Acute phosphate restriction leads to impaired fracture healing and resistance to BMP-2

Relationships between matrix mineralization, oxidative metabolism, and mitochondrial structure during ATDC5 murine chondroprogenitor cell line differentiation

The mechanistic relationships between the progression of growth chondrocyte differentiation, matrix mineralization, oxidative metabolism, and mitochondria content and structure were examined in the ATDC5 murine chondroprogenitor cell line. The progression of chondrocyte differentiation was associated with a statistically significant (p ≤ 0.05) ~2-fold increase in oxidative phosphorylation. However, as matrix mineralization progressed, oxidative metabolism decreased. In the absence of mineralization, cartilage extracellular matrix mRNA expression for Col2a1, Aggrecan, and Col10a1 were statistically (p ≤ 0.05) ~2-3-fold greater than observed in mineralizing cultures. In contrast, BSP and Phex that are associated with promoting matrix mineralization showed statistically (p ≤ 0.05) higher ~2-4 expression, while FGF23 phosphate regulatory factor was significantly lower (~50%) in mineralizing cultures. Cultures induced to differentiate under both nonmineralizing and mineralizing media conditions showed statistically greater basal oxidative metabolism and ATP production. Maximal respiration and spare oxidative capacity were significantly elevated (p ≤ 0.05) in differentiated nonmineralizing cultures compared to those that mineralized. Increased oxidative metabolism was associated with both an increase in mitochondria volume per cell and mitochondria fusion, while mineralization diminished mitochondrial volume and appeared to be associated with fission. Undifferentiated and mineralized cells showed increased mitochondrial co-localization with the actin cytoskeletal. Examination of proteins associated with mitochondria fission and apoptosis and mitophagy, respectively, showed levels of immunological expression consistent with the increasing fission and apoptosis in mineralizing cultures. These results suggest that chondrocyte differentiation is associated with intracellular structural reorganization, promoting increased mitochondria content and fusion that enables increased oxidative metabolism. Mineralization, however, does not need energy derived from oxidative metabolism; rather, during mineralization, mitochondria appear to undergo fission and mitophagy. In summary, these studies show that as chondrocytes underwent hypertrophic differentiation, they increased oxidative metabolism, but as mineralization proceeds, metabolism decreased. Mitochondria structure also underwent a structural reorganization that was further supportive of their oxidative capacity as the chondrocytes progressed through their differentiation. Thus, the mitochondria first underwent fusion to support increased oxidative metabolism, then underwent fission during mineralization, facilitating their programed death.

Prx1 cell subpopulations identified in various tissues with diverse quiescence and activation ability following fracture and BMP2 stimulation

The expression of Prx1 has been used as a marker to define the skeletal stem cells (SSCs) populations found within the bone marrow and periosteum that contribute to bone regeneration. However, Prx1 expressing SSCs (Prx1-SSCs) are not restricted to the bone compartments, but are also located within the muscle and able to contribute to ectopic bone formation. Little is known however, about the mechanism(s) regulating Prx1-SSCs that reside in muscle and how they participate in bone regeneration. This study compared both the intrinsic and extrinsic factors of the periosteum and muscle derived Prx1-SSCs and analyzed their regulatory mechanisms of activation, proliferation, and skeletal differentiation. There was considerable transcriptomic heterogeneity in the Prx1-SSCs found in muscle or the periosteum however in vitro cells from both tissues showed tri-lineage (adipose, cartilage and bone) differentiation. At homeostasis, periosteal-derived Prx1 cells were proliferative and low levels of BMP2 were able to promote their differentiation, while the muscle-derived Prx1 cells were quiescent and refractory to comparable levels of BMP2 that promoted periosteal cell differentiation. The transplantation of Prx1-SCC from muscle and periosteum into either the same site from which they were isolated, or their reciprocal sites showed that periosteal cell transplanted onto the surface of bone tissues differentiated into bone and cartilage cells but was incapable of similar differentiation when transplanted into muscle. Prx1-SSCs from the muscle showed no ability to differentiate at either site of transplantation. Both fracture and ten times the BMP2 dose was needed to promote muscle-derived cells to rapidly enter the cell cycle as well as undergo skeletal cell differentiation. This study elucidates the diversity of the Prx1-SSC population showing that cells within different tissue sites are intrinsically different. While muscle tissue must have factors that promote Prx1-SSC to remain quiescent, either bone injury or high levels of BMP2 can activate these cells to both proliferate and undergo skeletal cell differentiation. Finally, these studies raise the possibility that muscle SSCs are potential target for skeletal repair and bone diseases.

