We would like to thank Alexandra Joyner for her support when this protocol was being established, Edwina McGlinn and Yi-cheng Chang for sharing retinoic acid. The Australian Regenerative Medicine Institute is supported by grants from the State Government of Victoria and the Australian Government.

All the experiments should be carried out following the local governmental and institutional guidelines of ethical handling of laboratory animals.
1. Preparations Prior to the Day of Bone Culture
<ol>
	<li>Set up timed mouse matings to obtain fetuses and pups from embryonic day 14.5 (E14.5) and onward. 
	NOTE: The culture of long bones can be successfully applied to different mouse strains; in the present protocol, outbred Swiss Webster wild-type mice are used.</li>
	<li>Prepare dissection medium (adapted from Houston et al.15): dilute &#945;-minimum essential medium (&#945;-MEM) or Dulbecco&#8217;s modified Eagle&#8217;s medium (DMEM) 1/13 in phosphate-buffered saline (PBS) and 2 mg/mL bovine serum albumin (BSA) and filter sterilize through a 0.22 &#181;m, 33 mm diameter syringe filter. Store aliquots at -20 &#176;C.</li>
	<li>The day before extraction of the fetuses, prepare the serum-free bone culture medium composed of DMEM containing 0.2% BSA, 0.5 mM L-glutamine, 40 U/mL penicillin/streptomycin, 0.05 mg/mL ascorbic acid, and 1 mM betaglycerophosphate. Filter sterilize through a 0.22 &#181;m, 33 mm diameter syringe filter and store at 4 &#176;C for up to 1 month.</li>
	<li>On the day of the culture and prior to mouse culling, prepare 24-well plates and 60 mm dishes with dissection medium and keep them ice cold. Prewarm the bone culture medium in a 37 &#176;C water bath. Spray 80% (v/v) ethanol on the tools (tweezers and small scissors) to be used for fetus handling. Transfer a binocular scope to a Class II biosafety cabinet.</li>
</ol>
2. Culture of Fetus and Newborn Tibia and Femur
<ol>
	<li>Cull the pregnant mouse through cervical dislocation at the desired gestational stage (ranging from E14.5 to E18.5). If newborn pups are used, remove them from the mother one by one and cull by decapitation.</li>
	<li>Place the mouse on her back and sterilize the abdominal region by spraying 80% (v/v) ethanol on its surface.</li>
	<li>Cut the skin and the abdominal muscle with small scissors to access the uterine horns.</li>
	<li>Extract the uterus from the abdominal cavity with the help of tweezers and small scissors, removing the mesometrium and cutting the base of the horns. Place the uterus in a 60 mm Petri dish with ice-cold dissection medium and keep the culture dish on ice during the whole procedure.</li>
	<li>Transfer the Petri dish with the uterus to the biosafety cabinet and work there from now on.</li>
	<li>Separate individual fetuses with scissors by cutting between the sacs.</li>
	<li>Transfer individual sac under a dissection stereomicroscope in a clean 60 mm dish with dissection medium and open them up with tweezers to separate the fetuses from the placentas and clean them from membranes. 
	NOTE: Work with one embryo at a time, while keeping the rest on ice.</li>
	<li>Decapitate the fetuses and transfer the body to a clean new 60 mm dish with a 1 mL cut sterile pipette.</li>
	<li>Remove the skin of the fetuses or pups with tweezers starting from the back and peeling it out till the toes.</li>
	<li>Separate the hindlimbs from the body by cutting with the tweezers close to the spine and transfer them to a clean dish with ice-cold dissection medium.</li>
	<li>Separate the tibia from the femur with tweezers by carefully introducing them between the surface cartilage of distal femur and proximal tibia.</li>
	<li>Remove the hip bones from the proximal femur and the calcaneus bone and the fibula from the tibia.</li>
