Inflammation during pregnancy can cause cleft lip – 06/23/2023 – Science

Researchers from the University of São Paulo (USP) and the University College London, in the United Kingdom, demonstrated in an animal model that cleft lip and palate, a condition also known as cleft lip, is due to the association of two factors: one genetic and the other associated with occurrence of inflammation during pregnancy —in the period of formation and development of the embryo.

In an article published in the journal Nature Communications, the group describes how the gene-environment relationship can cause craniofacial malformation. The study was conducted at the Human Genome and Stem Cell Studies Center (CEGH-CEL), a Fapesp Research, Innovation and Dissemination Center (Cepid) based at the Biosciences Institute (IB-USP).

“Our group has been monitoring families with cases of cleft lip for years and there was a suspicion that, for the malformation to occur, an environmental component would be necessary, in addition to the genetic one. Because, when carrying out the genetic sequencing of these people, we saw that, despite many of them had a mutation in the CDH1 gene, an important portion did not have the malformation. A piece was missing that would fully explain what led to the occurrence of cleft lip”, says Maria Rita Passos-Bueno, CEGH-CEL researcher who coordinated the research .

According to Passos-Bueno, another element that reinforces the hypothesis is that, among the people monitored, there is a large variation in relation to the severity of the cracks. “People with the same genetic mutation may not have a cleft lip, have only an opening in the lip or roof of the mouth, or even have both the lip and roof of the mouth affected”, he says.

The researcher explains that when there is a mutation in one of the alleles of the CDH1 gene (which encodes the E-cadherin protein), the result can be the development of cleft lip and also a type of gastric cancer. The mutation interferes with the migration process of neural crest cells – present in embryonic development and which differentiate to form bones, cartilage and connective tissue of the face, among other cell types.

With impaired neural crest migration during embryonic development, the differentiation process is impaired, which may result in cleft lip.

However, emphasizes Passos-Bueno, this variant alone does not completely explain the hereditary issue of cleft lip. “When both alleles of CDH1 are affected, the embryo dies. When one allele is normal and the other is mutated, there is compatibility with life and, in most cases, there is no malformation. This phenomenon of heredity is called of incomplete penetrance: there is a genetic mutation, but it is not translated into the phenotype”, explains Passos-Bueno.

In the search for the missing piece to assemble the puzzle, the researchers began to investigate any environmental factor that could contribute to the malformation process.

“Data from the population with cleft lip show that obesity, diabetes and other pro-inflammatory conditions such as maternal infection [episódios de febre durante a gestação], are risk factors for a child to be born with clefts. But we needed to show how this relationship took place. The results of our study showed that inflammatory molecules called cytokines [secretadas por células do sistema imune] induce hypermethylation of the CDH1 gene [modificação bioquímica que altera o padrão de expressão do gene]”, says Passos-Bueno.

It is the phenomenon that scientists call epigenetics, that is, biochemical changes in cells caused by environmental stimuli (in this case inflammation) that promote the activation or silencing of genes without causing changes in the genome (mutations).

“The challenge of the study was to show this relationship between genetics and the environment, that is, the factor that leads to the methylation specifically or primarily of the CDH1 gene in a pregnant woman carrying the hereditary mutation who presents some stage of pro-inflammation during pregnancy”, says Lucas Alvizi, who at the time of the research was a Fapesp postdoctoral fellow. Alvizi is currently a researcher at University College London.

It is worth mentioning that methylation is a biochemical modification that consists of the addition of a methyl group to the DNA molecule through the action of enzymes. It is a natural and necessary process for the functioning of the organism, by which the expression of genes is modulated. However, when this process becomes unregulated –as in the case of CDH1 hypermethylation– it can cause cell dysfunction and contribute to the development of diseases and malformations.

In addition to in vitro tests with human cells, the researchers carried out experiments with mice and frogs to prove that inflammation generated hypermethylation in the CDH1 gene. And they proved that the addition of a methyl group to a specific stretch of DNA made the gene transcription process more difficult, resulting in less migration of neural crests.

“We exposed the cells and embryos of mice and frogs with a mutation in one of the alleles of the CDH1 gene to environmental factors, in this case, bacteria particles that induce inflammation. Then we took females with normal copies of the gene and exposed them to the same condition And we observed that only the offspring of the female carriers of the mutation had defects in neural crest migration, which may explain the appearance of the fissure”, reports Alvizi.

Passos-Bueno explains that mutations in the CDH1 gene can also result in a type of hereditary stomach cancer. “Recent works showed that some families had fissures and cancer, however, this is something more rare. In future studies, we intend to investigate the relationship between these two factors [genético e ambiental] with stomach cancer”, he says.

Another future objective of the team is to understand which pro-inflammatory states during pregnancy, associated with the genetic makeup of the embryo, are sufficient to cause cleft lip. This knowledge, in Passos-Bueno’s assessment, can guide actions capable of preventing malformation.

The study Neural crest E-cadherin loss drives cleft lip/palate by epigenetic modulation via pro-inflammatory gene-environment interaction can be read here.