Some of the researchers involved are part of the Zika Unicamp Network, created in 2016, after the epidemic in Brazil, to develop research that contributes to tackling the serious impacts caused on public health
Brazilian research published in the magazine Brain, Behaviour, and Immunity unveils one of the mechanisms by which the Zika virus causes neurological complications in adult patients and microcephaly in fetuses. The discovery opens up the possibility for new studies to look for drugs capable of inhibiting the worsening of the disease.
In the work, which was supported by Fapesp, scientists demonstrated a correlation between the neurological complications of Zika and high levels of Gas6, a protein that helps the virus enter cells. They also showed that the main sources of Gas6 in these cases are peripheral monocytes, a group of immune system cells.
In its active form, Gas6 binds to TAM family receptors (Axl, Tyro3 and Mer) and, after entering cells, is capable of repressing the body's inflammatory response, facilitating viral replication and leading to worsening of infection by zika.
“The virus itself induces the expression of Gas6, which appears at a higher level in patients with the severe form of the disease. These levels are linked to the increase in cytokine signaling suppressors [SOCS-1], responsible for blocking type 1 interferon antiviral responses. The more potent this mechanism, the worse the patient's prognosis”, explains professor José Luiz Proença Modena, from the Institute of Biology at the State University of Campinas (IB-Unicamp) and one of the supervisors of the work.
The study had the participation of three groups: the one coordinated by Modena, which analyzed serum samples from patients with Zika, including pregnant women; that of professor Fábio Trindade Maranhão Costa, also from IB-Unicamp; and that of Jean Pierre Schatzmann Peron, from the Department of Immunology of the Institute of Biomedical Sciences of the University of São Paulo (ICB-USP) and the Pasteur-USP Scientific Platform (SPPU), an institute of the Pasteur Network constituted in partnership with the university, which carried out tests on mice.
Some of the researchers are part of the Zika Unicamp Network, created in 2016, after the epidemic in Brazil, to develop research that contributes to combating the serious impacts caused on public health by diseases transmitted by the Aedes aegypti mosquito. It also had scientific cooperation from the A*Star Infectious Diseases Laboratory in Singapore. This partnership has already resulted in other published studies, such as the one that identified a marker for Zika.
“The Zika Network worked as an embryo of this type of partnership, which continues to emerge and expand. It brought together competent people with complementary lines, combining expertise, with positive results. Collaborative activity contributes to the quality of work”, says Costa.
In 2015, the Zika virus became a public health concern, starting in South America and then spreading to more than 94 countries. First discovered in 1947 in Uganda (Africa), it was not considered a threat to human health until outbreaks recorded in the 2000s.
In Brazil, approximately 214 thousand probable cases of Zika were reported in 2016. The following year, there were 17 thousand records, falling to 8 thousand in 2018. From January to May this year, according to the Ministry of Health, there are 2.006 cases probable.
The increase in Zika records has been accompanied by the growth of microcephaly, a rare neurological disorder in which a baby's brain does not fully develop. In 2015 alone, there were more than 2.400 records of microcephaly in the country. Previously, between 2010 and 2014, 781 cases had been reported throughout the period.
The Zika epidemic in Brazil occurred in regions historically endemic for dengue. The two viruses (both from the Flavivirus genus) have the same transmission vector, Aedes Aegypti, and the symptoms of the diseases are also similar (fever, headache, redness in the eyes, joint pain and spots on the body).
Although Zika infection is generally asymptomatic, recent data show the link between the disease and the development of neurological syndromes, such as Guillain-Barré, encephalitis and meningitis in adults, and congenital malformations, such as microcephaly, in newborns. It has been demonstrated that the virus can cross the brain and placental barriers, in this case reaching fetal tissues.
Modena recalls that, for dengue, it had already been shown in the literature that the virus can interact with Gas6 and use this mechanism to enter phagocytes and replicate. And now research has revealed how it works in cases of Zika.
Understanding the path
To correlate Gas6 levels with neurological complications associated with Zika, the researchers analyzed the serum of patients (using an immunoenzymatic test) included in a cross-sectional study carried out between February 2016 and June 2017 in different hospitals in the city of Campinas.
Samples were evaluated from 57 patients with mild disease (called non-neuro), 19 with neurological complications after Zika infection (neuro), 14 with neurological complications but not linked to the disease, and 13 healthy patients. Neuros showed higher levels of Gas6, with an increase in suppressors of cytokine signaling (SOCS-1).
In parallel with these tests on patient samples, the group guided by Peron worked with immunocompetent adult mice, that is, with an immune system capable of fighting the virus (C57BL/6 and SJL strains).
“We inoculated the virus already coated with Gas6 in pregnant animals and in non-pregnant adult animals. In adults, the viral load on the first day after infection was much higher compared to animals that received the virus alone, without Gas6. Which shows that the protein helps with infection. Among the puppies, there was a high number with congenital malformations, they had a smaller head and general size”, says Lilian Gomes de Oliveira, first author of the article together with João Luiz da Silva Filho.
To be able to bind to cellular receptors, Gas6 needs to undergo carboxylation, a chemical reaction that allows interaction with other molecules. The researchers then tested the use of the drug warfarin in vitro and realized that it was able to inhibit or reduce the replication of the virus.
“By deciphering this mechanism we open the possibility of new analyzes that allow drug intervention. We showed that warfarin treatment in cell cultures is effective in inhibiting virus multiplication. We haven’t assessed whether it will work in the clinic, but it is a door that is opening”, says Modena.
To Agência FAPESP, Peron highlights that the results not only contribute to a better understanding of the pathogenesis of Zika infection and its serious outcomes, but also open avenues that can target Gas6 as a therapeutic tool. Peron is currently coordinating a project that studies the immunopathogenesis of COVID-19 in experimental models, also supported by FAPESP.
In total, the article published by the group has 46 authors and received support from FAPESP through several projects (16/00194-8; 17/26170-0, 16/12855-9, 16/21259-0, 18/13866- 0, 17/02402-0, 16/07371-2, 17/11828-0, 17/26908-0, 17/22062-9, 18/13645-3, 20/02159-0, 17/22504-1 and 20/02448- 2).
Read the article Gas6 drives Zika virus-induced neurological complications in humans and congenital syndrome in immunocompetent mice.
original article published on the Agência Fapesp website.