An investigation of the effect of acrylamide on fracture healing in rats

BACKGROUND

The aim of this study was to investigate the effects of acrylamide (AA) on fracture healing histologically, biochemically, and radiologically in a rat femur fracture model.

METHODS

Scanning electron microscopy (SEM) imaging and Fourier transform infrared spectroscopy (FTIR), and UV (ultraviolet)-Vis (visible) spectrophotometer examination were performed for acrylamide characterization. In this study, after the femur fracture model was created, the groups were formed to include eight rats in each group (G) as follows: G1: 15th-day control, G2: 15th-day AA, G3: 30th-day control, G4: 30th-day AA. In G2 and G4, 5mg/kg acrylamide was administered 3 times a week by gastric gavage. The fracture was evaluated radiologically according to Lane-Sandhu scoring and histologically according to Huo scoring. The weight changes of the rats were recorded. Albumin, total protein, cholesterol, HDL, LDL, triglyceride, ALP, LDH, vit. D, PTH, Ca, P, WBC, Hb, Plt values were examined in the blood samples. The data were analyzed using the SPSS program.

RESULTS

The characterization properties of acrylamide were confirmed. No significant weight change was observed in the rats during the study. When blood values were compared, a statistically significant difference was determined between albumin, total protein, phosphorus, white blood cell (WBC), and hemoglobin groups (p=0.41, p=0.00, p=0.003, p=0.019, and p=0,017, respectively). According to the histological score comparisons, G3 was significantly different from G1, G2, and G4 (p<0.05), and G4 was significantly different from G1 and G2 (p<0.05). According to Lane-Sandhu scoring, there was a significant difference between G2 and G3 and G4 (p: 0.0, p: 0.034), G1 and G3 (p: 0.001), respectively.

CONCLUSION

AA adversely affects fracture healing even at low doses, as in the present study. According to the results of this study, the authors recommend a diet poor in acrylamide during fracture treatment. Therefore, further human studies are required to find out the complex effect of AA on bone healing and the body.

An Expert Perspective on Phosphate Dysregulation With a Focus on Chronic Hypophosphatemia

Because of their rarity, diseases characterized by chronic hypophosphatemia can be underrecognized and suboptimally managed, resulting in poor clinical outcomes. Moreover, serum phosphate may not be measured routinely in primary care practice. Authors participated in several working sessions to advance the understanding of phosphate homeostasis and the causes, consequences, and clinical implications of chronic hypophosphatemia. Phosphate levels are regulated from birth to adulthood. Dysregulation of phosphate homeostasis can result in hypophosphatemia, which becomes chronic if phosphate levels cannot be normalized. Chronic hypophosphatemia may be underrecognized as serum phosphate measurement is not always part of routine analysis in the primary care setting and results might be misinterpreted, for instance, due to age-specific differences not being accounted for and circadian variations. Clinical consequences of chronic hypophosphatemia involve disordered endocrine regulation, affect multiple organ systems, and vary depending on patient age and the underlying disorder. Signs and symptoms of chronic hypophosphatemic diseases that manifest during childhood or adolescence persist into adulthood if the disease is inadequately managed, resulting in an accumulation of clinical deficits and a progressive, debilitating impact on quality of life. Early identification and diagnosis of patients with chronic hypophosphatemia is crucial, and clinical management should be started as soon as possible to maximize the likelihood of improving health outcomes. Furthermore, in the absence of a universally accepted description for "chronic hypophosphatemia," a definition is proposed here that aims to raise awareness of these diseases, facilitate diagnosis, and guide optimal phosphate management strategies by improving monitoring and assessment of patient response to treatment. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Lepidium sativum: Bone healer in traditional medicine, an experimental validation study in rats