	<li>Carefully remove the soft tissue from the femur and the tibia by nipping and pulling it off. 
	NOTE: It is important to remove as much soft tissue as possible, taking special care in removing the tissue that connects the two cartilage poles, but avoiding damaging the cartilage, the perichondrium, and the bones.</li>
	<li>Place the four bones (left and right tibias and femurs) in the first well of the 24-well plate with a plastic 1 mL sterile pipette. Alternatively, to compare the effect of different treatments on left and right limbs, place contralateral limbs in different wells. 
	NOTE: Extra care should be taken when the bones are transferred to the wells, as they can easily stick to the pipette.</li>
	<li>Proceed the same way with as many fetuses as necessary. 
	NOTE: Change the dish with the dissection medium as soon as it gets too clouded, as it is important to see clearly the dissected bones.</li>
	<li>When all the desired bones are transferred to the wells, remove the dissection medium with a plastic 1 mL sterile pipette and take extra care not to aspirate the bones.
	<ol>
		<li>Depending on the purpose of experiment, pictures can be taken of the bones before removing the dissection medium, as timepoint zero of the experiment. Take pictures with a microscope attached to a digital camera and annotate the exposure and scale used. To ensure easy and reliable measurements, take pictures with good contrast to distinguish the mineralized part.</li>
	</ol>
	</li>
	<li>Add 1 mL of culture medium to each well. If any treatment is intended on the bones (doxycycline, tamoxifen, growth factors, etc.), it should be added now.</li>
	<li>To observe the effect of growth inhibition in the culture conditions, treat the left tibias with retinoic acid (RA, 500 nM), while incubating the right tibias with an equivalent volume of vehicle (dimethyl sulfoxide [DMSO], final concentration 0.1%) as a control.</li>
	<li>Leave the bones to grow for two days or more in a cell culture incubator under standard cell culture conditions (at 37 &#176;C in a 5% CO2 incubator).</li>
	<li>To assess proliferation, add 5-ethynyl-2&#8217;-deoxyuridine (EdU) or 5-bromo-2&#8217;-deoxyuridine (BrdU) to the medium at a final concentration of 10 &#181;M 1&#8722;2 h before fixation. 
	NOTE: The stock concentration of EdU is 20 mM. 
	CAUTION: EdU and BrdU are thymidine analogues and can be toxic and mutagenic.</li>
	<li>Thaw 4% paraformaldehyde (PFA) and fix the bones by immersion in PFA in individual 2 mL tubes. 
	CAUTION: PFA is toxic and designated as a probable human carcinogen. Avoid breathing paraformaldehyde powder and vapors. EdU and BrdU are thymidine analogues and can be toxic and mutagenic.</li>
	<li>After a brief 10 min fixation in PFA at room temperature, transfer bones to PBS for picture acquisition at final timepoint. Then place bones back into PFA for overnight fixing at 4 &#176;C.</li>
	<li>After fixation bones can be processed for desired downstream applications.</li>
</ol>
3. Measurement and Analysis of the Full Length of the Bone and of the Mineralized Region
<ol>
	<li>Use an image editing software to measure the length of the bones, taking into account the scale of the image. Measure both total length of the bone and the mineralized region. Start the measurements from the first dark cells at one end until the last ones at the other end. 
	NOTE: The mineralized region is characterized by the darker color and is easily distinguished from the cartilage.</li>
	<li>To calculate the growth rate, defined as the average increase in length per day, divide the difference between the final length of the bone and the initial one by the number of days in culture.</li>
</ol>

