Fitzgerald Lab

PINK1 in Parkinson’s disease

Molecular mechanisms associated with PINK1-Parkinson’s disease

Karan Sharma

Mutations in mitochondrial PTEN-induced putative kinase 1 (PINK1) are a common cause of recessively inherited Parkinson’s disease. However, the mechanisms by which PINK1 can lead to the death of dopaminergic neurons at the substantia nigra remain elusive. To study the disease, we primarily utilize human iPSC-derived dopaminergic neurons cultured in vitro. In addition to observing “the well-defined” canonical mitophagy impairment upon mitochondrial membrane depolarization, we observe metabolic differences in PINK1 loss of function dopaminergic neurons, related to but not limited to the mitochondria. By diving deeper through collaborative multi-omic approaches, i.e., phospho/proteomics and lipidomics, and using these datasets as a reference entry point, we have identified 1. increased cholesterol biosynthesis leading to a build-up of cholesterol in PINK1 knock-out dopaminergic neurons and 2. PINK1 influences dopamine metabolism via the regulation of Tyrosine Hydroxylase, the rate-limiting enzyme for dopamine synthesis. In these projects, we aim to investigate the molecular mechanisms through which PINK1 influences these altered pathways in dopaminergic neurons in the hope of incorporating therapeutics that could in future benefit patients affected by Parkinson’s disease.

This study is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) Research Training Group MOMbrane 654651/GRK2364. MOMbrane aims to investigate the various functions of the mitochondrial outer membrane (MOM) as well as its structure, regulation and biogenesis. The MOMbrane includes ten PhD students in different institutes in Tübingen, each focusing on different aspects of the MOM. The project is carried out in collaboration with partner labs at the Weizmann Institute in Rehovot (Israel). Link to the RTG MOMbrane website. https://www.mombrane.de/

The role of the mitochondrial outer membrane protein Miro1 in Parkinson’s disease

Miro1 function in dopaminergic neurons

Lisa Schwarz (Alumni)

We introduced disease-associated (RHOT1 R272Q) and functional (RHOT1 S156A, and K572R) Miro1/RHOT1 mutations in human iPSCs using gene editing. Healthy and edited iPSCs can then be differentiated into other cell types including neurons (Schwarz, Casadei and Fitzgerald. 2021). We studied the function of Miro1 using these domain and pathway specific mutations by assessing  mitochondrial turnover, mitophagy metabolism and calcium handling (Schwarz and Fitzgerald, 2022, Schwarz et al. 2022).

This study is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) Research Training Group MOMbrane 654651/GRK2364. https://www.mombrane.de/

Miro1 retention at depolarized mitochondria in Parkinson’s disease

Layla Drwesh

Miro1 is a mitochondrial outer membrane protein with atypical two GTPase domains surrounding two central EF-hands (calcium binding domains). Its primary function is to facilitate mitochondrial movement along the microtubules by anchoring mitochondria via adaptor proteins TRAK1/2 to molecular motors. Mitochondrial trafficking is necessary for proper mitochondrial distribution for neuronal health. In addition to mitochondrial motility, Miro1 is heavily implicated in mitochondrial quality control since its depletion is a well-known marker of classical CCCP induced mitophagy. Furthermore, Miro1 interacts with PINK1 (Weihofen et al., 2009) and Parkin (Birsa et al.,2014, Klosowiak et al., 2016) making it an important player in PINK1-Parkin mediated mitochondrial quality control. Miro1 was tied to PD biology following the discovery that LRRK2 promotes Miro1 removal by forming a complex with it (Hsieh et al., 2016). In the same study it was shown for the first time using human fibroblasts from patients that Miro1 degradation is impaired in sporadic PD leading to delayed mitophagy. However, it is still unclear why Miro1 retention following mitochondrial depolarization occurs in some PD cells and not others. To address this gap and better understand the frequency of Miro1 retention in PD, this study aims to measure Miro1's response to mitochondrial depolarization in an independent cohort of PD patients and healthy controls from Tübingen. We utilize available biomaterials such as fibroblasts and blood for this investigation. By validating Miro1 as a robust cellular hallmark for PD, this research will contribute to therapeutic interventions targeting the Miro1-defected phenotype in PD patients.

This project is funded by The Michael J Fox Foundation. MJFF-021967.

BEST - Biomarker evaluation to support clinical translation in schizophrenia

Maria Zarani & Richard Wüst

Psychosis represents a group of diseases signified by enormous heterogeneity. As a consequence, diagnosis, prognosis, and treatment decisions for individual patients are pretty challenging. Within the project, we shall optimize biomarker signatures of patients with high risk for schizophrenia and with defined psychotic disease. This will be achieved by integration of multimodal patient data and subsequent validation of biomarker signatures with the help of patient-derived neurons.

The project is funded through the BMBF (FRN: 01EK2101A) and is carried out in collaboration with four partners; LMU München, ZI Mannheim, NMI Reutlingen and the Hertie Institut for Clinical Brain Research/University Hospital for Psychiatry Tübingen (HIH/UKPP). The validation of mitochondrial readouts will be performed by the HIH/UKPP.

The role of the endosomal-lysosomal system in atypical Parkinson’s disease/Corticobasal syndrome

Katharina Stegen (Alumni), Lisa Schwarz (Alumni) and Julia Fitzgerald

Dysfunction of the endosomal-lysosomal system is a phenomenon that traverses many neurodegenerative diseases including Alzheimer’s diseases, Parkinson’s disease and other rarer neurodegenerative diseases such as progressive supranuclear palsy (PSP) and corticobasal syndrome/ degeneration (CBS/CBD). The endosomal lysosomal system is formed and driven by changes in pH and therefore the ion exchangers that reside in the membranous compartments of the endosomal lumen are critical for correct pH regulation. These exchangers are crucial and major defects often cause severe mental retardation. We are investigating changes to the endolysosomal system related to the sodium hydrogen exchanger 6 (NHE6) that could contribute towards susceptibility to develop neurodegenerative diseases in later life.

This project was funded by the Fortüne program of the Medical Faculty, University of Tübingen. This project is carried out in collaboration with Rejko Krüger (LCSB, Luxembourg and Luxembourg Institute of Health, Luxembourg).

Mitochondrial DNA as a biomarker for Parkinson’s disease

Julia Fitzgerald, Gerrit Machetanz, Anne Grünewald (LCSB, Université du Luxembourg)

Sporadic forms of Parkinson’s disease are the most prevalent but they are difficult to model in the laboratory because there is no known gene mutation that can be introduced or corrected to generate isogenic controls. Statistically, large cohorts are needed to compare healthy individuals with sporadic Parkinson’s disease patients. This poses a problem because culturing patient-derived cell lines in parallel for such large cohorts requires specialist robotics, it is invasive for patients and is also expensive. To overcome this, we are collecting biofluids from a large cohort of Parkinson’s disease patients including sporadic and familial cases where mitochondrial proteins are affected. We will look for changes in mitochondria in these cells to try to identify subgroups of patients that may in future benefit from medicines that target mitochondrial dysfunction.

This project is funded by The Michael J Fox Foundation. MJFF-15744, MJFF-021147