Gene therapy of fractures

Ultrasound, gene therapy and stem cells

Maxim Rousseau, Polit.<url>, based on the materials of Science: Tiny bubbles and a bit of gene therapy heal major bone fractures in pigs

A group of scientists combined gene therapy, stem cells and ultrasound to help heal broken bones. The new method will have to help in severe cases of non-fusion of fractures, when part of the bone is missing or severely damaged. So far, success has been achieved in the experiment on pigs, but the authors of the article published in the journal Science Translational Medicine hope that their method will help people as well.

Usually, when fractures do not heal, doctors use a bone graft, when a fragment of bone tissue is taken from the patient himself, most often from the pelvic bones. But the procedure of taking a fragment is complicated, painful for the patient and increases the overall recovery time. If a bone fragment is taken from a deceased person, then before implantation it is sterilized, being deprived of proteins and other signaling molecules, which makes it difficult to restore the bone.

Scientists have long wanted to learn how to grow a new bone without using a graft. They filled the voids in the bone tissue with collagen, which attracts mesenchymal stem cells that can give rise to osteocytes – bone tissue cells. But mesenchymal stem cells can turn not only into osteocytes, but also into adipose or connective tissue cells. For several years, researchers have been trying to control the transformations of mesenchymal stem cells using bone morphogenetic proteins (BMP) – signaling molecules that are responsible for the formation of bone tissue in the body. The task was complicated by the fact that in order for cellular differentiation to occur, mesenchymal stem cells must be exposed to these proteins for at least a week, and when injected into the fracture site, the proteins disperse in just a few hours.

Then scientists led by Dan Gazit, a specialist in regenerative medicine from Cedars-Sinai Medical Center in Los Angeles, tried to solve this problem by inserting additional copies of genes responsible for the synthesis of bone morphogenetic proteins into the genome of stem cells themselves. Specially modified viruses were used to deliver the desired gene to the cells. But it was not possible to achieve sufficient efficiency. Now they have applied a new way of delivering genes that does not require the use of viruses.

Collagen is injected into the fracture site and waits for a couple of weeks until mesenchymal stem cells populate the tissue. Then they create a solution containing numerous fragments of a DNA molecule with a copy of the gene of interest in gas-filled bubbles enclosed in a thin lipid envelope. After injecting this solution into the fracture site, they direct ultrasound to this area. The ultrasonic pulses of the wand explode microbubbles, punching nanoscale holes in neighboring stem cells, which allows genes to penetrate into the cell.

In 2014, Dan Gazit and his colleagues tested this technique first on non-therapeutic reporter genes in animal experiments. Then they moved on to the genes of two bone morphogenetic proteins: BMP-2 and BMP-7. As a result, the growth of bone tissue increased, but not enough to effectively heal fractures.

Success awaited scientists in experiments with the BMP-6 protein. Using the same procedure, they directed the gene encoding this protein into the mesenchymal stem cells of experimental pigs, in which a one-centimeter-long section of bone was surgically removed.

After eight weeks, the gaps in the pigs' bones were filled with bone tissue and the fracture marks were completely healed. The use of stem cells in combination with gene therapy turned out to be no less effective treatment than transplantation of a fragment of an animal's own bone tissue.

The head of the Center for Plastic and Reconstructive Surgery at the Cedar-Sinai Medical Center, David Kulber, who himself did not participate in this study, calls the results of the experiment of great clinical significance and believes that this technology of stimulating bone growth is really remarkable. Orthopedic scientist from the University of Texas Johnny Huard also believes that the results obtained by Dan Gazit and his colleagues are exactly what is needed for progress in this area. But he also notes that all the experimental animals in the experiment were under a year old. Young animals have more mesenchymal stem cells than old ones, but serious fractures are much more common in elderly patients. Therefore, Johnny Huard suggests, even before the start of clinical trials of the new method on humans, to conduct a series of experiments with adult experimental animals to make sure of its effectiveness.

Portal "Eternal youth" http://vechnayamolodost.ru  18.05.2017