Genetically engineered mice pave the way for personalized medicine in a rare disease

Des souris génétiquement modifiées ouvrent la voie à une médecine personnalisée dans une maladie rareNeurobiology of diseases (2022). DOI: 10.1016/j.nbd.2022.105896″ width=”800″ height=”530″/>

Graphic abstract. Credit: Neurobiology of disease (2022). DOI: 10.1016/j.nbd.2022.105896

An international research team led by Dr. Ana Guadaño at the Alberto Sols Biomedical Research Institute (IIBM, a combined CSIC-UAM center) and involving the Complutense University of Madrid (UCM), used the editing techniques of CRISPR genes to incorporate in mice a mutation of the MCT8 protein responsible for transporting thyroid hormones inside the cell.

Patients with mutations in this protein suffer from Allan-Herndon-Dudley syndrome, a rare sickness which takes the form of severe neurological alterations, in which each patient may reveal a different MCT8 mutation.

This study, published in Neurobiology of diseasedescribes the first avatar model of the disease, i.e. the first animal model with the same genetic alteration as diverse the patients.

“The development of avatar models that faithfully reproduce the alterations of patients carrying this same mutation is the first step towards a targeted therapy. In particular, it lays the foundations to allow us to study the possible ‘genetic repair’ of this mutation animal modeland to assess whether this serves to avoid or reverse the severe neurological alterations that exist in these patients,” explains Carmen Grijota, researcher in the Department of Cell Biology at UCM and IIBM.

Genetically engineered mice pave the way for personalized medicine in a rare disease

Tertiary structure of the MCT8 homology model in the outward-open conformation. (A) The MCT8 structure was predicted using the Robetta server based on the cryo-electron microscopy structure of the outward-open conformation of human MCT1 (PDB: 6LYY). The model was refined to remove residues that were not accurately predicted (>5 Å error). Side (left) and top (right) cartoon views of the MCT8 structure were generated with PyMOL software. Proline 321, the mutated residue in two AHDS patients, is shown as red rods. (B) 3D alignment of MCT8 (light blue) and MCT8-P321L (dark blue) models show a decrease in distance between TMHs in the mutant. The P321L mutation alters the amino acid interaction network in MCT8. Changes in TMH position between the two models are indicated by red arrows (right panel). The MCT8-P321L structure was predicted as described in A. 3D alignment was performed using Pymol software. The P321L mutation alters the amino acid interaction network in MCT8 (left panel). While the P321 residue only interacts with S194 of TMH1, the P321L mutant also interacts with I197 of TMH1 and W431, L434 and V435 of TMH8. Intra-protein interactions of MCT8 and MCT8-P321L were assessed by RINGS 2.0 and predicted amino acid interaction networks were plotted by Pymol. Residues are represented by colored bars. (C) A comparison of the inner pocket structure of MCT8 (yellow) and MCT8-P321L (green) shows a drastic change in the shape and size of the pocket. MCT8 (light blue) and MCT8-P321L (dark blue) are shown as cartoons with the internal cavity shown as a surface in yellow and green respectively. The direction of hormonal influx was represented by blue arrows. The structure of triiodothyronine (T3) was shown as yellow rods. CASTp server and PyMOL were used for substrate binding pocket volume analysis and image generation. Credit: Neurobiology of disease (2022). DOI: 10.1016/j.nbd.2022.105896

Same neurological and motor alterations in avatars and humans

This study used mice carrying the “P321L” mutation. Tests were conducted to study the behavior, anxiety levels, and motor coordination ability of the mice. The animals’ brains were then extracted and specific stains applied to examine and study different types of neurons.

“Finally, extensive computational analysis was conducted to understand how the mutation might affect the structure of the MCT8 carrier, and therefore its transport function. thyroid hormones“, says Víctor Valcárcel, researcher at the IIBM and co-author of the article.

Alterations seen in mice included cerebral hypothyroidism (lack of thyroid hormone in the brain), hyperthyroidism (excess thyroid hormone in other tissues), alterations in the distribution of neurons in the Cerebral cortex, and a reduction in GABAergic neurons. Alterations were also noted in motor coordination, as well as anxious behaviors in mutant mice. All of these results reflect the characteristic alterations of patients with the disease.

According to the scientists, the next steps in their research would involve administering drugs that mimic the activity of thyroid hormones, but do not require MCT8 to enter cells, as they use other different transporters. “The idea is to know if these drugs can reach the brain of the mutant mouse and improve all these alterations”, explains the researcher of the IIBM, Marina Guillén.

More information:
Víctor Valcárcel-Hernández et al, A CRISPR/Cas9-designed avatar mouse model of monocarboxylate transporter 8 deficiency displays distinct neurological alterations, Neurobiology of disease (2022). DOI: 10.1016/j.nbd.2022.105896

Provided by Complutense University of Madrid

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