Focusing on the mitochondrial expression of TSPO as a marker and promoter of neuroinflammation

Lead Research Organisation: Royal Veterinary College
Department Name: Comparative Biomedical Sciences CBS

Abstract

Accumulation of damaged mitochondria is a hallmark of ageing cells and it is particularly debilitating in post-mitotic cells, making the brain particularly vulnerable. Senescent mitochondria undergo structural and functional alterations that reduce their capacity to generate ATP by oxidative phosphorylation, but increase their production of damaging reactive oxygen species (ROS). Such damaged and dangerous mitochondria are normally removed by mitophagy, but ROS inhibits this defence mechanism (1). The opportunity therefore exists for a positive feedback in which damaged mitochondria accumulate and perpetuate their existence. This deleterious outcome may be especially problematic in microglia, because ROS accumulation promotes their activation, and such activation is widely held to underscore neurodegenerative mechanisms (2). Interestingly, microglial activation involves markedly increased expression of the mitochondrial translocator protein (TSPO) receptor (3-5), and changes in this expression can be monitored in animals and patients using radio-labelled ligands detectable by positron emission tomography (PET), such as ligand [18F]GE-180 developed by our collaborators (6).

Consistent with this background, our most recent data highlight that TSPO overexpression increases cellular oxidative stress and an impairment of the Parkin-mediated selection of mitophagy (7). However, it remains unclear whether the TSPO-mediated inhibition of mitophagy contributes to the activation of the microglia and hence if the impaired clearance of defective mitochondria has a role in sustaining their immune response.
Another uncertainty is whether the redox state of the cell influences the affinity of the radio-ligand to the TSPO. If it does, the interpretation of PET images becomes problematic, not least because the redox state can change with age.
We will explore these problems by adopting in vitro and in vivo protocols to modulate TSPO expression and monitor its contribution to cell mitophagy in microglia, correlating the findings with ROS and anti-ROS signalling mechanisms to examine the binding affinity of TSPO ligands and how this may change with age.
This work will outline a fundamental and regulatory pathway, TSPO-dependent, for the activation of the brain's immune cells by impacting the ontology of mitophagy in microglial adaptation via selection of mitochondria during stress conditions. Proof of concept to improve TSPO targeting for advanced PET imaging of neuroinflammation will be also obtained.

Publications

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publication icon
Singh A (2018) Common Traits Spark the Mitophagy/Xenophagy Interplay. in Frontiers in physiology

Studentship Projects

Project Reference Relationship Related To Start End Student Name
BB/M017192/1 01/10/2015 30/09/2019
1655762 Studentship BB/M017192/1 01/10/2015 30/09/2019 Aarti Singh
 
Description The breadth of results we have produced indicate that TSPO possesses an inherently pro-inflammatory role in microglial cells in response to toxins. The accumulation of TSPO, which is an acknowledged factor in neuroinflammation, takes part in the inflammasome assembly by interacting with NLRP3, a multisubunit complex which allows the release of IL-IB, a key pro-inflammatory cytokine.
We did find that in TSPO null microglial cells the inflammasome is indeed unable to assemble likely due to the high degree of mitochondrial quality control by targeted autophagy. Our work hints at the mechanistic role played by TSPO in the adaptation of mitochondrial function to an inflammatory phenotype. This can pave the way to novel chemical strategies to mark and alleviate innate inflammatory response in the Central Nervous System by targeting TSPO which is found overexpressed in neurodegenerative conditions such as Parkinson's disease, Alzheimer's diseases and Multiple Sclerosis.
Exploitation Route Treating inflammation.
Sectors Healthcare,Pharmaceuticals and Medical Biotechnology

 
Title Generation of TSPO KO microglial cells 
Description CRISPR/Cas9 genome editing was undertaken to induce a short deletion in the TSPO gene, resulting a deleterious frameshift. 
Type Of Material Cell line 
Year Produced 2016 
Provided To Others? No  
Impact The cell line potentiates identifying the role of TSPO in neuroinflammation 
 
Description Biophysical Society Meeting 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact 6000 scientists from a variety of disciplines came together for a 5 day event allowing students to share their research and for senior scientists to share the latest significant scientific findings.
Year(s) Of Engagement Activity 2018
 
Description Early Career Mitochondrial Meeting Poster 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact 50 early career mitochondrial scientists attended this meeting where students and post doctoral scientists gave talks, looked at posters and discussed research activities.
Year(s) Of Engagement Activity 2017
 
Description Invited Talk in conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Invited presentation on mitochondrial regulation of inflammation and new regulatory mechanisms we have unveiled.
Year(s) Of Engagement Activity 2018
 
Description Poster Presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact More than 60 scientists attended this meeting discussing about the latest discoveries in the field of autophagy.
Year(s) Of Engagement Activity 2019
URL https://autophagy-uk.com/2019/01/25/2019-meeting-glasgow/
 
Description Poster Presentation for visiting Students 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact 20-30 prospective postgraduate students visited the campus to see what projects are on offer as well has have been undertaken by other students. At least 4 students have since expressed interest in joining our group.
Year(s) Of Engagement Activity 2018
 
Description Presentation at TSPO meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Professional Practitioners
Results and Impact A small scale TSPO meeting for scientists that work on or in areas related to the protein. Both PIs, Post-docs and PhD students shared their latest findings allowing for much discussion into work that has been done and is currently being done to increase our knowledge of the role of TSPO.
Year(s) Of Engagement Activity 2018