Nanofusion explodes potential of artificial mitochondria

Artificial mitochondria generated from exosome fusion can create energy that throws a lifeline to damaged cells.

Mitochondria are the body’s powerhouses, tiny energy-generators located in our cells, pumping out energy for growth, repair and all our vital functions. But what happens when the power fails – where’s the battery back-up?

Longevity.Technology: Mitochondria crank out 90% of the energy that keeps you alive and they also aid cell growth, survival and death, help generate hormones, assist in calcium storage for cell signaling and have their own unique DNA to help them perform their specialised functions. There are a number of companies and institutions working hard to create artificial organs, but what if we could create artificial organelles, throw a lifeline to damaged cells from the inside out? Like a power bank that rescues a dying iPhone, exosomes were turned into powerful nanoreactors that reduced cellular damage by reducing ROS toxins and prolonged the life of the cell.

Cell organelles have multiple enzymes that work together to execute important cellular functions. Researchers at the Center for Soft and Living Matter within the Institute for Basic Science (IBS) in South Korea have successfully mimicked these nano spatial compartments to create artificial mitochondria. Publishing in Nature Catalysis, the authors state that this new technology could be used to construct artificial organelles that can supply ATP or other useful molecules to cells in damaged or diseased tissues [1].

This was achieved through reprogramming of ‘exosomes’, which are small vesicles (diameter ~120 nm) that cells use for intercellular signaling. The researchers carried out the experiments using microfluidic droplet reactors, which generated small droplets that were of similar size as typical cells. (diameter ~10 nm) The researchers first aimed to facilitate controlled fusion of these exosomes within the droplets while preventing unwanted fusions.

They accomplished this by tailoring the exosome surfaces with molecules called catechol, which is a chelating agent that forms complexes with metal ions. This was in turn done by attaching the catechol onto antibodies that target specific cell markers, such as CD9. The complex-forming property of catechol allows them to drive fusions between exosomes when they are mixed with metal ions such as Fe3+. The membrane fusion occurs when the catechols on the surfaces bind to the iron and bring the vesicles to close proximity to one another.

Read more on mitochondria from Mike Murphy of MitoQ here.

The researchers tested the effectiveness of this system by loading one type of exosomes with calcein-Co2+ and another with EDTA. When the two vesicles fuse and the contents are mixed, EDTA grabs the Co2+ away from calcein, which then allows the latter to fluoresce.

The team realised they were successful when they detected of the fluorescence signal, and the fusion was further confirmed by the doubling of the measured exosome diameter.

These customised exosomes were then preloaded with different reactants and enzymes, which turned them into biomimetic nano factories. This allows them to produce high-value biomolecules by performing desired biocatalytic transformations in a spatially-confined manner which is not possible using conventional laboratory test tubes.

The next step was to determine exactly how well these mini reactors can be taken up and internalised by the cells. The cells derived from human breast tissues were fed with fused exosome nanoreactors, and their internalisation over the next 48 hours was observed using various markers and a confocal laser scanning microscope (CLSM). It was found that cells were able to take up these customised exosomes and the fused exosomes were able to successfully manufacture fluorescent products even while being inside the cells[1].

Armed with this knowledge, the team sought to create functional artificial mitochondria that are capable of producing energy inside the cells. To achieve this, ATP synthase and bo3 oxidase were reconstituted into the earlier exosomes, which were in turn fused to create nanoreactors that can produce ATP using glucose and dithiothreitol (DTT). It was found that the fused exosomes were capable of penetrating deep into the core part of a solid spheroid tissue and produce ATP in its hypoxic environment. The activities of these simple organelles were accompanied by marked reduction of reactive oxygen species (ROS) generation. In contrast, free enzymes were unable to penetrate inside these tightly packed spheroids cell[1].

“Taken together, our results highlight the potential of these exosomes as nanoreactors in regulating the metabolic activity of cells inside spheroids, and in attenuating cell damage due to hypoxia,” notes CHO Yoon-Kyoung, the corresponding author of the study [2]. It is hoped that further research into such artificial organelles will present a new paradigm in various fields such as disease diagnosis and treatment, biotechnology, medicine, and the environment.