Bone Regeneration Could Be Triggered By A Gene-Activated Matrix

Gene-activated matrix combined with a bone transcriptional factor, Cbfa1 that induce bone formation may be a key advancement in treating bone loss due to periodontal diseases, trauma, or congenital disorders, researchers say.


These results were recently published in Wound Repair and Regeneration, Volume 15, June 2007.


Millions of Americans are afflicted with periodontal diseases that cause destruction of supporting structures of teeth: periodontal ligament (PDL), alveolar bone, and cementum. The process can lead to the loss of attachment, with destruction of the connective tissue matrix and cells. Loosening and eventual loss of teeth may follow. However, despite considerable research efforts in this area, regeneration of the periodontium remains an elusive goal of periodontal therapy. Now good news is that bones that refuse to heal in periodontal diseases may one day be set straight by a gene-activated matrix (GAM) method that enhances bone wound healing according to the new research from a team led by Dr. Qisheng Tu in Chen lab at Tufts University, Boston.


As bone biology researchers already know, Cbfa1, or core-binding factor 1 (Cbfa1), a runt domain transcription factor and its cognate enhancer, also referred to as runt-related transcription factor 2 (Runx2), is identified as a "master gene" required for osteoblastic differentiation and bone formation. Scientists are studying whether Cbfa1 can affect bone regeneration in Cbfa1 deficiency mice. "Compared with wild-type normal mice, bone wound healing was dramatically delayed in Cbfa1 heterozygous mice that miss one copy of cbfa1 gene, characterized by the presence of a small amount of bone formation near the base of the wounds.", said Dr. Qisheng Tu, a scientist of oral biology at Tufts University.


Considering the key role of Cbfa1 in osteoblast differentiation, it can be deduced that Cbfa1 may also play an important role in bone regeneration and may induce an embryonic (regenerative) environment in the injured adult tissues.


To test Cbfa1 as a possible treatment, Dr. Tu and his colleagues worked with 22 mice with periodontal window wounds and femoral defects that were being treated with pain-relieving drugs. The mice were divided into two groups randomly. In group I, bone defects were filled with Cbfa1-GAM with a dose of 1.2 mg plasmid Cbfa1 DNA per wound. Control sponges in group II were comprised of biodegradable, biocompatible collagen without plasmid DNA. Animals were euthanized at 7 and 14 days after the transplantation. Histological analysis and immunohistochemical staining demonstrated that compared with controls, there was increased new bone formation that almost filled the wound defects 14 days after surgery in the Cbfa1-GAM group.


"Our results indicate that the application of Cbfa1-GAM could increase the relative volume of new bone matrix in the defects more than two-fold," said Dr. Qisheng Tu, "Consistently, the data demonstrated that the Cbfa1-GAM significantly up-regulated the expression of Cbfa1 in submandibular defects as early as day 7, and remained at a high level until 14 days after surgery," he added.















However, unique to this study is that the researchers use the GAM method to deliver reagents, which offers an alternative and safer approach to virus-based tissue-engineering applications routinely used before. This method was designed specifically to provide an ideal environment for tissue regeneration and engineering, with which therapeutical genes can be delivered, in a polymer gel matrix, directly to actually injured bone, muscle, and ligament. The GAM could serve as a platform technology for local gene delivery in various tissues and organs. The carrier serves as a scaffold that holds exogenous genes in situ until endogenous wound-healing cells arrive. Up to 50% of available healing repair cells will get gene transfer. Then the cells in the matrix carrier act as local in vivo bioreactors, producing new gene-coding proteins that augment tissue repair and regeneration. GAM implantation at sites of bone injury is associated with retention and expression of the gene of interest for at least 6 weeks. "At day 7, we observed that the GAM porous architecture provided scaffolding to promote cell ingrowth. The local granulation tissue fibroblasts, along with capillaries, migrated into the GAM. The osteogenic progenitor cells within the tissue uptook the local plasmid DNA and transiently expressed the gene. This leads to a significant augment in periodontal bony tissue regeneration," Dr. Tu said.



Although more research is necessary, Cbfa1-GAM treatment could help to give a happy ending to the tragic stories of patients who suffer from bone loss due to periodontal diseases, trauma, or congenital disorders. In addition to studying Cbfa1's role in bone healing, Chen lab is examining the effects of too little or too much Cbfa1 on skeletal development. In the end, they may not need to use much protein to make the GAM effective. Those are things they're looking at now. Clinical trials will be the next step goal in the future.


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