Bioengineers made mutant, solar-powered hamster cells
Plant cells have a structure called a chloroplast. Animal cells don't. Animal cells consume food that is provided to them after the animal eats and breaks it down into simple components. On the other hand, using chloroplasts, plants make their own food from air, water, and sunlight. But what if animal cells could be equipped with chloroplasts? And why would anyone want to do that?
You may remember from biology classes that plants use the energy from sunlight to split water molecules, which then combine with carbon dioxide to form sugars that feed the plant cells. This is called photosynthesis (photo-: light, -synthesis: building). This all takes place in the chloroplast of plant cells. A by-product of this process is oxygen, which the plant releases.
Scientists are considering how the production of oxygen inside the body could be helpful. Here are some medical examples of when it is needed more than for just the usual supply to tissues.
- In coronary artery disease, clogging of arteries that surround and feed the heart results in poorer blood supply and the oxygen it carries. Poor circulation often also occurs in patients with diabetes.
- In wounds, the blood vessels are cut or crushed, so less blood with oxygen can be delivered. Body cells sent to the injury also need oxygen, but they may not get it.
- Also, when organs or tissues suffer from trauma or disease, they need to be repaired or replaced. A special kind of science called tissue engineering can make that possible with donor cells from the body that are placed on scaffolds to grow; the structure is made inside or outside the body. Examples are small arteries, an artificial bladder, skin grafts, cartilage, and a trachea. But growing the replacement cells often suffers from insufficient oxygen.
Many methods have been used and proposed to add oxygen to areas inside the body: flooding the injury with high concentrations of oxygen, adding artificial blood substitutes that carry more oxygen, using gene therapy, or applying materials to dressings (hydrogen peroxide, nanoparticles with oxygen bubbles, nanofibers with oxygen-releasing chemicals like CaO₂, etc.).
Some researchers have also inserted plant cells (algae) themselves!
Cyanobacteria (blue-green algae) like Synechococcus elongatus was added to rat hearts and survived 1-2 hours. The alga Chlamydomonas reinhardtii was tried on frogs and zebrafish, and the cells survived a few days. Another alga Chlorella was tested in gels or lab-grown tissues and lasted a few days to a week.
In 2024, researchers at Tokyo University, Waseda University, and the RIKEN Center for Sustainable Resource Science successfully implanted chloroplasts from the alga Cyanidioschyzon merolae into hamster cells. Although chloroplast implantation had been done by others earlier in different species, this was the first time photosynthetic activity was maintained in these "planimal" cells. It wasn't long, just two days, but it was still a first.
You might wonder why algae and their chloroplasts have been mentioned, and not higher forms of plants like leaves from flowers or trees. We think of algae as large mats of cells covering ponds and lakes, but they are made up of single-celled organisms. Each cell can exist independently. They are among the oldest of plant life on Earth, too.
As such, the chloroplasts in algae cells are different from those in flowering plants. Floral plant chloroplasts begin as a structure called a proplastid and then change as the plant ages from a seed to seedling to full-fledged plant. In fact, other types of plastids can come from the protoplastid and reside in different parts of the plant to produce flower colors (chromoplast), storage compartment in roots, seeds, tubers (leucoplast), or developing leaves (etioplast, which stores material later changing to chlorophyll in chloroplasts). Gerontoplasts are old-age chloroplasts formed when plants reach the end of their life.
But chloroplasts from algae rarely change into other plastids. It might be this stability that allowed the Japanese team to succeed.
They confirmed that cells had taken up chloroplasts with fluorescent dyes and viewing under a microscope. See below from Matsunaga's study.
Next, they exposed the hamster "planimal" cells to light and measured the photosynthetic function. When they compared it to isolated chloroplasts (outside of the algae cells), they found that chloroplasts cultured with hamster cells for a day had more than half of the photosynthetic power and virtually the same after 2 days in culture. After four days, they lost the ability. The scale they used might seem small for efficiency, but regular chloroplasts in plant cells only get up to 0.6, simply because nature is not very efficient. But these results showed no loss of function after two days inside hamster cells.
In addition to providing medical science with cells that can produce oxygen which benefits others in the immediate vicinity, inserting chloroplasts into animal cells might have another benefit. The researchers reminded us that tissues grown in the lab could suffer from lack of oxygen because of the many layers of cells packed together. For example, it is possible to grow artificial organs, skin transplant sheets, and artificial meat in the lab.
