungs compared to young FIP mice. In the 72 h study, aged FIP mice exhibited a higher mortality rate (89%) compared to young FIP mice (42%) (p < 0.001). Aged FIP non-survivors also exhibited a trend towards elevated IL-6, TAT, CFDNA, CCL2, and decreased IL-10, and impaired bacterial clearance compared to young FIP non-survivors.

CONCLUSION

To our knowledge, this is the first study to investigate the impact of age on survival using the FIP model of sepsis. Our model includes clinically-relevant supportive therapies and inclusion of both sexes. The higher mortality rate in aged mice may reflect increased inflammation and worsened organ injury in the early stage of sepsis. We also observed trends in impaired bacterial clearance, increase in IL-6, TAT, CFDNA, CCL2, and decreased IL-10 and ADAMTS13 activity in aged septic non-survivors compared to young septic non-survivors. Our aging model may help to increase the scientific validity of preclinical research and may be useful for identifying mechanisms of age-related susceptibility to sepsis as well as age-specific treatment strategies.

The heart-bone connection: relationships between myocardial infarction and osteoporotic fracture

Myocardial infarction (MI) and osteoporotic fracture (Fx) are two of the leading causes of mortality and morbidity worldwide. Although these traumatic injuries are treated as if they are independent, there is epidemiological evidence linking the incidence of Fx and MI, thus raising the question of whether each of these events can actively influence the risk of the other. Atherosclerotic cardiovascular disease and osteoporosis, the chronic conditions leading to MI and Fx, are known to have shared pathoetiology. Furthermore, sustained systemic inflammation after traumas such as MI and Fx has been shown to exacerbate both underlying chronic conditions. However, the effects of MI and Fx outside their own system have not been well studied. The sympathetic nervous system (SNS) and the complement system initiate a systemic response after MI that could lead to subsequent changes in bone remodeling through osteoclasts. Similarly, SNS and complement system activation following fracture could lead to heart tissue damage and exacerbate atherosclerosis. To determine whether damaging bone-heart cross talk may be important comorbidity following Fx or MI, this review details the current understanding of bone loss after MI, cardiovascular damage after Fx, and possible shared underlying mechanisms of these processes.

Temporal dynamics of immune-stromal cell interactions in fracture healing

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state-of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing.

The miR-19a/Cylindromatosis Axis Regulates Pituitary Adenoma Bone Invasion by Promoting Osteoclast Differentiation

BACKGROUND

The presence of bone invasion in aggressive pituitary adenoma (PA) was found in our previous study, suggesting that PA cells may be involved in the process of osteoclastogenesis. miR-19a (as a key member of the miR-17-92 cluster) has been reported to activate the nuclear factor-кB (NF-кB) pathway and promote inflammation, which could be involved in the process of the bone invasion of pituitary adenoma.

METHODS

In this work, FISH was applied to detect miR-19a distribution in tissues from patients with PA. A model of bone invasion in PA was established, GH3 cells were transfected with miR-19a mimic, and the grade of osteoclastosis was detected by HE staining. qPCR was performed to determine the expression of miR-19a throughout the course of RANKL-induced osteoclastogenesis. After transfected with a miR-19a mimic, BMMs were treated with RANKL for the indicated time, and the osteoclast marker genes were detected by qPCR and Western Blot. Pit formation and F-actin ring assay were used to evaluate the function of osteoclast. The TargetScan database and GSEA were used to find the potential downstream of miR-19a, which was verified by Co-IP, Western Blot, and EMSA.

RESULTS

Here, we found that miR-19a expression levels were significantly correlated with the bone invasion of PA, both in clinical samples and animal models. The osteoclast formation prior to bone resorption was dramatically enhanced by miR-19, which was mediated by decreased cylindromatosis (CYLD) expression, increasing the K63 ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6). Consequently, miR-19a promotes osteoclastogenesis by the activation of the downstream NF-кB and mitogen-activated protein kinase (MAPK) pathways.

CONCLUSIONS

To summarize, the results of this study indicate that PA-derived miR-19a promotes osteoclastogenesis by inhibiting CYLD expression and enhancing the activation of the NF-кB and MAPK pathways.

