LRRK2 control of synapse - a delicate balancing exercise

14 December 2012

LRRK2 is a known drug target for the treatment of Parkinson’s. However, it was not clearly understood how LRRK2 regulated synaptic function. This situation has now been remedied by Samer Matta at the Bart De Strooper lab (VIB Center for the Biology of Disease, KU Leuven), who, working with the Patrik Verstreken lab from the same department, demonstrated that this regulation depends on the phosphorylation of endophilin A. This finding has important consequences for the development of LRRK2-based Parkinson’s drugs.

How do LRRK2 mutations cause Parkinson's disease? 
Samer: The most common mutation of LRRK2 (the so-called G2019S mutation) shows increased phosphorylation activity. This disrupts synaptic function, but how it did this was not clear until now. Using genetic and biochemical studies with fruitfly models and mammalian cells, we were able to show that LRRK2 phosphorylates endophilin on S75 in both models. This allows LRRK2 to regulate the function of endophilin A at the synapse, helping it to function correctly.

Why is this finding so important?
Patrik: We were able to identify this new, and physiologically important, substrate on the basis of research with two kinds of flies – flies with LRRK loss of function and flies with Parkinson-related LRRK2-G2019S gain of kinase function. This, remarkably, showed us that both too much (in the case of a G2019S mutation) and too little (in the case of, for example, pharmacological inhibition of LRRK2) endophilin-A phosphorylation has a negative effect on the synapse.

This has important implications for the development of drugs. It is now clear that the current track for drug development, i.e. LRRK2 inhibition, is not right for all cases. Too much inhibition of phosphorylation activity causes the same problems as the ones we are trying to remedy. Given that we now know at least one of proteins that have to be correctly phosphorylated, we can in principle start to investigate which LRRK2 inhibitors inhibit exactly enough and not too much.  An interesting challenge.

Several groups were involved in this research. How did this collaboration work?
Bart: I love these spontaneous collaborations where a very diverse group of experts put their heads together to solve an important problem. We ourselves had hit the wall with our LRRK2 research on mouse models but, thanks to Patrik's hospitality and expertise, Samer Matta discovered a new track. The fact that the fruit fly, in contrast to the mouse, has a phenotype in the synapse, suddenly opened the door to molecular mechanisms. The genetic screen in Patrik's lab identified endophilin as an interactor with LRRK2. Together we then looked at phosphorylation assays processed by our colleagues at Janssen R&D, while Kris Gevaert's team (VIB Department of Medical Protein Research, UGent) worked on identifying the phosphorylation site of endophilin using mass spectroscopy.  We also made use of fruit fly genetics, live imaging, electron microscopy, electrophysiology and biochemistry to achieve our final result. The enthusiasm and open communication of everyone involved was in my mind the most important ingredient in our fantastic multisite collaboration.  Everyone learned from everybody.

Was the collabortaion with Janssen R&D with an eye to the development of new Parkinson’s drugs?
Patrik: This work is primarily important from an LRRK2 biology viewpoint. We now hope to continue developing the endophilin assay so it can be used for drug screening.  Eventually the results will in fact be used to develop drugs that act on the cause of Parkinson's.  But it is my experience that developing drugs is a specialty in itself is and that we must guard against oversimplification and thinking that an article in a top journal will automatically result in a new drug.

Scientific Publication
LRRK2 controls an EndoA phosphorylation cycle in synaptic endocytosis
Matta et al., Neuron 2012

From left to right, top:
Bart De Strooper, Patrik Verstreken
bottom: Raquel da Cunha, Samer Matta

© VIB, 2013