India is a land of spices and medicinal plants. Ayurvedic medications and methods are commonly practised in India for curing several ailments. Lepidium sativum (garden cress) is an important herb that belongs to Brassicaceae family. It is believed that the plant has its origin in Ethiopia but is now cultivated throughout the world. The plant is well-known in Ayurveda for its beneficial properties it holds. The present study describes the fracture healing property of the methanolic and aqueous extract of Lepidium sativum seeds. For the study, 21 Charles foster rats were used. They were grouped into three groups each containing seven rats: control, methanolic, and aqueous group. Rats were anesthetized using ether vapors and fractures were induced in each rat from all the three groups using hand held three-point bending technique. The broken bone fragments were then stabilized using splints. The control group was administered with normal saline, along with food and water, post-fracture. The methanolic group was administered with the methanolic extract of Lepidium sativum seeds at dose of 400 mg/kg given orally, post-fracture along with food and water. The third group received aqueous extract of the seeds in doses of 550 mg/kg orally, along with daily food and water intake for a period of 8 weeks. The results were evaluated both radiologically and biochemically. X-rays were done on day 0, 2^nd week, and 4^th week post-fractures to look for the callus formation and serum levels for calcium, phosphorus, and alkaline phosphatases were evaluated on 0 day, 1 week, 2^nd week, 4^th week, 6^th week, 8^th week, and 10^th week post-injury. It was observed at the end of the study period that the methanolic group had significant callus formation starting at the 2^nd week itself post-fracture. The serum levels of calcium, phosphorus, and alkaline phosphatases at 4^th, 6^th, and 8^th weeks had significant P values in the methanolic group rats.

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.

Clustering of temporal gene expression data with mixtures of mixed effects models with a penalized likelihood

MOTIVATION

Clustering algorithms like K-Means and standard Gaussian mixture models (GMM) fail to account for the structure of variability of replicated data or repeated measures over time. Additionally, a priori cluster number assumptions add an additional complexity to the process. Current methods to optimize cluster labels and number can be inaccurate or computationally intensive for temporal gene expression data with this additional variability.

RESULTS

An extension to a model-based clustering algorithm is proposed using mixtures of mixed effects polynomial regression models and the EM algorithm with an entropy penalized log-likelihood function (EPEM). The EPEM is used to cluster temporal gene expression data with this additional variability. The addition of random effects in our model decreased the misclassification error when compared to mixtures of fixed effects models or other methods such as K-Means and GMM. Applying our method to microarray data from a fracture healing study revealed distinct temporal patterns of gene expression.

AVAILABILITY AND IMPLEMENTATION

https://github.com/darlenelu72/EPEM-GMM.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Hypophosphatemia Regulates Molecular Mechanisms of Circadian Rhythm

Transcriptomic analysis showed that the central circadian pathway genes had significantly altered expression in fracture calluses from mice fed a low phosphate diet. This led us to hypothesize that phosphate deficiency altered the circadian cycle in peripheral tissues. Analysis of the expression of the central clock genes over a 24-36 hour period in multiple peripheral tissues including fracture callus, proximal tibia growth plate and cardiac tissues after 12 days on a low phosphate diet showed higher levels of gene expression in the hypophosphatemia groups (p < 0.001) and a 3 to 6 hour elongation of the circadian cycle. A comparative analysis of the callus tissue transcriptome genes that were differentially regulated by hypophosphatemia with published data for the genes in bone that are diurnally regulated identified 1879 genes with overlapping differential regulation, which were shown by ontology assessment to be associated with oxidative metabolism and apoptosis. Network analysis of the central circadian pathway genes linked their expression to the up regulated expression of the histone methyltransferase gene EZH2, a gene that when mutated in both humans and mice controls overall skeletal growth. These data suggest that phosphate is an essential metabolite that controls circadian function in both skeletal and non skeletal peripheral tissues and associates its levels with the overall oxidative metabolism and skeletal growth of animals.