Systemic inflammatory and gut microbiota responses to fracture in young and middle-aged mice

Age is a patient-specific factor that can significantly delay fracture healing and exacerbate systemic sequelae during convalescence. The basis for this difference in healing rates is not well-understood, but heightened inflammation has been suggested to be a significant contributor. In this study, we investigated the systemic cytokine and intestinal microbiome response to closed femur fracture in 3-month-old (young adult) and 15-month-old (middle-aged) female wild-type mice. Middle-aged mice had a serum cytokine profile that was distinct from young mice at days 10, 14, and 18 post-fracture. This was characterized by increased concentrations of IL-17a, IL-10, IL-6, MCP-1, EPO, and TNFα. We also observed changes in the community structure of the gut microbiota in both young and middle-aged mice that was evident as early as day 3 post-fracture. This included an Enterobacteriaceae bloom at day 3 post-fracture in middle-aged mice and an increase in the relative abundance of the Muribaculum genus. Moreover, we observed an increase in the relative abundance of the health-promoting Bifidobacterium genus in young mice after fracture that did not occur in middle-aged mice. There were significant correlations between serum cytokines and specific genera, including a negative correlation between Bifidobacterium and the highly induced cytokine IL-17a. Our study demonstrates that aging exacerbates the inflammatory response to fracture leading to high levels of pro-inflammatory cytokines and disruption of the intestinal microbiota.

Acute bone loss following SARS-CoV-2 infection in mice

The novel coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has infected more than 650 million people worldwide. Approximately 23% of these patients developed lasting "long-haul" COVID symptoms, including fatigue, joint pain, and systemic hyperinflammation. However, the direct clinical impact of SARS-CoV-2 infection on the skeletal system including bone and joint health has not been determined. Utilizing a humanized mouse model of COVID-19, this study provides the first direct evidence that SARS-CoV-2 infection leads to acute bone loss, increased osteoclast number, and thinner growth plates. This bone loss could decrease whole-bone mechanical strength and increase the risk of fragility fractures, particularly in older patients, while thinner growth plates may create growth disturbances in younger patients. Evaluating skeletal health in patients that have recovered from COVID-19 will be crucial to identify at-risk populations and develop effective countermeasures.

Pathophysiological mechanism of acute bone loss after fracture

BACKGROUND

Acute bone loss after fracture is associated with various effects on the complete recovery process and a risk of secondary fractures among patients. Studies have reported similarities in pathophysiological mechanisms involved in acute bone loss after fractures and osteoporosis. However, given the silence nature of bone loss and bone metabolism complexities, the actual underlying pathophysiological mechanisms have yet to be fully elucidated.

AIM OF REVIEW

To elaborate the latest findings in basic research with a focus on acute bone loss after fracture. To briefly highlight potential therapeutic targets and current representative drugs. To arouse researchers' attention and discussion on acute bone loss after fracture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bone loss after fracture is associated with immobilization, mechanical unloading, blood supply damage, sympathetic nerve regulation, and crosstalk between musculoskeletals among other factors. Current treatment strategies rely on regulation of osteoblasts and osteoclasts, therefore, there is a need to elucidate on the underlying mechanisms of acute bone loss after fractures to inform the development of efficacious and safe drugs. In addition, attention should be paid towards ensuring long-term skeletal health.

Reambulation following hindlimb unloading attenuates disuse-induced changes in murine fracture healing

Patients with bone and muscle loss from prolonged disuse have higher risk of falls and subsequent fragility fractures. In addition, fracture patients with continued disuse and/or delayed physical rehabilitation have worse clinical outcomes compared to individuals with immediate weight-bearing activity following diaphyseal fracture. However, the effects of prior disuse followed by physical reambulation on fracture healing cellular processes and adjacent bone and skeletal muscle recovery post-injury remains poorly defined. To bridge this knowledge gap and inform future treatment and rehabilitation strategies for fractures, a preclinical model of fracture healing with a history of prior unloading with and without reambulation was employed. First, skeletally mature male and female C57BL/6J mice (18 weeks) underwent hindlimb unloading by tail suspension (HLU) for 3 weeks to induce significant bone and muscle loss modeling enhanced bone fragility. Next, mice had their right femur fractured by open surgical dissection (stabilized with 24-gauge pin). The, mice were randomly assigned to continued HLU or allowed normal weight-bearing reambulation (HLU + R). Mice given normal cage activity throughout the experiment served as healthy age-matched controls. All mice were sacrificed 4-days (DPF4) or 14-days (DPF14) following fracture to assess healing and uninjured hindlimb musculoskeletal properties (6-10 mice per treatment/biological sex). We found that continued disuse following fracture lead to severely diminished uninjured hindlimb skeletal muscle mass (gastrocnemius and soleus) and femoral bone volume adjacent to the fracture site compared to healthy age-matched controls across mouse sexes. Furthermore, HLU led to significantly decreased periosteal expansion (DPF4) and osteochondral tissue formation by DPF14, and trends in increased osteoclastogenesis (DPF14) and decreased woven bone vascular area (DPF14). In contrast, immediate reambulation for 2 weeks after fracture, even following a period of prolonged disuse, was able to increase hindlimb skeletal tissue mass and increase osteochondral tissue formation, albeit not to healthy control levels, in both mouse sexes. Furthermore, reambulation attenuated osteoclast formation seen in woven bone tissue undergoing disuse. Our results suggest that weight-bearing skeletal loading in both sexes immediately following fracture may improve callus healing and prevent further fall risk by stimulating skeletal muscle anabolism and decreasing callus resorption compared to minimal or delayed rehabilitation regimens.