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The authors have nothing to disclose.

Bone ex vivo culture methods have been used for some time to assess the biology of bone growth28, but have been seldom applied to murine long bones. With the development of imaging techniques, ex vivo bone culture offers an attractive way to study bone growth in real time in a setting closely resembling the in vivo conditions. In this scenario, it is important to define the conditions in which the growth of long bones is comparable to their growth in vivo.
In the presen...

Organ growth has to be tightly tuned to prevent the appearance of growth disorders, and involves the regulation of multiple cell types, molecular pathways and crosstalk among different parts of the body. Imaging techniques are essential to address the changes occurring over time in a growing embryo, both in normal conditions, as well as after a perturbation is induced in the system. Embryos with intrauterine development, such as the widely used rodent models, present an additional challenge for live imaging and drug treatment, which can be partially overcome by using ex vivo culture techniques. To successfully recapitulate the in vivo processes and obtain meaningful results, it becomes crucial to find the right culturing conditions for each organ or tissue.
Most bones of the mammalian skeleton grow through endochondral ossification, where the embryonic cartilage (composed of cells called chondrocytes) drives longitudinal growth and is gradually replaced by bone. This process happens at the growth plates, located at the end of the long bones, where three zones can be distinguished: resting, proliferative, and hypertrophic1,2. First, the round progenitor chondrocytes in the resting zone transition into the cycling columnar chondrocytes in the proliferative zone. During the next stage of differentiation, these chondrocytes become hypertrophic and start secreting type X collagen. Hypertrophic chondrocytes orchestrate the subsequent steps of ossification: they secrete key signaling molecules, such as connective tissue growth factor, bone morphogenetic proteins and Indian hedgehog, and direct the mineralization of the matrix, recruit blood vessels to the central part of the bone, and, upon apoptosis, allow osteoblasts (bone-forming cells) to invade the matrix to form the primary ossification center3,4. The mineralized matrix facilitates the penetration of blood vessels through which osteoblasts migrate to replace this degraded cartilage with a bone matrix5. Most osteoblasts invade the cartilage matrix from the perichondrium, a fibrous layer that wraps the cartilage6. Alternatively, a proportion of hypertrophic chondrocytes are able to survive and transdifferentiate to osteoblasts7,8,9. The final length of the bone is due to the accumulated growth of the transient cartilage, whose growth rate in turn depends on the number and size of the hypertrophic chondrocytes, and their matrix production10. Additionally, it was recently shown that the duration of the last hypertrophy phase correlates with the final length of the bone11. Therefore, tight regulation of the proliferation and differentiation of these cells is required to ensure proper bone size.
Despite of the substantial knowledge acquired over the years on the organization and development of the growth plates, most of these conclusions are based on the observation of fixed histological sections. Tissue sectioning provides valuable information about this process, but can be ridden with technical artifacts, so it cannot be always reliably used to estimate morphological or size changes between different stages. Additionally, as bone growth is a dynamic process, the static two-dimensional (2D) images offer a limited insight into the movement of the cells in the growth plate, while time-lapse imaging on live tissue could offer valuable information on the behavior of the chondrocytes in the growth plate.
All these limitations can be potentially resolved using ex vivo bone cultures. While bone culture protocols have been developed some time ago, they were limitedly applied to murine long bones. Most of the studies use chick bones due to the technical advantages offered by the chick model12,13. Organotypic cultures (air/liquid interface) were applied to chick embryonic femurs, which were maintained in culture for 10 days14. The sophisticated genetic tools available in mouse make this model very appealing to be used in ex vivo bone culture. The studies that used mice to look into bone growth worked mostly with metatarsal bones15, probably due to their small size and greater numbers obtained per embryo16. Although traditionally considered long bones, metatarsi enter senescence (characterized by reduced proliferation and involution of the growth plate17) earlier than other long bones in vivo, and therefore their continuous growth ex vivo does not really recapitulate the in vivo process. For the purposes of this article, we will use the term long bones for bones from the proximal and intermediate limb regions. Several previous studies used long murine bones, such as tibia, in ex vivo cultures and observed a substantial growth of the cartilage but little ossification18. We also used tibial cultures recently, mainly to study chondrocyte dynamics19. Other studies used femoral heads from young mice20 or only the distal part of the femur for culture21. Some more recent works successfully combine the ex vivo culture of full bones with time-lapse imaging to acquire three-dimensional (3D) movies of chondrocytes in living mouse tissue22,23. The authors managed to observe previously unnoticed events in the rearrangement of chondrocytes to the proliferative zone23 in a good example of the potential application of bone ex vivo culture. The alternative, i.e., analyzing static images, requires indirect and complex techniques. This was exemplified by a recent study assessing the importance of transversally-oriented clones for cartilage growth, where genetic tracing with multicolor reporter mouse strains coupled with mathematical modeling were used24. Therefore, ex vivo culture might help gain insight into dynamic processes in a faster and more straightforward way.
Here, we present a method for murine long bones culture, which can be combined with different molecular treatments and/or with time-lapse live imaging. This protocol adapts the methods used in previous reports15,18,25, but addresses some additional issues and focuses on long bones such as the tibia, rather than metatarsal bones. Finally, it explores the potential of using statistically powerful paired comparisons by culturing left and right bones separately in the presence of different substances.

