For the first time in humans, Zika syndrome susceptibility linked to genetic background

February 02, 2018

Neural progenitor cells (NPC) derived from congenital Zika syndrome (CZS) affected and non-affected twins show different rates of virus infection and different RNA expression of genes associated to neural development. The expression imbalance happens even before the infection with the Zika virus in vitro. These results confirm the hypothesis of a genetic or epigenetic influence on susceptibility to CZS and microcephaly. The findings were published in Nature Communications on Friday, 2 February 2018.

The researchers, lead by dr. Mayana Zatz and Maria Rita Passos-Bueno - geneticists from the Human Genome and Stem Cell Research Center from the University of São Paulo (USP) -, also concluded that a single gene cannot explain the cases of CSZ development nor the brain resistance to Zika virus.

About 6% to 12% of the babies born from mothers infected with the Zika virus during pregnancy will have the CZS. Why not all of them are affected by the syndrome is yet to be explained. This study shed lights on the genetic components associated to it.

"If the baby has these genetic susceptibility factors, we believe he will not have microcephaly unless he is infected by the Zika virus. Maybe we can identify these people and prioritize them in a future vaccine strategy", says dr. Mayana Zatz.

Twins as a clue to genetic studies

Twins provide unique information to answer whether a certain condition has an environmental or a genetic cause. If genetic factors are determinant to a congenital disease, there must be more concordance between the pair of identical (monozygotic) twin babies than between the non-identical or dizygotic twins. Identical siblings should be more often both affected, than dizygotic twins that will be more likely "discordant" (one affected and one non-affected).

If the environment leads to the condition, the pattern observed in the two siblings of non-identical will be the same as observed in identical twins. It means that either none of the siblings will be affected, or both, or just one of them, independently of being monozygotic or dizygotic.

Search for twins

The study started in 2016, during Zika epidemics in Brazil. Mayana Zatz and her team looked for twins in which at least one baby had microcephaly. They accomplished to get in touch with families from 9 pairs of twins from 6 Brazilian states.

Two pairs were identical twins, with both affected; one pair was non-identical but also had both affected; and 6 pairs were non-identical and discordant - one affected and one unaffected. This first scenario contributed to the hypothesis of genetic influence on Zika infection during fetal development.

Experiments

From these babies, three pairs of non-identical, discordant twins had their blood samples collected and used to generate human induced pluripotent stem cells (hiPSC) - cells that can produce almost any other type of cell. Later, the hiPSC were transformed into neural progenitor cells (NPC) - these can lead to the cells that form the brain and other parts of the central nervous system.

The NPCs were infected with a Brazilian Zika virus strain. After four days, the plaques with cells derived from the affected babies had significanlty less cells than the plaques from the non-affected ones. Analysis of neurospheres - cells grown in 3D structures - showed similar growth impairment from the affected twins' cells. Non-infected cultures from affected and non-affected derived NPCs used as control presented no differences after the same time.

Using a fluorescence technique, researchers observed a larger amount of Zika virus in cells derived from affected babies compared to the cells from the healthy ones. More experiments pointed that the neural progenitor cells from babies with the syndrome produced significantly more viral RNA copies and more viral unities capable of infection. In short, they were more infected and did not proliferate as much as the cells from their protected siblings.

"In the laboratory, the cells mimicked what happened with the babies. Also, the results were the same for the three pairs of twins. We demonstrated that the infection is not random. It reinforces our hypothesis of a genetic component increasing the susceptibility to congenital Zika syndrome", says dr. Zatz.

Mechanisms

In order to identify this possible genetic component, the team analyzed all the gene sequence from 8 pairs of twins and 10 other babies that developed the Zika syndrome as compared to normal controls. The exome analysis did not identify one gene variation capable of determining, alone, the susceptibility to the infection - instead, it excluded this possibility.

The RNA sequencing came next. It allows scientists to measure gene expression - which genes are silenced or which are activated and sending messages to produce proteins in the cell. This is different from the previous DNA sequencing,that shows how genes are but not how they express themselves

The RNA test from the 6 twins indicated a group of genes capable of distinguishing the more susceptible cells from the more resistant ones. The largest alteration occurred with DDIT4L gene, 12.6 times less expressed in the affected cells. Its related protein is an inhibitor of mTor signaling - a pathway involved in cell growth and cell death. Previous studies associated the mTor pathway and Zika virus replication.

The RNA sequencing also detected lower expressions of FOXG1 and LHX2 genes in the cells from babies with CZS. These genes participate in the brain regionalization process - characterized by the development of cerebral areas during fetus growth. FOXG1 has also been linked to congenital brain disorders. The LHX2 gene, 9,6 times less present in affected cells, is responsible for attenuating the Wnt signaling, engaged in neural differentiation.

