Researchers at the Federal University of Sओo Paulo (Unifesp) have developed a three-dimensional bioprinted model of the brain using mouse cells to study the neurological function of the SARS-CoV-2 virus. In addition, the group managed to create an adapted version of the pathogen capable of infecting rodent nerve cells. The group expects that these two achievements – Described In the magazine Advanced Biology – Help make research on the effects of COVID-19 on the central nervous system cheaper and faster.
“Our proposal was to create three-dimensional bioprinted models that could be used to study the mechanism of virus attack, the action of drugs and other topics. SARS-CoV-2, which infects humans, does not infect mice, until then the alternative was to use genetically modified animals that express human receptors. [a proteína ACE-2, à qual o vírus se liga para invadir as células]. But we wanted an adapted version of the virus specifically for the nerve cells of these animals, “he says. Marimélia Porcionatto Professor and Project Coordinator at Escola Paulista de Medicina (EPM-Unifesp). Funded By FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo).
The work was supported by a team of virologists Juliana Marikato And Luiz Mario Jenini, professors at EPM-Unifesp – the latter too Supported By FAPESP.
The so-called bioinch, created by the group, is a mixture of natural compounds with nerve cells that feed the 3D printer. The model was developed in previous works and allows cells to survive the bioprinting process, migrate into space and interact with each other, as if they were nerve fibers. According to the researchers, the protocol was developed with mouse cells, but uses biocompatible materials that may be adapted for future human cells (agencia.FAPESP.br/37767/).
“Now, in addition to the astrocytes, we have added neurons to the model. Because they are so sensitive, however, these cells were added later, as if they were sown in bioprinted material. Thus, the neurons not only integrated themselves into the model, but also interacted with astrocytes.” He explains. Bruna Alice Gomes de Mello The first author of the work, completed in his time Post doctorate At EPM-Unifesp.
The researchers explain that more neural cell types may be added in the future, increasing the complexity of the model and bringing it closer to the nerve fibers.
Currently, other three-dimensional models are organoids and spheroids, groups of self-organizing cells in laboratory cultures. “Our model has greater fertility than organoids and spheroids. In addition, it can be produced in large quantities”, informs Porcionato.
Adapted virus
Spheroids, structures made up of neural stem cells and also called neurospheres, were important for the development of mouse-adapted SARS-CoV-2. For this they were incubated for seven days with SARS-CoV-2 infecting humans.
Some of the viral particles that survived and were replicated were then isolated and placed in a new culture of neurospheres. The procedure was repeated four times, when enough viruses were found to perform the tests.
As a result, the genetic sequence of the virus showed that it lost mutations compared to those used in the first incubation stage. The adapted coronavirus came even closer to Wuhan’s original strain, which triggered the epidemic.
Vero cell lines, commonly used as models for human infection, were subjected to both normal and adaptive viruses, which showed a reduced ability to infect cells other than mice.
An interesting result obtained in the 3D bioprinted model was that the astrocytes had 30 times more replication capacity than the neurons of the adapted virus, indicating the relevance of these cells to infection of the central nervous system by SARS-CoV-2.
“The pathogen can only be present in the cell, but cannot be replicated at the problem point for the organism. The results show that there are viral particles reproduced and kept outside the cell, which can infect others,” Melo reports.
Additionally, during the transition, researchers observed an increase in the expression of chemokines, the molecules that attract immune system cells. Thanks to their presence, the so-called inflammatory cytokines were reduced.
“This means that our model reproduces what happens in the organism, being the best choice for cells in two-dimensional plates, organoids and spheroids. Can, for example, the microglia and endothelial cells present in the blood-brain barrier, which are located inside the blood vessels of the brain.
With the model, researchers hope to reduce not only the cost of this type of research but also the use of animals in the laboratory. The work was also supported by FAPESP through three other projects (18 / 12605-8, 19 / 01255-9 And ).