<table><tbody><tr><td>5-Ethynyl-2&#039;-deoxyuridine</td><td>Santa Cruz</td><td>CAS 61135-33-9</td><td></td></tr><tr><td>5-Bromo-2&amp;prime;-deoxyuridine</td><td>Sigma</td><td>B5002</td><td></td></tr><tr><td>50 mL Conical Centrifuge Tubes</td><td>Falcon</td><td>352070</td><td></td></tr><tr><td>60 mm TC-treated Center Well Organ Culture Dish, 20/Pack, 500/Case, Sterile</td><td>Falcon</td><td>353037</td><td></td></tr><tr><td>Adobe Photoshop</td><td>Adobe</td><td>CS4</td><td></td></tr><tr><td>Ascorbic acid</td><td>Sigma</td><td>A92902</td><td></td></tr><tr><td>Base unit for the scope</td><td>Zeiss</td><td>435425-9100-000</td><td></td></tr><tr><td>Betaglycerophosphate</td><td>Sigma</td><td>G9422</td><td></td></tr><tr><td>Binocular scope</td><td>Zeiss</td><td>STEMI-2000</td><td></td></tr><tr><td>Bovine Serum Albumin (BSA) fraction v</td><td>Roche/Sigma</td><td>10735086001</td><td></td></tr><tr><td>DigiRetina 500 camera</td><td>Aunet</td><td></td><td></td></tr><tr><td>Dissection kit</td><td>Cumper Robbins</td><td>PFS00034</td><td></td></tr><tr><td>DMEM</td><td>Gibco</td><td>11960044</td><td></td></tr><tr><td>DMSO</td><td>Sigma</td><td>D8418</td><td></td></tr><tr><td>Eppendorf 2 mL tubes</td><td>Eppendorf</td><td>0030120094</td><td></td></tr><tr><td>Ethanol 96%</td><td>Merk</td><td>159010</td><td></td></tr><tr><td>Forceps Dumont#5 Inox08</td><td>Fine Science Tools</td><td>T05811</td><td></td></tr><tr><td>Heracell 150 CO&lt;sub&gt;2&lt;/sub&gt; incubator</td><td>Thermo Fisher</td><td>51026282</td><td></td></tr><tr><td>Minimum Essential Medium Eagle</td><td>Sigma</td><td>M2279</td><td></td></tr><tr><td>Multiwell 24 well</td><td>Falcon</td><td>353047</td><td></td></tr><tr><td>Paraformaldehyde</td><td>Sigma</td><td>158127</td><td></td></tr><tr><td>Penicillin-Streptomycin (10,000 U/mL)</td><td>Gibco</td><td>15140-122</td><td></td></tr><tr><td>Plastic pipettes 1 mL Sterile Individually wrapped</td><td>Thermo</td><td>273</td><td></td></tr><tr><td>Syringe filter 0.2 um</td><td>Life Sciences</td><td>PN4612</td><td></td></tr><tr><td>Terumo syringe 20 mL</td><td>Terumo</td><td>DVR-5174</td><td></td></tr><tr><td>Tretinoin (retinoic acid)</td><td>Sigma</td><td>PHR1187-3X</td><td></td></tr><tr><td>Trinocular scope</td><td>Aunet</td><td>AZS400T</td><td></td></tr></tbody></table>

culturing and measuring fetal and newborn murine long bones

Long bones are complex and dynamic structures, which arise from endochondral ossification via a cartilage intermediate. The limited access to healthy human bones makes particularly valuable the use of mammalian models, such as mouse and rat, to look into different aspects of bone growth and homeostasis. Additionally, the development of sophisticated genetic tools in mice allows more complex studies of long bone growth and asks for an expansion of techniques used to study bone growth. Here, we present a detailed protocol for ex vivo murine bone culture, which allows the study of bone and cartilage in a tightly controlled manner while recapitulating most of the in vivo process. The method described allows the culture of a range of bones, including tibia, femur, and metatarsal bones, but we have focused mainly on tibial culture here. Moreover, it can be used in combination with other techniques, such as time-lapse live imaging or drug treatment.