Bifidobacterium longum supplementation improves age-related delays in fracture repair

Age-related delays in bone repair remains an important clinical issue that can prolong pain and suffering. It is now well established that inflammation increases with aging and that this exacerbated inflammatory response can influence skeletal regeneration. Recently, simple dietary supplementation with beneficial probiotic bacteria has been shown to influence fracture repair in young mice. However, the contribution of the gut microbiota to age-related impairments in fracture healing remains unknown. Here, we sought to determine whether supplementation with a single beneficial probiotic species, Bifidobacterium longum (B. longum), would promote fracture repair in aged (18-month-old) female mice. We found that B. longum supplementation accelerated bony callus formation which improved mechanical properties of the fractured limb. We attribute these pro-regenerative effects of B. longum to preservation of intestinal barrier, dampened systemic inflammation, and maintenance of the microbiota community structure. Moreover, B. longum attenuated many of the fracture-induced systemic pathologies. Our study provides evidence that targeting the gut microbiota using simple dietary approaches can improve fracture healing outcomes and minimize systemic pathologies in the context of aging.

Effect of age on femur whole-bone bending strength of mature rat

BACKGROUND

Skeletally mature rodents are frequently used in studies of bone health and bone healing, some of them requiring longitudinal observations that span a significant portion of the animals' adulthood. However, changes in whole bone mechanics associated with the natural aging of adult rats have not been extensively characterized.

METHODS

Femurs from skeletally mature Wistar rats in three age groups of 24-week (young adult), 39-week (middle-age), and 54-week (late middle-age) were tested under three-point bending load in the anterior-posterior direction. Mechanical properties and geometric properties of the femurs from the two older groups were compared to the 24-week rats.

FINDINGS

Significantly greater strength, rigidity, and post-yield deformation were found in the 54-week group when compared to the 24-week group. The oldest group also demonstrated greater leg length, anteroposterior width, and cross-sectional moment of inertia over the youngest group. Of the intrinsic properties, the highest ultimate stress was found in the 39-week and was significantly higher than the 24-week group. The ultimate strain increased with age, and the difference between the youngest and the oldest group was statistically significant.

INTERPRETATION

The results suggest that femoral bending properties and geometric properties are continually modified from young adult to late-middle-aged animals. Knowing the baseline bone strength and rigidity throughout adulthood of a rodent breed helps guide animal selection in study design.

Dietary Hempseed Decreases Femur Maximum Load in a Young Female C57BL/6 Mouse Model but Does Not Influence Bone Mineral Density or Micro-Architecture

Numerous seed and seed extract diets have been investigated as a means of combating age-related bone loss, with many findings suggesting that the seeds/extracts confer positive effects on bone. Recently, there has been rising interest in the use of dietary hempseed in human and animal diets due to a perceived health benefit from the seed. Despite this, there has been a lack of research investigating the physiologic effects of dietary hempseed on bone. Previous studies have suggested that hempseed may enhance bone strength. However, a complete understanding of the effects of hempseed on bone mineralization, bone micro-architecture, and bone biomechanical properties is lacking. Using a young and developing female C57BL/6 mouse model, we aimed to fill these gaps in knowledge. From five to twenty-nine weeks of age, the mice were raised on either a control (0%), 50 g/kg (5%), or 150 g/kg (15%) hempseed diet (n = 8 per group). It was found that the diet did not influence the bone mineral density or micro-architecture of either the right femur or L5 vertebrae. Furthermore, it did not influence the stiffness, yield load, post-yield displacement, or work-to-fracture of the right femur. Interestingly, it reduced the maximum load of the right femur in the 15% hempseed group compared to the control group. This finding suggests that a hempseed-enriched diet provides no benefit to bone in young, developing C57BL/6 mice and may even reduce bone strength.

Activation of canonical Wnt signaling accelerates intramembranous bone regeneration in male mice

Canonical Wnt signaling plays an important role in skeletal development, homeostasis, and both endochondral and intramembranous repair. While studies have demonstrated that the inhibition of Wnt signaling impairs intramembranous bone regeneration, how its activation affects intramembranous bone regeneration has been underexplored. Therefore, we sought to determine the effects of activation of canonical Wnt signaling on intramembranous bone regeneration by using the well-established marrow ablation model. We hypothesized that mice with a mutation in the Wnt ligand coreceptor gene Lrp5 would have accelerated intramembranous bone regeneration. Male and female wild-type and Lrp5-mutant mice underwent unilateral femoral bone marrow ablation surgery in the right femur at 4 weeks of age. Both the left intact and right operated femurs were assessed at Days 3, 5, 7, 10, and 14. The intact femur of Lrp5 mutant mice of both sexes had higher bone mass than wild-type littermates, although to a greater degree in males than females. Overall, the regenerated bone volume in Lrp5 mutant male mice was 1.8-fold higher than that of littermate controls, whereas no changes were observed between female Lrp5 mutant and littermate control mice. In addition, the rate of intramembranous bone regeneration (from Day 3 to Day 7) was higher in Lrp5 mutant male mice compared to their same-sex littermate controls with no difference in the females. Thus, activation of canonical Wnt signaling increases bone mass in intact bones of both sexes, but accelerates intramembranous bone regeneration following an injury challenge only in male mice.

