Making Cartilage to Heal Broken Bones

Gage Crump and his colleagues at the University of Southern California have used the regeneration of zebrafish jawbone to demonstrate that the regeneration of damaged bones does not necessarily require a recapitulation of the same processes that occur during embryonic development. Even though this work used zebrafish as a model system, it may provide some of the underlying principles for treating difficult fractures.

Cartilage production is critical for healing full-thickness bone injuries. In order to understand how this bone-producing cartilage is generated, Crump and his coworkers turned to the genetically malleable and relatively more simple zebrafish system. Zebrafish are vertebrates, like humans, but these animals retain a remarkable capacity to regenerate many of their organs.

When human bones fracture, a small cartilage callus forms that is replaced by bone that bridges small, but not large, gaps in the bone.

In zebrafish, however, the cartilage callus continues to expand and fills even very large gaps in broken bones. This cartilage is replaced throughout the bone by bone. This allows zebrafish to heal even very large fractures.

These days, patients with severe bone fractures may have a surgeon insert metal pins and even plates to help set bone. In more severe cases, bone grafts are used to span gaps, and stem cell-based treatments have been tested in a few clinical trials as well.

About six million people in the U.S. suffer bone breaks each year, and even though most of these patients recover fully, about 300,000 are slow to heal and some may not heal at all. Complications include post-traumatic arthritis, growth abnormalities, delayed union and misaligned union.

Hundreds of professional football players have invested in stem cell treatments to treat injuries, even though the evidence for the efficacy of such treatments is, sometimes, sparse. One report even tells of an NFL linebacker who paid $6,000 for a 1-milliliter vial of donated placenta tissue containing stem cells to be injected into his injured knee.

The bone surface contains thin lining called the “periosteum” that contains a stem cell population that helps maintain bone mass throughout one’s life. In Gage’s laboratory, his team identified a gene called Indian Hedgehog a (IHHa), which is responsible for inducing these periosteal stem cells to switch from bone production to cartilage production. Mutant zebrafish strains that lack the IHHa gene are unable to make cartilage in response to bone injury and heal poorly from bone fractures.


Crump said that an “exciting finding from our work is that, somewhat counterintuitively, cartilage is critical for healing full thickness bone injuries. By understanding how this bone-producing cartilage is generated in the simpler zebrafish model, we hope to find ways to create more of this unique cartilage tissue in patients to better heal their bones.”

According to this paper, which was published in the journal Development, 2016; dev.131292 DOI: 10.1242/dev.121292; instead of the more traditional approach of using bone cells or bone-like materials to heal broken bones, stimulating endogenous bone-based stem cells that make this special kind of fracture-healing cartilage might be a more effective strategy.

How Skeletal Stem Cells form the Blueprint of the Face

A new study from the laboratory of University of Southern California (USC) Stem Cell researcher J Gage Crump, who is at the Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research, has identified the key molecular signals that control the critical timing of the development of the vertebrate face.

Previous work has demonstrated that two molecular signals, in particular the JaggedNotch and Endothelin 1 signaling, are integral for shaping the face. Loss of either of these signals results in facial deformities in zebrafish and humans. This illustrates the essential contribution these signaling pathways make to the development of the face.

Lindsey Barske, a researcher in Crump’s laboratory and her colleagues utilized sophisticated genetic, genomic, and imaging tools to study face formation in zebrafish and showed that the Jagged-Notch and Endothelin 1 pathways work in tandem to control when and where the facial stem cells form face-specific cartilage.

In the lower part of the face, the Endothelin 1 signal accelerates cartilage formation early in development, but in the upper face, the Jagged-Notch signal transduction pathway produces signals that prevent stem cells from making cartilage until later in development.

Barske and her colleagues discovered that these timing differences in facial stem cell activity and facial cartilage production play a major role in making the upper and lower cartilage regions of the face.

The earliest blueprint of the facial skeleton is established by intersecting signals that control when stem cells transform cartilage into bone. It also appears that small tweaks to the timing of these events accounts for the different skull shapes observed in vertebrate animals. Also, small, nuanced changes in facial cartilage production and ossification can also account for the diverse array of facial shapes observed in humans.

This work was published in PLOS Genetics 12(4): e1005967. doi:10.1371/journal.pgen.1005967.