Bone culture can be performed starting from different stages. In Figure 1A-D, a comparison between cultured tibia and freshly extracted ones at equivalent stages is shown. The first observation is that up to two days of culture the size achieved is comparable to the in vivo bone growth for both cartilage and mineralized bone (Figure 1A,B,D). Longer culture periods lead to bigger differences betwe...

Watch this Scientific Journal Video about Culturing and Measuring Fetal and Newborn Murine Long Bones at JoVE.com

Culturing and Measuring Fetal and Newborn Murine Long Bones

Here, we present a method for ex vivo culture of long murine bones at both fetal and newborn stages, suitable for analyzing bone and cartilage development and homeostasis in controlled conditions while recapitulating the in vivo process.

Long bones are complex and dynamic structures, which arise from endochondral ossification via a cartilage intermediate. The limited access to healthy ...

culturing-and-measuring-fetal-and-newborn-murine-long-bones

Universidad San Sebastian

Research

JoVE Journal

Developmental Biology

8.1K Views.  Monash University. Here, we present a method for ex vivo culture of long murine bones at both fetal and newborn stages, suitable for analyzing bone and cartilage development and homeostasis in controlled conditions while recapitulating the in vivo process.

Video: Culturing and Measuring Fetal and Newborn Murine Long Bones

Measuring Bone Remodeling and Recreating the Tumor-Bone Microenvironment Using Calvaria Co-culture and Histomorphometry

Bone is a connective tissue constituted of osteoblasts, osteocytes, and osteoclasts and a mineralized extracellular matrix, which gives it its strength and flexibility and allows it to fulfill its functions. Bone is continuously exposed to a variety of stimuli, which in pathological conditions can deregulate bone remodeling. To study bone biology and diseases and evaluate potential therapeutic agents, it has been necessary to develop in vitro and in vivo models.
This manuscript describes the dissection process and culture conditions of calvarias isolated from neonatal mice to study bone formation and the bone tumor microenvironment. In contrast to in vitro and in vivo models, this ex vivo model allows preservation of the three-dimensional environment of the tissue as well as the cellular diversity of the bone while culturing under defined conditions to simulate the desired microenvironment. Therefore, it is possible to investigate bone remodeling and its mechanisms, as well as the interactions with other cell types, such as the interactions between cancer cells and bone.
The assays reported here use calvarias from 5-7 day old BALB/C mice. The hemi-calvarias obtained are cultured in the presence of insulin, breast cancer cells (MDA-MB-231), or conditioned medium from breast cancer cell cultures. After analysis, it was established that insulin induced new bone formation, while cancer cells and their conditioned medium induced bone resorption. The calvarial model has been successfully used in basic and applied research to study bone development and cancer-induced bone diseases. Overall, it is an excellent option for an easy, informative, and low-cost assay.

The ex vivo culture of bone explants can be a valuable tool for the study of bone physiology and the potential evaluation of drugs in bone remodeling and bone diseases. The presented protocol describes the preparation and culture of calvarias isolated from newborn mice skulls, as well as its applications.

Bone is a connective tissue constituted of osteoblasts, osteocytes, and osteoclasts and a mineralized extracellular matrix, which gives it its strength ...

Cancer Research

Culture of Murine Embryonic Metatarsals: A Physiological Model of Endochondral Ossification

The fundamental process of endochondral ossification is under tight regulation in the healthy individual so as to prevent disturbed development and/or longitudinal bone growth. As such, it is imperative that we further our understanding of the underpinning molecular mechanisms involved in such disorders so as to provide advances towards human and animal patient benefit. The mouse metatarsal organ explant culture is a highly physiological ex vivo model for studying endochondral ossification and bone growth as the growth rate of the bones in culture mimic that observed in vivo. Uniquely, the metatarsal organ culture allows the examination of chondrocytes in different phases of chondrogenesis and maintains cell-cell and cell-matrix interactions, therefore providing conditions closer to the in vivo situation than cells in monolayer or 3D culture. This protocol describes in detail the intricate dissection of embryonic metatarsals from the hind limb of E15 murine embryos and the subsequent analyses that can be performed in order to examine endochondral ossification and longitudinal bone growth.