Early effects of ovariectomy on bone microstructure, bone turnover markers and mechanical properties in rats

Background

Fragility fracture is one of the most serious consequences of female aging, which can increase the risk of death. Therefore, paying attention to the pathogenesis of postmenopausal osteoporosis (PMOP) is very important for elderly women.

Methods and materials

Forty 12-week-old female rats were divided into two groups including the ovariectomy (OVX) group and the control group. Four rats in each group were selected at 1, 4, 8, 12 and 16 weeks after operation. Vertebral bones and femurs were dissected completely for micro-Computed Tomography (micro-CT) scanning, biological modulus detection and histomorphological observation.

Results

In OVX group, bone volume/total volume (BV/TV), bone trabecular connection density (Conn.D) and trabecular bone number (Tb.N) decreased significantly with time (P < 0.05). The elastic modulus of femur in OVX group was lower than that in control group, but there was no significant difference between them (P > 0.05). Over time, the tartrate resistant acid phosphatase (TRAP), osteocalcin (BGP), type I procollagen amino terminal propeptide (PINP) and type I collagen carboxy terminal peptide (CTX-I) in OVX group increased significantly (P < 0.05). The micrographs of the OVX group showed sparse loss of the trabecular interconnectivity and widening intertrabecular spaces with time.

Conclusion

The bone loss patterns of vertebral body and femur were different in the early stage of estrogen deficiency. The bone turnover rate of OVX rats increased, however the changes of biomechanical properties weren’t obvious.

Sex differences in systemic bone and muscle loss following femur fracture in mice

Fracture induces systemic bone loss in mice and humans, and a first (index) fracture increases the risk of future fracture at any skeletal site more in men than women. The etiology of this sex difference is unknown, but fracture may induces a greater systemic bone loss response in men. Also sex differences in systemic muscle loss after fracture have not been examined. We investigated sex differences in systemic bone and muscle loss after transverse femur fracture in 3-month-old male and female C57BL/6 J mice. Whole-body and regional bone mineral content and density (BMC and BMD), trabecular and cortical bone microstructure, muscle contractile force, muscle mass, and muscle fiber size were quantified at multiple time points postfracture. Serum concentrations of inflammatory cytokines (IL-1β, IL-6, and TNF-α) were measured 1-day postfracture. One day postfracture, IL-6 and Il-1B were elevated in fracture mice of both sexes, but TNF-α was only elevated in male fracture mice. Fracture reduced BMC, BMD, and trabecular bone microstructural properties in both sexes 2 weeks postfracture, but declines were greater in males. Muscle contractile force, mass, and fiber size decreased primarily in the fractured limb at 2 weeks postfracture and females showed a trend toward greater muscle loss. Bone and muscle properties recovered by 6 weeks postfracture. Overall, postfracture systemic bone loss is greater in men, which may contribute to sex differences in subsequent fracture risk. In both sexes, muscle loss is primarily confined to the injured limb and fracture may induce greater inflammation in males.

Altered canalicular remodeling associated with femur fracture in mice

We previously showed that femur fracture in mice caused a reduction in bone volume at distant skeletal sites within 2 weeks post-fracture. Osteocytes also have the ability to remodel their surrounding bone matrix through perilacunar/canalicular remodeling (PLR). If PLR is altered systemically following fracture, this could affect bone mechanical properties and increase fracture risk at all skeletal sites. In this study, we investigated whether lacunar-canalicular microstructure and the rate of PLR are altered in the contralateral limb following femoral fracture in mice. We hypothesized that femoral fracture would accelerate PLR by 2 weeks postfracture, followed by partial recovery by 4 weeks. We used histological evaluation and high-resolution microcomputed tomography to quantify the morphology of the lacunar-canalicular network at the contralateral tibia, and we used quantitative real-time polymerase chain reaction (RT-PCR) and RNA-seq to measure the expression of PLR-associated genes in the contralateral femur. We found that at both 2 and 4 weeks postfracture, canalicular width was significantly increased by 18.6% and 16.6%, respectively, in fractured mice relative to unfractured controls. At 3 days and 4 weeks post-fracture, we observed downregulation of PLR-associated genes; RNA-seq analysis at 3 days post-fracture showed a deceleration of bone formation and mineralization in the contralateral limb. These data demonstrate notable canalicular changes following fracture that could affect bone mechanical properties. These findings expand our understanding of systemic effects of fracture and how biological and structural changes at distant skeletal sites may contribute to increased fracture risk following an acute injury.

