A recent study1 from the University of California, Davis, demonstrates that a biomedical tool can successfully transfer genetic material to alter defective genes in developing fetal brain cells. The device, which has been tested in animals, may be able to halt the growth of genetically based neurodevelopmental diseases, including Angelman syndrome and Rett syndrome, before birth.
“The implications of this tool for treating neurodevelopmental conditions are profound. We can potentially correct genetic anomalies at a foundational level during critical periods of brain development,”
said senior author Aijun Wang, a UC Davis professor of surgery and biomedical engineering. The study was a collaboration between the Wang Lab and the Murthy Lab at UC Berkeley.
The researchers are looking to turn this technology into medicines for genetic problems that can be detected during prenatal testing. The medicines could be administered in the womb to prevent more damage as cells develop and mature.
Messenger RNA Delivery
Proteins are essential for the proper functioning of our body. In certain hereditary situations, genes express (create) more or less protein than the body requires. In such instances, the body may become dysregulated.
The scientists found a way to deliver messenger RNA (mRNA) to cells that will be translated to functional proteins. This delivery method uses a unique lipid nanoparticle (LNP) formulation to carry mRNA.
The objective is to introduce (transfect) mRNA genetic material into the cells. The mRNA then would translate instructions to build proteins.
Lipid Nanoparticles
In a recent Nature Nanotechnology paper, Wang, Murthy and their team described a new LNP formulation to safely and efficiently deliver mRNA. LNPs carrying mRNA need to arrive at the cells, where they will be taken in through a process known as endocytosis. There, the cell breaks the LNP carrier, which allows the mRNA cargo to be released.
“The LNPs developed in this study use a new acid degradable linker that enables the LNPs to rapidly degrade inside of cells. The new linker also enables LNPs to be engineered to have lower toxicity,”
said Niren Murthy, professor of bioengineering at the University of California at Berkeley and co-investigator on this project.
Histological examination of brain sections indicates that the majority of td-Tomato-positive cells are localized within the GE, VZ, and SVZ. Credit: ACS Nano, DOI: 10.1021/acsnano.4c05169
Toxicity and efficiency go hand in hand. If the uptake efficiency is low, researchers will need to use a large number of nanoparticles. This means that multiple dosages or high amounts can result in a toxic immunological response.
“The biggest hurdle to deliver mRNA to the central nervous system so far has been toxicity that leads to inflammation,”
Wang said. The study showed that the LNP method is more efficient at mRNA translation, reducing the need for potentially toxic doses.
Angelman Syndrome Gene
The current paper discusses using LNP technology to deliver Cas9 mRNA to treat central nervous system genetic disorders in utero. The researchers used their method to investigate the gene responsible for Angelman syndrome, a rare neurodevelopmental disorder.
In a genetic condition, damage accumulates during gestation and soon after birth. Research shows that it is more efficient to deliver therapies to the brain cells before the blood-brain barrier in babies is fully formed.
So, the earlier the correction happens, the better. The objective was to halt the disease progression in-utero.
The researchers injected the LNP with the mRNA into the fetal brain’s ventricles in a mouse model. The mRNA translates into CAS9, a protein that works like scissors for gene editing. The produced CAS9 will edit the gene responsible for Angelman syndrome.
“The mRNA is like the Lego manual that has instructions to put the pieces together to form functional proteins. The cell itself has all the pieces to build CAS9. We just have to supply the mRNA sequence, and the cell will take and translate it into proteins,”
Wang explained.
Neurons Transfected
In delivering the mRNA that translated into CAS 9, the study demonstrated that the LNP tool was highly effective. Using tracers, the researchers could see all the neurons that were edited inside the brain.
Their research showed that the brain’s developing neural stem and progenitor cells absorbed the nanoparticles. In the mouse model, nanoparticles caused gene editing in 30% of brain stem cells.
“Transfecting 30% of the whole brain, especially the stem cells, is a big deal. These cells migrate and spread to many places across the brain as the fetus further develops,”
Wang said.
As the fetal development continued, the stem cells proliferated and migrated to form the central nervous system. The study revealed that more than 60% of the neurons in the hippocampus and 40% of neurons in the cortex were transfected.
This is an extremely promising strategy for treating genetic disorders of the central nervous system. When the babies were born, many of the neurons could have been repaired. This means the infant may be born with no symptoms. of the genetic disorder that they were at risk for.
Wang expects to see an even higher percentage of transfected cells in a diseased mouse model.
“Bad neurons with mutation may be killed by the accumulation of disease symptoms and good neurons may stay and proliferate. This could lead to amplified therapeutic efficiency. If we know well enough how cells work, we can leverage this knowledge to cooperate with the naturally occurring pathways in the cell,”
he said.
- Kewa Gao, Hesong Han, Matileen G. Cranick, Sheng Zhao, Shanxiu Xu, Boyan Yin, Hengyue Song, Yibo Hu, Maria T. Clarke, David Wang, Jessica M. Wong, Zehua Zhao, Benjamin W. Burgstone, Diana L. Farmer, Niren Murthy, and Aijun Wang. Widespread Gene Editing in the Brain via In Utero Delivery of mRNA Using Acid-Degradable Lipid Nanoparticles. ACS Nano, DOI: 10.1021/acsnano.4c05169
Top image credit: ACS Nano, DOI: 10.1021/acsnano.4c05169