We present a protocol to dissect and culture embryonic day 15 (E15) murine metatarsal bones. This highly physiological ex vivo model of endochondral ossification provides conditions closer to the in vivo situation than cells in monolayer or 3D culture and is a vital tool for investigating bone growth and development.

The fundamental process of endochondral ossification is under tight regulation in the healthy individual so as to prevent disturbed development and/or ...

A RANKL-based Osteoclast Culture Assay of Mouse Bone Marrow to Investigate the Role of mTORC1 in Osteoclast Formation

Osteoclasts are unique bone-resorbing cells that differentiate from the monocyte/macrophage lineage of bone marrow. Dysfunction of osteoclasts may result in a series of bone metabolic diseases, including osteoporosis. To develop pharmaceutical targets for the prevention of pathological bone mass loss, the mechanisms by which osteoclasts differentiate from precursors must be understood. The ability to isolate and culture a large number of osteoclasts in vitro is critical in order to determine the role of specific genes in osteoclast differentiation. Inactivation of the mammalian/mechanistic target of rapamycin complex 1 (TORC1) in osteoclasts can decrease osteoclast number and increase bone mass; however, the underlying mechanisms require further study. In the present study, a RANKL-based protocol to isolate and culture osteoclasts from mouse bone marrow and to study the influence of mTORC1 inactivation on osteoclast formation is described. This protocol successfully resulted in a large number of giant osteoclasts, typically within one week. Deletion of Raptor impaired osteoclast formation and decreased the activity of secretory tartrate-resistant acid phosphatase, indicating that mTORC1 is critical for osteoclast formation.

This manuscript describes a protocol to isolate and culture osteoclasts in vitro from mouse bone marrow, and to study the role of the mammalian/mechanistic target of rapamycin complex 1 in osteoclast formation.

Osteoclasts are unique bone-resorbing cells that differentiate from the monocyte/macrophage lineage of bone marrow. Dysfunction of osteoclasts may result ...

Isolation, Culture, and Differentiation of Bone Marrow Stromal Cells and Osteoclast Progenitors from Mice

Bone marrow stromal cells (BMSCs) constitute a cell population routinely used as a representation of mesenchymal stem cells in vitro. They reside within the bone marrow cavity alongside hematopoietic stem cells (HSCs), which can give rise to red blood cells, immune progenitors, and osteoclasts. Thus, extractions of cell populations from the bone marrow results in a very heterogeneous mix of various cell populations, which can present challenges in experimental design and confound data interpretation. Several isolation and culture techniques have been developed in laboratories in order to obtain more or less homogeneous populations of BMSCs and HSCs invitro. Here, we present two methods for isolation of BMSCs and HSCs from mouse long bones: one method that yields a mixed population of BMSCs and HSCs and one method that attempts to separate the two cell populations based on adherence. Both methods provide cells suitable for osteogenic and adipogenic differentiation experiments as well as functional assays.

In this article, we present methods to isolate and differentiate bone marrow stromal cells and hematopoietic stem cells from mouse long bones. Two different protocols are presented yielding different cell populations suitable for expansion and differentiation into osteoblasts, adipocytes, and osteoclasts.

Bone marrow stromal cells (BMSCs) constitute a cell population routinely used as a representation of mesenchymal stem cells in vitro. They reside within ...

Murine Hind Limb Long Bone Dissection and Bone Marrow Isolation

Investigation of the bone and the bone marrow is critical in many research fields including basic bone biology, immunology, hematology, cancer metastasis, biomechanics, and stem cell biology. Despite the importance of the bone in healthy and pathologic states, however, it is a largely under-researched organ due to lack of specialized knowledge of bone dissection and bone marrow isolation. Mice are a common model organism to study effects on bone and bone marrow, necessitating a standardized and efficient method for long bone dissection and bone marrow isolation for processing of large experimental cohorts. We describe a straightforward dissection procedure for the removal of the femur and tibia that is suitable for downstream applications, including but not limited to histomorphologic analysis and strength testing. In addition, we outline a rapid procedure for isolation of bone marrow from the long bones via centrifugation with limited handling time, ideal for cell sorting, primary cell culture, or DNA, RNA, and protein extraction. The protocol is streamlined for rapid processing of samples to limit experimental error, and is standardized to minimize user-to-user variability.

