Electric Field Stimulation Enhances Healing of Post-Traumatic Osteoarthritic Cartilage

Injuries to cartilage caused by trauma have almost no ability to heal on their own. These injuries are sufficiently painful and debilitating that they remove men and women members of the military from strenuous combat activities and from many other physical activities that are part of everyday living. Cartilage injuries and the osteoarthritis (OA) that results also affect personnel who have already left military service, as well as their dependents. Our proposed work will use novel techniques to recruit to the site of cartilage damage those cells that have the capacity to heal cartilage injuries. If successful, this approach will ameliorate the initial damage and also prevent the development of OA. To test our strategy, we will experimentally induce OA-like lesions in canine cartilage, both in cultured cartilage pieces called explants and in a model in vivo system, the knee cartilage of dogs. We will then amplify the repair process by using direct current (DC) electric fields (EFs) to recruit cartilage cells (called chondrocytes) to the site of the experimental cartilage wounds. Our approach is based upon extensive data showing that EFs of strengths from 1-10V/cm can induce directed movement (galvanotaxis) in all types of musculoskeletal cells we and others have tested in vitro.

Since chondrocytes native to the cartilage are deficient not only in moving to lesions, but also in the actual maturation and tissue integration necessary to heal cartilage lesions, we will use mesenchymal stem cells from the synovial lining (a.k.a., SDSCs) as cartilage progenitor cells that can be ethically harvested and can enhance the repair of cartilage. We will further amplify the repair process by applying DC EFs that will recruit SDSCs to heal the experimental cartilage lesions in canine cartilage, both in vitro and in vivo. Hence, we hypothesize that galvanotaxis may be a useful tool for promoting the migration of both endogenous cartilage cells and SDSC cartilage progenitor cells to sites of articular cartilage defects and that the recruited cells will promote healing of damage due to OA in individuals exposed to trauma.

Our project consists of two specific aims. First, we will test how effectively EFs can improve the ability of the native cartilage cells to move into the defective area and repair the cartilage there. We will test this both in explants of canine knees, and in knees of living, adult dogs. Second, we will test migration into the defect site and repair capabilities of SDSCs and how EFs may enhance their potential to migrate to the wound site and generate functional cartilage there. The use of DC EFs offers a strategy for helping the cells home to the defect site, and this strategy is a huge improvement over other means of using chemicals for directing cell migration.

Each collaborator on our team offers a unique viewpoint and experience, allowing a unique synergy amenable to testing our novel idea: Dr. Clark Hung, PhD, a biomedical engineer and Dr. Chloë Bulinski, PhD, a cell biologist, have collaborated on mechanotransduction and in vitro motility studies of musculoskeletal cells for a dozen years. Dr. Roy Aaron, MD, an orthopaedic surgeon and clinician-scientist, is a pioneer in the clinical use of EFs for musculoskeletal tissue repair; he has recently collaborated with the Hung/Bulinski team to develop model 3D cell constructs. Dr. James Cook, DVM, PhD, a leader in animal models for OA and cartilage repair, has used his vast experience with the canine model in work with Dr. Hung on cartilage tissue engineering and repair for nearly a decade. Last, the work of Dr. Ruggero Cadossi, MD, CSO of the Italian biotech company IGEA Clinical Biophysics, focuses on electrostimulation for tissue repair and cancer therapy; as a scientific consultant he offers electrode design insights needed for these 3D studies. The collective expertise of our unique team can eventually move galvanotaxis strategies for cartilage repair from the benchtop to the bedside.

Our project is especially innovative as no previous study has used DC EFs to enhance migration of cells to heal cartilage damage nor have EFs been tested as activators of the cellular changes that stem cells have to undergo in order to heal the tissue. Further, our choice of SDSCs as stem cells is an attractive innovation, as SDSCs remain abundant and retain their capacity to carry out repair even in the face of inflammatory cytokines or advanced age of the donor or recipient.

The studies we propose are highly relevant to the Department of Defense for two reasons. First, we directly address OA that can be caused by trauma, excess load-bearing, or genetic defects. Second, many results from the canine model we have chosen for our study will translate directly into therapies for humans; they will also help develop therapies for the >5,000 military dogs in current use in combat and in therapy, as most of these animals are large breeds that are subject to hip dysplasia or injuries from bearing excess weight or from injury.