Age-Dependent Changes in Bone Architecture, Patterning, and Biomechanics During Skeletal Regeneration

Mouse digit amputation provides a useful model of bone growth after injury, in that the injury promotes intramembranous bone formation in an adult animal. The digit tip is composed of skin, nerves, blood vessels, bones, and tendons, all of which regenerate after digit tip amputation, making it a powerful model for multi-tissue regeneration. Bone integrity relies upon a balanced remodeling between bone resorption and formation, which, when disrupted, results in changes to bone architecture and biomechanics, particularly during aging. In this study, we used recently developed techniques to evaluate bone patterning differences between young and aged regenerated bone. This analysis suggests that aged mice have altered trabecular spacing and patterning and increased mineral density of the regenerated bone. To further characterize the biomechanics of regenerated bone, we measured elasticity using a micro-computed tomography image-processing method combined with nanoindentation. This analysis suggests that the regenerated bone demonstrates decreased elasticity compared with the uninjured bone, but there is no significant difference in elasticity between aged and young regenerated bone. These data highlight distinct architectural and biomechanical differences in regenerated bone in both young and aged mice and provide a new analysis tool for the digit amputation model to aid in evaluating the outcomes for potential therapeutic treatments to promote regeneration.

Altered collagen chemical compositional structure in osteopenic women with past fractures: A case-control Raman spectroscopic study

Incidences of low-trauma fractures among osteopenic women may be related to changes in bone quality. In this blinded, prospective-controlled study, compositional and heterogeneity contributors of bone quality to fracture risk were examined. We hypothesize that Raman spectroscopy can differentiate between osteopenic women with one or more fractures (cases) from women without fractures (controls). This study involved the Raman spectroscopic analysis of cortical and cancellous bone composition using iliac crest biopsies obtained from 59-cases and 59-controls, matched for age (62.0 ± 7.5 and 61.7 ± 7.3 years, respectively, p = 0.38) and hip bone mineral density (BMD, 0.827 ± 0.083 and 0.823 ± 0.072 g/cm3, respectively, p = 0.57). Based on aggregate univariate case-control and odds ratio based logistic regression analyses, we discovered two Raman ratiometric parameters that were predictive of past fracture risk. Specifically, 1244/1268 and 1044/959 cm-1 ratios, were identified as the most differential aspects of bone quality in cortical cases with odds ratios of 0.617 (0.406-0.938 95% CI, p = 0.024) and 1.656 (1.083-2.534 95% CI, p = 0.020), respectively. Both 1244/1268 and 1044/959 cm-1 ratios exhibited moderate sensitivity (59.3-64.4%) but low specificity (49.2-52.5%). These results suggest that the organization of mineralized collagen fibrils were significantly altered in cortical cases compared to controls. In contrast, compositional and heterogeneity parameters related to mineral/matrix ratios, B-type carbonate substitutions, and mineral crystallinity, were not significantly different between cases and controls. In conclusion, a key outcome of this study is the significant odds ratios obtained for two Raman parameters (1244/1268 and 1044/959 cm-1 ratios), which from a diagnostic perspective, may assist in the screening of osteopenic women with suspected low-trauma fractures. One important implication of these findings includes considering the possibility that changes in the organization of collagen compositional structure plays a far greater role in postmenopausal women with osteopenic fractures.

Systemic bone loss following myocardial infarction in mice

Myocardial infarction (MI) and osteoporotic fracture are leading causes of morbidity and mortality, and epidemiological evidence linking their incidence suggests possible crosstalk. MI can exacerbate atherosclerosis through the sympathetic nervous system (SNS) activation and β₃ adrenoreceptor-mediated release of hematopoietic stem cells, leading to monocytosis. We hypothesized that this same pathway initiates systemic bone loss following MI, since osteoclasts differentiate from monocytes. In this study, MI was created with left anterior descending artery ligation in 12-week-old male mice (n = 24) randomized to β₃ -adrenergic receptor (AR) antagonist (SR 59230A) treatment or no treatment for 10 days postoperatively. Additional mice (n = 21, treated and untreated) served as unoperated controls. Bone mineral density (BMD), bone mineral content (BMC), and body composition were quantified at baseline and 10 days post-MI using dual-energy x-ray absorptiometry; circulating monocyte levels were quantified and the L5 vertebral body and femur were analyzed with microcomputed tomography 10 days post-MI. We found that MI led to circulating monocyte levels increases, BMD and BMC decreases at the femur and lumbar spine in MI mice (-6.9% femur BMD, -3.5% lumbar BMD), and trabecular bone volume decreases in MI mice compared with control mice. β₃ -AR antagonist treatment appeared to diminish the bone loss response (-5.3% femur BMD, -1.2% lumbar BMD), though these results were somewhat inconsistent. Clinical significance: These results suggest that MI leads to systemic bone loss, but that the SNS may not be a primary modulator of this response; bone loss and increased fracture risk may be important clinical comorbidities following MI or other ischemic injuries.