Here we present a protocol for the dissection of hind limb long bones (femurs and tibiae) from the laboratory mouse. We further describe a rapid technique for bone marrow isolation from these bones that utilizes centrifugation for removal of bone marrow from the bone marrow space.

Investigation of the bone and the bone marrow is critical in many research fields including basic bone biology, immunology, hematology, cancer metastasis, ...

Immunology and Infection

Biological Compatibility Profile on Biomaterials for Bone Regeneration

Large non-union bone fractures are a significant challenge in orthopedic surgery. Although auto- and allogeneic bone grafts are excellent for healing such lesions, there are potential complications with their use. Thus, material scientists are developing synthetic, biocompatible biomaterials to overcome these problems. In this study, we present a multidisciplinary platform for evaluating biomaterials for bone repair. We combined expertise from bone biology and immunology to develop a platform including in vitro osteoclast (OC) and osteoblast (OB) assays and in vivo mouse models of bone repair, immunogenicity, and allergenicity. We demonstrate how to perform the experiments, summarize the results, and report on biomaterial biocompatibility. In particular, we tested OB viability, differentiation, and mineralization and OC viability and differentiation in the context of &#946;-tricalcium phosphate (&#946;-TCP) disks. We also tested a &#946;-TCP/Collagen (&#946;-TCP/C) foam which is a commercially available material used clinically for bone repair in a critical-sized calvarial bone defect mouse model to determine the effects on the early phase of bone healing. In parallel experiments, we evaluated immune and allergic responses in mice. Our approach generates a biological compatibility profile of a bone biomaterial with a range of parameters necessary for predicting the biocompatibility of biomaterials used for bone healing and repair in patients.

The number of novel biomaterials engineered for repairing large bone lesions is continuously expanding with the aim to enhance bone healing and overcome the complications associated with bone transplantation. Here, we present a multidisciplinary strategy for pre-clinical biocompatibility testing of biomaterials for bone repair.

Large non-union bone fractures are a significant challenge in orthopedic surgery. Although auto- and allogeneic bone grafts are excellent for healing such ...

Bioengineering

Cantilever Bending of Murine Femoral Necks

Fractures in the femoral neck are a common occurrence in individuals with osteoporosis. Many mouse models have been developed to assess disease states and therapies, with biomechanical testing as a primary outcome measure. However, traditional biomechanical testing focuses on torsion or bending tests applied to the midshaft of the long bones. This is not typically the site of high-risk fractures in osteoporotic individuals. Therefore, a biomechanical testing protocol was developed that tests the femoral necks of murine femurs in cantilever bending loading to replicate better the types of fractures experienced by osteoporosis patients. Since the biomechanical outcomes are highly dependent on the flexural loading direction relative to the femoral neck, 3D printed guides were created to maintain a femoral shaft at an angle of 20&#176; relative to the loading direction. The new protocol streamlined the testing by reducing variability in alignment (21.6&#176; &plusmn; 1.5&#176;, COV = 7.1%, n = 20) and improved reproducibility in the measured biomechanical outcomes (average COV = 26.7%). The new approach using the 3D printed guides for reliable specimen alignment improves rigor and reproducibility by reducing the measurement errors due to specimen misalignment, which should minimize sample sizes in mouse studies of osteoporosis.

The present protocol describes the development of a reproducible testing platform for murine femoral necks in a cantilever bending set-up. Custom 3D printed guides were used to consistently and rigidly fix the femurs in optimal alignment.

Fractures in the femoral neck are a common occurrence in individuals with osteoporosis. Many mouse models have been developed to assess disease states and ...

