Mitochondria are more than just the powerhouse of the cell
By Roxanne Lee, Environmental Science and Policy, 2019
The importance of mitochondria cannot be understated. These organelles, found in large numbers within the cells of most eukaryotic organisms, are responsible for the energy production that keeps cells and the beings they make up functioning. But this isn’t all that they do. As Northeastern University biology professor and researcher Dori Woods succinctly put it, “Mitochondria are more than just the powerhouse of the cell.”
Mitochondria also play key roles in vital functions like apoptosis (cell death) and steroid hormone biosynthesis. Beyond that, researchers suspect that they may also play roles in other cell behaviors and intracellular interactions. For all of their importance, however, there’s much we still don’t know about them.
Technical hurdles have made these ubiquitous organelles traditionally difficult to study, with many techniques for isolation masking the properties of any given individual mitochondrion. At present, most methods employed for the study of mitochondria require that cells are broken up, and mitochondria are scooped up as a result. This method can be rather inexact, as non-mitochondria materials can be incorporated in the sample, like proteins or other intracellular organelles. In addition, even though mitochondria have a variety of shapes and external and internal traits, they are studied in undifferentiated masses numbering in the millions, further increasing the difficulty of studying individual mitochondria and their functions. So, if you want to study pure mitochondria populations in order to determine their effects on cell behavior as Woods and her team wanted to, what can you do?
In order to better study mitochondria, Woods and her colleagues invented a modified version of fluorescence-activated cell sorting (FACS).
In order to better study mitochondria, Woods and her colleagues invented a modified version of fluorescence-activated cell sorting (FACS). FACS is a subset of flow cytometry, a technique that examines the physical and chemical properties of individual cells by flowing them past laser beams and sorting the cells based on the resulting frequencies. As size is one of the greatest barriers to the observation of mitochondria — normal cells range in size from 10 to 25 microns, and mitochondria are usually in the 0.4 to 0.5 micron range — the technique can’t be used on mitochondria as it typically exists. To circumvent this, Woods, in association with BD Biosciences, a global medical technology company, patented a modified version of FACS that downsizes the technology to the nanoscale level so that it is capable of examining mitochondria, refining it to the point of examining these as single organelles. The “cell” in FACS was replaced by mitochondria, thus designating the new technology as “FAMS.”
FAMS sorts and isolates mitochondria without cross-contaminating or fusing them with each other.
The team confirmed the technology performed as intended by using fluorescent dyes to label mitochondria and seeing if the technology could sort intended mitochondria from the rest, which it did. They showed that FAMS could sort mitochondria without damaging them by looking for and finding DNA in the sorted mitochondria, since intact and undamaged mitochondria contain DNA. The team proved the sorted mitochondria were still functional by confirming they could still generate ATP after being given ADP. ADP is a molecule in the body that supplies cells with energy among other functions. One of mitochondria’s key functions is converting ADP into ATP, a complex organic molecule that fuels many processes in the cell.
FAMS sorts and isolates mitochondria without cross-contaminating or fusing them with each other. It not only sorts mitochondria, but sorts it based on characteristics like size, activity, protein make-up, and dynamics. The technology can also separate based on combinations of traits as well as individual ones. Because of FAMS, researchers can evaluate mitochondria subpopulation dynamics within the context of a single cell for the first time. The technology can examine any cell pieces individually, not just mitochondria, opening up the potential for cross-disciplinary utilization.
With this new technology, Woods next hopes to further study the nuances of mitochondria behavior, such as its communication with the nucleus, especially within the context of human fertility and reproduction.