Mice lacking substance P have normal bone modeling but diminished bone formation, increased resorption, and accelerated osteopenia with aging

Substance P (SP) is a sensory neuropeptide that is expressed by the neurons innervating bone. There is considerable evidence that SP can regulate bone cell function in vitro, but it is unclear whether SP modulates bone modeling or remodeling in vivo. To answer this question we characterized the bone phenotype of mice with deletion of the Tac1 gene expressing SP. The phenotypes of 2-month-old and 5-month-old SP deficient mice and their wildtype controls were characterized by using μCT imaging, static and dynamic bone histomorphometry, and urinary deoxypyridinoline cross-links (DPD) measurement. No differences in bone phenotypes were observed between the 2 strains at 2 months of age. By 5 months both the wildtype and SP deficient mice had developed cancellous osteopenia, but relative to the wild-type mice the SP deficient mice had significantly greater cancellous bone loss. The SP deficient mice also exhibited decreased bone formation, increased osteoclast number, and increased urinary DPD levels. Cortical defect early repair was delayed in 5-month-old mice lacking SP. Collectively, these findings indicate that SP signaling is not required for bone modeling, but SP signaling reduces age-related osteopenia and accelerates cortical defect reparation, data supporting the hypothesis that SP is an anabolic physiologic regulator of bone metabolism.

Effect of Single Versus Multiple Fractures on Systemic Bone Loss in Mice

Systemic bone loss after initial fracture contributes to an increased risk of secondary fracture. Clinical research has revealed an association between the risk of future fracture and the number or magnitude of prior fractures. However, the change in systemic bone mass after single versus multiple fractures is unknown. We used ipsilateral femur and tibia fractures as multiple fractures and a femur or tibia fracture as a single fracture to investigate the influence of single versus multiple fractures on systemic bone mass. Seventy-two adult male C57BL/6J mice underwent transverse osteotomies of the ipsilateral femur and/or tibia with subsequent internal fixation. The dynamic change of in vivo whole-body BMD was assessed at 4 days, 2 weeks, and 4 weeks after fracture. The microstructure of the L₅ vertebral body and contralateral femur was assessed using micro-CT (μCT) and biomechanical tests (vertebral compression test and three-point bending test) at 2 and 4 weeks. Tartrate-resistant acid phosphatase (TRAP) staining, sequential fluorescence labeling, and systemic inflammatory cytokines were also quantified. A greater decrease in whole-body BMD was observed after multiple than single fractures. The trabecular bone volume fraction, trabecular number, and trabecular thickness of the L₅ vertebral body were significantly reduced. There were no significant differences in cortical thickness, trabecular bone microstructure, or bone strength in the contralateral femur. At 4 days and 2 weeks, we observed significant increases in the serum levels of IL-6 and TNF-α. We also observed an increase in the osteoclast number of the L₅ vertebral body at 4 days. These data indicate that systemic bone loss might increase with the number or severity of prior fractures, and the mechanism may be partly associated with an increased osteoclast number and a more severe inflammatory response. © 2020 American Society for Bone and Mineral Research (ASBMR).

Bifidobacterium adolescentis supplementation attenuates fracture-induced systemic sequelae

The gut microbiota is an important contributor to both health and disease. While previous studies have reported on the beneficial influences of the gut microbiota and probiotic supplementation on bone health, their role in recovery from skeletal injury and resultant systemic sequelae remains unexplored. This study aimed to determine the extent to which probiotics could modulate bone repair by dampening fracture-induced systemic inflammation. Our findings demonstrate that femur fracture induced an increase in gut permeability lasting up to 7 days after trauma before returning to basal levels. Strikingly, dietary supplementation with Bifidobacterium adolescentis augmented the tightening of the intestinal barrier, dampened the systemic inflammatory response to fracture, accelerated fracture callus cartilage remodeling, and elicited enhanced protection of the intact skeleton following fracture. Together, these data outline a mechanism whereby dietary supplementation with beneficial bacteria can be therapeutically targeted to prevent the systemic pathologies induced by femur fracture.

