Forsøksdyr: Characterization and treatment of PKU mouse models

Godkjenningsdato 18.05.2020

Godkjenningsperiode 18.05.2020-17.05.2024

Phenylketonuria (PKU) is a rare genetic metabolic disease caused by a mutation in the gene for Phenylalanine Hydroxylase (PAH); an enzyme that breaks down the amino acid phenylalanine (phe). Mutated PAH is misfolded and unable to fulfill its role, leading to a neurotoxic build-up of phe in blood and brain that untreated will result in irreversible physical- and mental retardation. Today’s treatment of PKU is a life-long phe-free diet (a diet without proteins), which severely reduces the patient's life quality.

Our group is researching the possibility of treating PKU with pharmacological chaperones (PCs); small molecules that will refold and rescue the misfolded, non-functioning PAH. The refolded PAH will then be able to break down phe, making it possible for the patient to eat a normal diet.
An important tool in this research is the PKU mouse model with the mutation R261Q that was developed in 2016. We are in the process of a detailed characterization, trying to understand how the mutated PAH in this model works and affects the mouse so that we can use it correctly as a model for PKU patients.

The mice will go through several behavioral and motor function tests and a group of mice will be single-stalled in metabolic cages for 48 hours. In the treatment trials with PCs they will be dosed by gavage or tail i.v. and given an i.p. injection, followed by blood samples. Some of the mice will have a pump implanted subcutaneously under general anesthesia or have a tail-catheter inserted and they will receive analgesia after the insertion to relieve any pain. In all procedures, we will work hard to reduce the level of stress and discomfort/pain for the animals.

A fully characterized R261Q mouse model will be an important tool in further research of PKU. If we find a PC that refolds the mutated PAH of this mouse model (increasing its activity and reducing the levels of phenylalanine) this will be a large step towards finding a treatment that will increase the life quality of PKU patients.

To be able to fully characterize the R261Q mouse model we need to compare homozygote mutant to their WT and heterozygote siblings. It will also be fruitful to compare them to a well established PKU mouse model, the Enu1 mouse. We will test the effect of pharmacological chaperones on R261Q mice in treatement trials with 4 groups of 6 mice. There will also be a need for surplus mice (with unwanted genotype) to reach an age above 6 weeks for several reasons; to keep otherwise single males company, for practicing new methods and due to backlog in genotyping.
In total we are applying for 1236 R261Q mice and 248 Enu1 mice.

The PCs are first screened in cells to make sure that the ones that are tested in mice are effective. Power calculations make sure that we are using the correct number of animals in each experiment. Several measures are taken to optimize the wellbeing and welfare of the animals; analgesia, anesthesia, endpoints and environmental enrichment.