Human body is built from about 20.000 gene products, mostly proteins. Scientists have gained insight into gene function by analyzing natural gene mutations which often cause inborn genetic disease. In experimental animals scientists can also delete genes and repress their function using various available tools. These approaches have yielded valuable insight into how genes work and how diseases emerge. However, an ability to enhance gene expression-limited to those cells where the gene is naturally expressed - is currently lacking. Such a gene Knock Up technology may be useful to better model and treat human diseases. For example Parkinson's disease PD can rise from duplication or triplication of a gene called alpha-synuclein (aSyn). Scientists have attempted to create animal models for PD by integrating extra copies of aSyn into mouse genome. However, currently this results in aSyn expression in wrong cells and aSyn expression is also devoid of its physiological regulation. As a result, each aSyn transgenic animal line displays a different phenotype or no phenotype at all.
One of the objectives of this project is to create a gene Knock Up tool which allows to increase gene expression limited to naturally expressing cells. We have achieved this via conditional modulation of negative regulation elements in the gene 3' untranslated region or 3’UTR, a sequence in the DNA which controls the stability of the derived RNA copy, a step prior protein synthesis. Using this approach we have created aSyn-cKU animals, which we are currently analyzing for PD. When successful the new PD model may allow discovery of how PD progresses which in turn would allow generation and testing of new treatments. We have also used the cKU approach to create mice where expression of dopaminergic neurotrophic factor GDNF can be increased. GDNF is a secreted protein which supports function of dopamine neurons which die in PD resulting in loss of control over voluntary movement. Injection of GDNF into the brain has been tested in 6 clinical trials in PD, with billions of euros spent to reach that point. However, there are several problems and the conclusion is still elusive. GDNF acts based on chemoattraction. Hence the re-growing dopamine cell extensions – axons - do not grow back to original innervation targets but towards GDNF injection site in the brain where GDNF concentration is the highest, which may contribute to the observed low efficacy and to side effects. Using GDNF cKU mice we were able to ask and answer, does increase in endogenous GDNF expression manifest a better treatment route for PD. Unfortunately, the answer turned out to be a “no”. We found that increase in endogenous GDNF expression before, during or after implementing lesion to midbrain dopamine neurons to induce PD does not influence PD outcome in a meaningful manner, contrary to the expectations. This unexpected result prompted us to ask why there is then GDNF in the first place, what is its function in the striatum, the principle organizing center of dopamine function. We discovered that GDNF levels regulate dopamine levels and that too high GDNF level likely contributes to schizophrenia (SCZ) PMID: 35618883. We have now taken this unexpected discovery further and found that excess GDNF specific response including global gene expression pattern in visible in about 20% of SCZ patients (Runneberger et al submitted).