Region-dependent bone loss in the lumbar spine following femoral fracture in mice

We previously showed that after femur fracture, mice lose bone at distant skeletal sites, including the lumbar vertebrae. This bone loss may increase the risk of subsequent vertebral fractures, particularly if bone is lost from high-strain bone regions, which are most commonly found adjacent to the superior and inferior endplates of the vertebral body. To determine regional bone loss from the lumbar spine following femur fracture, we evaluated the cranial, center, and caudal portions of the L5 vertebral bodies of Young (3 month-old) and Middle-Aged (12 month-old) female C57BL/6 mice two weeks after a transverse femur fractures compared to Young and Middle-Aged uninjured control mice. We hypothesized that greater bone loss would be observed in the cranial and caudal regions than in the center region in both Young and Middle-Aged mice. Trabecular and cortical bone microstructure were evaluated using micro-computed tomography, and osteoclast number and eroded surface were evaluated histologically. In Young Mice, fracture led to decreased trabecular and cortical bone microstructure primarily in the cranial and caudal regions, but not the center region, while Middle-Aged mice demonstrated decreases in trabecular bone in all regions, but did not exhibit any changes in cortical bone microstructure after fracture. No significant differences in osteoclast number or eroded surface were observed at this time point. These data suggest that bone loss following fracture in Young Mice is concentrated in areas that contain a large amount of high-strain tissue, whereas bone loss in Middle-Aged mice is less region-dependent and is restricted to the trabecular bone compartment. These results illustrate how systemic bone loss after fracture could lead to decreases in vertebral strength, and how distinct regional patterns and age-dependent differences in bone loss may differentially affect vertebral fracture risk.

Advances and Promises of Nutritional Influences on Natural Bone Repair

Impaired fracture healing continues to be a significant public health issue. This is more frequently observed in aging populations and patients with co-morbidities that can directly influence bone repair. Tremendous progress has been made in the development of biologics to enhance and accelerate the healing process; however, side-effects persist that can cause significant discomfort and tissue damage. This has been the impetus for the development of safe and natural strategies to hasten natural bone healing. Of the many possible approaches, nutrition represents a safe, affordable, and non-invasive strategy to positively influence each phase of fracture repair. However, our understanding of how healing can be hindered by malnutrition or enhanced with nutritional supplementation has lagged behind the advancements in both surgical management and the knowledge of molecular and cellular drivers of skeletal fracture repair. This review serves to bridge this knowledge gap as well as define the importance of nutrition during fracture healing. The extant literature clearly indicates that pre-existing nutritional deficiencies should be corrected, and nutritional status should be carefully monitored to prevent the development of malnutrition for the best possible healing outcome. It remains unclear, however, whether the provision of nutrients beyond sufficiency has any benefit on fracture repair and patient outcomes. The combined body of pre-clinical studies using a variety of animal models suggests a promising role of nutrition as an adjuvant therapy to facilitate fracture repair, but extensive research is needed, specifically at the clinical level, to clarify the utility of nutritional interventions in orthopedics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:695-707, 2020.

Dynamic Change of Lumbar Structure and Associated Factors: A Retrospective Study

Objective

To determine whether lumbar anatomy parameters are in dynamic change and related factors.

Methods

This is a retrospective study. Participants who did lumbar computed tomography (CT) scanning in Shandong University Qilu Hospital from October 2017 to March 2019 were selected. The 476 participants were randomly selected as male or female, with the age ranging from 17 to 87 years (mean, 55.19; standard deviation, 14.28 years). All the measurements were taken based on the CT scanning image and the measurement of lumbar morphology was conducted using picture archiving and communication systems (PACS). The angle between the horizontal alignment and pedicle center on median sagittal view, the angle between upper endplate and lower endplate on median sagittal view as well as transverse section angle (TSA) using Magerl point in the axial view was determined by reconstructive CT analysis.

Results

In the overall participants, the angle between the horizontal alignment and pedicle center on median sagittal view of lumbar one to three was significantly decreased with aging, from 3.90° ± 2.81° to −4.18° ± 6.86° (P = 0.002), 5.60° ± 2.89° to −4.14° ± 5.90° (P = 0.030), and 4.75° ± 2.95° to −2.87° ± 4.68° (P < 0.001), respectively. Additionally, the angle between the horizontal alignment and pedicle center on median sagittal view in male participants of lumbar two was dramatically decreased, from 4.83° ± 2.79° to −4.45° ± 5.97° (P = 0.30). And that of lumbar three in female participants was significantly decreased, from 4.56° ± 2.52° to −2.88° ± 5.03° (P = 0.029). Furthermore, of the overall participants, the angle between upper endplate and lower endplate on median sagittal view of lumbar one to four was associated with aging (P < 0.001, P < 0.001, P = 0.015, P < 0.001, respectively). The angle of lumbar one, two and four in male participants and lumbar one to four in female participants were all significantly related to aging (all P < 0.05). Moreover, in the participants overall, the TSA of lumbar one to three was significantly associated with aging (P = 0.015, P = 0.006 and P = 0.007, respectively). In addition, this angle in lumbar one to lumbar four in male participants were all negatively associated with aging (P = 0.017, P = 0.001, P = 0.005 and P = 0.036, respectively).