Using Real-Time Cell Metabolic Flux Analyzer to Monitor Osteoblast Bioenergetics

Bone formation by osteoblasts is an essential process for proper bone acquisition and bone turnover to maintain skeletal homeostasis, and ultimately, prevent fracture. In the interest to both optimize peak bone mass and combat various musculoskeletal diseases (i.e., post-menopausal osteoporosis, anorexia nervosa, type 1 and 2 diabetes mellitus), incredible efforts have been made in the field of bone biology to fully characterize osteoblasts throughout their differentiation process. Given the primary role of mature osteoblasts to secrete matrix proteins and mineralization vesicles, it has been noted that these processes take an incredible amount of cellular energy, or adenosine triphosphate (ATP). The overall cellular energy status is often referred to as cellular bioenergetics, and it includes a series of metabolic reactions that sense substrate availability to derive ATP to meet cellular needs. Therefore, the current method details the process of isolating primary, murine bone marrow stromal cells (BMSCs) and monitoring their bioenergetic status using the Real-time cell metabolic flux analyzer at various stages in osteoblast differentiation. Importantly, these data have demonstrated that the metabolic profile changes dramatically throughout osteoblast differentiation. Thus, using this physiologically relevant cell type is required to fully appreciate how a cell's bioenergetic status can regulate the overall function.

Real-time cell metabolic flux assay measures the oxygen consumption rate and extracellular acidification rate, which corresponds to mitochondrial and glycolytic adenosine triphosphate production, using pH and oxygen sensors. The manuscript explains a method to understand the energy status of osteoblasts and the characterization and interpretation of the cellular bioenergetic status.

Bone formation by osteoblasts is an essential process for proper bone acquisition and bone turnover to maintain skeletal homeostasis, and ultimately, ...

Biology

Precise Growth Plate Injury Study Using Trilineage Fluorescent Mice

Tricolor Transgenic Murine Model for Studying Growth Plate Injury

The cartilage growth plates in the bones of children enable limb lengthening but are weak relative to the bone, making them prone to fracturing when bones are overloaded.&#160;Better treatments for severely fractured growth plates are needed because the response to injury is a bony bridge that prematurely fuses the growth plate, leading to stunted and/or crooked limbs. Murine models of growth plate injury are advantageous for mechanistic studies, but&#160;are challenging because it is difficult to visualize and precisely injure the small growth plates in young mice.&#160;We describe here an improved growth plate injury model using transgenic mice with tri-lineage fluorescent reporters for collagen types I, II, and X.
These mice show native fluorescence associated with the three primary substrata of the growth plate. A growth plate injury similar to a Salter-Harris Type II injury is created reproducibly with a bur using the hypertrophic section of the growth plate as a reference during live imaging under fluorescence stereo microscopy guidance. Frozen histology analysis of the native fluorescence simplifies assessing the cellular response to injury. This methodology represents a substantial leap in growth plate injury research, providing a detailed and reproducible method for investigating pathology and evaluating new therapeutic strategies.

This protocol describes an improved mouse model for adolescent bone growth plate injuries. Using transgenic mice with tri-lineage fluorescent reporters for collagen types I, II, and X, the primary matrices associated with three different substrata of the growth plate, injury placement is guided by native fluorescence under the microscope.

The cartilage growth plates in the bones of children enable limb lengthening but are weak relative to the bone, making them prone to fracturing when bones ...

Medicine

Utilizing Low Oxygen Tension to Reduce Hematopoietic Cells in Murine Bone Marrow Stromal Cell Cultures

Currently, there remains a lack of universally accepted markers to prospectively isolate a homogeneous population of skeletal stem cells (SSCs). For this reason, BMSCs, which support hematopoiesis and contribute to all the functions of the skeleton, continue to be widely used to study multipotent mesenchymal progenitors (MMPs) and to infer SSC function. Moreover, given the breadth of transgenic murine models used to study musculoskeletal diseases, the use of BMSCs also serves as a powerful tool to examine the molecular mechanisms regulating MMPs and SSCs. However, common isolation procedures for murine BMSCs result in over 50% of recovered cells being of hematopoietic origins, potentially hindering the interpretation of the data generated during these studies. Here, we describe a method using low oxygen tension or hypoxia for the selective elimination of CD45+ cells in BMSC cultures. Importantly, this method can be easily implemented to not only reduce hemopoietic contaminants but to also enhance the percentage of MMPs and putative SSCs in BMSC cultures.

A routine culture of bone marrow stromal cells (BMSCs) leads to the isolation of heterogeneous cell populations, with many cells being of hematopoietic origins. Here, we describe a method that utilizes low oxygen tension to greatly reduce hematopoietic contaminants in murine BMSC cultures.

Currently, there remains a lack of universally accepted markers to prospectively isolate a homogeneous population of skeletal stem cells (SSCs). For this ...