Much of Dario’s current work is focused on deciphering how autosomal dominant missense mutations that hyper-activate the LRRK2 protein kinase, predispose humans to Parkinson's disease.

LRRK2 mutations are the most frequent cause of inherited Parkinson's disease, accounting for at least 5% of familial and 1-2% of idiopathic Parkinson’s disease. Parkinson's disease affects an estimated 7 million people worldwide and all attempts to slow the progression of Parkinson’s have thus far failed. 

The cardinal symptoms, shaking, rigidity, and slowness of movement arise from degeneration of dopaminergic neurons located within the substantia nigra. Dementia and behavioural disorders are unfortunately also common in the advanced stages of the disease.

The therapeutic efficacy of LRRK2 inhibitors are currently being tested in clinical trials. They represent one of the most promising therapeutic strategies currently under evaluation for slowing Parkinson’s disease progression, at least for patients possessing LRRK2 mutations.

Dario’s research focuses on understanding how LRRK2 is regulated and functions and how mutations in this protein kinase lead to Parkinson’s disease.

Dario’s lab in collaboration with Matthias Mann showed that LRRK2 phosphorylates a subgroup of Rab proteins (Rab3A/B/C/D, Rab8A/B, Rab10, Rab12, Rab29, Rab35, and Rab43) at a conserved Thr/Ser residue (Thr73 for Rab10), located at the centre of the effector binding switch-II motif [1, 2]. 

Consistent with Rab proteins comprising disease-relevant substrates, Dario's lab have demonstrated that all established pathogenic mutations enhance LRRK2 mediated Rab protein phosphorylation in a manner that is blocked by diverse LRRK2 inhibitors [1-3]. 

LRRK2 phosphorylation of Rab proteins blocks the ability of Rab proteins to interact with cognate effectors such as GDI and guanine nucleotide exchange factors, thereby trapping the phosphorylated Rab protein in the GTP bound state on the membrane where it has been phosphorylated [1, 2]. 

Recent work identified a novel group of effectors including RILPL1, RILPL2, JIP3 and JIP4 that bind preferentially to LRRK2 phosphorylated Rab8 and Rab10 [2, 4]. The work of Dario’s collaborator Suzanne Pfeffer at Stanford University (https://biochemistry.stanford.edu/suzanne-pfeffer) has revealed that LRRK2 phosphorylated Rab8A and Rab10, in complex with RILPL1/RILPL2, inhibit the formation of primary cilia that are implicated in controlling a Sonic hedgehog-driven neuroprotective pathway that could provide a mechanism by which LRRK2 is linked to Parkinson’s disease [5]. 

Dario's research has also revealed that other proteins encoded by genes implicated in Parkinson’s disease including Rab29 [6] and VPS35 [7], regulate phosphorylation of Rab proteins via LRRK2. They have also developed new methods to interrogate LRRK2 pathway activity in cell and mouse models [8] as well as humans [9]. They have recently identified a novel protein phosphatase termed PPM1H that counteracts LRRK2 signaling by selectively dephosphorylating Rab proteins [10].

Key gaps remain in our knowledge of how LRRK2 is regulated and functions that Dario's laboratory is working hard to address. These include understanding how Rab29, VPS35, the immune system, and other Parkinson’s disease genes and risk variants impact on the LRRK2 pathway. Individual functions of the different Rab proteins that are phosphorylated by LRRK2 and the effectors that interact with these after they are phosphorylated need to be identified, as well as establishing how this impacts downstream biology. It will be important to comprehend what are the most relevant Rab substrates that link LRRK2 to Parkinson’s disease. Much evidence suggests that LRRK2 regulates the endo-lysosomes through an unknown pathway that Dario's lab aims to decipher. Understanding how PPM1H and other protein phosphatases control the LRRK2 pathway is also an important question.

For an up to date list of Darion’s publications, click here: Google Scholar

Declaration of Interests

References

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2. Steger, M., Diez, F., Dhekne, H. S., Lis, P., Nirujogi, R. S., Karayel, O., Tonelli, F., Martinez, T. N., Lorentzen, E., Pfeffer, S. R., Alessi, D. R. and Mann, M. (2017) Systematic proteomic analysis of LRRK2-mediated Rab GTPase phosphorylation establishes a connection to ciliogenesis. Elife. 6,e31012 (https://elifesciences.org/articles/31012)
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4. Waschbüsch, D., Purlyte, E., Pal, P., McGrath, E., Alessi, D. R. and Khan, A. R. (2019) Structural basis for Rab8a GTPase recruitment of RILPL2 <em>via</em> LRRK2 phosphorylation of switch 2. bioRxiv, 739813 (https://www.biorxiv.org/content/10.1101/739813v1)
5. Dhekne, H. S., Yanatori, I., Gomez, R. C., Tonelli, F., Diez, F., Schule, B., Steger, M., Alessi, D. R. and Pfeffer, S. R. (2018) A pathway for Parkinson's Disease LRRK2 kinase to block primary cilia and Sonic hedgehog signaling in the brain. Elife. 7, e40202 (https://elifesciences.org/articles/40202)
6. Purlyte, E., Dhekne, H. S., Sarhan, A. R., Gomez, R., Lis, P., Wightman, M., Martinez, T. N., Tonelli, F., Pfeffer, S. R. and Alessi, D. R. (2018) Rab29 activation of the Parkinson's disease-associated LRRK2 kinase. EMBO J. 37, 1-18 (https://www.embopress.org/doi/full/10.15252/embj.201798099)
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8. Lis, P., Burel, S., Steger, M., Mann, M., Brown, F., Diez, F., Tonelli, F., Holton, J. L., Ho, P. W., Ho, S. L., Chou, M. Y., Polinski, N. K., Martinez, T. N., Davies, P. and Alessi, D. R. (2018) Development of phospho-specific Rab protein antibodies to monitor in vivo activity of the LRRK2 Parkinson's disease kinase. Biochem J. 475, 1-22 (https://portlandpress.com/biochemj/article-lookup/doi/10.1042/BCJ20170802)
9. Fan, Y., Howden, A. J. M., Sarhan, A. R., Lis, P., Ito, G., Martinez, T. N., Brockmann, K., Gasser, T., Alessi, D. R. and Sammler, E. M. (2018) Interrogating Parkinson's disease LRRK2 kinase pathway activity by assessing Rab10 phosphorylation in human neutrophils. Biochem J. 475, 23-44 (https://portlandpress.com/biochemj/article-lookup/doi/10.1042/BCJ20170803)
10. Berndsen, K., Lis, P., Yeshaw, W. M., Wawro, P. S., Nirujogi, R. S., Wightman, M., Macartney, T., Dorward, M., Knebel, A., Tonelli, F., Pfeffer, S. R. and Alessi, D. R. (2019) PPM1H phosphatase counteracts LRRK2 signaling by selectively dephosphorylating Rab proteins. Elife.8, e50416 *https://elifesciences.org/articles/50416)