Conclusion

Lumbar anatomy parameters are in dynamic change in an age and gender dependent manner. During spine surgery in elderly patients, more attention should be paid to these anatomic changes.

Fluorine-contained hydroxyapatite suppresses bone resorption through inhibiting osteoclasts differentiation and function in vitro and in vivo

Objectives

Fluorine, an organic trace element, has been shown to unfavourably effect osteoclasts function at a low dose. Use of hydroxyapatite (HA) has been effective in exploring its roles in promoting bone repair. In this study, we used HA modified with fluorine to investigate whether it could influence osteoclastic activity in vitro and ovariectomy‐induced osteoclasts hyperfunction in vivo.

Materials and methods

Fluorohydroxyapatite (FHA) was obtained and characterized by scanning electron microscope (SEM). Osteoclasts proliferation and apoptosis treated with FHA were assessed by MTT and TUNEL assay. SEM, F‐actin, TRAP activity and bone resorption experiment were performed to determine the influence of FHA on osteoclasts differentiation and function. Moreover, HA and FHA were implanted into ovariectomized osteoporotic and sham surgery rats. Histology and Micro‐CT were examined for further verification.

Results

Fluorine released from FHA slowly and sustainably. FHA hampered osteoclasts proliferation, promoted osteoclasts apoptosis, suppressed osteoclasts differentiation and function. Experiments in vivo validated that FHA participation brought about an inhibitory effect on osteoclasts hyperfunction and less bone absorption.

Conclusion

The results indicated that FHA served as an efficient regulator to attenuate osteoclasts formation and function and was proposed as a candidature for bone tissue engineering applications.

Systemic Bone Loss After Fracture

A history of prior fracture is the most reliable indicator of prospective fracture risk. Increased fracture risk is not confined to the region of the prior fracture, but is operant at all skeletal sites, providing strong evidence of systemic bone loss after fracture. Animal and human studies suggest that systemic bone loss begins shortly after fracture and persists for several years in humans. In fact, bone quantity and bone quality may never fully return to their pre-fracture levels, especially in older subjects, demonstrating a need for improved understanding of the mechanisms leading to systemic bone loss after fracture in order to reduce subsequent fracture risk. Although the process remains incompletely understood, mechanical unloading (disuse), systemic inflammation, and hormones that control calcium homeostasis may all contribute to systemic bone loss. Additionally, individual factors can potentially affect the magnitude and time course of systemic bone loss and recovery. The magnitude of systemic bone loss correlates positively with injury severity and age. Men may also experience greater bone loss or less recovery than women after fracture. This review details the current understanding of systemic bone loss following fracture, including possible underlying mechanisms and individual factors that may affect this injury response.

Incident fracture is associated with a period of accelerated loss of hip BMD: the Study of Osteoporotic Fractures

Bone loss following a fracture could increase the risk of future fractures. In this study, we found that elderly women who had an upper body fracture or multiple fractures lost more bone at the hip than those who did not fracture. This suggests a possible systemic bone loss response initiated by fracture.

INTRODUCTION

A prior fracture is one of the strongest predictors of subsequent fracture risk, but the etiology of this phenomenon remains unclear. Systemic bone loss post-fracture could contribute to increased risk of subsequent fractures. Therefore, in this study, we investigated whether incident fractures, including those distant to the hip, are associated with accelerated loss of hip bone mineral density (BMD) in elderly women.

METHODS

We analyzed data from 3956 Caucasian women aged ≥ 65 years who were enrolled in the Study of Osteoporotic Fractures and completed hip BMD measurements at study visit 4 (year 6) and visit 6 (year 10). Clinical fractures between visits 4 and 6 were ascertained from triannual questionnaires and centrally adjudicated by review of community radiographic reports. Subjects provided questionnaire information and clinical variables at examinations for known and potential covariates. Generalized linear models were used to calculate average annual percent change in total hip BMD between visits 4 and 6 for each incident fracture type and for upper body and lower body fractures combined. A subset of women (n = 3783) was analyzed for annual total hip BMD change between study visits 4 and 5 and between study visits 5 and 6 to evaluate change in total hip BMD during these 2-year intervals.

RESULTS

Women with incident upper body fracture or incident lower body fracture exhibited reductions in total hip BMD of 0.89 and 0.77% per year, respectively, while women who did not fracture exhibited reductions in total hip BMD of 0.66% per year during the 4-year period. Accelerated loss of hip BMD was isolated to the 2-year time interval that included the fracture. Loss of total hip BMD was not affected by the number of days from fracture to follow up DXA.

CONCLUSIONS

Systemic bone loss following fracture may increase the risk of future fractures at all skeletal sites. There is a need for improved understanding of mechanisms leading to apparent accelerated bone loss following a fracture in order to reduce subsequent fracture risk.