Molecular pathogenesis of fracture nonunion

Fracture nonunion, a serious bone fracture complication, remains a challenge in clinical practice. Although the molecular pathogenesis of nonunion remains unclear, a better understanding may provide better approaches for its prevention, diagnosis and treatment at the molecular level. This review tries to summarise the progress made in studies of the pathogenesis of fracture nonunion. We discuss the evidence supporting the concept that the development of nonunion is related to genetic factors. The importance of several cytokines that regulate fracture healing in the pathogenesis of nonunion, such as tumour necrosis factor-α, interleukin-6, bone morphogenetic proteins, insulin-like growth factors, matrix metalloproteinases and vascular endothelial growth factor, has been proven in vitro, in animals and in humans. Nitric oxide and the Wnt signalling pathway also play important roles in the development of nonunion. We present potential strategies for the prevention, diagnosis and treatment of nonunion, and the interaction between genetic alteration and abnormal cytokine expression warrants further investigation.

The translational potential of this article

A better understanding of nonunion molecular pathogenesis may provide better approaches for its prevention, diagnosis and treatment in clinical practice.

Transcriptional Mechanisms of Secondary Fracture Healing

PURPOSE OF REVIEW

Growing evidence supports the critical role of transcriptional mechanisms in promoting the spatial and temporal progression of bone healing. In this review, we evaluate and discuss new transcriptional and post-transcriptional regulatory mechanisms of secondary bone repair, along with emerging evidence for epigenetic regulation of fracture healing.

RECENT FINDINGS

Using the candidate gene approach has identified new roles for several transcription factors in mediating the reactive, reparative, and remodeling phases of fracture repair. Further characterization of the different epigenetic controls of fracture healing and fracture-driven transcriptome changes between young and aged fracture has identified key biological pathways that may yield therapeutic targets. Furthermore, exogenously delivered microRNA to post-transcriptionally control gene expression is quickly becoming an area with great therapeutic potential. Activation of specific transcriptional networks can promote the proper progression of secondary bone healing. Targeting these key factors using small molecules or through microRNA may yield effective therapies to enhance and possibly accelerate fracture healing.

Correlation between RUST assessments of fracture healing to structural and biomechanical properties

Radiographic Union Score for Tibia (RUST) and modified RUST (mRUST) are radiographic tools for quantitatively evaluating fracture healing using a cortical scoring system. This tool has high intra-class correlation coefficients (ICCs); however, little evidence has evaluated the scores against the physical properties of bone healing. Closed, stabilized fractures were made in the femora of C3H/HeJ male mice (8-12 week-old) of two dietary groups: A control and a phosphate restricted diet group. Micro-computed tomography (µCT) and torsion testing were carried out at post-operative days (POD) 14, 21, 35, and 42 (n = 10-16) per group time-point. Anteroposterior and lateral radiographic views were constructed from the µCT scans and scored by five raters. The raters also indicated if the fracture were healed. ICCs were 0.71 (mRUST) and 0.63 (RUST). Both RUST scores were positively correlated with callus bone mineral density (BMD) (r = 0.85 and 0.80, p < 0.001) and bone volume fraction (BV/TV) (r = 0.86 and 0.80, p < 0.001). Both RUST scores positively correlated with callus strength (r = 0.35 and 0.26, p < 0.012) and rigidity (r = 0.50 and 0.39, p < 0.001). Radiographically healed calluses had a mRUST ≥13 and a RUST ≥10 and had excellent relationship to structural and biomechanical metrics. Effect of delayed healing due to phosphate dietary restrictions was found at later time points with all mechanical properties (p < 0.011), however no differences found in the RUST scores (p > 0.318). Clinical relevance of this study is both RUST scores showed high correlation to physical properties of healing and generally distinguished healed vs. non-healed fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:945-953, 2018.

Mouse models of bone healing: fracture, marrow ablation, and distraction osteogenesis

Three commonly used murine surgical models of bone healing [closed fracture with intramedullary fixation, distraction osteogenesis (DO), and marrow ablation by reaming] are presented. Detailed surgical protocols for each model are outlined. The nature of the regenerative processes and the types of research questions that may be addressed with these models are briefly outlined. The relative strengths and weaknesses of these models are compared to a number of other surgical models that are used to address similar research questions.

