Study published at the Journal of Neurochemistry reveals that mice infected by the Zika virus during pregnancy and that developed microcephaly have lower activity of an enzyme called Ndel1 – important for the processes of proliferation, differentiation and migration of neurons during embryonic development.
The discovery, already patented, could, in the future, serve as the basis for the development of a biomarker for the early diagnosis of microcephaly in babies infected with Zika in the embryonic period.
“We don't have good biomarkers for early diagnosis [ainda na fase embrionária] of the congenital syndrome associated with Zika infection. The discovery of this relationship between enzymatic activity and brain size is just the beginning of the journey, but it brings a lot of hope. Currently, diagnosis is limited to measuring brain size using ultrasound or tomography. Or it is based on imprecise measurements of the circumference of the skull after birth, when there is little chance of reversing the situation”, he comments. Miriam Hayashi professor at the Department of Pharmacology at Escola Paulista de Medicina (EPM-Unifesp) and research coordinator.
Supported by FAPESP, the investigation was conducted in partnership with the group led by Patrícia Garcez at the Federal University of Rio de Janeiro (UFRJ). The results also showed positive effects of treatment with interferon-beta – a drug used for multiple sclerosis and which has been tested on animals infected with Zika. In experiments with mice, the drug prevented problems in neuronal development, in addition to restoring the activity of the Ndel1 enzyme to levels similar to those in uninfected rodents.
Experimental model
The team analyzed Ndel1 activity in animals infected with the Zika virus. Developed by UFRJ researchers, the experimental model allowed researchers to correlate infection with enzymatic activity and the action of interferon-beta at different stages of embryonic development, thus determining the risks of neurodevelopmental disorders.
“We observed that the infection is associated with a reduction in the activity of the Ndel1 enzyme in the animals' brains. We were able to vary conditions such as, for example, injecting the virus into the ventricle of embryos while still in the mother's womb. We also varied the viral load and the different stages of development of the embryo, which suggests that enzymatic activity has excellent diagnostic power”, he states. João Nani FAPESP scholarship holder and co-author of the study.
The researcher also emphasizes that low enzyme activity does not necessarily mean lower expression or lower protein quantity of the enzyme. “In this study, we suggest that enzymatic activity may be related to two factors: the breakdown of chemicals produced by brain cells [clivagem de neuropeptídeos, questão que ainda precisa ser comprovada em estudos in vivo ], or the ability of this enzyme to interact with other proteins. This is an enzyme with great interaction with important proteins and a decrease in its activity can alter important molecular dynamics”, he says.
Maternal-fetal infection
As Hayashi points out, infection with the Zika virus during pregnancy can cause a series of malformations in the offspring, including microcephaly. However, it is worth highlighting that a set of different factors can culminate in microcephaly or other brain damage during pregnancy, including those triggered by infections such as toxoplasmosis, rubella, cytomegalovirus and herpes simplex, for example.
“Why did we decide to investigate this enzyme in cases of Zika infection? Because it is an excellent model for maternal-fetal infections in general. We know that the infection tends to trigger a series of responses and, during pregnancy, this can cause complications for embryogenesis”, he explains.
The researchers say that the Ndel1 enzyme has been extensively studied, especially due to its importance for neurological development and diseases such as schizophrenia and depression. This is because, highlights Hayashi, it is associated with the formation of complexes in the intracellular cytoskeleton of the neuron and in the proliferation, differentiation and migration of neurons during embryogenesis, which are crucial processes for the formation of the brain.
Examples of this interaction with cytoskeletal proteins have been demonstrated, such as its association with the LIS1 protein, which leads to a disease called lissencephaly, or smooth brain, in which the child is born without cortical gyri. Ndel1 is also one of the main ligands of the most studied schizophrenia susceptibility gene, called DISC1 (Disrupted-in-Schizophrenia 1).
Previous studies have also demonstrated that mutations in the gene NDE1 (which encodes a protein similar to Ndel1, called NDE1) have been associated with severe cases of microcephaly. Experiments with animal models showed that inactivation of the gene NDE1 or the enzyme Ndel1 inhibits neuronal migration at the beginning of embryo formation.
“We also demonstrated significantly lower Ndel1 activity in individuals with a first episode of psychosis without prior treatment with antipsychotics and in medicated patients with chronic schizophrenia. This suggests, but it has not yet been possible to prove, that the activity of the Ndel1 enzyme is a potential biomarker of early stages and resistance to treatment in schizophrenia”, says Hayashi.
The study Assessing the role of Ndel1 oligopeptidase activity in congenital Zika syndrome: Potential predictor of congenital syndrome endophenotype and treatment response can be read at: https://onlinelibrary.wiley.com/doi/abs/10.1111/jnc.15918