Fibroblast blood vessels
Small molecules instead of viral vectors
Researchers from the Houston Methodist Medical Center, in collaboration with colleagues from Stanford University and the Cincinnati Children's Clinic, have developed a method for converting fibroblasts into endothelial cells lining the inner surface of blood vessels. (Fibroblasts are cells that are contained in large quantities in many tissues of the human body and form scars in areas of damage.)
Other groups of researchers managed to make this transformation, but all earlier methods involved the use of viral particles. The role of viral particles (vectors) was to deliver DNA containing genes of transcription factors to target cells, under the influence of which gene expression changed in such a way that the cells acquired endothelial properties.
According to the head of the study, Dr. John Cooke, this approach is associated with a number of problems. It is very difficult to execute, and the use of viral vectors implies the likelihood of damage to the chromosomes of the target cell.
The new method proposed by the authors is not only technically simpler, but also safer due to the replacement of viral vectors with small molecules. At the first stage, fibroblasts are exposed to small segments of double-stranded RNA, known as poly-I:C (polyinosin:polycytidic acid), which binds to TLR3 (toll-like receptors-3) expressed on their surface. This triggers a reaction in cells that normally develops in response to exposure to the virus. In an earlier paper, the authors demonstrated that this mechanism is the most important step in the process of reprogramming fibroblasts into other types of cells.
After poly-I:C treatment, chromatin is reorganized in fibroblast nuclei, which makes it possible to activate the expression of previously blocked genes. Therefore, the subsequent influence of factors directing the differentiation of immature cells into endothelial cells, including vascular endothelial growth factor (VEGF), allows achieving the desired result.
Fibroblasts (on the left, the nuclei are colored blue) turn into endothelial cells of blood vessels under the influence of small molecules and growth factors. The evidence of transformation is presented in the right image, where the red color indicates the presence of a CD31 protein specific to blood vessel cells.
The authors state that the application of the described approach ensured the conversion of 2% of the treated fibroblasts into endotheliocytes. This indicator is comparable with the results obtained by other research groups using viral vectors and other methods of gene therapy. However, Dr. Cook assures that the preliminary, not yet published, results indicate the possibility of increasing the number of transforming cells by up to 15%.
As part of the second part of the work, human cells transformed using a new method were injected into immunodeficient mice with impaired blood flow to the hind limbs. After some time, the animals recorded the appearance of new functioning blood vessels formed by human cells, and improved blood supply to the extremities.
The authors believe that modifications of their proposed approach can be used to obtain various types of cells of interest from the point of view of regenerative medicine. They also note that before the introduction of this method into clinical practice, it is necessary to conduct carefully planned experiments on animals.
In the near future, they plan to analyze the possibility of using endotheliocytes obtained from fibroblasts to accelerate the healing of ischemic tissue damage by improving blood supply in the affected area.
Article by Nazish Sayed et al. Transdifferentiation of Human Fibroblasts to Endothelial Cells: Role of Innate Immunity is published in the journal Circulation.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of the Houston Methodist:
Reprogrammed cells grow into new blood vessels.
18.11.2014