Radiobiology-Biophysics

Research axes

Mitochondria, the cell powerhouse, are essential in cellular bioenergetics. These organelles are organized as individual components or as tight network in the whole cytoplasm and play a central role in life and death processes, mainly through regulations of energy supply, ions fluxes control and production of essential metabolites. Mitochondria possess their own DNA, maternally inherited, which is maintained by specific proteins, different from the ones that maintain nuclear chromosomes. This mitochondrial DNA (mtDNA) is crucial for mitochondrial functions since it encodes most of the respiratory chain subunits. Damages within mtDNA could result into large pathological consequences in Human. This has been thoroughly documented in several phenomena such as mitochondrial dysfunctions, ageing, cancer. Some of the causes of these damages have been characterized ranging from dysfunctions during replication processes, to deleterious effects of reactive oxygen species. Many questions related to mtDNA stability are still under investigations:

 

How do cells deal with mtDNA disorders such as mutation of DNA maintenance proteins or DNA damage?
 

What is the mitochondrial behavior following X-ray exposure?

Deciphering mtDNA maintenance at the molecular level

In a first axis, we investigate the mtDNA maintenance mechanisms at the molecular level, to better understand how key processes such as replication, transcription, DNA damage repair and compaction are intertwined. Deciphering the interplay between these mechanisms and how they are affected in pathological conditions such as mutation of mtDNA maintenance proteins or overload of mtDNA damage is crucial to understand the basis of mtDNA disorders. 
 

To this aim, we are mainly working in vitro with biophysics single-molecule approaches using microfluidic systems, as well as bulk biochemistry techniques. The two state-of-the-art biophysics techniques we currently use in the lab are acoustic force spectroscopy (AFS) and total internal reflexion fluorescence microscopy (TIRFm). In AFS, a DNA molecule is attached between a polystyrene bead and a glass surface, and the bead can be manipulated with acoustic force, thus applying tension on the nucleic acid molecule. The analysis of force-extension curve of the DNA in absence or presence of recombinant mtDNA maintenance proteins, either wild-type or mutated, gives insight about their binding strength and mode. In TIRFm, the DNA molecules are attached to a glass surface and binding of recombinant mtDNA maintenance proteins labelled with a fluorophore can be directly visualized, in real-time.

Using these approaches, we have for example characterized the protein TFAM, a mitochondrial transcription factor that also plays a critical role in compacting the mtDNA.

Investigating the effects of ionizing radiations at the cellular and mitochondrial levels

 

In a second axis, we investigate the mitochondrial behavior following X-ray exposure. Indeed, exposure of cells to ionizing radiation such as X-rays has many impacts on mitochondria, including, for example, the generation of damage to mitochondrial DNA, activation of energy production, and an increase in mitochondrial fission. We are therefore looking at the effects of X-ray exposure on mitochondrial parameters in human cell lines, either in basal state or after treatment with radiosensibilizing or radioprotective compounds targeting the mitochondria.
 

One goal of our studies is to tackle the current radioresistance challenge in cancer radiotherapies. Indeed, as mitochondrial metabolism is strongly involved in tumorigenesis and in response to ionising irradiations, we investigate the ability of selected compounds to target mitochondria in order to increase radiosensitization processes.

X-ray irradiation can be performed on site, on the PAVIRMA platform.

Collaborations and fundings