Researchers from the University of Cincinnati (UC), the University of Illinois Urbana-Champaign (UI), and the University at Buffalo (UB) used an optogenetic technique to bring together mitochondria and lysosomes in human stem cells, to revitalize the cells’ fission process. Mitochondria are dynamic organelles that constantly undergo the processes of fission — separating — and fusion — coming together— in healthy cells. An imbalance in these processes can lead to neurodegenerative diseases such as dementia and certain cancers. Previous research showed that lysosomes, another type of organelle, can induce mitochondrial fission. Once they are brought in contact with mitochondria, lysosomes act like tiny scissors, cutting and dividing the mitochondria. The researchers attached two different proteins to the mitochondria and the lysosomes within the stem cells, and stimulated the proteins with blue light. The light-activated proteins bound to each other to form one new protein. In the process, they brought the mitochondria and lysosomes together. “Optogenetics borrows these light-sensitive proteins from plants and uses them in animal cells,” said UI professor Kai Zhang, who developed the optogenetic tools for controlling mitochondria and lysosomes with blue light. “By attaching such proteins to organelles, one can use light to control the interaction between them, such as mitochondria and lysosomes shown in this work.” A superresolution image of the endoplasmic reticulum, in green, lysosomes, in pink, and mitochondria, in red. Using the light-activated proteins, the mitochondria and lysosomes are brought together to conduct mitochondrial fission. A research team used the technique of optogenetics to jump-start the fission process by bringing the lysosomes and mitochondria together within cells. Optogenetics enables precise control of specific cell functions using light. Courtesy of Jiajie Diao/University of Cincinnati. The researchers used photoactivatable dimerizers with blue light to induce the mitochondria-lysosome contact and tracked the optogenetic induction of mitochondrial fission in living cells in real time to measure the fission rate. The optogenetic technique partially restored the mitochondrial functions of cells exhibiting defects in mitochondrial fission and hyperfused mitochondria. “We found that it can recover the mitochondrial function,” UC professor Jiaje Diao said. “Some of the cells can even go back to normal. This proves that by just using some simple light stimulation we can at least partially recover the mitochondrial function of the cell.” Although other processes can be used to induce mitochondrial fission, the optogenetic technique provides highly localized spatial control, allowing for a targeted approach to mitochondria-lysosome contact. Only cells exposed to the light are affected. In addition, mitochondrial fission increases in the area exposed to light, while other areas remain unchanged. The optogenetic method is safer than other methods because it does not involve chemicals or toxic agents. Chemically induced mitochondrial fission can result in mitochondrial damage and cellular toxicity. The optogenetic technique mobilizes a cellular mechanism that protects mitochondria, the researchers said. “What we have is actually the natural process, we’re just making it faster,” Diao said. “So, it’s not like a chemical or a therapy or a radiotherapy where you need to reduce the side effects.” When instigated by the optogenetic tool, mitochondrial fission is reversible. After light excitation is withdrawn, the lysosomes and mitochondria can separate and mitochondrial fusion can be restored. In addition, the optogenetic method maintains the integrity of functional proteins, whereas biological methods may require functional proteins to be deleted. Diao believes the optogenetic technique could be especially useful for patients with oversized mitochondria, which must be divided into smaller segments in order for the cell to regain normal function. The technique could also be used to continually separate the mitochondria in cancer cells into ever smaller pieces until the cells can no longer function. “Eventually the cancer cells will be killed because mitochondria are their energy,” Diao said. The team is exploring how to use its optogenetic technique to promote mitochondrial fusion in cells where mitochondria are too small to come together as they should. Further research from Zhang’s lab will include developing new optogenetic systems that work with different colors of light, including green, red, and infrared, since a longer wavelength will be needed to penetrate human tissue. “We would like to further expand the toolbox by introducing multicolor optogenetic systems to give us multiple ways to control how organelles behave and interact,” Zhang said. “For instance, one color makes organelles come together, while the other color forces them apart. This way, we can precisely control their interactions.” The team hopes to progress from using human stem cells for its research to testing the efficacy of its technique in animal models, as a step toward eventually testing the technique in humans through clinical trials. Diao said that other research groups are studying the use of magnetic fields and acoustic vibrations to accomplish results similar to the team’s light-based technique. The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-31970-5).