In conclusion, the results indicate that the development of the Zika syndrome in babies is not aleatory, it depends on neural progenitor cells susceptibility. It is possibly related to variants in several genes or to mechanisms that control gene expression and protein production.
-end-
EMBARGOED: 02-FEB-2018 10:00 London time (GMT) / 05:00 US Eastern Time (ET) 19:00 Japanese time / 21:00 Australian Eastern Time

Discordant congenital Zika syndrome twins show differential in vitro viral susceptibility of neural progenitor cells

Study first authors include Luiz Carlos de Caires Junior, Ernesto Goulart and Uirá Souto Melo, from the Human Genome and Stem Cell Research Center - USP, and Bruno Henrique Silva Araujo, from the Brazilian Biosciences National Laboratory (LNBio). The work was coordinated by Maria Rita Passos-Bueno and Mayana Zatz, from the Human Genome and Stem Cell Research Center - USP.

This study was supported by grants from FAPESP, CNPq and AACD.

For news media only:

Source contact info:


Corresponding author
Mayana Zatz
mayazatz@usp.br
**Interviews can be performed in English, Portuguese and French.

Media Contact:

Brasil
Núcleo de Divulgação Científica da USP
55-11-2648-1422 / 1423

Other countries

Ana Paula Chinelli
Mobile +49 171 114 5483
WhatsApp +55 11 97205-1612
anachinelliusp@gmail.com

Suggested figures to be found in the article

Fig.1 g
Computed tomography scans from two pairs of twins participant in the study show typical abnormalities (second and forth images) associated with congenital Zika syndrome and microcephaly.

Fig.2 h
Neurospheres produced from cells of babies affected by congenital Zika syndrome and later infected with Zika virus grow less than neurospheres from the non-affected. This can be seen by comparing the size of the spheres on the top figures (non-affected - they are larger) with the size of the spheres on the bottom figures (affected - the small spheres are more abundant).

fig .3 e
Cells derived from babies born with the congenital Zika syndrome and later infected with Zika virus (4th column) have larger quantity of virus (red stains) than cells derived from 'healthy' babies (2nd column). Blue stains show cell nuclei. The first and the third column are control groups, not infected with the virus.

University of Sao Paulo Scientific Outreach Unit

Related Brain Articles from Brightsurf:

Glioblastoma nanomedicine crosses into brain in mice, eradicates recurring brain cancer
A new synthetic protein nanoparticle capable of slipping past the nearly impermeable blood-brain barrier in mice could deliver cancer-killing drugs directly to malignant brain tumors, new research from the University of Michigan shows.

Children with asymptomatic brain bleeds as newborns show normal brain development at age 2
A study by UNC researchers finds that neurodevelopmental scores and gray matter volumes at age two years did not differ between children who had MRI-confirmed asymptomatic subdural hemorrhages when they were neonates, compared to children with no history of subdural hemorrhage.

New model of human brain 'conversations' could inform research on brain disease, cognition
A team of Indiana University neuroscientists has built a new model of human brain networks that sheds light on how the brain functions.

Human brain size gene triggers bigger brain in monkeys
Dresden and Japanese researchers show that a human-specific gene causes a larger neocortex in the common marmoset, a non-human primate.

Unique insight into development of the human brain: Model of the early embryonic brain
Stem cell researchers from the University of Copenhagen have designed a model of an early embryonic brain.

An optical brain-to-brain interface supports information exchange for locomotion control
Chinese researchers established an optical BtBI that supports rapid information transmission for precise locomotion control, thus providing a proof-of-principle demonstration of fast BtBI for real-time behavioral control.

Transplanting human nerve cells into a mouse brain reveals how they wire into brain circuits
A team of researchers led by Pierre Vanderhaeghen and Vincent Bonin (VIB-KU Leuven, Université libre de Bruxelles and NERF) showed how human nerve cells can develop at their own pace, and form highly precise connections with the surrounding mouse brain cells.

Brain scans reveal how the human brain compensates when one hemisphere is removed
Researchers studying six adults who had one of their brain hemispheres removed during childhood to reduce epileptic seizures found that the remaining half of the brain formed unusually strong connections between different functional brain networks, which potentially help the body to function as if the brain were intact.

Alcohol byproduct contributes to brain chemistry changes in specific brain regions
Study of mouse models provides clear implications for new targets to treat alcohol use disorder and fetal alcohol syndrome.

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.

Read More: Brain News and Brain Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.