Form and Function of the Mitochondrial Retrograde Response

Project Information

FIRM

Grant agreement ID: 819600

DOI

10.3030/819600

Project closed

EC signature date 13 March 2019

Start date 1 April 2019

End date 31 March 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 450 060,00

EU contribution

€ 1 450 060,00

Coordinated by

QUEEN MARY UNIVERSITY OF LONDON
United Kingdom

Periodic Reporting for period 4 - FIRM (Form and Function of the Mitochondrial Retrograde Response )

Reporting period: 2023-03-01 to 2025-02-28

Summary of the context and overall objectives of the project

The project FIRM is advancing the understanding of the adaptive signalling in mammalian cells. It achieves this by characterising the molecular mechanisms which govern the mitochondrial retrograde response (MRR): the process via which stressed mitochondria retro-communicate with the nucleus. The driving hypothesis of the project is that in mammals the efficient communication between mitochondria and nucleus relies on the formation of contacts which facilitate the redistribution of cholesterol required for the activity of transcription factors.
The cellular reprogramming, driven by the mitochondrial dysfunction, is therefore depending on an axis established by physical tethering: a paradigm shift which advances our understanding of the inter-organelles’ communication.
In detail we are investigating how the accumulation of cholesterol on the outer mitochondrial membrane, which is a signature of modified mitochondrial function, relays stress to the nucleus to command pace and quality of genes transcription.
We are now assessing the molecular nature of the tethering between mitochondria and nucleus by using state-of-the-art techniques in biochemistry and cell imaging merged with novel protocols of analysis.
This effort of research is therefore set to unveil messengers and molecular effectors that define form and function of the mitochondrial retrograde response both in health and diseases.
Specifically, three aims are being addressed:
I. Elucidate the contribution of cholesterol trafficking in mitochondrial retrograde response and associated pathways;
II. Establish if remodelled, mitophagy-defiant mitochondria, associate with the nucleus;
III. Assess the control of abnormal cellular growth via mito-nuclear microdomains;
Completion of the experimental plan will provide the mechanistic knowledge on a novel signalling conduit which stands uncharacterised. This will explain how the communication between mitochondria and nucleus is regulated advancing our understanding of the biology which govern the co-existence of organelles bearing two distinct genomes.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Hitherto we have:
i) corroborated cholesterol as signalling molecule involved in the mitochondrial retrograde response (MRR);
ii) demonstrated that mitochondria form contacts with the nucleus (referred to as Nucleus Associated Mitochondria, NAM) to facilitate MRR;
iii) uncovered that the formation of contacts between mitochondria and nucleus shapes cell signalling;
By combining fluorescent and ultrastructural protocols imaging together with biochemistry and molecular biology methodology we have shown that:
a) the overexpression of the 18kD Translocator Protein (TSPO), which sits on the outer mitochondrial membrane, is required for the physical interaction between the organelles (Figure 1); b) mitochondrial autophagy (mitophagy) negatively regulates MRR preventing the retro-communication with the nucleus.
Furthermore, we showed that c) the formation of NAM relies on the formation of a proteic complex which sees TSPO on mitochondria and AKAP-95 on the nucleus (Figure 2). Along with clarifying the precise topology of the tether we are now profiling the signalling depending on the formation of NAM as well as testing their regulatory role in cell pathology.
The accomplished work consolidates the scientific architecture on which the project stands besides shedding further light on the complex signalling which defines mitochondrial retro-communication with the nucleus.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The ongoing efforts of research are concluding the outstanding objectives of the first two AIMs and developing the experiments of the third one.
We are in this way completing the analysis of the signalling network which defines MRR in mammalian cells and how this prime as well as sustain transition to pathology.
The molecular and pharmacological protocols enrolled to profile cholesterol as messenger in the mitochondrial retro-communication with the nucleus are now complemented by lipidomic analysis.
Omics approaches are also being used to unveil the nature of the proteins involved in the formation of the Nucleus Associated Mitochondria (NAM) and the transcribed set of genes unique to the interaction.
Concomitantly we are scrutinising the domains of Reactive Oxygen Species accumulation and propagation via NAM which impact the homeostasis of Ca2+ in the perinuclear and nuclear regions.
In addition, we are also deciphering the role of the autophagy mediators, their position and redistribution in the facilitation of the interaction between mitochondria and nucleus.
Completion of the analysis will enlighten on the events and dynamics of the mito-nuclear interaction, clarifying their regulatory mechanisms as well as inform on their reversibility following stress.
An exhaustive understanding of the composition and regulation of the mito-nuclear tethering will inform the understanding of the MRR at the basis of abnormal cellular growth currently developed in AIM III.
Signalling and molecular traits linked to mito-muclear conjunction are currently being investigated in cells of the mammary gland at different stages of their pathology with the goal to learn the NAM role in malignant reprogramming. This will be followed by in vitro and in vivo experiments paired to combine measurements of the cellular proliferative capacity with the progression of tumor mass.
All this will complete the analysis of the mito-nuclear communication, detail its metabolic signatures, signalling and regulatory molecules both in cell physiology and pathology.

Figure 2

Figure 1