3D Printing of Stem Cells on Bioceramic Molds to Reconstruct Skulls

Skull defects or injuries can be very difficult to repair. However, an Australian research team has pioneered a new technique that can regrow skulls by applying stem cells to a premade scaffold with a 3D printer.

This research team consists of a surgeon, a neurosurgeon, two engineers, and a chief scientist. This five-person team is collaborating with a 3D printing firm that is based in Vienna in order to manufacture exact replicas of bone taken from the skulls of patients.

The protocol for this procedure utilizes stem cells and 3D printers, and is funded by a $1.5 million research grant that is aimed at reducing costs and improving efficiency of the Australian public health service.

The first subjects for this procedure will include patients whose skulls were severely damaged, or had a piece of their skull removed for brain surgery, and require cranial reconstruction. The skull reconstructions will take place at the Royal Perth Hospital. The first trial will commence next year. If this procedure proves to be successful it could reduce the risk of complications and surgical time, and provide massive cost savings.

If a patient has a skull injury or some other skull issue, pieces of skull bone were removed bone and stored it in a freezer for later implantation into the skull. Unfortunately, this procedure often resulted in infection or resorption of the bone. Alternatively, titanium plates can be used but these eventually they degrade, and therefore, are not ideal.

Neurosurgeon Marc Coughlan, who is a member of the five-person research team that developed this procedure, said this protocol represents the first time stem cells have been used on a 3D printed scaffold to regrow bone. “What we’re trying to do is take it one step further and have the ceramic resorb and then be only left with the patient’s bone, which would be exactly the same as having the skull back,” Coughlan told The Australian.

If this procedure proves successful, it could revolutionize cranial reconstruction surgeries. According to health minister Kim Hames, “This project highlights some of the innovative and groundbreaking research that is under way in WA’s public health system, and the commitment of the government to supporting this crucial work.”

We will keep tabs on this clinical trial to determine if it works as well as reported.

Stem Cell Helps for Patients with Head and Mouth Injuries

Craniofacial tissue regeneration, particularly bone regeneration has advanced remarkably in the past decade. In fact, facial bone re-growth with stem cells has proven less invasive and more effective than traditional bone regeneration treatments.

A partnership between researchers at the University of Michigan School of Dentistry, the Michigan Center for Oral Health Research and the Ann Arbor-based Aastrom Biosciences Inc. generated a clinical trial that involved 24 patients whose injuries required jawbone reconstruction.

In this clinical trial, patients received either experimental tissue repair cells or traditional guided bone regeneration therapy. The experimental cells in this trial are under development by Aastrom Biosciences and are called “ixmyelocel-T.” Ixmyelocel-T is a patient-specific stem cell from a patient’s bone marrow. It is a mixture of several different types of bone marrow-based stem cells.

Principle investigator and assistant professor at the U of M School of Dentistry Darnell Kaigler explained his rationale for his clinical trial: In patients with jawbone deficiencies who also have missing teeth, it is very difficult to replace the missing teeth so that they look and function naturally. This technology and approach could potentially by used to restore areas of bone loss so that missing teeth can be replaced with dental implants.”

This treatment is best suited for individuals with large defects. Such defects, that result from trauma, disease, or birth defects are very complex, since they involve several different tissue types (bone, gum, and skin). This makes them very challenging to treat. Since ixmyelocel-T is made from the patient’s own stem cells, it generates something completely living and compatible with the patient’s immune system rather than something man-made.

To date, the results from this trial have been very promising. Six-twelve weeks after treatment, patients in this clinical trial receive dental implants, and those who were treated with tissue repair cells had greater bone density and faster bone repair than those who received the traditional guide bone regeneration therapy. Additionally, the group who had received the tissue replacement therapy required fewer secondary bone grafting upon receiving their implants.

The cells for this therapy were extracted from bone marrow aspirations from the hip. Aastrom uses a proprietary system to process and grow the bone marrow stem cells, but once they were ready, they were placed into various areas of the mouth and jaw.

The next step in this research is to use more clinical trials with larger number of patients. Unfortunately, these stem cell treatments are probably 5-10 years away from FDA approval and regular use.

William Giannobile, who is the director of the Michigan Center for Oral Health Research and also the chair of the U-of-M Department of Periodontics and Oral Medicine, is one of the co-principal investigators on this project.