The significance of serum phosphate level on healing index and its relative effects in skeletally immature and mature patients with hypophosphatemic rickets

The aim of this study was to find out the ideal cut-off level of phosphate for safe healing when deformity correction and concomitant lengthening are indicated in the two different skeletal maturity groups of patients with rickets. Thirty-nine hypophosphatemic rickets patients were selected for the study and were divided into two groups: 27 skeletally immature (group IM) and 12 skeletally mature (group M). The outcomes were evaluated with respect to the healing index (HI), laboratory findings, and complications with the mean follow-up of 5.1 years (range, 3.1-7.9). The healing index (HI) of group IM was 1.44 month/cm and HI of group M was 1.68 month/cm. The negative correlation between the level of serum phosphate and HI in group M (coefficient=-0.94) was evaluated to be less than the correlation in group IM (coefficient=-0.50), indicating that the HI is more likely to be affected by serum phosphate in group M than in group IM. Preoperative serum phosphate levels of 2.3 mg/dL and 2.6 mg/dL were analyzed to be the cut-off values of group IM and group M, respectively, in which the cut-off points divided the series into two groups having the most significantly different HI.

Generation of closed transverse fractures in small animals

The most common procedure that has been developed for use in rats and mice to model fracture healing is described. The nature of the regenerative processes that may be assessed and the types of research questions that may be addressed with this model are briefly outlined. The detailed surgical protocol to generate closed simple transverse fractures is presented, and general considerations when setting up an experiment using this model are described.

A2B adenosine receptor promotes mesenchymal stem cell differentiation to osteoblasts and bone formation in vivo

The differentiation of osteoblasts from their precursors, mesenchymal stem cells, is an important component of bone homeostasis as well as fracture healing. The A2B adenosine receptor (A2BAR) is a Gα(s)/α(q)-protein-coupled receptor that signals via cAMP. cAMP-mediated signaling has been demonstrated to regulate the differentiation of mesenchymal stem cells (MSCs) into various skeletal tissue lineages. Here, we studied the role of this receptor in the differentiation of MSCs to osteoblasts. In vitro differentiation of bone marrow-derived MSCs from A2BAR KO mice resulted in lower expression of osteoblast differentiation transcription factors and the development of fewer mineralized nodules, as compared with WT mice. The mechanism of effect involves, at least partially, cAMP as indicated by experiments involving activation of the A2BAR or addition of a cAMP analog during differentiation. Intriguingly, in vivo, microcomputed tomography analysis of adult femurs showed lower bone density in A2BAR KO mice as compared with WT. Furthermore, A2BAR KO mice display a delay in normal fracture physiology with lower expression of osteoblast differentiation genes. Thus, our study identified the A2BAR as a new regulator of osteoblast differentiation, bone formation, and fracture repair.

The biology of fracture healing

The biology of fracture healing is a complex biological process that follows specific regenerative patterns and involves changes in the expression of several thousand genes. Although there is still much to be learned to fully comprehend the pathways of bone regeneration, the over-all pathways of both the anatomical and biochemical events have been thoroughly investigated. These efforts have provided a general understanding of how fracture healing occurs. Following the initial trauma, bone heals by either direct intramembranous or indirect fracture healing, which consists of both intramembranous and endochondral bone formation. The most common pathway is indirect healing, since direct bone healing requires an anatomical reduction and rigidly stable conditions, commonly only obtained by open reduction and internal fixation. However, when such conditions are achieved, the direct healing cascade allows the bone structure to immediately regenerate anatomical lamellar bone and the Haversian systems without any remodelling steps necessary. In all other non-stable conditions, bone healing follows a specific biological pathway. It involves an acute inflammatory response including the production and release of several important molecules, and the recruitment of mesenchymal stem cells in order to generate a primary cartilaginous callus. This primary callus later undergoes revascularisation and calcification, and is finally remodelled to fully restore a normal bone structure. In this article we summarise the basic biology of fracture healing.