NASA and the Indiana University (IU) School of Medicine Collaboration

The Integrative Systems Biology Program (ISB) of USACEHR has an ongoing collaboration with NASA and the Indiana University (IU) School of Medicine to comprehend the molecular etiology behind the bone healing and regeneration process, a mission-critical research area common to both Military and Space Science programs.

The majority of modern battlefield wounds occur to the extremities (55%), where the wounds are predominantly open fractures. Large segmental bone defects are caused by mangling extremity injuries sustained by Warfighters (i.e., warfare ballistics; high-energy vehicular trauma), invariably resulting in a prolonged recovery. Fewer than one in five soldiers with segmental bone defects return to active duty, and less than half of these soldiers ever regain civilian employment. Segmental bone defects are equally morbid for civilians, typically brought on by trauma (fractures from accidents and sports) and disease (bone cancer, osteoporosis, infections, and other degenerative diseases). Clinical management of bone defects typically involves bone grafting or lengthening procedures, but these approaches have significant drawbacks, such as infection and prolonged rehabilitation. Long disuse of bones further compromises the healing process and takes a toll on the muscle healing in particular. Clearly, bone defects are anatomically and medically complex injuries that are remarkably difficult to treat.

Surgeons have increasingly utilized synthetic grafts, fabricated from biodegradable scaffolds that deliver therapeutic agents into the bone defects to facilitate healing. The most widely used therapeutic agent is bone morphogenetic protein-2 (BMP-2), which is the only FDA-approved drug for treating bone defects to date. However, with the increasing clinical use of BMP-2, a growing concern of various side effects has emerged. These include postoperative inflammation and associated adverse effects, , as well as inappropriate adipogenesis. Another major concern is that carcinogenesis has been potentially attributed to BMP-2 treatment, and this calls for its immediate replacement. Our academic collaborator, Dr. Melissa Kacena from Indiana University School of Medicine, has proposed a therapeutic alternative to BMP-2. This new drug showed remarkable efficacy in bone healing. In order to extend knowledge of this drug, we plan to test its efficacy in microgravity. Microgravity provides a bone disuse condition that can effectively models the prolonged skeletal unloading condition prescribed by ground rehabilitation programs.

In this context, another important research area is focused on the effects of weightlessness on bone health. Microgravity in spaceflight results in prolonged disuse of bone and muscle. This promotes bone loss and would potentially complicate bone healing and remodeling trajectory. Thus, spaceflight provides an environment for examining drug healing efficacy on disused bone. Some of the major limitations of typical 'on Ground' unloading models, such as restraint related stress, are absent in spaceflight. On the other hand, other extraterrestrial conditions, such as radiation exposure, are likely to also impact the healing process.

The hypotheses of this study is that (i) bone disuse during rehabilitation complicates healing; (ii) microgravity results in bone disuse and, therefore, presents a condition to test the efficacy of drugs during the skeletal unloading condition and (iii) microgravity adversely influences bone regeneration through altered release of growth factors, energy metabolism, and inflammatory response.

Our objectives are to (i) explore the utility of spaceflight as a bone disuse model for military relevant bone regeneration studies; (ii) characterize the underlying molecular mechanisms associated with bone health in spaceflight and (iii) investigate a potential alternative to BMP-2 as a therapeutic intervention for bone defects.

The specific aims are to:

  • Investigate the effect of microgravity on bone loss and healing trajectory in spaceflight
      - Characterize the underlying molecular perturbations during healing of bone defects in spaceflight.
  • Investigate the efficacy of BMP-2 and an alternative treatment for bone defects in spaceflight
      - Characterize and compare the molecular mechanisms of the two drug interventions.

Methods and Design:

Segmental bone defects were induced with the established protocol developed at the Indiana University at the Kennedy Space Center (KSC) laboratory. Baseline measures such as X-rays, radiograph images and in vivo micro-computed tomography, were performed immediately after surgery to ascertain success. The study involved a total of 80 mice, (40 in spaceflight, 40 on ground) with each of these cohorts divided into predesigned groups based on their treatment methods. A healthy set of 10 mice was used as the control group.

Mice went into spaceflight on the SpaceX-10 launch within 24 hours of surgery on March 27, 2017. After approximately one month on board the International Space Station (ISS), astronauts anesthetized, collected blood, and then euthanized the mice. This was followed by removal of the hind limbs and subsequent freezing of the limbs and remaining carcass. Upon return from spaceflight, the mice were shipped to USACEHR for tissue collection. In addition, mice used for control runs were also shipped to USACEHR. USACEHR and IU teams jointly collected 46 tissues from each mouse. The NASA tissue sharing program, which coordinates with many research entities across the globe, has banked 12 of the tissues for each mouse. A total of more than 6,000 individual tissue samples were collected from these mice at USACEHR under ISB supervision from April 27 to May 4, 2017.

This study has captured worldwide attention and numerous media outlets have reported on our work. Following are links to some of the reports.