Researchers have for the primary time characterised a novel molecular mechanism of the early stages of programmed cell death or apoptosis, a process which plays an important role in prevention of cancer.

The study, which is published today (Friday 2nd June 2023) in Science Advances, was led by Dr Luke Clifton on the STFC ISIS Neutron and Muon Source (ISIS) in Oxfordshire, alongside co-lead Professor Gerhard Gröbner on the University of Umeå and partners on the European Spallation Source in Sweden. It’s probably the most recent in a series of research collaborations by this team, investigating the cellular proteins accountable for apoptosis.

Apoptosis is important for human life, and its disruption could cause cancerous cells to grow and never reply to cancer treatment. In healthy cells, it’s regulated by two proteins with opposing roles often known as Bax and Bcl-2.

The soluble Bax protein is accountable for the clearance of old or diseased cells, and when activated, it perforates the cell mitochondrial membrane to form pores that trigger programmed cell death. This could be offset by Bcl-2, which is embedded throughout the mitochondrial membrane, where it acts to stop premature cell death by capturing and sequestering Bax proteins.

In cancerous cells, the survival protein Bcl-2 is overproduced, resulting in uninhibited cell proliferation. While this process has long since been understood to be necessary to the event of cancer nonetheless, the precise role of Bax and the mitochondrial membrane in apoptosis has been unclear until now.

Dr Luke Clifton, STFC ISIS Neutron and Muon Source scientist and co-lead creator, explains: “This work has each advanced our knowledge of fundamental mammalian cell processes and opened exciting possibilities for future research. Understanding what things appear to be when cells work properly is a very important step to understanding what goes unsuitable in cancerous cells and so this might open doors to possible treatments.”

The team used a method often known as neutron reflectometry (conducted using the advanced ISIS Surf and Offspec instruments) which enabled them to check how Bax interacts with lipids within the mitochondrial membrane. This built on their previous studies of membrane-bound Bcl‑2.

Using neutron reflectometry on SURF and OFFSPEC, they were capable of study in real time the best way that the protein interacts with lipids present within the mitochondrial membrane, in the course of the initial stages of apoptosis. By employing deuterium-isotope labeling, they determined for the primary time that when Bax creates pores, it extracts lipids from the mitochondrial membrane to form lipid-Bax clusters on the mitochondrial surface.

Through the use of time-resolved neutron reflectometry together with surface infrared spectroscopy within the ISIS biolab, they were capable of see that this pore creation occurred in two stages. Initial fast adsorption of Bax onto the mitochondrial membrane surface was followed by a slower formation of membrane-destroying pores and Bax-lipid clusters, which occurred concurrently. This slower perforation process occurred on timescales of several hours, comparable to cell death in vivo.

That is the primary time that scientists have found direct evidence of the involvement of mitochondrial lipids during membrane perturbing in cell-death initiated by Bax proteins.

Dr Luke Clifton continues: “So far as we will tell, this mechanism by which Bax initiates cell death is previously unseen. Once we all know more concerning the interplay between Bax and Bcl-2 and the way it pertains to this mechanism, we’ll have a more complete picture of a process that is prime to human life. This work really shows the capabilities of neutron reflectometry in structural studies on membrane biochemistry.”

The finding builds on previous studies by the team on the molecular mechanism of membrane-bound Bcl-2 to tell a more complete understanding of the early stages of apoptosis.

The unique findings here won’t only have a big impact in the sector of apoptosis research but may even open gateways for exploring Bax and its relatives as interesting targets in cancer therapy similar to by tuning up their cell-killing potential.”

Professor Gerhard Gröbner, University of Umeå scientist and co-lead creator

Future research is planned at ISIS to further elucidate the molecular mechanism of apoptosis and particularly, to characterize the interplay between Bax and Bcl-2. It’s hoped that it will yield insights which can open recent avenues of research to proceed to develop our understanding of the cellular processes vital for human life.

Source:

UK Research and Innovation

Journal reference:

Clifton, L. A., et al. (2023) Creation of distinctive Bax-lipid complexes at mitochondrial membrane surfaces drives pore formation to initiate apoptosis. Science Advances. doi.org/10.1126/sciadv.adg7940.