New insights into mitochondrial quality control

Department name: Neuroscience, Physiology and Pharmacology University College London
Supervisors: Primary: Prof Josef Kittler (UCL) and Dr Nick Brandon (AstraZeneca)

Mitochondria are key organelles essential for ATP generation, calcium buffering and apoptotic signalling. In brain cells with complex morphologies including neurons and astrocytes, mitochondrial trafficking is crucial to match mitochondrial positioning to localised energy and calcium buffering demands. Correct mitochondrial dynamics and quality control systems are essential to maintain a functional mitochondrial network and disruption of these processes has been observed in several neurodegenerative diseases, including Parkinson’s, Alzheimer’s, Motor neuron and Huntington’s diseases (MacAskill et al., 2010; Devine et al., 2015).

Damaged mitochondria can be selectively targeted by several quality-control systems to facilitate their clearance by mitochondrial autophagy (mitophagy). The canonical mitophagic pathway involves the kinase PINK1 (PTEN-induced putative kinase 1) and the ubiquitin ligase parkin. PINK1 accumulates on the outer mitochondrial membrane of damaged mitochondria in its full-length form. It then recruits and phosphorylates parkin from the cytosol which then ubiquitinates multiple substrates on the outer mitochondrial membrane (such as Mfns, TOM20, TOM40 and Miro1/2 amongst others). This serves as a critical initiating step in triggering the mitophagic process (Birsa et al., 2014; Devine et al., 2015). Loss-of-function mutations in parkin and PINK1 are associated with rare recessive forms of Parkinson’s disease, which highlights the critical importance of mitophagy in maintaining neuronal health (Devine et al., 2015).

The initial steps of PINK1/parkin dependent mitophagy are becoming very well understood primarily from work in transformed cell lines. In contrast in primary cells such as neurons and astrocytes the mechanisms of mitochondrial ubiquitination including trafficking and clustering of damaged mitochondria prior to and during mitophagy are far less clear. Interestingly we have also found differences in mitophagy rates in primary neurons versus astrocytes. This suggests there may be key molecular differences in astrocytes versus neurons that could provide important new mechanistic insight into the mitophagy pathway. This also suggests that astrocytes may be an important locus for disrupted mitochondrial quality control in neurological diseases including Parkinson’s disease and a locus for therapeutic intervention.

The project will use a combination of well-established biochemical and imaging assays to further investigate key differences between the mitophagic process in rodent primary neurons and astrocytes. In particular we will compare damage induced Parkin translocation, mitochondrial ubiquitination of key substrates (e.g. Miro) and mitochondrial clustering rates in astrocytes versus neurons and whether activity levels of mitochondrial de-ubiquitinases differ in these two key cell types. This will be combined with state of the art approaches for imaging mitochondrial astrocyte dynamics in situ in brain slices (Stephen et al., 2015) upon mitochondrial damage. The above approaches will then be used to further investigate mitochondrial damage in mouse models of Parkinson’s disease.

Applications

Applicants should send a CV and supporting statement (both in PDF format) to [Email Address Removed] by midnight on Monday 29th February 2016.